Extreme oxygen isotope signature of meteoric water in magmatic zircon from metagranite in the Sulu orogen, China: Implications for Neoproterozoic rift magmatism

After many studies on geochronology, geochemistry and petrology of the eclogite from Bixiling have been done,its formation and metamorphic history are well known now. However,little work about elements and isotopes changes during the UHP metamorphism was conducted. The garnet Pb isotopes from Bxiling eclogites were studied by the stepwise-leaching technique in this paper. The Pb isotopic compositions obtained by different individual steps are various; However,the evolution trends of Pb isotopic compositions of different garnets and different progresses are almost consistent. The Pb-Pb isochron ages are about 3 billion years,which are different from the ages of protolith formation and UHP metamorphism obtained by precursors. Although the ages perhaps have no geologic significance,the results of stepwise-leaching may reflect that Pb isotopic compositions of the eclogite from Bixiling are mixture of materials from mantle and upper crust. In brief,the protolith of the eclogite was originated from mantle materials,and during rapid exhumation after the Triassic collison,the eclogites were matesomatized by the hydrous fluid with the upper crust Pb isotopic compositions.

Protolith

Isochron dating

Geochronology

Isotope Geochemistry

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Research on protolith of eclogite in main hole of Chinese Continental Scientific Drill project and its genetic instructions

The Journal of Geology (2013)

Jian Hu

Eclogite was the most common metamorphic rock in orogenic belt, it contained abundant geodynamic information. According to the contact relationship of country rocks, the eclogite from 0~2 000 m in the main hole of the Chinese Continental Scientific Drill (CCSD) could be classified into three types: symbiotic eclogite gneiss;eclogite adjacent to ultrabasic rocks and symbiotic eclogite ultrabasic rocks. Compared to the geochemical differences with the three types of eclogites, the authors considered that the protoliths of these rocks were probably the basic-untrabasic complex evolved from the single magma chamber by cumulation and fractional crystallization. The main source materials of these protoliths were derived from the enriched mantle by partial melting in subduction zone of oceanic crust downthrusted to the mainland under a back-arc extensional magmatism.

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Ultramafic rock

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