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

本文对加利福尼亚内华达山脉南部岩基中地壳泥质垂坠的高温变质和岩浆岩作用进行了岩石学研究。研究的主要目标是：(1)确定大尺度岩体演化过程中基岩变质沉积垂体的部分熔融程度；(2)量化基岩和垂体衍生熔体的双组分混合效率以及垂体熔体融入大型花岗岩类岩体的效率。本研究旨在验证已存在的浅层地壳同化在复合基质量收支中的重要性。受晚白垩世大型花岗类岩体侵入的影响，研究区泥质体经历了广泛的高变质作用和局部岩浆岩作用。该地区底石器岩石和组成均匀的泥质岩的Sr、Nd、O同位素比值明显不同。因此，这些同位素比率将被用作主要工具，以便：(1)区分岩基衍生和泥质衍生的熔体，以及(2)限制两者在混染白色体和岩基内的混合。岩石学研究矿物和熔融反应在混染岩以及主要和微量元素化学将补充同位素数据。科迪勒拉岩基与变质沉积岩的部分熔体的地壳杂化意义是一个有争议的话题，对量化显生宙岩浆弧的地壳再循环有重要应用。这项研究应该对这种同化和杂交的程度和限制提出重要的限制。

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.