Metamorphic evolution,protolith and tectonic implications of mafic granulite from the Chentang area,Central Himalaya
This paper presents petrography,bulk-rock geochemistry,zircon U-Pb dating,and Hf isotope studies on high-pressure mafic granulites from the Chentang area,Central Himalaya.We identify metamorphic evolution and protolith features of mafic granulites and thus explore the tectonic significance.The mafic granulites showed obvious melting features in outcrops,symplectites of clinopyroxene and plagioclase were preserved which might be the decompression products of eclogite-facies metamorphism.The metamorphism of the mafic granulites was divided into three stages:(1)high-pressure granulite-facies metamorphism consists of Grt-Cpx-Pl-Rt-Qz under P-T conditions of 1.0～1.3GPa and 730～800℃;(2)mid-pressure granulite-facies metamorphism consists of Grt-Cpx-Opx-Pl-Ilm-Rt-Qz at 0.78～0.82GPa and 820～890℃;(3)amphibolite-facies metamorphism was characterized by wide occurrence of amphibole,under 0.6～0.7GPa and 660～740℃.Zircon U-Pb dating indicates that the high-pressure granulite-facies metamorphism occurred at 15～14Ma and the protolith age was～1800Ma.Based on the bulk-rock TiO2 content,the mafic granulites can be divided into two groups.Group Ⅰ exhibits low TiO2 but high εNd(t)and shows E-MORB REE patterns,which were associated with the back-arc setting.Group Ⅱ shows OIB alike REE pattern and has TiO2,REE,Th/Ta,and lower Mg#,Nb/La,and εNd(t).Geochemical evidence suggests that Group Ⅱ shows a similar magma source to Group Ⅰ but underwent significant crustal contamination during magma ascent.The Paleoproterozoic magmatic records were spread along the north-south direction,from the north Ama Drime Massif to Chentang,to the south Arun Valley.The exposure of the Paleoproterozoic records which were widely distributed in the Lesser Himalayan Sequence were related to the Cenozoic rift activity.Besides,this study confirms that the northern Indian margin was at the convergent plate boundary with widespread arc/back-arc magmatism rather than in a rift setting during the Paleoproterozoic(1.9～1.8Ga)era.
Central HimalayaMafic granuliteMetamorphismProtolithTectonics
NETL
NSTL
万方数据
维普
