关键词: 建平杂岩, 变基性岩, 岩石成因, 板块构造, 新太古代, 辽西

Abstract:

Based on the field work, LA-ICP-MS ziron U-Pb geochronology and geochemistry of the amphibolite and granulite from Jianping metamorphic complex in Western Liaoning Province, this study suggests that the metamorphic event of late Neoarchean and early Paleoproterozoic are mainly focused in 2 465-2 453 Ma and the age of crystallization is ~2 593 Ma. The two types of samples have relatively high Al₂O₃ (average is 14.49%) and high TiO₂ (average is 1.15%), which are similar to the rocks originated from ocean basalt. Mg# values  of samples have a larger variation(35-63)which indicate that magma maybe contaminated by mantle substances during their ascent. Ce/Yb-Ce diagram reflect that samples stem from garnet lherzolite mantle. Amphibolite and most granulites are characterized by enriched LREE ((La/Yb)N=5.67-10.87), and obvious depletion of Nb, Ta, Ti, which is similar to that of island arc basalt, while flat curve has a character of N-type MORB. Comprehensive analysis shows that the mafic magmatism is formed in an active continental margin tectonic setting in the late Neoarchean, and then metamorphosed during the process of collision. So it is suggested that the study area exists a tectonic regime similar to modern plate in late Neoarchean.

Key words: Jianping complex, metabasite, petrogenesis, plate tectonics, Neoarchean, Western Liaoning Province