SGER: Testing the Viability of (U-Th)/He Thermochronology in Complex Tectonic Systems

加州北部海岸山脉和造山带的折返是地球动力学过程和地表过程相互作用的结果，地球动力过程驱动着隆起，地表过程响应着隆起的速度和模式。已有多种方法被用来确定挖掘模式，但由于大规模地球动力学、热力和景观演化过程之间的反馈和联系，很难对这些估计施加强有力的、可量化的限制。迫切需要一种技术来限制浅层地壳(低温)岩石的轨迹，以限制活动造山带的抬升和折返。最近，(U-Th)/He热计时法已被确定为一种潜在的工具，有助于定量地限制折返和隆升。(U-Th)/He系统具有闭合温度低(磷灰石为~60-70℃)的优点，因此原则上它记录了最后几公里的去顶。作为一种低温温度计时器，(U-Th)/He在地貌学研究中具有同样的特点，但它在复杂的热历史和/或构造历史地区的应用也引发了疑问。目前还不确定这个工具是否能从复杂的信号中提取有意义的信息，该信号既包含挖掘历史，也包含由挖掘驱动的不可避免的热反馈。在这个项目中，我们将应用(U-Th)/热计时技术，结合景观演化、热力学和地球动力学模拟，评估(U-Th)/He测年是否可以可靠地应用于不处于热或地貌稳定状态的活动构造地区。

Exhumation in the northern California Coast Ranges, and orogens in general, results fromthe interplay of geodynamic processes that drive uplift and surface processes that respond to therates and patterns of uplift. A variety of approaches have been used to determine patterns ofexhumation, but placing robust, quantifiable constraints on these estimates is difficult because ofthe feedbacks and linkages among large scale geodynamic, thermal, and landscape evolutionprocesses. There is a critical need for a technique to constrain the trajectory of rocks at shallow-crustal (low-temperature) levels to constrain uplift and exhumation in active orogenic belts. Mostrecently, (U-Th)/He thermochronometry has been identified as a potential tool to helpquantitatively constrain exhumation and uplift. The (U-Th)/He system has the advantage of a lowclosure temperature (~ 60-70 C for apatite) and thus in principal it records the last fewkilometers of unroofing. As a low-T thermochronometer the same characteristics that make (U-Th)/He so appealing for geomorphic studies also raise questions about its utility in regions ofcomplex thermal and/or tectonic histories. It is uncertain whether this tool can extract meaningfulinformation from a complex signal that incorporates both the exhumation history and theinevitable thermal feedbacks driven by that exhumation. In this project we will apply (U-Th)/Hethermochronometry coupled with landscape evolution, thermal and geodynamic modeling, toevaluate if (U-Th)/He dating can be confidently applied in regions of active tectonism that are notin thermal or geomorphic steady-state.