MOUNT OGDEN GRANITE by Dennis Charles Temple A thesis submitted to the faculty of the University of Utah in partial fulfillment of the requirements for the degree of Master of Science Department of Mineralogy University of Utah June 1969 This Thesis for the Master of Science Degree by Dennis Chafrles Temple has been approved June 1969 ACKNOWLEDGEMENTS Especial thanks are given to Dr. Bronson Stringham, under whose supervision this thesis was undertaken and carried to the completion of the field work and petrographic studies. Dr. James A. Whelan was instrumental in the writing and final preparation of this thesis, through his encouragement and kind supervision• The assistance of Dr. A. J, Eardley was of great help in under­ standing structural relationships. The Anaconda Company materially assisted in the final prepa­ ration of this thesis. iii TABLE OF CONTENTS ABSTRACT , vii INTRODUCTION 1 Purpose •••• 1 Location •••• 1 Accessability • • 1 Field and Laboratory Studies 2 Previous Work 3 Geologic Setting • 3 PRECAMBRIAN ROCKS 5 Gneissic Granite • 5 Meta-Diorite • • 9 Hornblende-Labradorite Gneiss 11 Feldspar Gneiss •*.. •.• 13 Pegmatites 14 Boundary Between Gneissic Granite and Migmatite •. 15 Age Determination 16 CAMBRIAN STRATIGRAPHY 17 Tintic Quartzite 17 Ophir Shale 18 Cambrian Limestone and Dolomite •. • • 18 QUATERNARY SEDIMENTS 19 Lake Bonneville Terraces 19 Canyon Gravels 19 iv STRUCTURE • 20 Thrust Sheets 20 Taylor Thrust . 20 Ogden Thrust • ..• 21 Wasatch Fault 22 ECONOMIC GEOLOGY 2* GEOLOGIC HISTORY 26 REFERENCES 29 VITA • 30 v LIST OF ILLUSTRATIONS PLATE 1, LOCATION MAP Folder PLATE 2. GEOLOGIC MAP Folder PLATE 3. GEOLOGIC SECTIONS Folder vi ABSTRACT The area of gneissic granite on the west side of the Wasatch Mountains, immediately east of Ogden, Utah, was mapped on U. S. Geol. Survey 7-1/2 minute quadrangle topographic sheets. The gneissic granite has foliation of variable intensity and is finer grained than the migmatite to the south. There is a gradational contact between gneissic granite and migmatite. Within the gneissic granite there are numerous inclusions that have been grouped into three general types: Meta-diorite, Hornblende-labradorite gneiss, and Feldspar gneiss. Unconformably overlying the Precambrian rocks are the follow­ ing Cambrian sediments: Tintic quartzite, Ophir shale, and Cambrian limestone and dolomite. Quaternary deposits occur as Lake Bonneville terraces and canyon gravels. Structures consist of the Ogden and Taylor thrusts, the normal Wasatch fault, and east-west trending folds. Within the map area the Ogden thrust is younger and cuts the Taylor thrust. Both of these structures have been transversely folded. The steep western edge of the Wasatch Mountains is determined by the Wasatch fault. vii INTRODUCTION This study was undertaken to determine the rock types present and their relationships in that part of the Precambrian Farmington Canyon complex exposed on the west side of the Wasatch Mountains, immediately east of Ogden, Utah, Gneissic granites were known to exist on the west side of Mt, Ogden, but the relationship of these rocks with the metamorphic rocks to both the north and south was not known. Since past mapping in this part of the north-central Wasatch range was done on a regional scale, a detailed study of gneissic granite facies was made to better understand the geology of the Wasatch Mountains, Location The area studied (Plate 1) is within the Wasatch Mountains, immediately east of Ogden, Utah, It occupies a triangle, in parts of T5 and 6N, R1W and T5N, R1E, Salt Lake Base Line and Meridian, with its west side along the valley front, Gneissic granite is restricted to the west side of the range except at the southeast corner, where it extends one mile down the east side of the range In Strawberry Canyon. Accessability The only paved road within the area is State Highway 39 in Ogden Canyon, Dirt roads are present along the front of the range for the length of the area studied. Foot trails are present in the bottom of Waterfall Canyon and in Taylor Canyon, The trail in Taylor Canyon forks approximately one half mile up the canyon with the south fork going first to Malans Peak and then to the upper portion of Waterfall Canyon, Another trail is present along the south side of Ogden Canyon for approximately one mile from its start at the foot of the range north of Taylor Canyon, On the east side a work road in Snow Basin Ski Area extends to the crest of the range south of Ogden Peak, Field and Laboratory Studies Field mapping was done during the fall of 1961, spring and fall of 1962, and the summer of 1963. The work was first recorded on aerial photographs and then transferred to U.S. Geol. Survey, 7-1/2 minute quadrangle topographic sheets (Plate 2). Due to the rugged nature of the terrain and the lack of roads, many days were spent on foot in order to reach all the