A Study of Mylonitic Rocks From Major Fault Zones

James R. Anderson 

Dept. of Geological Sciences

SUNY-Binghamton 

Binghamton, New York 13901

USGS CONTRACT NO. 14-08-0001-17757 

Supported by the EARTHQUAKE HAZARDS REDUCTION PROGRAM

OPEN FILE NO. 80-1154

U.S. Geological Survey 

OPEN FILE REPORT

This report was prepared under contract to the U.S. Geological Survey 

and has not been reviewed for conformity with USGS editorial standards 

and stratigraphic nomenclature. Opinions and conclusions expressed 

herein do not necessarily represent those of the USGS. Any use of trade 

names is for descriptive purposes only and does not imply endorsement by 

the USGS.
ANNUAL TECHNICAL REPORT 

CONTRACT NO.: 14-08-001-17757 

NAME OF CONTRACTOR: The Research Foundation of State University of New York

PRINCIPAL INVESTIGATOR: James R. Anderson

Dept. of Geological Sciences

SUNY-Binghamton

Binghamton, New York 13901

GOVERNMENT TECHNICAL OFFICER: Dr. Jack Pfluke

SHORT TITLE OF WORK: A study of mylonitic rocks from major fault zones

EFFECTIVE DATE OF CONTRACT: 2/14/79

CONTRACT EXPIRATION DATE: 2/14/81

AMOUNT OF CONTRACT: $70,000

DATE: 5/12/80

Sponsored by the

U. S. GEOLOGICAL SURVEY

No. 14-08-001-17757

The views and conclusions contained in this document are those of the 

authors and should not be interpreted as necessarily representing the 

official policies, either expressed or implied, of the U. S. Government.
A. INTRODUCTION

The objectives of this study are to learn about the role of mylonitic rocks 

(and other cataclastic rocks) in the mechanics of faulting and to learn 

about the physical and chemical conditions of their formation. Knowledge of 

the conditions of formation of the fault rocks leads directly to knowledge 

of the former conditions within exposed fault zones. The type of evidence 

being sought is petrographic and petrochemical in nature; principal types 

of information being sought are textural and microchemical evidence of 

chemical reations that may accompany fault displacement, microchemical and 

mineralogical evidence of the history of physical conditions in the fault 

zones, and bulk chemical, microchemical and mineralogical evidence of the 

movement of volatiles and dissolved chemical species in the fault zones. 

The first year of this study has involved:

1) sampling and field observation of fault zones in six 

areas of southern California;

2) preparation of petrographic thin sections of the 

collected samples;

3) electron microprobe analysis of mineral grains 

within selected samples;

4) whole rock chemical analysis of selected samples ' 

using rapid silicate analysis methods;

5) purchase and installation of automation instrumentation

for our electron microprobe.

The sampled zones represent a broad range of depths of exposure, from near 

surface fault zones with gouge to broad, deep shear zones with high-grade 

cataclastic rocks. The results indicate that, for the studied zones at 

least, cataclasis at shallow to moderate depth (perhaps in a range of 0-15km) 

is accompanied by extensive hydration and/or carbonation of the fault rocks. 

Two deeper zones examined showed less extensive hydration and little 

carbonation, but such effects are significant at least locally within some 

parts of these deeper zones. For zones with extensive hydration and/or 

carbonation, the hydration/carbonation occurred over a broad range of physical 

conditions from amphibolite facies through greenschist facies to nearsurface conditions. Textural evidence points to much of the hydration and 

carbonation occurring during active shearing. Microchemical data indicate
that the geothermal gradients of the low- to medium-grade zones were 

intermediate. No evidence of significant transitory heating has been 

found.

