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Origin and Emplacement of the Academy Pluton, Fresno County, California

Mack, Seymor and Saleeby, Jason B. and Farrell, John E. (1979) Origin and Emplacement of the Academy Pluton, Fresno County, California. Geological Society of America Bulletin, 90 (4). pp. 633-694. ISSN 0016-7606. https://resolver.caltech.edu/CaltechAUTHORS:20140808-140343042

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Abstract

The Academy Pluton is located in the western Sierra Nevada foothills northeast of Fresno, California (Fig. 1). It cuts the northern end of the Kings-Kaweah ophio-lite belt, which forms a 125-km-long northwest-trending zone of highly deformed mafic and ultramafic country rocks between the Kings and Tule Rivers of the foothills region (Saleeby, 1975, 1976a, 1976b). The Academy Pluton is one of a number of Jurassic and Early Cretaceous plutons which have intruded and metamorphosed the ophiolitic rocks; these crosscutting plutons form the western margin of the Sierra Nevada Batholith in the latitude of the Kings-Kaweah ophiolite belt. They range in composition from olivine-hornblende melagabbro to hornblende-biotite granodiorite, and many of then appear to have been preferentially emplaced into the structurally weakened zone provided by the disrupted ophiolite belt (Saleeby, 1975, 1976b). To the east, the main body of the Sierra Nevada Batholith is underlain primarily by more silicic middle to Late Cretaceous plutons which range in composition from granodiorite to granite. North of the Academy area, this compositional trend is found to exist all along the western Sierra Nevada foothills. The Guadalupe complex east of Merced (Best, 1963), the Pine Hill gabbro east of Sacramento (Springer, 1971), and the Bucks Lake Pluton (Hietanen, 1973) at the north end of the western metamorphic belt are representative of the more basic and older plutons comprising the western margin of the Sierra Nevada Batholith. The Academy Pluton is one of the most complexly zoned plutons in the western sierra Nevada. The earliest reference to the pluton was by Macdonald (1941), who described the pluton as being composed of hypersthene-bearing quartz diorite. His map (1941, P1.1) showed an indefinite contact between hypersthene-bearing quartz diorite and surrounding pyroxene-free quartz diorite and tonalite. The present investigation has established that pyroxene-free quartz diorite and tonalite lying peripherally to the morth and east of Macdonald's contact is part of the Academy Pluton but tonalite South of the pluton cuts across the Academy structure and thus represents a later magmatic esisode. In preliminary studies, the senior author of this paper noted that there were at least three, and possibly four, ring-like zones comprising the pluton and that the innermost zone was composed of more basic rock than the outermost zones. The difficulty in explaining the gradational contacts and the apparent reversed zoning in the pluton prompted this study.


Item Type:Article
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http://dx.doi.org/10.1130/GSAB-P2-90-633DOIArticle
http://gsabulletin.gsapubs.org/content/90/4_Part_II/633PublisherArticle
http://bulletin.geoscienceworld.org/content/90/4_Part_II/633PublisherArticle
Additional Information:© 1979 The Geological Society of America. Received 31 May 1978. Revision received 27 November 1978. Accepted 7 December 1978. The writers are grateful to Paul C. Bateman, Myron G. Best, Bruce A. Blackerby, Clifford A. Hopson, and John P. Lockwood for their critical review of the manuscript. This investigation was supported by California State University, Fresno research grants which helped defray the cost of field work and thin-section preparation. The contribution of Charles A. Brook, Dale Ortman, Gary S. Zumwalt, and Gary H. Girty to the detailed sampling of the Academy Pluton is especially acknowledged. Theresa L. Keck assisted during parts of the petrographic and mineralogic studies.
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Funding AgencyGrant Number
California State University, FresnoUNSPECIFIED
Issue or Number:4
Record Number:CaltechAUTHORS:20140808-140343042
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20140808-140343042
Official Citation:Seymor Mack, Jason B. Saleeby, and John E. Farrell Origin and Emplacement of the Academy Pluton, Fresno County, California Geological Society of America Bulletin, April 1979, v. 90, p. 633-694, doi:10.1130/GSAB-P2-90-633
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:48253
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:08 Aug 2014 21:36
Last Modified:03 Oct 2019 07:01

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