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THESis

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3 1293 008913

This is to certify that the
thesis entitled
CHEMICAL VARIATION OF THE TEPHRA FALL BENEATH THE

RAINIER MESA ASH FLOW SHEET: IMPLICATIONS FOR
INCREMENTAL GROWTH OF A LARGE MAGMA BODY

presented by

Kristin Terese Huysken

has been accepted towards fulfillment
of the requirements for

_M:_S_.___degree in W1 Sciences

M4 1M

Major professor/

 

March 30, 1993
Date

 

0-7639 MS U is an Affirmative Action/Equal Opportunity Institution

 

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University

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TO AVOID FINES return on or before date due.

DATE DUE DATE DUE DATE DUE i

       

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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MSU In An Affirmative Action/Equal Opportunity lnditution
chS-DJ

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

- .—

CHEMICAL VARIATION OF THE TEPHRA FALL BENEATH THE RAINIER MESA
ASH-FLOW SHEET: IMPLICATIONS FOR INCREMENTAL GROWTH OF A
LARGE MAGMA BODY

BY

Kristin Terese Huysken

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE
Department of Geological Sciences

1993

ABSTRACT

CHEMICAL VARIATION OF THE TEPHRA-FALL BENEATH THE RAINIER MESA
ASH-FLOW SHEET: IMPLICATIONS FOR INCREMBNTAL GROWTH OF A LARGE
MAGMA BODY

BY

Kristin Terese Huysken

Tephra-fall deposits underlying, and associated with, large—
volume, chemically zoned ash-flow sheets have been thought to
represent the uppermost fractionated portion of large zoned magma
bodies. This hypothesis is evaluated by analyzing the tephra-fall
deposits beneath.the voluminous, chemically-zoned Rainier Mesa ash-
flow sheet. Significant chemical variation in both whole rock and
individual pumice samples indicates that the eruptive processes may
be more complex than this simple interpretation suggests. The
tephra-fall deposits span the entire chemical range (approximately
67—78% $102) of the high-silica portion of the Rainier Mesa ash—flow
sheet. Significant chemical zoning of small ash-flow layers within
the tephra-fall sequence are consistent with eruption from a small
chemically zoned magma body. Increased upsection chemical evolution
amon the small ash-flow layers indicates that the magma became
increasingly evolved with time. Because of the very small volume
of the small ash-flow layers, and the significant chemical variation
within each layer (up to 6% variation in Sioz), the large volume
Rainier Mesa magma body could not have been in place before the
eruption of the tephra-fall sequence. The Rainier Mesa magma body
may have been incrementally emplaced and periodically erupting
throughout its emplacement history. This has general implications

for the emplacement and evolution of large-volume magma bodies.

ACKNOWLEDGMENTS

First, I thank my family, especially my parents Bud and
Micki Huysken" for' ever jpresent emotional and financial
support throughout the course of my education.

Sincere appreciation and. thanks are extended to :my
advisor, Tom Vogel, for his thoughtful insight, intense
interest, and willingness to offer guidance relating to both
this thesis and to my education in general. I am grateful to
my committee members Bill Cambray, Dave Matty, and.Kaz Fujita.
They have provided useful discussion throughout the course of
this project, as well as helpful and appreciated comments in
their review of this thesis. I am especially grateful to Dave
.Matty for sparking my interest in igneous processes and (along
with Steve Stahl and Reed Wicander) steering in the direction
of graduate school.

I thank Larry McKague and Lee Younker for their parts in
getting me to the Test Site each year and Larry McKague for
the excellent photographs of the tephra—fall sequence. I
would like to acknowledge Bill McKinnis and Barbara for their
assistance at the Test Site.

Thanks to Tim.Flood for his very insightful discussions,
and intense excitement regarding this project. Thanks also to

iii

Jim Mills for the excellent dissertation on the Timber
Mountain Tuff. The information was invaluable to the
prosecution of this study.

Fellow petrology students Tom Weaver and Tim Woodburne
are thanked for their camaraderie and moral support.

Finally, special thanks go to Matt Casselton, Alex
Guimaraes, and Maureen Walton who couldn't be closer if they

were family.

iv

TABLE OF CONTENTS

LIST OF FIGURES .......................................... vi
INTRODUCTION .............................................. l

Rainier Mesa Member .................................. 2

Magma Evacuation Dynamics ............................ 4
DESCRIPTION OF THE TEPHRA-FALL SEQUENCE ................... 7
SAMPLE SELECTION AND PREPARATION ......................... 13
MAJOR ELEMENT VARIATION .................................. 18
TRACE ELEMENT VARIATION .................................. 25
CHEMICAL VARIATION WITH STRATIGRAPHIC POSITION ........... 3O
RARE EARTH ELEMENT VARIATION ............................. 36
DISCUSSION ............................................... 39
APPENDICES ............................................... 49
BIBLIOGRAPHY ............................................. 80

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

10.

LIST OF FIGURES

Location of the Southwest Nevada
Volcanic Field .............................. 3

Zr vs. silica for the Rainier Mesa
ash-flow sheet and the underlying
tephra-fall sequence ........................ 5

Schematic eruption dynamics of the
Rainier Mesa ash-flow sheet ................. 6

Generalized stratigraphy of major volcanic
units of the Southwest Nevada Volcanic
Field and approximate ages .................. 8

Tephra-fall sequence underlying the Rainier
Mesa ash-flow sheet ........................ 10

a.) Small ash—flow layer within the
tephra-fall sequence. b.) 52 m ash flow
within the tephra-fall sequence ............ ll

Generalized stratigraphic column of the
tephra-fall sequence at a.) Rainier Mesa
location and b.) Pahute Mesa location ...... 14

Major element variation of small ash-flow
layers within the tephra—fall sequence

and the overlying Rainier Mesa ash-flow

sheet ...................................... 20

Trace element variation of small ash-flow
layers within the tephra-fall sequence

and the overlying Rainier Mesa ash-flow

sheet ...................................... 26

Major and trace element variation with
stratigraphic position (depth), for small
ash-flow layers within the tephra-fall
sequence ................................... 31

vi

Figure 11.

Figure 12.

Figure 13.

LIST OF FIGURES (continued)

Chondrite normalized REE patterns for

small ash-flow layers within the

tephra—fall sequence and the high-silica
portion of the Rainier Mesa ash-flow

sheet ..................................... 37

_Average REE abundances for small

ash-flow layers within the tephra-fall .
sequence ................................... 38

Schematic diagram depicting the

interpreted emplacement of the Rainier
Mesa magma body ............................ 44

vii

INTRODUCTION

The Rainier Mesa ash—flow sheet contains emu extremely
large chemical variation. It is a large (1200 knfi), 11.6 m.y.
old cooling unit that ranges in composition from S6 to 78%
SELL (Mills, 1991). Ninety percent of the Rainier Mesa ash
flow possesses a silica content greater than 66%, and is
defined by Mills (1991) as the high—silica portion of the ash—
flow sheet.

Large volume ash-flow sheets are of great importance in
interpreting high-level magmatic systems. They represent a
virtually instantaneous sampling of a large portion of the
magna. body (Smith, 1979; Hildreth, 1981). Accordingly,
numerous studies indicate that the chemical stratigraphy of
OutflOW’ sheets produced. by these eruptions is inversely
related to the chemical zoning within the magma body (e.g.
Smith, 1979; Hildrethq 1981). In a general way, most
chemically—zoned ash-flow sheets correspond.tx> this simple
picture.

Whereas:many pyroclastic flows represent, in large scale,
a stratigraphic inversion of chemical zoning in the magma
body, many are also complicated by complex eruption dynamics,
multiple vents, topographic barriers, and pyroclastic flow
dynamics (Trial and Spera, 1990). Numerical calculations
indicate that compositional breaks and complex cooling breaks
can be caused solely by the dynamics of pyroclastic flow

(Valentine, et al., 1991, 1992).

2

Regardless of these complexities, eruption of a
chemically zoned system typically begins with the eruption of
the highest silica upper portion of the magma followed by the
lower, more mafic component as time progresses (Blake, 1981) .

Small pre-caldera eruptive deposits are just as important
in understanding the mechanics of large volume magmatic
systems as the main ash-flow sheet. These deposits are
usually thought to be pre-eruptive "burps" from the uppermost,
high silica portion of the larger magma body. For this reason,
they have often been neglected in studies of voluminous
magmatic systems.

A tephra-fall sequence occurs immediately beneath the
Rainier Mesa ash—flow sheet at two locations on the Nevada
Test Site (NTS) . Eruptions which produced these deposits were

precursors to the large caldera-forming eruption.

Rainier Mesa Member

The Rainier Mesa Member is a 1200 km3 ash flow sheet, the
eruption of which led to the collapse of the Timber Mountain
Caldera approximately 11.6 m.y. ago (Byers et al., 1976;
Broxton et al., 1989). It is part of a system of seven
calderas that make up the Southwest Nevada Volcanic Field
(SWNVF) (Fig. l) . This voluminous deposit is chemically and
mineralogically zoned and has been interpreted by Mills (1991)
to be the result of eruption from a chemically stratified

chamber. Chemical variations within the Rainier Mesa Member

 

  
      
         

 

 

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Location of the Southwest Nevada Volcanic Field
The dashed line outlines the extent of the Timber Mountain
Tuff.

The Timber Mountain Calderas, Oasis Valley Caldera,
Claim.Canyon Caldera Segment, and Sleeping Butte Caldera

Segment are reported as the Timber Mountain-Oaisis valley
Caldera Complex (after Carr et al., 1984; Noble et al.,
1984; and Vogel et al., 1987).

4

indicate both a high silica (approximately 66-78%) and low
silica trends (approximately 56-66%) (Mills, 1991) . Figure 2
illustrates these trends through SiO2 -Zr relationships.

Beneath the Rainier Mesa Member lie a series of layered
tephra-fall deposits interbedded with small, discrete ash—flow
layers. The purpose of this study is to test whether the
tephra-fall sequence underlying the Rainier Mesa ash-flow
sheet represents eruption from the uppermost fractionated

portion of the Rainier Mesa magma body.

Mafia Evacuation gynamics

A simple model of chamber evacuation (Fig. 3) illustrates
magma withdrawal from a layered system occurring radially,
where magma is drawn toward the eruptive vent from all
directions (Blake, 1981; Blake and Ivey, 1986; Spera, 1983;
Spera et al., 1986). Figure 3 is a schematic diagram
illustrating the dynamics of chamber evacuation. Evacuation
isochrons illustrate the position of the magma that will
simultaneously reach the vent as eruption progresses. The
high-silica and lower—silica fields indicate compositional
layering in a chemically layered and zoned system, and the
arrows show the direction of magma movement toward the vent.
Over time, eruption taps progressively deeper levels of the
chamber while still maintaining contribution from the roof
magma. The resulting deposits are a collection of

compositionally zoned tephra deposits consisting of a more

 

 

 

 

 

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Figure 2. Zr vs. silica for the Rainier Mesa as-flow sheet
and the underlying tephra-fall sequence.

 

 

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Figure 3. Schematic eruption dynamics of the Rainier Mesa
ash-flow sheet.

7

silicic basal unit, and grading upward to more mafic
compositions (Blake, 1981). Though the model presented here
is a schematic oversimplification, the main ash-flow sheet of
the Rainier' Mesa. Member is interpreted. to have erupted
generally in this manner (Mills, 1991). This type of eruptive
sequence would indicate the tephra-fall deposits preceding the
eruption of the main ash-flow sheet should tap predominately
the uppermost portion of the magma body. Consequently, in a
layered magma system such as the Rainier Mesa Member, the ash-
fall deposits should consist of the most fractionated upper
portion of the magma.

