Plutonism Across the Tujunga-North American Terrane Boundary: A Middle to Upper Crustal View of Two Juxtaposed Magmatic Arcs

南加州的岩石学研究揭示了两个并列的中生代岩浆弧的中上地壳部分，一个是科迪勒拉造山带的原生地体，另一个是“外来的”图章格或圣盖博地体。先后侵入和定年的岩体及其热光晕的结晶热气压测量，为追踪两地造山带地壳的变深历史提供了“地壳钉子”。由于第三纪变质核杂岩中伸展滑脱断裂的下板块和中生代基底逆冲断裂的上板块这两种截然不同的构造环境，深中生代地壳现在暴露在地表。该提案的目标是记录中生代地质发展的本质，并将其作为地壳深度跨越地界的函数，并利用这些信息来限制科迪勒拉地区的增生历史。本文概述了这两个地块的岩体和寄主组合的岩石学研究。该方法以现场为基础，但包括岩石学、化学、同位素和矿物学研究，以评估从源区开始到上升和就位的深部套的演化。研究表明，这两个地体是在白垩纪中期形成的，如果不是在侏罗纪中期形成的话。图戎加地体表面上的“外来”性质，在很大程度上源于它的部分派生自中地壳。迄今为止的工作已经确定了地壳剖面，其中一个位于16至30公里的深度。这些中地壳岩石与浅层地壳岩石表现出明显的特征差异，包括元古代斜长岩+绿绿岩的赋存，以及中生代丰富的岩体，从罕见的钙二云母花岗岩到各种中间火成岩套，包括闪长岩、石英闪长岩和闪长岩。

Petrological studies in southern California have revealed middle to upper crustal portions of two juxtaposed Mesozoic magmatic arcs one being a native terrane of the Cordilleran orogen and the other "exotic" Tujunga or San Gabriel terrane. Crystallization thermobarometry of successively intruded and dated plutons and their thermal aureoles have provided "crustal nails" to track the variable depth history of orogenic crust in both terranes. Deep Mesozoic crust is now exposed at the surface by virtue of two contrasting tectonic settings - lower plates of extensional detachment faults in Tertiary metamorphic core complexes and upper plates of Mesozoic basement-cored thrust faults. The goal of this proposal is to document the nature of Mesozoic are development as a function of crustal depth across the terrane boundary and to utilize this information to constrain the accretionary history of this region of the Cordillera. This proposal outlines a petrological investigation of the plutons and host assemblages in both terranes. The approach is field based but includes petrologic, chemical, isotopic, and mineralogic studies to evaluate evolution of the plutonic suites from their inception at the source region to the condition of their ascent and emplacement. Work to suggests that the two terranes were accreted by mid-Cretaceous, if not by the middle Jurassic. Much of the apparent "exotic" nature of the Tujunga terrane stems from its partial derivation from the middle crust. Work to date has identified crustal sections that one resided at depths to 16 to 30 km. These middle crustal rocks exhibit several distinct characteristic differences from that at shallower crustal levels including the occurrence of Proterozoic anorthosite + charnockite and an abundance of Mesozoic plutons ranging from unusally calcic two-mica granitoids to a variety of intermediate igneous suites including diorite, quartz diorite, and tonalite.