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GEOCHEMISTRY OF THE UPPER DILIMAN TUFF UNIT IN
MANILA, SOUTHWEST LUZON, PHILIPPINES: INSIGHTS
ON ITS ORIGIN AND COMPARISON WITH TAAL AND
LAGUNA CALDERA PYROCLASTIC FLOWS

presented by

MARIA CARMENCITA B. ARPA

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GEOCHEMISTRY OF THE UPPER DILIMAN TUFF UNIT IN MANILA,
SOUTHWEST LUZON, PHILIPPINES: INSIGHTS ON ITS ORIGIN AND
COMPARISON WITH TAAL AND LAGUNA CALDERA PYROCLASTIC FLOWS
By

Maria Carmencita B. Arpa

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE
Department of Geological Sciences

2005

ABSTRACT
GEOCHEMISTRY OF THE UPPER DILIMAN TUFF UNIT IN MANILA,
SOUTHWEST LUZON, PHILIPPINES: INSIGHTS ON ITS ORIGIN AND
COMPARISON WITH TAAL AND LAGUNA CALDERA PYROCLASTIC FLOWS
By

Maria Carmencita B. Arpa

The upper Diliman Tufi‘ is a basaltic to dacitic pyroclastic flow, which overlies
the sequence of tuffaceous deposits found north of the southwest Luzon volcanic field in
the vicinity of Manila, Philippines. Pumice fragments from this deposit are high-K basalt
to dacite (50—65 wt. % SIOz). These pumices are glassy with 1—3 % phenocrysts content,
mainly plagioclase and pyroxene. Mingling textures occur and there is variability in
glass compositions for a single pumice. Disequilibrium features are also seen in the
phenocrysts. Bulk trace element composition and mineral chemistry indicate mingling of
magmas. The chemical variation in the deposit can be explained by mixing of melts
produced by different degrees of partial melting. Volcanism in Luzon is produced largely
from subduction and in the southwestern portion, extension. During subduction, the
overriding crust is modified by emplacement of subduction-related magmas and partially
melted by hot basaltic intrusions generated in the mantle wedge beneath southwest
Luzon The location of the actual vent or source volcano of the upper Diliman Tuff
deposit is uncertain; comparisons show that it is chemically distinct with respect to
deposits from adjacent Taal and Laguna calderas. Differences with these volcanic

centers are seen in terms of major and trace element compositions.

ACKNOWLEDGEMENT

It was lucky for me that Tom Vogel, Lina Patino and Tim Flood did fieldwork in
the Philippines. I thank Tom for helping me collect my samples. I’d also like to thank
my adviser, Lina Patino for all her help, guidance and patience. I’m thankfiil for having
Tom Vogel and Kaz Fujita in my committee. Taking their classes also, has been very
informative for me and important in making me understand my research. I appreciate all
the classes I took here at MSU. I also learned a lot from classmates and meetings of the
petrology group — Dave, Karen, Beth, Chad and Ryan.

I thank PHIVOLCS for the work experience and maturity: RSP for encouraging
and inspiring us; Rene Solidum for letting me study the cores; Remon, Mabel, Toto,
Mylene, Hannah and Peejay for their help; Norman for being a cool boss.

I thank my friends for keeping me sane: friends from Owen Hall - Ma-an, Gizelle,
Andrew, Nate, Tim and Stacy.

I thank Jéréme for encouraging me and for being the best part of my stay here.

Finally, I thank my father, my mother, my sister Tet and my niece Amber for their

support and most of all, example.

iii

TABLE OF CONTENTS

ListofTables
List ofFigureI
Introduction

Geologic setting ofSouthwest Luzon .. ..

Taal caldera”

Laguna caldera

General geology 6f Manila
Pyroclastic deposits In Manila

Groundmass.......

PlagIoclase
Pyroxene............... .. .

Enclaves

Geochemistry"
Whole rock geochemistryI

Majorelementcompositions..........................................
Traceelementcompositions..........................................
Mineralchemistry.............................
PlagIoclase

Pyroxene ..
Glasschemistry..

Discussions” .. .
EvaluatiOn cf cryStal fractionation
Evidence of magma mingling...
Evaluation of partial melting...
Pressure and temperature estimates .
Source comparison with Taal and Laguna caldera

Model for the origin and evolution of the upper Diliman Tufl‘
Conclusions

References

iv

\IO‘UtUtw

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15
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16

17
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18
19
20
21
22

25

26

75

LIST OF TABLES

Table l. Samplelocation 26

Table 2. Bulk rock major and trace element concentrations for pumice
fragments in the upper Diliman Tuff. Oxides listed in wt.%, trace
elements in ppm (parts per million)... 27

Table 3. Major element concentrations of plagioclase, pyroxene,
groundmass glass and magnetite from select pumice fragments... 34

LIST OF FIGURES

Formatting note
Images in this thesis are presented in color

Figure l. (a) Tectonic setting of the northern half of the Philippines,
showing the location of opposing subduction zones (Manila Trench
and Philippine Trench) and the left-lateral Philippine Fault in
between. The enclosed area is enlarged in the next map (Fig. 1b)
and includes southwest Luzon and the study area (b) A map
showing the west facing volcanic arc, Bataan Arc (dashed line), and
the location of Macolod corridor. The symbols represent active
(triangle), potentially active (filled circle), and inactive (open circle)
volcanoes. Taal and Laguna calderas are labeled The enclosed
area covers the extent of the surface geologic map of Metro Manila
showninfigure2..

Figure 2. Surface geology map of Metro Manila The upper Diliman Tufi‘
is shown in green Sample location is indicated by red circles and

beside it is the site number........

Figure 3. 011th photos
(a) An excavation for a building showing an approximately 10 m
thick pyroclastic flow (PF) deposit and other units below. This is
located in Cubao, Quezon City. The upper pyroclastic flow deposit
is correlated with the upper Diliman Tuff and although this site was
not sampled, it shows a thickness for the unit and other deposits
below
(b) Pyroclastic flow deposit sampled in site 040303-01
(Brgy. Malanday, Quezon City).
(c) Pyroclastic flow deposit sampled in site 040303-02
(ULTRA, Pasi g).
(d) Pyroclastic flow deposit sampled in site 040404-03

(Kalayaan Ave., Pasig)...

Figure 4. Stratigraphic logs of selected sample sites. Correlation of the

upperDilimanTuffunit(shaded green) is shown...

Figure 5. Photo of a core sample (EH-07). The unit contains heterogenous

pumice clasts-mafic, felsic and banded pumice.

Figure 6. Figure 6. A close-up of the core samples from PIVSl-9. 28 (a)

and BH-07 (b). Two c1asts,a mafic m(dark) and felsic (light) pumice

clast, in BH—07 are outlined...

vi

40

41

42

43

45

Figure 7. Photograph of groundmass in plane polarized light showing
vesiculation and mingling (dark and light glass). For pmnice

040303-1C the points with analysis are shown (see table 3)...

Figure 8. Photos in crossed polars of plagioclase as glomerocryst and
isolated phenocrysts. Zoning can be seen. The groundmass rs
mostly glass with crystallites... .. ... .... ....

Figure 9. Pyroxenes in sample 040303-2C, a clinopyroxene in plane
polarized light (a) and an othopyroxene 1n crossed polars (b)
withmagnetiteinclusions...

Figure 10. A photo of enclave l in PIVSl-9.28A showing microlitic
groundmass of mostly plagioclase and plagioclase glomerocryst in
crossed polars. The close up of plagioclase phenocrysts in this

enclave, shows nmnerous inclusions and rounded grain edges... ....

Figure 11. (a) Enclave 2 in PIVSl-9.28A under crossed polars showing
acicular crystallites in the groundmass and one larger plagioclase

lath. (b) Enclave 3 1n PIVSl-9. 28A under plane polarized light

containing zoned plagioclase and clinopyroxene...

Figure 12. Total alkalis versus silica diagram The "samples plot.” 1n the

basalt to the trachydacite field...

Figure 13.Majorelementvariation with silica... ..

Figure 14. The pumices are enriched 1n Fe and m the AFM triangle, some

plot 1n the tholeiitic field...

Figure 15. Total alkalis versus Mg#. A separate trend can be seen for the

basaltic samples with high P205...

Figure 16. Trace element spider diagrams. Two groups were identified
based on the spidergrams. One group consists of the basaltic high

P205 pumices (a). Majority of the pumices are included in pattern b. ..

Figure 17. Trace element variation with silica. Note the higher and lower

concentrations trends onb for the same value ofsilica...

Figure 18. RE spidergrams. The samples include 50—64 wt.% S102. A
tight pattern is formed despite the range in silica, with decreasing
concentration from light to heavy REE and a slightly concave

upward trendtowards the middletoheavy REE

vii

46

47

48

49

50

51

52

53

54

55

56

57

Figure 19. Generally the An content (values include rim and core analyses)
of the plagioclases decrease in higher silica pumices. Plagioclases
from enclaves found in pumice PIVSl-9.28A are included... .. 58

Figure 20. Plagioclase from different pumices, bulk silica content is
indicated, showing the An values for the rim and core. Analysis on
the enclaves is also included... 59

Figure 21. Classification of the pyroxenes in the samples. The pyroxenes
plot in the diopside-augite and hypersthene fields... 60

Figure 22. Two groups of pyroxenes can be seen in terms of MIT i ratios.
Both groups have similar range of Mg # (Al/Ti vs. Mg#). The group
with higher Al/T i includes only clinopyroxenes (Al/T i vs. Wo%). .. 61

Figure 23. Variation in glass composition for the pumice fragments. The
first plot shows groundmass glass silica against bulk silica The
second plot is Mg0 versus 8102 in glass, note that enclave 2 and 3
plot outside the trend... 62

Figure 24. Almost constant Mg # for the upper Diliman Tuff pumices as
8102 values increase, does not show a fractionation trend... 63

Figure 25. (a) Higher values of Fe0’lMg0 for bulk compositions of
samples 040303-11 and IF (circled). (b) Higher values of
F e0*/Mg0 for glass compositions of enclave 2 and 3 ................................... 64

Figure 26. Mixing line for glass compositions. The end members cover the
range of compositions but the fit of the mixing line is a little offset.
Note glass from enclave 2 and enclave 3 plot outside the trend... 65

Figure 27. The same plot as figure 26 but using bulk pumice compositions.
Note samples 040303-11 and IF (circled) fall way off the trend... 66

Figure 28. (a) La/Yb ratios for the upper Diliman Tuff show a scatter
and a wide range from 6.5 to 11.5. (See Figure 12 for symbols).
(b) La/Yb ratios for Taal and Laguna pumices in the andesitic range
(56—60 wt.% Si02) plotted with respect to the distance of these
centers from the volcanic front (Bataan arc). Location of the source
vent for the upper Diliman Tuff is unknown; the values are
represented by the shaded area. This graph shows higher values for
Laguna pumices, which may be interpreted as lower degrees of
melting, compared with Taal pumices. The upper Diliman 1s
intennediatebetweenthetwo... . 67

viii

Figure 29. Geothermometry for coexisting orthopyroxene and
clinopyroxene in pumice. Temperature estimates were done using
QUILF (Andersen et al., 1993). Samples 040303-33 and
040303-2C have additional constraint from magnetite and give

temperatures 0f850t0 900°C with smaller uncertainty......

Figure 30. Comparison of major and trace element compositions of upper
Diliman Tuff and deposits from Taal and Laguna calderas. Sr
values clearly distinguish Taal deposits. Differences between the
upper Diliman Tufi‘ and Laguna Tuff can be seen in Mg0, Ti02, and

Zr. Taal data (Martinez, 1997; Listanco, 1993; MikliusetaL, 1991);

Laguna data (MSU data)...

Figure 31. The clearest distinction between Laguna deposits and the upper
Diliman tuff is the Mg#. Upper Diliman and Taal pumices and

lavas are more primitivethanLaguna pumices...

Figure 32. Trace element spidergrams show little difference between the

upperDilimantuffand Lagunapumices......

Figure 33. REE distribution for the upper Diliman tuff shows a tight

pattern from low silica to high silica pumices while Laguna REE

concentrations have more variation.

Figure 34. Model forthe evolution ofthe upper Diliman tuff...

Figure 35. Model for the evolution of the upper Diliman Tufi (continued). .. ....

ix

68

69

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71

72

73

74

Introduction

There are several layers of pyroclastic deposits (Diliman Tufi) found in the
Manila area, Southwest Luzon, Philippines. This study will focus on the uppermost unit
(upper Diliman T ufi), which has pumice fragment compositions that range from basalt t0
dacite. Although the volcanic source of this deposit is unknown, there are several
possible sources: the nearest volcanoes to the north and northwest and to the south and
southeast.

The first objective of this study is to chemically characterize the upper Diliman
Tufi‘ and to compare it with deposits fi'om known sources in the vicinity. Two possible
source volcanoes were chosen for comparison. One is Laguna caldera which is 40 km to
the southeast; it is the nearest volcanic center to the deposits. The other is Taal caldera,
60 km to the south. The youngest deposit from Taal caldera, a scoria pyroclastic flow
dated 5,000 years ER, is found just south of Manila Martinez, 1997). Older deposits of
Taal caldera have more silicic compositions (Listanco, 1993). Laguna caldera also has
several units of pyroclastic flow deposits, but the stratigraphy is less constrained than
Taal (Catane et al., 1998, unpublished report). Comparison, therefore, will be done to a
range of deposits from Taal caldera, including Volcano Island, and Laguna caldera

The second objective is to determine possible processes that produced the range in
$102 content of the pumice fragments in the unit. Possible processes that can produce
silicic rocks are fractional crystallization, partial meting of crustal rocks and assimilation.
In evaluating the processes, the conditions set from the geologic setting must be
considered. Presently, volcanism in west Luzon is due to the subduction of the South

China Sea Plate along the Manila Trench. Knittel and Defant (1988) suggested that prior

to subduction in the Manila Trench, the Philippine arc evolved from a mantle source
more enriched than a MORB source. This conclusion is based on isotopic compositions
of pre-Manila Trench subduction-related intrusives in Luzon and the modem arc. Since
subduction began in the Manila Trench, source materials for some volcanoes in Luzon
have been more enriched in Large Ion Lith0phile Elements (LILE) and radiogenic Sr as a
result of dehydration of the subducted crust and terrigenous sediments from Emasia
(Knittel et al., 1988, Defant et al., 1988, Mukasa et al., 1994, Castillo and Newhall,
2004).