This study indicates that chemical variation and
compositional distribution of the tephra-fall sequence beneath
the Rainier Mesa Member are inconsistent with the above model.
Furthermore, it is demonstrated that the large Rainier Mesa
magma body probably was not present in its entirety at the

time the tephra—fall deposits were erupted.

DESCRIPTION OF THE TEPHRA-FALL SEQUENCE ‘

The tephra-fall sequence is well exposed at two locations
on the Nevada Test Site (NTS). One section is located on the
southwest side of Rainier Mesa, and the other is located on
the south side of Pahute Mesa (Fig. 1). At both locations,
the tephra-fall sequence unconformably overlies older deposits
(Tiva Canyon Member on Rainier Mesa and the Grousse Canyon

Member on Pahute Mesa (Fig. 4)). It is truncated above by the

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0-11 Ma
0-13 Ma
6.5 Ma
1km Canyon Tnfl‘ 7.5 Ma
Rhyolite lavas of Shoshone 9.0 Ma
W
Mafic 1am 9-10 Ma
Ammonia 11.4 Ma -
Timba' Talks
Moan ' T
tam n6 Rainier Mesa 11.6 Ma
Rhyolite lavas of Fortymile “-13 Ma
Canyon
Tiva Canyon
Yucca Mm.
Pah Canyon 13 Ma
Topopah
Summp
13.5 Ma
135 Ma
Belted Range om
Tnfl Canyon
14 Ma
Tub Swings
Dacite lavas and breach 14 Ma
Lithic Ridge Tufl 14 Ma
Rhyoiite of Kawich Valley 15 Ma
“Older” m3: 15 Ma
Sanidine-rich tut! 15 Ma
Tufl‘ of Yucca Flat 15 Ma
Redneck Valley ‘1‘qu 16 Ma
Figure 4 . Generalized stratigraphy of major volcanic units of the

Southwest Nevada Volcanic Field and approximate ages (after Byers et al.,
1989) .

9
basal surge deposit of the Rainier Mesa ash-flow sheet.

The tephra fall underlying the Rainier Mesa ash-flow
sheet (Fig. 5) comprise a series of layered deposits that
consist of sorted pumice layers and ash beds; and, unsorted,
massive layers of pumice-rich ash often containing minor
lithic and obsidian (i.e. non-vesiculated glass fragments).

Pumice-fall layers make up a large portion of the total
tephra-fall unit. They consist of moderateLy to very well
sorted light gray to brown pumice fragments. The individual
pumice fragments range from sand-sized to cobble-sized clasts
but are typically 0.5 to 10 cm in diameter. Pumice-fall
layers are often well stratified.and.exhibit normal or reverse
grading possibly due to changes in eruption velocity. They
often contain minor amounts obsidian and lithic fragments.

Ash layers within the tephra-fall sequence typically
range in thickness from approximately 0.25 cm to about 4 nu
They are light- to medium-gray or light- to medium-brown in
color. Medium grained layers of glass fragments containing
abundant lithic fragments are commonly included in the tephra-
fall deposits. As with all tephra-fall deposits, the texture
and particle composition is dictated by gravity, wind, and
eruption velocity (Gas and Wright, 1987).

Interbedded with the tephra-fall layers are
numerous, very poorly sorted, unstratified, discontinuous
layers of pumice and lithic fragments in an ash matrix (Fig.

6). They commonly pinch and swell and exhibit flow

10

 

Figure 5. Tephra—fall sequence underlying the Rainier Mesa
ash—flow sheet (Pahute Mesa location).

11

 

Figure 6. a.) Small ash-flow layer within the tephra—fall
sequence. b.) 52 m ash flow within the tephra-fall sequence
(Pahute Mesa location).

12

characteristics such as flow casts and basal zones of reworked
material, typically 2—5 cm in thickness, presumably ripped up
from the underlying layer. These layers have been interpreted
by Warren and Valentine (1990), as small ash-flow layers.
Lithic fragments typically constitute only a minor portion of
these layers. The small ash-flow layers also occasionally
contain plant root remains in the top few centimeters. The
most noticeable characteristic of these small ash—flow layers
is the color change that each layer exhibits from base to top
(Fig. 6) . Each small ash-flow layer grades from basal white
(or light gray), upward to brown. Typically, the ash matrix
and small pumice fragments change color, while the larger
pumices (>1.5 cm) remain white or light gray throughout an
individual layer.

A channel cut is present in section on Pahute Mesa. The
cut is approximately 2 m across, and 3 m deep with steep
walls. It is filled with very poorly sorted gray ash and
pumice deposits, and unconformably overlain by a pumice-fall
layer.

Also included in this section is a 52 m thick ash-flow
layer. Unlike the abundant small zoned ash-flow layers, this
thick layer exhibits no change in color from base to top.
There is a 0.3 m surge deposit of white ash at the base,
overlain by an additional 51.7 m of fine white ash matrix
containing boulder—sized lithic and pumice fragments (up to 50

and 20 cm respectively) (Fig. 6). Though this deposit is

13
thick, it is not laterally traceable indicating that the flow

most likely fills a localized channel or depression.

SAMPLE SELECTION AND PREPARATION

Because of the excellent exposure and stratigraphic
control, samples for this study were collected extensively
from.the two well—exposed sections on Pahute Mesa and Rainier
Mesa. Figure 7 illustrates the stratigraphic positions from
which glassy pumice and whole-rock samples were collected.

In general, glassy pumice fragments are better indicators
of chemical processes taking place within magma bodies than
whole-rock samples (Hildreth and.Mahood, 1985; Flood, et al.,
1989; Schuraytz, et al., 1989; Vogel, et al., 1989; Mills,
1991). Glassy'pumice fragments represent solidified packets of
the liquid and crystal portions of the magma being erupted
from.a vent at a given instant in time (Flood, 1989). Whole—
rock samples represent an average composition of material
being deposited from an eruption over a given period of time.
For this reason, glassy pumices fragments were collected for
analysis from the entire tephra—fall sequence to ensure
representation of the entire chemical variation of the
sequence.

The small ash-flow layers within the tephra-fall
sequence, however, often did not contain pumice fragments
large enough for analysis. 'In fact, even when the small ash-

flow layers did contain pumice fragments large enough for

Figure 7. Generalized stratigraphic column of the tephra-
fall sequence at a). Rainier Mesa location and b.) Pahute

Mesa location. Samples collected from the bottom and the

top of each small ash-flow are labelled. The depth of each
sampled layer beneath the overlying main ash-flow sheet is
also shown.

14

15

RainierMeaaah-flowfiea helowmain

ash-flow sheet (In)

 

14.49

17.79

19.66

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24.19

25.31

27.12

 

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Depth henedh main ash-flow diced-1

10.4

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14.6

35.0
35.7

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17
analysis, they did not reflect the same degree of color change
from the bottom to the top of the layer as did the ashy
matrix. In these cases whole—rock samples were collected,
across the color change from the top to the bottom of each
small ash-flow layer.

Determination of the chemical variation among the
different layers was also a priority. To achieve this,
representative small ash-flow layers from the entire tephra-
fall sequence were sampled.

Altogether, more than one hundred glassy pumice
fragments, previously collected by John Brannon (personal
communication, 1988), and.77 whole-rock samples from 14 small
ash-flow layers within the tephra-fall sequence were analyzed
for major and trace element abundances (Appendix 1).

Major and trace element analyses of Cr, Ni, Cu, Zn, Rb,
Sr, Y, Zr, Nb, La, and Ba, were obtained using x—ray
fluorescence (XRF) methods described by Mills (1991). U.S.
Geological Survey (USGS) whole rock standards run both as
known and unknown concentrations were used as a means of
measuring the error of analysis. For XRF analyses, whole rock
standard errors of less than or equal to 1% were accepted with
the following exceptions. Cr, Ni, and Cu concentrations were
generally below XRF detection limits. Errors of La and Ba
were generally greater than 10 ppm, however these two trace
elements were also analyzed for, using instrumental neutron

activation analysis (INAA).

18

Additional trace element and selected rare earth element
(REE) abundances were obtained from 35 samples (Appendix 1)
using INAA. methodology also described by Mills (1991).
Associated errors are reported in Appendix 2.

Samples for INAA were chosen from small ash-flow layers
within the tephra-fall sequence. Samples were selected which
stratigraphically represented layers throughout the tephra—
fall sequence and also displayed significant chemical
variation based on XRF analyses.

Prior to analysis of whole-rock samples,
lithic fragments large enough to be identified with the
unaided eye were removed.

This study focuses on both the tephra fall and the small
ash-flow layers comprising the tephra-fall sequence. For
clarity, the term tephra—fall sequence is used when referring
to the sequence as a whole. Tephra fall refers to deposits
that were erupted into the air and subsequently deposited. In
addition, small ash-flow layers refer to the ash-flow deposits
contained within the tephra-fall sequence, whereas main ash—
flow sheet or Rainier Mesa ash—flow sheet refers to the
voluminous (1200 kn?) caldera-forming ash flow that overlies

the tephra-fall sequence.

MAJOR ELEMENT VARIATION
Major and trace element analyses were performed on 116

pumice fragments and 77 whole—rock samples collected from two

19
stratigraphic sections of the tephra-fall sequence beneath the
Rainier Mesa ash-flow sheet. In each case, the chemical range
obtained from the pumice samples was nearly the same as that
of the whole-rock samples for the two sections (Appendix 1).
Typically, chemical trends defined by the whole-rock samples
often possess slightly less variation than individual pumices.
This effect is due to the fact that because whole-rock samples
are an average composition, some of the variation is masked.

Figure 8 illustrates major element variation plotted
against SiOW rmunalized to 100%, for whole-rock samples from
each section. Major element variation of the overlying
Rainier Mesa ash-flow sheet (Mills, 1991) is also shown for
comparison. (Analyses of individual pumice fragments are
listed in appendix 1). lkiall cases, the tephra—fall analyses
occur within the high-silica portion of the Rainier Mesa ash-
flow sheet.

Within the tephra-fall deposits, all of the major element
abundances decrease with increasing silica. 'The overlying
Rainier Mesa ash—flow sheet is characterized by points of
inflection within the TiOz, FeO, MgO, A1203, NaZO, and trends
at approximately 65% SiOT. This may be due to the removal of
phenocryst phases (Mills, 1991), however, because of their
mobility in glassy pumice fragments, this interpretation for
the alkalies may be tenuous. The total silica range of the
tephra-fall sequence underlying the Rainier Mesa ash-flow

sheet is about 67% to 78% SiO2 -— nearly the entire range of

 

 

 

 

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Figure 8. Major element variation of small ash-flow layers
within the tephra-fall sequence and the overlying Rainier
Mesa ash-flow sheet. Open squares = Rainier Mesa location;
Solid squares s Pahute Mesa location; Open triangles a Main
ash-flow sheet.

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Figure 8 (continued).

 

24

 

 

 

 

 

 

1.0 I I I. r

0.0 - ‘
I 0.0 - "
C.

en b '

0.2 - "‘

O

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“0000707000
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Figure 8 (continued).

25
the high—silica portion of the Rainier Mesa ash—flow sheet.
Similarly, the chemical ranges of IUQO3 (12-17.5%), FeO
(0.5—3.5%), MgO (0.1—1.1%), andmCaO (0.5—2.75%) of the tephra-
fall sequence, as ‘well as the other major oxides, are
characterized by significant chemical variation -— virtually
equivalent to that of the entire high-silica portion of the

overlying Rainier Mesa ash-flow sheet.

TRACE ELEMENT VARIATION

Trace element variation of the tephra-fall sequence is
also very similar to the high—silica portion of the overlying
Rainier Mesa ash-flow sheet. This may indicate that processes
controlling trace element distribution in the tephra-fall
sequence and in the Rainier Mesa ash-flow sheet are the same.

