Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Ernst, W.G. Search for Related Content GeoRef GeoRef Citation

Paragenesis and thermobarometry of Ca-amphiboles in the Barcroft granodioritic pluton, central White Mountains, eastern California

Geological and Environmental Sciences Department, Stanford University, Stanford, California 94305-2115, U.S.A.

Correspondence: ^* E-mail: ernst{at}geo.stanford.edu

Mid-Mesozoic to Tertiary igneous activity reflects arc evolution along the Sierra + White-Inyo sector of the continental margin. The Ca-amphibole + biotite ± augite-bearing Middle Jurassic Barcroft pluton consists of intergradational, quartzose gabbro-diorite, metadiorite, voluminous mafic-to-felsic granodiorite, and rare alaskite-aplite. It was emplaced along the Barcroft structural break—a major ENE-striking suture juxtaposing mid-Mesozoic bimodal metavolcanics on the north against metamorphosed Lower Cambrian platform strata on the south. The Cretaceous, two-mica McAfee Creek Granite intruded both wall rocks and the Barcroft granodioritic pluton on the east. Geologic mapping and petrochemical studies have documented the structure and metaluminous geochemistry of the Barcroft body.

Analyses of Ca-clinoamphiboles from 16 Barcroft rocks allow the assignment of P-T conditions of crystallization/recrystallization based on experimentally determined and calculated clinoamphibole thermobarometers. Combined with earlier studies of country-rock metamorphism, and oxygen isotopic investigations of mineral assemblages in both plutons and wall rocks, four stages in the P-T evolution of the Barcroft pluton have been identified: Stage 1, partial melting of a mafic protolith at ~25 km or greater depth, then onset of crystallization of refractory hornblende and other ferromagnesian phases at ~915 ± 25 °C attending magma ascent. Stages 2 3, crystallization of progressively more actinolitic hornblende during decompression cooling and stalling of the pluton at a depth of 10–12 km, as temperature declined over the interval ~760–650 °C. Stage 4, subsolidus recrystallization/exsolution of nearly stoichiometric actinolite ± grunerite attending deuteric alteration over the range ~395–545 °C at a depth of 4–5 km. Mineral assemblages of stages 1 4 are disposed progressively inward, indicating that the Barcroft pluton lost heat along intrusive contacts with the wall rocks, cooling, annealing, and re-equilibrating in the process. The Cretaceous McAfee Creek Granite transected this ENE-trending thermal zonation, but exerted little effect on Ti + Al contents (and ¹⁸O values) of Barcroft amphiboles.

This article has been cited by other articles:

				H. L. Lledo and D. M. Jenkins Experimental Investigation of the Upper Thermal Stability of Mg-rich Actinolite; Implications for Kiruna-Type Iron Deposits J. Petrology, February 1, 2008; 49(2): 225 - 238. [Abstract] [Full Text] [PDF]

				W.G. Ernst Contact metamorphism of the White Mountain Peak metavolcanic complex, eastern California American Mineralogist, January 1, 2005; 90(1): 1 - 12. [Abstract] [Full Text] [PDF]