Geochemistry and petrogenesis of the Heyu batholith in the southern margin of the North China block.

Heyu batholith in Waifang Mountain,Henan Province,located in the southern margin of the North China block.It is a multi-stage intrusion with a total area of outcrop up to 784km2.Heyu batholith mainly consists of biotitic monzogranite and can be subdivided into 6 units.LA-ICP-MS zircon U-Pb dating of the Heyu batholith porphyry gives concordant ages of 148.2~135.3Ma.SiO2,Al2O3 and MgO contents are 67.16%~75.43%,13.29%~15.92% and 0.26%~1.12%,respectively.Heyu batholith is high K calc-alkaline and metaluminous-peraluminous,with K2O+Na2O8.0%,Na2O/K2O=0.82~1.43,ACNK=0.94~1.09.The rocks are relatively enriched in LREE and depleted in HFSE((La/Yb)N=14.5×10-6~49.9×10-6,average 27.2×10-6).Variable Sr content comparing with typical adakite(102×10-6~848×10-6,average 290×10-6) and low Y and Yb contents(Y=3.21×10-6~17.3×10-6;Yb=0.43×10-6~2.16×10-6),and slightly negative Eu anomaly(δEu=0.57~0.89) suggest that the fractional crystallization of the magma is obvious and a feldspar residual in the source is unlikely.The initial ISr ratio range from 0.7071 to 0.7090,and the eSr(t) value is 40.8~65.9.Negative eNd(t) value(-16.4~-11.2) with old tDM2 ages of 1.85~2.27Ga and negative eHf(t) values(-25.39~-5.25) with old tDM2 age of 1301~2846Ma suggest that the batholith was probably formed by partial melting of the south Qinling and Yangtze crystalline basement with the participation of Xiong'er Group and Taihua Group.In combination with the regional tectonic evolution,we suggested that the crust in the study area was thickened in early stage of intra-continental subduction of the Qinling orogenic belt intra-continent collision during Mesozoic,and the mantle-derived magma upwelling,and thereby the Heyu batholith formed in the southern margin of the North China Block.