Trace element abundances for the small ash-flow layers
within each tephra-fall section are expressed relative to SiO2
in Figure 9. 'Trace element variation of the overlying Rainier
Mesa ash-flow sheet is shown for comparison (Mills, 1991) . Of
the analyzed trace elements for the tephra-fall sequence, only
Rb shows clear enrichment with increasing silica. The
remaining trace elements either decrease with increasing
silica, have constant concentrations, or do not display well
defined trends due to scatter. Th is characterized by large
variation (10-30 ppm) at:near1y constant silica (75-78% SiOz).
Large variation (approximately 11 to 40 ppm Th) has also been

reported for the Rainier' Mesa ash-flow sheet at nearly

26

 

 

 

 

 

 

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an
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Figure 9.

 

 

 

 

 

 

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b a ‘ a
00 fl “ 70 70 fl
”3

Trace element variation of small ash-flow layers

within the tephra-fall sequence and the overlying Rainier
Symbols are the same as in Figure 8.

ash-flow sheet.

27

 

 

 

 

 

 

 

 

 

 

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Figure 9 (continued).

28

 

 

 

 

 

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Figure 9 (continued).

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Figure 9 (continued).

10

Ta

 

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3O
constant silica (Mills, 1991). Significant Th variation at
constant silica has been accounted for in the Rainier Mesa
Member by the existence discrete magma packets being erupted
simultaneously from the Rainier Mesa magma body (Mills and

Vogel, personal communication, 1992).

CHEMICAL VARIATION WITH STRATIGRAPHIC POSITION

Because the tephra-fall deposits should be inversely
related to the composition of the magma body from which they
were erupted (see Figure 3), it is useful to plot elemental
abundance against relative stratigraphic position (i.e. depth
from the base of the Rainier Mesa ash—flow sheet) of each
small ash-flow layer within the tephra-fall sequence.

In Figure 10, major and trace element abundances are
plotted against stratigraphic position of the tephra—fall
deposits, expressed as relative depth, so that the chemical
variation may be inspected as a function of relative time of
eruption. There are two major observations that are important
in this figure.

The first major observation is that each small ash-flow
layer (expressed as a different plot symbol) exhibits a
distinct trend when plotted against its relative stratigraphic
position (expressed as relative depth) within the sampled
section. This trend typically progresses from a more evolved
magma at the base to a less evolved magma toward the top of

each layer (e.g. in the diagranlof FeO vs. relative depth, the

Figure 10. Major and trace element variation with
stratigraphic position (depth), for small ash-flow layers
within the tephra-fall sequence. Each plot symbol denotes a
separate small ash flow within the sequence.

31

32

 

 

 

 

 

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33

 

 

 

 

 

 

 

 

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34
§

 

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8388gtgiu

35
sample with the lowest FeO concentration in each layer is
located at the bottonlof the flow). This within—layer trend is
more distinct in the Rainier Mesa section than in the Pahute
Mesa section.

The difference in the two sections is the result of
greater sampling density from the Rainier Mesa section. In
the Rainier Mesa section, thicker layers are present, and
generally more samples were collected per layer than from
Pahute Mesa. Many layers from the Pahute Mesa section,
however, are still characterized by this within—layer trend.

Interestingly, the small ash-flow layers from Rainier
Mesa thicken towards to top of the section while their
chemical variation decreases. For example, there is an
increase in total FeO from 1.3 to 3.3 wt.% in the small ash—
flow layer at the base of this section. This increase occurs
over a vertical thickness of less than one meter. However,
the uppermost layer exhibits in increase fronnonly 0.75 to 1.3
wt.% over a vertical thickness of about 5 meters (Fig. 10).

The second major observation is that there is a larger
scale trend of the entire tephra-fall sequence. This trend is
opposite that of each individual layer (that is, the small
ash-flow layers become increasingly evolved toward the top of
each section).

Trace element patterns relative to depth within and among
small ash-flow layers within the tephra-fall sequence follow

patterns similar to those of the major oxides. The small ash—

36
flow layers within the tephra-fall sequence are chemically
zoned with respect to trace elements. As with the major
elements, these trace elements produce a within-layer trend of
decreased.magmatic evolution toward the top of each small ash-
flow layer. In addition to the within-layer trace element
behavior is a larger scale trend from layer to layer. This is
one of increasing magmatic evolution towards the top of the

section.

RARE EARTH ELEMENT VARIATION

Chondrite normalized Rare Earth Element (REE)
concentrations for the small ash-flow'layers fronleach section
are plotted. in ZFigure ll. REE concentrations for the
overlying Rainier Mesa ash—flow'sheet are shown for comparison
(Mills, 1991). As with major and trace element abundances,
the REE variation of the tephra-fall sequence is similar to
that of the high—silica portion of the overlying Rainier Mesa
ash-flow sheet. With the exception of the heavy rare earth
elements, the variation of the small ash-flow layers within
the tephra-fall sequence is as variable as the high-silica
portion of the Rainier Mesa ash-flow sheet. This may be an
artifact of the small number of samples from the tephra-fall
sequence for which REEs were analyzed. Another possibility
may be that there was assimilation of the surrounding wall
rock, or addition of another magma after the eruption of the

tephra fall but prior to caldera collapse. Gaps in the REE

37
Rdmkrhhnaauwhn

‘m VVVY—V T—r" T'f'vv

 

 

 

 

 

100
10
I
.‘ 1141111411L11L17
LICI IIIIEII Tb YIILII
lhhmnhhxasufion
‘m IVUIT'IVTVITfirI
100
10
I
.‘7llelllLAJIAALA
IICI .mln"fll . Vino
lhmmrhmaaaflbflqwahuu

 

1"IWTUU11'jTW

 

 

IICb ONE! Tb Vbhl

Figure 11. Chondrite normalized REE patterns for small ash-
flow layers within the tephra-fall sequence and the high-
silica portion of the Rainier Mesa ash-flow sheet.

 

 

 

 

 

 

 

 

 

’°°° 'aABase
1 4‘
1m
? IX
5 ‘0
Iowa
‘1.

1
:114-.11.1lll,.1
LICI SIEU Tb yuLu
Mean Layer Values
PdmmehkmnuxWMI
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177LigJAIIAJJA..L1
um um m mm

Mean Layer Values

Figure 12. Average REE abundances for small ash-flow layers
within the tephra-fall sequence.

39
data is a function of sample selection (see section on sample
selection and preparation).

The REE relationship among the small ash-flow layers are
plotted in Figure 12. The mean rare earth elemental values
for each layer arejplotted to illustrate the change in average
layer concentrations among the different ash-flow layers from
the bottom to the top of the tephra—fall sequence. The first
erupted layers are relatively LREE and Eu enriched, and become
increasingly depleted with each subsequently erupted ash-flow
layer. This is the same overall trend observed for the major
and trace elements with depth. That is, the layers become

increasingly evolved upsection.

DISCUSSION

This study indicates that in the case of the Rainier Mesa
ash-flow sheet, the associated tephra-fall deposits are
essential for interpreting development of the large magma
body. TWO lines of evidence indicate that the tephra-fall
deposits underlying the 1200 kn? Rainier Mesa ash-flow sheet
could not have been erupted from the uppermost fractionated
portion of a large, chemically zoned, magma body. First, the
variation of the tephra—fall sequence is chemically equivalent
to the entire high-silica portion of the overlying Rainier
Mesa ash-flow sheet. ‘This high-silica.portion of the ash—flow
sheet makes up about 90% of this voluminous (1200 km?)

deposit. Because the tephra-fall deposits represent a very

40

small volume, it would be highly unlikely for the observed
range of chemical composition of the tephra-fall sequence to
be present if it were erupted from. only the uppermost
fractionated portion of the very large volume Rainier Mesa
:magma body; This conclusion is stronger if one considers that
the tephra—fall sequence was not produced by a single
continuous eruption, but rather a series of very small
eruptions.

Secondly, each small ash—flow layer within the tephra-
fall sequence is also characterized by significant chemical
variation. The volume of one of these ash-flow layers is
negligible (probably less than 0.01 kn?) compared to that of
the entire Rainier Mesa ash-flow sheet (1200 knB). With this
in mind, it would be extremely difficult to produce the
observed chemical variation in these layers by periodic
eruption from the uppermost fractionated portion of a very
large magma body.

The possibility that each of the small ash-flow layers
could have been erupted from deeper levels of the large-volume
Rainier Mesa magma body (i.e. the classical eruption dynamics
are incorrect) is disproved by the trend of a increased
chemical evolution towards the top of the section. There is
no reasonable way by which the within-layer trend an_d the
opposing amongelayer'trend could be achieved if the small ash-
flOW'layers were erupted flnmn a very large-volume (>1200 km”

Rainier Mesa magma—body.

41

The evidence presented indicates that a large volume
Rainier Mesa magma body was not likely to have been present
throughout eruption of the tephra fall. The following model
is one possibility for the origin of this tephra—fall
sequence. In any model for the origin of these deposits, the
following observations must be accounted for:

1.) The tephra—fall sequence is chemically

equivalent to the entire high—silica trend of the

overlying Rainier Mesa ash-flow sheet.

2.) Small aSh-flOW' layers present within the
tephra-fall sequence indicate numerous separate
eruptions during the time of deposition of the

tephra-fall sequence.

3.) Each small ash—flow layer within the tephra-
fall sequence is characterized by an upward
chemical change from the base to the top of the
layer. This change is one of a more silicic base

grading upward to a more mafic top.

4.) The entire sequence is characterized by a more
mafic component at the base of each section, which
grades upward to a more silicic component at the

top.

42

The fact that the tephra—fall is chemically equivalent to
the high—silica portion of the Rainier Mesa ash-flow sheet,
strongly suggests that the tephra fall belongs to the same
petrologic system as the large Rainier Mesa ash-flow sheet.
The presence of discrete numerous small ash-flow layers and
evidence of plant growth between layers suggests there was
some period of quiescence between ash-flow eruptions.

Because each small ash-flow layer is compositionally
zoned, it is reasonable to assume that they erupted from a
compositionally zoned magma body. The magma body would have
to be small (or thin) in order to account for the degree of
variation observed in these layers. Large—scale compositional
variation among the ash-flow layers is consistent with
periodic eruption from a continually evolving magma body.

The discontinuity of the small ash-flow layers suggests
that a separate vent erupted.eachLof the tephra—fall sections.
They indicate that the ash—flows probably did not flow far
from their source.

The most probable model for the evolution of the magma
body is a situation where the large—volume Rainier Mesa magma
body is produced by a small, thin, tabular, shallow,
chemically zoned nagma body that incrementalLy grew larger
with time and periodically erupted, producing small ash-flow
layers that are, in essence, "snapshots" of the magma body’s
evolution” Because the section from Rainier Mesa contains the

least evolved small ash-flow layers, the magma body only

43

needed to initially exist beneath it. This magma body ranged
from at least 67 to 74% silica (the silica variation of the
stratigraphically lowest ash-flow layer in the Rainier Mesa
section); and eruption from this small (or thin) magma body
produced.the first small chemically zoned.ash—flow layer (Fig.
13a). The next, slightly more chemically evolved small ash-
flow layer would have been erupted after recharge, growth, and
differentiation of this small initial magma body.

