兴蒙造山带贺根山-黑河一线产出有大量晚古生代A型花岗岩,其成因及形成环境一直存在争议.贺根山-黑河A型花岗岩带形成于晚石炭世-二叠纪(325～260Ma),二叠纪进入岩浆作用高峰期.该花岗岩带主要表现为准铝质-弱过铝质(A/CNK=0.89～1.13)高钾钙碱性系列；高度富集LREE,Eu负异常明显；微量元素表现为富集Th、Pb和La元素,亏损Ba、Sr、Ce、P和Ti元素.研究表明晚石炭世-二叠纪古亚洲洋正处于向西伯利亚板块俯冲阶段,贺根山-黑河A型花岗岩带应该形成于该俯冲带的弧后伸展环境.俯冲导致的软流圈上涌形成弧后的伸展环境,同时为大规模高温岩浆形成提供了热源,以及部分物源,这种壳-幔混合岩浆在深部结晶分异后沿弧后伸展断裂体系快速侵位是该花岗岩带形成的原因.%Late Paleozoic A-type granites are widely distributed in Hegenshan-Heihe segment of the Inner Mongolia-Da Hinggan Mountains orogenic belt.Their tectonic environments and petrogenesis remain controversial.A-type granites in Hegenshan Heihe segment were emplaced in Late carboniferous-Permian period (325～260Ma),and the magmatic activities entered into the peak period in Permian.The A-type granite belt is metaluminous or slightly peraluminous (A/CNK=0.89～1.13) and belongs to the high-K,calc-alkaline series.On the chondrite-normalized REE diagram,all plutons are enriched in LREE,but show significant negative Eu anomalies.Their primitive-mantle normalized spidergrams display negative Ba,Sr,Ce,P,Ti and positive Th,Pb,La anomalies.Researches show that the ancient Asian oceanic plate still subducted into the Siberia plate between Late carboniferous and Permian,so the subducton-related back-arc extensional environment is thought to have been responsible for the formation of Hegenshan-Heihe A-type granites.The continental back-arc extension was probably related to the subduction slab rollback or the break-off induced upwelling of hot asthenospheric mantle.This process provided the thermal flux for melting the overlying lower crust at a high temperature,and also resulted in the mixing of the crust and the mantle-derived magmas.The mixed magma emplacement along the continental back-arc extension fault system after fractional crystallization in the depth was responsible for the formation of the Hegenshan-Heihe A-type granites belt.
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