ORIGIN OF THE LATE-PALEOZOIC
PLUTONIC MASSIFS OF MOROCCO
M. S.

MICHIGAN STATE UNIVERSITY

ELLA RUTH TEWS WILLIAMS
1975

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ABSTRACT

ORIGIN OF THE LATE-PALEOZOIC
PLUTONIC MASSIFS OF MOROCCO
BY

ELLA RUTH TENS WILLIAMS

Throughout northwestern Africa are small (less than 200 sq. km.)
late-Paleozoic massifs. These are shallowly emplaced into unmetamor-
phosed Paleozoic sediments and always produce a well defined contact
metamorphic aureole. The Tichka Massif is the only well exposed massif
with over 2000 meters of vertical relief developed. In contrast, the
other massifs have barely been unroofed.

The Tichka massif contains basic rocks surrounding tear-drop
shaped granitic pods. At the contact of the massif with the overlying
sediments large masses of granite occur. Lithologic and geochemical
data (Vogel and Walker, l975; Preston §t_al,, in preparation) show that
the granite and basic magmas coexisted and have independent origins.
Preston gt_gl. (in preparation) suggest that the basic rocks are mantle
derived melts and that the granites are crustal derived melts.

Compositionally the granitic massifs fall near the univariant
liquidous line in the Ab, An, 0r system and this suggests that these
rocks originate by fractional fusion of crustal rocks. Those massifs
which are associated with relatively large negative gravity anomalies

(-40 mgals) are nearly identical in composition and are statistically

different from those that are not associated with negative gravity
anomalies.

There is no evidence to support a subduction zone model for the
origin for these late-Paleozoic massifs. It is proposed that the
massifs are a response of the continental crust to initial spreading
and rifting of North America from Africa. On the basis of the ages
of these massifs the age of the initial activity would be about 320

m.y.b.p.

ORIGIN OF THE LATE-PALEOZOIC
PLUTONIC MASSIFS OF MOROCCO

By

Ella Ruth Tews Williams

A THESIS

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

MASTER OF SCIENCE

Department of Geology

1975

ACKNOWLEDGMENTS

I would like to thank all those who contributed to the ideas
and discussions in this paper, and to thank Dr. H. Stonehouse, Dr. W.
Cambray, Dr. T. Vogel, and Dr. C. Cress for reading the manuscript.
Special thanks go to John Preston, Dane Williams, and Bruce Walker

for help in sample preparation and support.

ii

TABLE OF CONTENTS

Introduction ............... . . .......... l
Tichka . . . . . . ....................... 4
Other Moroccan Massifs . . . . . . . . . . . . . ........ 12
Discussion ........................ . . . . 18
Conclusions . . ......................... 23
References Cited ......................... 26
Appendix. . . . . . . ...................... 29

LIST OF TABLES

Table 1. Chemical Analyses (Weight Percent) of the

Granite Margins and Pods ................. l0
Table II. Modal Analysis (Percent) of Granite Pods

and Margins ....................... ll
Table III. Comparison of Variables of Granite Margins

and Pods ......................... 16
Table IV. Modal Analyses of Moroccan Massifs ............ 30
Table V. Chemical Analyses of Moroccan Massifs ........... 3l

iv

LIST OF FIGURES

Figure l. Hercynian Massifs of Morocco .............. 6

Figure 2. Modal Analysis (Quartz, K-feldspar, Plagioclase)
of Moroccan Granites .................. 9

Figure 3. Anorthite-Albite-Orthoclase CIPW Normative
Analysis for Moroccan Granites ............. 15

Figure 4. Quartz-Orthoclase-Plagioclase CIPW Normative
Analysis for Moroccan Granites ............. 2l

INTRODUCTION

The late-Paleozoic (Hercynian) granitic massifs that occur in
Morocco are typical of those that occur throughout Northwest Africa.
These massifs are usually less than 200 square kilometers, shallowly
emplaced into unmetamorphosed Paleozoic sediments, and have contact
metamorphic aureoles surrounding them (Termier, 1936; Morin, 1951;
Vandenven, 1969).

The Tichka Massif (Vogel and Walker, 1975) is the only well exposed
Hercynian massif in Morocco with 2000 meters of vertical relief (Figure
l). In contrast, the other Hercynian massifs in Morocco have only been
barely unroofed and the outcrops are relatively poor, with a maximum
relief of about 200 meters.

