ZIRCON SHRIMP GEOCHRONOLOGY AND GEOCHEMISTRY OF LATE PERMIAN HIGH-MG ANDESITES IN SELUOHE AREA, JILIN PROVINCE, CHINA

Abstract

High-Mg andesites occur in Seluohe, Jilin, China, which are dated at 252 ± 5 Ma by the SHRIMP zircon U-Pb method, indicating that they were generatod in the Late Permian. The high-Mg andesites (SiO2 59.08% - 65.67%) are geochemically characterized by high MgO (3.68% - 5.30 %) and high Mg# (0.62 - 0.68, avg. 0.66) in association with enrichments of Cr (203.17 × 10-6 - 379.70 × 10-6, avg. 258.79 × 10-6) and Ni (98.13 × 10-6 - 249.35 × 10-6, avg. 137.00 × 10-6). These andesites are strongly enriched in light rare earth elements (Ce 39.14 × 10-6 - 48.74 × 10-6) and large-ion-lithophile elements (such as Cs, K, Pb, Rb and Ba), and are also characterized by depletion of high-field-strength elements (such as Ta, Ti, Nb and P) and heavy rare earth elements (Yb 0.95 × 10-6 - 1.27 × 10-6, Y 10.80 × 10-6 - 13.13 × 10-6, (La/Yb) N13.27 - 16.66). In addition, the andesites have low Sr concentrations (158.62 × 10-6 - 369.77 × 10-6, avg. 258.52 × 10-6). Considering that the high-Mg andesites are a medium-K, cale-alkaline suite with assimilaton-fractional crystallization, it is suggested that Seluohe high-Mg andesites were most likely derived from the partial melting of enriched mantle wedge materials induced by hydrous fluid from subducted sediments in a subduction zone and then experienced assimilaton-fractional crystallization during ascending. It is thus concluded that Paleo-Asian ocean plate was presumably in the process of subduction during the late Permian, and the collision between North China and Jiamusi-Khanka plates might lake place after the Permian.