Subcretion Versus Relamination: Testing Processes of Lower Crustal Modification in the Klamath Mountain Accretionary Province

构造碰撞带代表大陆地壳形成和/或物理和化学变化的位置。因此，确定在碰撞事件中有多少大块岩石（地体）被添加到地壳或从地壳中移除是很重要的。从时间、极端温度、热源和地质后果（包括潜在的经济矿床）等方面了解这些环境的热历史也很重要。传统的地体添加理论涉及在现有的大陆岩石下放置寒冷的海洋地体。然而，最近的理论提出了一个过程（再分层），在这个过程中，热的、部分融化的岩石被安置在地壳的底部。这项研究将在克拉马斯山地质省（CA和OR）测试这些理论，那里的古再分层潜力很大。该研究还将为未来其他地方的再分层研究提供最佳实践，并将开发克拉马斯省的详细热历史，可用于更好地了解经济资源、区域地质历史和景观发展。最后，由于该地区的经济越来越依赖旅游业，为促进生态旅游而设计的其他产品包括面向公众的实地指南和基于网络的信息资源。由于复层作用涉及热变质沉积岩在地壳底部的侵位，因此会产生许多独特的地质特征，特别是：上覆岩层的快速升温和变质作用，以及由于下地壳中复层变质沉积岩的污染而导致弧岩浆的下地壳变质。该研究将通过详细的野外填图和取样，严格限定相对于岩浆作用的变形和高变质作用的时间。高品位杂岩和关键钉钉岩体中锆石和金红石的高精度（CA-ID-TIMS） U-Pb年龄将为造山事件提供年龄约束。这些年龄将与现场和微观结构数据以及P-T估计（矿物平衡和伪剖面）相结合，以形成完整的压力-温度-时间-变形（P-T-t- d）历史。在时间和空间上跨越增生事件的区域取样将获得锆石，并将通过LA-ICPMS分析氧同位素（SIMS）和Hf同位素的年代，以表征岩浆来源和污染物的时空变化，从而表征再分层引起的下地壳结构的变化。

Tectonic collision zones represent locations in which continental crust is formed and/or physically and chemically modified. It is therefore important to determine how large masses of rock (terranes) are added to or removed from the crust during collision events. It is also important to understand the thermal history of these environments in terms of timing, temperature extremes, sources of heat, and geologic consequences, including potential for economic mineral deposits. Traditional theories for terrane addition involves emplacement of cold oceanic terranes beneath existing continental rocks. However, recent theories suggest a process (relamination) in which hot, partially melted rocks are emplaced at the base of the crust. This research will test these theories in the Klamath Mountain geologic province (CA and OR), where the potential for ancient relamination is strong. The research will also develop best practices for future studies of relamination elsewhere and will develop a detailed thermal history of the Klamath province that can be used to better understand economic resources, regional geologic history, and landscape development. Lastly, because the economy of the area is becoming increasingly dependent on tourism, additional products designed to promote eco-tourism include field guides and web-based information resources for the general public.Because relamination involves emplacement of hot metasedimentary rocks at the base of the crust, a number of distinctive geologic features should result, in particular: rapid heating and metamorphism of the overlying terranes and lower-crustal modification of arc magmas due to contamination by relaminated metasedimentary rocks in the lower crust. The research will tightly constrain the timing of deformation and high-grade metamorphism relative to magmatism through detailed field mapping and sampling. High-precision (CA-ID-TIMS) U-Pb ages on zircon and rutile from high-grade migmatites and key pinning plutons will provide age constraints of orogenic events. These ages will be combined with field and microstructural data and P-T estimates (mineral equilibria and pseudosections) to develop a complete Pressure-Temperature-time-Deformation (P-T-t-D) history. Regional sampling of plutons that span accretionary events in both time and space will yield zircons that will be analyzed for oxygen isotopes (SIMS) and dated and analyzed for Hf isotopes by LA-ICPMS to characterize temporal and spatial changes in magma sources and contaminants, and thereby the changes in the lower crustal architecture caused by relamination.