Crustally-derived granites in the Panzhihua region, SW China: Implications for felsic magmatism in the Emeishan large igneous province

Abstract

In the Panxi region of the Late Permian (~260Ma) Emeishan large igneous province (ELIP) there is a bimodal assemblage of mafic and felsic plutonic rocks. Most Emeishan granitic rocks were derived by differentiation of basaltic magmas (i.e. mantle-derived) or by mixing between crustal melts and primary basaltic magmas (i.e. hybrid). The Yingpanliangzi granitic pluton within the city of Panzhihua intrudes Sinian (~600Ma) marbles and is unlike the mantle-derived or hybrid granitic rocks. The SHRIMP zircon U-Pb ages of the Yingpanliangzi pluton range from 259±8Ma to 882±22Ma. Younger ages are found on the zircon rims whereas older ages are found within the cores. Field relationships and petrography indicate that the Yingpanliangzi pluton must be <600Ma, therefore the older zircons are interpreted to represent the protolith age whereas the younger analyses represent zircon re-crystallization during emplacement. The Yingpanliangzi granites are metaluminous and have negative Ta-Nb PM anomalies, low εNd (260 Ma) values (-3.9 to -4.4), and high I Sr (0.71074 to 0.71507) consistent with a crustal origin. The recognition of a crustally-derived pluton along with mantle-derived and mantle-crust hybrid plutons within the Panxi region of the ELIP is evidence for a complete spectrum of sources. As a consequence, the types of Panxi granitoids can be distinguished according to their ASI, Eu/Eu*, εNd (T), εHf (T), T Zr(°C) and Nb-Ta PM values. The diverse granitic magmatism during the evolution of the ELIP from ~260Ma to ~252Ma demonstrates the complexity of crustal growth associated with LIPs. © 2010 Elsevier B.V.