The records of the evolution of Precambrian lithospher: the evidences of petrology and geochemistry of basic rocks on Hainan island
海南岛前寒纪岩石圈演化的记录：基性岩类岩石地球化学证据

The different characteristics of petrology and geochemistry for all kinds of basic rocks with different times record the tectonic setting and the evolutionary history of lithosphere at Precambrian era on Hainan Island. At the Paleo-Mesoproterozoic era, the meta-basic-ultrabasic rocks on eastern Hainan are oceanic low K arc tholeiite with the features of mafic-basaltic komatiite evidently, originated from highly depleted mantle and are formed under the tectonic setting of volcanic arc. Anyway, at the same time, in western Hainan, a kind of transitional basalt with low depleted mantle origination between MORBs and tholeiites is produced, the magma storeroom is a kind of partial melting mixture made up of mantle wedge located over old-diving depleted belt and crust material being involved into mantle wedge from depleted belt. Their tectonic setting is back-arc or inter-arc spreading basin. In Meso-Neoproterozoic era, the meta-basic-ultrabasic rocks in western Hainan have different petrological and geochemical compositions at the Paleo-Mesoproterozoic era in eastern Hainan, they are different rock types with different time, different origination and different tectonic setting. The meta-basic-ultrabasic rocks in western Hainan are mafic-ultramafic komatiite originated from highly depleted mantle and being formed under the setting of the edge of oceanic ridge. Hereby, we can speculate that the evolution of lithospher during Precambrian has undergone two events of the diving of paleoplate in the Paleo-Mesoproterozoic era and the rift of continent on Meso-Neoproterozoic era at least, following the appearence of ocean basin.