The lithologic relationships within Tichka have been studied by
Vogel and Walker (1975). The Tichka Massif contains dioritic rocks
surrounding granitic tear-shaped pods. The massif is capped with
granites with abundant aplites and pegmatites. Vogel and Walker (1975)
presented a model for the emplacement of Tichka Massif and their study
provided evidence that viscous granitic pods moved upward, surrounded
by an envelope of heterogeneous assemblage of dioritic rocks. Near the
roof of the massif larger masses of granite coalesced, whereas the
granitic pods ceased to rise when the dioritic magma crystallized,
freezing the shapes of the granitic pods. The field evidence of the
Tichka Massif indicates the coexistence of the granitic magmas with the

mafic magmas.

2

Work done by Preston §t_al, (in preparation) based on detailed
major element geochemistry in the Tichka Massif has rejected the pos—
sibility that the pods differentiated from the surrounding dioritic
material. He proposed that the Tichka Massif resulted from emplacement
of mantle derived gabbroic material into the base of the crust which
produced the granitic melts. The mantle material is represented by the
gabbros and mafic diorites found in close relationship with the granitic
pods. Granite coalesced at the margins of the massif resulting in an
envelope of granite occurring at the contact of the massif and meta-
sediments. The evolution of a hydrous fluid phase from the granitic
and dioritic magmas produced aplites, pegmatites, quartz veining,
muscovite, cavities, and alteration products. The margins were subjected
to stress during crystallization and post crystallization as indicated
by the granular textures of the rocks.

The margins of the other Hercynian massifs in Morocco (Zaer,
Oulmes, Aguelmous, and Midelt; Figure 1) appear to be lithologically
similar to the margins of Tichka and are also composed of granites
with abundant aplite and pegmatites (the two massifs north of Marrakech
were not studied).

The purpose of this study is to use Tichka as a model for the
origin of the other, less well exposed massifs in Morocco. The chemical
variation of these massifs can be evaluated by Presnall and Bateman's
(1973) work on equilibrium and fractional fusion. They showed that
repeated penetration of continental crust by mantle derived magmas would
unavoidably produce fusion of the lower crust. In their evaluation of
the chemical variation of the Sierra Nevada Batholith they concluded

that equilibrium fusion was a viable model for the generation of these

3

rocks. In Northwestern Africa there is little evidence of repeated
penetration of the continental crust by andesitic or basaltic magmas
and therefore, heat fOr equilibrium fusion was insufficient. However,
fractional fusion of the crust, producing true granitic liquids, nay
have occurred. Using Presnall and Bateman's (1973) arguments, fusion
models for these massifs can be evaluated.

The gravity data (Van den Bosch, 1971) can also serve as a guide
in comparing the massifs of Morocco. Most of the massifs of Morocco
have relatively large gravity negative anomalies (approximately 40 mgal)
associated with them (Figure 1). 0f the massifs studied, the Midelt
and Tichka massifs do not have negative gravity anomalies. There is
only one gravity station near the Tichka Massif and gravity determinations
in the High Atlas areas are difficult due to their great relief.
However, based on the rock types exposed within Tichka, no negative
gravity anonaly would be expected. The Tichka Massif contains large
amounts of relatively basic and intermediate rocks with abundant granite
present only near the roof of the massif. Therefbre, in terms of
gravity, one would expect that the gravity over the Tichka Massif should
be similar to Midelt. The gravity data suggests that those massifs
with the large negative gravity anomalies have no basic rocks associated
with them. In terms of the Tichka model these can be interpreted as a
complete separation of the granitic magma from the basic magma and that
the basic rocks are present, but are at a lower level in the crust.
The Midelt Massif should be similar to the Tichka Massif but erosion

has not cut through the granitic cap.

TICHKA

The Tichka Massif, located in the southwestern High Atlas
Mountains (Figure l), exposes a series of leucocratic granitic—
biotitic, quartz monzonite tear-shaped pods surrounded by rocks
ranging in composition from gabbros to granodiorites (Vogel and Walker,
1975). The more mafic dioritic rocks are thought to be the product
of differentiation from a mafic mantle magma (Preston gt 31., in
preparation). The mafic diorite is uniquely characterized by numerous
veins of quartz-albite stringers which suggest the mafic diorite was
saturated with water. Foliation of the diorite is consistently parallel
to the granitic pods which indicates that most of the deformation
occurred by flowage within the diorite. The pod shape of the granites
indicates their diapiric movement upward. Contact relationships
indicate the overlapping crystallization histories and coexistence
of the granitic and dioritic magma. Aplites and pegmatites are
abundant in the marginal pods, but decrease in frequency approaching
the center of the massif. The margins of the Tichka Massif are charac-
terized by large masses of granites with abundant aplitic and
pegmatitic dikes. Where stoping of the overlying sediments has occurred
there is an increase of biotite and aplites in the granites. The
Tichka Massif is surrounded by metasandstones and carbonates.

