Cambrian and Tectonic Depositional History of Northern Himalayas

India Project Description:

The goal of this project is to test models for the assembly of core Gondwanaland through an integrated study with stratigraphic, macrofaunal, geochronological, and sedimentological approaches. The project focuses on Cambrian rocks of the Tethyan Himalaya of India, Bhutan and Tibet that provide an extensive record of the interval during which eastern and western sectors of Gondwanaland merged. Sedimentological data is providing the first detailed sedimentological analysis of much of the northern Indian margin in the Cambrian. The nature and timing of a Late Cambrian-Early Ordovician tectonic event recorded in the Tethyan Himalaya and in other places in East Gondwanaland is being explored as well. The abstract of our first paper to result from this project is published in EPSL; its abstract is given below:

The isotope geochronology of isochronously deposited Cambrian strata from different tectonostratigraphic zones of the Himalaya confirms new stratigraphic, sedimentological, and faunal evidence indicating that the Himalaya was a single continental margin prior to collision of India with Asia.   Lesser, Greater, and Tethyan Himalaya represent proximal to distal parts of a passive continental margin that has been subsequently deformed during Cenozoic collision of India with Asia. Detrital zircon and neodymium isotopic data presented herein discount the prevailing myth that the Lesser Himalaya has an unique geochronologic and geochemical signature that is broadly applicable to modeling the uplift history of the Himalaya. The conclusion that all pre-Permian Lesser Himalaya strata lack young detrital zircons that are present in the Greater and Tethyan Himalaya underpins previous arguments that the Main Central Thrust forms a fundamental crustal boundary that separates the Indian craton from an accreted terrane to the north. The supposition that Himalayan lithotectonic zones differ in detrital zircon age populations has also been used to reconstruct the unroofing history of the Himalaya during foreland basin development in the Cenozoic. Our data conflict with the underlying assumptions implicit in these studies in that samples of similar depositional age from both the Lesser and Tethyan Himalaya contain detrital zircons with similar age spectra.

Similarities between the Kathmandu Complex and the Tethyan Himalaya support stratigraphic continuity between the age-equivalent Greater Himalayan protolith and the Tethyan. Assuming that the complex rooted along the Main Central Thrust, these strata would simply have escaped intense metamorphism during Cenozoic tectonism. Alternatively, the complex may represent a part of the Tethyan Himalaya that was emplaced during an early stage of movement along a south-directed thrust fault located near the present-day structural position of the South Tibetan Fault System.

Additional Details on the India Project

Refereed Publications/Guidebooks:

• Hughes, N.C., Peng, S.-C., Bhargava, O.N., Ahluwalia, A.D., Walia, S. Myrow, P.M., and Parcha, S.K., in review, Early Tsanglangpuan (late early Cambrian) trilobites from the Nigali Dhar syncline, and the Cambrian biostratigraphy of the Tal Group, Lesser Himalaya, India: Geological Magazine, submitted 9/’03. 

• Myrow, P.M., Hughes, N.C., Paulsen, T., Williams, I., Parcha, S.K., *Thompson, K.R., Bowring, S.A., Peng, S.-C., and Ahluwalia, A.D., 2003, Integrated tectonostratigraphic analysis of the Himalaya and implications for its tectonic reconstruction. Earth and Planetary Science Letters, v. 212, p. 433-441.