An Apatite/Zircon (U-th)/He Thermochronometric Study of the Rapid Tectonic Denudation of an Oblique Crustal Section-Southern Sierra Nevada, California

项目概述PI建议在最南端的Sierra内华达州地区制作一系列（U-The）/He磷灰石和锆石热年代学剖面，作为对Sierran岩基岩石在最晚的白垩纪-早古近纪时期通过低角度拆离断层作用进行的快速构造剥蚀的测试。这一阶段的剥蚀暴露了一个倾斜的地壳剖面，穿过最南端的Sierra内华达州岩基，古深度约为35 km。磷灰石-He研究在更大的塞拉利昂内华达州地区北部的持久性揭示了一个长期的波长高浮雕河流为主的地形在同一时间间隔的高站造山高原。与此形成鲜明对比的是，南部岩基的最深处暴露在始新世早期的海洋环境中，并伴随着构造剥蚀。这些深刻的沿着走向变化的古地貌的Sierran岩浆弧可以连接到构造移除的亚岩基地幔岩石圈下最南端的Sierra-北部莫哈韦沙漠地区的浅平板段俯冲洋板块，以及相关的构造底侵的Franciscan沟亲和变质组合。PI的已经确定了一系列已知的和明显的高层次岩基剥离片沿着最南端的塞拉利昂和北方莫哈韦沙漠地区，似乎代表了部分上地壳岩石被剥离系统。他们还确定了现代地形异常和异常结构纹理叠印在南部Sierra地区的基底岩石中，这对应于岩基就位压力测量中陡梯度的开始及其隐含的剥蚀深度。他们认为这些区域代表了接近分离带的下盘复合体的热膨胀，在分离带中，最北的拆离岩席从造山高原边缘崩落。垂直磷灰石和锆石热年代学剖面建议在这些地区作为非常快速的冷却和构造剥蚀的测试。这些剖面将沿着恒定的海拔剖面向南延伸到岩基暴露的最深处，以进一步测试区域快速冷却，并测试随时间推移逐渐加深剥蚀程度的可能的向南迁移。更广泛的目标是将南部Sierra地区的古地貌演化与岩石圈尺度的构造和动力学联系起来，并将这些发现与全球重要的问题联系起来，即深部结晶基底岩石的向上迁移和表面暴露，以及与之相关的旅游，侵蚀，构造剥蚀，以及下地壳和上地幔的演化。拟议的研究计划为期三年，包括一个强有力的样品收集计划，矿物分离、地球化学分析以及新数据与现有地质和地球化学数据集的综合。该项目需要联合PI及其技术人员的部分努力，并构成加州理工学院博士学位的主要组成部分。论文。

PROJECT SUMMARYThe PI's propose to produce a series of (U-The)/He apatite and zircon thermochronologic profiles in the southernmost Sierra Nevada region as a test of the very rapid tectonic denudation of the Sierran batholithic rocks by low-angle detachment faulting in latest Cretaceous-early Paleogene time. This phase of denudation exposed an oblique crustal section through the southernmost Sierra Nevada batholith to a paleodepth of ~35 km. Apatite He studies in the greater Sierra Nevada region to the north have revealed the persistence of a high standing orogenic plateau with long wavelength-high relief fluvial dominated topography during the same time interval. In marked contrast the deepest level exposures of the batholith to the south had subsided to marine conditions by early Eocene time in conjunction with tectonic denudation. These profound along strike variations in the paleogeomorphology of the Sierran magmatic arc can be linked to the tectonic removal of the sub-batholithic mantle lithosphere beneath the southernmost Sierra-northern Mojave Desert region by a shallow flat-slab segment of the subductingoceanic plate, and the related tectonic underplating of Franciscan trench-affinitymetamorphic assemblages. The PI's have identified an array of known and apparent high-level batholithic detachment sheets along the southernmost Sierra and northern MojaveDesert region that appear to represent part of the upper crustal rocks that were displacedby the detachment system. They have also identified modern topographic anomalies andanomalous structural-textural overprints in the basement rocks of the southern Sierraregion which correspond to the onset of steep gradients in batholith emplacementbarometry and its implicit depth of denudation. They interpret these areas to represent theremnants of footwall complexes proximal to the breakaway zones where the northernmost detachment sheets calved off the edge of the orogenic plateau. Verticalapatite and zircon thermochronologic profiles are proposed across these zones as a test ofvery rapid cooling and tectonic denudation. These profiles will be extended southwardalong constant elevation profiles to the deepest exposed levels of the batholith in order tofurther test for regional rapid cooling, and to test for a possible southward migration inprogressively deeper levels of denudation with time. The broader goals are to relate thepaleogeomorphic evolution of the southern Sierra region to lithosphere-scale tectonicsand dynamics, and to relate these findings to the globally important problem of theupward migration and surface exposure of deep crystalline basement rock as related touplift, erosion, tectonic denudation, and the evolution of lower crust and upper mantle.The proposed research program runs for a period of three years and includes a vigorousprogram of sample collecting, mineral separation, geochemical analysis, and thesynthesis of the new data with existing geological and geochemical data sets. The projectwill entail partial efforts of the joint PI's and their technical staff, and constitute a majorcomponent of a Caltech Ph.D. Dissertation.