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

构造碰撞区是大陆地壳形成和（或）物理和化学变化的地点。因此，必须确定在碰撞事件中有多大的岩石（岩石）块被添加到地壳或从地壳中移除。从时间、极端温度、热源和地质后果（包括经济矿藏的潜力）方面了解这些环境的热历史也很重要。传统的地幔增重理论认为，冷大洋地幔侵位在现有大陆岩石之下。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、部分熔化的岩石被安置在地壳的底部。这项研究将测试这些理论在克拉马斯山地质省（CA和OR），在那里的潜力，古代再分层是强大的。该研究还将为其他地方未来的再分层研究开发最佳实践，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，旨在促进生态旅游的其他产品包括面向公众的实地指南和网上信息资源，由于再分层涉及热变质沉积岩在地壳底部的就位，因此应产生一些独特的地质特征，特别是：上覆火山岩的快速加热和变质作用，以及下地壳中再层变沉积岩的混染导致的弧岩浆的下地壳改性。这项研究将通过详细的实地测绘和取样，严格限制变形和高级变质作用相对于岩浆作用的时间。高品位混合岩和关键针扎岩体中锆石和金红石的高精度（CA-ID-TIMS）U-Pb年龄将提供造山事件的年龄约束。这些年龄将与现场和显微构造数据和P-T估计（矿物平衡和假截面）相结合，以开发一个完整的压力-温度-时间-变形（P-T-t-D）的历史。在时间和空间上跨越增生事件的岩体的区域采样将产生锆石，这些锆石将被分析氧同位素（西姆斯），并通过LA-ICPMS测定和分析Hf同位素，以表征岩浆源和污染物的时间和空间变化，从而反映由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.