Abstract:

The high-Mg andesite occurring in the Zhangsangou and Jinyinbie Formation-Complex in southern Jilin Province is dated at (2 493±12) Ma by the SHRIMP zircon U-Pb method, which indicates that it was generated in the Neoarchean period. The high-Mg andesite belongs to the cal-calkaline series. It is geochemically characterized by SiO₂ content of 53.93%-57.90%, high MgO (6.54%-8.82 %) and high Mg^# (0.68-0.71, avg. 0.69), associated with enrichments of Cr (270.66×10^-6-1 117.30 ×10^-6，avg. 443.62×10^-6) and Ni (141.74×10^-6-542.98×10^-6，avg. 250.50×10^-6). According to its high MgO, Cr and Ni, the high-Mg andesite is relate to the partial melting of mantle peridotites in genesis. On the other hand, the andesite is strongly enriched in light rare earth elements (Ce:38.34×10^-6-59.34×10^-6) and large-ion-lithophile elements (such as Sr, Cs, K, Pb, Rb and Ba), and is also characterized by depletion of high-field-strength elements (such as Nb, Ta, Ti and P) and heavy rare earth elements (Yb:1.38×10^-6-1.57 ×10^-6), which demonstrates geochemical characteristic of the arc volcanic rock. The high-Mg andesite was most likely derived from the products of interaction of slab-derived fluid or melt with mantle peridotites. It can thus be concluded that the high-Mg andesite was derived from the subduction zone and  there occurred the modern plate tectonics in the Neoarchean period.

Key words: Neoarchean, high-Mg andesite, geochemistry, Zhangsangou Formation-Complex, Jinyinbie Formation-Complex, Seluohe Group