巴音戈壁盆地新尼乌苏凹陷下白垩统碎屑锆石U-Pb年代学及其地质意义  

U-Pb Chronology of Detrital Zircons from Lower Cretaceous in Xinniwusu Sag,Bayingobi Basin and Its Geological Significance

作　　者：童勤龙[1] 叶发旺[1] 秦明宽[1] Tong Qinlong;Ye Fawang;Qin Mingkuan(CNNC Beijing Research Institute of Uranium Geology,National Key Laboratory of Remote Sensing Information and Image Analysis Technology,Beijing 100029,China)

机构地区：[1]核工业北京地质研究院,遥感信息与图像分析技术国家级重点实验室,北京100029

出　　处：《地球科学》2023年第10期3613-3630,共18页Earth Science

基　　金：国防科工局“基于航空高光谱和伽马能谱的铀矿勘查技术研究”项目资助.

摘　　要：为了限定巴音戈壁盆地新尼乌苏凹陷含铀目的层巴音戈壁组上段沉积年限和物源,为该地区早白垩纪盆山关系及铀矿物质来源提供制约,采集该套地层中的砂岩进行岩相学、全岩地球化学和碎屑岩锆石U-Pb定年和分析.岩石薄片观察显示该套地层具有近源沉积特征.K、Rb、La、Th、Zr、Sc、Hf、REE等元素及比值特征显示源岩主要为来自不同构造背景的中酸性岩.碎屑锆石年龄峰值主要集中在430 Ma、250 Ma和270 Ma,最年轻碎屑锆石年龄为125±1 Ma.结合上覆地层苏红图组中玄武岩K-Ar年龄,将研究区巴音戈壁组上段沉积时间限定在(125±1)~(111.3±2.1)Ma之间;凹陷北部巴音戈壁组上段下部沉积物源主要来自于东北部善达庙、欧布拉格地区,中部物源主要来自于西南部沙拉扎山乌力吉、尚丹和东部图克木隆起等地区;凹陷南部巴音戈壁组上段物源主要来自于南部诺尔公-红古尔玉林构造带和北部沙拉扎山隆起.巴音戈壁组上段中部物源剥蚀区发生明显变化,表明早白垩世晚期盆地内部发生了差异性隆升和下降,研究区东北部相对下降,而西南部相对抬升,致使沉积物源方向以东北部为主转为以西南部和东部为主.Petrography,whole rock geochemistry,and in-situ U-Pb dating of the detrital zircons from the sandstones of the uranium-bearing target formation in the Xinniwusu sag of the Bayingobi basin were used to limit the sedimentary age and provenance of Lower Cretaceous of Bayingobi Formation,and constrain the relationship between the Early Cretaceous basins and mountains and the source of uranium minerals.Photomicrographs show that the formation has the characteristics of proximal deposition.The characteristics of K,Rb,La,Th,Zr,Sc,Hf,REE and their ratios indicate that the source rocks are mainly intermediate-acid rocks from different tectonic backgrounds.The peak ages of detrital zircons are mainly 430 Ma,250 Ma and 270 Ma,and the youngest is 125±1 Ma.Combined with the K-Ar age of the basalt in the overlying Cretaceous Suhongtu Formation,the sedimentation age of the upper member of Bayingobi Formation in the study area was limited to(125±1)-(111.3±2.1)Ma.The lower part of the upper member of the Bayingobi Formation in the northern part of the Xinniwusu sag are mainly derived from Shandamiao and Wubulage areas in the northeastern Langshan.In the middle part,the provenance mainly comes from Wuliji,Shangdan and Tukmu uplift of the Shalazhashan structural belt.The provenance of the upper member of Bayingobi Formation in the southern part of the Xinniwusu sag mainly comes from the Nuru-Honggueryulin structural belt in the south and the Shalazhashan uplift in the north.The provenance area changed obviously in the middle part of the Upper Bayingobi Formation indicates that differential uplift and decline occurred in the Bayingobi basin during the late Early Cretaceous.The northeastern part to the study area was relatively declined,while the southwestern part was relatively uplifted,which changed the principal direction of sediment source from the northeast in the early to the west and east.

关 键 词：巴音戈壁盆地 新尼乌苏凹陷 碎屑锆石U-Pb定年 物源 砂岩型铀矿 地球化学 构造 

分 类 号：P548[天文地球—构造地质学]