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Sm-Nd and SHRIMP U-Pb zircon geochronology of high-pressure granulites in the Sanggan area,North China Cratontiming of Paleoproterozoic continental collision [查看] J.H.Guo、M.Sun、F.K.Chen、M.G.Zhai

Abstract High-pressure(HP)mafic granulites are widely distributed as sheet-like and lenticular bodies within highly deformed tonalitic gneisses in the Sanggan area.North China Craton.THey have clockwise isothermal decompression and isobaric cooling P-T paths implying continental collision tectonics,Whole-rock analyses of 15 samples define a Sm-Nd isochron yielding an age of 2547±87Ma withεNd(t)=2.7.Corresponding Nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites.A combined Sm-Nd mineral+whole-rock isochron from one of these samples yields an age of 1813±23Ma，taken to represent the metamorphic age at an early stage on the cooling path.SHRIMP U-Pb zircon analyses of three HP mafic granulite samles give uniform weighted mean 207Pb/206Pb ages of 1817±12,1817±12 and 1819±16Ma，these ages are interpreted to date metamorphism of the HP granulites and,with the Sm-Nd mineral＋whole-rock result,strongly suggest that the time of continental collision was at ca.1.82Ga.An additional sample records two age populations;one at 1803±9Ma and an older one at 1872±16Ma。The latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at ~1.82Ga.These results confirm the Paleproterozoic age of assembly of the North China Craton