Texturally there is only minor difference between the Tichka
margins and the Tichka pods. The Tichka pods have undergone less
stress and therefore the degree of sericitization, granulation, and

4

Figure l

Generalized geologic map of the southern
two-thirds of Morocco showing the location of the
Hercynian massifs. The massifs studied in detail
are numbered: 1. Zaer, 2. Oulmes, 3. Aquelmous,
5. Midelt, and 8. Tichka (and inset). Those
massifs which are associated with negative gravity
anomalies are massifs numbered 1, 2, 3, 4, 6,

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suturing appear to be much less. Within the margins of the massif the
xenomorphic-granular aplitic material is typified by an abundance of
granophyric growths and alteration of plagioclase and biotite to seri-
cite and chlorite. The marginal quartz monzonites and porphyritic
granites commonly display a distinct orientation of the mafic minerals
and occasionally of the quartz. Intersertal quartz often is feund
surrounding grains or clusters of grains. Boundaries are highly sutured
and there is an abundance of poikiolitic and granophyric textures common
to all rock types of the margins of the massif. Stress features f0und
in the marginal granites are thought to be the product of pressure
exerted by the rising of the underlying magma. Hydrous fluids which
passed through the margins caused alteration products to form.

The marginal rocks and pods of the massif are clearly composed of
granites and a few quartz monzonites, leuco-quartz-diorites, and
granodiorites (Figure 2).

Chemical comparison of the Tichka pods with the Tichka margins
indicates a significant decrease of CaO, Ti02, Fe203, and an increase
in SiO2 in the margins (Table 1). Differences are also shown by
variable amounts of albite, anorthite, and K-feldspar (Table II).

The differences found between the pods and margins may be due
to alteration by hydrothermal solutions or assimilation of country
rock. The pods and margins have no significant differences in Rb and
K/Rb values which support the hypothesis that they are from a common

parental material.

Figure 2 Modal analyses of Moroccan massifs.
In all figures only the granitic margins and

pods are included for the Tichka Massif.

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TABLE I
Chemical Analyses (Weight Percent) of the Granite Margins and Pods
(1) (2) (3) (4) (5) (6)

Zaer Oulmes Aguelmous Midelt Tichka Tichka
Margins Pods**

$102 72.5 72.2 73.0 71.5 78.2 69.3
s.e. 1.4 1.0 1.0 2.0 0.8

Al 03 13.4 12.8 12.2 12.1 12.5 13.2
s.$. 0.4 0.5 0.3 0.9 0.3

Fe203* 0.8 0.7 1.1 2.0 1 2.3
s.e. 0.3 0.2 0.3 0.4 0 2

M90 0.1 0.1 0.2 0.4 0.4 0.6X
s.e. 0.1 0.1 0.1 0.2 0.2

CaO 0.7 0.5 0.5 1.4 0.7 1.8
s.e. 0.2 0.1 0.1 0.3 0.3

1102 0.1 0.1 0.1 0.2 0.1 0.4
s.e. 0.1 0.1 0.1 0.1 0.1

Na20 3.4 3.4 2.9 3.8 4.3 3.4x
s.e. 0.3 0.3 0.2 0.4 0.5

K20 5.0 4.5 5.0 4.4 3.7 3.7
s.e. 0.4 0.3 0.1 0.3 1.4

Rb ppm 387 458 332 330 75 119
s.e. 43 37 47 83 12

K/Rb 129 86 147 144 309 303
s.e. 11 11 25 23 43

*FeO calculated as Fe203
**Data by Preston et_al,, 1975

(1) Average of 9 samples
(2) Average of 8 s amples
(3) Average of 8 samples
(4) Average of 8 samples
(5) Average of 7 samples
(6) Average of 13 samples

