摘要
青藏高原东南部地区新生代时期是否存在一个连接青藏高原与南海的大陆规模古水系系统一直广受争议。本文以红河南侧云南思茅盆地为研究区，通过对盆地内古新世-渐新世地层的沉积学和碎屑锆石U—Pb年龄谱分析，并与邻区已有相关结果对比分析，以揭示古水系的演化。结果表明：古新世一晚始新世等黑组砂岩的碎屑锆石u—Pb年龄谱展示出190—240Ma、260—280Ma、450—540Ma、1700—1900Ma和2400—2600Ma等多年龄组的组合特征，而晚始新世-渐新世勐腊组砂岩碎屑锆石U—Pb年龄谱表现出一个显著高峰年龄谱，集中在220—240Ma。等黑组碎屑锆石年龄谱与邻区的可可西里、松潘-甘孜、北羌塘、义敦和扬子西部碎屑锆石年龄谱具有可比性，与区域地层、岩相古地理证据共同指示古新世-晚始新世存在连接青藏高原与南海的古红河水系。勐腊组不同年龄峰值区间数量的减少说明物源区明显缩小，其年龄组与思茅盆地西侧的临沧花岗岩的年龄较为接近，指示其可能物源为临沧花岗岩，表明晚始新世-渐新世期间古红河失去了其北部上游大部分流域。综合古高度与区域构造等地质学证据，我们推测晚始新世期间，青藏高原东南部地区响应印度-欧亚板块碰撞开始发生红河断裂左行走滑和兰坪-思茅地块顺时针旋转等，导致连接青藏高原与南海的古红河水系失去了其上游的大部分流域，现代红河格局形成。
The paleo-Red River is suggested to have been a continental-scale drainage system connecting the Tibetan Plateau to the South China Sea. However, the evolution of the paleo-Red River is still under debate. This study carries out detrital zircon U-Pb geochronologic and sedimentary analyses of 6 samples from the Paleocene to Oligocene age Denghei and Mengla formations （Fms.） of the Simao Basin, Jinggu County （ 23.7° N, 100.6° E）, Yunnan Province, to constrain the nature of the paleo-drainage system of the Red River. Sedimentary and sandstone petrographic analyses reveal that the Paleocene-Eocene Denghei Fm. was likely deposited in a braided river environment, while the Late Eocene-Oligocene Mengla Fm. was in an alluvial fan environment. Microscopic characteristics of the obtained sandstone samples are well-sorted and are sub-rounded to sub-angular monocrystalline grains; The detrital zircon grains are dominated by clear plate-type structures or oscillatory zoning in CL images, indicative of magmatic origins. The detrital zircon U-Pb results reveal multiple age groups at 190-240 Ma, 260- 280 Ma, 450-540 Ma, 1700- 1900 Ma and 2400-2600 Ma for the Denghei Formation, but only one conspicuous peak at 220-240 Ma for the Mengla Fro. The detrital zircon U-Pb age groups of the Denghei Fm. are comparable with those of the Hoh-Xil, Songpan-Ganzi, northern Qiangtang, Yidun, western Yangtze Terranes, indicating that the Paleocene-Eocene Simao Basin had consistent catchment with the upper and lower Jinshajiang Segments. Available sedimentary stratigraphy and lithofacies paleogeography results show that there widely existed Paleocene- Eocene fluvial sediments in the Three River region, which distributed parallel to the major sutures, indicating their association with an ancient connected fluvial system. Thus, there likely existed a paleo-Red River connecting the Tibetan Plateau and the South China Sea. The reduction of the peak range of Mengla Formation indicates that the source area is significantly narrowed, mainly tr
出处
《第四纪研究》
CAS
CSCD
北大核心
2018年第1期130-144,共15页
Quaternary Sciences
基金
国家自然科学基金项目（批准号：41272185、41672358和41620104002）、国家重大科学研究计划项目（批准号：2013CB956400）和国家重点基础研究发展计划项目（批准号：2017YFC0602803）和中国科学院战略科技先导专项项目-B类（批准号：XDB03020400）共同资助