The tephra-fall section from Pahute Mesa possesses less
chemical variation than the Rainier Mesa section (Figs. 8 and
9). For example, the silica content from the Rainier Mesa
location ranges from 67 to 78%, whereas the silica content
from the Pahute Mesa location ranges only from about 74-78%.
Because of this constraint, the small ash—flow layers from
Pahute Mesa are not required to erupt until the magma body
evolved to a silica content of 74-75.5% (the silica range of
the first erupted small ash-flow layer from the Pahute Mesa
location) (Fig. 13b). When these small ash-flow layers were
erupted, the magma body must have been at least 10 km wide in
order to underlie both tephra-fall sections (Fig. 1). At this
time the entire magma body ranged in silica from at least 67%
(the lowest silica concentration of the first erupted small
ash-flow layer from Rainier Mesa) to 75.5% (the highest silica
content of the ash—flow layers at the base of the Pahute Mesa
section). Basal layers of section two range in silica from

only 74 to 75.5%. This indicates that only the upper portion

44

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
   
 

    
  
 

 

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Figure 13. Schematic diagram depicting the interpreted
emplacement of the Rainier Mesa magma body. Possible
chemical configuration and location of Rainier Mesa magma
body: a). after initial emplacement beneath the Rainier
Mesa location; b). during the first eruptions at the Pahute
Mesa location; c). during eruption of the uppermost small
ash-flow layers in the tephra-fall sequence; d). and
immediately prior to the caldera-forming eruption of the
Rainier Mesa ash-flow sheet.

45

of the zoned magma body erupting these layers was being
tapped. This pattern of eruption, growth, and recharge
continued with time until the magma body ranged in silica from
67 (silica content of the first erupted layer) to 78% (the
highest silica content of the last erupted small ash-flow
layer in the tephra—fall sequence at each location) (Fig.
13c). °By the time the Rainier Mesa ash-flow sheet was
erupted, the magma body must have been at least 37 km wide if
it were to underlie the tephra-fall sequence at both sample
locations and extended to the furthest caldera boundary (Fig.
13d). In this case the magma body would only have to be 0.75
km thick in order to produce 1200 kn? of material.

Direct evidence for a growing magma body with time is
obtained from the correlation of chemical variation with
thickness of each small ash-flow layer from the Rainier Mesa
location. Here, ash-flow layers become thicker towards the
top of the section (Fig. 7), while the within-layer variation
decreases toward the top of the section (Fig. 10). This trend
could occur as a result of tapping a progressively larger
magma body with time. In other words, it is reasonable to
assume that as the magma body grew in size, the chemical
zoning would not be as intense as the smaller, initial magma
body.

Regardless of whether this model for the Rainier Mesa
magmatic system is correct, the evidence against the existence

of a large magma body, present in its entirety throughout the

46

duration of eruption of the tephra—fall sequences, is solid.
This interpretation has general implications for the
emplacement of large—volume high-level silicic magmas. It is
reasonable to consider emplacement of large-volume, high—level
magmas as a step by step progression of smaller processes
contributing to the overall emplacement of the large magma
body.

In conclusion, the tephra-fall sequence underlying the
Rainier Mesa ash-flow sheet is compositionally equivalent to
it. The tephra-fall sequence has been considered the first
erupted material from the uppermost fractionated portion of
the 1200 kn? Rainier Mesa magma chamber. The chemical range
of pumices and whole-rock samples from. the tephra-fall
sequence (67-78% SiOz, for example) indicates that eruption
from the most fractionated top of a 1200 kn? chemically zoned
magma body was not the source of these deposits.

Small scale chemical zoning within small ash-flow layers
contained in the tephra-fall sequence is characterized by less
evolved compositions, upward. This trend is consistent with
the eruption of a chemically zoned magma. Superimposed on the
within—layer trends are opposing large-scale among—layer
trends; consistent with eruption of a continuously evolving
magma.

Because the volume of each small ash-flow layer is
negligible compared to that of the high-silica portion of the

Rainier Mesa ash—flow, eruption dynamics and time constraints

47
on magma chamber evolution most likely indicate that the
large-volume Rainier Mesa magma body was emplaced
incrementally and that each small ash-flow layer provides a

window into Rainier Mesa Member’s magma body development.

APPENDICIES

49

Appendix 1. Major and trace element analyses of whole rock
samples from small ash-flow layers and from individual pumice
fragments in the tephra-fall sequence beneath the Rainier Mesa
ash-flow sheet.

Small ash-flow layer: from the Rainier Mesa section

 

 

 

 

 

 

Sample R17A;24 R17A;13 R17A;12 R17A;ll R17A;7 R17A;2
Weight Percent Oxide (wt. ‘2)

1'0, 7032 66.58 65.10 66.27 68.03 6856
TX» 021 052 056 046 037 034
111,0, 13.75 1534 16.19 15.04 15.08 15.18
FeO 1.14 3.08 2.87 2.52 2.00 1.96
Rho 0n (H2 an (m1 0% 0%
M30 0.35 1.07 0.95 1.03 0.81 0.74
010 0.47 1.63 1.36 156 1.84 1.65
NyO 333 340 141 357 351 352
190 536 4.23 4.12 4.28 4.88 4.95
2,0, 0.01 0.03 0.04 0.03 0.03 0.03
Total 9555 96.00 94.73 94.87 96.63 97.01

X-rey Fluonscence (pm)
c: 051 001 00? 00) mm 00)
Ni 0.00 1.00 1.43 6.83 0.00 4.78
o: 001 on) 001 0a) 0a) mm
Zn 66.42 79.61 72.60 7359 4423 48.37
Rb 165.66 13616 12275 146.71 145.33 153.02
Sr 72.69 29272 313.53 280.41 337.39 303.50
Y 38.04 3658 38.99 41.98 32.37 2858
2: 239.64 359.20 545.62 339.97 244.87 245.04
Nb 24.45 20.62 20.16 17.45 13.03 22.10
1.. 66.12 73.39 110.98 67.49 73.03 71.73
Be 281 838 1980 791 939 952
“Mvam

151 Ema 336
15 1m03 1&39
Eu 21m 307
10 10w 7%

Ce 13684 137.42
Yb um) 14&
I» 16% 16m
111 23.64 22.97
Cr n25 16w
Ba m0 um

C: 5n 4n
& 8n 6n
TI 1.40 1.14
Tb 23.44 25.53

Appendix 1. Continued.

Snelluh-flowhyendlefmnkainietMueeeaion

 

SO

 

 

 

 

 

 

 

 

Sample R17A;1 11173;“ R17B;7 R17B;5.5 R178;4.5 R17B;3.5
amkoilo .
1k), . 66.80 665? 67.62 #22 6939—19308
T10, 0.36 0.39 0.43 034 0.31 0.36
111,0, 15.55 15.20 15.07 14.67 14.69 14.61
FeO 2.16 1.66 1.80 1.49 1.55 1.93
M00 0.08 0.11 0.11 0.10 0.10 0.09
M30 0.74 0.44 0.43 0.47 050 0.42
C60 1.93 1.03 0.94 0.78 0.79 1.04
146,0 3.66 3.41 3.42 3.16 3.12 3.21
K,O 4.85 6.02 5.85 5.71 5.49 5.33
1m» 0m, 0m 0m 0m 0m 0m
Total 96.16 96.87 95.72 95.96 96.17 96.1 1
Xonyflnonmce @pnY
CI 131 2.63 0.00 an: 4.85 0.00
Ni 6.81 16.82 0.1!) 4.42 7.35 0.00
01 0.54 0.1!) 4.06 0.11) 0.1!) 3.10
211 47.92 62.37 69.47 54.25 67.52 73.57
Rb 133.89 158.98 167.43 177.46 177.33 164.18
Sr 380.09 121.18 121.22 96.19 101.26 143.94
Y 32.27 31.21 36.10 34.18 32.31 37.50
21' 246.13 359.31 394.55 323.96 269.87 295.59
Nb 6.60 12.36 7.24 24.29 23.44 18.07
LI 94.42 68.15 90.17 92.57 53.74 60.61
86 1188 824 857 677 444 427
In“ (mu)
'5 2934 33.20 2930
LI 185.88 377.45 186.73
811 29.86 40.14 26.38
H! 7.75 10.70 7.58
Ce 138.70 ‘ 256.89 170.28
Yb 14.60 14.1!) 13.10
Lu 15.29 15.1!) 11.18
1h n14 M33 ' H94
Cr 15.89 3.43 8.42
Be 1456 1082 746
C: 4.06 2.90 3.28
Sc 6.61 4.93 3.50
In 1.10 0.92 1.14
Tb 21.91 27.66 25.32

 

Appendix 1. Continued.

Smallesh—flowlayenfmthekahierMeueeaim

 

51

 

 

 

 

 

 

 

 

scape 1117132 RI7B;0 R16;2 1115.0 R14;7 1114;55
Imaflhumouuhil)

'1Rx EMS 64“ 1E§"""EHT"""EH8 66m
183 043 057 023 028 038 037
111,0, 14.97 1620 1307 1355 13.79 13.92
ho mm 311 Ln 1” us n”
MM) 0w (m9 0m 0m 0m 0m
M30 0.61 1.01 032 050 0.75 0.68
CIO 130 2.42 0.72 0.85 134 134
10,0 337 338 3.10 335 337 352
KO 533 4.70 5.47 520 4.82 4.90
142 m» 0m 0m 001 003 mm
Tom 9532 9601 96.74 94.44 95.90 9554

mfiem (pun)

'7} ‘ME “87 . 0. . 334 ME
m 001 122 001 001 001 mm
01 00) 16M. mm 001 znu 7m
20 7227 65.88 1247.10 47.14 139.65 85.87
Rb 157.19 145.30 17640 174.60 160.12 160.59
Sr 168.38 395.08 72.90 105.89 193.83 187.47
Y 32.99 34.19 33.88 3951 38.09 41.06
2: 35691 293.00 188.99 207.19 21647 210.87
Nb 17.88 16.84 25.91 22.71 22.35 20.90
1.1 88.41 60.64 60.24 75.97 57.13 88.89
a. 530 768 255 358 454 292

0MA@wn

151 :nflf5 ”30 aLa“—"‘Tfl§3
La 35261 17694 18376 16645
Eu 3333 15.07 20.00 19.13
m' 9% 6” 6% 6n
c: 23698 129.16 138.34 128.55
Yb 14a 15m 165 M91
L0 1559 1647 1853 1559
111 2257 28.08 26.99 22.07
c: 5m 53 13% 10
a. 885 334 503 442
c. 357 4.75 5.47 4.36
Sc 5.67 3.68 661 457
T6 101 Ln 135 Ln
Tb 30.85 2830 25.74 2638

52

Appendix 1. Continued

Small ash-flow layers firm the Rainier Mesa section

 

 

 

 

 

 

Sample R14;4 R14;1.5 R13;18.5 R13;9 R13;3.5 R13;0.5
Weight Percun Oxide (wt. 50)

‘50, 70.69 69.27 6855 68.93 68.83 69.60
T10, 0.35 0.37 0.28 0.29 0.27 0.28
41,0, 14.27 14.05 15.26 15.32 14.89 14.83
&0 1% 2w LM Lu. LN 15
11400 0.08 0.09 0.08 0.08 0.08 0.09
Mfi) 0m 0m 0m 0M. 00 0“
(2.0 129 1.44 1.05 0.93 0.91 0.97
Nap 3.15 3.21 3.15 3.02 3.13 3.28
K20 5.00 4.84 5.56 5.34 5.24 5.31
9,0, 0.03 0.05 0.04 0.04 0.02 0.03
mm %w ww 9fl2 ”M um ww

X—ray Fluorescence (ppm)
Cr 9% mm 00) 4% 190’ mm
m 154 0% mm 001 001 am
Cu 5“ m» 5% 001 291 4n
Zn 58.81 57.04 56.37 59.71 53.96 57.40
Rb 158.28 149.97 173.54 174.40 17671 163.49
Sr 168.99 207.48 148.52 123.17 111.70 12655
Y 36.34 40.32 36.66 39.45 31.80 35.80
Zr 187.56 197.36 222.36 229.57 223.96 228.03
Nb 2655 12.18 2922 26.26 23.61 7.41
La 61.01 7052 53.69 85.14 55.30 58.33
a. 69 342 327 292 6 158
INAA (ppm?

