Chronology and Geochemistry on Mesozoic Diorite from the Xi′anli Iron Ore Area in Pingshun, Shanxi Province

The Shanxi Pingshun region is located in the west limb of a large-scale anticline of Taighang Mountain and is to the southeast of the Taihang upwell of Lüliang-Taihang fault block. It is one of the most important skarn iron ore concentration areas in North China. The Mesozoic dioritic rock was the source rock for skarn Fe deposits. In this paper, the work carried out on zircon SHRIMP dating and geochemical analysis of Mesozoic magmatic rocks is described. The results of zircon ages for the gabbro and diorite were 123 Ma and 126 Ma, respectively (within the same intrusion periods). Magmatic rocks in the region were metaluminous high-K calc-alkaline series rocks and all the samples (Erfengshan diorite, Xi′anli gabbro and diorite) were characterized by similar REE patterns with enriched LREE (ΣLREE on average is 94.64 μg/g, 110.73 μg/g and 118.63 μg/g). The fractionation between LREE and HREE was not very strong since (La/Yb)_N on average were 9.47, 9.17 and 9.70. The Eu anomaly was not obvious as δEu on average were 1.00, 0.96 and 1.04. The gabbro and diorite were enriched Ba, Th, U, and other LILEs had the characteristic of high Sr and strongly depleted HFSEs (Nb, Ta). Combined with previous research results, indications are that the magmatic rocks were mainly from the mixing members between mantle-derived magma and the low crust-derived magma. High Nb/Ta (17 to 22, on average is 19) and Zr/Hf values (35 to 40, on average is 37) were inherited from the magmatic source features. This indicated that the mantle source was replaced by subducted slab melt/fluid. The geodynamic setting is Mesozoic destruction and a lithospheric thinning event in the North China Craton. However, the diversity of the mechanism should also be noted.