In this study, major and trace element compositions of pumices and their
component minerals shall be used to correlate to a source volcano, and to understand the
origin and evolution of the magma that produced the deposits. Data include XRF and
LA-ICP-MS analyses of individual pumice fragments. Microprobe analyses of the mafic
and felsic glass in the mixed pumices and individual minerals will test the relationship of
the magmas with respect to each other. Mineral chemistry will give estimates of pressure
and temperature conditions during crystallization, which will have implications on the

depth of the reservoir.

Geologic setting of Southwest Luzon

Manila is located north of the southwest Luzon volcanic field where both Laguna
and Taal calderas are found. The southwest Luzon volcanic field is a region consisting of
straw-volcanoes, monogenetic centers and calderas(01es et al., 1995). Volcanoes in
southwest Luzon can be related to eastward directed subduction in the Manila Trench and
extension in the Macolod Corridor (Knittel et al., 1988; Defant et al., 1988; Forster et al.,
1990) (Figure la-b).

The Philippine are, which includes most of Luzon Island, probably developed on
Philippine Sea basaltic crust. It was part of the Philippine Sea Plate before the
development of the Philippine mobile belt, which is marked by subduction zones to the
east and west (Rangin et al., 1995). Subduction along the west margin, offshore of
Luzon, is along the Manila Trench The eastward subduction of the South China Sea
Plate in the Manila Trench started between Late Oligocene to Middle Miocene (Hayes
and Lewis, 1984). The South China Sea opened in the Middle Oligocene/Early Middle
Miocene, around 32-15 Ma B.P. (Taylor and Hayes, 1983; Pautot and Rangin, 1989).
Manila Trench extends from 13° to 20° N, trends North-South, and is almost linear
instead of arcuate due to the indentation caused by the subduction of the axial ridge of the
South China Sea offshore of Central Luzon (Hayes and Lewis, 1984; Pautot and Rangin,
1989). The dip of the subducting slab also changes from North to South along the trench
and becomes almost vertical towards the southern end (Cardwell et al., 1980). Volcanism
in Southwest Luzon from this subduction occurs around 100 to 200 km above the
Wadati-Beniofi‘ zone (Cardwell et al., 1980). The area where the dip of the subducting

slab is almost vertical is marked by the Palawan-Mindoro collision, which involves the

North Palawan Continental Terrane (Figure 1a) (Cardwell et al., 1980; McCabe et al.,
1985). It was suggested that slivers of this continental tenane could have been
assimilated by the magmas of some southern Luzon volcanoes (Knittel and Defant,
1988). Seismic refraction and reflection sections taken offshore of Central Luzon (15.5°
N) show that the Manila Trench has a well developed accretionary prism and that
hemipelagic sediments are subducted and not scrapped off with the turbidites (Hayes and
Lewis, 1984). This information is important in evaluating magrnatism related to
subduction where dehydration, and probably melting of the sediments, are envisioned
(Castillo and Newhall, 2004).

In southwest Luzon, there are volcanoes located east of the west-facing volcanic
are that are not above a subducted slab. These structures and volcanoes, dated 6 Ma to
present (Oles, et al., 1995), defined the Macolod Corridor (Figure. 1b.), which is a NE-
SW trending rift zone crossing the Philippine arc in SW Luzon (Defant et al., 1988,
Forster et al., 1990). The direction of extension in the corridor was suggested to have
changed from N-S and NNW to NW and finally to E-W rifting (Pubellier et al., 2000).
Volcanism from 2 Ma to present may be related to the E-W extension. The present E-W
extensional direction could be a reaction to the collision of the Palawan block with the
Philippine arc (Pubellier at al., 2000). This collision began around 10 Ma (Rangin et al.,
1995). Generally there is a counter-clockwise rotation of Luzon above this collision
reflected by the higher rate of convergence in the northern part of Manila Trench as
compared to the south (Pubellier et al., 2000). More recent studies involving GPS
modeling show left-lateral transtensional movement in the Macolod Corridor at a rate of

11-13 mm/yr. (Galgana et al., 2004).

There is also another subduction on the east side of the Philippines (Figure. 1a)
but it may not be related to the present volcanism in SW Luzon or the past activities of
Laguna or Taal calderas. The west-facing subduction in the Philippine Trench is a
younger feature and the slab does not reach below SW Luzon (Cardwell et al., 1980).
Volcanic centers related to subduction in the Philippine Trench are located in the Bicol

arc farther to the southeast.

Taal Caldera

Taal caldera is located just slightly east of the Bataan arc, which forms the trench-
side volcanic 01min for the subduction in the Manila trench (Figure. 1b). The depth of the
slab beneath Ta] is estimated to be 200 km (Cardwell et al., 1980). Caldera formation
stage was from 140,000 to 5,3 80 years ago and produced calc-alkaline andesitic to dacitic
ignimbrite eruptions (Listanco, 1993). The youngest caldera eruption is basaltic and
occurred around 5,000 years B.P. (Martinez, 1997). Composition of Taal lavas are
significantly influenced by subducted terrigenous sediments of the South China Sea basin
(Miklius et al., 1991; Castillo and Newhall, 2004). Based on fiactional crystallization
modeling, the silica variation for Taal lavas is due to mixing of melts from separately

evolving fractionation systems supplied by melts from a heterogenous mantle source

(Miklius et al., 1991).

Laguna Caldera
Laguna caldera is located around 30 km east of Taal (Figure. 1b). The caldera is

difficult to outline but it is generally in Laguna de Bay lake. Laguna de Bay is a horst

and graben feature composed of N-S trending structures that have been modified by
volcanism. The caldera outline proposed by Wolfe and Self (1983) coincides with the
middle lobe of Laguna de Bay. The Laguna Tuffs include flat-lying volcanics, flows,
tuffs, and coarse agglomerates (Corby, 1951). Welded ignimbrites are extensive around
the caldera margin. The episode of magmatism attributed to Laguna caldera occurred
between 2.3 to 0.9 Ma based on K-Ar dates in andesitic and rhyolitic lava and tufi'
deposits (Oles et al., 1995). Radiocarbon dating of a pyroclastic flow deposit gives an
age of around 47,000 B.P. (Catane et al., 1998, unpublished report). Deposits from
Laguna contain pumice fragments compositions between 53 to 69 wt. % Si02 (Flood et
al., 2004). Flood et al. (2004) suggested that the high silica magmas of Laguna were
generated by partial melting or assimilation of previously emplaced calc-alkaline material

based on high NazO/K20 ratios.

General geology of Manila

The Metro Manila (MM) region can be physiographically divided from west to
cast into the coastal region, Quezon City plateau, Marikina valley, and the Antipolo
Highlands (Figure 2). Recent alluvial deposits overlie the Marikina valley and coastal
regions. Underlying pyroclastic deposits are well exposed in the Quezon City plateau.
Pyroclastic deposits from Taal caldera cover the southernmost part of MM (Martinez,
1997). The Antipolo Highland is the southern extension of the Sierra Madre Range and
is composed partly of old volcanics and sedimentary rocks that are included in an
ophiolite suite (Arcilla, 1991). Marikina valley and Quezon City plateau are a graben and

horst produced by movements along the Valley Fault (Marikina Fault) (Alvir, 1929;

Gervasio, 1968). The Marikina valley extends southward into the western lobe of

Laguna de Bay.

Pyroclastic deposits in Manila

The pyroclastic deposits found in Manila belong to the Guadalupe Tufi‘ formation
This formation is characterized as consisting of angular chunks of volcanic debris with a
thickness that may vary from 1,300 to 2,000 meters (Corby, 1951). The type section is at
Guadalupe in Manila along the Pasig river. Corby (1951) mentioned that these are
probably fine grained facies of the Laguna Tufl‘ farther east. The Laguna Tufi‘s however
were still assigned as a separate formation and only includes the volcanics in the vicinity
of Laguna de Bay (Corby, 1951). Another study divided the Guadalupe Tuff into 5..
members, namely Alat conglomerate and Diliman Tufl‘ (Teves and Gonzales, 1950).
Diliman Tufi‘ is the tuff sequence in the formation with the type section in the Diliman
area in Quezon City. The Diliman Tuff consists of flat-lying beds of fine-grained, vitric
tuffs and welded volcanic breccias with minor amounts of tuffaceous sandstones
(Gonzales et al., 1971). An 18 to 21 m exposure in Guadalupe shows an upper
stratigraphic section of the tufl‘s that include three horizons of erosional surfaces marked
by fossil soil or decayed tuff (Gervasio, 1968).

This study focuses only on the upper unit of the Diliman Tufi'. Data for this unit
are gathered from short cores (10 m), long core (40 m) and outcrops. The short cores
intersected only one set of pyroclastic flow deposits. In all the short cores, two types of
pyroclastic deposits were identified. One group of correlated cores, which includes

borehole 7 (BH07), shows a pyroclastic flow deposit that contains coarse lapilli size

pumice, scoria (mafic pumice) and banded pumice. Below this pyroclastic flow unit are
finer grained layers interpreted as surge and fall deposits. The second group, which is not
part of this study, can be seen in borehole 15. BH-15 recovered thick tuffs (mostly fine
ash) rich in accretionary lapilli and interbedded with ash layers containing lapilli-sized
pumice and scoria. These are interpreted as pyroclastic surge and fall deposits.
Associated with the deposits in BH-15 are unwelded and fine grained pyroclastic flows
that are either pmnice-rich or scoria-rich. Outcrop exposures where samples were taken
are at sites 040303-1 (Quezon City), 040303-2 (Pasig) and 040303-3 (Pasig) (Figure. 3b-
d). The pyroclastic flow deposit at site 040303-1 is lithic-rich and slightly weathered
with a soily matrix Pumice samples from this unit are colored black and brown, and
some are banded. The pyroclastic flow deposit at 040303-2 is 7 m thick and is composed
of coarse lapilli-sized mafic pumice and finer, lighter pmnice and banded pumice clasts.
At site 040303-3, the pyroclastic flow unit is around 10 m thick and overlies
paleosol/weathered ash and a tuffaceous fluvial deposit. It consists of mostly light brown
to white pmnice clasts. Correlation of outcrops and core samples gives a stratigraphic
sequence consisting of (from top to bottom): a) a coarse grained pyroclastic flow deposit
with black to light gray/white pumice clasts; b) a weathered ash (possibly a soil); c) a
thick sequence of fines-rich surge and fall deposits; and d) another coarse grained

pyroclastic flow deposit (Figure 4).

A

Methods

A total of 23 pumice fragments from 3 outcrops of a pyroclastic flow deposit in
Metro Manila were sampled (Table 1). Additional samples were collected from borehole
cores archived by the Philippine Institute of Volcanology and Seismology (PHIVOLCS).
Pumice fragments (18) were picked from cores, which sampled the pyroclastic flow unit
for this study. The small size of some prnnice clasts limits the sampling. For the
analytical methods tlmt were applied, a minimum of 1.0 gram of dry sample is required.
The pumice clasts are within the lapilli size range (2-64 mm) (figures 5 and 6). Pumice
fragment variety based on color (light, dark and handed) was considered in sampling
For the comparison study, pumice fragments from several pyroclastic flow units from
Laguna caldera were also collected

Pumice samples from the Diliman Tufl‘ unit were all hand ground using an opal
mortar and pestle. Smaller samples from Laguna units were hand ground and the rest
were powdered using an aluminum flat plate grinder after passing through a chipmrmk.
There are two recipes for the fused glass disks: the Low Dilution Fusion (LDF) and High
Dilution Fusion (HDF). The standard is the LDF. For smaller samples, the HDF had to
be used In the LDF, 3.0000 +/- 0.0005 grams (g) of finely ground pumice powder were
diluted by adding 9.0000 +/- 0.0005 g lithium tetraborate (Li2B401) flux and 0.5 g
ammonium nitrate (NH4N03) as an oxidizer. For the HDF, only 1.0000 +/- 0.0005 g of
pumice powder is mixed with the same amount of flux and 0.16 g oxidizer. Fifieen HDF
disk were made and the rest of the samples were fused into LDF disks. For a sample
weighing 21.500 g, half of the proportions in the LDF recipe were used making smaller

disks. The dry mixed powder was melted in platinum crucibles at 1000°C of oxidizing

flame for >20 minutes while being stirred with an orbital mixing stage. Platinum molds
were used to make the glass disk.

Analysis for major and trace element were done using a Rigaku S/Max X-ray
Fluorescence Spectrometry (XRF) and additional trace element and rare-earth element
analysis by Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA ICP-
MS) at Michigan State University. Major element data from the XRF were calculated
using fundamental parameters and trace elements were calculated using a linear
regression. For LA ICP-MS analyses, strontium determined by XRF was used as an
internal standard. Element concentration was based on linear regression method using
BHVO-l, W-2, JB-I, JB-2, JB-3, JA-2, and BIR standards. The same glass disks were
used for both XRF and LA ICP-MS.

Electron microprobe analysis was done at the Department of Geological Sciences,
University of Michigan using an SX 100 CAMICA microprobe. A beam size of 5
microns at a beam current of 10 nA was set for the mineral analyses. Plagioclase and
pyroxene compositions were analyzed in seven pumice clasts, and glass compositions

were determined in nine pumice fragments.