B. AREAS SAMPLED

Initial field work was conducted in April, 1979 and further field work 

was accomplished during January, 1980. The six areas sampled are briefly 

described below. The first five areas were discussed in more detail in a 

previous technical report.

a) One area studied was along Upper Lytle Creek Ridge in the 

Telegraph Peak quadrangle. 80 samples were collected along a two mile 

traverse from the San Andreas Rift zone in Lone Pine Canyon, SW across 

several small shear zones and a 2000 ft. wide cataclastic zone of the 

Punchbowl fault zone and continuing to the bottom of the canyon occupied 

by the North Fork of Lytle Creek. A variety of rock types, cataclastic 

textural types, and grades of cataclasis were found here.

b) A mylonite zone in the Crafton Hills NW of Yucaipa in the 

Yucaipa quadrangle was investigated. Samples were collected along a 3500 ft. 

section across strike of the zone. Well-exposed within the mylonite zone 

is a discrete thrust fault with a thin zone of re-cataclasized mylonite. "' 

Overall the mylonite zone is characterized by abundant blastomylonites of 

various bulk compositional types, plus some uncataclasized, shallow-level 

intrusive igneous rocks.

c) Another area sampled is in the Mescal Creek quadrangle along 

the Angeles Creek Highway on Blue Ridge between the Punchbowl and Fenner 

faults. Several small shear zones are well-exposed in roadcuts.

d) Samples were collected from two thin thrust zones in the 

eastern Sierra Pelona in the Ritter Ridge quadrangle. The fault rocks 

associated with these thrusts are gouges and non-coherent breccias.

e) The classic area in Cucamonga Canyon (Alf, 1948; Hsu, 1955) was 

sampled in order to provide a look at a relatively deep-seated cataclastic 

zone and for comparison with other zones.

f) A week of field work was conducted in portions of the eastern 

Peninsula Ranges mylonite zone (described by Sharp, 1967, 1979) in the
Borrego and Palm Desert 15' quadrangles. Samples of cataclastic and, 

where present, noncataclastic rocks were collected from a number of 

locations, most of which are in the Borrego Valley-dark Valley area. 

The eastern Peninsulan ranges zone is of interest because within it are 

cataclasized plutonic rocks of the southern California batholith. Since 

the parent rocks are relatively well-behaved with respect to chemistry, 

this zone provides a good opportunity to test the degree of chemical 

exchange with a pore fluid or with surrounding rock, with pore fluid as 

the diffusion media, during cataclasis. Also, the zone represents 

cataclasis at considerable depth, although the preliminary petrographic 

work indicates that a range of depths are represented in the zone; the 

high-grade conditions postulated by Theodore (1970) do not apply to all 

of the mylonites exposed in the zone.

C. PETROGRAPHIC AND MICROCHEMICAL OBSERVATIONS

Samples collected from the various areas have been petrographically examined 

for evidence of any chemical reactions that accompanied the faulting process. 

Within the shallower zones, such as the Punchbowl zone and Crafton Hills 

zone, there is evidence of a number of retrograde reactions; the results 

of several hydration reactions are pervasively present. Within the more 

deeply exposed zones, the Black Belt zone in the San Gabriel Mtns. and the 

eastern Peninsular Ranges zone, the extent of similar hydration reactions 

is more limited; little or no retrograde reaction effects have accompanied 

cataclasis in the Cucamanga Canyon rocks studied, but retrograde hydration 

reactions are locally important in parts of the eastern Peninsular Ranges 

zone. No evidence of prograde reactions which might have accompanied fault 

zone activity has been found.

Some types of possible reactions, either prograde or retrograde, 

are evidenced by changes of the composition of participating minerals over 

time. For instance, in an appropriate mineral assemblage, the composition 

of Ca-amphibole can vary with changing P-T conditions. The compositions of 

these amphiboles in the actinolite-hornblende series are in fact good 

indicators of relative grade and the ratio of P/T. The mineral compositions 

and compositional zoning relationship in individual mineral grains have
been determined with the electron microprobe. Although a number of 

reactions have been investigated this way, the most useful information has 

come from looking at the results of the family of retrograde reactions 

that produces compositional variation in Ca-amphibole.

