| 唐王陵砾岩碎屑锆石U-Pb年代学及其构造古地理意义 |
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| 引用本文： | 张卫刚,陈刚,康昱,陈强,杨甫,任战利,戴成城.唐王陵砾岩碎屑锆石U-Pb年代学及其构造古地理意义[J].岩石学报,2020,36(6):1870-1896. |
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| 作者姓名： | 张卫刚 陈刚 康昱 陈强 杨甫 任战利 戴成城 |
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| 作者单位： | 大陆动力学国家重点实验室, 西北大学地质学系, 西安 710069;中国石油长庆油田分公司, 西安 710021;长安大学地球科学与资源学院, 西安 710054;自然资源部煤炭资源勘查与综合利用重点实验室, 西安 710021 |
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| 基金项目： | 本文受国家自然科学重点基金项目（41630312）、西北大学大陆动力学国家重点实验室科技部专项经费（No.BJ14252）、中国地质调查局海相油气资源调查项目（1212011220761）和国家基础科学人才培养基金（XDCX2019-28）联合资助. |
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| 摘 要： | 鄂尔多斯(地块)盆地南缘唐王陵砾岩的沉积时代长期存在晚前寒武纪(或震旦纪)与奥陶纪之争,沉积环境和物源组成也存在不同认识,是盆地南缘海相沉积地层及构造古地理研究关注的热点争议问题。本文采用碎屑锆石U-Pb年代学和岩石地球化学研究方法,综合分析探讨了唐王陵砾岩的沉积时代、物源组成及其构造古地理环境。结果表明:唐王陵砾岩自下而上三个组段的砂岩夹层样品、共计396颗碎屑锆石U-Pb谐和年龄数据主要分布在2531～2364Ma(n=25)、2120～1618Ma(n=268)、1230～940Ma(n=29)和905～744Ma(n=10)等四个年龄区间,相应的峰值年龄分别为2440Ma、1800Ma、1090Ma和810Ma,各组段样品单颗粒锆石最小年龄为829±11Ma、820±17Ma和744±8Ma。这一测年结果与盆地西南缘的震旦系正目观组和罗圈组碎屑锆石U-Pb年龄分布基本相似,但明显缺少其近邻剖面奥陶系平凉组碎屑锆石接近454Ma的高频年龄组分,表明唐王陵砾岩的沉积时代更接近新元古代晚期或震旦纪。碎屑锆石年龄谱物源示踪与岩石地球化学、沉积建造特征等综合分析结果揭示,唐王陵砾岩沉积具有来自(华北)鄂尔多斯陆块与祁连-北秦岭(杂岩)地体的双向混合物源特征,总体属于含有多套滑塌和水下扇堆积的滨浅海相碳酸盐岩和碎屑岩沉积建造组合体,主体形成于鄂尔多斯地块南缘新元古代晚期的被动大陆边缘伸展断陷海盆环境。唐王陵砾岩碎屑锆石测年数据接近1. 09Ga和0. 81Ga的年轻峰值年龄组分,提供并支持祁连-北秦岭地区存在格林威尔期Rodinia大陆聚合-裂解相关的构造岩浆活动事件,指示(华北)鄂尔多斯陆块与北秦岭地体至少在唐王陵砾岩沉积之前的格林威尔期曾经历过拼贴聚合-陆缘增生作用;随后受Rodinia大陆裂解事件的影响,鄂尔多斯地块南缘拼贴增生型大陆边缘发育形成了包括唐王陵砾岩在内的新元古代晚期陆缘滨浅海滑塌-碎屑流沉积。
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| 关 键 词： | 鄂尔多斯盆地 唐王陵砾岩 锆石U-Pb定年 岩石地球化学 沉积物源 构造古地理 |
| 收稿时间： | 2019/1/2 0:00:00 |
| 修稿时间： | 2020/3/1 0:00:00 |
Detrital zircon U-Pb geochronology and tectono-paleogeographic implications of Tangwangling conglomerate deposits in the southern margin of Ordos Basin |
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| ZHANG WeiGang,CHEN Gang,KANG Yu,CHEN Qiang,YANG Fu,REN ZhanLi,DAI ChengCheng.Detrital zircon U-Pb geochronology and tectono-paleogeographic implications of Tangwangling conglomerate deposits in the southern margin of Ordos Basin[J].Acta Petrologica Sinica,2020,36(6):1870-1896. |
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| Authors: | ZHANG WeiGang CHEN Gang KANG Yu CHEN Qiang YANG Fu REN ZhanLi DAI ChengCheng |
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| Institution: | State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;PetroChina Changqing Oilfield Company, Xi''an 710021, China;School of Earth Science and Resources, Chang''an University, Xi''an 710054, China;MNR Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Xi''an 710021, China |
