U/PB zircon, strontium, and oxygen isotopic and geochronological study of the southernmost Sierra Nevada Batholith, California

摘要: The southernmost Sierra Nevada offers a view into the deep levels of Mesozoic batholithic belt which constitutes much range to north, and represents one major tectonic features western North America. main crystalline rocks study area are (1) intrusive suite Bear Valley, middle Cretaceous tonalite batholith complex with coeval gabbroic intrusives, (2) gneiss Tehachapi Mountains, consists Early orthogneiss subordinate paragneiss, local domains having granulite facies metamorphic assemblages. orthogneisses dominantly tonalitic in composition, significant layers granodioritic granitic lesser dioritic gneiss. Quartz-rich psammitic metasedimentary marble constitute framework assemblage plutonic were emplaced. Field relations demonstrate assimilation material magmas, magma mixing between mafic, tonalitic, materials. Significant both homogenization inhomogenization recognized isotopically within mixed rocks. U/Pb zircon studies have resolved two igneous suites third postdeformational all lying 90 120 Ma. first (gneiss Mountains) was emplaced at ∼115 Ma, exhibits penetrative high-temperature deformation developed or near solidus conditions. A number discordance patterns, along physical properties zircon, suggest minor inheritance Proterozoic limited open system behavior response 100 Ma event. ± 3 Valley crosscuts older suite, but also synplutonic deformation. Mainly concordant ages indicate crystallization age, some discordances occur due entrainment zircon. fabrics these crosscut by granodiorite Claraville (90 Ma) pegmatite dikes (∼95 Ma). shows strong high initial ^(87)Sr/^(86)Sr δ^(18)O. Zircon populations from paragneiss quartzite samples dominated detrital grains. Strontium oxygen isotopic data on geochronology sample simple twocomponent mantle-derived magmas partial complete melt products Sedimentary admixtures for may be as 45%, no higher than about 15%. Modeled values 10–20% metasediment typical orthogneisses. Initial correlates directly δ^(18)O, generally inversely Sr content. Some subtle complexities O involvement cryptic component. Such component could early Phanerozoic ensimatic accretionary terranes that structurally beneath observed sequence, altered oceanic crust sediments introduced mantle source subduction. One aims this seek out remnants sialic Mountains. No such found, our strongly components link magraatic systems anatexis continent-derived sedimentary