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个超伸展的地壳块，先前的造山运动使其变厚了100 ~ 100 Ma。该地区还以斑岩铜矿床（图1）而闻名，斑岩铜矿主要形成于地壳压缩末期。然而，由于后续伸展对地貌的极端解剖，地壳缩短及其与斑岩铜矿形成关系的时空约束有限。在该省的大部分地区，挤压特征保存得很差，但变质核杂岩为研究伸展前历史提供了一个窗口。该博士项目将利用收缩构造和在选定的岩心复合体中保存的中下地壳的出土残余物来约束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。项目目的和方法本项目旨在确定盆地和山脉省内伸展前压缩的大小和寿命的时空模式，并与斑岩型铜矿形成模式进行比较。这将通过构造和岩石学调查，结合地温压测量、U-Pb锆石、Lu-Hf石榴石和原位Rb-Sr云母测年来实现。本课程有三个目标：1 .识别收缩构造并约束古应力场学生将识别和描述在一系列变质岩心复体中保存的收缩构造，以约束伸展前的古应力场。根据关键变质岩心杂岩的最大埋藏深度估算地壳厚度。将使用地温测量和Lu-Hf石榴石年代学来确定选定岩心杂岩的最大埋藏幅度和时间。最大埋藏深度将作为地壳厚度的代表，阐明地壳增厚的时空格局。对同构造云母进行原位Rb-Sr测年（例如图2）或对收缩构造中的锆石进行U-Pb测年[2,3]将对断层运动进行绝对的限制，使学生能够建立一个跨区域压缩的时空图像，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.