RELATIONSHIP BETWEEN STRUCTURE AND MINERALOGY OF THE SHERMAN GRANITE, SOUTHERN PART OF THE LARAMIE RANGE, WYOMING - COLORADO

88 Pages·03.777 MB·English

by  HARRISON, JACK EDWARD

COPYRIGHTED
by
Jack Edward Harrison
1951
RELATIONSHIP BETWEEN STRUCTURE AND
MINERALOGY OF THE SHERMAN GRANITE,
SOUTHERN PART OF THE LARAMIE
RANGE, WYOMING-COLORADO
i
BY
JACK EDWARD HARRISON
A.B., DePauw University, 1948
I
THESIS
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY
IN THE GRADUATE COLLEGE OF THE
UNIVERSITY OF ILLINOIS. 19S1
URBANA. ILLINOIS
UNIVERSITY OF ILLINOIS
THE GRADUATE COLLEGE
MAY 17, 1951
I HEREIN RECOMMEND THAT Till". THESIS PREPARED I XDER M\
JACK EDWARD HARRISON
SUPERVISION P.Y
ENTITLED RELATIONSHIP BETWEEN STRUCTURE AND MINERALOGY
OF THE SHERMAN GRANITE, SOUTHERN PART OF THE LARAMIE RANGE,
WYOMING - COLORADO
P>E ACCEPTED IX I'ARTIAI. FULFILLMENT UF THE REOL'I REM EXTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY
TI ( nai JI ol I In Ms
I li ail nl I H]»""m nt
Recommendation concurred inf
Committee
on
tfiHW^ Final Examination!
t Required for doctor's decree t>ut not for master's.
M440
ii
TABLE OF CONTENTS
CHAPTER PAGE
I. INTRODUCTION 1
II. GENhnAL GEOLOGY 5
III. FIELD RELATIONS ALNu PETROGRAPHY 6
Mixed Rock 7
Schist and Gneiss 9
Hornblende-Pyroxene-Plagioclase hock 10
Anorthositic Rock3 10
Metanorite 11
Syenite 11
Raggedtop Gneisses 11
Sherman Granite 12
Type I, Coarse Sherman Granite 14
Type II, Quartz Monzonite 20
Type III, Gneissic quartz Monzonite 23
Paragenesis 24
Inclusions in Sherman Granite 25
Aplite Dikes 28
Pegmatites 32
Lamprophyre Dikes 32
Mineralization 32
Paleozoic and Younger Rocks 33
IV. STRUCTURE 34
Structure in Sherman Granite 34
Structure in Other Rock Types 35
Method of Plotting Structure 35
Major Structural Trends 37
V. CORRELATION OF STRUCTURE AND MINERALOGY IN THE
SHERMAN GRANITE 38
Methods of Determining iniineral Percentages in
the Rocks 38
Method of Plotting Mineral Percentage Values. . .. 39
Possible Sources of Error 40
Diagrammatic Structure-Mineralogy Relationships . . 42
Origin of Foliation 44
Origin of Composition 49
Interpretation of Correlation Diagrams 59
VI. SUMMARY AND CONCLUSIONS 64
BIBLIOGRAPHY 66
PLATES 69
ill
Acknowledgment s
The writer wishes to acknowledge the help and encouragement
received from Dr. A. F. Hagner of the University of Illinois
department of Geology under whose direction this work was done.
Dr. Hagner and Dr. W. H. Newhouse of the University of Chicago
were very generous in making available unpublished data on the
Raggedtop gneisses. The work of Newhouse and Hagner in the
Laramie Range suggested this study, and the writer acknowledges
their advice and has drawn freely upon their knowledge of Laramie
Range geology. Dr. C. A. Chapman of the University of Illinois
has made many helpful suggestions during the preparation of the
manuscript. The work was done while the writer was a Fellow of
the Graduate College at the Jniversity of Illinois.
I. INTRODUCTION
Recent quantitative studies of gneisses in the Laramie Range
by Newhouse and Hagner (1947) have resulted in the idea that
structure of the host rock is a dominant factor controlling the
composition of gneisses and schists. The Sherman granite, which
is exposed in the southern part of the Laramie Range (Fig. 1),
was selected for a quantitative study for three reasons: (1) a
similar study had been made by Newhouse and Hagner on associated
gneissic rocks which made it possible to correlate and compare
results; {'d) most of the geologic contacts were mapioed previously,
and thus nearly all of the field time could be devoted to a study
of the granite; and (3) the area is of batholithic dimensions
and is readily accessible. The problem was to determine whether
any relationship existed between structure and composition of the
granite, to explain the significance of any correlation or lack
of correlation discovered, and to determine the relation of the
Sherman granite to the Raggedtop gneisses studied by Newhouse and
Hagner.
The field study was conducted during the summer seasons of
1949 and 1950. Laboratory investigations were begun during the
fall of 1949 and completed during the winter of 1950-1951. Map
ping was done primarily on aerial photographs in Wyoming and on
the Home and Livermore topographic sheets in Colorado. The geo
logic map (Plate I) is a compilation of data from several sources.
The eastern contacts are taken from unpublished master's theses
done at the University of Wyoming and from the map of the Sherman
quadrangle (Darton, et al, 1910). The western contacts are
-
Torrington
- 42*
1
WYOMING

