Neoproterozoic subduction of the south section of Qin-Hang orogenic junction belt: Evidence from the geochronology and geochemistry for the metabasite in Guizi melange, western Guangdong Province, South China

The Yangtze and Cathaysia blocks had integrated and formed the Qin-Hang orogenic juncture belt (QHOJB) along Jiangshan-Shaoxing fault since Neoproterozoic. The complex tectonic evolution of the QHOJB have attracted considerable attentions. The Guizi melange is located in the southern section of QHOJB. According to the field geological observations, the tectonic blocks are strongly deformed metamorphic metabasite and deep-sea chert, matrix rocks are quartzite, mica-schist and manganese enriched siliconargilaceous rock with Bouma sequence. A set of U-Pb zircon geochronological and elemental data for the metabasite from Guizi melange are present in this paper. The metabasite yields a weighed mean 206Pb/238U age of 94811Ma. Based on the SiO2, Na2O, K2O, these samples belong to calc-alkaline series except for a small portion of tholeiitic series. CIPW standard mineral compositions are similar to quartz tholeiite-olive tholeiite. They also show high TiO2 (average 1.85%), P2O5 (average 1.85%), no or slightly negative Eu anomaly, moderate LREE/HREE fractionation (presented by chondrite normalized (La/Yb)(N)=2.65 similar to 3.89, LILE (Rb, Ba, Th, U) enriched and HFSE (Nb, Zr, Hf) slightly depleted characteristics. Such geochemical signatures indicate that they are typical subduction-related arc volcanic rocks. In addition, Nb (7.56x10(-6)similar to 16.11x10(-6)), Nb/U (18.39 similar to 25.65), (Nb/La)(N) (0.76 similar to 0.94, primary mantle normalized) are similar to those Nb-enriched basalts instead of typical island arc basalts. Combining with geological and geochemical study, this paper suggests the Guizi tectonic melange is the record of Neoproterozoic paleo South China Ocean subduction in the southern section, providing an important clue for the southeast boundary of QHOJB.