Petrology And Geochemistry Of Mesozoic Ore-Bearing Diorites In Taershan-Erfengshan, Southern Part Of The Taihang Mountain

The Taershan-Erfengshan iron skarn deposits, which located in the south Taihang mountains, central North China Craton(NCC). The diorites that hosted Taershan-Erfengshan deposits, namely Taershan and Erfengshan intrusions, yielded zircon U-Pb ages of 128.7±3.0Ma ~131.2±2.2Ma, which are in accordance with other Fe-skarn-related intrusions in eastern NCC, suggesting that they were related to same tectonic events. The existence of inherited Neo Archean and Paleoproterozoic zircons indicates the primary magmas of the Taershan and Erfengshan diorites are closely related to the lower crust of the NCC.Based on detailed observations in the Taershan-Erfengshan area and previous research results, we confirm that the skarn type iron deposit related dioritic rocks comprise monzonite(porphyritic quartz monzonite), monzodiorite and dioritic porphyrite. The dioritic rocks show porphyritic texture and massive structure, with mineral assemblage of plagioclase, K-feldspar, pyroxene, hornblende and accessory minerals of sphene、magnetite、ilmenite andapatite, etc.The geochemical data of ore-bearing diorites indicate that Taershan diorite belongs to calc-alkalic aluminum diorite and Erfengshan diorite belongs to alkaline aluminum diorite. The Harker diagram and Rb/Nd – Rb diagram of the Taershan-Erfengshan diorites indicate they are derived from one common source by different degrees of partial melting. At the same time, they also have similar geochemical characteristics, such as low contents of Si O2(57.17% ~ 65.51%), high contents of alkaline(Na2O = 5.07% ~ 6.72%,K2O= 2.27% ~ 6.77%), low Mg# values,enriched in LILEs(Sr、Ba) and LREEs and depleted in HFSEs(Ni、Ta、Ti). This paper infers that the primitive magma of the Erfengshan pluton was derived from the lower degree of melt from the source materials, whereas the Taershan pluton was derived from the higher degree of melt from the source.In comparison with the chronology and geochemistry data of Pingshun-Xi’anli、Anlin and Laiwu diorites, we propose that the Tershan-Erfengshan diorites wereoriginated from lithospheric thinning of the NCC. Besides, the destruction of NCC extended to the Midwest of Taihang mountain in Early Cretaceous. The asthenosphere upwelling caused by the delamination of lower crust in Handan-Xingtai triggered the partial melting of lower crust in Taershan-Erfengshan area and played an important role in the formation of skarn-type Fe deposits.