outcrops within the area. Outside the Precambrian area, the work was done by field sightings with more reliance on the photographs, which show the contacts clearly. While the field work was in progress, forty-one thin section slides were prepared and studied at the University of Utah, from specimens typical of the rocks present. During the winter of 1965 additional thin section study was done at Arizona University. All rock descriptions are based on these studies. Previous Work The first published geological study of this area was made by members of the U. S. Geological Exploration of the 40th Parallel, who described the sedimentary rocks present but did no detailed work on the Precambrian rocks which they correlated with the Precambrian rocks to the south. Eliot Blackwelder (1910) reported on this area, but did not attempt to separate the various Precambrian rocks. A. J. Eardley (1944) defined the general area of granite rocks, while doing his study of the North Central Wasatch Mountains. Eardley and Hatch (1940) described the major Precambrian rock types in this area. Geologic Setting The area under study is located in the north central portion of the Wasatch Mountains, which in turn is the westernmost range of the Rocky Mountain Provence. The eastern edge of the Basin and Range provence is marked by the Wasatch fault along the west side of this area. All of the sediments that overlie the Precambrian rocks of interest are tilted to the east due to elevation of the west side of the Wasatch range. Also, this area is within the northern Utah highland of Eardley (1944). Due to these two factors, Precambrian rocks now have a vertical exposure of nearly 5000 feet in this area (Plate 3). The following types of Precambrian rocks are exposed: Gneissic granite, Meta-diorite, Hornblende-labradorite gneiss, Feldspar gneiss, 4 Migmatite, and Pegmatite dikes. Along the northeastern side of this area the following Cambrian rocks are exposed: Tintic quartzite, Ophir shale, and limestone and dolomite of the Hartmann, Lynch and Bluebird formations which were not differentiated in this study. Quaternary sediments occur as Lake Bonneville beach terraces and canyon gravels. All of the rocks in this area, except the Quaternary deposits, have been affected by moderate folding due to north-south com­ pression. The Taylor thrust and Ogden thrust cut through the area and finally the Wasatch fault has elevated these rocks to their present position. PRECAMBRIAN ROCKS Gneissic Granite The area studied is defined by exposures of gneissic granite. The west side is limited by Lake Bonneville beach terraces, except between Taylor Canyon and Ogden Canyon, where Cambrian sediments extend to the valley* From Ogden Canyon northward to Jumpoff Canyon the gneissic granite is present along the lower slopes of the range. South of Ogden Canyon* the gneissic granite is present in Taylor Canyon and below the crest of the range until just south of Ogden Peak, where it extends a few hundred feet onto the east side. Southward in Strawberry Canyon, the gneissic granite extends about one mile down the canyon. The southern boundary is defined by the presence of migmatite, extending from the south side of Strawberry Canyon in a nearly straight line to between Strongs and Hues canyons at the west edge of the range. A wedge of Cambrian sediments is present along the bottom one half mile of the south side of Taylor Canyon that taper southward until it feathers out at the south edge of the area studied* Tintic quartzite in this wedge is responsible for the cliffs present south of Taylor Canyon* The Heta-diorite, Komblende-labradorite gneiss, and Feldspar gneiss fades are inclusions in the gneissic granite* Due to variations in foliation and abundance of mafics, no one description of hand specimen*appearance is representative of the whole mass* The majority of outcrops are red to green-gray, weakly foliated granite. The red tones are due to weathering, oxidation of mafic constituents and pale red microcline. On fresh faces, a random mixture of light and dark minerals refects a green-gray color. Variations of up to 20% in the abundance of mafic con­ stituents is responsible for similar variation in color lightness. Fine fracturing parallel to foliation and faults create irregularly tabular weathering fragments. Changes in general appearance can be expected within 1000 feet of any point. The most prominent variation is in foliation. Throughout most of the area foliation is weak and reflected by orientation of mafic constituents. Randomly scattered are abundant locations of moderate foliation, where all of the minerals appear to be oriented. Some of these areas can be related to faults, in­ clusions, or the migmatite south of the study area. No attempt was made to map foliation intensity due to the abundance of variation, irregular distribution, and very gradational contacts.