【作者】 潘少逵；

【导师】 姜常义；

【作者基本信息】 长安大学 ， 矿物、岩石、矿床学， 2009， 硕士

【摘要】 小热泉子组位于准噶尔板块的大南湖岛弧带内,分布于调查区康古尔大断裂带以北地区。虽然前人对大南湖岛弧带有较深入的研究,但是就小热泉子组来说,研究程度仍然有限。所以,本文通过对小热泉子组火山岩进行岩相学、同位素年代学、稀土元素和微量元素地球化学等方面的系统研究,科学论证了小热泉子组火山岩的岩浆性质、岩浆演化过程和岩石成因。通过野外调查和室内的研究相结合,取得了以下几点粗浅的认识:1、小热泉子组火山岩主要岩石类型为:玄武岩、玄武质安山岩、粗面岩、粗面安山岩、粗面英安岩、英安岩、流纹岩,安山质、英安质、流纹质火山角砾岩和凝灰岩,深灰色蚀变含砾中-粗粒岩屑砂岩,深灰色蚀变砂质砾岩。2、在小热泉子组内采取新鲜流纹岩石样品,经过北京离子探针实验中心SHRIMP锆石U-Pb测年法,测试其形成年龄为325±3.2Ma,属早石炭世德坞阶。3、小热泉子组火山岩稀土元素总量较高,轻稀土元素富集,重稀土元素亏损,并且重稀土元素分馏程度较弱,轻稀土元素分馏程度较强。富集大离子亲石元素,高场强元素尤其是Nb,Ta强烈亏损,相容元素V、Cr、Ni强烈亏损。表现为岛弧环境下的钙碱性火山岩特征。4、小热泉子组火山岩从基性到酸性都有分布。基性火山岩为岛弧环境下典型的钙碱性玄武岩,由被俯冲板片脱水反应形成富LILE和LREE的流体交代的上覆地幔楔橄榄岩部分熔融而形成。中性火山岩为基性火山岩经过自身的分离结晶演化而形成。酸性岩则是由俯冲的洋壳上覆楔形地幔的部分熔融形成的幔源岩浆发生底侵作用,加热导致莫霍面附近地壳部分熔融而形成。5、小热泉子组火山岩分离结晶的主要矿物为单斜辉石,斜长石的分离结晶在岩浆演化过程中作用较弱。中基性岩浆在上升侵位过程中受到一定程度的同化混染,但仍以源区富集为主。更多还原

【Abstract】 Xiaorequanzi Formation lies in Dananhu island-arc belt in Junggar plate. It is located in the north of Kanggul Fault belt in the investigation area. Although predecessors have in-depth research for Dananhu island-arc belt,to Xiaorequanzi Formation,it still in relatively low limitation.So,this paper scientifically demonstrates the nature,process and cause of formation of Xiaorequanzi Formation igneous rocks according to systematically research in petrography, geochronology,rare earth elements and trace elements geochemistry. Through the integration of wild investigation and study-in-door,we get some initial understanding as follows:1 .The main volcanic rock types of Xiaorequanzi Formation are basalt, basaltic andesite, trachyte, trachytic andesite, trachytic dacite, dacite, rhyolite;andesitic, dacitic, rhyolitic volcanic breccia and tuff; dark gray alteration in gravel - coarse-grained lithic sandstone, dark gray sandy breccia.2.Rhylite samples are collected from Xiaorequanzi Formation volcanic rocks,its formation age is 325±3.2Ma by SHRIMP U-Pb zircon determination in the centre of Beijing Ion probe,belonging to Germany-Docking stage of Early Carboniferous.3. Xiaorequanzi Formation volcanic rocks have characters of high volume of REE, LREE enrichment, LREE enrichment , HREE loss, and week degree of REE fractionation, strong degree of LREE fractionation. It was LILE enrichment and correspondingly HFSE depletion,especially Nb,Ta. Compatible elements such as V,Co,Ni are strongly depleted. It has the characteristics of volcanic rocks calc-alkaline volcanic rocks in the island arc tectonic environment.4. Xiaorequanzi Formation volcanic rocks vary from mafic volcanic rocks to acid volcanic rocks. Mafic volcanic rocks are typical calc-alkaline basalts in island arc environment. They are formed by partially melting from the mantle wedge peridotites which had metasomatism with LILE and LREE-rich fluid released by underlying subduction slab. Intermediate volcanic rocks of Xiaorequanzi Formation are formed by fraction and crystallization evolvement of its own basic volcanic rocks. Acid volcanic rocks are formed by partially melting from earth’s crust rocks near the Moho which were heated by underplating of mantle magma melt by mantle wedge overlying the subduction slab. The main fractional and crystallizational mineral are clinopyroxene, the fraction and crysrallization of plagioclase get minor effection in the process of magmatic evolution. Intermediate and mafic volcanic rocks are contaminated and assimilated at certain degree in the process of magma rise emplacement.更多还原