Geochemical Characteristics and Tectonic Significance of Granite from Nanfen Metamorphic Core Complexes in Liaoning

The Gongchangling granite is the part of Nanfen metamorphic core complex and is also an important part of the Precambrian basement of Anshan-Benxi area. In order to investigate the tectonic significance of North China craton in Neoproterozoic to Paleoproterozoic, the Gongchangling granite in the Nanfen metamorphic core complex was selected as the research object. LA-ICP-MS U-Pb analyses of 2 zircon samples yield the upper intercept ages of 2 505±14 Ma (MSWD=1.30, n=70) and 2 507±11 Ma (MSWD=1.16, n=80), which represents the crystallization time of the magma. The studied samples have high SiO₂ of 70.14% to 75.36%, K₂O of 3.12% to 6.84%, Al₂O₃ of 11.78% to 13.75% and total alkali (Na₂O+K₂O) of 7.8% to 9.64%.The samples show Rittmann index(δ) from 1.98 to 2.94, and AR from 3.6 to 9.1, which suggests that the granite is enriched in silicon and alkali. A/CNK=0.95-1.23, with the majority of more than 1.11, indicate that it is peraluminous rock. Results show ∑REE=177.15×10^-6-505.64×10^-6, La_N/Yb_N=8.14-29.92, obvious fractionation of LREE to HREE, enriched LILE, such as Rb, Th, Zr, Hf, depleted of Nb, Ti and other elements. The geochemical characteristics of rocks indicate that the Gongchangling granite was formed by partial melting of the crustal argillite in the collision tectonic setting of the continental block through differentiation and crystallization. It is indicated that the Anshan-Benxi area was in the transition period in 2.50 Ga from post-collision to stable stage after assemblage of the continental blocks.