In this study, we present whole-rock geochemistry and Sm-Nd data; zircon trace element, U-Pb, and Lu-Hf data; titanite U-Pb dating; and structural analysis of igneous and metasedimentary rocks of the Sawtooth metamorphic complex that provide insight into regional metamorphism, partial melting, and crustal thickening in the Idaho batholith segment of the Cordilleran orogen. Four magmatic events are revealed: (1) pre-tectonic felsic magmatism at ca. 156 Ma, (2) syn-tectonic mafic and felsic magmatism between ca. 100 Ma and ca. 92 Ma, (3) felsic magmatism concurrent with late-stage deformation at ca. 89–84 Ma, and (4) post-tectonic felsic magmatism at ca. 77 Ma. The multiple generations of felsic magmatism include a variety of sedimentary- and igneous-derived granitoids distinguished by zircon trace element compositions (e.g., U/Ce versus Th and Ce/Sm versus Yb/Gd) and were sourced from progressively more evolved crustal components as shown by Lu-Hf and Sm-Nd isotopic data. U-Pb data of metamorphic zircons and titanites from high-grade metasedimentary rocks suggest that regional metamorphism occurred from ca. 100–93 Ma, which was characterized by granulite-facies partial melting and concurrent growth of metamorphic zircons and garnets. The episodic magmatism in the Sawtooth metamorphic complex records pervasive melt migration in a hot, mid-crustal setting at ca. 100–92 Ma and additional magma ascent in a cool, upper-crustal setting at ca. 77 Ma. The uplift of the Sawtooth metamorphic complex from mid- to upper-crust was likely caused by underthrusting at lower crustal levels coupled with erosion and thinning of the upper crust. This work suggests that the crust of the Cordilleran hinterland in the Idaho batholith region underwent significant thickening from ca. 100–84 Ma, and a crust of Andean-like thickness was probably achieved by ca. 84 Ma. By ca. 77 Ma, the central Idaho crust started to thin likely due to mid-crustal flow and surface erosion. The new data from the Sawtooth metamorphic complex are consistent with the two major magmatic flare-ups in the Late Jurassic and Late Cretaceous in the U.S. Cordilleran orogen.

中文翻译：

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美国科迪勒拉腹地的中生代地壳熔融和变质作用：来自爱达荷州中部锯齿变质复合体的见解

在这项研究中，我们提供了全岩地球化学和 Sm-Nd 数据；锆石微量元素、U-Pb 和 Lu-Hf 数据；钛石 U-Pb 测年；锯齿变质复合体的火成岩和变沉积岩的结构分析，提供对科迪勒拉造山带爱达荷州基岩段的区域变质作用、部分熔融和地壳增厚的深入了解。揭示了四个岩浆事件：（1）约 156 Ma, (2) 同构造基性岩浆和长英质岩浆作用之间的约。100 马和约。92 Ma，(3) 长英质岩浆作用与大约在晚期变形同时发生。89-84 Ma，和 (4) 大约在构造后的长英质岩浆作用。77 马。多代长英质岩浆作用包括各种以锆石微量元素组成（例如，U/Ce 与 Th 和 Ce/Sm 与 Yb/Gd），并且来源于逐渐演化的地壳成分，如 Lu-Hf 和 Sm-Nd 同位素数据所示。来自高品位变质沉积岩的变质锆石和钛铁矿的 U-Pb 数据表明区域变质作用发生于约 100-93 Ma，以麻粒岩相部分熔融和变质锆石和石榴石同时生长为特征。Sawtooth 变质复合体中的间歇性岩浆活动记录了大约 10 年在炎热的中地壳环境中普遍的熔体迁移。大约 100-92 Ma 和额外的岩浆上升在凉爽的上地壳环境中。77 马。锯齿变质杂岩从中地壳向上地壳的隆升很可能是由于下地壳水平的逆冲作用以及上地壳的侵蚀和减薄造成的。这项工作表明，爱达荷州基岩地区科迪勒拉腹地的地壳从大约 10 年开始显着增厚。100-84 Ma，大约在 100-84 Ma 形成了类似安第斯山脉的厚度的地壳。84 马。通过约。77 Ma，由于中地壳流动和地表侵蚀，爱达荷州中部地壳开始变薄。锯齿变质复合体的新数据与美国科迪勒拉造山带晚侏罗世和晚白垩世的两次主要岩浆爆发一致。