meng gu guo dong nan bu ba yin su he tu wan gu sheng dai zao zhong sheng dai er chang hua gang yan di qiu hua xue te zheng ji qi dui gou zao huan jing de yue shu
Located between the northern margin of Erlian-Hegenshan suture zone and the pericontinental accretion zone of the southeastern margin of the Siberia plate,the Bayinsukhtu granitic body is an intrusive complex composed of monzonitic granites emplaced at Carboniferous and Triassic-Jurassic respectively.Geochemical analyses suggest that both of the two periods of monzonitic granites are characterized by high contents of silica,Al2O3 and alkali,low contents of calcium and magnesium.They are enriched in LILE and depleted in HFSE,with moderately enrichment of LREE,weak fractionation of LREE from HREE and negative Eu anomalies(δEu = 0.35-0.66).Based on the petrologic and geochemical features,the Carboniferous monzonitic granite is classified as mainly high-K,calc-alkaline,metaluminous to weakly peraluminous syn-orogenic I-type granite,while the latter is A-type granite.Isotope geochemistry of the Carboniferous granite shows that values of eNd(t) and(87Sr/86Sr)i range from 0.9 to 1.5,and from 0.700 62 to 0.704 82,respectively,which indicates that the granitic magma was likely derived from a young mantle source or an accretionary island arc with some degree of crustal contamination.However,the Triassic-Jurassic granite has lower eNd(t) but higher(87Sr/86Sr)i values relative to the Carboniferous granite,ranging from-0.3 to 0.3 and from 0.709 96 to 0.710 19,respectively.This indicates the granite derived from the same source with relatively high degree of crustal contamination.The dating of zircons from the monzonitic granites determined by LA-ICP-MS yielded a weighted age of(296±3.5) Ma,indicating that in the late Carboniferous the studied area was a syn-collision pericontinental tectonic environment.According to geochemical analysis of Late Triassic-Early Jurassic granite,it is presumed that the syn-collisional magmatism lasted till Triassic-Jurassic,probably suggestive of a long duration of collision.