Regional Differences of Magmatism in the Okinawa Trough

Zong Tong; Zhai Shikui; Yu Zenghui

doi:10.3799/dqkx.2016.085

Abstract：Okinawa Trough is a young and active back-arc basin located at active continental margin in the western Pacific, which is in the initial stage of spreading and characterized by widespread extensional faults and intense volcanic activities.Dis-tribution and geochemistry of rocks show distinct differences of magmatism in the central and southern Okinawa Trough,but the reason is unclear so far.To explore this issue,we study comprehensively published petrologic and geochemical data,com-bined with Pb isotopic composition of basalts in Okinawa Trough in this paper.It is found that mantle source beneath Okinawa Trough and the trench-arc-basin system in which the Okinawa Trough is located belongs to Indian Ocean-type mantle,and ba-salts derived from southern Okinawa Trough are products of higher degree of mantle melting relative to basalts from middle Okinawa Trough.Basalts derived from Okinawa Trough are affected by the subduction component and extent of the effect of subduction component on magma source in the southern Okinawa Trough is higher than that in the middle Okinawa Trough, and the cause may be subducted depth of plate (southern:100-150 km;middle:about 200 km);only a few basalts are similar to MORB-type,which is considered to be an important characteristic and evidence of spreading in the Okinawa Trough.On the basis of the above analysis,we suggest that the studies of magmatism in the Okinawa Trough shall be focused on the following aspects in the future:identification and distribution of basement rocks,the types and characteristics of magmatic mantle source,the restriction mechanism and contribution of subduction to magmatism,and the internal relation between magmatism and hydrothermal activities.