【作者】 柳长峰；

【导师】 万晓樵；

【作者基本信息】 中国地质大学（北京） ， 古生物学与地层学， 2010， 博士

【摘要】 内蒙古中部地区构造上属于兴蒙造山带和华北板块北缘,是研究北方造山带古生代地壳增生演化的重要地区,该区出露有大量古生代-早中生代岩浆岩,在空间上以索伦-西拉木伦缝合带为界,分为南北两条近东西向的岩浆岩带,但前人对其研究较少。本文在区调填图的基础上,选择四子王旗地区代表性的岩体进行详细的岩石学、岩石地球化学及同位素年代学研究。共获得13个锆石LA-ICP-MS U-Pb年龄:哈达敖包闪长岩508±10 Ma、活佛滩闪长岩331±5 Ma和323.1±3.4 Ma、西圪旦辉长岩302±2 Ma、北极各正长花岗岩264±3.4Ma,阿玛乌苏花岗闪长岩267±9Ma、乌尔塔高勒庙角闪正长岩、二长花岗岩、正长花岗岩及侵入其中的石英脉分别为271±18 Ma、256±3Ma、261±2Ma和230±12Ma、布龙二长花岗岩239±4Ma、格尔图白云母正长花岗岩和白云母二长花岗岩脉为238±6Ma和224±8Ma。结合区域资料,将研究区古生代-早中生代的岩浆作用划分为4个时期:早古生代(508~420Ma)、石炭纪-早二叠世(340~281 Ma)、中二叠世-早三叠世(281~245 Ma)和中-晚三叠世(239~203 Ma)。岩石地球化学数据显示,哈达敖包岩体、白乃庙变质火山岩和西圪旦岩体具有岛弧岩浆特征,是不同时期洋壳俯冲的产物;活佛滩岩体具有类似大陆碱性玄武岩的性质,可能形成于弧后拉张环境;北极各岩体、大庙-阿玛乌苏岩体广泛发育暗色镁铁质微粒包体,是岩浆混合形成的I型花岗岩,乌尔塔高勒庙角闪正长岩为碱性A型花岗岩,这三个岩体与俯冲板块断离引起的岩浆底侵作用相关,代表同碰撞-碰撞晚期背景;乌尔塔高勒庙二长花岗岩具高Sr低Y特征,暗示为起源于加厚地壳,形成与碰撞后环境;格尔图白云母正长花岗岩属强过铝花岗岩(A/CNK≥1.1),具明显的稀土元素“四分组”效应,是分异岩浆与流体作用的结果,可能经历一定程度的地壳混染,非真正意义上的S型花岗岩,属于造山后岩浆热事件,应代表造山的结束。对内蒙古中部地区古生代-早中生代岩浆岩的岩石地球化学特征和年代学研究结果表明,西伯利亚板块和华北板块碰撞拼合时间应该为280~260Ma之间,南北岩浆岩带的岩石组合及活动期次大致可以对比,支持以索伦-西拉木伦一线作为缝合带最终位置。更多还原

【Abstract】 Middle part of the Inner Mongolia sited on northern margin of the North China platform and paleozoic Xing-Meng orogenic belt, where the Paleozoic-Early Mesozic igneous rocks are widely distributed in this area, is an important district for crustal growth and recycling research. Those igneous rocks can be divided into the south and north belts by the Solonker suture zone.Based on the geological mapping, petrologic, geochemical and geochronological stuidies were carried out for typical plutons in Siziwangqi area. 13 samples of zircons have been run for U-Pb geochronological dating using LA-ICP-MS techniques: Hadaaobao diorite (508±10 Ma), Huofotan diorite (331±5 Ma, 323.1±3.4 Ma), Xigedan gabrrotic (302±2 Ma), Beijige syenogranite(264±3.4Ma), Amawusu granodiorite (267±9Ma), zircons from hornblende-syenite, monzogranite, syenogranite, quartz vein of Wuertagaolemiao pluton yielded U-Pb ages of 271±18 Ma, 256±3 Ma, 261±2 Ma, 230±12Ma respectively; the Bulong monzogranite and the Geertu muscovite granite formed at 239±4Ma and 238±6Ma (MSWD =0.91), respectively; zircons from muscovite monzogranite vein which intruded into the Geertu pluton, gave a mean 235U/206Pb age of 224±8Ma (MSWD =5.7). Based on these new data and other reliable data Published in recent years, four stages of magmatism are identified: Early Paleozoic(508~420Ma), Carboniferous- Early Permian(340~281 Ma), Middle Permian- Early Trias(281~245 Ma) and Middle–late Trias(239~203 Ma).Samples from Hadaaobao pluton, Bainaimiao volcanic rocks and Xigedan gabrrotic show geochemical features characteristic of island arc, were the products of different stages in the oceanic slab subduction. Geochemistry of the Huofotan diorite show features characteristic of continental alcaline basalt, which belong to back-arc setting. There are abundant mafic microgranular enclaves (MMEs) which generated by magma mixing, occurring in the Beijige pliton and Damiao-Amawusu pluton, indicates an affinity to I-type granite. Geochemistry of the Wuertagaolemiao Hornblende-syenite with high Ga/Al ratio and high abundance of Zn, Y, Nb,indicates an affinity to A-type syenitic magmas. Those plutons correlated with the upwelling of asthenosphere caused by the breaking-off of subduction slab. The Wuertagaolemiao monzogranite with high Sr content(407-626×10-6), low Y and Yb content (Y=2.2-4.8×10-6, Yb=0.27-0.45×10-6), suggest it was partial melts from post-collisional over-thickened lower crust. The Geertu muscovite granites show a spectacular tetrad effect in their REE distribution patterns as well as non-CHARAC (charge-and-radius-controlled) trace element behavior, caused by intense interaction of the residual melts with aqueous hydrothermal fluids. Those characters indicates that the Geertu muscovite granites are not typical S-type granites, belong to post-orogenic setting, represented the ending of orogeny. In combination with the previous studies on regional geology, it can be concluded that the final collision between the Siberian plate and the North China craton happened between280 Ma and 260 Ma. The igneous rock assemblage and geochronological of south and north belts can be contrasted, so Solonker -Xar Moron River as the collisional suture between the Siberian plate and the North China craton is believable.更多还原