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/或物理和化学改造的位置。因此，重要的是要确定在碰撞事件期间，大量岩石(地体)是如何添加到地壳中或从地壳中移除的。同样重要的是要了解这些环境的热史，包括时间、极端温度、热源和地质后果，包括经济矿藏的潜力。传统的地体增加理论涉及在现有大陆岩石下侵位冰冷的大洋地体。然而，最近的理论提出了一个过程(重新分层)，在这个过程中，热的、部分熔融的岩石侵位在地壳的底部。这项研究将在克拉马斯山脉地质省(CA和OR)检验这些理论，那里的古代重新分层潜力很大。这项研究还将为未来在其他地方重新分层的研究开发最佳实践，并将开发克拉马斯省详细的热史，可用于更好地了解经济资源、区域地质史和景观开发。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野外指南和基于网络的信息资源。由于重新分层涉及热的变质沉积岩在地壳底部的侵位，因此应该产生一些独特的地质特征，特别是：由于下地壳中重新变质的变质岩的污染，上复地体的快速加热和变质作用以及弧岩浆的下地壳改造。这项研究将通过详细的野外测绘和取样，严格限制相对于岩浆作用的变形和高级变质作用的时间。来自高品位混合岩和关键钉扎岩体的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限制。这些年龄将与野外和显微构造数据以及P-T估计(矿物平衡和假剖面)相结合，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采样将产生锆石，这些锆石将被分析氧同位素(SIMS)，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，从而描述重新分层作用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.