Contributions from the detrital approach to unravelling the timing of India-Asia collision and Himalayan evolution

Knowledge of the timing of India-Asia collision and associated Tethyan closure in the region is critical to advancement of models of crustal deformation.   One of a number of methods traditionally used to constrain the time of India-Asia collision is the detrital approach. This involves determination of when Asian material first arrived on the Indian plate, with most recent estimates documenting collision at ca 60 Ma (e.g. Hu et al, Earth Science Reviews 2016). However, more recently, such data and a number of other approaches providing data previously used to determine the timing of India-Asia collision, have been controversially re-interpreted to represent collision of India with an Island arc, with terminal India-Asia collision occurring significantly later, ca 34 Ma (e.g. Aitchison et al, J. Geophysical Research 2007). Clearly, for the detrital approach to advance the debate, discrimination between Asian detritus and arc detritus is required. Such a discrimination was proposed in Najman et al (EPSL 2017), dating the timing of terminal India-Asia collision at 54 Ma. However, this evidence is far from universally accepted.  For example, such data are at variance with various palaeomagnetic studies which suggest that an oceanic Transtethyan subduction zone existed 600-2300 kms south of the Eurasian margin in the Paleocene  (e.g. Martin et al, PNAS 2020) and therefore these authors propose different explanations to explain the detrital data.  This presentation will discuss the uncertainties associated with our current understanding of the timing of India-Asia collision.