Petrogenesis of diabase from accretionary prism in the southern Qiangtang terrane, central Tibet: Evidence from U- Pb geochronology, petrochemistry and Sr- Nd- Hf- O isotope characteristics.

The Bangong- Nujiang suture ( BNS) between the Lhasa and Qiangtang terranes is an important boundary and its petrogenesis is controversial. Diabase from the accretionary prism in the southern Qiangtang terrane yields a zircon U- Pb age of 181.3 ± 1.4 Ma. All the diabases show tholeiitic basalt compositions, gentle enrichment patters of light rare earth elements ( REE), variable enrichment in incompatible element concentrations (e.g. Th and Rb), and no anomaly in high field strength elements (e.g. Nb and Ta), similar to that of enriched mid-ocean ridge basalt ( E- MORB). They have relatively homogeneous whole rock Nd (ε Nd(t) = 7.3-9.1) and zircon Hf- O isotopic compositions (ε Hf(t) = 14.8-16.1, and δ18 O = 4.57-6.12‰), possibly indicating melting of the depleted mantle and no significant crustal contamination during the petrogenesis. The element variations suggest that the diabases were formed by plume-ridge interaction at a mid-ocean ridge within the Bangong- Nujiang ocean. [ABSTRACT FROM AUTHOR]