U‐Pb Zircon Dating of the Granitic Conglomerates of the Hutuo Group: Affinities to the Wutai Granitoids and Significance to the Tectonic Evolution of the Trans‐North China Orogen
U‐Pb Zircon Dating of the Granitic Conglomerates of the Hutuo Group: Affinities to the Wutai Granitoids and Significance to the Tectonic Evolution of the Trans‐North China Orogen
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DOI：
10.1111/j.1755-6724.2006.tb00310.x
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发表时间：
2006-12
期刊：
影响因子：
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通讯作者：
Jian Zhang;Guochun Zhao;Li Sanzhong;M. Sun;Liu Shuwen;X. Xia;Yanhong He
中科院分区：
文献类型：
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作者：
Jian Zhang;Guochun Zhao;Li Sanzhong;M. Sun;Liu Shuwen;X. Xia;Yanhong He
摘要/ Abstract摘要：五台杂岩与相邻的富平、衡山杂岩相结合，是横贯华北造山带中段最好、最经典的剖面，一般分为东西两大块。不整合在五台杂岩和富平杂岩上的滹沱群被认为是该地区最年轻的岩石地层单元，对解释前寒武纪历史和整个华北造山带的演化具有重要意义。由于缺乏对该组沉积岩物源的认识，阻碍了对沉积环境和构造意义的认识。利用LA‐ICP‐MS对虎沱组最低层岩石地层花岗岩卵石进行了U‐Pb锆石年龄测定，并结合前人的岩石地层、年代学、构造和变质学资料，为该区沉积物源和构造演化提供了新的约束条件。虎沱群的层序由下至下为基底砾岩和火山碎屑岩（豆村亚群），经碎屑沉积物、板岩、白云岩和大理岩（东野亚群），上至上部为砂岩和砾岩（郭家寨亚群）。斗村亚群基底砾岩中花岗岩砾石的207Pb/206Pb加权平均年龄在2517 ~ 2566 Ma之间，与太古宙晚期五台花岗岩体的207Pb/206Pb加权平均年龄相同，表明其来源于五台花岗岩体（2566 ~ 2515 Ma）。综合新资料和前人研究成果，结合虎沱群火山岩的火成岩锆石结晶年龄（2087±9 Ma），认为虎沱群沉积于东地块西缘西向俯冲过程中，在五台弧后发育的与俯冲有关的逆弧前陆盆地环境。该盆地经历了长期的沉积作用，并在~ 1850 Ma碰撞事件期间最终关闭，导致华北克拉通的最终合并。
Abstract: The Wutai Complex associated with the adjacent Fuping and Hengshan Complexes represents the best and classical cross‐section in the middle segment of the Trans‐North China Orogen, generally divided into Eastern and Western Blocks. Unconformably overlying the Wutai and Fuping Complexes is the Hutuo Group considered as the youngest lithostratigraphic unit in the region and important both for interpreting Precambrian history as well as the overall evolution of the Trans‐North China Orogen. Lack of knowledge about provenance of the sedimentary rocks in this group has hindered understanding of the depositional environments and tectonic significance. LA‐ICP‐MS was applied to obtain U‐Pb zircon ages for the granitic pebbles, the lowest lithostratigraphic rock of the Hutuo Group, which, combined with previous lithostratigraphic, geochronological, structural and metamorphic data, provides new constraints on the sedimentary provenance and tectonic evolution of the region. The sequence of the Hutuo Group ranges upward from lower basal conglomerates and volcaniclastic rocks (Doucun Subgroup), through clastic sediments, slates, dolomites and marbles (Dongye Subgroup), to sandstones and conglomerates at the top (Guojiazhai Subgroup). Zircons from granitic pebbles preserved in the Doucun Subgroup basal conglomerates give weighted mean 207Pb/206Pb ages between 2517 Ma and 2566 Ma, which are the same as those for the late Archean Wutai Granitoids, indicating that the pebbles were derived from the Wutai granitic intrusions (2566‐2515 Ma). Based on the new data and previous studies, combined with an igneous zircon crystallization age of 2087±9 Ma obtained for volcanics in the Hutuo Group, the Hutuo Group was deposited in a subduction‐related retro‐arc foreland basin environment that developed behind the Wutai arc during the eastward‐directed subduction of the Western Block beneath the western margin of the Eastern Block. This basin underwent long‐lived sedimentation and finally closed during the ∼1850 Ma collisional event that resulted in the final amalgamation of the North China Craton.