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| Abstract: | The southern margin of the Ordos (Block or) Basin (S-OB) is commonly regarded as the west part of the southern margin of North China Block (S-NCB), involved in the Phanerozoic multiple orogeny of the North Qinling Belt (NQB). Tangwangling conglomerate, outcropped in the S-OB, has long been controversial on sources and ages, which is important not only for identifying its coeval tectono-palaeogeography, but also for understanding the correlation of the NCB and North Qinling Terrane (NQT) enveloped in the NQB. Here, LA-ICPMS zircon U-Pb dating of 3-interlayered sandstone samples from Tangwangling conglomerate deposits is carried out to qualify the conglomerate deposit ages and sources. More than 396 analyzed zircons of all the tested samples show rounded or oval shapes with CL imaging oscillatory zones and Th/U values of 0.23~1.51, suggesting a magmatic origin. The concordant ages of all the analysed zircons display a wide spectrum with the age range of 2696~744Ma, which is almost similar to the age pattern of each samples. The largest population of zircons exhibits ages of 2120~1618Ma (n=268) with a dominant peak at 1.8Ga, and the subordinate populations display ages of 2531~2364Ma (n=25), 1230~940 Ma (n=29) and 905~744Ma (n=10), corresponding to the peak ages of 2.44Ga, 1.09Ga and 0.81Ga, respectively. This age spectrum indicates that the detritus of the Tangwangling conglomerate were mainly sourced from the Early Precambrian high-grade metamorphic bedrocks of the NCB and subordinately from the Late Precambrian metamorphic complex and igneous rocks of the NQB, in which the youngest peak age of 0.81Ga with the youngest single detrital zircon age of 744±8Ma suggests the conglomerate deposit age to be no more than 810~744Ma, approaching to the Late Neoproterozoic or Sinian Period. This dating result is similar to that of the Sinian Luoquan and Zhengmuguang formations exposed in the southwest Ordos Basin, but different from or lack of the dominant peak-aged 454Ma zircons of the Ordovician Pingliang Formation outcropped in the S-OB. Furthermore, all the analysed sand-mudstone and shale samples from Tangwangling conglomerate deposits are mainly located at the passive continental margin area in the tectonic setting discrimination charts of major and trace elements. While, the redox sensitive parameters of trace and rare elements of the analysed mudstone samples mainly indicate a volatile neritic-littoral sedimentary environment. All above data integrated with sedimentary facies reveal that Tangwangling conglomerate deposits, sourced bidirectionally from the NCB and NQB, were developed limitedly in a rift passive continental margin along the S-OB of the S-NCB during the Late Neoproterozoic Sinian Period. It can be therefore supported that the continental margin of the S-NCB amalgamated with the NQT as a whole experienced a rift extensional sedimentary process during the Sinian Period, which is most probably close to the Rodinia break-up event after the Grenvillian collision especially following the post-collisional uplifting process (ca. 1.09~0.81Ga). |
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| Keywords: | Ordos basin Tangwangling conglomerate Zircon U-Pb dating Geochemistry Sediment source Tectono-Paleogeography |
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