Paleocene adakitic porphyry in the northern Qiangtang area, north-central Tibet: Evidence for early uplift of the Tibetan Plateau
Paleocene adakitic porphyry in the northern Qiangtang area, north-central Tibet: Evidence for early uplift of the Tibetan Plateau
复制标题
DOI：
10.1016/j.lithos.2014.11.003
复制
发表时间：
2015
期刊：
影响因子：
3.5
通讯作者：
Hongrui Zhang;Tiannan Yang;Z. Hou;J. Jia;M. Hu;Jinwei Fan;M. Dai;K. Hou
中科院分区：
文献类型：
--
作者：
Hongrui Zhang;Tiannan Yang;Z. Hou;J. Jia;M. Hu;Jinwei Fan;M. Dai;K. Hou
这些岩脉位于与冲断带平行或次平行的北西-东向逆断层上，具有同碰撞的特征。新的La - icp - ms锆石206pb /238U和岩浆生物石40ar /39Ar结果表明，岩脉在约64 Ma时结晶，岩脉的整体地球化学特征表明，岩脉具有高Sr/Y和La/Yb比、低Y和低Yb含量的双晶质特征。它们的低MgO、Ni和Cr含量以及正的锆石ε hf (t)和体积ε nd (t)值表明，这些埃达质岩石是幼年增厚下地壳部分熔融的结果。综合现有的年代学、地球化学和构造资料，认为青藏高原的地壳缩短和隆升是一个长期的过程，包括一个快速的早期阶段和一个缓慢而稳定的后期阶段。与碰撞有关的岩浆活动在这两个阶段之间的过渡时期达到顶峰。
Uplift of the Tibetan Plateau and related crustal shortening are key issues in understanding collisional geodynamics, and magmatic rocks that formed in this compressional setting provide clues to the processes involved. Numerous granitic porphyry dikes have been identified in the Angsai area of the northern Qiangtang block in north-central Tibet. These dikes were emplaced along NW–SE-striking reverse faults that run parallel or sub-parallel to the thrust belt, suggesting that they are syn-collisional. New LA-ICP-MS zircon206Pb/238U and magmatic biotite40Ar/39Ar results demonstrate that the dikes crystallized at ca. 64 Ma, and the bulk geochemistry of the dikes shows that they are adakitic, with high Sr/Y and La/Yb ratios, and low Y and Yb contents. Their low MgO, Ni, and Cr contents, along with positive zirconεHf(t) and bulkεNd(t) values, suggest that the adakitic rocks were the result of partial melting of a juvenile thickened lower crust. Our new data indicate the uplift of north-central Tibet which started as early as 64 Ma. Synthesizing available geochronological, geochemical, and structural data, it seems that the crustal shortening and uplift of the plateau is a long-lived process consisting of a rapid early stage, and a slow and more constant later stage. Collision-related magmatic activity peaked at the time of transition between those two stages.