Age dating,geochemistry and petrogenesis of the Arenshaobu gabbro masses in the Wurinitu region,northern Inner Mongolia

The present paper deals,in detail,with the major element,trace element and rare earth element characteristics of the Arenshaobu gabbro masses in the Wurinitu region,northern Inner Mongolia,with the stress on the petrogenesis,origins of the primitive magmas and their geological implications.The Arenshaobu gabbro masses have SiO2 contents of 49.62 %,Al2O3 contents of 17.34 %,CaO contents of 8.94%,TiO2 contents of 1.44%,and P2O5 contents of 0.26%.The gabbro masses are enriched in LILE,and depleted in HFSE.The higher Mg# values(0.28–0.68,with an average of 0.52) suggest the origin of the mantle-derived primitive basaltic magmas with lower degrees of crystallization and differentiation during the ascending processes of the magmas.The zircon U-Pb ages are dated at 309 ± 2 Ma,indicating that the crystallization ages of Arenshaobu gabbro masses may be dated back to the Late Cretaceous.The crystallization temperatures are measured at 928℃ for quartz,and 1206℃ for plagioclase.The depths for the magmatic colling and mineral cocrystallization are more than 10 km,and the crystallization of the Arenshaobu gabbro masses occurred in the deeper-seated magma chambers.The continental-margin arc geochemical signatures of the Arenshaobu gabbro masses have mirrored that the subduction,replacement and enrichment in the mantle source areas might have taken place prior to the formation of the magmas.