白云鄂博地区金伯利岩岩石学、地球化学及石榴子石研究意义OA

The breakup of the Columbia supercontinent is a key process in Precambrian plate tectonics and crustal geodynamic evolution.The Mesoproterozoic rift systems developed on the northern margin of the North China Craton(NCC)provide an extensive record of this major geological event.Although the Bayan Obo rift is a significant epicontinental rift zone on the northern margin of the NCC,as an important epicontinental rift zone on the northern margin of the North China Block,the relationship between its deep-seated magmatism,supercontinent breakup,and cratonic tectonic evolution remains unclear.This paper investigates kimberlites in the Bayan Obo area,discussing their petrogenesis,tectonic setting,and metallogenic significance through systematic analyses of field geological survey,petrology,geochemistry,and garnet mineralogy.The Bayan Obo kimberlites occur as dykes or pipes intruding the Bilute Formation of the Mesoproterozoic Bayan Obo Group;they exhibit porphyritic and brecciated textures,with significant alteration such as serpentinization,talcization,and carbonatization.Whole-rock geochemistry shows that the rocks have SiO2 contents of 31.5％～42.9％,MgO of 29.7％～36.8％,Mg#≈0.9,and generally low TiO2,consistent with deep-seated Mg-rich and Ti-poor ultramafic rocks.They are characterized by low total rare earth element(REE)contents,significant light REE enrichment,and distinct negative Eu anomalies,well preserving primitive magma signatures that correlate well with the ore-bearing kimberlites in Mengyin and Wafangdian.Garnets in the kimberlites are dominated by almandine(66％～67％),with high FeO and Al2O3 and low MgO and CaO,classified as amphibolite-facies Type G4 crust-derived garnets.Geothermobarometry yields garnet formation temperatures of 791±50 to 876±50℃and pressures of ca.1.4±0.3 GPa,corresponding to a mantle heat flow of ca.60 mW/m2.This heat flow is higher than that of typical ancient cratons,indicating an extensional setting characterized by lithospheric thinning setting.This study suggests that the Bayan Obo kimberlites originated from low-degree partial melting of garnet lherzolite in the lithospheric mantle of the northern NCC and formed in a Mesoproterozoic extensional tectonic regime triggered by the breakup of the Columbia supercontinent.A total of 139 diamond grains and indicator minerals,such as garnet,spinel,and diopside,have been discovered in this area,indicating favorable metallogenic conditions and great prospecting potential for diamonds.