Multiproxy Isotopic and Geochemical Analysis of the Siwalik Sediments in NW India: Implication for the Late Cenozoic Tectonic Evolution of the Himalaya

• Published in: Tectonics (Washington, D.C.) D.C.), 2019-01, Vol.38 (1), p.120-143
• Main Authors: Mandal, Sanjay Kumar, Scherler, Dirk, Romer, Rolf L., Burg, Jean‐Pierre, Guillong, Marcel, Schleicher, Anja M.
• Format: Article
• Language: English
• Subjects: bulk‐silicate Sr‐Nd isotopic composition; Cenozoic; Denudation; detrital zircon U‐Pb age; Erosion; Evolution; Fluvial deposits; Fluvial sediments; foreland basin; Geochemistry; Geochronology; Geochronometry; Geological time; Himalaya; Isotopes; Miocene; Mountains; Pleistocene; Provenance; River sediments; Rivers; Sediment; sediment provenance; Sediments; Topography (geology); Trace elements; Uplift; Zircon
• ISSN: 0278-7407; 1944-9194
• DOI: 10.1029/2018TC005200

Provenance analysis of the Sub‐Himalayan Late Miocene‐Pleistocene foreland basin deposits (Siwaliks) from the Dehradun reentrant area provides a 10‐Myr long record of the denudation history and tectonic evolution of the northwestern Indian Himalaya. We studied Siwalik sediments exposed along the Mohand‐Rao and Haripur‐Khol sections, using detrital zircon U‐Pb geochronology, major and trace elements, and Sr‐Nd isotope geochemistry. Results suggest that the erosion pattern has been relatively stable since the Late Miocene with sediments derived from the Tethyan Himalayan (THS), Greater Himalayan (GHS), and outer‐ (oLHS) and inner‐Lesser Himalayan (iLHS) sequences. Provenance data indicate that erosional unroofing of the Lesser Himalayan Crystalline sequences (LHCS) initiated around 6 Ma, possibly related to out‐of‐sequence movement of the Ramgarh‐Munsiari Thrust. Our data also suggest erosional recycling of older foreland basin deposits into younger Siwaliks since ~5.5 Ma, which may indicate the time of thrust propagation from the Lesser Himalaya into the foreland basin. While the iLHS has been exposed to erosion since at least ~10 Ma, the Siwaliks were dominated by materials derived from the GHS and THS sources. We interpret these results as an indication that tectonic uplift and erosion of the orogenic wedge occurred in response to duplexing of the iLHS and concomitant high topography and rock uplift rate in the Greater and Tethyan Himalaya. Comparing the provenance of the Siwalik sediments with that of the modern Ganga and Yamuna river sediments further indicates that deposition during the Late Cenozoic was most likely accomplished by southward flowing transverse Himalayan rivers, analogous to the modern ones. Key Points We present a geochemical, Sr‐Nd isotopic, and detrital zircon U‐Pb geochronological data set of the Late Miocene to Pleistocene Siwalik sediments from two temporally constrained sections in the Dehradun reentrant of NW Indian Himalaya Sediments were derived from relatively invariant sources since the Late Miocene Sediments were supplied by southward directed transverse rivers analogous to rivers feeding the foreland basin at present