x Average of 5 samples

s.e. = standard error

11

TABLE II

Modal Analyses (percent) of Granite Pods and Margins

(1) (2) (3) (4) (5) (6)
Zaer Oulmes Aguelmous Midelt Tichka Tichka*
Margins Pods

Quartz 36.0 37.7 31.8 34.0 37.7 29.0
s.e. 3.5 1.4 2.1 3.8 0.9 2.8
K-spar 20.6 23.7 35.8 40.3 36.2 25.5
s.e. 3.1 3.2 1.8 3.4 3.1 4.4
Albite 26.7 24.1 17.0 16.4 16.9 26.6
s.e. 4.0 2.5 2.0 3.0 2.5 2.7
Anorthite 6.5 4.0 6.7 2.8 5.7 11.5
s.e. 1.5 0.4 1.1 0.8 0.9 1.
Biotite 5.1 .9 7.7 5.8 2.8 ---
s.e. 1.5 1.0 2.7 3.6 0.6
Chlorite 0.5 0.2 0.0 0.5 0.8 ---
s.e. 0.2 0.1 0.0 0.4 0.3
Muscovite 4.7 7.4 1.1 0.3 0.0 0.0
s.e. 2.1 1.8 0.6 0.1 0.0 0.0

1., in preparation.

*Data from Preston, gt

1) Average of 8 sanples
2) Average of 5 samples
3) Average of 5 samples
4) Average of 4 samples
5) Average of 7 samples
6) Average of 13 samples

s.e. = standard error

OTHER MOROCCAN MASSIFS

The Zaer, Oulmes, and Ageulmous massifs are located in the Central
Meseta of Morocco. The Midelt massif is located in the High Plateau
between the High Atlas and Middle Atlas range (Figure 1). Only the
tops of these intrusions are eroded exposing granitics, aplites, and
pegmatites. The intruded sediments range in age from Cambrian to
Carboniferous. In all cases, when the sediments surrounding the massifs
can be observed, there is a narrow well developed contact metamorphic
aureole (Termier, 1936; Vandenven, 1969). Potassic rich aplite veins
and quartz rich pegmatites commonly cut the granites and are often
associated with muscovite zones. Granite in contact with metasediments
show slight textural changes but no distinct chill zone. The granites
are highly sheared in some areas.

There is no significant variation in textural parameters between
the margins of the massifs. All show similar textures to the margins
of the Tichka Massif.

Because of the nature of the outcrops, samples were collected
most thoroughly in the Tichka Massif. The purpose of this sample
plan was to determine the relationship of the granitic pods and the
surrounding mafic material (Preston, in preparation). The marginal
rocks of the other massifs were sampled to obtain a suite of the
greatest variation of each massif. This variation was then studied to
compare the massifs both compositionally and texturally.

Modal analysis was accomplished by point counting thin sections
stained for potassium with Na-cobaltinitrate (Bailey and Stevens, 1959).
Plagioclase composition was determined by Tsuboi method (Morse, 1968).

12

13

Chemical analyses were done by standard X-ray fluorescence methods
of diluted powder pressed pellets using USGS standard rocks. Na and Mg
were determined from these pellets by microprobe analyses. Rb was
determined by the Reynolds method (Reynolds, 1967; Wilband, 1975).

One purpose of this study is to compare the chemistry of the
massifs. A test of equality of the means (Tuckey's Test, Snedecor
and Cochran, 1973) was performed to determine if significant differences
of any compositional variable exist between the massifs. As shown
by Table III there are significant differences between the massifs in
the compositional variables weight per cent K20, CaO, Ti02, Fe203,
Rb, K/Rb, MgO, Si02, and volume per cent muscovite, anorthite, albite
and k-feldspar. In Table III, there is no significant difference in
variables between massifs that have the same letter. The most con-
spicuous differences between massifs is the decrease of Rb (Table I
and Table III) in the Tichka Massif in comparison with Midelt, Zaer,
Oulmes, and Aguelmous.

The more mafic nature of the Midelt and Tichka massifs is shown
by the significant increase in M90, CaO, Fe203 percent. The Tichka
Massif also is significantly decreased in percent K20 (Table I and
Table III). The presence of micas is found in all massifs; however,
only Zaer and Oulmes are significantly enriched in muscovite.

