Magmatic anhydrite in granitic rocks: First occurrence and potential petrologic consequences
- 1 March 2000
- journal article
- research article
- Published by Mineralogical Society of America in American Mineralogist: Journal of Earth and Planetary Materials
- Vol. 85 (3-4), 430-435
- https://doi.org/10.2138/am-2000-0404
Abstract
The Cajon Pass Deep Scientific Drillhole penetrated a minimum of 1 km of Late Cretaceous (?) intermediate plutonic rocks containing magmatic anhydrite, which occurs as both matrix grains and relic microphenocrysts within poikilitic hornblende, plagioclase, and sphene. Phase equilibria of coexisting silicates, oxides, and apatite support petrographic evidence of hypersolidus anhydrite, indicating that intermediate rocks from a mafic-felsic calc-alkalic suite (or suites) crystallized from about 800 to 700 °C at Ptot ~6 kb from hydrous and oxidized, sulfate-saturated andesitic to dacitic magma. The occurrence of anhydrite as inclusions within early crystallizing phases and its association with sulfate-enriched apatite indicates that, despite the potentially rapid destruction of matrix anhydrite by subareal weathering, petrologic evidence of the nature of such volatile-rich magma systems can be retrieved. If found to be widespread by future work, such evidence could be useful in understanding the mechanisms of volatile enrichment in explosive sulfur-rich volcanic systems and the potential relative roles of metasomatized lithospheric mantle sources and shallow-level mixing/assimilation processes in Cordilleran arc magma systems.This publication has 4 references indexed in Scilit:
- The Sierra Crest Magmatic Event: Rapid Formation of Juvenile Crust during the Late Cretaceous in CaliforniaInternational Geology Review, 1997
- A Comparison of Structures in the Andean Orogen of Northern Chile and Exhumed Midcrustal Structures in Southern California, USA: An Analogy in Tectonic Style?International Geology Review, 1996
- Chapter 3: Mid-crustal emplacement ofMesozoic plutons, San Gabriel Mountains, California, and implicationsfor the geologic history of the San Gabriel terranePublished by Geological Society of America ,1990
- The iron-titanium oxides of salic volcanic rocks and their associated ferromagnesian silicatesBeiträge zur Mineralogie und Petrographie, 1966