“Sm 37.40 30.28
La 227.30 180.61
Eu m24 18w
Hf 7% 7%
c: 15206 13820
Yb 15m 14”
15 16% 14n
“111 26.73 23.04
c1 1057 360
a. 555 486
ca 560 438
& 4% 3m
Ta La Lw
115 23.62 22.77

 

53

Appendix 1. Continued

Small ash-110w layen from the Rainier Mesa section

 

 

 

 

 

 

 

 

 

 

Smpu R1226 R1222 R1238 R1235 1:12:13 R12;7.5
fiEEUQumomk6681
‘1mz flh4 8Efl'""'1EH""'1§IF“"‘1§ms 6E3
1K3 033 034 033 035 042 036
Ann 140 "37 M21 10% 560 14a
FCC 166 1.82 1.70 1.88 229 2.06
MM) 0m) mu m» M» 0m 0w
M30 057 0.70 0.68 0.79 1.10 0.85
cg) 1w um L3 126 124 1%
mp 328 3.32 337 3.49 3.40 334
mp an 431 4”. 4n 4a 4a
mm Mb 002 0m 0m 0m 0%
Total 9659 96.84 9732 9604 96.80 9620
W (pun)
a. 11w 1%. 95""‘10M"“"1Efl 5n
Ni 000 0.00 0.00 0.00 20.03 425
01 203 364 0.00 1223 946 157
26 5752 53 90 5365 63.48 69 07 5668
Rb 15042 155.34 147.18 155.41 15661 151.47
8: 14601 173.28 166.42 175.48 169 53 171.18
Y 35.75 3447 39.61 38.47 4644 4658
2: 223 80 214.43 217.66 233.28 271 78 21071
N0 2836 34.82 29.97 24.99 18 89 19.08
h «m nu am am um um
84 139 163 279 208 166 '26
1110 (m)

‘fifi n44

15 “an

En 18a

H! 10

(2 inmo

Yb 14”

16 14h

1b 368

Cr 7.05

Ba «n

c. 4n

Sc 3n

Ta 1.07

1h 2m»

54

Appendix 1. Continued

SmallaahoflowlayenfrommekainierMeaaacction

 

 

 

 

 

 

 

 

 

 

Sunfle 11124.75 R12;0 R3200 R3188 83156 R3;120
WM (911. I.)

'52:, 67.16 684! 7724 7426 7321 W
TR; 044 042 011 010 014 020
41,0, 15.44 1530 12.79 12.62 12.91 1239
an 20 2“. 0n 0m 0m 13
MR) 0m 0w 007 007 0m mm
Mg) 0n 0“. 0n 00 0x1 03
cm) L” 138 0m 0“ 0« 0n
188.0 3.49 353 2.94 2.89 2.85 2.91
mp 451 4n 4» 8H 40 40
mm 0m 0m 0m 0m 0m 0m
Total 9608 97.11 96.29 9643 96.78 9622

X-ray fluorescence (pun)
Cr 118 0 . . 005 100
N1 4%. 'un 0m 00) M» 0m
01 m0 001 mm mm M» 0m
20 91.18 77.43 39.15 30.72 3233 43.00
Rb 13395 13294 23896 22460 21213 19882
s: 20L81 17725 1771 2237 5118 8320
Y um mm an 2M3 2m7 um
21 257.91 243.50 88.81 78.99 10205 115.25
Nb 22.78 17.06 28.11 26.63 28.79 2750
1.. 4351 35.44 1551 31.46 31.28 3451
a. 1% n8 u 1n 1% 2w
NM (ppm)

151 500 uflf“"'1m5 RHT"""1E5
L. 25224 19633 7839 8018 5642
Ba 2420 2507 116 225 435
111 7.84 725 3.67 4.01 3.88
C: 15667 14081 5927 7258 5820
Yb 18.80 1625 13.90 13.80 12.60
La 2126 1412 1441 1529 1059
111 2687 17.67 24.62 27.45 1620
c1 1799 1427 464 635 1009
a. 501 488 137 213 247
c. 558 3.85 5.80 6.07 6.63
Sc 626 393 413 464 334
'n 166 124 206 137 1«
Th B64 52M H43 90 130

55

Appendix 1. Continued

Smallaah-flowlayenfmmmekainierMeuaeaion

 

 

 

 

 

 

 

 

 

 

Sample R338 R33 R2;30 R1;129 R1;117 R1;94
‘EEU%umOflhfim§)

110, “ET—73.15 74M 74.88 7457
1m; 0m 0m 0m 0n 0n 00
41,0, 1222 12.40 12.15 11.63 1204 1232
an 111 131 0a 0a 0n 0”
Md) 0m mn 0m. 0m 0%. mx
M30 0.42 065 0.19 0.14 026 0.23
C60 0.65 0.67 0.42 0.47 0.45 050
194,0 3.03 3.04 328 3.10 321 320
16,0 4.48 424 4.68 4.66 4.64 4.67
mm, 0m M» 0m 0m MM 001
161.1 95.94 95.76 95.96 95.90 9637 9651

X-ray “nonsense (an)
Cr ”0&1 0R1 0aF""'1E0"""1fl0"""1fl0
N1 000 623 129 000 614 2940
On 000 0.00 0.00 000 000 1.66
Zn 4590 5217 2059 2239 2675 7421
Rb 22611 213.74 24652 235.40 224 86 237.02
s: an um um um 1H5 mu
Y mu an 2u2 an ”a mm
2: 107.49 133.08 80.72 80.61 78 78 91.76
m an an 255 mu an MM
La 1859 5126 969 4053 5124 4070
a. an E6 0 81 83 95
0446”»

'16 200 E61
1.. 7852 53.85
En 391 0”

H1 402 in
(2 6876 5032
Yb 14m 18m
16 M41 14m
It 325 1mm
c1 827 345
a. n1 1%

c. 83 8”
Se 5m in
1. 2n 196
It 1553 1524

Appendix 1. Continued

Small Rah-flow layers from the Rainier Meaa section

56

 

 

 

 

 

 

 

 

 

83mph R1;78 R1;54 R131 R1:18 Rl;14 R11
Whamnmunhaumflh
‘1fii ‘fl64 ffi§"""1&w ‘263"""1flfi"""‘1flfi
110, 0.13 0.14 0.12 0.11 0.16 0.17
41,0, 1232 1232 11.89 1238 11.95 12.15
a0 0n 0%; 0K) 021 H6 122
800 MM 0m MM 0m 0m1 0%
M30 028 031 023 0.69 035 0.42
cuo 051 058 054 048 062 063
10,0 327 3.40 3.08 2.85 293 3.06
14,0 461 451 4.48 4.73 4.42 436
mm 0m 0m 0m 0m 0m 0m
Tour 95.81 95.98 96.47 9678 97.47 97.11
X-ray fluorescence (ppm)
cr oar----mn. "MB 1dB 1M0 ‘0w
N1 630 840 858 000 523 699
01 m» 00) 0m 00) 001 12%
25 283.55 1134.93 2636 35.77 22.97 692.77
Rb - 23302 22424 21L82 18587 17676 17959
9 mm «a um um aw 8u9
Y 28.49 3127 2256 30.82 20.05 21.03
2: 8681 82.40 7857 10065 8660 99.38
Nb 19.46 1855 20.03 15.11 1696 15.06
15 73.84 4520 3521 831 47.42 42.92
a. 0 34 20 38 119 192
mm (mm)

'36 31h 26m 7002

15 59m 50m 61R

En up 8%. 2n

Rf 3.77 353 350

Ce 580 £92 “11

Yb um) n21 12m

15 1676 8.82 11.47

'm 303 123 190

c: 8m 9m 7%

Ba 127 179 229

C8 H29 85 H64

& 8w 1” 4a

15 232 L34 L74

Tb 12w 15%. 15W

57

Appendix 1. Continued.

Small ash-flow layers from the Pahute Mesa section

 

 

 

 

 

 

 

Smmh 901 NR9 9018 9025 930 004
TMERTm60060668)

110, 72.06 7134 70.38 72.10 70.42 70.42
In, 0m 00 00 00 00 00
AhO, 1291 1317 1319 1348 1357 1366
960 1.29 1.79 1.43 1.64 155 1.57
MR) 0m 0m 0m 0m 0m 00
M30 0.20 0.02 0.09 0.18 0.39 0.43
C80 0.86 0.97 1.04 1.05 0.72 0.73
193,0 3.33 3.22 3.54 3.38 3.52 3.31
14,0 453 4.45 4.41 4.47 4.93 5.04
Km m0 0m 0m am 0m 00
Total 95.45 95.28 94.35 96.60 95.41 95.46

X-ray fluorescence (ppn)
Cr 2.17 1.38 3.83 0.00 3.15 0.00
N1 M» 0m mm 001 001 00)
01 m0 2“ mm 16M 5% H28
Zn 57.01 59.97 55.95 63.07 71.08 64.01
Rb 16311 15858 15540 15103 15118 15254
Sr 15248 170.29 190.99 191.49 95.18 92.20
Y 32.98 32.74 35.44 30.72 34.81 41.12
Zr 167.07 207.40 19274 200.98 21213 21676
Nb 1619 320 735 1069 1891 1664
15 78.04 164.99 139.77 126.26 134.68 179.09
R. 159 190 283 241 69 57
0066p»

.5; 528
15 9mm
Bu 0.51
Hf us
(5 090
Yb 20
15 0M
1h u58
Cr 328
a. 3m
Ca 357
Sc 2.50
Ta 1.36
1h 00

 

58

Appendix 1. Continued.

Smallssh-flowlsyersfrcmthePahIIeMesaseaion

 

 

 

 

 

 

 

 

 

Smfle P239 P24A;2 P24A;7 P24A115 P24;1 P24:7
fiEEflHumOdepn
'1Rx flBT"""n21 ’TNIT’ H68 200"""“nzr
110, 0.16 022 009 0.10 0.13 0.11
41,0, 13.49 1231 11.96 11.93 12.42 1232
FeO 1.44 1.91 1.07 0.98 133 1.12
Md) m0 m0 007 0m 0m. 0m
Mfi) 0a 00 00 00 00 m0
QC 069 0.98 0.47 0.49 0.62 054
144,0 329 297 3.12 3.02 3.07 3.07
11,0 4.97 4.64 4.89 4.95 4.93 4.98
9,0, 0.01 0.02 0.01 0.01 0.01 0.01
10ufl 9511 9631 9634 9638 9515 9495
X-ray “Somme (pun)
u- 001 180 431* our---mn ‘2n
M 0d) 300 mm mm 001 mm
(5 0m) 8m 90 0a» 060 mm
75 61.63 63.94 57.11 56.85 6258 5931
Rb 15242 160.23 167.79 17214 173.24 171.89
s: 8647 8602 23.43 30.85 66.72 48.12
Y 38.94 4222 4152 43.70 3951 38.84
21 189.86 133.09 122.06 13091 154.61 134.24
Nb 21.65 2685 28.05 2821 2722 18.60
15 10821 10174 6425 10261 8233 7142
a. 1% 0 0 45 70 0
muA0wm
'1; 5a. ifl $0
15 83.00 3826 33.74
BI 0a 00 00
HI 6“ 6n 551
Ce 15355 8557 73.93
Yb 2“ 8H 30
15 00 0M 0%
n. 80) 061 220
c: 333 350 3.28
e. 26 ‘04 09
c: in 40 3m~
Sc 192 204 10
Ta 1.35 1.54 1.48
Tb 110 101 110

 

59

Appendix 1. Continued.

