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Potassic Granophyre Associated with Precambrian Diabase, Sierra Ancha, Central Arizona

Smith, Douglas and Silver, Leon T. (1975) Potassic Granophyre Associated with Precambrian Diabase, Sierra Ancha, Central Arizona. Geological Society of America Bulletin, 86 (4). p. 503. ISSN 0016-7606.

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Lenses of granitic and syenitic granophyre unusually rich in potassium crop out at and near the roof of a Precambrian sill complex of olivine diabase intruded into the Apache Group. The lenses locally are 45 m thick; the diabase is 210 to 240 m thick in the same area. Granophyre contains 7 to 11 wt percent K2O, whereas intruded rocks of the Dripping Spring Quartzite contain 9 to 14 wt percent K_2O. The sedimentary rocks were enriched in potassium before emplacement of diabase, probably during diagenesis while saturated with saline water. The granophyre apparently was mostly liquid when emplaced. Chemical data, together with arguments based on mineralogy, textures, and field relations, indicate that most of the granophyre was derived from Dripping Spring Quartzite. The granophyre, however, contains more Na, Ca, and P and less K than the sedimentary rocks. Rocks representing a differentiated fraction of diabase magma are concentrated below the granophyre at the roof of the complex. The unusual crystallization profile may reflect an influx of water from the overlying sedimentary rocks into the magma. The influx of water may have been responsible for the extensive interaction between magma and country rock. Country rock fused during the interaction appears to have migrated to local structural highs. Because the evidence that the granophyre formed largely from country-rock material is unusually clearcut, this granophyre may serve as a petrogenic model for some other silica-rich igneous rocks associated with intrusions of basaltic magma.

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Additional Information:© 1975 Geological Society of America. Received March 4 1974; Revised manuscript received September 16, 1974. Much of the data presented here was gathered for a Ph.D. thesis by Smith at the California Institute of Technology. Work there was supported by National Science Foundation Grants GA-287 and GA-1324, with additional support from U.S. Atomic Energy Commission contract AT(04-3)-427, Calt-767-56 . Andrew Shride provided valuable information on the geology of the area. Gordon Gastil participated in the initial discovery of the granophyre masses of Reynolds Creek. We appreciate careful reviews of the manuscript by D. S. Barker, G. M. Boone, and W. Hamilton.
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Atomic Energy CommissionAT(04-3)-427
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Caltech Division of Geological and Planetary Sciences2435
Issue or Number:4
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Official Citation:DOUGLAS SMITH and LEON T. SILVER Potassic Granophyre Associated with Precambrian Diabase, Sierra Ancha, Central Arizona Geological Society of America Bulletin, April, 1975, v. 86, p. 503-513, doi:10.1130/0016-7606(1975)86<503:PGAWPD>2.0.CO;2
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:61372
Deposited By: Tony Diaz
Deposited On:21 Oct 2015 18:59
Last Modified:03 Oct 2019 09:07

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