新特提斯东西部蛇绿岩型铬铁岩的成因和地球动力学暗示

In recent decades podiform chromitites have attracted the attention of economic geologists as a potential target for the recovery of Platinum-Group Elements (PGE: Os, Ir, Ru, Rh, Pt and Pd). It is agreed that PGE in chromitites do not occur in solid solution within chromian spinel but they tend to form discrete phases the so-called “Platinum-Group Minerals” (PGM). Despite a great body of work, the exact links between PGM and ophiolitic chromitite formation are hotly debated. In addition, previous studies on the Os-isotope composition of ophiolitic chromitites revealed intriguingly variable 187Os∕188Os ratios. However, it is still unclear whether ancient Re depletions, inputs of radiogenic Os, mantle metasomatism or melt-fluid interaction are responsible for the measured Os isotope heterogeneities in podiform chromitites. It is supposed that combined mineralogical and isotopic studies may effectively explain the mechanism that is responsible for the formation of chromitites, thus providing significant information on their origin. In this proposal, we aim to recover PGM grains from the podiform chromitites of Eldivan ophiolite complex (Çankiri), Turkey and Kiogar ophiolite complex, SW China, using the hydroseparation (HS) technique in an attempt to obtain a representative assessment of the PGE-mineralogy in the investigated chromitites. Moreover, whole-rock analysis of the Re-Os isotopic system in the chromitites is expected to shed light on the processes that govern 187Os/188Os variations in the upper mantle of the chosen areas. In addition, Re-Os isotopic correlations will lead to age constraints with respect to major magmatic and/or deformational events indicative of the petrologic history of Neotethyan mantle. Lastly, a comparative study based on new and pre-existing mineralogical and compositional data between western and eastern Neotethyan chromitites is anticipated to complete the picture of mantle's petrogenetic evolution in the two branches of Neotethyan Ocean, from its initial spreading to its final emplacement onto the continental margin.

“豆荚状”铬铁岩中铂族元素(PGE)以“铂族矿物(PGM)”形式存在, 是探讨铂族元素成因和地球动力学演化的重要窗口，但现有研究对PGM与蛇绿岩中铬铁岩的成因关联仍不清晰。本项目拟在申请者前期工作基础上，选择土耳其Eldivan(Çankiri)和中国西南Kiogar蛇绿混杂体中的“豆荚状”铬铁岩为研究对象，采用水力分离技术 (hydroseparation)分离出代表性铂族矿物(PGM)，并从矿物学、同位素地球化学的角度对其开展精细研究，以揭示其成因及地球动力学意义。此外，通过铬铁岩的全岩Re-Os研究探索研究区上地幔中控制187Os/188Os比值变化的关键过程，通过Re-Os同位素相关研究为新特提斯地幔中曾经发生的大规模岩浆及(或)形变事件提供年代约束。基于本项目及前人研究数据的对比研究，尝试恢复新特提斯洋东西支从开始扩张到就位于大陆边缘的整个演化过程。

“豆荚状”铬铁岩中铂族元素(PGE)以“铂族矿物(PGM)”形式存在, 是探讨铂族元素成因和地球动力学演化的重要窗口，但现有研究对PGM与蛇绿岩中铬铁岩的成因关联仍不清晰。本项目拟在申请者前期工作基础上，选择土耳其Eldivan(Çankiri)和中国西南Kiogar蛇绿混杂体中的“豆荚状”铬铁岩为研究对象，采用水力分离技术 (hydroseparation)分离出代表性铂族矿物(PGM)，并从矿物学、同位素地球化学的角度对其开展精细研究，以揭示其成因及地球动力学意义。此外，通过铬铁岩的全岩Re-Os研究探索研究区上地幔中控制187Os/188Os比值变化的关键过程，通过Re-Os同位素相关研究为新特提斯地幔中曾经发生的大规模岩浆及(或)形变事件提供年代约束。基于本项目及前人研究数据的对比研究，尝试恢复新特提斯洋东西支从开始扩张到就位于大陆边缘的整个演化过程。