羌塘地块白垩纪剥蚀—冷却事件  

Cretaceous denudation—cooling in Qiangtang Block

作　　者：郑波 陈文彬[3] 王增振 冯丽霞 张艳雄 万友利[3] 吴林[6] ZHENG Bo;CHEN Wenbin;WANG Zengzhen;FENG Lixia;ZHANG Yanxiong;WAN Youli;WU Lin(Qiangtang Institute of Sedimenlary Basin,Soulhu est Petroleum University,Chengdu 610500;School of Geoscience and Technology,Southwest Petroleum University,Chengdu,610500;Chengdu Centre,China Geological Survey,Chengdu,610081;China Deep Exploration Center,Chinese Academy of Geological Sciences,Beijing,100037;School of Emergency Science,Xihua University,Chengdu,610039;Institute of Geology and Geophysics,Chinese Academy of Sciences,Reijing,100029)

机构地区：[1]西南石油大学羌塘盆地研究院,成都610500 [2]西南石油大学地球科学与技术学院,成都610500 [3]中国地质调查局成都地质调查中心,成都610081 [4]中国地质科学院地球深部探测中心,北京100037 [5]西华大学应急学院,成都610039 [6]中国科学院地质与地球物理研究所,北京100029

出　　处：《地质论评》2020年第5期1143-1154,共12页Geological Review

基　　金：国家自然科学基金重大研究计划重点支持项目(编号:91955204)的成果。

摘　　要：本文报导了青藏高原内部羌塘地块三个钻孔岩芯中9件样品的锆石(U—Th)/He年龄,除始新统两件样品的锆石(U—Th)/He热史信息尚未重置外,其余样品年龄均集中在白垩纪,且年龄值随高程变化较小,指示存在白垩纪剥蚀—冷却。羌塘地块西部QD-17井记录了早白垩世(约127~114 Ma)的剥蚀—冷却,东部QZ-16井记录了晚白垩世(约92~64 Ma)的剥蚀—冷却。白垩纪剥蚀—冷却得到区域上低温热年代学数据统计和构造—沉积事件的响应。羌塘地块、拉萨地块和喜马拉雅地块的低温热年代学数据统计结果显示,拉萨地块北部和羌塘地块(高原内部)广泛分布白垩纪—早始新世的低温热年代学年龄,拉萨地块南部至喜马拉雅地块(高原南缘)则广泛分布晚中新世以来的低温热年代学年龄,这种年龄分布格局暗示高原内部和南缘经历了明显不同的剥蚀—冷却历史。参考高原南缘晚中新世以来的快速剥蚀—冷却过程,推测高原内部也存在白垩纪快速剥蚀—冷却事件。拉萨地块北部、羌塘地块及其以北区域广泛出现早白垩世沉积间断及沉积不整合,也指示白垩纪期间的快速剥蚀。结合区域构造演化分析,该白垩纪剥蚀—冷却可能是早白垩世班公湖—怒江洋关闭后拉萨地块与羌塘地块碰撞的结果,指示在新生代印度—欧亚大陆碰撞之前,高原内部的地壳可能已经存在明显的缩短、加厚变形以及相应的剥蚀—冷却。Objectives:This work aims to investigate a probable Cretaceous denudation—cooling process in the inner part of Xizang(Tibetan)Plateau before the Cenozoic India—Eurasia collision.Methods:We carried out a preliminary zircon(U—Th)/He study based on samples from 3 boreholes in the central Xizang Plateau and compiled a number of low temperature thermochronological age data,including zircon(U—Th)/He,apatite fission track and(U—Th)/He ages,throughout the Qiangtang Block,Lhasa Block,and Himalaya Block,by analyzing their temporospatial distributions and potential links with some specific geological events and tectonic background,to discuss an early denudation—cooling process in the Qiangtang Block.Results:Zircons of 9 samples from 3 boreholes in the Qiangtang Block give(U—Th)/He ages of from 127 to 114 Ma in the well QD-17,from 92 to 64 Ma in the well QZ-16,and 88±5 Ma in the well QK-1,respectively.These ages are weakly correlated with their altitudes and show a trend of decreasing from the top down and from west to east.Conclusions:The zircon(U—Th)/He age pattern from boreholes indicates an obvious denudation—cooling process during Cretaceous in the Qiangtang Block.The statistical result of thermochronological ages show a distribution pattern that the inner part of Xizang Plateau holds older ages from Cretaceous to Early Eocene,while the marginal part of Xizang Plateau has much younger ages from Late Miocene to Pleistocene.They together indicate an early denudation—cooling process during Cretaceous in the inner part of Xizang Plateau.This earlier cooling before the widely known Cenozoic one triggered by India—Eurasia collision can be linked to an Early Cretaceous tectonic unconformity from the northern Lhasa Block to the north front of Xizang Plateau and is quite probably the consequence of the closure of the Meso-Tethys Ocean and following collision of the Lhasa Block and the Qiangtang Block.

关 键 词：剥蚀—冷却 白垩纪 拉萨地块北部 羌塘地块 

分 类 号：P534.53[天文地球—古生物学与地层学]