1. Amphibole data.

The reactions which can occur in a fault rock are obviously a 

function of the starting mineral assemblage, which is itself a function 

of bulk composition and the physical conditions of mineral growth. Many 

of the Pelona schist rocks from the Punchbowl fault zone and also some of 

the mylonites from the Crafton Hills zone contain Ca-amphiboles in the 

actinolite-hornblende series (Ca-amphiboles are present in samples from 

other areas studied as well, but we haven't analyzed any as yet). A typical 

observed reaction is the retrogradation of hornblende to form more actinoli tic 

amphibole plus chlorite, epidote, and minor amounts of other minerals. 

In rocks with an assemblage including albite or oligoclase, epidote, 

quartz, chlorite, and amphibole, the amphibole composition is sensitive to 

changes in both P and T.

Figure la is a plot of electron microprobe data from amphibole 

grains in RA-ll-L showing Al(IV) vs. Al(VI). These parameters are calculated 

by converting the weight percent data to cation percents and then normalizing 

the cation values to an ideal chemical formula for Ca-amphibole. This ideal 

formula is:

(Na,K) 0-1 (Ca,Na) 2 (Mg,Mn,Fe2+ ,Fe3+ ,Al VI ,Ti) 5 (Si,Al IV ) 8022 (OH,F) 4

The normalization used forces the sum of all cations, excluding Na, K, and Ca, 

to be 13. This makes some assumptions about site occupancy, but the use of 

another normalization method would only modify the plots slightly and would 

not alter the conclusions. The treatment of Ca-amphibole data is discussed 

at length by Laird (1977).

Figure Ib is a plot of Al(IV) vs. the sum of Al(VI) + Ti + Fe(3+), 

where Fe(3+) is calcualted by the assumption of a total plus-charge of 46 

for the ideal formula. Both figures show essentially the same things. 

Within RA-ll-L amphibole grains is a great compositional range and the entire
range can be found within single, compositionally zoned grains. The more 

aluminum-rich points (analyses are from spots with diameters of 10 microns) 

are from darker cores within the grains; these represent hornblende formed 

under conditions of amphibolite or epidote-amphibolite facies metamorphism. 

Moving away from the dark cores out to the light-colored rims, the grains 

zone to more actinolitic compositions (pure actinolite has no Al(IV). The 

actinolitic compositions formed under greenschist facies conditions.

The interpretation of this zoning pattern is not without some 

ambiguity. However, the published and unpublished work of this author 

(Anderson, 1977a, 1977b, and in press) and Laird (1977) have shown that 

under medium- to low-grade metamorphic conditions that certain minerals are 

not very susceptible to solid-state diffusion and re-equilibration, but 

instead tend to preserve the history of changing composition with time by 

means of preserved compositional zoning. Ca-amphibole is one of these 

minerals that tends to preserve compositional zoning due to growth. The 

overprint of a distinct low-grade event upon older hornblende seems to 

result in rather sharp optical and compositional boundaries between newly 

formed actinolite and remnant hornblende. As metamorphic grade increases up 

into middle to high amphibolite facies, the effect of solid-state diffusion 

begins to be more significant, although of course any diffusion process is 

also dependent upon the time-scale involved.

If the amphibole zoning in RA-ll-L is the product of mineral growth 

over time rather than some diffusion process, then the amphibole grains 

record a history of changing conditions within the fault zone. The grains 

grew as the rock was being brought upward in the fault zone or as the whole 

Punchbowl fault zone was brought up with the Upper Lytle Creek Ridge block 

between the San Andreas and San Jacinto faults. Obviously, this block must 

have undergone uplift and erosion in order to expose the low- to medium-grade 

cataclastic zone. The preferred alignment of actinolite grains with the 

fluxion structure in the mylonitic schist indicates that the Punchbowl fault 

zone was active as this uplift occurred. Actually, there is evidence of 

even relatively recent, but minor, activity in the fault zone in the form of 

an apparent bedrock-gravel fault contact.

