东昆仑造山带新生代早期构造事件的碎屑裂变径迹年代学证据

An Early Cenozoic Tectonic Event in Eastern Kunlun Orogen,Evidence from Detrital Fission Track Geochronology

东昆仑造山带作为青藏高原北部地貌向北衰减的第一条构造地貌边界,其新生代构造过程是检验和揭示板块碰撞远程变形效应、机制及空间拓展过程的关键.基于东昆仑造山带系统的碎屑锆石裂变径迹测试分析,揭示东昆仑造山带新生代早期构造演化过程,为板块作用远程效应过程提供年代学证据.碎屑裂变径迹分析表明东昆仑造山带前新生代地层在埋藏后经历了古新世-始新世以前的差异性退火作用(约300～200℃),峰值年龄解析获得最年轻峰值年龄(P1)主体集中在42～59Ma,代表了东昆仑造山带锆石裂变径迹差异性退火作用的结束年龄.区域性热历史重建及区域资料一致表明,古新世-始新世阶段,东昆仑造山带发生了区域性构造隆升作用,表明东昆仑造山带在印度欧亚板块碰撞后随即成为青藏高原岩石圈(地壳)变形的前缘,这进一步暗示了青藏高原岩石圈地壳变形具有明显的刚性块体特征,而现今地壳流动变形特征可能是地壳分层加厚、多圈层多机制共同作用的结果.

The eastern Kunlun Orogen, as a southernmost morphotectonic transition belt of northward attenuation in topograph- ic relief across the northern Tibetan plateau, is a key area in examining and recovering the processing and mechanisms of the far-field lithospheric deformation. In this paper, we try to illustrate the Early Cenozoic tectonic processing in the eastern Kun lun Orogen based on a systematic detrital zircon fission track （ZFT） study. It is indicated that widely distributed pre-Cenozoic strata in the study area experienced a ZFT differential resetting （-300--200 ℃） at around Paleocene-Eocene postdating their burying. Binomial fitting for the single grain ages yielded youngest peak ages （Pl） that mainly fall between 42--59 Ma, which corresponds to a ceasing timing for the differential resetting of detrital, Regional thermal history. Relevant data concordantly suggest that the eastern Kunlun Orogen experienced a regional tectonic uplift in Paleocene-Eocene, which coincides with the timing of the India-Asian collision, which implies that the Kunlun Orogen occurred as a deformation frontier instantly as the Indian plate collided with Asian plate. Our study provides an evidence that the Tibetan lithosphere （or curst） deformation at early stage is essentially of rigid plate, rather than the present day of significant continuous deformation, which might be a combined result by several mechanisms of lithospheric layers thickened respectively.