Determination of the Magnitude of Metasediment-Derived Melt Assimilation in the Southern Sierra Nevada Batholith

本研究是对加利福尼亚州内华达山脉南部中地壳泥质悬垂的高温变质和混合岩化的岩石学研究。主要目标是：(1)确定大型深成作用过程中基岩变质悬垂的部分熔融程度；(2)量化基岩和悬垂熔体之间双组分混合的效率，以及悬垂熔体融入大花岗岩深成岩体的效率。这项研究旨在测试先前存在的浅地壳同化在复合岩基质量收支中的重要性。晚白垩世大型花岗质深成岩体的侵位使研究区的泥岩经历了广泛的高级变质作用和局部混合岩化作用。本区石器时代岩石的锶、钕、氧同位素比值和成分均一的泥质岩特征明显。因此，这些同位素比率将被用作主要工具，以便：(1)区分岩基来源的熔体和泥岩来源的熔体，以及(2)限制两者在混合岩白质小体和岩基内的混合。混合岩浆岩中矿物和熔融反应的岩石学研究以及常量元素和微量元素化学将补充同位素数据。Cordilleran岩浆岩与变质主岩部分熔体的地壳混合意义是一个有争议的问题，对于定量研究显生宙岩浆弧中的地壳循环具有重要的应用价值。这项研究应该对这种同化和杂交的程度和限度施加重要的限制。

9815024SaleebyThis study is a petrologic investigation of the high temperature metamorphism and migmatization of mid- crustal pelitic pendants from the southern Sierra Nevada batholith, California. The primary goals are: (1) determine the extent of partial melting of batholith metasedimentary pendants during the large scale plutonism, and (2) quantify the efficiency of two-component mixing between batholith- and pendant-derived melts and the incorporation of pendant melts into large granitoid plutons. This study is designed to test the importance of assimilation of pre-existing shallow crust in the mass budget of the composite batholith. The pelites of the study area underwent extensive high-grade metamorphism and local migmatization in response to the intrusion of large granitoid plutons during the late Cretaceous. The isotopic ratios of Sr, Nd, and O of the batholithic rocks and the compositionally uniform pelite are distinct in the area. Hence, these isotopic ratios will be used as the principal tool in order to: (1) distinguish between batholith-derived and pelite-derived melts, and (2) constrain the mixing between the two in both migmatitic leucosomes and within the batholith. Petrographic studies of mineral and melting reactions within the migmatitic pelite as well as major and trace element chemistry will complement the isotopic data. The significance of crustal hybridization of Cordilleran batholiths with partial melts from metasedimentary host rocks is a controversial topic with important applications to quantifying crustal recycling in Phanerozoic magmatic arcs. This study should put important constraints on the extent and limits of such assimilation and hybridization.