Tectonic controls on porphyry copper formation in the western USA

项目背景美国西部的盆岭省是一片超伸展的地壳，其厚度在100 Ma以上的造山作用下增加。该地区还以其斑岩铜矿而闻名（图1），主要形成于地壳挤压末期。然而，由于随后的延伸，地壳缩短的空间和时间限制及其与斑岩铜矿形成的关系是有限的极端解剖景观。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个了解前伸展历史的窗口。该博士项目将利用保留在选定核心复合体中的收缩结构和中地壳至下地壳的挖掘残余来限制伸展前地壳厚度的模式以及压缩的时间和持续时间，以研究与斑岩铜形成的潜在联系。项目目标和方法本项目旨在确定盆岭省伸展前压缩的规模和寿命的空间和时间模式，以与斑岩铜矿形成模式进行比较。这将通过构造和岩石学研究结合地质温压法、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：一曰：识别收缩结构和约束古应力场学生将识别和表征保留在一系列变质核杂岩中的收缩结构，以约束伸展前的古应力场。第二章：根据关键变质核杂岩的最大埋藏深度估算地壳厚度将使用地热测压法和Lu-Hf石榴石地质年代学来确定选定核杂岩最大埋藏深度的大小和时间。最大埋藏深度将作为地壳厚度的代用指标，说明地壳增厚的时间和空间模式。第三章：对收缩变形的持续时间和停止施加绝对限制同构造云母的原位Rb-Sr测年（例如图2）或收缩构造内锆石的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压缩空间和时间图像，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.