Small ash-flow layers from the Pahute Mesa section

 

 

 

 

 

 

Sample P24;27 PO;O.5 PO;3 P0;6 Pl;0.5 Pl;3
Weight Percent Oxide (wt. %)
s102 74.30 6979 71.31 73.66 73.94 74.16
TiO2 0.08 0.16 0.13 0.09 0.10 0.10
Algh 12.14 14.18 13.30 12.92 12.28 12.07
FeO 1.07 1.43 1.09 0.89 0.89 0.87
MnO 0.07 0.07 0.06 0.06 0.06 0.06
MgO 0.12 0.25 0.17 0.00 0.08 0.07
CaO 0.43 0.71 0.70 0.56 0.62 0.63
Nag) 2.95 3.28 3.02 2.63 2.95 2.97
K20 5.11 4.38 4.70 5.01 4.98 4.97
9,0, 0.01 0.01 0.01 0.01 0.01 0.01
Total 96.25 94.26 94.49 95.83 95.91 95.91
X-ray Fluorescence (ppm)

Cr 8.16 0.62 0.65 2.18 0.00 0.00
Ni 0.00 12.09 6.40 3.00 6.30 5.65
Cu 1.67 1.35 0.00 0.00 0.00 0.00
Zn 62.03 37.01 27.33 23.85 29.45 26.45
Rb 171.54 166.34 171.77 175.29 179.09 169.29
Sr 19.39 71.38 63.12 22.60 43.79 43.19
Y 43.29 26.93 27.26 23.86 28.55 28.28
Zr 130.93 118.98 102.01 86.96 98.79 94.67
Nb 24.80 15.20 17.27 18.30 20.03 18.03
La 60.85 60.16 52.45 71.19 63.85 48.59
Ba 0 12 54 179 76 192
__ INAA (ppm)

Sm 5.34 5.68 5.80

La 29.54 24.90 34.46

Eu 0.40 0.22 0.31

Hf 4.48 3.73 4.08

Ce 66.95 60.87 70.36

Yb 2.88 2.38 2.76

Lu 0.49 0.31 0.48

Th 29.24 19.05 27.62

Cr 9.41 3.28 6.17

Ba 176 137 118

Cs 5.73 4.74 5.55

Sc 4.79 2.58 3.44

Ta 1.38 1.30 1.38

Tb 0.91 0.66 0.79

Appendix 1. Continued.

60

SMuh-flowhyenfmmehhmcmm

 

 

 

 

 

 

 

 

Sample P1;6 P1;10 ”:20 P1;25 P2z2 92:6
fiEEfiGEFEEE)

'56, M. 71.13 13.n——mr——m. .
T10, 0.16 0.12 0.09 0.09 0.08 0.07
AUG, 1295 1259 12J0 1212 1202 1224
FeO 1.29 1.11 0.89 0.78 0.90 0.67
34110 0.07 0.06 0.06 0.06 0.06 0.06
Mfi) an (ms am ms 001 am1
0.0 0.74 0.72 0.57 0.58 0.58 0.55
N50 2.81 2.85 2.78 2.83 2.98 2.97
lip 4.84 4.90 5.04 5.06 4.96 5.01
Pp, 0.02 0.01 0.00 0.01 0.00 0.00
Total 961!) 96.43 96.01 95.30 95.44 97.35

Km W (ppn)
Cr 0. . . . .
Ni 6.14 31.47 1.55 9.32 2.67 0.00
Cu 0.00 0.1!) 0.00 0.1!) 2.42 0.00
211 30.69 27.23 28.64 23.56 29.70 24.13
Rb 166.24 167.24 180.75 182.72 185.14 186.89
Sr 85.61 64.45 37.08 37.88 28.53 14.51
‘1 32.80 29.18 21.61 19.23 21.99 28.14
2: 114.47 93.56 99.78 95.02 84.59 77.65
Nb 15.38 16.68 23.13 19.33 21.80 20.91
LI 95.29 82.87 69.92 79.44 62.43 37.32
B. 154 167 0 75 0 69
mhkwwfi

'15 1% 1a an
L: 113.09 24.90 24.21
Eu 2.30 0.22 0.19
111' 9.16 3.73 3.92
C: 183.26 60.87 60.73
Yb 2.72 2.38 2.81
Lu 0.41 0.31 0.48
Th 19.12 19.05 29.48
C: 9.59 5.51 4.49
B: 798 128 1 15
C: 3.53 4.06 5.62
Sc 5.04 1.97 3.63
T: 1.07 1.16 1.55
Tb LN 0.71 0.73

 

61

Appendix 1. Continued

Smnll ash-flow layer: from the Pahute Mesa section

 

 

 

 

 

 

 

Sunple P2;8 P3;0 P3;6 P3;12
WciEt percent Oxide (wt. 92)

110, 74.03 73.43 73.58 72.55
fig am 0n 0% 0m
A120, 11.95 12.29 11.98 12.25
FeO 0.76 1.00 0.79 0.88
MnO 0.06 0.07 0.06 0.06
1430 0.02 0.13 0.12 0.32
C20 0.55 0.65 0.57 0.56
N220 2.85 2.73 2.82 2.70
no 4% 5m 5n 5n
Pp, 0m 0m 0m 0m
Total 95.34 95.57 95.19 94.58

X-ny fiuonscence (ppm)
Cr 0.00 25.68 0.00 2.24
Ni 0.00 54.42 0.00 0.00
Cu 0.00 0.00 0.00 7.43
211 35.10 35.86 35.57 33.07
Rb 190.70 190.88 183.15 190.09
Sr 24.94 55.75 37.40 44.10
Y 31.96 30.84 30.61 30.52
Zr 77.91 92.60 87.39 89.05
Nb 12.06 ' 12.44 13.99 15.48
L: 70.86 86.70 69.66 83.91
B: 0 18 0 0
mwamn

1111 6.28 5.87 5.68
La 0.00 30.96 27.60
1311 0.16 0.26 0.24
Hf 3.94 4.28 3.80
Ce 61.01 68.68 62.49
Yb 2.79 2.72 2.48
L11 0.50 0.51 0.42
111 30.50 30.85 24.49
Cr 4.49 5.43 3.28
Ba 71 157 139
C: 5.49 6.28 4.14
Sc 3.46 4.10 2.43
Ta 1.58 1 46 1.38

Tb 0.67 0.58 0.96

Appendix 1. Continued.

62

lepn-fall sequence (mm plaice W)

 

 

 

 

3“ mm m0 M13C M14A M143 M208
Weight Percent Oxide (wt. ‘5)
810, 77.27 76.80 75.43 75.83 75.37 76.25
TIC, 0.08 0.07 0.14 0.13 0.14 0.08
111.0, 12.56 12.49 14.06 1323 13.70 13.00
FeO 0.83 1.04 1.25 1.36 1.24 1.“)
mo 0.“ 0.“ 0. 1 3 0.“ 0.07 0.08
M‘O 0.25 0. 16 0.49 0.25 0.37 0.22
C80 0.61 0.77 0.62 0.75 0.88 0.50
Nqo 292 3m 238 3n 313 371
11,0 5.40 5.45 4.99 5.27 5.08 5.14
no, 0m 0m am 001 0m 0m
Tall 97.14 96.5 1 95.73 95.“) 94.24 95.24
X-ny Phloem (fill!)

Cr 6.50 600 2.60 0.“) 2.40 6.90
Ni 0.“) 5.80 0.20 10.80 0.“) 8w
0) 60.20 61.40 60.30 65.00 60.“) 63.30
Zn 33.30 21w 45.40 66.20 45$ 55.50
Rb 198.” 203.10 185.30 195.30 193.“) 192.20
51’ 33.10 53.10 53.1» 97.80 131.30 53.“)
Y 35.60 34.40 48.40 39.30 38.50 40.10
Zr 81.30 85.60 114.“) 132.00 130100 105.“)
Nb 30.70 12.80 26.80 20.70 29.20 33.“)
LI 21.30 20.00 18.70 24.70 22.20 35.10
Be 176 219 422 377 318 237

° mapknlnesbegimingwithbahthelaleandefmthePnhmeMeu section. Sunplenamesbegiminx wilhtheieuer

RuefmlhehinierMeusectim.

Appendix 1. Continued.

63

Tephra-fell sequence (individual pumice fugments)

 

 

 

 

Sample M20F M200 M21,1A M21,1D M21.2D M21,2E
Weight Percent (wt. %)
810, 76.72 76.57 76.22 71.00 75.64 76.13
T10, 0.08 0.09 0.10 0.42 0.10 0.10
A120, 12.70 12.84 13.02 15.08 13.34 13.39
FeO 0.98 0.77 1.24 2.61 1.13 0.84
MnO 0.08 0.08 0.09 0.09 0.08 0.08
M30 0.01 0.19 0.09 0.56 0.05 0.05
C30 0.53 0.50 0.59 1.81 0.50 0.49
Ne,0 3.75 3.65 3.43 3.84 3.77 3.51
K20 5.13 5.29 5.20 4.47 5.38 5.39
P20, 0.01 0.01 0.01 0.12 0.01 0.01
Total 95.96 95.32 95.49 95.23 94.18 95.61
X-ny fluorescence (ppn)

Cr 0.00 7.30 4.30 6.90 3.80 0.00
Ni 3.70 0.00 9.90 9.00 0.00 0.00
Cu 60.50 57.00 61.60 64.00 59.60 58.60
211 52.80 48.60 58.50 79.30 72.00 52.70
Rb 190.70 185.40 187.30 147.40 160.50 164.60
Sr 49.00 46.80 67.60 249.70 28.20 27.10 '
Y 40.40 40.60 38.30 37.90 39.90 38.10
Zr 92.80 95.60 116.30 279.80 150.40 149.30
Nb 24.00 27.90 32.60 16.50 23.20 18.60
L: 59.90 37.70 43.40 82.50 37.40 54.20
B: 248 284 370 640 168 131

64

Appendix 1. Continued.

Tephra-fall sequence (individual pumice fragments)

 

 

 

 

Sample M21,3E M21.3F M21.4D M21.6J M21.6Q M22.1D
Weiylt Percent (wt. %)
SiO, 77.09 76.71 67.53 74.07 72.45 75.65
TiO2 0.08 0.08 0.39 0.20 0.22 0.1 l
A130, 12.92 12.74 17.00 14.25 14.39 13.73
FeO 0.83 1.16 2.68 1.46 1.33 1.02
MnO 0.09 0.08 0.15 0.08 0.09 0.08
M30 0.53 0.10 0.61 0.19 0.25 0.04
C30 0.48 0.52 1.79 0.80 0.92 0.55
N320 3.16 3.53 4.98 3.86 5.36 3.46
K20 4.80 5.05 4.86 5.06 4.97 5.35
P20, 0.01 0.01 0.01 0.02 0.03 0.01
Total 95.14 95.58 96.00 94.79 92.70 95.06
X-ray Fluorescence (ppm)

Cr 8.30 2.60 6.50 0.00 8.80 16.10
Ni 0.00 20.30 0.00 0.80 0.00 0.00
Cu 59.40 59.80 59.00 61.60 57.40 56.30
Zn 68.20 56.00 103.90 52.60 44.90 52.00
Rb 166.30 1801!) 164.20 157.50 160.70 160.90
Sr 47.30 50.90 307.80 97.80 130.70 43.00 '
Y 41.90 41.10 42.70 34.70 35.00 46.60
2: 125.50 99.10 505.70 219.20 249.40 185.40
Nb 17.50 23.90 16.60 24.60 23.20 34.20
La 43.20 44.20 130.40 92.40 58.70 55.20
Ba 231 232 938 541 683 241

Appendix 1. Continued.

