SHRIMP Zircon U-Pb Ages and Geochemical Characteristics of the Neoproterozoic Granitoids in the Huangling Anticline and Its Tectonic Setting

SHRIMP zircon U-Pb dating of the Neoproterozoic Maoping series (Sandouping (rock suite) granites exposed in the southern part of the Huangling anticline shows that the formation time of Sandouping biotite-hornblende tonalite intrusion, Jinpansi hornblende-biotite tonalite intrusion, and Longtanping monzogranite are 863 +/- 9, 842 +/- 10, and 844 +/- 10 Ma, respectively. Their geochemical features include A/CNK=0.98-1.06, from metaluminous to weakly peraluminous, delta=1.37-1.53, Sm/Nd=0.17-0.24, and Rb-N/Yb-N=1.1-3.62. These indicate that the granite rocks are supersaturated SiO2 calc-alkaline granitoids. The characteristic of Sr-Nd isotopic composition is that the values of epsilon(Nd)(t) and epsilon(Sr)(t) are -12.4 to -11.0 and 20.2-32.2, respectively. It also suggests that the material source of the granite rocks mainly originated from the crust, and they formed in a volcanic arc tectonic environment. These facts suggest that the occurrence of Neoproterozoic granitoids in the southern part of the Huangling anticline should be related to an arc environment along an active continental margin caused by southward subduction of oceanic crust beneath the northern Yangtze craton, and the formation age is not later than 863 Ma.