The data shown in Figures la and Ib can be put to further use, as 

the composition of amphibole depends not only upon relative grade, but also
upon the relative P/T ratio. The interpretation of the P/T ratio does not 

strongly depend on whether the interpretation of the zoning mechanism is 

completely correct. Comparing the RA-ll-D data to the results of Leake 

(1965), Raase (1974), Graham (1974), and Laird (1977), these amphiboles 

were formed under intermediate P/T conditions, similar to the regional 

metamorphic conditions of the Dalradian rocks in southwestern Scotland and 

of intermediate pressure areas in the regionally metamorphosed Paleozoic 

rocks of western New England. The overall mineral assemblage in RA-ll-L is 

appropriate for making the comparisons.

Another sample of Pelona schist, RA-23-A, from a shear zone on 

Blue Ridge to the NW of location RA-11 has Ca-amphibole with characteristics 

similar to those of the Ca-amphibole in RA-ll-L. Figures 2a and 2b show 

the plots for RA-23-A amphibole. The compositional range for RA-23-A 

amphibole is not as great as for that of RA-ll-L amphibole, but the overall 

trends are similar. The amphibole in RA-23-A also formed under intermediate 

P/T conditions.

Figures 3a and 3b are plots for amphibole in sample RA-7-E, a 

mylonite from the Crafton Hills zone. The analyzed points clustered at 

higher values of Al(IV) are hornblende cores which were probably pre-cataclastic 

in origin. The more actinolitic points, with lower Al(IV), are overgrowths 

on the horneblende cores and appear to have been formed during cataclasis. 

While the pre-cataclastic hornblende cores may have formed at a somewhat 

lower P/T ratio than any of the Upper Lytle Creek Ridge - Blue Ridge amphiboles, 

the actinolitic overgrowth is compositionally very similar to cataclastically 

formed, overgrown amphibole in the two preceding samples, RA-23-A and RA-ll-L, 

and the two samples to follow, RA-16-B and RA-ll-E.

Plots for Ca-amphibole in sample RA-16-B are shown in Figures 4a 

and 4b. RA-16-B is a sample of Pelona schist from a small shear zone 

adjacent and parallel to the main cataclastic zone of the Punchbowl fault 

zone on Upper Lytle Creek Ridge. As in the other cases above, the more 

hornblendic compositions with higher Al(IV) are from cores which are overgrown 

by more actinolitic rims produced during shearing.
Another analyzed sample with Ca-amphibole is RA-ll-E, from the 

same location as RA-ll-L. Plots for RA-ll-E are shown in Figures 5a and 

5b. These compositions are similar to those in the previous plots, except 

that the hornblende cores may have formed a somewhat higher grade 

conditions than were responsible for the hornblende cores in other analyzed 

fault rocks from the Upper Lytle Creek Ridge-Blue Ridge area. These and 

the above amphiboles formed under conditions of intermediate P/T.

2. Other reactions

One of several commonly observed reactions in the shallow- to 

moderate-depth (low- to medium-grade) cataclastic rocks is the alteration 

of plagioclase (typically with an original composition of Ab(70)An(30), but 

varying from case to case) to reaction products of nearly pure albite, plus 

epidote and/or calcite. In the studied rocks from the Crafton Hills zone 

and the Punchbowl zone, commonly both epidote and calcite were produced. 

In some samples, the plagioclase has been altered, at lower grade than the 

preceding reaction, to sericite (fine-grained white mica of varying 

composition), calcite, and perhaps epidote.

