Their study reveals that the major collisional events between India and Asia were limited to a relatively brief interval in the Early Cenozoic, contradicting the theory of ongoing subduction throughout the epoch. The findings emphasize that the widespread uplift of the Tibetan Plateau primarily stemmed from mantle dynamics that followed the initial collision, particularly in the Late Cenozoic.
Instead of a uniform collisional history, the region exhibits a complex geological mosaic of terranes assembled over hundreds of millions of years from the Early Paleozoic to the Mesozoic. These terranes and their sutures were reactivated briefly during the early collision phase, rather than acting as a monolithic orogenic belt evolving throughout the Cenozoic.
Evidence from seismic tomography and helium isotopic studies delineates Indian plate subduction to depths of 200-300 kilometers, largely confined beneath the Yarlung-Zangpo Suture, the southern fringe of the Tibetan Plateau. Moreover, paleomagnetic data inconsistencies regarding the size of Greater India are addressed by highlighting a decoupling between surface cover and deeper basement rock. This scenario favors a model of shallow, soft subduction reaching no more than 300 kilometers, which better aligns paleomagnetic and geological shortening estimates.
The Himalayan orogeny is now interpreted as having two distinct phases. The first, occurring between 55 and 45 million years ago, involved soft to hard continental collision and localized deep subduction, leading to crustal thickening via thrusting. The second, from 30 to 10 million years ago, saw a dramatic shift to post-collisional processes. These were driven by upwelling asthenospheric mantle following lithospheric foundering, culminating in crustal melting, the emplacement of leucogranites, formation of metamorphic core complexes, and domal uplift across the region.
These insights question the validity of interpreting paleomagnetic and seismic datasets strictly through the lens of continuous collision and deep underthrusting. Many previously accepted tectonic interpretations appear to conflate syn-collisional and post-collisional features, overlooking key differences in timing, thermal regimes, and driving mechanisms.
As a result, the study calls for a paradigm shift in understanding continental tectonics, urging that future geodynamic models of the India-Asia convergence give greater weight to post-collisional mantle-driven uplift rather than prolonged collisional compression. This revision has broader implications for how geologists interpret tectonic evolution at convergent plate boundaries worldwide.
Research Report:A revisit to continental collision between India and Asia.
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