Reconstruction of the deformed collision zone Between India and Asia by backward motion of lithospheric blocks

TLDR

The study aims to reconstruct the evolution of the India‑Asia collision zone using a synthesis of tectonic data. The authors model the collision by treating lithospheric deformation as confined to narrow shear zones, moving block contours back along fault boundaries while assuming coherent shortening or stretching at convergent or extensional margins, and iteratively computing displacement maps and Euler poles to trace the collision back to its onset. The reconstruction yields time‑step solutions consistent with available data, enabling kinematic solutions for poorly constrained regions, and shows that extrusion accounted for roughly 30 % of India‑Siberia convergence overall, ranging from 3 % to 60 % across epochs, with the latest map matching GPS observations.

Abstract

On the basis of a synthesis of tectonic data available on the India‐Asia collision, we present a first attempt to reconstruct the evolution of the collision zone. Assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed, we define block contours from the fault pattern and move back the blocks along their boundary faults. Along convergent or extensional boundaries, the crust is assumed to shorten or stretch coherently. Step‐by‐step, we go backward in time to finally reach the collision onset. For each time step, we find a solution compatible with the data set available and the position of the adjacent blocks for each block. The search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking. For each step, we calculate large‐scale displacement maps, and determine Euler poles for each block. For the most recent time step, the map proposed is compared to GPS motions. The deformation budget implies that extrusion absorbed ∼30% of the convergence between India and Siberia during the entire collision span, but varied with time, accounting for as little as 3% or as much as 60% of this convergence at different epochs.