The association of epidote and albitic plagioclase is quite common 

in samples from the Crafton Hills zone and the Punchbowl zone. If any 

significant heating had accompanied faulting in these rocks, it might be 

expected that the dehydration reaction of epidote plus albite to form 

plagioclase would have occurred. This and similar reactions are observed 

in medium-grade regional metamorphic rocks. To date, we have not found any 

petrographic or microchemical evidence of this or any other dehydration 

reaction which accompanied cataclasis. This is an apparent indication that 

any frictional heating that accompanied displacement along the fault zones 

was not great enough to initiate such medium-grade metamorphic reactions 

(and certainly not nearly sufficient enough to initiate the formation of 

pseudotachylite by melting).

Garnet is observed to have been hydrated to chlorite and minor 

amounts of other minerals in a number of samples. Several samples from the 

eastern Peninsular Ranges zone have a less common reaction, the hydration 

of garnet (plus K-feldspar) to biotite and minor epidote. Figure 6 is a
photomicrograph of garnet in sample RA-27-E in which this reaction has 

occurred. The reaction shown in Figure 6 and other hydration reactions 

such as the sericitization of K-feldspar shown in Figure 7 (sample RA-26-D) 

show that cataclasis within the exposed rocks of eastern Peninsular Ranges 

zone did not all occur at very high grade conditions, as may be the case 

for the rocks from Coyote Mtn. described by Theodore (1970).

D. WHOLE ROCK CHEMISTRY

To date we have analyzed about 40 whole rock samples of cataclastic and 

non-cataclastic rocks using standard rapid silicate analysis methods 

(primarily atomic absorption and colorimetric determinations, depending on 

the particular element). We have just begun to work on the samples from 

the eastern Peninsular Ranges mylonite zone and hopefully these will begin 

to answer some of the questions of interest that can be addressed by these 

methods. Until more data is available, it is not worthwhile to speculate 

on the interpretation of the data other than to say that no obvious trends 

of exchange, depletion, or enrichment with respect to major elements has 

been found for the suite of rocks collected within and near the Punchbowl 

fault zone. The chemical data is shown in Appendix A.

Figures 8a, 8b, and 8c show various plots of whole rock chemical , 

data from a mylonite zone in Guatemala investigated by one of our students, 

Peter Muller (1980, Ph.D. Thesis, SUNY-Binghamton). The fault zone is within 

the Agua Fria granodiorite in the Los Amates quadrangle. Protomylonitic 

granodiorite has suffered exchange of Na«0 for K20 while maintaining 

approximately constant total Na 20 + K^O. The apparent uniformity of this 

process over a large volume of granodiorite suggests a circulating pore 

fluid system within the fault zone.

E. PRELIMINARY CONCLUSIONS BASED ON RESULTS TO DATE 

The results from the studied zones lead to several conclusions about the 

nature of the fault zones at depth when the faults were active. The geothermal 

gradient was apparently moderate over a long period of time and there is no 

evidence of any significant transitory frictional heating (or any other sort 

of rapid temperature rise). The zones had relatively high fluid pressures 

compared to the load pressure, as evidenced by the abundance of hydration
10

and carbonation reaction products and by the absence of evidence of 

significant frictional heating. In the case of the Punchbowl fault zone, 

fault activity continued over a period of time during which either rock 

slices or the entire zone was being brought upward.

On the surface, these conclusions would appear to contrast 

somewhat with those of Sibson (1977, 1979). However, Sibson has pointed 

out that there may be differences in relative fluid pressures from one 

fault zone to another, thereby producing differences in the amount of 

frictional heating. The fault zones observed in this study would seem 

incapable of producing silicate melts, which is the current interpretation 

of pseudotachylites (at least some of these) found in various fault zones. 

Fault zones with high relative fluid pressures would tend to have less heat 

generated by friction; these zones would therefore not have rapid transitory 

rises in temperature and would tend to have lower geothermal gradients 

than "dry" fault zones with lower relative fluid pressures.

