High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS
High Throughput Petrochronology and Sedimentary Provenance Analysis by Automated Phase Mapping and LAICPMS
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DOI：
10.1002/2017gc007109
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发表时间：
2017-10
期刊：
影响因子：
3.7
通讯作者：
P. Vermeesch;M. Rittner;E. Petrou;J. Omma;C. Mattinson;E. Garzanti
中科院分区：
文献类型：
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作者：
P. Vermeesch;M. Rittner;E. Petrou;J. Omma;C. Mattinson;E. Garzanti
大多数地质年代学研究的第一步是从主岩中提取可测年的矿物，这很耗时，去除了结构背景，并增加了样品交叉污染的机会。本文提出了一种将快速扫描电子显微镜(SEM)和能量色散X射线光谱仪(EDS)与激光烧蚀电感耦合等离子体质谱仪(LAICPMS)相结合的快速原位分析的新方法。给定抛光的手部样品、岩相薄片或颗粒座，扫描电子显微镜/能谱仪的自动相图(APM)可生成化学和矿物学图，从中提取可测年矿物的X-Y坐标。这些坐标随后被传递到激光消融系统进行同位素分析。我们将APM+LAICPMS方法应用于三个火成岩、变质和沉积案例研究。在第一个案例研究中，对来自根西岛的一块抛光的花岗岩平板进行了锆石扫描，得到了609±8 Ma的加权平均年龄。第二个案例研究了柴达木地体北部(青海，中国)超高压地体中的副片麻岩。用LAICPMS分析了107个小型(25µm)变质锆石，确定了419 Ma±4 Ma的峰期变质年龄。第三个也是最后一个案例研究使用APM+LAICPMS生成一个大型物源数据集，追踪安哥拉25种现代沉积物的物源，记录了1,500公里外橙河沉积物的沿岸漂移。这些实例表明，APM+LAICPMS是一种提高地质年代学数据数量和质量的有效和经济的方法。
The first step in most geochronological studies is to extract dateable minerals from the host rock, which is time consuming, removes textural context, and increases the chance for sample cross contamination. We here present a new method to rapidly perform in situ analyses by coupling a fast scanning electron microscope (SEM) with Energy Dispersive X‐ray Spectrometer (EDS) to a Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LAICPMS) instrument. Given a polished hand specimen, a petrographic thin section, or a grain mount, Automated Phase Mapping (APM) by SEM/EDS produces chemical and mineralogical maps from which the X‐Y coordinates of the datable minerals are extracted. These coordinates are subsequently passed on to the laser ablation system for isotopic analysis. We apply the APM + LAICPMS method to three igneous, metamorphic, and sedimentary case studies. In the first case study, a polished slab of granite from Guernsey was scanned for zircon, producing a 609 ± 8 Ma weighted mean age. The second case study investigates a paragneiss from an ultra high pressure terrane in the north Qaidam terrane (Qinghai, China). One hundred seven small (25 µm) metamorphic zircons were analyzed by LAICPMS to confirm a 419 ± 4 Ma age of peak metamorphism. The third and final case study uses APM + LAICPMS to generate a large provenance data set and trace the provenance of 25 modern sediments from Angola, documenting longshore drift of Orange River sediments over a distance of 1,500 km. These examples demonstrate that APM + LAICPMS is an efficient and cost effective way to improve the quantity and quality of geochronological data.