Collaborative Research: Geochronology of Carbonate Mineralization in the Lithosphere

固体地球在长期的地质碳循环中起着重要作用。 大气、海洋和地幔来源的CO2或富CO2流体与岩石圈中的硅酸盐矿物和/或溶解阳离子反应，在各种地质环境（区域变质作用、接触变质作用、俯冲带变质作用、大陆和海洋地壳中的热液和成矿系统、沉积盆地和风化作用）中形成次生碳酸盐矿物。 因此，通过这些碳酸化反应的二氧化碳进入次生碳酸盐的净速率，时间尺度和通量对全球碳循环平衡施加一阶控制，并通过流体流动和这些不同的岩石圈背景下的相关构造过程作为更广泛的化学运输的监视器。 为了询问和量化这些问题的速率，时间和CO2（和热液流体流一般）在岩石圈内的地质（即1万年）的时间尺度，准确和精确的碳酸盐地质年代计是必需的。 碳酸盐岩地质年代学已被证明是一个重大的挑战，由于自然的复杂性和分析的局限性。 本研究的重点是提高我们的能力，直接测量碳酸盐成矿时间的精炼和验证的U/Pb和Sm/Nd碳酸盐地质年代计。 其发展重点将是碳酸盐岩中较少测试的Sm/Nd系统，以及随后Sm/Nd和U/Pb数据的整合和交叉检查。 这项开发将利用BU和其他地方已经开发的新的分析和样品制备技术。 初步数据表明，碳酸盐矿物测年的Sm/Nd确实存在，但确切的上下文和身份的可测年的矿物？的发生并不清楚。 该团队将寻求通过以下方式完善碳酸盐地质年代学：1）仔细的样品表征，以确定最终被测年的确切矿物及其地质产状; 2）完善样品制备方法，以分离和提取可测年的共成因相，用于精确的Sm/Nd和U/Pb地质年代学分析; 3）建立测试碳酸盐地质年代学准确性的协议。 该项目将探索碳酸盐成矿的三种野外背景，包括1）区域变质碳酸盐，2）与硫化物/硫酸盐或成矿系统相关的热液碳酸盐，3）在温泉和海底形成的现代碳酸盐。该项目将为固体地球科学家提供新的工具，1）探索，量化，阐明了固体地球在全球地质碳循环中的作用; 2）探讨了岩石圈中流体流动的速率、时间和通量以及相关的化学输运和构造过程。 通过在BU和斯坦福大学的本科课程和高中外展计划，学生将接受教育，以固体地球在更广泛的地球科学问题，包括碳管理，气候和地球演化的相关性。 该项目将汇集两个地球化学家与互补的工具和利益，并将有助于建立新的实验室基础设施在斯坦福大学的早期职业PI。 推动这项研究的BU研究生将在BU和斯坦福大学实验室工作。

The solid earth plays a major role in the long-term geologic carbon cycle. Atmospheric, oceanic, and mantle derived CO2 or CO2-rich fluids reacts with silicate minerals and/or dissolved cations in the lithosphere to form secondary carbonate minerals in a variety of geological environments (regional metamorphism, contact metamorphism, subduction zone metamorphism, hydrothermal and ore-forming systems in the continental and oceanic crust, sedimentary basins, and weathering). The net rate, timescales, and fluxes of CO2 into secondary carbonates via these carbonation reactions thus exerts a first order control on the global carbon cycle balance, and serves as a monitor of broader chemical transport via fluid flow and related tectonic processes within these diverse lithospheric contexts. In order to interrogate and quantify these matters of rate, timing, and flux of CO2 (and hydrothermal fluid flow in general) within the lithosphere over geologic (i.e. 1 Myrs) timescales, an accurate and precise carbonate geochronometer is required. Carbonate geochronology has proven to be a significant challenge due to natural complexities and analytical limitations. This study is focused on improving our ability to directly measure the timing of carbonate mineralization by refining and validating both the U/Pb and Sm/Nd carbonate geochronometers. Its developmental emphasis will be on the less-frequently tested Sm/Nd system for carbonates, and on the subsequent integration and cross-checking of Sm/Nd and U/Pb data. This development will take advantage of new analytical and sample preparation techniques that have already been developed at BU and elsewhere. Preliminary data suggest that carbonate minerals datable by Sm/Nd do exist, though the exact context and identity of the datable mineral?s occurrence is not clear. The team will seek to refine carbonate geochronology by, 1) careful sample characterization to identify the exact minerals that are ultimately being dated as well as their geological occurrence, 2) refining sample preparation methods to separate and extract datable co-genetic phases for precise Sm/Nd and U/Pb geochronological analysis, 3) establish protocols for testing the accuracy of carbonate geochronology. Three field contexts of carbonate mineralization will be explored including 1) regional metamorphic carbonate, 2) hydrothermal carbonate associated with sulfide/sulfate or ore forming systems, and 3) modern carbonates forming at hot springs and on the sea floor.This project will provide new tools that solid-earth geoscientists can use to 1) explore, quantify, and illuminate the role of the solid-earth in the global geological carbon cycle, and 2) explore the rate, timing, and flux of fluid flow and associated chemical transport and tectonic processes in the lithosphere in general. Through undergraduate coursework and high school outreach programs in place at BU and Stanford, students will be educated as to the relevance of the solid earth in broader geoscience issues including carbon management, climate, and earth evolution. The project will bring together two geochemists with complementary tools and interests and will contribute to the establishment of new lab infrastructure at Stanford for an early career PI. The BU graduate student who will drive this research will contribute to work in both the BU and Stanford labs.