The Dongjiangkou granitic pluton is exposed in the South Qinling terrain between the Shang-Dan and the Mian-Lue suture zones.This granitic pluton generally contains abundant mafic enclaves of different types.Results of zircon U-Pb dating for a granite and two mafic enclaves by using the LA-MC-ICPMS technique show that the Dongjiangkou granitic pluton crystallized in 223Ma and mafic enclaves formed simultaneously in 222Ma.This magmatism of early Mesozoic constrains the time of tectonic transformation from compression to extension in the Qinling orogenic belt.Hf isotopic composition of zircons obtained by the LA-MC-ICPMS technique suggests that the granitic pluton resulted from a mixing-mingling process between mantle-derived mafic magma and crustal-derived granitic magma.The mafic magma originated likely from depleted mantle,while basement rocks of the South Qinling(or Yangtze) terrain contributed major material source for the granitic pluton.This magmatic activity is attributed to lithospheric delamination during the post-orogenic stage of the Qinling orogenic belt.
The metamorphic rock belt in central Jiangxi Province, located in the compound terrain among the Huaxia terrain, the Yangtze terrain and the Caledonian fold zone of South China, is composed dominantly of meta argillo arenaceous rocks and small amounts of amphibolites. They underwent amphibolite facies metamorphism. The meta argillo arenaceous rocks show large variations in major element compositions, but have similar REE patterns and trace element compositions, incompatible element and large ion lithophile element enrichments [high Th/Sc (0.57～3.59), La/Sc (1.46～12.4) and La/Yb (5.84～19.0)] and variable Th/U ratios, with ∑REE=129～296 μg/g, δEu=0.51～0.86, (La/Yb)N=3.95～12.9. The rocks have a large variation range of Nd isotopic mode age tDM from 1 597 to 2 525 Ma and low eNd(0) from -9.9 to -15.8. The metamorphic rocks belt in central Jiangxi Province was likely formed in a tectonic environment of the passive continental margin of the Huaxia massif. The source region, from which the argillo arenaceous rocks were derived, was composed dominantly of upper crustal sources (Al and K rich granitic or/and sedimentary rocks of Early Proterozoic) and experienced good sorting, slow deposition and more intense chemical weathering. According to the whole rock Sm Nd isochron ages [(1 113±49)～(1 199±26) Ma] of plagioclase amphibole (schist) and Nd isotopic mode age tDM (1 597～2 525 Ma) of meta argillo arenaceous rocks, the metamorphic rocks belt was formed in Midproterozoic between 1 100～1 600 Ma.
