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The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona

Citation

Silver, Leon Theodore (1955) The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:04212014-145355832

Abstract

The Johnny Lyon Hills area is located in Cochise County in southeastern Arizona. The rocks of the area include a central core of Lower pre-Cambrian igneous and metamorphic rocks surrounded by a complexly faulted and tilted section of Upper pre-Cambrian and Paleozoic strata. Limited exposures of Mesozoic and Tertiary sedimentary and volcanic rocks are present at the north end of the map area. Late Tertiary and Quaternary alluvium almost completely surrounds and overlaps upon the older rocks.

The older pre-Cambrian rocks include a section of more than 9000 feet of generally moderately metamorphosed graywackes, slates and conglomerates of the Pinal schist injected in zones by somewhat younger rhyolite sheets. The original sediments were deposited in a geosyncline whose extent probably included large parts of Arizona, New Mexico and west Texas. During the Mazatzal Revolution the Pinal schist was deformed into northeast-trending, steeply dipping and plunging structures and the entire local section was overturned steeply toward the northwest. The pre-Cambrian Johnny Lyon granodiorite was emplaced as a large epi-tectonic pluton which modified the metamorphic character of part of the Pinal schist. Larsen method determinations indicate an age of about 715 million years for this rock, which is about the minimum age compatible with the geologic relations.

The Laramide orogeny produced numerous major thrust faults in the area involving all rocks older than and including the Lower Cretaceous Bisbee group. Major compression from the southwest and subsequent superimposed thrusting from the southeast and east are indicated. Minimum thrust displacements of more than a mile are clear and the probable displacements are of much greater magnitude. The crystalline core behaved as a single structural unit and probably caused important local divergences from the regional pattern of northeast-trending compressive forces. The massif was rotated as a unit 40 degrees or more about a northwest-trending axis overturning the pre-Cambrian fold axes in the Pinal schist.

Swarms of Late Cretaceous(?) or Early Tertiary(?) lamprophyric dikes cross the Laramide structures and are probably related to the large Texas Canyon stock several miles southeast of the map area. Intermittent high angle faulting, both older and younger than the dikes, has continued since the Laramide orogeny and has been superimposed on the older structures. This steep faulting combined with the fundamental northwesterly Laramide structural grain to produce the northwesterly trends characteristic of the mountain ridges and valleys of the area.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Cochise County, greywacke, slate, conglomerate, Pinal schist, Laramide orogeny
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Geology
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Campbell, Ian
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1955
Additional Information:Supplemental Files Information: Geologic map of the Johnny Lyon Hills Area, Cochise Co., Arizona: Supplement 1 from "The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona" (Thesis). Date(s) Collected: 1949/1952. Geographic Location Bounding Box: -110.167 Degrees East; -110.25 Degrees West; 32.25 Degrees North; 32.083 Degrees South. Geologic sections of the Johnny Lyon Hills Area, Cochise Co., Arizona: Supplement 2 from "The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona" (Thesis). Dragoon, Arizona Topographic Map: Supplement 3 from "The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona" (Thesis). Date(s) Collected: 1943. Geographic Location Bounding Box: -110.0 Degrees East; -110.25 Degrees West; 32.25 Degrees North; 32.0 Degrees South. Happy Valley, Arizona Topographic Map: Supplement 4 from "The structure and petrology of the Johnny Lyon Hills area, Cochise County, Arizona" (Thesis). Date(s) Collected: 1945. Geographic Location Bounding Box: -110.25 Degrees East; -110.5 Degrees West; 32.25 Degrees North; 32.0 Degrees South.
Record Number:CaltechTHESIS:04212014-145355832
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:04212014-145355832
Related URLs:
URLURL TypeDescription
https://doi.org/10.22002/D1.622DOISupplement 1 in CaltechDATA: Geologic map of the Johnny Lyon Hills Area, Cochise Co., Arizona
https://doi.org/10.22002/D1.621DOISupplement 2 in CaltechDATA: Geologic sections of the Johnny Lyon Hills Area, Cochise Co., Arizona
https://doi.org/10.22002/D1.620DOISupplement 3 in CaltechDATA: Dragoon, Arizona Topographic Map
https://doi.org/10.22002/D1.619DOISupplement 4 in CaltechDATA: Happy Valley, Arizona Topographic Map
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8196
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:21 Apr 2014 22:55
Last Modified:29 Jan 2018 20:57

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