10

Petrography

The pumice clasts in the upper Diliman Tufi‘ are varied in terms of color and
texture. Mafic, felsic and banded pumice fragments are present and there is a range in the
degree of vesiculation. Generally, the pumices are glassy and finely vesiculated. Sample
PIVSl-9.28A contains non-vesiculated black bands. The phenocrysts make up only 1 to
3 % of the bulk Sometimes they occur as glomerocrysts. Coarse phenocrysts are around
1 to 2.5 mm for the longest side but usually the crystals are smaller. The mineral phases
are plagioclase, clinopyroxene, orthopyroxene and magnetite. Magnetite is sometimes
included in pyroxene and plagioclase. Amphibole and mica are found only in the most
silicic samples. Trace phases are apatite and zircon. Mingled pumice clasts show
banding of light and dark glass. Even pumice fragments that do not show obvious
mingling in hand sample may show mingling microscopically. Some pumice fragments

contain enclaves.

Groundmass

The groundmass is mostly glass. It is brown to dark brown in the most mafic
pumice samples and clear glass in the higher silica pumice samples. The dark color can
also be due to oxide crystallites in the glass, but the oxide specks are most common in the
mafic purnioes. Sometimes dark brown to black bands are present (040303-1M) and the
groundmass appears mottled. In sample 040303-1C, which is a banded pumice,

groundmass is light to dark brown glass (Figure. 7).

11

Plagioclase

Plagioclase crystals are the most abundant phase and are commonly fractured
Crystals are typically euhedral to subhedral and some with rounded edges (Figure 8).
Sieved texture and glass inclusions are present and for some, only at concentric zones or
at the core. Zoned crystals are present which can show distinct zones or irregular
boundaries. Normal, reverse and oscillatory zoning occurs. The coarsest plagioclase lath

is 1.7 m2.

Pyroxene
The second most abundant phase is pyroxene (Figure 9). Both clinopyroxene and
orthopyroxene are present. Some show slight resorption and few are zoned The coarsest

pyroxene crystal is 1.6 m2.

Enclaves

Enclaves are present in samples PIVSl-9.28A and BH07-Ol-Sl. There are three
kinds of enclaves found in PIVSl-9.28A based on texture. The first (Figure 10) is
microlitic with glomerocrysts of plagioclase. It is composed mostly of plagioclase with
some clinopyroxene. The plagioclase glomerocrysts are zoned, with corroded edges and
are sieved. The second (Figure 11a) consists of acicular plagioclase crystallites with one
larger plagioclase lath. It is almost cryptocrystalline. The third (Figure 11b) is
porphyritic with around 40% phenocrysts-mostly plagioclases that are zoned and
resorbed and few smaller clinopyroxenes. In sample BH07-01-Sl, the enclave is non-

vesiculated, black and banded with trace plagioclase crystallites.

12

Geochemistry
Whole rock geochemistry

The samples were prepared differently, mostly by LDF but some by HDF, due to
limitations in the amount of sample. Detection limits in HDF samples are poor for trace
elements. The 10 samples prepared by HDF will be excluded in the trace element plots.
Samples with less than 95 wt. % total are considered altered and were excluded from the

data set (T able 2). All oxide values were normalized to 100 % for plotting.

Major element compositions

The pumice clasts for the upper Diliman Tuff mrit have 8102 compositions
ranging fi'om basalt to dacite (50—65 wt. % 8102) (Figure 12) with the andesitic to dacitic
compositions being in the high-K range (Figure 13). Major element variations with silica
show increasing K20 (1-4 wt.%) and NazO and a decreasing trend for the other major
elements (figure 13). The samples also have high FeO values (5-11 wt.%) compared with
average island arc volcanics (0.5-7 .4 wt. %) (Winter, 2001), and decrease at a greater rate
compared with MgO. It should be noted that two samples (040303-11 and 040303-1F)
have lower MgO value and do not plot on the general MgO trend. Some samples
(040303-1A, B, E, F, G, H, I, K, M) have unusually high P205 concentrations (1.14 to
2.78 wt. %). The average value for P205 in island arc volcanics is 0.1 to 0.5 (Winter,
2001).

The most basaltic samples (040303-1A, B, E, F, G, H, I, K, M), with the
exception of PIVSl-9.28A, have the lowest total alkalis values and plot in the tholeiitic

field (Figure 14). In a plot of total alkalis versus Mg# (Figure 15), they have a separate

l3

 

trend to the rest of the samples. The basaltic andesite to dacite samples have high total
alkalis values compared to the previous group. These samples plot in the lower basaltic
trachyandesite to trachydacite field. The lowest silica samples in this set are PIVSl-

9.28A, PIVSl-9.48A, PIVSl-10.97A (open triangles) (Figure 12).

Trace element compositions

Spider diagrams for the upper Diliman Tuff pumices show a typical island arc
pattern (Figure 16), having pronounced depletion in Nb and Ti and enrichment in LIL
elements. Two patterns were recognized. The first is for the mafic group with high P205
(Figure 16a) mentioned in the major element section The pattern for this group shows
distinctive positive spikes for U, La, Pb and P. It also has lower concentrations for LILE,
such as Rb, Ba, K, and Pb compared to the higher SiO2 pumices. On the otherhand, the
spidergrarn for the second group of pumices (Figure 16b) (53 to 65 wt % Si02) shows an
overall decreasing trend fi'om incompatible to compatible elements, with obvious positive
spike for Pb and depletion in Nb and Ti.

Trace element variations with silica (Figure 17) are plotted to show trends in
concentrations and influences in later element ratio plots. Values for Sr decrease, while
Rb increase, with increasing silica HF S (High Field Strength) elements such as Nb, Th
and Zr increase slightly with increasing 8102. A steep negative slope can be seen for V.
For Yb and Lu, one trend has consistently higher concentrations for the same values of
silica

Chondrite—normalized REE distribution shows a tight pattern for a silica range of

50 to 64 wt. % (Figure 18). The pattern displays enrichment in light REE (LREE)

l4

relative to heavy REE (HREE) with concentration values typical for representative hi gh-
K basaltic andesites and andesites. The Eu anomaly is very small and there is only a very

slight depletion in the middle heavy REE.

Mineral chemistry
Plagioclase

Plagioclase compositions range from An 55 to An 90 (Table 3). Crystals show the
normal increase in An content with decrease in bulk Si02 content of the pmnice clasts
(Figure 19). As mentioned, the plagioclases are zoned Maximum difference between
core and rim is 12% An. Both normal and reverse zoning are present. In a zoned
plagioclase in sample 040303-3B (whole rock=63.33 wt.% SiO2) core to rim An content
goes from 61 to 50% An. Sample 040303-1N (whole rock=56.1 wt.% Si02) contains a
plagioclase with oscillatory zoning that goes from 73 to 81 to 79% Art A reverse zoned
plagioclase in sample PIVS1-9.28A (whole rock—152.62 wt.% 8102) has 67% An in the
core and 80% An in the rim (Figure 20).

As mentioned, there are 3 types of enclaves in sample PIVSl-9.28A initially
based on texture (see petrography section). Plagioclase chemistry in each enclave turned
out to be distinct (Figure 20). Enclave 1 has plagioclase with An content ranging from
52% to 68%. A large zoned plagioclase phenocryst (p11) has reverse zoning from An 53
(core) to An 53 (rim). Groundmass plagioclases (p12 to p14) have An 52 to An 52. In
enclave 2, there is only one plagioclase (An 49) large enough to be analyzed. The

plagioclases in enclave 3 have the highest Anorthite content (An 75 to An 93).

15

Pyroxene

Two types of pyroxenes are found in the pumice samples (Figure 21):
clinopyroxene with W033 Em5Fs15 to W045En41Fsl4 and orthopyroxene with Wo3En55Fs3o
to Wo£n7oF525 (Table 3). Both clinopyroxene and orthopyroxene are found in pumice
samples with bulk Si02 of 61 .23 to 63.33 wt. %. Only clinopyroxene is found in the
lower silica pumice samples. In the enclaves, both enclave l and enclave 3 have
clinopyroxene (W0 35En45Fs2o to WomEm2Fstg). Mg # for the pyroxenes range from S3
to 64. Two groups are also identified using Alfl‘ i ratio (Figure 22). The group with a
lower ratio includes all the orthopyroxenes and most of the clinopyroxenes. The group
with a higher ratio includes all clinopyroxenes in enclave 1 and a clinopyroxene in its

host pumice, PIVS1-9.28A.

Glass Chemistry

Glass compositions range from 54.32 to 66.04 wt. % Si02 for the 9 pumice
samples analyzed (Table 3). Bulk $102 is plotted with glass Si02 to show that glass
composition is variable for individual pumices (Figure 23). A significant range is seen
in samples BHO7-03-P3, 040303-1C, 040303-2C, and BH07-03-C (54.32 to 65.28 wt.
%). Pumice P1VSl-9.28A, which is basaltic with anorthitic plagioclases, has 64.55 to
66.04 wt % SiO2 glass. Glass compositions in the enclaves are also analyzed (Table 3).

In the MgO versus SiO2 diagram, enclaves 2 and 3 plot below the trend (Figure 23).

16

Discussion
Evaluadon of crystal fractionation

Although fractional crystallization is consistent with some element variation
trends with silica (Figure 17), other parameters are inconsistent with fractional
crystallization. For the majority of the samples, there is no clear fractionation trend that
goes from more primitive to more evolved as seen from the plot of Mg# versus SiO2
(Figure 24). In addition, the REE patterns have a narrow distribution for the entire range
of silica composition (Figure 18). This can also be seen in the RE variation with
increasing silica where the RE concentrations increase only slightly or are almost
constant. Note also that for the HREE, there are two concentration trends for the same
value of SiO2 (Figure 17). Fractional crystallization, provided there is no large
fiactionation of pyroxenes and garnets, would produce parallel and increasing
concentration REE patterns as silica increases, which is not the case for the upper
Diliman Tuff pumice fragments. Certain groups, such as the most basaltic samples that
plot in the tholeiitic field, have trends that probably reflect slight olivine fractionation.
Relative to the rest of the samples with higher total alkalis, this group (i.e., tholeiitic)
shows more pronounced decrease in Mg# (Figure 15). The samples with higher total
alkalis, although with silica values from 53 to 64 wt. %, have a narrow Mg# range, which
could reflect suppression of olivine crystallization by addition of an alkali-rich silicic
component (Dungan, 2005). Two populations can be seen in the plot of FeO/MgO versus
Si02 for the glass and bulk compositions (Figure 25). In the bulk compositions, samples
040303-11 and F have the higher FeO/MgO ratio (Figure 25a). Glass in enclaves 2 and 3

have higher FeO/MgO (Figure 25b). This group (enclave 2 and 3 and pumice samples)

17

probably represents a basaltic intrusion where again there were some fiactionation of

olivine, since the reason for the high ratio is low values for MgO.

Evidence of magma mingling

The pyroclastic flow deposit in this study consists of a mixture of pumices with a
range of compositions. Mingling within pumice fragments, disequilibrium textures in the
crystals, and heterogeneity in the glass compositions are interpreted as evidence for the
mingling or mixing of magmas. Disequilibrium features in the minerals such as zoning
may indicate mixing/mingling of different composition liquids. To illustrate this, the
composition of plagioclases for rim and core in pumice and enclaves are shown in
separate graphs (Figure 20). When a mafic melt is introduced into a magma body,
reverse zoning is observed while normal zoning can reflect fractional crystallization or
mixing with a more silicic melt. Enclave 3 has the most anorthitic plagioclase core with
the rims less anothitic. Enclave 1 has plagioclases (the core of a zoned phenocryst and
grormdmass plagioclases) with similar anorthite content to the plagioclases in higher
silica pumice samples (>60 wt. %). For the zoned plagioclase in enclave 1, the rim has
higher anorthite. Reversely zoned plagioclases in the host prunice PIVSl-9.28A have
core compositions similar to either plagioclase rim composition of enclave 1 or
plagioclase compositions in enclave 3.

The chemistry and texture of the glass in the pumices clearly shows mingling. A
mixing line can be fitted in the data set (Figure 26). The fit depends on the end points
chosen. Samples BH07-03-C-gm4 (54.32 wt.% S102) and PIVSl-9.28A-gm1 (65.05 wt.

% Si02) as end points covers the entire range of compositions though the fit is slightly

18

offset. Glass analyses from enclave 2 and 3 do not fit in this line whereas enclave 1 glass
fits with the trend. A mixing line can also be fitted through the bulk pumice
compositions (Figure 27). In this diagram, samples that plot in the tholeiitic field
(040303-1) deviate from the trend, and this is more pronounced in samples 040303-11

and F.

Evaluation of partial melting

La/Yb ratio can be used to show relative degrees of partial melting. La/Yb values
for all the pumice samples fiom the upper Diliman Tuff have a range of around 6.5 to
11.5. The distribution is such that basaltic samples with 5057 wt.% Si02 have values of
7.5 to 11.5; andesitic samples (whole rock-=58—62 wt.% Si02) have around 6.5 to 11; and
samples with 8102 wt. % of 63 to 65 have ratios from 6.5 to 10 (Figure 28a). From this,
it appears that there is no pattern for La/Yb ratio with increasing differentiation.
However, this variation could represent different batches of melts. The higher silica
samples are not related to the low silica samples by fractional melting based on La/Yb
ratio since the low silica samples have the higher ratio. The higher silica (andesitic to
dacitic) samples were produced by higher degrees of partial melting compared to the
basaltic samples. Furthermore, there appears to be two batches of basaltic melts: one
have the highest La/Yb ratio in the data set and the other has lower ratios and consists of
the tholeiitic samples (Figure 28). The first group of basaltic samples mentioned has high
alkali content, consistent with low degree partial melting. The partial melts produced
could mix or mingle. Mingling was already discussed in the previous section, and the

chemical variations in the samples can be interpreted as a result of mingling of different

19

 

melts. The enclaves could represent remnants of earlier crystallized magmas that were
partially melted by a new intrusion or mafic magma that was intruded into another.
Adding more heterogeneity, some of these intrusions are tholeiitic and some are calc-

alkaline, as shown from major element compositions.

