Tectonic Implications of Partial Melting in the Ruby Mountain-East Humboldt Metamorphic Core Complex, Northeastern Nevada

深层地壳的物理和化学组成是不可能在原位检查的。因此，地球的这一部分一直是谜，尽管它在造山活动期间对地球化学运输具有重要意义，例如在矿床的产生中也很重要。对深部地壳的研究只能通过对从深处挖掘出来的岩石进行检查来进行，而本研究的重点是对内华达州红宝石-东洪堡山脉深处暴露的山芯的岩石进行这样的研究。暴露在这个范围内的岩石是变质岩，它们起源于地球表面，在落基山脉形成期间由于埋藏而承受了升高的压力和温度。事实上，这些岩石在足够深的地方开始融化，这种融化导致了岩石物理性质的重大变化，类似于一块冰开始融化时所观察到的变化，在压缩力的作用下，开始快速移动。在本研究中要检验和测试的假设是，这种融化（其产物可以在今天的岩石露头中观察到）在多大程度上促进了这些高级变质岩的快速隆起、挖掘和进入山脉核心的就位。在山脉的岩心中暴露出许多这样的部分熔融深地壳变质带，本研究结果将直接适用于其他地体，并可能对整个山带的演化具有深远的意义。资金将允许P.I.和他的研究生收集必要的数据，以验证以下假设：内华达州红宝石山脉-东洪堡山脉的部分融化，通过流变学和应变率的相关变化，开始变质的下地壳岩石进入中地壳，为变质核复杂的形成奠定了基础。本研究将采用主要和辅助矿物热气压计（包括新的Ti-in-quartz热气压计的应用）、原位U/Th-Pb和Sm-Nd地质年代学以及扩散模型来约束变质岩部分熔融的条件和时间。这项研究的独特之处在于，它不仅确定了变质作用的绝对时间和相对时间，而且确定了特定的部分熔融反应及其进展，以及它们与变质岩心复合体的冷却和挖掘历史的关系。这一研究结果将对目前可能正在发生深熔作用的活动造山带核心的下地壳状况产生影响。作为这项研究的一部分，收集的样本和数据被纳入MetPetDB（美国国家科学基金会资助的变质地球化学数据库），以扩大现有的公共数据集，并作为新用户的例子，展示MetPetDB作为合作工具的使用。

The physical and chemical makeup of the deep crust is impossible to examine in situ. Thus, this part of the earth has remained enigmatic despite its significance for geochemical transport during episodes of mountain building as is important, for example, in the generation of ore deposits. Study of the deep crust can only be undertaken through examination of rocks that have been exhumed from great depths, and the focus of this research is to conduct such a study on rocks of a deeply exposed mountain core in Nevada, the Ruby-East Humboldt range. Rocks exposed in this range are metamorphic and, having originated at the Earth's surface, were subjected to elevated pressures and temperatures as a result of burial during the formation of the Rocky Mountains. In fact, these rocks were at sufficient depth that they began to melt and this melting caused major changes in the physical properties of the rock, similar to changes observed in a block of ice when it begins to melt and, subjected to forces of compression, begins to move rapidly. The hypothesis to be examined and tested in the present study is the degree to which this melting (the products of which can be observed in the present day rock outcroppings) contributed to the rapid upheaval, exhumation, and emplacement of these high-grade metamorphic rocks into the core of the mountain range. Many such partially-melted deep crustal metamorphic belts are exposed in the cores of mountain ranges, and the results of this study will be directly applicable to these other terranes, and may have profound implications for the evolution of mountain belts in general.Funding will allow the P.I. and his graduate student to gather the data necessary to test the hypothesis that partial melting in the Ruby Mountains-East Humboldt Range, Nevada, through related changes in rheology and strain rates, initiated emplacement of metamorphosed lower crustal rocks into the middle crust to set the stage for metamorphic core complex formation. This research will employ major and accessory mineral thermobarometry (including an application of the new Ti-in-quartz thermobarometer), in situ U/Th-Pb and Sm-Nd geochronology, and diffusion modeling to constrain the conditions and timing of partial melting of metapelitic rocks. What is unique about this study is that it will determine both the absolute and relative timing of not simply prograde/peak metamorphism, but of specific partial melting reactions, their progress, and how they relate to the cooling and exhumation history of a metamorphic core complex. Results of this study will have implications for present day lower crustal conditions in the cores of active orogenic belts that may be undergoing anatexis. Samples and data collected as part of this research, incorporated into MetPetDB (the NSF-funded database for metamorphic geochemistry), acting to broaden the existing public dataset and serve as an example to new users, demonstrating the use of MetPetDB as a tool for collaboration.