【作者】 赵磊；

【导师】 吴泰然；

【作者基本信息】 北京大学 ， 构造地质学， 2008， 博士

【摘要】 内蒙古乌拉特中旗、达茂旗以及白云鄂博地区呈北东东向出露一条镁铁-超镁铁岩带,东西断续出露约200多公里,南北宽约10多公里,构造位置上处于华北板块北缘中段,距离其北边的索伦缝合带仅有100km,在华北板块北缘构造岩浆演化中具有代表性和重要意义。SHRIMP锆石U-Pb和K-Ar定年,显示它们主要形成于二叠纪(242~287Ma),能够反映晚古生代华北板块与西伯利亚板块的构造演化史。乌拉特中旗温更地区由角闪辉长岩和橄榄辉长岩组成的混杂堆晶岩系,主要造岩矿物为橄榄石、辉石、斜长石及角闪石等。角闪辉长岩表现为大离子亲石元素(LILE)K、Rb、Sr、Ba明显富集,高场强元素(HFSE)Nb、Ta、Zr相对亏损。橄榄辉长岩表现为贫SiO2、高MgO,富集大离子亲石元素K、Rb、Sr、Ba和轻稀土(LREE),个别高场强元素Nb亏损。根据AlZ-TiO2、Wo-En-Fs以及An-Mg′图解,结合其微量元素地球化学特征可以判断角闪辉长岩类形成于岛弧环境,橄榄辉长岩产于弧后盆地环境。白云鄂博地区白音珠日和苏木以南呼和恩格尔附近出露的杂岩体,由中心向外依次出现角闪橄榄岩、角闪辉长岩和闪长岩,具有环状分布的特征,并以闪长岩为主。杂岩体的各类岩石均表现为大离子亲石元素(LILE)K、Rb、Sr、Ba明显富集,高场强元素(HFSE)Nb、Ta、Zr、Hf相对亏损。根据AlZ-TiO2、An-Mg′、Hf/3-Th-Ta以及Hf/3-Th-Nb/16图解,结合其微量元素地球化学特征可以判断呼和恩格尔杂岩体形成于活动大陆边缘。在达茂旗东北推喇嘛庙南15km的哈日哈达-车根达来地区,断续出露一套由变质橄榄岩、变质辉长岩、变质基性熔岩以及高镁闪长岩组成的蛇绿混杂岩。其中,变质橄榄岩类SiO2含量为39.08%~40.45%,TiO2含量为0.02%~0.03%,Mg′为87.10~90.33,;变质辉长岩表现为大离子亲石元素(LILE)K、Rb、Sr、Ba明显富集,高场强元素(HFSE)Nb、Ta、Zr相对亏损,以及高镁闪长岩的出露都与SSZ型蛇绿岩特点相符。结合岩体在矿物地球化学、元素地球化学、同位素地球化学、地质年代学以及构造环境等多方面的特征对比,可以表明,沿乌拉特中旗、白云鄂博和达茂旗出露的镁铁-超镁铁岩带形成于二叠纪早期的岛弧或活动大陆边缘环境,与古亚洲洋板块向华北板块北缘下部俯冲消减有关。更多还原

【Abstract】 A mafic-ultramafic rocks belt is discontinuously exposed from Wulatezhongqi, Damaoqi to Bayan Obo Region, Inner Mongolia, NEE extending over 200km long and 10km wide. The belt belongs to the mid-segment of the northern margin of the North China Plate and it is 100km away from Solonker suture, so it is important and representative in the tectonic evolution of the northern margin of the North China Plate. According to SHRIMP U-Pb zircon age and K-Ar age, these rocks formed in the Permian, so the belt can reflect the tectonic history of the North China Plate and the Siberia Plate during the Permian.Two types of cumulate gabbros are exposed in Wulatezhongqi area, including amphibole gabbros and olive gabbros. The major petrogenetic minerals in the Wengeng gabbros are olive, pyroxene, plagioclase and hornblend. The amphibole gabbros show geochemical characteristics of enriched in LILE(K、Rb、Sr、Ba), and depleted in HFSE (Nb、Ta、Zr). The geochemistry of the olive gabbros is characterized by low SiO2 and high MgO contents, enriched in LILE(K、Rb、Sr、Ba) and LREE, and unfractionation in HFSE. According to the diagrams of AlZ-TiO2, Wo-En-Fs and An-Mg′, the amphibole gabbros are suggested to be generated at an island arc and the olive gabbros are formed in a back-arc basin setting.Huheengeer Complex shows a concentric zone in rock distribution: hornblende-peridotite, hornblende-gabbro and diorite from the core to margin successively in Bayan Obo Region, Inner Mongolia. The Complex also shows geochemical characteristics of enriched in LILE(K、Rb、Sr、Ba), and depleted in HFSE (Nb、Ta、Zr、Hf). According to the diagrams of AlZ-TiO2, An-Mg′, Hf/3-Th-Ta and Hf/3-Th-Nb/16, the Huheengeer Complex is suggested to be generated at an active continental margin, and it should be a record of Paleoasian ocean plate subduction to northern side of north China plate.An ophiolitic melange belt is discontinuously exposed in Harihada- Chegendalai area to the south of Tuilamamiao in NE of Damaoqi. The ophiolitic mélange in the belt are mainly composed of metamorphic peridotites, metamorphic gabbros, metamorphic basic lavas and high-Mg diorites. The metamorphic peridotites display SiO2 (39.08%~40.45%),TiO2 (0.02%~0.03%), Mg′(87.10~90.33). The metamorphic gabbros show geochemical characteristics of enriched in LILE(K、Rb、Sr、Ba), and depleted in HFSE (Nb、Ta、Zr). Furthermore, there are some high-Mg diorites exposed. In summary, the Daomaoqi ophiolitic mélange formed in a supra-subduction zone (SSZ).Combining with contrast of mineral geochemistry, element geochemistry, geochronology and tectonic setting, it shows clearly that the mafic-ultramafic rocks belt be generated at an island arc or active continental margin in Early Permian, and it should be a record of Paleoasian ocean plate subduction to northern side of north China plate.更多还原