Geochronology, petrogenesis and tectonic implications of granites from the Fuxin area, Western Liaoning, NE China

摘要

New geochemical and Sr–Nd isotopic data from the Ping'andi granitic pluton in the Fuxin area, which straddles the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB) border, are presented here to discuss the geochronology, petrogenesis and tectonic implications. Petrographically, the Ping'andi granites contain monzogranites to minor granodiorites. They are high-K calc-alkaline series, silica-rich (SiO2=66–78 wt.%), peraluminous (A/CNK=0.98–1.10), with enrichment in LREE (Lan/Ybn=6.51–8.53), moderately negative Eu anomalies (Eu/Eu*=0.33–0.90), with enrichment in LILE (Rb and K) and with depletion in HFSE (Nb, Ti and P). They also have slightly negative and positive εNd(t) (-1.1–0.4), low initial ISr (0.70587–0.70620) and young depleted-mantle model ages (TDM2=911–1027 Ma). The emplacement of the Ping'andi granites took place at 150 Ma as revealed by whole rock Rb–Sr isochron age. The petrography, geochemistry and isotopic compositions indicate that they are I-type and were the result of partial melting of mixed sources composed of a juvenile component and a pre-existing crust, coupled with plagioclasedominated fractionation, and that there was a significant crustal growth in the Phanerozoic in the northern margin of the NCC. The formation of the Ping'andi granites was related to the tectonic transformation from the convergent tectonic regime of Paleo-Asian Ocean to that of the Paleo-Pacific Ocean, which also induced the huge NNE-trending Jurassic granite belt and Mo–Cu metallogenic belt in eastern China.