A
K
S
A
R
B
E
(frn/rh SHERMAN N
1 QUAD.
Laramie
^ Cheyenne i
w
Al»
105* 104*
COLORADO
Location map of Sherman Granite area studied, Laramie
Range, Wyoming- Colorado
40 MILES
Figure 1
compiled from the unpublished work of Newhouse and Hagner and
from the map of the Sherman quadrangle. The southern contacts
are from the Colorado State Geologic Map (U. S. G. S., 1935).
The Wyoming part of Boulder Ridge (Fig. 2) is shown on the Laramie
quadrangle (Darton, et al, 1910) and has been used as slightly
modified by Beckwith (1938). The Colorado extent of Boulder
R.74W. «. 73 W.
EXPLANATION
o o °
0
Paleozoic and younger sedimentt.
Pre-Cambrian Sherman granite.
vS*
Pre-Cambrion rock*,
undifferentiated.
Strike and dip of foilotton
-j- Horizontal folation
T o u lt
~^~ Contact
R. 75 W.
T.
II
N.
Geology by J. E. Horriton, 1991
14 »•
Reconnaissance Map of
BOULDER RIOGE
Figure 2
4
nidge has been compiled from the Colorado State Geologic Map and
from a location map made by Boos and Aberdeen (1940, p. 698).
The writer has modified the positions of contacts in several
places, and complex boundaries have been generalized in the area
south of the Williams ranch (Plate 1). All structure shown on the
map (Fig. 2; Plate 1) was mapped by the writer.
An attempt was made to get statistical coverage of the area
by inaking traverses across the strike of the granite about 3 miles
apart, exposures in much of the region are good, but in some
areas this is not the case. In addition there are places where
the planar features of the granite are poorly developed or absent.
These factors made it impossible to get data necessary for complete
statistical coverage. The data obtained, however, are sufficient
to indicate that there is a correlation of composition to struc
ture of the Sherman granite.
II. GENERAL GEOLOGY
The area of Pre-Cambrian rocks studied forms part of the
Laramie Range In the southeastern part of Wyoming and extends a
few miles into Colorado (Fig. 1). Sherman granite is the main
t
Pre-Cambrian rock unit in the southern part of the Laramie Range
(Plate 1) and is exposed principally in the area of the Sherman
quadrangle in Wyoming.
Other Pre-Cambrian map units include mixed rock, schist and
gneiss, and hornblende-pyroxene-plagioclase rock in the southern
I part. Anorthositic rocks, metanorite, syenite, and the Raggedtop
gneisses occur in the northern part of the map area. These two
i major groups of rocks are separated by Sherman granite.
Paleozoic, Mesozoic, and Cenozoic sediments outcrop on the
east and west margins of the Pre-Cambrlan area. The Paleozoic
rocks are Casper formation (Penn.) which is principally sandstone
and limestone. Mesozoic rocks include various kinds of sediments, i
i
and Cenozoic rocks are principally gravels and alluvium. Detailed j
descriptions of these rocks are given by Darton and Siebenthal j
(Darton, et al, 1910). |
The general geologic history of the region has been discussed j
by Blackwelder (1909), Fowler (ly30), and Knight (1944). A brief |
review of the history shows burial of the Pre-Cambrian complex
beneath a thick sedimentary cover, uparching and peneplanation,
followed by partial burial under continental deposits. Most of
(
the present surface was established in Pliocene time (Blackwelder, j
1909). The Pliocene surface has been modified slightly by wind
erosion and rejuvenated streams in later times which have pitted
and slightly dissected the old peneplain.