Early Paleozoic Granite in the Talate Mining District, Chinese Altay, and its Geological Significance for the Altay Orogenic Belt

摘要

Zircon dating,geochemical and Nd-Sr isotopic analyses have been determined for samples from two granitic intrusions in the Talate mining district,Chinese Altay.Our data suggest that these intrusions were emplaced from 462.5 Ma to 457.8 Ma.These rocks have strong affinity to peralumious S-type granite and are characterized by prominent negative Eu anomalies(δEu=0.20–0.35),strong depletion in Ba,Sr,P,Ti,Nb,Ta and positive anomalies in Rb,Th,U,K,La,Nd,Zr,Hf.Nd-Sr isotopic compositions of the whole rock show negativeεNd(t)values(-1.21 to-0.08)and Mesoproterozoic Nd model ages(T2 DM=1.20–1.30 Ga).Their precursor magmas were likely derived from the partial dehydration melting of Mesoproterozoic mica-rich pelitic sources and mixed with minor mantle-derived components,under relatively low P(≤1 kbar)and high T(746–796℃)conditions.A ridge subduction model may account for the early Paleozoic geodynamic process with mantle-derived magmas caused by Ordovician ridge subduction and the opening of a slab window underplated and/or intraplated in the middle–upper crust,which triggered extensive partial melting of the shallow crust to generate diverse igneous rocks,and provided the heat for the crustal melting and juvenile materials for crustal growth.