内蒙古东北部阿龙山地区早白垩世A型花岗岩特征及其意义

内蒙古东北部阿龙山地区的早白垩世花岗岩岩体就位于火山喷发形成的塌陷破火山口中央或火山断裂中，岩石类型有石英二长（斑）岩、晶洞正长花岗岩、文象碱长石英正长岩等。岩石普遍具文象结构、晶洞构造，但未见碱性暗色矿物；岩石化学上具高硅、富碱和富铝、低钛镁等特征，且岩石中富集高场强元素（HFSE），在微量元素蛛网图中出现Sr、Ba相对亏损，稀土配分曲线呈轻稀土富集的不对称右倾“海鸥”型，δEu亏损中等，岩石具较低的εNd（t）值（-3．00）和低的86Sr／87Sr初始值（0．708734）。以上岩体的岩石学、主微量元素及同位素特征表明，岩体具有铝质A1型花岗岩的特征，其成因与陆内巨量火山喷发造成的伸展、崩塌机制有关，反映了非造山板内拉张的构造环境。

Geochemical Characteristics and Tectonic Significance of Early Cretaceous A -type Granite in Alongshan area, Northeastern Inner Mongolia

The Early Cretaceous granitic pluton from Alongshan area, northeast Inner Mongolia, is situated in the central caldera collapse or volcanic fault, and composing of quartz monzonite, druse syenogranite and graphic alkali - quartz syenite. The rocks are featured with graphic and druse structure; and get no alkali dark -colored mineral; high in silicon, alkali, aluminium and low in titanium and magnesium in geochemistry; rich in high field strength elements, relative depletion in strontium and barium on the primitive mantle normalized spider diagram, with asymmetry right - incline rare earth element pattern and moderate Europium negative anomaly ; low in εNd （t） value （ - 3.00） and 86Sr/87 Sr initial value （0.708734）. The above petrological and geochemical characteristics of those granites all indicate they are belong to A1 - type granite, which thus confirmed they are formed fellowing extension and dilapidation triggered by bulk volcanic eruption in the extensional non -orogenic intraplate environment.