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引用本文:李玉娟. 内蒙古扎木廷火山岩年代学、地球化学与中生代构造体制转换[J]. 中国地质, 2021, 48(1): 264-283.
LI Yujuan. Geochronology and geochemistry of the volcanics in the Zamuting, Inner Mongolia and its transfromation of Mesozoic tectonic system[J]. Geology in China, 2021, 48(1): 264-283(in Chinese with English abstract).
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内蒙古扎木廷火山岩年代学、地球化学与中生代构造体制转换
李玉娟
福建省地质调查研究院, 福建 福州 350013
摘要:
大兴安岭火山带晚中生代火山岩的起源、演化及形成的构造背景一直存在争议。文章对出露于扎木廷地区白音高老组火山岩进行LA-ICP-MS锆石U-Pb定年,结果显示流纹岩及粗面岩分别形成于(131.6±1.2)Ma和(126.9±1.5)Ma,与白音高老组第二段火山沉积夹层中动植物化石鉴定结果一致,表明形成于早白垩世早期。流纹岩及粗面岩属碱性系列火山岩,具高硅、富碱、低铝、贫镁、钙和高FeOT/(FeOT+MgO)比值特征;相对富集大离子亲石元素Rb、Th、U、Pb,强烈亏损高场强元素Nb、Ta、Ti、P和Ba、Sr,流纹岩具A型花岗岩特征。微量元素与稀土元素特征表明流纹岩及粗面岩均来自于地壳的熔融,二者具有相同的岩浆来源。白音高老组火山岩形成于造山后的伸展构造背景,反映了蒙古鄂霍茨克洋向南俯冲与额尔古纳-兴安陆块碰撞拼合后,大兴安岭地区开始由挤压向伸展构造体制转换,软流圈地幔上涌底侵使下地壳发生了部分熔融,导致流纹岩喷发,残留相进一步熔融继而导致大规模粗面岩喷发。
关键词:  白音高老组  A型花岗岩  伸展构造  早白垩世  扎木廷高吉高尔火山盆地  地质调查工程
DOI:10.12029/gc20210118
分类号:P588.14;P597;P595
基金项目:中国地质调查局“内蒙古1∶50 000扎木廷高吉高尔、军马场、军马场一队、综合服务站等4幅区域地质矿产调查”项目(DD20160048-06)资助。
Geochronology and geochemistry of the volcanics in the Zamuting, Inner Mongolia and its transfromation of Mesozoic tectonic system
LI Yujuan
Fujian Institute of Geological Survey, Fuzhou 350013, Fujian, China
Abstract:
As the origin, evolution and tectonic setting of late Mesozoic volcanic rocks in the Great Hinggan Range volcanic belt have always been controversial, our project carried out geochronology and geochemistry studies of the volcanics in the Zamuting area. LA-ICP-MS zircon U-Pb dating of the he Baiyingaolao Formation volcanic rocks in the Zhamuting area reveals that rhyolite and trachoma were formed at 131.6±1.2 Ma and 126.9±1.5 Ma respectively, which are consistent with the identification results of the animal and plant fossil in the Second Member volcanics of the Baiyingaolao Formation, indicating that the volcanic rocks were formed in the early Cretaceous. The rhyolites and trachyandesites of this region belong to alkali series volcanic rocks, with characteristics of high silicon, rich in alkali, low aluminum, low magnesium and calcium, as well as high FeOT/(FeOT+MgO) ratio; the rocks are relatively enriched in the large ion lithophile elements Rb, Th, U and Pb, and have a strong deficit in the high-field strong elements such as Nb, Ta, Ti, P, Ba and Sr; the rhyolitic rocks have the characteristics of A-type granite. The studies on trace elements and rare earth elements indicate that both rhyolite and trachyandesites are derived from the melting of the crust and have the same magmatic source. The Baiyingaolao volcanic rocks were formed in the post-orogenic extensional tectonic environment, which reflects that after the southward subduction of the Mongolia Okhotsk Ocean and the collision and integration of the Eerguna-Xingan landmass, the Da Hinggan Mountains volcanic region began to transform from compression to extensional tectonic system. The upwelling and underplating of asthenosphere mantle caused the partial melting of the lower crust, which led to the eruption of rhyolite. The further melting of residual phases led to large-scale eruption of trachyte.
Key words:  Early Cretaceous  A type rhyolite  extensional structure  Baiyingaolao Formation  Zamuting Gaojigaoer  Inner Mongolia  geological survey engineering