摘要
The LA-ICP-MS zircon U-Pb dating yields a 206Pb/238U age of 394.9 ± 2.3Ma (MSWD =1.5) for rhyolite porphyry in the Baishantang mine,Gansu,implying its Late Devonian intrusion.Geochemistry analyses show that the rocks are typically potassium-rich (K2O=4.34%~8.75%) and peraluminous (A/CNK= 1.12~1.65).REE is characterized by obvious negative Eu anomalies.The elements K,Rb,Ba,U and Pb are rich in the rhyolite while Nb,Ta,Sr,P,Ti are depleted.The geochemical data,coupled with the published Sr-Nd isotopic analysis,indicate that the Baishantang rhyolite was most likely generated by partial melting of the old crust material.We propose that the rhyolite was formed at a continental volcanic arc that was closely related to subduction.