Pressure and temperature estimates

Mineral compositions can be used to determine the temperature and pressure of
crystallization Total Al/T i in clinopyroxene can be correlated to the crystallization
pressure (Figure 22) (Thompson, 1974; Pilet et al., 2002). Based on Ti and A1
compositions, it can be interpreted that clinopyroxenes in enclave 1 crystallized in a
higher pressure regime. Al/Ti ratios in clinopyroxene and plagioclase compositions
imply a batch of magma at lower pressure and temperatme, and melts coming fi'om
higher temperature and pressure. To estimate temperatures of crystallization,
geothermometry was done for punrice samples containing both orthopyroxene and
clinopyroxene, using the software QUILF (Andersen et al., 1993) (Figure 29).
Temperature estimates for samples 040303-3B and 040303-2C have lower uncertainty
due to additional constraint from magnetite. The temperature estimated is around 850°C.
This temperature is for the magma from shallower levels. The samples from which this
temperature is estimated have the two types of pyroxenes and lower Al/T i ratio for the
clinopyroxene crystals. Clinopyroxene with higher Al/Ti ratio and the most calcic
plagioclase crystals are also found in the host pumice PIVSl-9.28A. The presence of
these crystals in this sample could mean that the host magma crystallized to some extent

at higher pressure or that the minerals are disaggregated grains from the enclaves.

20

Source comparison with Tool and Laguna Caldera

The source of the upper Diliman Turf is unkn0wn. Comparison with the nearest
vents for large-scale eruptions of pyroclastic deposits, Taal Caldera and Laguna Caldera,
shows that the deposits are different. Figure 30 shows selected major and trace element
variation with silica for the upper Diliman Tuff unit, Taal (Martinez, 1997, Listanco
1993, Miklius et al., 1991) and Laguna deposits (MSU data). The Manila deposits have
higher K20, Sr and Rb values as compared to Taal, and clearly, these cannot be
correlated. The trends for the upper Diliman Tuff are closer to Laguna pyroclastics.
However, differences can be seen, particularly in the low silica compositions in the Ti02
and MgO variation diagrams (Figure 30). Figure 31 includes samples with Si02 values
from 53 to 67 wt. % and shows that Manila samples are more primitive and have higher
Mg#, than Laguna samples for the same range of total alkalis. Nonetheless, spider
diagrams show little differences between Manila and Laguna pyroclastic flow deposits
(Figure 32). The REE pattern is also similar except for basaltic pumices. REE diagrams
for the deposits (Figure 33) show higher concentrations for the more basaltic pumice of
the upper Diliman Tuff compared with Laguna even though the samples for Laguna are
less basaltic (Si02 values ranging from 53 to 67 wt. % compared with Manila’s Si02
values from 50 to 65 wt. %). As a result, Laguna deposits have a wider range of REE
concentrations than the pattern shown by the deposits in Manila The similarities in trace
element concentrations and differences in major elements for the upper Diliman Tuff and
Laguna pyroclastic flows can be interpreted as a difference in source but with similarities

in differentiation processes.

21

Comparing the La/Yb ratios of the upper Diliman Tuff with Taal and Laguna
exclusively using the samples with S102 range of 56—60 wt.%, it appears that ratios
increase with increasing distance from the trench (Figure 28b). Taal deposits have La/Yb
ratios that range from 6 to 8 and Laguna deposits have ratios from 8.5 to 12. The wide

range of values for the deposits from Manila is intermediate between Laguna and Taal.

Model for the origin and evolution of the upper Diliman 114,0“

There are several models to explain the compositional variation, particularly
production of silicic magmas, in island arcs. F elsic volcanism in oceanic volcanic ares,
such as the Kennadec arc, can be explained by dehydration melting of underplated are
material (Smith et al., 2003). Silicic melts in the Costa Rican arc have been explained by
partial melting of relatively hot subduction related magmas that have ponded in the crust
(Hannah et al., 2002; Vogel et al., 2004). Models of melting caused by intrusion of hot
basalt into the deep crust show that a wide range of melt compositions can be produced
simultaneously (Annen and Sparks, 2002). Partial melting of the crust is caused by heat
transfer from the crystallizing basalt intrusions (Annen and Sparks, 2002; Vogel et al.,
2004). Generated melts in the crust and residual melt from the crystallizing basalt can
mix/mingle and end up in the same erupted deposit (Annen and Sparks, 2002).

The basaltic intrusions originate from the mantle. Water released from down-
dragged hydrated mantle peridotite or subducted lithosphere causes partial melting of
overlying mantle wedge peridotites (Tatsrnni, 1989; Grove et al., 2003). In subduction
zones, most of the water introduced into the system comes from the hydrated subducting

crust and sediments (Tatsumi, 1989; Peacock, 1990; Giggenbach, 1992).

22

The model proposed here for the generation of magma that was erupted as the
upper Diliman Tuff is partial melting of the overriding crust by hot basaltic intrusions
originating from a metasomatised mantle wedge. Figure 34 and 35 illustrate the
processes involved Sources for Luzon volcanoes are typical for subduction zones where
there is enrichment in LILE canied by aqueaous fluids from the subducted slab (Knittel
et al., 1988, Defant et al., 1988, Mukasa et al., 1994). Generally, the amount of fluids
released during subduction decreases with depth, but a series of hydration and
dehydration reactions as depth increases brings fluids to deeper levels. At pressures
greater than 3.5 GPa, the stable hydrous phases are Phlogopite and K-amphibole.
Dehydration of these phases at depth releases more K (Tatsumi and Eggins, 1995 ). Taal
is located 200 km above the slab and at Laguna this distance is even greater (Cardwell et
al., 1980). Underneath these volcanic centers, melts are generated from small degrees of
partial melting in the mantle wedge at high pressure. The basalt melts then rise and stall
beneath the crust due to a buoyancy difference. Here it could crystallize and melt the
surrounding crust composed of earlier crystallized intrusions. The melts that have now
1mdergone some degree of differentiation, rise again and stall in mid-crust where they can
cause partial melting of previously emplaced magma. Previous intrusions that are being
partially melted by the new basalt intrusion are also subduction related. The earlier
intrusions are varied, being the result of accumulation through time. Excluding the
agglomerated tenanes, the whole Philippine are most probably developed from the
Philippine Sea Basaltic crust and this crust has since been modified by subduction
processes. The crustal rocks that were melted are unlikely to be the original basaltic

crust. The new partial melts and the residual basaltic to basaltic andesite melts from the

23

 

most recent intrusion mingled/mixed in the reservoir. After some time, another batch of
melt from the mantle is intruded into the crustal reservoir. These melts are less alkali
compared to the previous basalt intrusion. The different composition of the later basalt
intrusion could be due to higher degrees of partial melting and/or a different mantle
source. These melts mingled/mixed less with the cnrstal melts probably because there
was less time for mingling prior to being erupted Ponding of the melts in the lower crust
and mid—crust is based on the interpretation that most melts crystallized at a shallower
level. The choice of depth is based on a study that identified a low velocity zone beneath
southwest Luzon, i.e., at around 18 or 22 km, and the moho at 34 or 32 km depth (Besana
et al., 1995). A large percentage of the magma that was erupted as the upper Dihnan Tuff
probably originated from the mid-crust or shallower levels.

The actual vent where the upper Diliman Tuff was erupted from is unknown.
High LILE concentrations (similar with Laguna tuffs) indicate that the source is not along
the Bataan arc. The source instead, could be in the same tectonic setting as Laguna or
Taal, which means in the region of Macolod Corridor. Magma ascent was, most likely

influenced by structures in the area.

24

 

Conclusions

The source of the upper pyroclastic flow deposit in Manila is chemically distinct
from Laguna and Taal sources. They cannot be related by fractional crystallization, and
there are differences in the degrees of partial melting foreach source, which may or may
not reflect across arc variation The higher LILE concentrations of the pumice samples in
the upper Diliman Tuff relative to Taal can be interpreted to result from lower degrees of
partial melting in the source for the upper Diliman Tuff.

The basaltic to dacitic magma that was erupted as pyroclastic flows (upper
Diliman Tuff) represent mingled and mixed melts generated by different degrees of
partial melting. These melts were produced from melting of both the mantle wedge and a
modified crust. Some basaltic intrusions are probably partial melts originating in the
mantle wedge fluxed by fluids from dehydration reactions at greater depths. Fluids are
mainly introduced from subduction processes. Partial melting in the mantle wedge could
occur in different degrees or at different source regions producing the variation in the
basaltic melts. These melts rise and stall at the base of the crust where they can melt
surrounding crust and further differentiate before rising to shallower levels. The melts
can stall again at mid-crust below less dense, and probably more differentiated, materials
that could be more easily melted. The less mafic materials in the crust are probably
previous intrusions of subduction related magma that have accumulated and stalled
through time resulting in some heterogeneity in the cnrst. Before eruption, as the magma
rose, the melts mingled thus producing the varied composition deposit Pathways for the
magma before eruption could be related to the extensional environment in southwest

Luzon.

25

Table 1
Sample Location

Sample
PNSt-9.28-A

PlVS1-9.28-B
PlVS1-9.48-A
PlVSt-10.97—A
BHO1-O1-St
31101-01432
31107-0331
31107-03431
BHO7-O3-P2
131107-0393
31107-0341
31107-030
ems-(445M
BH16—(4—5)—B
ems-(4.51.0
BH16-(4-5)-D
ems-(451.15
BH16—(4—5)~F
040303-1A
0403034 3
040303-10
04030340
040303415
04030341:
04030310
040303111
0403034 1
O40303-1K
0403034111
040303411
040303-2A
040303-23
040303-20
04030320
04030321:
04030320
040303-3A
04030333
04030330
040303-315
040303—3F

Site

Diliman, QC
Diliman, QC
Diliman, QC
Diliman, QC
Novaliches, QC
Novaliches, QC
West Triangle, QC
West Triangle, QC
West Triangle, QC
West Triangle, QC
West Triangle, QC
Wed Triangle, QC
Valle Verde 4, Pasig
Valle Verde 4, Pasig
Valle Verde 4, Pasig
Valle Verde 4, Pasig
Valle Verde 4, Pasig
Valle Verde 4, Pasig
La Vista gate

La Vista gate

La Vista gate

La Vista gate

La Vista gate

La Vista gate

La Vista gate

La Vista gate

La Vista gate

La Vista gate

La V1313 gate

La \fista gate
ULTRA-wall
ULTRA-wall
ULTRA-wall
ULTRA-wall
ULTRA-wall
ULTRA-wall
Kalayaan road
Kalayaan road
Kalayaan road
Kalayaan road
Kalayaan road

UTM Coordinates
293.739 1620.799
291.815 1612.523
291.177 1610.35

26

Table 2

Bulkrockmalorandtraoaelemontoonconh‘atlons

 

PlV81-8.26- PIV81-9.28- PlV81-9.48- PlVS1-10.97-
Sample A B A A BH01-01-81 BH01-01-P2
8102 52.62 59.49 53.74 54.65 60.74 65.79
1102 1.07 1.03 1.07 1.09 1.01 0.55
A0203 17.24 16.75 17.11 17.42 17.14 18.42
F0203 10.47 7.43 10.28 9.36 6.4 6.2
MnO 0.18 0.2 0.19 0.19 0.22 0.21
11190 3.49 2.09 3.28 2.98 1 .95 3.53
CaO 9.05 4.89 8.28 7.82 4.21 2.62
11:20 2.82 4.36 2.95 3.33 4.25 0.81
K20 1.94 3.21 2.18 2.31 3.62 1.8
P200 1.1 0.56 0.93 0.86 0.46 0.06
Totals 98 99 98 98 97 95
Rb (XRF) 55 95 65 69 103 57
Zrth) 105 182 118 126 209 354
Sr (XRF) 672 695 666 688 582 265
V 287.39 62.21 262.53 237.45 44.81 69.72
Cr 0 3.47 0 0 3.37 2.79
Y 29.6 36.74 32.3 31.44 36.03 11.18
Nb 5.35 9.33 5.87 6.61 9.9 10.26
Ba 624.54 983.7 643.3 718.64 1044.53 584.13
La 30.3 39.6 32.32 31.65 39 19.77
Co 52.04 76.11 57.44 58.65 77.1 48.57
Pr 7.07 9.88 7.85 7.99 9.94 5.27
Nd 30.61 41.62 34.09 34.93 41.37 19.53
Sm 6.73 8.89 7.42 7.43 8.54 4.52
Eu 1.87 2.5 2.07 2.06 2.38 1.06
Gd 6.41 8.17 7.04 6.89 7.99 3.51
Tb 0.9 1.14 0.98 0.98 1.15 0.52
Dy 5.03 6.24 5.54 5.38 6.25 2.33
l-lo 1.02 1.27 1.11 1.07 1.24 0.44
Er 2.77 3.54 2.95 2.92 3.42 1.38
Yb 2.85 3.63 3.05 2.88 3.61 1.82
Lu 0.41 0.54 0.44 0.43 0.52 0.24
Hf 3.16 5.24 3.4 3.41 5.54 10.34
Ta 0.34 0.55 0.37 0.37 0.58 1 .08
Pb 9.3 18.62 8.95 11.32 22.26 13.68
Th 8.7 14.66 9.47 10.17 15.79 28.17
U 2.61 3.51 2.96 2.68 3.94 1.78

27

TableZcontlnued

Bulkrockmajorandtraceelemntooncentrationa

 