By combining information collected from chemical analyses and
gravity work (Van den Bosch, 1971), a comparison of the massifs can
be made. The rocks exposed in the Tichka massif indicate that no
negative gravity anomaly should exist. The Midelt Massif also shows
no gravity negative anomaly and in comparison with Tichka shows no

significant difference in chemical analyses of Fe203, CaO, and MgO

14

Figure 3 Normative proportions of Ab + An, Or, and 02
of the Moroccan massifs. Normalized to 100

per cent.

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TABLE III

Comparison of Variables of Granite Margins and Pods

Tichka Tichka
Variable Zaer Oulmes Aguelmous Midelt Margins Pods
MgO a a a a,b a,b b
NaZO a a a a a a
K20 a a,c a,c a,b,c b,c b
CaO b,c c c a,b b,c a
SiO2 a,b a,b a a,b c b
TiO2 a a a a a b
A1203 a a a a a a
Fe203 a,c a a,c b,c a,c b
Rb b,c b c b,c a a
K/Rb c,d c b,d b,d a,b a
Albite a,b a,b a a a b
Anorthite a,b,c b a,c b b,c a
Quartz a a a a a a
K-spar b b a a a b
Muscovite a a b b b b

Massifs with the same letter show no significant difference at o<= .05

using Tukey's Test.

17
(Table III). Therefore it is suggested that below the granitic cap
of the Midelt Massif is a mafic complex similar to that found exposed
in the Tichka Massif. The gravity negatives and more alkali nature
of the Aguelmous, Zaer, and Oulmes massifs suggest a large volume of
granitic material formed by the complete separation of the granitic
pods from the dioritic material with the dioritic rocks existing at

deeper levels of the crust.

DISCUSSION

Models for the emplacement of "granitic" batholiths are fundamental
to the theory of plate tectonics. The structural and igneous activity
associated with subduction zones have been extensively studied and well
documented and batholithic areas such as those characteristic of the
western United States are considered to be typical of subduction zones
marginal to continental masses (for example: Bateman and Eaton, 1967;
Hamilton, 1969a, 1969b; Dickinson, 1970; Wyllie, 1971). Experimental
petrology, geochemistry and modeling studies support an origin of these
batholiths that involves melting of lower crustal rocks by mantle
derived liquids after extensive crustal preheating caused by a long
episode of andesitic and basaltic volcanism. The intermediate rocks
characteristic of subduction zone batholiths appear to be the result
of mixing of mantle derived magmas and crustal derived magmas as well
as by equilibrium crystallization (Presnall and Bateman, 1973;
Younker, 1974).

In contrast to subduction zone igneous activity, very little is
known about granitic rocks that may be generated by other processes
in the plate tectonic theory. Plate rifting is a second major process
that generates igneous activity in the plate tectonic model. Most
documented rift zones contain abundant tholeiitic and/or alkaline
volcanics although some granitic rocks have been documented in rift
zones (Barberi §t_gl,, 1972). The nature of the igneous activity
associated with rifting is a function of the nature of the crust and
upper mantle, and their evolution preceding rifting. It has been
proposed that the late-Paleozoic thermal events in northwestern Africa

18

19
a response to the earliest stages of f0rmation of a zone of spreading
(Kanes gt 31,, 1973). If this is so, then these Hercynian granites
(260-320 m.y.) (Choubert §t_al,, 1965; Termier gt_al,, 1971) are a
direct manifestation of the interaction of spreading mantle dynamics
with continental crust. These thermal events may be unique in the
geologic record since they were preceded immediately by orogenic events
that represented the closing phase of continental drift.

Field characteristics of subduction zones include the presence
of blue schist metamorphism, lithostratigraphic melanges and the
evidence of shear underthrusting across subductive boundaries. Com-
pressional deformation is the dominant structural feature. Dickinson
and Hatherton (1968) proposed an increase in K20 away from the sub-
ductive boundary which would be related to the depth of origin of the
magma.

None of these characteristic features of subduction zones are
found in northwest Africa. Chemical analyses of the massifs show no
significant correlation of K20 and distance from the Atlantic coast
(r = .255, at 5% level) and the plots of K20 versus distance appear
to have a random distribution. Tensional features are the dominant
type of deformation in Morocco (Kanes gt_a1., 1973) and regional
metamorphism is absent (Termier, 1936).

Presnall and Bateman have shown that the Ab-An-Or-Qz system is
a close approximation of the lower crust and that the Ab-An-Qz system
can be used to interpret fusion models. In subduction zones, where
abundant heat flux is present, equilibrium fusion can drive the com-
position of the melt off the univariant liquidous line (line a-b,

Figure 4) towards the composition of the assumed lower crust (1c).

