Geosystems and Geoenvironment (Nov 2023)
Mountain height as a proxy for the cessation of active plate convergence
Abstract
Megathrust shear force along convergent plate margins exerts a primary control on the height/elevation of mountain ranges, which can be mechanically sustained. In the present study, we characterize the strength of megathrust (or ancient megathrust) across the Indo-Burmese Arc (IBA), NE-Himalaya, and Central India region by combining geodetic observations, and an analytical force balance model based on fault rheology. Geodetic measurements from the Indian sub-continent indicate that the Narmada-Son deformation zone along the Central Indian Tectonic Zone (CITZ), possibly acts as a diffuse plate boundary in recent times, segmenting the continental part of the Indian plate into two-component plates, respectively, i.e., the North-Indian plate and South-Indian plate. In the case of IBA, the presence of large scatter in geodetic data from the up-dip edge of the detachment leads to ambiguity in the exact nature of stain accumulation, subduction activity, and associated seismic hazards. Moreover, the discrepancy between the observed Maximum Mean Elevation (MME) and analytical force balance model predicted Tectonically Supported Elevation (TSE) for both CITZ and IBA regions, possibly indicate cessation of active convergence or weaker megathrust at present, along with the continuous erosional activity. While, the Shillong Plateau, and NE-Himalayan detachment, despite being part of overall same climatic/erosional conditions, show a good agreement between the TSE and MME, suggesting mountain heights in these regions are primarily controlled by the megathrust shear force. It appears that erosion process has limited impact in controlling the topographic height via mass removal process and megathrust shear force (strength of the megathrust) plays a major role. However, it is difficult to characterize the relative contribution of the individual processes.
