Petrogenetic and Tectonic Studies in an Exposed Cross- Section of Young (approx. 100 Ma) Continental Crust - Southern Sierra Nevada, California

内华达山脉南部从表层(火山)层到深层(花岗岩)层提供了一个斜面，穿过年轻的岩基生成的硅质地壳。区域填图和Pb/U锆石年代学研究表明，该地壳剖面具有约100 Ma的火成岩-变质组合的构造连续性，使其成为世界上最年轻的裸露陆壳剖面之一。这一部分观察到的成分和构造模式，结合地球物理和火山捕虏体数据，对唾液地壳成因和下大陆地壳的性质提出了重要问题。这项研究的一些具体目标包括：(1)在~100 Ma时添加到地壳中的一个明显的主要地幔起源的火成岩的同位素、岩石化学和岩石学特征，以及它在花岗质下地壳形成中的作用；(2)根据区域地图关系，研究该地幔火成岩套系对多种已存在的地壳物质施加的地壳熔融现象，这些物质是石器时代前的大部分框架结构的特征；(3)年轻地幔组分与原有地壳物质混合模型的建立及其在大型岩基成岩问题中的应用；(4)将适当的温度气压计应用于深部暴露，以改进地壳剖面模型，限制峰期变质和地壳熔融的物理条件；(5)对选定的韧性剪切带和断裂系统进行结构和年代学分析，这些韧性剪切带和断裂系统似乎与岩基侵位和火山喷发密切相关。这项研究的大规模目标是模拟促成南塞拉利昂地壳柱产生的主要组成部分和物质运输模式，并考虑这种现象对大陆结构和演化等更广泛问题的影响。

The southern Sierra Nevada offers an oblique section through young batholith-generated sialic crust from surface (volcanic) levels to deep (granulitic) levels. Regional mapping and Pb/U zircon geochronology reveal structural continuity through this crustal section for igneous-metamorphic assemblages of ~100 Ma, making it one of the youngest exposed continental crustal sections in the world. Compositional and structural patterns observed in this section in conjunction with geophysical and volcanic xenolith data pose important problems on sialic crustal genesis and the nature of lower continental crust. Some specific aims of the proposed research include (1) isotopic, petrochemical and petrographic characterization of an apparent major mantle-derived igneous suite that was added to the crust at ~100 Ma, and consideration of its role in the formation of a granulitic lower crust; (2) study of crustal melting phenomena imposed by this mantle igneous suite on a variety of pre-existing crustal materials that are known to characterize much of the pre- batholithic framework based on regional map relations; (3) con- struction of mixing models between the young mantle-derived component and pre-existing crustal materials and the application of these models to large-scale problems of batholith petrogenesis; (4) application of appropriate thermobarometers to deep-level exposures as a refinement of the crustal section model and for placing constraints on the physical conditions of peak metamorphism and crustal melting; and (5) structural and geochronological analysis of selected ductile shear zones and fault systems which appear to be intimately related to batholith emplacement and volcanic venting. Large-scale goals of this research are to model the major components and material transport patterns that contributed to the production of the southern Sierra sialic crustal column and to consider the implications of such phenomena for broader issues of continent structure and evolution.