The conclusions of this study not not support the conclusions of 

studies which suggest that significant frictional heating is a general 

phenomena applicable to major fault zones. Scholz and others (1979) have 

suggested that prograde metamorphic zones along the Alpine fault in New 

Zealand are the result of frictional heating and that the effects of the 

heating extend on the scale of kilometers beyond the fault zone proper. 

Such frictional heating would result in the growth of minerals under 

relatively low P/T conditions. Although the results of this study can't 

be extended to the Alpine fault zone, it does appear that a similar model 

cannot be applied to the Punchbowl fault zone and the immediately adjacent 

portion of the San Andreas fault zone. As this study proceeds, the problem 

of the relative importance of possible frictional heating needs to be 

addressed in other areas of the San Andreas system.

F. FUTURE DIRECTION OF RESEARCH

Future work will consist of further examination of collected samples plus 

the examination and sampling of other fault zones in the San Andreas system. 

Some of the questions to be addressed are: what were the relative P/T 

conditions in the fault zone; what were the fluid pressures relative to load
11

pressures; what mineral reactions occurred and did they occur during 

shearing. Also, the nature of the fluid system in the fault zone will be 

addressed by looking at the extent and nature of chemical alteration of 

fault rocks. This will continue to be approached using bulk chemical 

analysis, but eventually the use of other techniques such as stable 

isotope analysis would be highly desirable.

As further field sampling proceeds on other fault zones, it should 

be possible to begin to make some generalizations about portions of the 

San Andreas system. At the present time, keeping the results of this 

study plus those of other studies in mind, it appears that there may be 

considerable variations in the physical and chemical conditions from one 

fault zone to another; this needs to be carefully tested.

One useful technique that will continue to be used is to look at 

the compositional details of Ca-amphiboles in fault rocks. Ca-amphiboles 

have been used successfully in interpreting regional metamorphic terrains 

ever since the electron microprobe came into common usage; they also hold 

the promise of telling about the relative P/T conditions and grade within 

and around fault zones. Used with care (the overall mineral assemblage 

must be considered, for instance), interpretations of significant frictional 

heating in a fault zone can be tested if amphibole-bearing rocks are present.

G. BIBLIOGRAPHY

Alf, R. M., 1948. A mylonite belt in the southeastern San Gabriel Mountains, 

Calif.: Geol. Soc. Amer. Bull., v. 59, no. 11, p. 1101-1120.

Anderson, J. R., 1977a. The polymetamorphic sequence in the Paleozoic rocks of 

northern Vermont: a new approach using metamorphic veins as petrologic and 

structural markers Ph.D. thesis : California Institute of Technology, 656p.

Anderson, J. R., 1977b. Compositional zoning in minerals from low- to mediumgrade rocks of northern Vermont: testing the zoning mechanism: 

Geological Society of America Abstracts with Programs, v. 9, p. 235-236.

Anderson, J. R., in press. Metamorphic veins: markers of the polymetamorphic 

sequence in Vermont: submitted to Bull. Geol. Soc. Amer.

Graham, C. M., 1974. Metabasite amphiboles in the Scottish Dalradian: 

Contrib. Mineral. Petrol., v. 47, p. 165-185.

Higgins, M. W., 1971. Cataclastic rocks: U.S.G.S. Prof. Paper 687, 97p.
12

Hsu, K. J., 1955. Granulites and mylonites of the region about Cucamonga

and San Antonio Canyons, San Gabriel Mountains, California: Calif.

Univ. Pubs. Geol. Sci., v. 30, no. 4, p. 223-352. 

Leake, B. E., 1965. The relationships between tetrahedral aluminum and the

maximum possible octahedral aluminum in natural calciferous and subcalciferous amphiboles: Amer. Mineral, v. 50, p. 843-851. 

Laird, J., 1977. Phase equilibria in mafic schist and the polymetamorphic

history of Vermont Ph.D. thesis : California Institute of Technology, 445p. 

