Tectonic controls on porphyry copper formation in the western USA

项目背景美国西部的盆地和山脉省是一块超伸展的地壳，以前曾被100 Ma的造山作用增厚。该地区还以斑岩铜矿而闻名(图1)，主要形成于地壳挤压末期。然而，由于后来伸展对地貌的极端解剖，对地壳缩短及其与斑岩铜建造的关系的时空限制是有限的。在该省的大部分地区，挤压特征保存得很差，但变质核杂岩提供了一扇了解前伸展历史的窗口。该PHD项目将使用收缩结构和在选定的核心杂岩中保存的中下地壳残留物来限制伸展前地壳厚度的模式以及挤压的时间和持续时间，以调查与斑岩铜建造的潜在联系。项目目标和方法本项目旨在确定盆地和山脉省内伸展前挤压的规模和寿命的空间和时间模式，以与斑岩铜矿建造模式进行比较。这将通过构造和岩石学研究结合地质热压法、U-Pb锆石、Lu-Hf石榴石和原位Rb-Sr云母测年来实现[2]。有三个目标：1：识别收缩构造和约束古应力场。学生将识别和描述保存在一系列变质核杂岩中的收缩构造，以约束伸展前的古应力场。2：根据主要变质核杂岩的最大埋藏深度估计地壳厚度将使用地温压法和Lu-Hf石榴石年代学来确定选定的核杂岩中最大埋藏的规模和时间。最大埋藏深度将作为地壳厚度的替代指标，阐明地壳增厚的时间和空间模式。3：对同构造云母(如图2)的收缩变形持续时间和停止施加绝对限制，或对收缩构造内的锆石进行U-Pb测年[2，3]将对断层运动施加绝对限制，使学生能够构建整个区域的挤压空间和时间图像，可以与斑岩铜矿化进行比较。

Project Background The Basin and Range Province in the western USA is a hyperextended piece of the crust previously thickened by >100 Ma of orogenesis. The region is also notable for its porphyry copper deposits (Fig. 1), which mainly formed towards the end of crustal compression. However, due to the extreme dissection of the landscape by subsequent extension, spatial and temporal constraints on crustal shortening and its relationship to porphyry copper formation are limited. Across much of the province, compressional features are poorly preserved, but metamorphic core complexes offer a window into the pre-extensional history. This PhD project will use contractional structures and exhumed remnants of the middle to lower crust preserved within select core complexes to constrain patterns of pre-extensional crustal thickness and the timing and duration of compression to investigate potential links to porphyry copper formation. Project Aims and Methods This project aims to determine spatial and temporal patterns in the magnitude and longevity of pre-extensional compression within the Basin and Range Province to compare with patterns of porphyry copper formation. This will be achieved through structural and petrological investigation combined with geothermobarometry, U-Pb zircon, Lu-Hf garnet, and in-situ Rb-Sr mica dating [2]. There are three objectives: 1: Identify contractional structures and constrain the paleostress field The student will identify and characterize contractional structures preserved within a selection of metamorphic core complexes to constrain the pre-extensional paleostress field. 2: Estimate crustal thickness from the maximum burial depth of key metamorphic core complexes Geothermobarometry and Lu-Hf garnet geochronology will be used to determine the magnitude and timing of maximum burial in a selection of core complexes. Maximum burial depths will serve as a proxy for crustal thickness, elucidating temporal and spatial patterns of crustal thickening. 3: Place absolute constraints on the duration and cessation of contractional deformation In-situ Rb-Sr dating of syn-tectonic mica (e.g. Fig. 2) or U-Pb dating of zircons within contractional structures [2,3] will place absolute constraints on fault motions, allowing the student to build a spatial and temporal picture of compression across the region that can be compared with porphyry copper mineralisation.