88ml. 3407-03-81 SHOT-0341 Bl-lO'I-03-PZ Bl-107-03-P3 BH07-03-A SHOT-0&0
310: 59.54 63.25 64.53 61.23 58.8 57.42
TIC; 0.96 0.88 0.81 0.95 0.98 1.01
N203 16.2 16.39 16.63 16.29 16.15 16.47
F0203 7.91 5.93 5.36 7.36 8.24 8.95
M110 0.2 0.26 0.2 0.21 0.27 0.2
“90 2.49 1.94 1.55 2.31 2.62 2.98
COO 5.48 3.79 2.96 4.69 5.72 6.47
N020 3.83 3.83 3.79 3.54 3.77 3.44
K20 2.92 3.42 3.92 3 2.92 2.47
P105 0.47 0.32 0.26 0.42 0.53 0.58
Totals 98 97 96 97 98 99
Rb (XRF) 82 89 98 77 78 68
Zr (XRF) 156 206 220 174 153 132
3! (XRF) 535 417 382 465 523 586
V 172.35 77.87 82.34 114.28 173.17 200.23
Cr 3.05 3.38 3.48 3.16 3.15 3.3
Y 35.4 33.71 34.21 33.6 34.92 34.75
Nb 8.52 10.55 12.21 8.88 7.94 7.06
Ba 873.81 1042.46 1121.07 894.5 841.17 768.16
La 31.77 32.55 37.11 32.57 31.61 29.24
C. 62.13 70.56 79.24 64.67 60.86 57.61
Pr 8.18 8.15 9.31 8.21 8.02 7.7
Nd 35.03 32.99 36.99 34.47 34.55 33.05
8m 8.65 7 8.67 7.6 8.65 7.74
Eu 2.23 1.81 2.23 2.02 2.21 2.09
Gd 7.57 6.35 7.44 7.01 7.42 7.35
Tb 1.13 0.94 1.14 1.02 1.12 1.05
Dy 6.28 5.36 6 5.66 5.9 5.85
Ho 1.26 1.05 1.19 1.16 1.22 1.13
Er 3.9 3 3.93 3.18 3.87 3.3
Yb 4.57 3.36 4.91 3.31 4.48 3.58
Lu 0.67 0.48 0.7 0.49 0.65 0.51
Hf 5.47 5.61 6.64 5.09 5.13 4.12
TI 0.6 0.53 0.86 0.54 0.56 0.36
Pb 14.6 21.99 26.48 17.16 13.87 12.12
Th 12.2 14.34 15.95 12.75 11.43 10.7
U 2.69 3.02 3.75 2.7 2.71 2.22

28

Tablozcontlnuod

Bulkrocknnlorandtacoelenmuconoomratlom

Sample 31113-14514 31110-13513 331344-530 Bl'l16-(4-6)-D 31410-135145 ems-(4.514:

 

510; 64.43 61.34 31.92 61.39 63.35 61.1
110: 0.34 1.01 0.92 0.92 0.33 0.93
N20; 16.62 16.71 17.2 13.33 16.31 16.64
F0203 5.75 3.31 7.75 7.63 5.97 7.97
11110 0.21 0.12 0.13 0.13 0.2 0.17
1190 1.25 1.43 1.35 1.39 1.56 2
0.0 3.03 4.32 4.2 4.63 3.33 4.9
11130 3.73 2.33 3.45 3.23 4.16 3.15
K20 3.77 2.42 2.73 2.79 3.57 2.73
310. 0.3 0.4 0.35 0.39 0.35 0.41
rows 93 97 93 93 97 93
Rb man 105 33 77 74 96 93
am 212 137 139 174 194 194
snxm 403 332 537 535 439 439
v 70.75 111.54 107.32 142.05 124.32 33.73
01 0 0 3.3 9.74 10.03 0
v 33.91 22.13 23.47 30.04 22.42 33.76
Nb 12.3 3.75 3.97 9.79 7.93 11.33
Ba 1133.3 779.77 945.11 929.35 710.73 1023.37
La 37.53 24.99 30.13 30.71 23.31 33.71
Co 79.03 44.39 53.34 64.23 49.13 72.13
Pr 9.32 5.9 7.45 3.05 6.03 9.04
Nd 37.01 24.43 29.7 33.45 24.31 36.31
8111 7.39 5.36 3.53 9.19 7.41 7.3
E11 2.22 1.47 1.33 2.54 2 2.14
Gd 7.06 4.32 6.3 7.36 6.25 7.02
Tb 1.06 0.71 0.39 1.25 1 1.06
Dy 5.74 3.33 4.94 3.44 5.2 5.3
l-lo 1.19 0.77 0.93 1.3 1.1 1.13
Er 3.44 2.17 2.31 4.64 3.39 3.3
Yb 3.79 2.29 2.33 5.23 4.41 3.52
Lu 0.54 0.34 0.44 0.31 0.69 0.54
111 5.04 4.24 4.03 5.53 4.71 4.93
Ta 0.33 0.5 0.53 0.94 0.33 0.32
Pb 26.24 12.1 21.39 24.33 13.32 22.77
Th 14.4 11.27 12.34 12.42 9.59 13.53
1.1 4.52 2.17 3.42 3.53 3.27 3.96

29

Table 2 continued
Bulk rock major and trace element concentrations

 

30

Sample 04030314 04030313 04030310 04030310 04030316 04030311:
3102 51.34 50.94 60.91 53.39 51.27 52.39
110; 1,13 1.13 1.02 1.04 1.17 1.21
N203 13.24 13.75 17.04 17.04 13.3 19.34
1:020; 12.24 10.64 6.63 7.57 11.06 11.46
11110 0.16 0.33 0.25 0.35 0.15 0.12
1490 3.01 2.33 1.39 2.14 2.57 1.33
040 3.33 9.42 4.22 5.03 9.32 6.14
111130 2.51 2.73 4.22 4.11 2.71 2.61
K20 0.93 1.06 3.47 3.2 1.09 1.17
320. 1.25 2.57 0.5 0.64 2.03 1.46
101.10 93 96 93 96 93 93
Rb can 41 41 106 92 32 40
21011110 119 144 199 164 130 125
Swain 712 302 304 635 761 769
v 273.33 226.64 50.16 67.96 259.42 332.63
Cr 4.23 3.33 3.04 2.74 3.62 4.42
Y 46.53 45.39 35.26 35.36 39.73 72
Nb 5.54 3.44 10.24 9.33 5.67 6.03
. Ba 649 907.3 1095.93 1110.49 744.9 744.35
La 39.33 43.35 39.73 33.71 37.42 55.14
00 34.06 71.64 76.56 73.33 57.63 53.02
Pr 9.13 9.96 9.76 9.26 6.49 10.39
Nd 40.15 43.79 39.7 33.32 37.31 45.42
am 9.74 10.67 9.47 9.44 9.03 9.73
Eu 2.53 2.77 2.4 2.39 2.35 2.53
Gd 9.16 9.55 7.36 6.05 6.13 10.13
Tb 1.29 1.34 1.17 1.19 1.13 1.33
Dy 7.06 7.26 6.11 6.2 3.22 7.56
l-lo 1.43 1.46 1.21 1.27 1.24 1.32
Er 4.4 4.47 3.73 3.34 3.39 4.64
v11 5.02 5.06 4.53 4.55 4.47 4.73
Lu 0.75 0.75 0.33 0.63 0.34 0.69
111 3.9 4.56 6.12 5.65 4.02 3.33
Ta 0.4 0.46 0.33 0.59 0.4 0.3
Pb 9.39 9.5 23.1 16.24 6.69 9.12
111 6.64 10.37 15.4 13.37 9.04 9.54
u 2.97 7.54 3.46 3.14 3.41 3.55

Table 2 continued

Bulk rock major and trace element concentrations

 

Sample 04030346 040303-1H 040303-1l 040303-1K 040303431 040303410
3102 51.66 50.41 51.84 50.4 50.18 56.1
T102 1.16 1.31 1.19 1.22 1.08 1.11
N203 18.39 20.12 19.17 18.88 17.48 18.53
F0203 11.03 12.14 10.94 11.45 10.8 9.16
M110 0.15 0.23 0.21 0.21 0.16 0.29
M90 2.7 2.71 1 2.38 3.05 2.32
080 9.42 8.3 8.73 9.6 10.98 5.59
N820 2.62 2.64 2.92 2.61 2.55 3.7
K20 1.11 1.02 1.35 1.1 0.93 2.33
P205 1.75 1.14 2.66 2.13 2.78 0.87
Totals 97 95 96 96 98 97
Rb (XRF) 36 38 40 45 25 78
ZNXRF) 124 132 136 125 121 168
Sr (XRF) 738 699 800 761 756 662
V 277.75 275.95 290.06 263.16 311.75 105.74
01' 5.52 4.69 3.35 3.86 5.78 2.77
Y 40.41 38.74 38.14 38.2 34.07 40.77
Nb 5.89 6.42 6.29 5.83 5.23 8.61
Ba 666.74 692.01 898.03 762.46 633.6 883.93
La 35.73 36.4 37.05 35.84 32.98 37.44
Ce 57.19 62.87 61.8 59.12 56.07 72.5
Pr 8.47 8.99 8.7 8.36 7.62 9.85
Nd 37.18 39.36 37.69 37.14 33.1 43.27
Sm 9.18 9.72 9.43 9.17 8.03 10.63
Eu 2.4 2.53 2.44 2.35 2.15 2.78
Gd 8.18 8.57 8.18 8.03 7.45 9.22
Tb 1.18 1.23 1.18 1.14 1.04 1.32
Dy 6.43 6.73 6.39 6.32 5.59 7.3
l-lo 1.27 1.31 1.27 1.27 1.1 1.45
Er 4.03 3.97 3.84 3.79 3.47 4.47
Yb 4.56 4.6 4.42 4.33 3.94 4.98
Lu 0.67 0.66 0.64 0.63 0.58 0.73
Hf 3.96 4.42 4.7 4.2 3.82 5.64
Ta 0.39 0.45 0.48 0.42 0.4 0.6
Pb 8.7 12.88 9.74 9.4 8.06 15.88
Th 8.9 10.17 10.83 9.37 8.64 14.19
U 5.78 4.73 4.6 5.56 6.19 3.19

31

Tablezcontinued

Bulkrockmaiorandtraceelomentconcentratlona

SWO 040303-2A 040303-28 040303-20 040303-20 040303-2F 040303-26

 

SIC: 60.66 63.07 62.9 62.15 64.12 63.09
1101 0.92 0.84 0.87 0.86 0.84 0.85
N203 16.11 16.13 16.3 16.19 16.59 16.22
F0203 7.31 5.84 6.04 6.31 5.67 5.87
M00 0.2 0.2 0.2 0.19 0.17 0.19
M90 2.17 1.55 1.71 1.71 1.43 1.6
000 4.93 3.95 3.94 4.22 3.02 3.68
N810 4.11 4.23 4.14 4.39 3.62 4.53
K20 3.16 3.58 3.52 3.46 4.21 3.61
P205 0.44 0.6 0.37 0.52 0.32 0.36
T0188 99 97 96 98 97 98
Rb (XRF) 83 97 95 87 99 95
ZHXRF) 167 201 193 184 210 194
Sl’ (XRF) 489 431 423 483 394 430
V 137.2 80.82 82.07 96.27 70.38 86.71
01’ 3.36 3.82 2.87 2.68 3.23 3.96
Y 35.12 38.2 35.99 36.71 36.94 35.48
Nb 8.83 11.06 10 9.87 11.03 11.22
B. 9m.06 1079.72 1006.97 1005.31 1101.37 1054.15
LI 33.01 39.1 1 35 35.57 37.94 35.72
00 65.45 75.6 68.91 69.68 76.45 74.12
Pr 8.34 9.61 8.71 8.89 9.43 9.21
Nd 34.64 39.48 35.95 37.28 37.79 37.34
8111 8.74 9.49 8.71 9.09 8.1 8.98
Eli 2.21 2.4 2.22 2.35 1.93 2.28
Gd 7.54 8.17 7.66 7.84 7.33 7.53
Tb 1.11 1.24 1.16 1.19 1.03 1.14
Dy 6.22 6.48 6.24 6.31 5.73 6.28
Ho 1.26 1.32 1.28 1.29 1.14 1.26
Er 3.99 4.26 3.98 4.16 3.41 4.06
Yb 4.81 5.07 4.74 4.92 3.95 4.9
Lu 0.71 0.77 0.71 0.72 0.54 0.71
Hf 5.52 6.55 6.06 6 5.8 5.7
Ta 0.62 0.76 0.71 0.69 0.58 0.73
Pb 36.85 29.5 24.6 19.86 27.09 39.39
Th 12.6 15.28 14.2 13.83 16.06 13.52
U 2.91 4.26 3.21 3.31 3.59 3.77

32

TaleZcontlnued
Bulkrockmaiorandtraceelement concentrations

 

W0 040303-3A 04030343 040303-3C 0403034E 04030341:
3.02 63.29 63.33 61.99 58.71 61.67
110: 0.83 0.85 0.89 0.92 0.9
102°: 16.33 16.01 16.27 16.47 16.33
F0203 5.74 5.88 6.56 7.85 6.69
"no 0.19 0.2 0.2 0.24 0.19
M90 1.51 1.53 1.74 2.48 1.84
CaO 3.62 3.82 4.34 6.06 4.45
Mac 4.34 4.24 3.97 3.69 4.01 ‘
K20 3.76 3.71 3.48 2.92 3.42
P205 0.38 0.44 0.57 0.66 0.51
Totals 97 97 97 98 97
Rb (XRF) 105 110 102 85 102
Zr (XRF) 217 217 202 174 197
Sr (XRF) 420 436 463 536 494
V 58.58 63.89 102.65 132.19 89.4
Cr 3.4 4.61 5.03 4.24 4

Y 36.44 37.78 37.04 36.63 37.85
Nb 11.35 11.72 10.03 8.84 10.26
Ba 937.33 1010.33 918.5 818.31 856.2
La 33.43 35.08 32.37 30.67 32.6
06 69.38 72.42 65.09 60.79 64.39
Pr 8.52 9.12 8.22 8.13 8.22
Nd 34.36 37.38 34.13 34.96 34.79
Sm 7.42 9.13 7.81 8.77 8.08
E11 1.91 2.3 1.99 2.22 2.04
Gd 6.8 7.92 7.12 7.64 7.11
Tb 0.99 1.2 1.07 1.17 1.06
Dy 5.6 6.65 5.96 6.37 6.02
Ho 1.12 1.34 1.18 1.28 1.2
Er 3.29 4.32 3.54 4.07 3.61
Yb 3.82 5.1 4.02 4.75 4.06
Lu 0.53 0.75 0.58 0.71 0.58
Hf 5.44 6.84 5.36 5.87 5.72
Ta 0.54 0.77 0.52 0.63 0.54
Pb 23.69 27.7 31.42 17.88 18.12
Th 13.02 14.06 12.6 11.48 12.51
U 3.57 4.02 3.29 3.07 3.09

