Cretaceous to Cenozoic evolution of the northern Lhasa Terrane and the Early Paleogene development of peneplains at Nam Co, Tibetan Plateau
Cretaceous to Cenozoic evolution of the northern Lhasa Terrane and the Early Paleogene development of peneplains at Nam Co, Tibetan Plateau
复制标题
DOI：
10.1016/j.jseaes.2013.03.005
复制
发表时间：
2013-07-01
影响因子：
3
通讯作者：
Zhang, Liyun
中科院分区：
文献类型：
--
作者：
Haider, Vicky L.;Dunkl, Istvan;Zhang, Liyun
海拔高度高、保存完好的青藏高原平原是纳木错西北偏北、拉萨地体北方青藏高原的典型地貌特征。青藏高原平原被花岗岩类及其变质沉积岩建造所切割。利用锆石U-Pb和[U-Th]/He定年、磷灰石裂变径迹和[U-Th]/He定年等多种年代学方法，确定了花岗岩类侵位后的热历史，并确定了花岗岩类最终折返的时间和速率。LA-ICP-MS锆石U-Pb年代学结果表明，该岩体有两个狭窄的年龄组，分别为118 Ma和85 Ma，第三个年龄组记录了纳木错地区古新世火山活动（63-58 Ma）。低温热年代学表明，整个纳木错地区的锆石U-Th/He年龄集中在75 Ma左右，磷灰石裂变径迹年龄集中在60 Ma左右，磷灰石U-Th/He年龄集中在50 Ma左右。热年代学数据模拟表明，基底块体的折返发生在白垩纪末至早第三纪。到始新世中期，地势已经平坦，记录了一个薄的冲积沉积物序列覆盖了一部分夷平面。现今青藏高原地垒和地堑构造是青藏高原东西向伸展的一个晚新生代特征。新的热年代学数据精确地将夷平面作用的年龄划分到始新世早期，即大约在公元前200年至公元前200年之间。55和45 Ma。根据孟加拉盆地始新世地层中早白垩世锆石颗粒的存在，可以推断出侵蚀基准面。在纳木错地区的折返过程中产生的沉积物被输送到海洋中的早新生代河流系统，这表明夷平面发生在低海拔。(C)2013爱思唯尔有限公司保留所有权利。
Highly elevated and well-preserved peneplains are characteristic geomorphic features of the Tibetan plateau in the northern Lhasa Terrane, north-northwest of Nam Co. The peneplains were carved in granitoids and in their metasedimentary host formations. We use multi-method geochronology (zircon U-Pb and [U-Th]/He dating and apatite fission track and [U-Th]/He dating) to constrain the post-emplacement thermal history of the granitoids and the timing and rate of final exhumation of the peneplain areas. LA-ICP-MS U-Pb geochronology of zircons yields two narrow age groups for the intrusions at around 118 Ma and 85 Ma, and a third group records Paleocene volcanic activity (63-58 Ma) in the Nam Co area. The low-temperature thermochronometers indicate common age groups for the entire Nam Co area: zircon (U-Th)/He ages cluster around 75 Ma, apatite fission track ages around 60 Ma and apatite (U-Th)/He ages around 50 Ma. Modelling of the thermochronological data indicates that exhumation of the basement blocks took place in latest Cretaceous to earliest Paleogene time. By Middle Eocene time the relief was already flat, documented by a thin alluvial sediment sequence covering a part of the planated area. The present-day horst and graben structure of the peneplains is a Late Cenozoic feature triggered by E-W extension of the Tibetan Plateau. The new thermochronological data precisely bracket the age of the planation to Early Eocene, i.e. between ca. 55 and 45 Ma. The erosional base level can be deduced from the presence of Early Cretaceous zircon grains in Eocene strata of Bengal Basin. The sediment generated during exhumation of the Nam Co area was transported by an Early Cenozoic river system into the ocean, suggesting that planation occurred at low elevation. (C) 2013 Elsevier Ltd. All rights reserved.