小兴安岭西北部红彦地区早石炭世火山岩地球化学特征及其地质意义

小兴安岭红彦地区发育一套早石炭世火山岩.这套火山岩由玄武岩、安山岩、英安岩、流纹岩及凝灰岩组成.岩石地球化学特征研究表明,该区早石炭世火山岩属于典型的钙碱系列岩石,并具有富钾特点,相对富集轻稀土元素(LREE/HREE=4.19～ 13.83)和大离子亲石元素(Rb、Ba、Th、U),相对亏损高场强元素(Nb、Ta、Ti),具有活动大陆边缘型火山岩的特点.认为红彦地区早石炭世火山岩起源于富集的岩石圈地幔的部分熔融,岩浆在演化过程中以结晶分异作用为主,伴有少量的地壳混染作用,即AFC过程.结合区域构造认为红彦地区早石炭世火山岩形成于碰撞前的俯冲环境,可能与额尔古纳-兴安地块与松嫩地块的碰撞拼合密切相关.

Geochemical characteristics of Early Carboniferous volcanic rocks in Hongyan area of northwestern Xiao Hinggan Mountains and their geological significance

Early Carboniferous arc volcanic rocks lie in Hongyan area of northwestern Xiao Hinggan Mountains.The volcanic rocks consist of basalt,andesite, dacite and rhyolite.Petrological and geochemical studies indicate that the volcanic rocks are of typical calc-alkaline type and display relatively high-K features.They are enriched in LREE(LREE/HREE=4.19～13.83) and LILE(Rb,Ba,Th and U) with obvious depletion of Nb,Ta and Ti,which suggests an active continental margin environment.The authors hold that the volcanic rocks of Hongyan area were derived from partial melting of enriched lithosphere mantle and experienced mainly crystallization differentiation with a small extent of lower crust assimilation(AFC-type processes).In combination with regional structures and geochemistry of volcanic rocks,it is concluded that the Early Carboniferous volcanic rocks of Hongyan area were probably formed in a pre-collision subduction environment and might have been related to the collision and collage between Erguna-Xingan and Songnen blocks.