Geochemical characteristics and zircon U-Pb age of the gabbro-diorite in Jalaid Banner of Inner Mongolia and their geological significance

The gabbro-diorite in Jalaid Banner of Inner Mongolia shows typical calc-alkalic rock series. The rocks are enriched in LREE, LILE （K, Rb, Ba, Sr）, and U, and depleted in HFSE (Th, Ta, Nb, Ti), implying products of island-arc structure setting. The authors hold that the gabbro-diorite magma originated from lithospheric mantle, and the primary magma resulted from partial melting of mantle materials, with the mixture of small amounts of crust materials during the upward migration of the melt. LA-ICP-MS zircon dating shows that the formation age of the diabase, gabbro and diorite is 317.3Ma±1.1Ma (30 data points), 328.1Ma±1.3Ma (29 data points) and 325.2Ma±0.9Ma(32 data points) respectively. These are high-precision emplacement ages of intermediate-basic rock bodies obtained for the first time in Jalaid Banner area, which indicate that the subduction of oceanic crust existed in Jalaid Banner area at the end of early Carboniferous. The resulted obtained by the authors provide new evidence for further studying the Erenhot-Hegenshan collision collage belt which extended eastward to Jalaid area and its formation and evolution process.