Whole-rock Sr-Nd and zircon Hf isotopic data have been compiled for regional isotopic mapping. The 蔚Nd(t) values show large variations from 鈭?#xA0;7.0 to + 7.4 and Nd model ages (TDM) from 0.46 Ga to 1.43 Ga as well as the initial Sr isotopic ratios (Sri) from 0.7023 to 0.7174. The zircon 蔚Hf(t) values vary from 鈭?#xA0;4.6 to + 15.3 and give two-stage Hf model ages (TDM2) from 0.30 Ga to 2.09 Ga. The extremely large variations of whole-rock Sr-Nd and zircon Hf isotopes demonstrate strong isotopic heterogeneity of the source regions that are mainly dominated by juvenile components with significant old crustal participation. Furthermore, the late-stage granitoids in the NMTB, the CMEB and the AB generally have more negative 蔚Nd(t) values and more variable zircon 蔚Hf(t) values than those of the early-stage granitoids in the same belt, implying an increasing crustal signature from early- to late-stage in the assumed heterogeneous source regions within the same belt, which probably results from melting of shallower crust in parallel with a shift to more alkaline chemistry of the late granitoid magmas. By contrast, most late-stage granitoids in the SMXB and the BIJB have more positive 蔚Nd(t) values and homogeneous zircon 蔚Hf(t) values than those of the early-stage granitoids in the same belt, indicating more juvenile contribution to the source of the these granitoids.
The generation of the Early Mesozoic granitoid magmas in the NMTB and the CMEB was dominated by the ongoing closure of the Mongol-Okhotsk Ocean and some was probably related to a mantle plume process. They were possibly derived from subducted materials melting or juvenile components with some probable contributions from ancient continental crust. Early Mesozoic granitoid magmas in the SMXB, the AB and the BIJB were generated in a post-/non-orogenic setting after the closure of the Paleo-Asian Ocean and were the results of partial melting of crustal components in response to underplating of mantle-derived magmas, most likely linked to lithospheric thickening and delamination and asthenospheric upwelling. Early Mesozoic granitoid magmatism provides critical information on Mesozoic post-accretionary tectonic evolution of the Paleo-Asian Ocean and transitional tectonic regimes from Early Mesozoic subduction to Late Mesozoic closure of the Mongol-Okhotsk Ocean as well as post-accretionary continental growth.