Petrogenesis of the Maoliling pluton in Linhai County,Zhejiang Province: Constraints from geochronology,geochemistry and Sr-Nd-Hf isotopes

The Maoliling pluton,lithologically consisting mainly of quartz monzodiorite,quartz monzonite and fine-grained granite, is outcropped around Xianrenqiao and Maoliling of Linhai County,Zhejiang Province. LA-ICP-MS zircon U-Pb ages show that the quartz monzodiorites and fine-grained granites were emplaced at 105. 6 ± 1. 0Ma and 104. 8 ± 0. 9Ma,respectively. Geochemically,the quartz monzodiorites show metaluminous,calc-alkaline and potassium-rich signatures,and have relatively high concentrations of MgO, Fe 2 OT 3 and CaO with high Mg#values( 47. 6 ~ 50. 6),whereas the fine-grained granites show similar signatures in metaluminous and potassium-rich,but have lower contents of MgO,Fe 2 OT 3 and CaO with lower Mg#values( 41. 6 ~ 47. 0) than the quartz monzodiorites. The quartz monzodiorites are enriched in Rb,Th,U,Pb,and depleted in Nb,Ta,P,Ti,and have relatively high contents in Zr,Hf and Sr,with unconspicuous negative Eu anomalies( Eu / Eu*= 0. 77 ~ 0. 95). The fine-grained granites show similar trace and rare earth elements characteristics to those of quartz monzodiorites,but are more depleted in P,Ti and Sr,and display some degrees of negative Eu anomalies( Eu / Eu*= 0. 55 ~ 0. 78). The quartz monzodiorites and fine-grained granites show similar Sr and Nd isotopic compositions,with I Sr values of 0. 7088 and 0. 7079 ~ 0. 7088,and e Nd( t) values of- 7. 57 ~- 7. 56 and- 8. 06 ~- 7. 95, respectively. Meanwhile,they also have similar zircon Hf isotopic compositions,with e Hf( t) values of-12. 2 ~-6. 6 and-9. 6 ~- 4. 4,respectively. The integrated petrology,elemental and isotopic compositions suggest that the quartz monzodiorites and fine-grained granites from Maoliling pluton were most likely generated under a post-collisional extensional setting,and via a process including formation of parental magma by mixing of a underplated or an intraplated mantle-derived magma and an induced crustal-melted magma in the deep crust,then suffered differentiation during magma ascent to varying degrees and at last emplaced at a hypabyssal environment.