Timming of Lithospheric Extension in Northeastern China:Evidence from the Late Mesozoic Nianzishan A-Type Granitoid Complex

New zircon U-Pb dates obtained by laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS),whole-rock geochemical data and Sm-Nd and Rb-Sr isotopic data are presented for miarolitic alkaline granites,porphyritic syenite and rhyolites of the Nianzishan A-Type granitoid complex(NAGC)in the Great Xing'an Range-Songliao Basin in Northeast(NE)China.New crystallization ages of 112.95±0.93 and 114.1±1.71 Ma for granite and 118.6±0.51 Ma for porphyritic syenite were determined by high-precision LA-ICP-MS.The εNd(t)of the rocks range from +1.85 to+2.06,with Nd model ages(T(DM1))from 671 to 821 Ma,indicating that the NAGC originated from juvenile source rocks and exhibits geochemical characteristics of A1-and A-Type granite which formed in an extensional setting.We attribute the magmatism to regional extension and lithospheric thinning caused by the subduction of the western Pacific Plate about 120 to 100 Ma.

New zircon U-Pb dates obtained by laser ablation inductively coupled plasma mass spectrometry（LA-ICP-MS）,whole-rock geochemical data and Sm-Nd and Rb-Sr isotopic data are presented for miarolitic alkaline granites,porphyritic syenite and rhyolites of the Nianzishan A-type granitoid complex（NAGC）in the Great Xing’an Range-Songliao Basin in Northeast（NE）China.New crystallization ages of 112.95±0.93 and 114.1±1.71 Ma for granite and 118.6±0.51 Ma for porphyritic syenite were determined by high-precision LA-ICP-MS.The εNd（t）of the rocks range from +1.85 to+2.06,with Nd model ages(TDM1)from 671 to 821 Ma,indicating that the NAGC originated from juvenile source rocks and exhibits geochemical characteristics of A1-and AA-type granite which formed in an extensional setting.We attribute the magmatism to regional extension and lithospheric thinning caused by the subduction of the western Pacific Plate about 120 to 100 Ma.