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

本研究是对加州Sierra内华达州南部岩基中地壳泥质悬块高温变质和混合岩化作用的岩石学研究。 主要目标是：（1）确定在大规模深成作用过程中，岩基变沉积岩悬垂体部分熔融的程度;（2）量化岩基和悬垂体衍生熔体之间双组分混合的效率，以及悬垂体熔体并入大型花岗岩类岩体的效率。这项研究的目的是测试同化的重要性，预先存在的浅地壳的质量预算的复合岩基。研究区的泥质岩经历了广泛的高级变质作用和局部混合岩化反应的大型花岗岩类侵入体在晚白垩世。 本区岩基岩和成分均匀的泥质岩的Sr、Nd、O同位素比值明显不同。因此，这些同位素比值将被用作主要工具，以便：（1）区分岩基衍生和泥质岩衍生的熔体，和（2）限制混合岩浅色体和岩基内两者之间的混合。混合岩泥质岩内矿物和熔融反应的岩相学研究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寄主岩石部分熔体的地壳混合作用的意义是一个有争议的话题，在定量古生代岩浆弧中的地壳再循环方面具有重要的应用。这项研究应该对这种同化和杂交的程度和限度提出重要的限制。

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.