E-catalog        

Библиогр.: 65 назв.

A newly found tholeiitic intrusive suite in Chigu Tso of the Comei LIP (large igneous province), SE Tibet, provides new insight into the petrogenesis of tholeiitic intermediate rocks in LIPs. Zircon U-Pb dating results suggest that Chigu Tso intrusive suite is coeval to the Comei LIP at c. 132 Ma. The compositions of Chigu Tso intrusive suite exhibit a compositional continuum from dolerite, diorite to tonalite (SiO2=51.2-62.6 wt %). Mass balance calculations suggest that high FeO^/MgO (> 3.4) tholeiitic intermediate rocks (diorites and tonalites) in Chigu Tso could be generated by large degrees (~60-85 wt %) of fractional crystallization from low FeO^/MgO (~0.7) primary magmas. The occurrence of significant amounts of halogen-rich amphibole in tholeiitic intermediate rocks indicates volatile-rich conditions in the late differentiation stage and requires a prolonged shallow crustal magma chamber provides room for cooling and differentiation (up to 75 wt % fractional crystallization). Extensional stress field in rift zones are not favorable to generate shallow crustal magma chamber which results in limited site for producing highly evolved tholeiitic intermediate rock. The paucity of intermediate rocks in LIPs suggest that most silicic rocks should derived from partial melting of rather than fractional crystallization of basaltic materials.