Age of Initiation of the India‐Asia Collision in the East‐Central Himalaya

We document the stratigraphy and provenance of the lower Tertiary terrigenous sections in the Zhepure Shan region of the Tethyan Himalaya, southern Tibet, using petrographic and geochemical whole‐rock and single‐grain techniques. The Cretaceous–early Tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former Indian passive margin near the western end of the Zhepure Shan are conformably overlain by lower Tertiary clastic rocks. Sandstones in the Jidula Formation (Paleocene) mostly contain monocrystalline quartz grains of cratonic origin. In contrast, significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the Youxia (Early Eocene) and Shenkeza (post–Early Eocene) formations. Major, trace, and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the Jidula Formation consisted primarily of quartzose basement rocks, probably of Indian continental origin, whereas the sediments of the Youxia Formation were mainly derived from the uplifted Gangdese arc‐trench system associated with the obduction of the Asian subduction complex. The compositions of Cr‐rich spinels in the Youxia and Shenkeza sandstones resemble those from fore‐arc peridotites and were most likely derived from the arc and ophiolite rocks along the developing Yarlung‐Zangbo suture to the north. No spinels have been observed in the Jidula sandstones. Therefore, the early Tertiary detrital clastics in the Zhepure Shan record a marked change in provenance and sediment character and specifically at the time of deposition of the Youxia Formation, which contains a zone P‐8 foram assemblage. This change indicates that the onset of India‐Asia collision and the first development of the foreland basin immediately south of the India‐Asia suture zone occurred at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $50.6\pm 0.2$ \end{document} Ma in the both the western (Zanskar)