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Paleoproterozoic Granitic Magmatism and Metamorphism in Middle Part of Luliang Range, Shanxi Province

YU Jin-hai, WANG De-zi, WANG Ci-yin, WANG Li-juan   

  1. National Laboratory of Mineral Deposits, Department of Earth Sciences, Nanjing University, Nanjing 210093, China
  • Received:2004-12-20 Revised:2004-12-20 Online:2004-12-20 Published:2004-12-20

Abstract: The studies on geochronology and geochemistry of granitoid rocks in Middle Laliang Mountain,Shanxi Province indicate that there are two periods of granitic magmatism in Paleoproterozoic,occurring at ca.2 063 Ma and 1 806 Ma,respectively.The earlier adamellites are characterized by low Si02,MgO,Y and Yb concentration,high AI203,Na20,Sr,Ba concentration and high Sr/Y ratio.The later monzonitic granites are characterized by high Si02,Rb,Nb,Y and Yb concentration,low Na20,AL2O3,Sr concentration and low Sr/Y ratio.The later also exhibit lower(La/Yb)n ratio and markedly negative Eu anomalies,implying their different origins.Combined with the Sr-Nd isotopic characteristics,the Daorengou adamelites are interpreted as resulting from partial melting of Paleo-to Meso-Archean crustal materials within mantle depth,and interacting with mantle wall rocks.The Kuanping granites were produced by partial melting of the garnet granulite and decomposing of garnets in the lower crust.Geological and geochemical evidences indicate that these two periods of magmatism took place in different tectonic settings.The early adamellites were related with collision setting,and the later monzonitic granites were formed in post-orogenic setting.T-P estimates for middle-high-grade metamorphic rocks of Laliang Group indicatethat the Laliang Group experienced isothermal decompression(ITD)metamorphism with clockwise FFt paths at near same time as second granitic magmatism,indicating a rapid ascending process.The later post-orogenic granite and the metamorphism with ITD path occurred at about 1 800 Ma,when magmatism and middle-high-grade metamorphism were widespread and strong in whole North China,implying that the North China Block was in extension tectonic setting from then.