6S

Tephra-fall tequence (individual pumice human)

 

 

 

 

sunk MflUE MflAA MflMB M364 umum Luau
Weight Pennant (wt. 5)
510, 75.00 75.89 75.35 7721 77.41 76.26
um um um (m3 0m 0m 0%
41.0, 13.73 1326 13.68 12.97 1245 12.74
a0 15) 1m 1% an um 13
MM) 0m 0m mn‘ 007 007 0m
0m mx 004 0m1 0m 0m
QC 053 050 059 0.46 0.44 0.49
144,0 351 3.73 355 3.00 2.76 357
K43 532 531 551 537 5:7 551
no, am 001 002 001 001 am
nu mm “m um am ”a um
X-ray M (an!)
Cr 14.30 1420 15.60 22.60 1450 2050
Ni 49) 00) 00) 0a» mm mm
d: 62.70 58.90 53.00 56.30 53.90 61.00
26 53.60 59.70 52.40 53.30 52.70 57.30
Rb 17040 17250 16320 20860 20090 13320
s: 41.60 30.30 45.70 3230 23.00 3530
Y um um 4u0 0» mm um-
21 179.10 159.00 13300 124.60 114.30 138.60
Nb 39.30 3620 36.90 1420 31.90 23.10
1.. 39.10 32.30 62.90 2030 3430 5550
a. 287 271 210 180 100 20

66

Appendix 1. Continued.
Tephra-fall aequence (individual pumice fawn)

 

 

 

 

Samfle R713 R7F R8A R1 1A R1 1F R12F
Weight Percalt Oxide (wt. 5)
810, 69.99 75.15 77.84 75.68 75.88 73.51
TO, 0.34 0.20 0.19 0.16 0.16 0.26
“,0, 16.31 13.55 12.30 13.57 13.28 14.46
FeO 1.44 1.13 0.91 0.89 0.79 1.37
14:10 0.14 0.09 0.08 0.12 0.12 0.08
M30 2.73 0.70 0.65 0.31 0.16 0.55
C00 1.33 0.54 0.44 0.30 0.30 0.82
N220 3.79 3.32 2.81 3.13 3.48 3.16
K10 3.49 5.30 4.76 5.85 5.83 5.78
P30, 0.43 0.01 0.01 0.01 0.01 0.01
Tall 94.44 9554 95.13 94.68 95.27 95.70
X-ny Fluctucence (ppm)

Cr 23.50 18.10 17.10 0.00 0.30 0.1!)
Ni 0.1!) 0.1!) 0.1!) 0.00 0.00 0.00
Cu 59.70 58.10 56.90 57 .20 57.1!) 58.10
Zn 76.“) 61.60 51.50 63.50 63.90 50.80
Rb 126.70 204.1!) 184.1!) 191.80 187.30 207.80
Sr 131.70 61.1!) 38.40 24.60 21.50 102.1!)
Y 55.40 35.50 39.80 48.90 44.30 48.10
2: 292.40 195.40 150.” 204.60 213.10 222.50
Nb 18.1!) 21.80 27.40 30.30 33.90 30.1!)
La 91.50 40.50 34.90 16.30 0.00 29.30
Ba 11% 386 159 139 83 437

Appendix 1. Continued.

Tephra-fall tequence (individual pumice fragments)

67

 

 

 

 

Sample R1413 RISA 1116A R176 R1711 PMR-SURGE-E
Weight Pement Oxide (wt. 96)
s10, 73.81 74.67 73.87 72.49 75.84 7650
182 028 023 025 027 017 008
Alp, 14.44 13.86 14.48 14.87 13.08 13.14
FeO 124 1.04 1.26 1.28 1.00 0.76
mm) 0m 0m 0m 0m 0m m5
M30 0.48 0.31 037 039 0.13 0.00
CaO 0.75 0.65 0.68 0.66 0.32 0.73
114.0 3.02 3.06 2.97 3.96 3.58 3.19
16,0 5.86 6.07 5.99 5.92 5.75 552
mm 0m 0m 0m 0m 0m 0m
Total 95.13 94.88 96.38 95.01 95.70 95.83
)Hthmwmwwwn

Cr 00) 00> 2m 00) 26) mm
M 0m) 00) 00) mm mm mm
Cu 58.10 57.40 57.90 56.40 5720 58.00
a 44.40 5550 42.00 64.90 74.10 24.20
Rb 19200 203.20 19230 167.20 187.60 222.60
Sr 79.80 63.00 60.80 74.80 25.40 36.10
Y 4150 4350 47.70 55.00 47.10 55.40
2: 209.20 193.80 187.20 318.90 20250 85.80
Nb 37.80 38.50 34.00 38.00 39.00 4150
1.. 29.70 19.30 3120 1250 35.10 0.80
Ba 345 190 205 282 116 124

68

Appendix 1. Continued

Tephra-fall sequence (individual pumice fragments)
Sample PMR-SURGE-F PlA PlB P2.1A P2. 18 P2311

Weight Percent Oxide (wt. %)

 

 

Si02 75.87 76.55 77.68 77.31 77.45 76.97
TiO, 0.10 0.08 0.08 0.08 0.08 0.08
A120, 13.55 13.08 12.55 12.92 12.83 13.01
FeO 1.16 1.11 0.62 0.75 0.99 0.85
MnO 0.06 0.05 0.05 0.06 0.05 0.06
M30 0.1 1 0.02 0.00 0.00 0.00 0.00
C80 0.64 0.56 0.56 0.56 0.57 0.57
N820 3.22 2.87 3.00 2.54 2.59 2.95
K30 5.25 5.66 5.45 5.76 5.43 5.50
P10, 0.01 0.01 0.01 0.01 0.01 0.01
Total 96.29 95.20 95.65 95.69 96.31 95.04
X-ray Fluorescence (ppm)
Cr 0.00 0.00 1.30 7.00 3.90 0.00
Ni 5.20 0.80 0.00 0.00 0.00 0.00
Cu 60.20 62.70 58.00 56.00 56.90 59.20
Zn 53.40 52.70 31.20 29.60 34.10 30.40
Rb 203.40 214.80 202.90 218.90 203.50 204.20
Sr 32.60 29.50 29.50 26.70 25.30 32.00
Y 31.70 28.40 27.90 25.20 25.10 27.50
Zr 99.30 91.90 86.70 87.30 83.20 88.50
Nb 22.90 21.70 27.20 27.00 22.30 15.10
1.8 41.20 38.20 22.80 30.20 40.70 41.70

Ba 165 146 73 87 79 216

69

Appendix 1. Continued.

Tephra-fall sequence (individual pumice fragments)

 

 

 

 

fimfle 22m EMA 2MB Ema :m2A ram
Weight Pement Oxide (wt. ‘6)
$0 ma nm N” 7M6 7mo mu
no 0m m0 mn 0m 0m. 0%
400, 1308 1244 1251 1255 1268 1314
FeO 1.08 058 0.92 0.69 0.93 1.05
Md) 0%. mx mx 0%. mx mx
100 00) mm 00) 001 001 0m
C30 055 056 057 056 0.58 0.56
148.0 2.91 3.17 3.35 2.86 3.21 3.21
18,0 554 5.67 525 5.73 5.34 5.37
20, 0m 0m 001 0m 001 0m
Total 95.00 94.86 96.00 95.27 9552 94.42
X-ray Fluorescence (ppn)

c: 1.00 6.80 0.00 0.00 1.70 0.00
m m» 00) 00) 001 M» 0m
on 5950 57.80 5920 56.40 5750 58.90
Zn 3430 25.40 42.10 35.70 24.70 26.70
Rb 215.40 231.00 214.90 22680 214.40 20650
a nu um um um um um_
V 29.10 28.70 34.00 2820 33.00 38.10
2: 85.00 ' 7670 87.00 78.00 91.90 88.20
Nb 17.90 17.90 18.30 2600 29.30 29.70
1.. 18.70 20.80 45.70 4220 12.60 14.00
a. 123 171 103 322 78 96

Appendix 1. Continued.

70

Tephra-fall sequence (individual plaice frlunents)

 

 

 

 

Sample P3.3A P338 P3.4A P348 P4.1 P4.2D
Weight Pement Oxide (wt. Q»)
s10, 77.40 77.14 77.15 77.28 77.33 7725
fig 007 0m' 0m am 007 am
41,0, 12.72 12.86 13.04 12.84 12.69 12.69
FeO 0.72 0.83 0.74 0.93 0.76 0.83
Mfi) M» 0% (m6 0%» on; mm
mm on) am am 001 mm
C80 057 059 055 055 058 057
N50 3.07 2.81 258 2.49 2.96 2.93
K,O 5.37 5.63 5.76 5.72 5.53 559
14% 0m 0m 0m am 001 am
Tan! 9537 94.95 94.70 95.67 96.15 95.70
X-ny Homesceme (ppm)
C1 9m 221 um mm mm) mm
m on) M» on) mm on) M»
01 5720 $6.80 5720 56.60 56.30 57.80
Zn 2150 3270 3250 31.70 30.80 28.80
Rb 204.00 213.40 220.30 213.10 223.60 224.10
8: 34.00 3550 29.00 24.90 24.30 25.70
Y 3330 35.70 28.10 26.10 26.20 3220
Zr 77.10 83.10 101.20 99.90 83.30 81.80
Nb 29.40 34.40 24.20 ' 31.90 30.20 3450
Ls 920 0.20 29.80 30.70 30.10 39.80
a. 124 59 145 159 157 11

71

Appendix 1. Continued.

Tephra-fell sequence (individud plaice (laments)

 

 

 

 

Sample P420 P434 P4.3c Ps8 PSE M26
Weigh Pew Oxide (wt. ‘5)
SiO, 7686 77.18 77.06 7729 77.15 76.97
um 0m 0m' 0m 0m 0m 0m
41,0, 1325 12.75 12.86 12.65 12.76 12.99
FeO 0.79 0.76 0.81 0.86 0.84 0.79
Mfi) on; 0%. mm 0%. 0m. 0%
mg) um m» on) 061 0m am
can 057 057 058 059 062 050
N4) 2w 3n mu 3” 3m 3w
190 5.67 5.42 553 5.09 528 5.10
Pp, 001 0m 0m 0m 0m 0m
7641 9640 96.15 95.63 9687 9627 0.00
X-rsy Fluorescence (pm)

Cr 1.70 0.00 0.00 150 5.70 0.00
m m» 061 mm mm 001 001
Cu 55.40 5550 5690 57.10 57.10 0.00
74. 2630 23.60 41.40 31.00 34.70 5673
Rb 237.60 214.70 223.70 20600 21670 167.75
Sr 25.00 24.90 28.80 29.40 3680 4524
Y 28.70 2610 2330 2650 32.60 3438 '
z: 7830 7860 8350 8250 81.90 1022
Nb 33.00 31.70 3050 31.00 32.40 19.63
L. 3600 37.80 19.10 39.40 2630 80.17
8. 136 119 98 105 134 179

Appendix 1. Continued.

