Geology of a portion of the Coyote Mountains, Pima County, Arizona Item Type text; Thesis-Reproduction (electronic) Authors Kurtz, William Lang, 1931- Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 01/10/2021 01:58:09 Link to Item http://hdl.handle.net/10150/553880 GEOLOGY OF A PORTION OF THE COYOTE MOUNTAINS PIMA COUNTY, ARIZONA ty William L. Kurtz A Thesis submitted to the faculty of the Department of Geology in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in the Graduate College, University of Arizona 1955 Approved: 7 Director of Thesis Date 'j/u-a; LTOYOO Yo noirr is ' o T -o .0 :I UOG MI c.i-ir.. alesrfT A to yd-jjjoc'j erld" od" bsd'd'lindif: . — - »^Q-Q&0 - - w '■ i> srlc %o': a^asfneiiif: e*: erfj ‘to dn^ciLlll fu’ I ij :^:t\q n± - o :i:tic 10 / t : i aarZi-' ‘: ■ 1 ic L ts^si.CoO sdru," 3 e id ri V ^ S ' S This thesis has been submitted in partial fulfillment of require­ ments for an advanced degree at the University of Arizona and is deposited in the Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major depart­ ment or the dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, permission must be obtained from the author. SIGNED: CONTENTS ......... ...... • .... Page Introduction ; General statement Location........ Topography..... Regional Setting. =-UJ U) fO H fO U) =-UJ Previous Work.... 4 Methods......... Acknowledgements. Own Petrography and Petrology General Statement...................................... ........7 Quartz-monzonite General Statement............................................ 8 • Megascopic description....................................... 9 Microscopic description................. 10 Discussion..................................... ........... • *12 Diorite General statement........................................... 15 Megascopic description...................... l6 Microscopic description.....................................17 Discussion.................................................. 20 Granite General statement............... ^ i .. .22 Megascopic description......................................23 Microscopic description......;.i..23 Discussion................................................. .25 Meta-sediment General statement............................. .............. 26 Megascopic d e s c r i p t i o n . i ^ .27 Microscopic description..................................... 28 DiSCUSSion...... .29 Biotite gneiss ..... ........ ... General statement........................................... 31 Megascopic d e s c r i p t i o n . .31 Microscopic description;.................................... 32 Discussion.................................................. 33 Alaskite - General statement.......... ...... .. .; ...35 Megascopic description.............................. .36 Microscopic description. ..37 Discussion...................................................38 Pegmatites General statement....... .......1*0'- Megascopic description..................................... .42 Microscopic description..................................... 43 Discussion..................... 44 Miscellaneous Rocks .................... .45 Structure General Statement.... US' Internal structure.... 48 Shears, Faults, Joints 53 Origin of the Coyote Mountain Rocks 56 Summary.... 60 Bibliography 62 LIST OF FIGURES Fig. 1. Index Map facing 2 LIST OF PLATES Plate 1 Geologic Reconnaissance Map of a portion of In Pocket the Coyote Mountains, Pima County, Arizona Plate 2 A Inclusions........ i B Inclusions........................................... i Plate 3 A Meta -sediment............................... ii B Meta-sediment......... ............................. ' ii Plate 4 A Biotite gneiss................... ........... iii B Biotite gneiss....................................... iii Plate 5 A Pegmatites............................. iv B Pegmatite contact.................. iv Plate 6 A Pegmatite contact..'................. v B Lamprophyre.......................................... v Plate 7 A General Topography................................... vi B Sediment......... vi Plate 8 A Diorite.......... vii B Diorite.............................................. vii Plate 9 A Biotite gneiss..... ..................................viii B Meta-sediment.......... ............................. viii Plate 10 A Biotite after hornblende....................... ix B Porphyroclastic alaskit e............................. ix Plate 11 A Pegmatite......................... x B Pegmatite................................ x INTRODUCTION General Statement The rocks of the Coyote Mountains, Arizona, were studied in the field and in thin section in order to describe the rocks and their re­ lationships to each other, and to postulate a sequence of events which led to their formation. Seven rock types were distinguished: meta-sediment, diorite, quartz-monzonite, granite, biotite gneiss, alaskite, and pegmatite. Each of these rock types is described in detail. Several miscellaneous rocks are briefly described, namely: rhyolitic and lamprophyric dikes, Cretaceous (?) sediments, and volcanics. The principal internal structure is a planar parallelism which is developed within all the major rocks except the pegmatites. This planar parallelism has a general northwest strike and dips southwest at moder­ ate to steep angles. The area is bordered on the north by the Ajo Road fault, which separates the Coyote complex from the sediments and vol­ canics exposed north of the fault. All the rocks within the Coyote complex, except the pegmatites and dikes, show the effects of a regional synkinematic metamorphism with some metasomatism. This metamorphism has affected rocks of pos­ sible igneous and sedimentary origin. Tucson Roskruge Mtn. Quinlan ? Mtn. Sierrita Mtn. x \ Coyote Mtn. 10 Miles ZONA PIMA COUNTY 30Miles Pig. 1. Index Map showing location of area discussed in this report Location The Coyote Mountains are located in southern Arizona and com­ prise about thirty-five square miles of central Pima County (figure l). The presence of numerous ranch roads within the area and its location thirty miles west of Tucson, Arizona, along Highway 86 make the Coyote Mountains easily accessible. Pertinent information pertaining to the area studied is listed in the table below. Table 1 Location and Reference Material of the Coyote Mountains Pima County, Arizona Latitude 32° OO'N Longitude 111* 30'W Township Range Section 17S 8e 1,2,3,10,11,12 l6s 8e 13,14,15,22,23,24> 25,26,27,34,35,36 17S 9E 6,7 16S 9E 18,19,30,31 (Gila-Salt River Baseline) USGS 15* Series Topographic Maps. Pima County, Arizona. 194l Ed. Cocoraque Butte Quadrangle Palo Alto Ranch Quadrangle San Vicente Quadrangle Baboquivari Peak Quadrangle Aerial Photographs Agency— Soil Conservation Service Description— "L" Pima-Papago Indian Reservation Photo No. 8o8-8llj 855-860 3 • Topography The Coyote Mountains are elongated north-south and rise abruptly from the surrounding alluvial plain; In the portion studied by the writer several ridges that trend northwest to west-northwest are promi­ nent. These ridges are bounded on the west side of the mountain by a steep, rugged escarpment. The maximum relief is 3/325 feet. The in­ ternal structure of the rocks has only slight, local influence on the topography. Joints control the topography at the north end of the mountains and give the appearance of a series of sedimentary beds dip­ ping to the east. Prominent domes are found in several areas and are thought to be due to exfoliation (Pl.fA). Regional Setting The Coyote Mountains are located in the Basin-Range province which is characterized by isolated mountains separated by broad allu­ vial valleys. The Jurassic Chico-Shunie erogenic belt of Eardley (1951/ PI.13) extends across this area and several intrusions of in­ termediate igneous rocks may be associated with this orogeny. The Coyote and Quinlan mountains are situated at the north end of the Baboquivari mountain chain which extends northward for forty-five miles from the Mexican border. The Quinlan Mountains have several small north and northwest ridges, but the main ridge trends east-west and is cut off by the Pan Tak fault, which separates the grahodiorites of the Quinlans on the west from the rocks of the Coyote Mountains. The Coyote Mountains are separated from the volcanics in the Roskruge Moun­ tains by the A jo Road fault. The Roskruge Mountains describe a "V" with k the southern end trending northeast and the northern end trending northwest. The northwest trend continues into the Waterman Mountains and is finally lost in the Silver Bell Mountains. The general trend of the mountain system extending from the Mexican Border to the Silver Bell Mountains is north-south. : ' Previous Work Previous geological work in the Coyote Mountains has been of a general nature. The earliest information on the Coyote Mountains was published