| 西藏尼玛盆地北部古近系牛堡组物源及地质意义 |
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| 引用本文： | 密文天,朱利东,杨文光,杨林,黄辉.西藏尼玛盆地北部古近系牛堡组物源及地质意义[J].地球科学,2017,42(2):240-257. |
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| 作者姓名： | 密文天 朱利东 杨文光 杨林 黄辉 |
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| 作者单位： | 1.内蒙古工业大学矿业学院，内蒙古呼和浩特 010051 |
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| 基金项目： | 国家自然科学基金项目41002055内蒙古工业大学科学研究重点项目ZD201322教育部博士点基金项目20125122110010 |
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| 摘 要： | 班公湖-怒江缝合带内的尼玛盆地在青藏高原形成时记录的地质信息，有助于恢复其构造古地理从而为高原隆升过程提供沉积学证据，且目前对盆地北部坳陷古近系牛堡组的研究尚属薄弱.利用碎屑岩岩石学、锆石年代学、重矿物分析等方法对牛堡组进行了物源分析并对盆地构造演化进行了深入讨论.研究显示，早白垩世-古近纪，随着地壳缩短、逆冲断层及造山带发育，盆地北部演化为受构造活动控制的独立坳陷；北部坳陷牛堡组为南北双向物源，北部物源的母岩成分主要为以早白垩世虾别错花岗岩为代表的酸性岩浆岩，南部物源的母岩成分以沉积岩(硅质岩等) 和基性岩浆岩为主；碎屑锆石存在105~134 Ma、500~550 Ma、700~900 Ma、1 700~2 100 Ma及ca.2 500 Ma年龄峰值，其中105~134 Ma年龄是对班公湖-怒江洋壳俯冲在周边地体引发的岩浆事件的响应，进一步证实牛堡组碎屑岩的物源来自北部坳陷的南北两侧地体.挤压及逆冲变形决定了盆地北部坳陷的古地理特征，沉积过程及物源与区域隆升、侵蚀和岩浆活动联系密切.
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| 关 键 词： | 西藏 尼玛盆地 牛堡组 锆石U-Pb测年 物源分析 地球化学 |
| 收稿时间： | 2016-09-20 |
Provenance of the Niubao Formation and Its Geological Implications in the North Depression of the Nima Basin in the Tibet |
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| Abstract: | The Nima basin in the Bangong suture zone documented the geological information of the evolution of Tibetan Plateau, which helps to restore the tecto-paleogeography and provide the sedimentological evidences of uplift of the Plateau. However, the study of the NiuBao Formation of Paleogene strata in the north depression of the basin is still relatively weak. The provenance and tectonic evolution of Niubao Formation were analyzed by the methods of petrology, zircon U-Pb chronology and heavy minerals in this study. It is found that the north of Nima basin evolved into a depression controlled by collision and extrusion accompanied by the shortening of the crust and the activation of tectonic movements from Early Cretaceous to Paleogene, the north of Nima basin evolved into an depocenter controlled by tectonism. The Niubao Formation in the north depression is a bidirectional source. The source of north sediments primarily originated from the granites and acid magmatic rocks dominated by Early Cretaceous granitic rocks, while the source of south sediments were primarily sedimentary rocks, and basic or ultra-basic rocks. The detrital zircons of U-Pb ages have 5 peaks, namely 105-134 Ma, 500-550 Ma, 700-900 Ma, 1 700-2 100 Ma and near 2 500 Ma, and 105-134 Ma is believed to be responses to the subduction of the Bangong-Nujiang oceanic crust and volcanic activity in surrounding terrances. It is further confirmed that the Niubao Formation is derived from the north and south terranes of the northern depression. Palaeogeographic characteristics are determined by the extrusion and thrusting deformation. Sedimentary processes and sources are closely related to the uplift, erosion and magmatic activities in the Nima basin. |
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