西藏许如错地区洁居纳卓组碎屑锆石U-Pb年龄及其地质意义

U-Pb dating for detrital zircons from the Jiejunazhuo Formation in Xuru Co area and its geological significances

关键词:  许如错地区  上新世  洁居纳卓组  碎屑锆石U-Pb定年  物源分析  高原隆升

Key words:  Xuru Co area  Pliocene  the Jiejunazhuo Formation  U-Pb dating for detrital zircons  provenance analysis  Tibetan Plateau uplift

摘要:

在西藏许如错地区新识别出的洁居纳卓组为一套固结—半固结的粗碎屑岩建造。为探讨该地层的沉积时代和沉积物源，对1个砂岩样品进行了碎屑锆石U-Pb年代学分析。获得了4组有效年龄：10.1~17.2Ma、41.7~72.2 Ma、77.9~87.8Ma、463~1610Ma。结合岩石组合特征、ESR测试结果和区域年龄资料，认为洁居纳卓组可能形成于上新世。物源分析结果显示，许如错以南的查孜及附近地区的林子宗群、布嘎寺组火山岩是洁居纳卓组沉积物质的主要来源，古新世-中新世的侵入岩和晚古生代地层也为其提供了少量的沉积物质。洁居纳卓组发育于许如错南北向地堑盆地之内，是上新世高原隆升在冈底斯地区的沉积响应，是青藏高原局部构造差异隆升的结果。

Abstract:

The newly identified Jiejunazhuo Formation in Xuru Co area,Tibet,is mainly composed of semi-consolidated to consolidated coarse clastic rocks. In order to reveal its sedimentary time and sediment provenance,we carry out the U-Pb dating for detrital zircons of one sandstone sample from the Jiejunazhuo Formation. The results indicate that the effective ages obtained can be roughly divided into 4 groups:10.1~17.2 Ma (10 zircons),41.7~72.2 Ma (43 zircons),77.9~87.8 Ma (4 zircons),463~1610 Ma (8 zircons). Combining the lithological characteristics,ESR age of sandstone and previous age data in the region,it is believed that the Jiejunazhuo Formation was most likely formed in the Pliocene. Provenance analysis shows that the volcanic rocks of the Linzizong group and the Bugasi Formation in Chazi areas and neighboring regions in the south of Xuru Co,were the main sediment sources of the Jiejunazhuo Formation,and the Paleocene-Miocene intrusive rocks and Late Paleozoic strata also provided a small amount of sedimentary materials. The Jiejunazhuo Formation,which developed in the Xuru Co NS-trending graben basin,was the sedimentary response of the uplifting of Tibetan plateau during the Pliocene,and it was also the result of differential uplifting of the Gangdise areas during that time.