Raase, P., 1974. Al and Ti contents of hornblende, indicators of pressure

and temperature of regional metamorphism: Contrib. Mineral. Petrol.,

v. 45, p. 231-236. 

Scholz, C. H., J. Beavan, and T. C. Hanks, 1979. Metamorphism, argon

depletion, heat flow and stress in the Alpine fault: Proc. Conf. VIII -

Analysis of actual faults in Bedrock, U.S.G.S., p. 534-586. 

Sharp, R. V., 1967. San Jacinto fault zone in the Peninsular Ranges of

southern California: Geol. Soc. Amer. Bull., v. 78, p. 705-730. 

Sharp, R. V., 1979. Some characteristicx of the eastern Peninsular Ranges

mylonite zone: Proc. Conf. VIII - Analysis of Actual Faults in Bedrock,

U.S.G.S., p. 258-267. 

Sibson, R. H., 1977. Fault rocks and fault mechanics: Jour. Geol. Soc.

London, v. 133, p. 191-213. 

Sibson, R. H., 1979. Fault rocks and structure as indicators of shallow

earthquake source processes: Proc. Conf. VIII - Analysis of Actual

Fault Zones in Bedrock, U.S.G.S., p. 276-304. 

Theodore, T. G., 1970. Petrogenesis of mylonites of high metamorphic grade

in the Peninsular Ranges of southern California: Geol. Soc. Amer. Bull.,

v. 81, p. 435-450.
13

FORMULA PROPORTIONS Al VI

o

p 

tv>

o "-P- O

b> o

O

O

0 

ON

o 

fd

o

§

O

^ O

> OO

Os

H- hj 

3 M

O

W c+ 

fl'

3 O 

tl t-b 

M 

CD >

t-1 

W 

to

!-" <

M- W

I 

cr 

o

n>
FORMULA PROPORTIONS AlVI+Fe-*++Ti
o

o

FORMULA PROPORTIONS Al

o o

"r- *o

VI

o 

no o

t-1

o

3 o

^ 

n O

O

tr1

M 

<

O 

00

> 

I
U-t

O

Oi 

g 

O

s

CO

0.2

ore 2b. Plot of A1 IV vs. Al VI-^Fe^

Ca-anphibole in sample HA

0.2 0.4- 0.6

FORMULA PROPORTIONS Al

IV

1.0
3

s

S

g 

>

M 

fa

S 

S

ra 

0.2

0./4-

0.6

o.

i.

Figure 3a. Plot of 

for Ca-amphi"bole 

0.2 0.6 0.8 l.O 

FORMULA PROPORTIONS Al(lV)

1.2 
CO

1.0

1.2

En

CD 

e

EH

H 

H

EH

 H 

0.6

0.8

0.2

0.2

flllO

Figure 3b. Plot of Al

for Ga-amphibole in 

0.6 0.8 1.0 

FORMULA PROPORTIONS Al(lV)

1.
0.8

1.0

o

D 

I

M

0.2

0.6

FigiJre 4a. Plot of Al(lV

Ca-amphi"bole in sample 

0.2 . 0.6 0.8 1,0

FORMULA PROPORTIONS Al(lV)

1.2 
20

FORMULA PROPORTIONS Al(Vl)+Ti+Fe(3+)

o

o 

ro

o 

ON

O 

00 o

o 

ro

o

P 

§ *oo

w

> \->

% r

ro

H- O

O 

M O

CD Hj

M. > 

5 Mx -

CO M

I I-1

CD 

C?
FORMULA PROPORTICNS AlVI+Fe^

+-*Ti

21
22

 ""* I I if*

 Jill*'

511" ,

(line of

Figure 3b. Plot of Al^ vs. AlVI+Fe3++Ti for 

Ga-amphibole in sample RA-ll-E.

