西刚果夭折裂谷带内拉伸纪A型花岗岩的时代及地质意义OA

To investigate the tectonic setting of the West Congo aborted rift,zircon U-Pb geochronological and petrogeochemical analyses were performed on Quindegi granites in northwestern Angola.These granites yielded crystallization ages of(904±7)Ma and(905±6)Ma,corresponding to Neoproterozoic Tonian.The Quindegi granites are classified as A-type granites,originating from the fractional crystallization and assimilation of Gangila basaltic magmas.These granites are characterized by high silicon content(SiO2=64.35%-74.77%),low aluminum(Al2O3=12.52%-14.78%),rich potassium(K2O=4.09%-5.67%),and elevated TFeO(1.87%-6.04%).Their magmatic source is inferred to be high-temperature(TZr=783-891℃,avg.847 ℃),with a high 10 000Ga/Al ratio(avg.2.61)further supporting A-type affinity.Geochemically,the granites are enriched in light rare earth elements(LREE:La,Ce)and high-field-strength elements(HFSE:Zr,Hf),with marked depletion in HFSE(U,Ta,Nb,P,Ti)and large-ion lithophile elements(LILE:Sr).The pronounced depletion of HFSE,such as Nb,likely reflects crustal contamination related to thermal perturbations from external heat sources.Petrogeochemistry,zircon geochronological analysis,and the regional geological background indicated that the Quindegi granites were emplaced in a continental rift setting.They are part of the Bahia-Gangila Large Igneous Province and represent products of multiple-pulse magmatic activities.The West Congo Rift was an aborted intracontinental rift formed during the evolution of the Macaúbas Ocean driven by mantle plume activity.The abundant material supply and high-temperature heat input from the mantle plume created favorable conditions for the intrusion and emplacement of the Quindegi granite along the West Congo aborted rift.