33

Tfle3

Pladoclase compositions
Sample 310:
PN81—9.23A-pl0 43.07
PN81-9.20A-pl10-c 45.75
PN81-9.28A-pl10-r 45.38
PN81-9.28A-pl11-o 51.30
PNS1-9.20A-pl11-r1 48.25
PN81-9.28A-pl‘l1-r2 47.42
Enclave (01-03)
PIV81-9.28A-o1-pl1-c 53.38
PIV81-9.28A-e1-pl1-r1 50.73
PlV81-9.20A-et-pl1-rz 53.16
PN81-9.20A-e1-pl2 50.63
PlV81-9.20A-e1-pl3 53.82
PIV81-9.20A-01-p|4 54.31
PlV81-9.28A-02-p17 55.28
PlV81-9.28A-03—pl5-c 44.13
PN81-9.20A-03-p|5-r1 45.73
PN81-9.23A-a3-pl5-rz 44.32
PlV81-9.28A-e3-pl0-c 44.61
PlV81-0.23A-e3-pl6-r1 48.48
PN81-9.20A-o3-pl6-rz 45.07
BHOTO3-P3-pl1-c 52.44
81107039313114 55.22
BHO703-P3-pl2-c 53.81
31107033311124 54.39
0403031N-pI1-c 49.35
04030311131141 47.53
040303-1N-pl1-l 41%
0403031111313 47.41
040303-26-pl3 59.82
04030340914 55.61
040303-2F-pl1 58.69
040303-38-pl1-c 51.71
0403033301141 53.99
04030348-pl142 54.97
040303-33-p12-c 54.30
0403033331241 54.51
040303481034: 55.93
“0303-38-le1 54.97

N203
32.72
33.78
33.72
29.93
31 .87
31 .41

28.41
29.99
28 48
30.69
28.02
26.73
26.67
34.50
33.59
35.07
32.90
31.30
34.01

28. 25
26.90
28.07
27.28

30. 99
32.08
32.41
32.22

25.34
28.21

25.89

29.05
27.91
26.87
28.05
27.77
27.10
27.66

F00
0.77
0.68
0. 77
0. 73
0.80
0. 81

0.57
0.51
0.61
0.52
0.63
0.54
0. 56
0. 59
0. 85
0. 61
1.02
1.29
0.83

0.56
0. 56
0.59
0.50

0.57
0.57
0.61
0.75

0.42
0.50

0.54

0. 65
0. 52
0.59
0. 55
0. 51
0.53
0.57

34

17.23
17.99
18.16
13.67
16.13
15.83

11.76
13.81
11.77
13.69
11.02
10.59
10.02
18.85
17.65
18.86
17.44
15.36
18.69

11.35
10.30
11.11
10.53

14.86
15.96
16.50
16.07

7.21
10.89

8.54

12.46
10.96
10.24
10.72
10.59
10.35
10.70

N820
1.52
1.33
1.24
3.78
2.29
2.28

4.72
3.61
4.56
3.56
5.08
5. 32
5.49
0. 81
‘l. 35
0. 67
0.97
2.57
1.12

4.81
5.28
5.01
5.32

2.83
2. 36
2. 07
2.21

7.10
5.45

6.02

4.25
4.83
5.41
5.17
5.44
5. 60
5.18

K20
0.03
0.11
0.07
0.26
0.11
0.14

0.34
0. 26
0.47
0.22
0. 38
0. 42
0.71
0.04
0.04
0.05
0.11
0.11
-0.01

0.29
0.35
0.35
0.34

0.12
0.13
0.10
0.17

0.77
0.33

0.58

0.29
0.29
0.40
0.38
0.44
0.43
0.40

Total
98.49
99.69
99.96
99.87
99.56
98.03

99.49
99.07
99.20
99.56
99.11
98.89
98.83
99.01
99.28
99.70
97.34
99.26
99.98

97.84
98.77
99.17
99.83

98.90
98.91

100.03

98.92

101.52
101.38

100.53

98.65
98.67
98.60
99.39
99.63

100.04

99.90

Mn
85.46
89. 25
90.07
67.80
80.03
78.51

58.34
68.50
58. 41
67.93
54.69
52.55
49.73
93.52
87. 57
93.55
86.52
76.21
92.73

56.31
51.10
55.12
52.39

73.72
79.18
81 .88
79.73

35.74
54.05

42.39

61. 84
54.38
50. 81
53.18
52.54
51.36
53.07

Table 3 contlnued

Plagioclase compositions
Sample 810:
040303-3F-pl1-c 53.38
040303-3F-pl1-r1 52.87
0403033391142 53.55
040303-3F-pl2 53.70
040303s3F-pl3-c 52.47
040303-3F-pl3-r1 52.05
MOW-11M 54.10

N203
28.53
28%
28.21
28.66
27.91
28.23
27.98

F00
0.54
0.51
0.56
0.59
0.61
0.63
0.50

35

11.51
12.23
11.45
11.63
11.25
12.31
10.94

Map
4.64
4.56
4.37
4.80
4.80
4.35
5.22

K20
0.30
0.32
0.30
0.35
0.35
0.31
0.39

Total
99.00
100.30
98.86
100.21
97.53
98.30
99.32

%An
57.10
60.68
56.80
58.96
55.84
61.09
54.28

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LIQUSJ] euuew

 

 

 

 

Figure 1a. Tectonic setting of the northern half of the Philippines, showing the
location of opposing subduction zones (Manila Trench and Philippine Trench) and
the left lateral Philippine Fault in between. The enclosed area is enlarged in the
next map (Fig. 1b) and includes southwest Luzon and the study area.

 

Figure lb. A map showing the west facing volcanic arc, Bataan Arc (dashed line),
and the location of Macolod corridor. The symbols represent active (triangle),
potentially active (filled circle), and inactive (open circle) volcanoes. Taal and
Laguna calderas are labeled. The enclosed area covers the extent of the surface
geologic map of Metro Manila shown in figure 2.

40

120'54‘ 121°00' 121°05'
14°45‘ ‘

 

 

30 - $ Laguna de Bay
0 5
Kilometers LEGEND

 
 
     

 

SURFACE - Quaternary alluvium
GEOLOGY OF [:1 Taal pyroclastiee
METRO MANILA .. _
25' AND DIlIman |:= Pyroclastic flaw (PF) deposrt
ADJACENT AREAS Tuff PF and tuffaoeous sediments
- Conglomerates
mam "...:
mm: W m "" Basement complex

 

 

-
Active fault trace (dashed

I I I where inferred. hachures
indicate downthrown area)

 

 

 

 

Figure 2. Surface geology map of Metro Manila. The upper Diliman Tuff is
shown in green. Sample location is indicated by red circles and beside it is
the site number.

41

 

Figure 3a-d. Outcrop photos

a. An excavation for a building showing an approximately 10 m thick pyroclastic
flow (PF) deposit and other units below. This is located in Cubao, Quezon City.
The upper pyroclastic flow deposit is correlated with the upper Diliman Tuff and
although this site was not sampled, it shows a thickness for the unit and other
deposits below .

b. Pyroclastic flow deposit sampled in site 040303-01 (Brgy. Malanday, Quezon
City).

c. Pyroclastic flow deposit sampled in site 040303-02 (ULTRA, Pasig).

d. Pyroclastic flow deposit sampled in site 040404-03 (Kalayaan Ave., Pasig).

42

PlVS-1

 

 

 

 

 

50m
1‘
0!
2
.9.
a Pyroclastic
40- 0.5
U)
E BH-16
“"‘e'e" A 040303-3
3o 3 ° Pyroclastic flow
<6 ”.»° .
E , r: :1 Pyroclastic surge m
an 0': g Pyroclastic
PWOCIESNC i Pyroclastic 3 flow
surge flow
20
Weathered tuff Weathered
1—L tuff
10 Pyroclastic surge and
” fall
Pyroclastic flow
0 Consolidated
— y

 

Figure 4. Stratigraphic logs of selected sample sites. Correlation of the upper
Diliman Tuff unit (shaded green) is shown.

43

 

I Pyroclastic flow deposit

 

Figure 5. Photo of a core sample (BH-07).‘ The unit contains heterogenous
pumice clasts - mafic, felsic and banded pumice.

"s‘

 

 

\

Figure 6. A close-up of the core samples from PIVSl-9.28 (a) and
BH-07 (b). Two clasts, a mafic (dark) and felsic (light) pumice clast,
in BH-07 are outlined.

45

040303-1C-gm5

040303-1C-gm4

 

 

040303-1 N

.0.5 mm

Figure 7. Photograph of groundmass in plane polarized light showing vesiculation
and mingling (dark and light glass). For pumice 040303-1C the points with analysis
are shown (see table 3).

46

 

040303-3B

 

BH07-03-P3 .

1mm

Figure 8. Photos in crossed polars of plagioclase as glomerocryst and isolated
phenocrysts. Zoning can be seen. The groundmass is mostly glass with crystallites.

47

 

040303-2C

0.5 mm

Figure 9. Pyroxenes in sample 040303-2C, a clinopyroxene in plane polarized
light (a) and an othopyroxene in crossed polars (b) with magnetite inclusions.

48

 

. 0.1 mm

Figure 10. A photo of enclave l in PIVSl-9.28A showing microlitic groundmass
of mostly plagioclase and plagioclase glomerocryst in crossed polars. The close up
of plagioclase phenocrysts in this enclave, shows numerous inclusions and rounded
grain edges.

49

 

Enclave 3

Figure 11.

a. Enclave 2 in PIVSl-9.28A under crossed polars showing acicular crystallites in
the groundmass and one larger plagioclase lath.

b. Enclave 3 in PIVSl-9.28A under plane polarized light containing zoned
plagioclase and clinopyroxene.

50

 

 

 

 

 

 

 

 

 

16 rlrlTIrTIrllll IllIIIIITITIIIIIIIIIIITWI
_ Phonolite _‘
Na20+K20 Rhyolite -
orlllll ILJ lllLllllLllJlllllllllllllllllll
35 4O 45 50 55 60 65 70 75

Sio2

Figure 12. Total alkalis versus silica diagram. The samples plot in the basalt to
the trachydacite field.

PIVSIA BH01* BH07 {p BH16+

040303-1 A 040303-2 [:I 040303-3 E3 .

51

 

 

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Si02 3102

Figure 13. Major element variation with silica

52

FeO*

Tholeiitic

 

.. - ’-‘
if"
Cale-Alkaline
\l ‘l \l \l V \l \l \l v
Alk MgO

Figure 14. The pumices are enriched in Fe and in the AF M triangle, some plot
in the tholeiitic field.

53

 

 

 

 

9 r T r
.- as ‘
+
7 ~ {5‘} -
6 '" + $ ARI}, ..
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A
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Figure 15. Total alkalis versus Mg#. A separate trend can be seen for the
basaltic samples with high P205.

54

Rock/Primitive Mantle SunlMcDon. 1989-PM

 

  

 

 

 

 

 

 

 

 

    
   
 

 

 

 

 

 

 

 

 

1WD _ I T I I I I I I I I I I I I I I I I I I I =
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1 1 1 1 1 I I I 1 I I I I I I I I I I 1 I I I
CstBaTh u Nb K LaCePb Pr Sr P NerSmEu 11 Dy v YbLu
RoddPrimitive Mantle SunlMcDon. 1989-PM
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1 I I I 1 I I 1 I I 1 I 1 1 I r I I I I I I I I

CstBaTh U Nb K LaCePb Pr Sr P NerSmEu Ti Dy Y YbLu

Figure 16. Trace element spider diagrams. Two groups were identified based
on the spidergrams. One group consists of the basaltic high P205 pumices (a).
Majority of the pumices are included in pattern b.

55

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2000~I I I I IfII I I I I I I I I ITI‘ 200_fI I I I I I ITTIITI I I ITI‘
I I C 3
1500 :- —_ 150 :- -_
.. .1 i- .1
_ A D _ a _
Ba 1000 e A . FIE ~Rbioo — “£13 —
A‘ . A l- ” ..1
I A .. ‘ ‘ DE? ‘ r A d [15:] 0
(:3 1:15 3 3 I; 1L", :1
500 . 50 I ‘ j
.1 -4
1 -4
O 7 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 11 o 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 .1
900 T T I I I I T T T I I I I I I I I I T 20 TI I I I I I T I I I I I I I I I I I .1
800 i‘a‘A -* :
700 ‘ A [f.\L/:1 A A d 15 —"“
-1 A :
600 r A a + 19:1 .
5, Nb 10 Q; 33313 1
500 - * 13:3; - A g.. .
400 '1 5 g _-:
300 ~ 4 —
200 1 1 1 1 I 1 1 1 1 I 1 #1 I 1 1 1 1 0 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 .1
4m T I I I I I I I rT T I I I I I I T 400 I I I I I I I I I I I I I I I I I I I
A
300 Ag ‘
300 r — A
‘ A
Z' v 200 - ()3 ~
I
200 - .3 ‘EELEB C] ‘ ‘ I D0
A " Cf} 100 “ A #5 ‘
.11. %D
5‘ A A A *
100 113134 Lm1 1 I 1 1 1 1 I 1 1 1 0 1 1 4 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1
60 I I I I I I I I Tj I I I I I I I I I 6 I I r I I I I I I I I I I I I I T I I
5 ‘A‘ 5 [1 mg
L‘ A I
40 A -‘ 4 1‘": [:1 .I
La ‘4 ‘ ‘ 5' DEED Yb A I
n a.
4.. A A a Bill] _ 3 _ a A; v ..
20 ~ - 2 - .
I
10 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 1 1 1 L 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1
50 55 60 65 70 50 55 60 65 70
$102 3102

Figure 17. Trace element variation with silica. Note the higher and lower
concentrations trends of Yb for the same value of silica.