20

Figure 4 Normative propositions of Ab, An, and Or for
the Moroccan massifs. Normalized to 100 per cent
1C is composition of lower crust after Presnall

and Bateman (1973).

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However, in the case where heat flux is low, fractional fusion nay occur
and the composition of the melt would be restricted to the univariant
liquidous line a-b.

Figure 3 and Figure 4 show the normative amounts of the system
Ab+An, Or, 02 and of Ab, An, Or. The main feature illustrated by Figure
4 is distribution of compositions of the massifs near the univariant
liquidous line. Differences between massifs may be the product of the
heterogeneous composition of the lower crust. The more calcic nature
of the Midelt and Tichka massifs may be due to some mixing of more
basic magmas with the granitic magmas, or alternatively, they nay be
the result of more extensive mantle activity, causing an increase in
the availability of the heat source which would enable some partial
fusion off the a-b line. As partial fusion moves the liquid off the
a-b line the liquid would approach the composition of the lower crustal
material. However, the sporadic nature of the heat source which
initiated the melting would not result in the high temperature
necessary to complete equilibrium fusion.

The variation and minor scattering of points below the univariant
liquidous line probably results from a combination of factors, which
include contamination of the granitic melts by country rock, alter-

ation by hydrous fluids or by alkali metasomatism (Green, 1962).

CONCLUSIONS

It is clear from the above discussion that preheating of the crust
in Morocco during the Hercynian time was nowhere near that character-
istic of subduction zones. That is, the massifs are emplaced into
unmetamorphosed, relatively shallow water sediments and Paleozoic
volcanic rocks are only minor in the stratigraphic record (Termier,
1936). Thus there is no evidence that could support extensive preheating
of the crust which is a necessary prerequisite for equilibrium fusion
(Presnall and Bateman, 1973; Younker, 1974).

The igneous activity and faulting found in Morocco are proposed
to be the product of pre-rifting of the North African and North American
continents, beginning approximately 230 m.y. ago. Corroborating
evidence for continental rifting is the tensional features found in the
Late Paleozoic of Morocco (Padgett and Ehrlich, 1974; Kanes §t_a1.,
1973). Seismic investigations indicate these tensional patterns
continue offshore (Kanes gt_al,, 1973). Some tension in Morocco nay
be related to the African involvement of the closing phase of continental
drift (Kanes gt a1., 1973). Similar tensional features have been
documented in other hypothesized continental rift zones (Rod, 1962;
Florenson, 1968; Artemdov, 1971). LePichon et a1, (1973) attribute
the cause of tensional features in continental rift zones to heating
from below and thinning the lithosphere and perhaps by intrusions.

It is accepted that North America and North Africa are rifted
continental margins, although the exact position of the attachment
has not been defined. Recent work on continental reassemblies has
been done by several workers (Bullard et_al,, 1965; Dietz gt_al,, 1970;
LePichon and Fox, 1971; Vogt, 1973). Ages taken from drilling in the

23

24
Atlantic oceanic crust have dated the initial opening at 180 m.y.
(Taylor gt 91., 1968; Ewing §t_al,, 1970; Peterson gt_al,, 1970).
On the basis of the ages of the Moroccan Hercynian massifs, the
earliest stages of spreading would have occurred more than 100 m.y.
prior to the opening of the Atlantic Ocean. We propose here that
the massifs of Morocco are a response of continental crust to the
initial spreading and therefore, the age of the initial activity would
be at least 320 any.

The purpose of this paper has been to develop a model f0r the
melting and emplacement of lower crustal material that explains the
gross petrologic nature of the late-Paleozoic massifs of Morocco.
The origin of the granitic rocks is proposed to be the result of
fractional fusion of the lower crust with the heat source due to the
sporadic upwelling of gabbroic material related to the rifting event.

The events leading to the emplacement and crystallization of the
massifs can be summarized as fOllows:

l. Pre-rifting stages start 320 m.y. ago causing extension

and thinning of the lithosphere. The pre-rifting is
associated with upwelling of mantle material.

2. The uprising mantle material causes fractional fusion of

the lower crust.

