Tracing Lithosphere formation and evolution with highly siderophile elements and Os isotopes

高亲铁元素（HSE）与Os同位素的结合显示出它们是地幔形成和次生套印（地幔交代）的有力示踪剂。正是由于90年代初精确的Re-Os年代学的出现，大陆地壳与下伏岩石圈地幔的共同演化才首次得到广泛论证。大陆的形成和演化是地球科学最基本的方面之一，它与生命演化、矿石成因、地球物质循环等诸多问题密切相关。尽管经过数十年的深入研究，最早的大陆核是如何形成的，壳幔耦合是何时发生的，以及大陆岩石圈是如何演变的细节尚未确定。这是法兰克福大学正在进行的一项研究工作，在那里，Lu-Hf同位素系统越来越多地被用作获得地壳和地幔样品精确等时线年龄的有前途的工具。然而，这种方法仅限于熔融交代作用最小的地幔部分。由于Os在地幔中的相容性和在流体和熔体中的低丰度，Os同位素可以独特地“经受”二次叠印。这种套印的严重程度和影响可以通过HSE丰度模式来监测。我正在申请资金，将Os同位素和HSE丰度的测量带到法兰克福大学，使用现有的设施和仪器。一旦建立起来，我将把这项技术应用到纳米比亚的一小组橄榄岩捕虏体上，这些捕虏体的年龄目前还不清楚，它们是一个正在进行的地壳-地幔耦合项目的主题。

Highly siderophile elements (HSE) in combination with Os isotopes have revealed themselves as powerful tracers of mantle formation and secondary overprint (mantle metasomatism). It was owing to the advent of precise Re-Os geochronology in the early 90ies that the co-evolution of continental crust and underlying lithospheric mantle was first broadly demonstrated. The formation and evolution of continents is one of the most fundamental aspects of Earth Sciences that is closely related to questions of the evolution of life, ore genesis, the Earth’s material cycle, among many others. Despite decades of intensive research, the details of how the earliest continental nuclei formed, when crust-mantle coupling occurs and how the continental lithosphere evolves have yet to be determined. This is an ongoing research effort at Frankfurt University where the Lu-Hf isotope system is increasingly used as a promising tool to obtain precise isochron ages on crust and mantle samples. However, this approach is restricted to mantle portions where melt-metasomatism can be shown to be minimal. Because of the compatibility of Os in the mantle and much lower abundances in fluids and melts, Os isotopes can be singularly able to “weather” secondary overprints. The severity and the effects of such overprints can be monitored by HSE abundance patterns. I am applying for funds to bring the measurement of Os isotopes and HSE abundances to Frankfurt University, using facilities and instrumentation already available. Once instituted, I will apply the technique to a small suite of peridotite xenoliths from Namibia whose age is so far ill-constrained and which are the subject of an ongoing project on crust mantle coupling.