56

Rock/Chondrites REEs-Nakamura, 1974

l l l l r T l l l l l T l l l

 

1 000

I lllllll
11111111

100

lllllllll
llllllllI

 

10

T llmlll
l 1 llllllI

 

 

l l l l l l l l l l l l l l 1

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

 

Figure 18. REE spidergrams. The samples include 50—64 wt. % Si02. A tight
pattern is formed despite the range in silica, with decreasing concentration from
light to heavy REE and a slightly concave upward trend towards the middle to
heavy REE.

57

 

 

 

 

70 l I I I l I
65 — -
_ A 4
Bulk SiO _ A g A ~
2 _ W ‘
60 — 4
r -
— -l
I A AA 2
55 — —
:(PIVS1-9.28A) +63 CD ED Ml Mfg? :
50 L- I I I I I i -
30 4o 50 60 70 80 90 100

%An

Figure 19. Generally the An content (values include rim and core analyses) of the
plagioclases decrease in higher silica pumices. Plagioclases from enclaves found
in pumice PIVSl-9.28A are included.

All pumice A enclavel C39 enclave2 + enclave3 {k

58

 

 

I l I j I I I l fl 1 I I

040303-38 (63.33 Si02) c; d
fOUl'l mass

. 0
nm _ am . pl
rim _ 0

core AA ‘

 

 

 

 

I l l L 1 l l l l l

30 40 50 60 70 8 90 100 30 4O 50 60 70 80 90100

 

 

 

 

 

 

 

 

 

 

 

0
AA" PlVS1-9.28A %An
. I a r r r Enclave1
040303-1N (56.1 Si02)
rim L AA .
core-i- A A -
I l I I I I
l l l l l I
30 4o 50 60 7o 30 90 100 L .
%An
rim . .
I I I W I I
PIVS1-9.28A (52.62 Si02)
_ ‘ core _ i
' I l l l l 1
nm .. -i
/ f 30 40 so 60 7o 80 90100
0
we ‘ ‘ PlVS1-9.28A M"
Enclave 3
l L L l L l

 

 

 

3O 40 50 60 7O 8 90 100
%An

Figure 20. Plagioclase from different pumices, bulk silica content is indicated,
showing the An values for the rim and core. Analysis on the enclaves is also
included.

59

 

 

En Fs

Figure 21. Classification of the pyroxenes in the samples. The pyroxenes plot in the
diopside-augite and hypersthene fields.

BHO7—03-P3 CG?! 040303-1N A 040303-2C E] 040303-2F D 040303-3B E]
040303-3F a PIVSl-9.28A A enclave 1 o enclave3 {3

60

 

 

 

 

 

 

 

 

7 I I I I I l l I l I l I I I I I
I . l l
6 - ' A 1
O
5 — —
Al/Ti
- A [j q
4
#1239 {:2
i} AB CD
- '4} E] -
3 01:? Cl :3;
I 1 Bl I I l l I I l I I I I I I I l
50 55 60 65 70
Mg#
7 I l | r
O
6 _ O A -
O
5 — ——
Al/Ti
4 . CG: ACE ‘
a E”
3 ' Q filjl’lj *
2 D I I I I
0 10 20 30 40 50

%W0

Figure 22. Two groups of pyroxenes can be seen in terms of Al/Ti ratios. Both
groups have similar range of Mg # (Al/Ti vs. Mg#). The group with higher Al/T i
includes only clinopyroxenes (Al/T i vs. Wo%).

61

 

 

 

 

 

 

 

 

7O _ fT T r I I I I I I I I I I I I I I I _
C A 3
65 : § g a afi ‘_
Glass SiO2 :- A A A j
b- A —I
60 T {5 86 ‘_
C 3 g A :
55 _— i} A j
I— .-
" 'l
50 _ I I I I I I I I I I I I I I I I I I I 5
50 55 60 65 70
bulk SIOZ
4 I I I [A] I I I I I I I I I I I I I—r
A
3 ' A '
Glass MgO JA
2 - A AA —
A
1 _ AMA _
I .A
a a5 Ag
0 I I I I I I I I I‘I'I-I- I I I I I I I L
50 55 60 65 70
Glass SiO2

Figure 23. IVariation in glass composition for the pumice fragments. The first
plot shows groundmass glass silica against bulk silica. The second plot is MgO
versus SiO2 in glass, note that enclave 2 and 3 plot outside the trend.

Enclave 1 glass 63 Enclave 2 glass + Enclave 3 glass fi
PIVSl-9.28A pumice glass A all other pumice glass A

62

 

 

 

 

40 I I I I I I I I I I I I I fI I I I I
30 ' ‘
A AA <13 (CD
I [22%,]
Mg#20 # A EEC: -
#53'
.. A a
10 A
0 A I I I I I l I I I I I I I I I L I I
50 55 60 65 70

Figure 24. Almost constant Mg # for the upper Diliman tufi' pumices as SiO2
values increase, does not show a fractionation trend.

63

 

ZOfiTfirIIrrIIIIIIIIrI

Bulkpumice
15

BulkFeO*lMgO
10

 

1...
SPAAA ‘ q]: %mg¢

VIIIIIIIIIIIII
IIIIIILIIIIIIIIIIII

 

 

 

 

 

 

 

 

 

 

 

 

 

 

*- a
0 r- I I I I I I I I I I I I I I I I I I I
50 55 60 65 70
Bulk sso2
20 _ I I I I I I I I I I I I I I I I I I I -
: Glass :
- +
15 .- 1
.. + .1
Glass FeO*/MgO : ‘5 j
10 — _
I- ..
5 -— 595A —:
_ . A '-
: AAAAA b :
0 I- I I I I I I I I I I I I I I I I I I I _
50 55 60 65 70
Glass SiO2

I

Figure 25.

a. Higher values of FeO*/Mg0 for bulk compositions of samples 040303-11 and IF
(circled).

b. Higher values of FeO*/Mg0 for glass compositions of enclave 2 and 3.

 

0.10 I I

0.08 BH07-O3-C-gm4

0.06
Mg/Si

0.04

0.02

 

 

 

 

0.00 a
0.0 0.1 0.2 03

 

0.10 . , I I I i I

0.08

0.06
Mg/Si

0.04

0.02

 

 

 

 

0.00

Figure 26. Mixing line for glass compositions. The end members cover the
range of compositions but the fit of the mixing line is a little offset. Note glass
from enclave 2 and enclave 3 plot outside the trend.

65

 

I
A PlVS1-9.28A

A} _

0.08 '-
0.06 r
Mngi "

0.04 "

0.02 "‘

 

 

 

 

0.0 0.1 0.2 0.3 0.4
CalSi

 

0.08

0.06
Mngi
0.04

 

0.02

 

 

 

000 I I 1

Figure 27. The same plot as figure 26 but using bulk pumice compositions.
Note samples 040303-11 and IF (circled) fall way off the trend.

66

 

12

11 “

10

9

 

Lafo

6 I—

 

.9:

7 :-

 

 

 

 

l I l l I l

I I I I I I I I I I I I
I | I

A A‘ -
‘3’ C]
A

E]
[III
A

no

Ufa}

CI

ILLIIIIIIIIII

 

 

5
50

55 60 65

Sic2

 

12

 

11

10

LaPYb

©0-

<§fi£> <>

 

 

 

 

 

 

S6 - 60 wt. % Si02-

I I I I I I

 

 

Figure 28.
a. Lale ratios for the upper Diliman Tuff show a scatter and a wide range

from 6.5 to 11.5. (See Figure 12 for symbols).

b. La/Yb ratios for Taal and Laguna pumices in the andesitic range (56—60 wt.%
Si02) plotted with respect to the distance of these centers from the volcanic front
(Bataan arc). Location of the source vent for the upper Diliman Tuff is unknown,
the values are represented by the shaded area. This graph shows higher values for
Laguna pumices, which may be interpreted as lower degrees of melting; compared
with Taal pumices. The upper Diliman Tuff is intermediate between the two.

40 50 60 70
Laguna

80
Taal
distance from volcanic front

67

TIC)

1300

1200

1100

1 000

900

800

 

 

,wwi

040303-3F 040303-2C

040303-38 BHO7-03-P3

Figure 29. Geothermometry for coexisting orthopyroxene and clinopyroxene in
pumice. Temperature estimates were done using QUILF (Andersen et al., 1993).
Samples O40303-3B and 040303-2C have additional constraint from magnetite and
give temperatures of 850 to 900°C with smaller uncertainty.

68

 

 

 

 

 

20 I 1 I r I I I I I I I I I I I I l I I
1.5 “ O Q‘ ‘
L I .C V)

a “We. ., ‘
0.5 ' 2%: I ‘
00 I I I I I4 I I I I I I I I I I I I I

' 55 6O 65 7o

Sio2
4

IIVIIIIIIIVI/WIIII

   

r ‘9
‘ ‘<>‘ A.
3 w ‘
sax/98% *wgfiéfifi‘
K202 . é gwogz _
a O O
23 O
1 x _
O

IlIlIIIlIIllIiIIIIL

55 65 70

 

sso2

 

IIIIIIIIITTTIIIIIII

 

 

 

 

55

3502

 

400 I I I l I I I I I I l I I I/ J)! I I I I
2
300 M); -
Zr ow}, {

‘: 55$ Wax; v _;. m
‘ - O 2523 M 315%
100 II 83

.I

 

 

 

o I I I I I I I I I L I I J L I I I I I
50 55 60 65 70
sao2
200 I r I I I I I I I I I I I I I I I 1*T

   

I

 

 

 

150 AV -
.9 . i
Rb (I C [55; 5 I
100 j «i 5%-? —
_;exx. ,§x~%% ;
so , M ‘ i
'33 ..
<> :

o I I I I I I I I I I I I I I I I I I
50 55 60 65 70

$02
900 I I I fr 1’! T I I F I I I I T‘I—r

   

 

 

 

7oo " -
Sr —
500 '—
300 ‘
1 00 I L I I I I I l I l I l l I I l I I
50 55 60 65 70
3102

Figure 30. Comparison of major and trace element compositions of upper Diliman
Tuff and deposits from Taal and Laguna calderas. Sr values clearly distinguish Taal
deposits. Differences between the upper Diliman Tuff and Laguna Tuff can be seen in
MgO, TiOz, and Zr. Taal data (Martinez, 1997; Listanco, 1993; Miklius et al., 1991);
Laguna data (MSU data). Laguna <> Taal 33 Upper Diliman Tuff A

69

 

 

 

 

 

I
8 *- _
7 r- ..
6 - ..
N820+ K20
5 — _
4 _ ‘
X
3 '- —1
2 l l l l
0 1 0 20 30 40 50

Mg#

Figure 31. The clearest distinction between Laguna deposits and the upper Diliman
Tufi‘ is the Mg#. Upper Diliman and Taal pumices and lavas are more primitive
than Laguna pumices.

70

Rock/Primitive Mantle SunlMcDon. 1989-PM

 

    
 
 

 

 

 

 

    

: I I l I I l I I I I I I I I l I I I I l I I :
3 Upper Diliman Tuff I
100 :- '21
10 '_— ..
- 57 — 65 Sio2
1 I l l I l I LL; 1 l l l l l I I L l l l l
CstBaTh U Nb K LaCePb Pr Sr P Nd ZrSmEu Ti Dy Y Yb Lu
Rook/Primitive Mantle Sun/McDon. 1989-PM
1000 : I l I l I I I I I I I I I I I I I I I I I l =
2 Laguna pyroclastic flow deposit 2
_ A _
100 _—
10 :-
‘ 57 — 67 Si02 ‘
l l l I l l I l I l l l l l l I l l l I 1 L

 

 

 

CstBaTh UNb K LaCePb Pr Sr PNd ZrSmEu TiDy Y Yb Lu

Figure 32. Trace element spidergrams show little difference between the upper
Diliman Tufl‘ and Laguna pumices.

71

Rock/Chondrites REES-Nakamura. 1974

1000 I I l l l l f T r I T I I T

   

 

l I Inufi

L I Jllllll

 

10

63-65 Sio2

l 1 l l 1 l l l l L I I 1 J I

VLaCePrNdeSmEquTbDyI-Io ErTmYb Lu

Rook/Chondrites REES-Nakamura. 1974

1000 I I I I I I I l I I I I I I I

 

 

57-62 Si02

1 7 l l l l l l l l l 1 l l l I l

LaCePrNdeSmEquTbDyHo ErTmYb Lu

3 § '
j?
..P
If!
7 Q}
I: T "5‘

Rook/Chondrites REES-Nakamura. 1974

1000 IIITTIIITIIIIII

 

 

 

100
10
Laguna (53.54 Si02)
. MM (50 - 56 Si02)
1 l l l l 1 I l 1 l L l l l l l

LaCePr NdeSmEquTbDyHo ErTmYb Lu

Figure 33. REE distribution for the upper Diliman Tuff shows a tight pattern
from low silica to high silica pumices while Laguna REE concentrations have
more variation.

72

 
   

Trench Taal Laguna

CrustI

 

 

Mantle

 

 

 

 

 

1: Fluids introduced by the subducted slab (represented by dashed blue arrows)
metasomatise the mantle. Addition of fluids cause more melts to form and the melts rise
(red arrows).

2: The melts stall beneath the crust and crystallize. They partially melt the surrounding
crust comprised of previously emplaced arc magma

3: The melts rise, stall in mid-crust and partially melt surrounding crust (see figure 35).

Figure 34. Model for the evolution of the upper Diliman Tuff.

73

3a: Basaltic melts from deep in the upper mantle rise then stall at the lower crust.
These melts rise again and pond at the mid-crust and melt surrounding rocks.

Partial melting of calc-alkaline crust

10 Km
(most of the samples)

 
 
   
 
 

Crystallized earlier intrusion,
(Enclave 1 in PlVS1-9.28A)
being partially melted by
new intrusions

Basaltic intrusion
Melts rise 4__

 

Crust

Ponded melt (PlVS1-9.28A)

3b: New basaltic melts (tholeiitic) rise and intrude the previous intrusion. The different
melts are then erupted as a chemically variable pyroclastic flow deposit.