3. The superheating curstal material diapirically rises and

in the case of Tichka and Midelt it is accompanied by
differentiating mantle material. Granite coalesces at
the margins of the complex. A
4. In the other massifs (Zaer, Oulmes, and Aguelmous) the

mantle derived mafic magmas crystallized during the

25
fractional fusion of the crust. The granite melts are
emplaced as a unit into high levels of the crust.

Extensive study of subduction zones and rift zones has promoted
the current widespread acceptance of these tectonic features. The
nature of batholiths in these subduction zones has been well documented;
however, very little is known about the relationships of plutonism
and continental rfiting which is much more difficult to study and to
infer.

The record of rifting is well preserved in Northwest Africa and
along the Atlantic coast of North America (Dietz, 1966; Dewey and
Bird, 1970; Wilson, 1966). Deformation and faulting found in Morocco
is tensional in character which suggests the connection of the opening
of the Atlantic (Kanes §t_al,, 1973). The Hercynian granites in
Morocco represent the effect of initial spreading interacting with
continental crust.

Recently there has been much support for primary granitic melts
which are generated by fractionation of immiscible granitic liquids
from more basic melts (Roedder and Weiblen, 1970; De, 1974; McBirney
and Nahumura, 1974). Isotope tracer studies of these Moroccan granites
(currently in progress) may enable us to resolve the question of
primary immiscible granitic melts or granitic melts derived by crustal

fusion.

REFERENCES CITED

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of the Baikal Rift and mechanism of rifting: Jour. Geophys.
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Bailey, E. H. and Stevens, R. E., 1960, Selective staining of K-feldspar
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Bateman, P. C., and Eason, J. P., 1967, Sierra Nevada batholith:
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Dietz, R. S., 1966, Passive continents, spreading sea floors, and
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, Holden, J.C., and Sprol, W. P., 1970, Geotectonic evolution and
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26

27

Green, J. C., 1962, Alkali metasomatism in a thermal gradient, two
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, Francheteau, J., and Bonnin, J., 1973, Plate Tectonics: Elsevier,
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magmas of the Skaergaard intrusion: Carnegie Inst. Wash. Year Bookm
v. 73, p. 348-352.

Morin, P., 1951, Quelques problemes relatifs aux roches granitiques et
microgranitiques et a leur mineralisation dans la Maroc Central:
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Morse, S. A., 1968, Resived dispersion method for low plagioclase: Am.
Mineralogist, v. 53, no. 1, p. 105-115.

Padgett, G. V., and Ehrlich, R., 1974, Late Paleozoic source terranes
in Western Morocco: a linear array of tectonic islands (abstr.):
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Peterson, M. N. A., Edgar, N. T., Cita, H., Gardner, 5., Jr., 0011, R.,
Nigrini, C., and von der Broch, C., 1970, Initial Reports of Deep
Sea Drilling Project, v. 2, p. 413—472, U. S. Govt. Printing
Office, Washington, D.C.

Presnall, D. C., and Bateman, P. C., 1973, Fusion relations in the
system NaAlSi303-CaA15i208-KA1$i308-Si02-H20 and generation of
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Preston, J., 1975, Origin of the Tichka Massif, Morocco: Masters Thesis,
Michigan State Univ., 37 p.

28

Roedder, E., and Weiblen, P. W., 1970, Silicate liquid immiscibility
in lunar magmas evidenced by melt inclusions in lunar rocks: Sci.,
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, and Weiblen, P. 0., 1971, Petrology of silicate melt inclusions,
Apollo 11 and 12 and terrestrial equivalents: Proc. 2nd Lunar
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Cambridge, 507 p.

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Snedecor, G. W. and Cochran, W. G., 1973, Statistical Methods, Iowa
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Termier, H., 1936,Etudes geologiques sur 1e Maroc central et le Moyen At-
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et Memoires du Service Geologique, N. 234, Editions de Service
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Vandenven, G., 1969, Les terrains metamorphiques de la bordue Nord-Ouest
du Massif granitique des Zaer (region de Sibara, Maroc central):
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Vogel, T. A. and Walker, B. M., 1975, The Tichka Massif, Morocco -- an
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in press.

Vogt, P. R., 1973, Early events in the openings of the North Atlantic in
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S.K. and Tarling, D.H. (Editors): Academic Press, London, v. 2,
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Wilband, J., in press, Rapid method f0r background corrections in trace
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Younker, L. W., 1974, Role of mantle derived magmas in the production of
crystal melts: Ph.D. thesis, 72 p.

APPENDIX

29

 

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