Characteristics of the Paleozoic metabasite in Baoshan Terrane:Implications for the tectonic evolution

The Baoshan Terrane is located on the southeastern margin of the Tibetan Plateau. Previous studies of the magmatism of the Baoshan Terrane were mainly focused on the Mesozoic and Cenozoic periods, whereas the study of the Paleozoic magmatism was relatively insufficient. In this paper, zircon U-Pb geochronology, geochemistry and Sm-Nd isotopes are presented for metabasite of Pumanshao Group in Bangmai area, Baoshan, Yunnan Province. The metabasites can be divided into two groups:amphibolite and biotite-plagioclase amphibolite. Zircon U-Pb geochronologic study shows that the two groups were formed at 536.7Ma and 532.0Ma, respectively. Geochemical characteristics indicate that the protolith of amphibolite was basaltic andesites and that of biotite-plagioclase amphibolite was alkaline basalt. REE and trace element distribution and diagrams for discriminating the tectonic settings reveal that the two groups have geochemical features of E-MORB and OIB, respectively. Combined with the regional tectonic setting, the authors hold that metabasites are products of Proto-Tethyan ridge subduction. During Late Neoproterozoic-Early Paleozoic, like things in the Lasha and Himalaya terranes, the Baoshan Terrane was situated on the margin of Gondwana too and experienced accre-tionary orogeny.