The records of the evolution of Precambrian lithospher: the evidences of petrology and geochemistry of basic rocks on Hainan island.

The different characteristics of petrology and geochemistry for all kinds o f basic rocks with different times record the tectonic setting and the evol utionary history of lithosphere at Precambrian era on Hainan Island. At the Paleo-Mesoproterozoic era, the meta-basic-ultrabasic rocks on eastern Hain an are oceanic low K are tholeiite with the features of mafic-basaltic koma tiite evidently, originated from highly depleted mantle and are formed unde r the tectonic setting of volcanic are. Anyway, at the same time, in wester n Hainan, a kind of transitional basalt with low depleted mantle originatio n between MORBs and tholeiites is produced, the magma storeroom is a kind o f partial melting mixture made up of mantle wedge located over old-diving d epleted belt and crust material being involved into mantle wedge from deple ted belt. Their tectonic setting is back-are or inter-arc spreading basin. In Meso-Neoproterozoic era, the meta-basic-ultrabasic rocks in western Hain an have different petrological and geochemical compositions at the Paleo-Me soproterozoic era in eastern Hainan, they are different rock types with dif ferent time, different origination and different tectonic setting. The meta -basic-ultrabasic rocks in western Hainan are mafic-ultramafic komatiite or iginated from highly depleted mantle and being formed under the setting of the edge of oceanic ridge. Hereby. we can speculate that the evolution of l ithospher during Precambrian has undergone two events of the diving of pale oplate in the Paleo-Mesoproterozoic era and the rift of continent on Meso-N eoproterozoic era at least. following the appearence of ocean basin.