 

Upper Diliman Tuff unit
A
Partial melting of calc-alkaline crust A M It , 10 Km
(most of the samples) e 5 ”5e

   

prior to eruption
Tholeiitic melts intrude . . _
Previous intrusion A
(Enclave 2 & 3 in PlVS1-9.28A) Melts rise ‘

Crust

 

 
 
  

Tholeiitic melts —_—>

Figure 35. Model for the evolution of the upper Diliman Tuff (continued).

74

REFERENCES

Alvir, A (1929). A geological study of the Angat-Novaliches region Philippine J. of
Science: 40, 359-419.

Andersen, D, Lindsley, D. and Davidson, P. (1993). QUILF: A pascal program to assess
equilibria among F e-Mg-Mn-Ti oxides, pyroxenes, olivine, and quartz.
Computers and Geosciences: 19, 1333-1350.

Annen, C. and Sparks, R (2002). Efl‘ects of repetitive emplacement of basaltic intrusions
on thermal evolution and melt generation in the crust. Earth and Planetary Science
Letters: 203, 937-955.

Arcilla, C. (1991). Lithology, age and structure of the angat ophiolite Luzon, Philippine
Islands. MS Thesis. University of Illinois at Chicago.

Besana, G, Shibutani, T, Hirano, N, Ando, M, Bautista, B, Narag, I. and Punongbayan, R.
(1995). The shear wave velocity structure of the crust and uppermost mantle
beneath Tagaytay, Philippines inferred from receiver function analysis.
Geophysical Research Letters: 22, 3143-3146.

Cardwell, R, Isacks, B. and Karig, D. (1980). The spatial distribution of earthquakes,
focal mechanism solutions and subducted lithosphere in the Philippines and
Northern Indonesia regions. In DE Hayes (Editor), The tectonic and geologic
evolution of Southeast Asian seas and islands. AGU Geophysical Monograph: 23,
1-35.

Cas, R. and Wright, J. (1993). Volcanic successions: modern and ancient. London:
Chapman and Hall.

Castillo, P. and Newhall, C. (2004). Geochemical constraints on possible subduction
components in lavas of Mayon and Taal volcanoes, Southern Luzon, Philippines.
Journal of Petrology: 45, 1089-1108.

Catane, S. and Arpa, M. (1998). Large-scale eruptions of Laguna caldera: contributions
to the accretion and other geomorphic developments of Metro Manila and
adjacent provinces. PHIVOLCS internal report.

Corby, G. (1951). Geology and oil mssibilities of the Philippines. Manila: Dept. Agr.
Nat. Res, Phil. Tech Bull, 21.

De Boer, J, Odom, L, Ragland, P, Snider, F. and Tilford, N. (1980). The Bataan orogene:

eastward subduction, tectonic rotations, and volcanism in the Western Pacific.
Tectonophysics: 67, 251-282.

75

Defant, M, De Boer, J. and Oles, D. (1988). The western central Luzon volcanic arc, The
Philippines: two arcs divided by rifting? Tectonophysics: 145, 305-317.

Defant, M, Jacques, D, Maury, R, De Boer, J. and Joron, LL. (1989). Geochemistry and
tectonic setting of the Luzon arc, Philippines. Geol Soc Am Bull: 101, 663-672.

Dungan, M. (2005). Partial melting at the Earth’s surface: implications for assimilation
rates and mechanisms in subvolcanic intrusions. Journal of Volcanology and
Geothermal Research: 140, 193-203.

Fisher, R. and Schmincke, H (1984). Pyroclastic Rocg. Springer.

Flood, T, Vogel, T, Arpa, M, Patino, L, Catane, S. and Arcilla, C. (2004). Silicic magmas
erupted fiom the Laguna de Bay Caldera, Macolod Corridor, Luzon, Philippines:
geochemistry and origin. AGU Fall Meeting.

Forster, H, Oles, D, Knittel, U, Defant, M. and Torres, R. (1990). The Macolod Corridor:
A rift crossing the Philippine island arc. Tectonophysics: 183, 265-271.

Gal gana, G, Hamburger, M, Torres, R, McCaffrey, R. and Chen, Q. (2004). Crustal
deformation of Luzon Island, Philippines from GPS-based geodynamic models
and structural analyses of satellite imagery. AGU Fall Meeting.

Gervasio, F. (1968). The geology, structures and landscape development of Manila and
suburbs. Philippine Geologist: 22, 178-192.

Giggenbach, W. (1992). Isotopic shifts in waters from geothermal and volcanic systems
along convergent plate boundaries and their origin. Earth and Planetary Science
Letters: 113, 495-510.

Gonzales, B, Ocarnpo, V. and Espiritu, E. (1971). Geology of Southwestern Nueva Ecija
and Eastern Bulacan provinces, Luzon Central Valley. J. Geol. Soc. Philippines:
25, 3-41.

Grove, T, Elkins-Tanton, L, Parman, S, Chatterjee, N, Muntener, O. and Gaetani, G.
(2003 ). Fractional crystallization and mantle-melting controls on calc-alkaline
differentiation trends. Contrib Mineral petrol: 145, 515-533.

Hall, R, Fuller, M, Ali, J. and Anderson, C. (1995). The Philippine Sea Plate: magnetism
and reconstructions. In B Taylor and J Natland (Editors), Active margins and
marginal mins of the Western Pacific. AGU Geophysical Monograph: 88, 371-
401.

76

Hamburger, M, Cardwell, R. and Isacks, B. (1983). Seismotectonics of the northern
Philippine Island Are. In Hayes DE (ed). The tectonic and geologic evolution of

Soumeast Asian Seas and Islands, Part2. Am Geophys. Union Monogr.: 27, l —
22.

Hannah, R, Vogel, T, Patino, L, Alvarado, G, Perez, W. and Smith, D. (2002). Origin of
silicic volcanic rocks in Central Costa Rica: A study of a chemically variable ash-
flow sheet in the Tiribi Tuff. Bulletin of Volcanology: 64, 117-133.

Hayes, D. and Lewis, S. (1984). A geophysical study of the Manila Trench, Luzon,
Philippines 1. Crustal structure, gravity, and regional tectonic evolution. Journal
of Geophysical Research: 89, 9171-9195.

Hildreth, W. and Fierstein, J. (2000). Katmai volcanic cluster and the great eruption of
1912. GSA Bulletin: 112, 1594-1620.

Irving, E. (1947). Geomorphological implications of the Marikina drainage pattern Rizal
province, Luzon, Philippine Islands. The Philippine Geologist: 10, 1-12.

Karig, D. (1973). Plate convergence between the Philippines and the Ryuku Islands.
Maine Geology: 14, 153-168.

Knittel, U. and Defant, M. (1988). Sr isotopic and trace element variations in Oligocene
to recent igneous rocks from the Philippine island are: evidence for Recent
enrichment in the sub-Philippine mantle. Earth and Planetary Science Letters: 87,
87-99.

Knittel, U, Defant, M. and Raczek, I. (1988). Recent enrichment in the source region of
arc magmas from Luzon Island, Philippines: Sr and Nd isotopic evidence.
Geology: 16, 73-76.

Listanco, E. (1993). Space-time patterns in the geologic and magmatic evolution of
calderas: a case study at Taal Volcano, Philippines. Ph.D. Thesis, University of
Tokyo.

Martinez, M. (1997). Stratigraphy and geochemistry of Taal Caldera scoria pyroclastic
flow deposit, Philippines. MS. Thesis, Arizona State University.

McCabe, R, Alamasco, J. and Yumul, G. (1985). Terranes of the Central Philippines. In
DH Howell (Editor), Tectonostratigrgphic terrains of Circum-chific Region.
Circgm-Pacific energy and mineral resources. Earth Science: 1, 421-436.

McGovern, P. and Schubert, G. (1989). Thermal evolution of the Earth: effects of volatile

exchange between atmosphere and interior. Earth and Planetary Science Letters:
96, 27-37.

77

Miklius, A, Flower, M, Huifsmans, J, Mukasa, S. and Castillo, P. (1991). Geochemistry
of lavas fi'om Taal Volcano, Southwestern Luzon, Philippines: Evidence for

multiple magma supply systems and mantle source heterogeneity. Journal of
Petrology: 32, 593-627.

Mukasa, S, Flower, M. and Miklius, A. (1994). The Nd-, Sr- and Pb-isotopic character of
lavas from Taal, Laguna de Bay and Arayat volcanoes, southwestern Luzon,
Philippines: implications for are magma petrogenesis. Tectonophysics: 235, 205-
22 1.

Chile, E. Jr. (1995). Pyroclastic flow deposit of the Laguna Formation at Sitio Canlibot
and Sitio Cubanbaan. Bagumbayan, Teresa, Rizal. MS. Thesis, University of the
Philippines, Diliman.

Ocampo, V. and Martin, S. (1967). Report on the geology and section measurements in
southern Luzon Central Valley, Philippines. Unpubl. Report. Bu. Of Mines,
petroleum division, Manila

Oles, D, Knittel, U, Forster, H, Torres, R, Wolfe, J. and Bellon, H. (1995). Basaltic
volcanism associated with extensioml tectonics in the southern part of the Luzon
Island Are, The Philippines: Part I. Tectonic setting and volcanological evolution
Unpublished report, Institute of Mineralogy, RWTH Aachen, Germany and
Philippine Institute of Volcanology and Seismology, Philippines.

Ozawa, A, Tagarni, T, Listanco, E, Arpa, M. and Sudo, M (2004). Initiation and
propagation of subduction along the Philippine Trench: evidence from the
temporal and spatial distribution of volcanoes. Journal of Asian Earth Sciences:
23, 105-111.

Pautot, G. and Rangin, C. (1989). Subduction of the South China Sea axial ridge below
Luzon (Philippines). Earth and Planetary Science Letters: 92, 57-69.

Peacock, S. (1990). Fluid processes in subduction zones. Science: 248, 329-337.

Pilet, S, Hernandez, J. and Villemant, B. (2002). Evidence for high silicic melt circulation
and metasomatic events in the mantle beneath alkaline provinces: the Na-Fe-
augitic green-core pyroxenes in the Tertiary alkali basalts of the Cantal massif
(French Massif Central). Mineralogy and Petrology: 76, 39-62.

Pubellier, M, Garcia, F, Loevenbruck, A. and Chorowicz, J. (2000). Recent deformation
at the junction between the North Luzon block and the Central Philippines from
ERS-l Images. The Island Are: 9, 598-610.

Rangin, C, Stephan, J. and Muller, C. (1985). Middle Oligocene oceanic crust of South

China Sea jammed into the Mindoro collision zone (Philippines). Geology: 13,
425-428.

78

Rangin, C, Silver, E. and Tamaki, K. (1995). Closure of the Western Pacific marginal
basins: rupture of the oceanic crust and the emplacement of ophiolites. In B

Taylor and J Natland (Editors), Active margins and marginal basins of the
Western Pacific. AGU Geophysical Monograph: 88, 405-415.

Rollinson, H. (1993). Usinggeochemical data: evaluatiom present_ation, interpretation.
NY: Longman.

Rudnick, R and Fountain, D. (1995). Nature and composition of the continental crust: A
lower crustal perspective. Reviews of Geophysics: 33, 267-309.

Saxena, S. (1976). Two-pyroxene geotherrnometer: a model with an approximate
solution. American Mineralogist: 61, 643-652.

Smith, G. (2000). _E_ssenti_al volcgnology for the field stqu of continental volcamc rocjks;
An informal manual for "Field Studies in VolcgnologL”, University of New
Mexico.

Smith, I, Worthington, T, Stewart, R, Price, R. and Gamble, J. (2003). Felsic volcanism
in the Kermadec arc, SW Pacific: crustal recycling in an oceanic setting. In Larter,
D. and Leat, P. (editors). Inna-oceng subduction systems: tectonic and
magnatic pgocesss. Geol Soc, London, Special Publications: 219, 99-118.

Smith, R. (1979). Ash-flow magrnatism, in Chapin CE, and Elston WE, eds, Ash-flow
tuffs. Geological Society of America Special Paper 180.

Smith, W. (1924). Geology and mineral resources of the Philippine Islands. Manila:
Bureau of Science Publication.

Tatsumi, Y. (1989). Migration of fluid phases and genesis of basalt magmas in
subduction zones. Journal of Geophysical Research: 94, 4697-4707.

Tatsumi, Y. and Eggins, S. (1995). Subduction zone mggmatism. Blackwell Science. p.
109.

Taylor, B. and Hayes, D. (1983). Origin and history of the South China Sea basin. In
Hayes, D. (editor). The TectoniL and Geologic Evolution of Southeai Asiani Seas
and Islands. Am. Geophys. Union, Geophys. Monogr.: 23, 89-104.

Teves, J. and Gonzales, M. (1950). The geology of the university site — Balara area,
Quezon City. The Philippine Geologist: 4, 1 — 10.

Thompson, R. (1974). Some high-pressure pyroxenes. Mineral Mag: 39, 768-7 87 .

79

Torres, R, Miklius, A and Rimando, R (1986). Accomplishment report of the geological
survey of Morong Peninsula and Talirn Island. PHIVOLCS internal report.

Vogel, T, Patino, L, Alvarado, G. and Gans, P. (2004). Silicic ignimbrites within the
Costa Rican volcanic front: evidence for the formation of continental crust. Earth
and Planetary Science Letters: 226, 149-159.

Winter, J. (2001 ). An introduction to igaeous and metamorphic mtrology. NJ: Prentice
Hall. p. 299.

Wolfe, J. and Self, S. (1983). Structural lineaments and Neogene volcanism in
southwestern Luzon In DE Hayes (Editor), The Tectonic and Geologic Evolution
of Southth Asian Seas and Islands Part 2. Am. Geophys. Union Geophys.
Monogr.: 27, 157-172.

 

Zanoria, E. (1988). The depositional and volcanological origin of the Diliman
volcaniclastic formation, Southwestern Luzon, Philippines. Thesis. University of
Illinois at Chicago.

80

 

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