内蒙古得耳布尔地区中生代中-晚期火山岩的年代学、地球化学特征及其地质意义

对大兴安岭北段内蒙古根河市得耳布尔地区中生代中-晚期火山岩的岩相学、年代学及岩石地球化学进行研究,探讨该地区的构造演化。根据区域上的地层接触关系及前人获得的年龄数据,推断研究区存在早-中侏罗世火山岩。满克头鄂博组LA-ICP-MS锆石U-Pb测年结果为(155±1.8)Ma,成岩时代为晚侏罗世。玛尼吐组LA-ICP-MS锆石U-Pb测年结果为(124.1±0.8)Ma和(122.8±1.3)Ma,成岩时代为早白垩世。早-中侏罗世火山岩为高钾钙碱性准铝质火山岩,大离子亲石元素Ba、Sr强烈富集,高场强元素Nb、Ta亏损,形成于活动大陆边缘构造背景。满克头鄂博组为富硅、富钾、贫钠、贫钙的过铝质高硅流纹岩,Rb/Sr比值为4.1~10.3,具有S型花岗岩特征,是加厚下地壳部分熔融的岩浆在岩浆房内经晶粥体模型(MUSH)再次演化形成。玛尼吐组轻重稀土元素分馏明显,富集Zr、Rb、Th和U,亏损Sr、Ba、Nb、Ta、P和Ti,具有A型花岗岩特征,是在伸展构造背景下通过地壳降压熔融形成。综合前人研究成果,认为大兴安岭地区中生代中-晚期火山岩主要受蒙古-鄂霍茨克洋构造域控制。早-中侏罗世,蒙古-鄂霍茨克洋洋壳向南俯冲;中侏罗世晚期,蒙古-鄂霍茨克洋闭合,西伯利亚克拉通与中朝-蒙古板块碰撞;早白垩世,大兴安岭区域上表现为伸展的构造环境。

Geochronology,geochemistry and geological significance of Middle-Late Mesozoic volcanic rocks in Deerbuer area,Inner Mongolia

Petrography,geochronology and geochemistry of the Middle-Late Mesozoic volcanic rocks in Deerbuer area in Genhe City,Inner Mongolia,located in the northern part of the Great Xing an Range,have been studied to explore the tectonic evolution in this area.The existence of the Early-Middle Jurassic volcanic rocks can be inferred,according to the stratigraphic contacts and dating of previous studies in the region.LA-ICP-MS zircon U-Pb dating shows that the age of Manketouebo Formation is(155±1.8)Ma of the Late Jurassic.The dates of Manitu Formation are(124.1±0.8)Ma and(122.8±1.3)Ma,indicating the petrogenic age as the Early Cretaceous.The Early-Middle Jurassic volcanic rocks belong to high-K calc-alkaline series,quasi-aluminous volcanic rocks,with intense enrichment in LILEs(Ba,Sr)and depletion in HFSEs(Nb,Ta),implying that the rocks were formed in the tectonic setting of active continental margin.The Manketouebo Formation is composed of peraluminous high-silica rhyolite,which is enriched in silicon and K,depleted in Na and Ca,and the ratio of Rb/Sr is 4.1 to 10.3,with the characteristics of S-type granite.It is the product of further evolution of magma under MUSH model in magma chamber,which originally formed by the partial melting of thickened lower crust.LREE and HREE of the volcanic rocks of Manitu Formation show obvious fractionation.The volcanic rocks have the characteristics of A-type granite,with enrichment of Zr,Rb,Th and U,and depletion of Sr,Ba,Nb,Ta,P and Ti,and formed by crustal decompression melting in extensional background.Combined with previous research,it is concluded that the Middle-Late Mesozoic volcanic rocks in the Great Xing an Range were mainly controlled by the Mongolia-Okhotsk Ocean tectonic domain.In the Early-Middle Jurassic,the Mongolia-Okhotsk Ocean crust experienced southward subduction,and in the late Middle Jurassic,the Mongolia-Okhotsk Ocean was closed,and the Siberian Craton collided with Sino-Korean and Mongolian plates.In the Early Cretaceous,the Great Xing an Range was in an extensional tectonic environment.