0.2 0.6 0.8 1.0 1.2 

FORMULA PROPORTIONS A1 IV

1.6
23

Figure 6. Photomicrograph of garnet grain partially altered to biotite 

(along fractures) and minor epidote in sample RA-27-E. Plane polarized 

light, 2.5 mm field of view.

r \\'

-i x

Figure 7- Photomicrograph of alkali feldspar grains partially altered

to sericite along grain boundaries in sample RA-26-D. Crossed polarizers,

2.5 mm field of view.
Figure 8- Compositional plots for whole rock analyses of

uncataclasized and cataclasized Agua Fria granodiorite,

Los Amates quadrangle, Guatemala (Muller, 1980, Ph.D. thesis)

5.0-i

4.0-

Na.O

(wt.%) 3.0-

2.0-

I.O

 » 4

4

(4)

(+)

Figure 8a.

PROTOMYLONITIC 

4- MASSIVE

 INJECTION M10MATITE 

DIKE

i

.0-

.6-

-K22-

S%)

2-

6

 f

(+) 4

( ) "^

*" 4-

 f

"**4 4 Figure Sb.

 f

i i l I i i

Q 72 76 80

Si0
CM

10 -

K

NaO

20 

(wt.%)

8 -

2-

4-

6-

* + W *

PROTOMYLONITIC 

+ MASSIVE

 INJECTION MI6MATITE 

DIKE

68

Figure 

72

8c.

76

Si02 (wt.%)

80
26

Appendix A. Whole rock chemical analyses of cataclastic rock samples 

performed by rapid silicate analysis methods.
SAMPLE NO. RAT-A RA1-I RA2-B RA2-D RA3-I RA3-L RA3-P

Si02

Ti°2

A1203

Fe2°3

FeO

MnO

MgO

CaO

Na2°

K20

P2°5

H20+

co2

TOTAL

SAMPLE NO.

SiOp

Ti°2

Al203

Fe 203

FeO

MnO

MgO

CaO

Na20

KpO

P2°5

co2

45.6

1.2

18.1

2.3

7.1

0.3

8.8

10.3

1.8

1.8

0.1

NA

98.8

RA3-Q

71.4

0.6

13.6

1.2

2.8

0.1

2.0

1.6

2.4

2.3

0.1

0.7

NA

68.1

0.7

13.4

2.5

2.2

-

2.3

3.8

2.3

2.1

0.1 

0.8

NA

98.2

PA3-S

58.8

0.7

12.3

1.4

4-1

0.1

5.8

5.2

1.5

1.3

0.1 

2.8

6.8

72.2

0.2

H.7

1.0

0.7

-

0.1

2.1

3.9

3.1

0.1

0.3

NA

98.5

RA3-X

63.4

0.9

16.2

1.9

3.8

0.1

2.5

3.0

2.1

2.9

0.2

1.5

2.4

48.1

0.9

22.2

2.9

8.4

0.4

4.0

.7.8

3.3

0.3

0.1 

0.8

NA

99.2

RA4-A

65.5

0.7

16.5

1.8

3.0

0.1

2.1

2.7

3.7

2.9

0.2

0.9

NA

73.8

-

15.6

0.1

0.2

-

-

0.6

5,4

3.7

0.2

NA

99.6

RA4-G

63.5

0.4

14.4

0.7

1.5

0.1

1.0

5.3

3.8

2.7

0.1

1.5

5.5

51.0

1.3

15.7

2.7

4.2

0.1

4.1

6.8

2.9

2.4

0.3 

2.7

7.5

101.7

RA6-A

68.4

0.6

14.5

3.7

3.0

0.1

2.2

2.7

2.7

2.6

0.2 

1.2

NA

49.5

o;9.

15.5

1.9

8.8

0.2

6.4

10.8

2.9

0.8

0.1

0.9

NA

98.7

RA6-E

50.2

2.1

16.8

1.4

6.7

0.1

3.9

6.8

4.2

0.8

0.2 

2.1

5.3

TOTAL 99.0 100.9 100.9 100.1 100 .-6 101.9 100.6

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