Tephn-fsll sequuice (individual mice humans)

72

 

 

 

 

Smfle M401 M208 M21.1C 8421.10 8421.15 M21.ll-l
Weight Percent Oxide (In. ‘5)
SiO, 77.15 76.82 76.61 71.12 77.50 75.89
T10, 0.13 0.09 0.12 0.42 0.08 0.12
41,0, 12.75 12.90 13.1!) 14.78 12.73 13.30
FeO 0.94 0.96 1.10 2.68 0.89 1.18
M00 0.05 0.09 0.09 0.1 1 0.08 0.09
0.04 0.23 0.28 0.64 0.1 8 0.09
C80 0.64 0.48 0.63 1.71 0.47 0.64
198,0 2.32 3.16 3.24 3.87 2.88 3.27
K10 5.98 5.25 4.89 4.56 5.17 5.40
P30, 0.1!) 0.01 0.02 0.1 1 0.01 0.02
Km fluorescence (ppm)
T0881 0.1!) 0.1!) 0.00 0.00 0.00 0.00
Cr 0.1!) 0.1!) 0.1!) 0.1!) 0.00 0.00
Ni 0.1!) 0.00 01!) 0.“) 0.00 01!)
Cu 3.21 0.1!) 000 8.16 4.36 0.46
Zn 30.53 57.63 60.12 71.26 54.07 57.61
Rb 141.90 179.81 176.19 130.19 166.42 168.27
Sr 68.64 43.14 78.17 207.55 33.57 101.04 '
‘1 22.04 30.33 28.42 34.85 34.14 35.19
Zr 1 11.15 107.82 130.15 264.16 96.48 143.01
Nb 14.27 20.78 22.75 9.12 20.25 18.76
Ls 71.40 67.77 63.43 104.41 74.61 91.28
88 464 269 292 816 160 375

Appendix 1. Continued.

73

Tqihra-fall sequence (individual pumice (laments)

 

 

 

 

Sllnfle M21.11 M21.” M2121 M21211 M44 M48
“Mflflhumodkhm%)

810, 69.10 7695 77.18 76.93 7629 76.70
fig) 0m 0m mm mm 0m 0m
41,0, 1613 12.78 12.95 13.09 1353 13.07
&0 327 um 0m um mm 0%
MM) 0m 0m 0m. 0m 0m 0%
M30 0.78 0.18 0.43 032 0.12 0.08
0.0 232 053 0.48 0.53 0.64 0.65
146,0 3.66 326 297 3.08 2.38 2.47
no 3“. in 50) 5M’ 5» 591
mm am 0m 0m 0m 0m 0m

16» 061 um m» 061 mm mm

X-rey Fluorescence (ppm)

c: 000 mm 001 0a) 001 on)
m on) 2% m» on) mm mm
Cu 4.85 11.69 0.00 0.00 0.00 12.88
Zn 68.87 5627 52.97 5460 8825 32.80
Rb 103.38 164.70 164.54 16676 149.01 154.81

s: 33470 4213 4121 4669 6990 6735

Y 33.05 34.07 33.44 32.66 13.44 18.01

2: 31674 104.94 93.87 102.00 117.89 118.81

Nb 18.66 1955 23.79 11.13 13.59 1670
1.. 145.83 8656 54.95 79.06 104.95 8935

HI 887 319 162 136 555 360

Appendix 1.

74

Continued.

Tephra-fall sequence (individual punice fragments)

 

 

 

 

Smfle M2213 MZZJC 1422.18 8422-34 M22-3-2 1422-3-3
Wfififlhumoukhn%)
SiO2 75.16 74.91 76.04 7550 75.44 76.36
T10, 0.11 0.14 0.10 0.11 0.12 0.09
A130, 13.87 13.96 13.12 13.25 13.58 13.14
FeO 1.24 1.33 1.05 1.16 1.13 1.05
M00 0.08 0.08 0.08 0.08 0.08 0.08
M30 0.10 0.06 0.03 0.02 0.13 0.05
CaO 0.59 0.64 0.51 0.80 0.52 0.49
N830 3.41 3.54 3.62 3.25 3.40 3.41
190 5.42 5.32 5.43 5.81 5.60 5.32
Pp, 0.01 0.01 0.01 0.01 0.01 0.01
Total 0.00 0.00 0.1!) 0.1!) 0.00 0.00
X-ny Fluaescence (pun)

Cr 1 1.30 7.07 6.32 3.11 0.40 10.87
Ni 0.1!) 0.00 0.1!) 5.08 0.00 1.83
Cu 0.00 0.00 0.1!) 6.36 0.00 0.00
Zn 70.76 61.10 57.39 57.27 62.10 55.84
Rb 155.04 149.38 158.40 209.70 164.85 154.15
Sr 40.25 38.77 17.96 160.68 28.05 15.41
Y 38.91 36.06 39.43 42.71 40.19 38.82
Zr 184.65 183.28 145.40 169.39 165.52 142.86
Nb 20.09 21.69 27.00 21.81 26.21 12.63
La 72.61 61.80 18.71 51.94 64.16 39.43
Ba 169 191 120 155 0 130

75

Appendix 1. Continued.

Tephra-fall sequence (individual ptunice fragments)
Sample M401 M402 M4D-2 M4F M13A M20C

 

Weight Percent Oxide (wt. %)

 

 

 

SiOz 76.59 76.59 75.75 77.21 75.27 76.67
T10, 0.13 0.14 0.16 0.12 0.16 0.08
141,0J 13.17 13.01 13.64 12.79 14.32 12.86
FeO 0.97 1.00 1.27 0.85 1.36 0.82
M00 0.05 0.05 0.05 0.05 0.07 0.08
M30 0.09 0.07 0.20 0.05 0.68 0.04
C80 0.65 0.65 0.67 0.67 0.72 0.51
N820 2.46 2.61 2.68 2.49 2.73 3.65
K20 5.87 5.86 5.57 5.76 4.67 5.27
P20, 0.01 0.01 0.01 0.01 0.01 0.00
Total 0.00 0.00 0.00 0.00 0.00 0.00
X-ray fluorescence (ppm)
Cr 0.00 0.00 0.00 1.25 0.00 0.00
Ni 0.00 0.00 6.66 0.00 0.00 0.00
01 8.06 0.00 55.55 0.00 13.29 1.04
Zn 35.35 34.84 40.51 ‘ 32.68 46.68 49.90
Rb 154.13 155.33 160.57 143.33 158.“) 182.16
Sr 68.38 66.11 75.23 68.58 83.38 45.43
Y 20.91 18.12 20.44 23.72 23.06 31.49
Zr 113.58 116.12 I 130.59 109.00 147.21 114.18
Nb 17.52 14.24 16.54 18.16 10.85 21.25
L8 63.93 78.01 76.64 59.45 58.77 60.96

38 369 377 352 415 184 155

76

Appendix 1. Continued.

Tephra-fall sequence (individual pnnice fragments)
Sample M22-3-4 M22-3-5 M22-3-6 M22-4-1 M22-4-2 M224-3

Weight Percent Oxide (wt. %)

 

 

810, 75.90 76.27 75.84 75.39 75.88 76.13
T10, 0.10 0.10 0.09 0.10 0.09 0.09
111,03 13.40 13.13 13.42 13.80 13.40 13.49
FeO 1.15 1.08 1.08 1.14 1.07 1.05
MnO 0.08 0.08 0.08 0.08 0.08 0.08
M30 0.03 0.03 0.07 0.25 0.17 0.23
C80 0.52 0.49 0.49 0.51 0.51 0.47
Na,0 3.54 3.53 3.53 3.39 3.20 3.26
K20 5.26 5.28 5.37 5.31 5.57 5.19
P20, 0.01 0.01 0.01 0.01 0.01 0.01
Taal 0.1!) 0.00 0.00 0.00 0.00 0.00
X-ray Fluorescence (ppn)

Cr 3.70 6.10 0.“) 4.64 4.15 20.22
Ni 1.27 0.00 1.82 3.59 0.00 0.00
Cu 0.85 0.00 0.00 0.00 3.24 0.00 _
Zn 57.42 64.04 61.43 62.32 53.94 61.01
Rb 155.69 158.79 158.23 159.17 177.17 155.24
Sr 18.47 14.87 14.81 23.53 19.32 14.80
Y 41.35 42.98 42.20 39.95 37.93 39.06
Zr 158.55 143.1% 140.48 164.40 149.10 141.99
Nb 22.16 21.34 23.56 22.71 25.68 24.59
La 42.36 35.41 32.57 49.47 46.91 15.77
Ba 25 116 60 0 0

77

Appendix 1. Continued.

Tephra-fall sequence (Individual punice fragments)

 

 

 

 

amp: M345 Mn46 10381 M344 'M344 M344
Weight Percent Oxide (wt. ‘5) I
810, 75.02 7622 75.06 7457 77.12 77.68
10, (M0 am m» 0m 0m. 0m
41,0, 13.98 1337 13.67 13.83 12.89 12.48
no 122 L” 117 132 06; um
MM) am (me 0m 0m 0m 0%
MM) 0m 03 am. 005 001 mm
ex) 0” 00 061 067 0a 0a
146,0 3.49 3.18 3.97 4.05 3.10 2.73
14,0 5.37 5.19 529 5.28 5.47 5.63
an 001 0m 0m 0m 0m 0m
16» on) m» our 001 mm mm
X-ray Fluorescence
c: 1191 1336 1827 1395 1390 724
m on) 001 531 061 001 mm
01 2a) 1rm 061 an 2w 001
731 5751 97.02 6609 54.93 3151 3154
Rb 153.88 151.93 157.48 151.31 235.08 218.66
Sr 29.65 17.86 3229 42.17 24.94 37.11
Y 39.70 40.44 43.15 40.49 31.72 2677 .
a ram 163 wu4 1a“ «a mu
Nb 2354 25.75 22.94 1034 15.02 1637
1.. 5323 29.77 17.96 10273 2.49 35.99
8. xx 49 41 48 0 0

Appendix 1. Continued.

Tqitn-fall sequence (individual pumice framents)

78

 

 

 

 

Sample M25-1-3
Weight Percent Oxide (wt. ‘5)
810, 77.22
T10, 0.06
Al,0, 12.71
FeO 0.71
Mac 0.06
M30 0.1!)
CaO 0.63
N50 3.08
K,0 551
P,0, 0.01
Total 0.00
X-rey Fluorescence (ppu)

Cr 8.43
m 0m
Cu 2.33
Zn 27.93
Rb 230.41
Sr 37.43
Y 25.80
Zr 61.77
Nb 17.66
Ls 28.89
Ba 62

79

Appendix 2. Average error of standard whole rock INAA
analyses. Standard concentrations are from Govindaraju, 1989.

WholeRockStandardsusedforlNAA

 

SY-2

STM-l

 

Av.
error

(Pt-II)

Av.
error

(Wm)

 

3.20

1.10

 

3.10

2.40

 

.17

.10

 

.70

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BIBLIOGRAPHY

BIBLIOGRAPHY

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Blake, 8., and Ivey, N., 1986, Magma-mixing and the dynamics
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Broxton, D.E., Warren, R.G., Byers, F.M., Jr., and Scott,
R.B., 1989, Chemical and mineralogic trends within the
Timber Mountain—Oaisis Valley caldera complex, Nevada;
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Byers, F.M., Jr., Carr, qu}, and Orkild, P.P., 1989, Volcanic
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Allen and Unwin, 528 p.

Civetta, L., Galati, R., and Santacroce, R., 1991, Magma
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Cook, E.F., ed., 1966, Tufflavas and Ignimbrites: Elsevier,
212 p.

Donnelly-NOlan, J.M., 1988, A magmatic model of Medicine Lake
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Duffield, w.A., and Ruiz, J., 1992, Evidence for the reversal
of gradients in the uppermost parts of silicic magma
reservoirs: Geology, v. 20, p. 1115—1118.

Dunbar, N.w., and Hervig, R.L., 1992, Volatile and trace
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80

Farmer, G.L., Broxton, D.E., Warren, R.G., and Pickthorn, W.,
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ash-flow tuffs and related volcanic rocks at the Timber
Mountain/Oasis Valley Caldera, Complex, SW Nevada:
implications for the origin and evolution of large-volume
silicic magma bodies: Contributions to Mineralogy and
Petrology, v. 109, p. 53-68.

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