Crust first–mantle second and mantle first–crust second; lithospheric break-up scenarios along the Indian margins

Abstract

Compared segments of the East and West Indian passive margins have different evolutions and crustal architecture. The East Indian margin is less magmatic. It results from a crust first–mantle second break-up scenario of a continent experiencing two rift events. The West Indian margin is more magmatic. It results from a mantle first–crust second break-up scenario of a continent experiencing four rift events. The architecture across both margins can be divided into stretching, thinning and hyperextension zones. The East Indian margin is characterized by oceanward-dipping listric normal faults that accommodate thinning in the thinning and hyperextension zones, and a zone of exhumed mantle separating continental and oceanic crusts. The West Indian margin in contrast is characterized by landward-dipping listric faults that accommodate magma-assisted thinning in the thinning and hyperextension zones, and no exhumed mantle. The final break-up affects the lith-ospheric mantle layer in the East Indian case and the crustal layer in the West Indian case. Although the tem-perature-dependent rheologies of these two last unbroken layers are somewhat different, seismic interpretation suggests that they are both broken by upward-convex normal faults, which succeeded the development of listric faults. They appear to be the first spontaneously formed faults in the break-up-delivering process, although their nucleation may be magma-assisted. The main difference between the controlling factors of the aforementioned break-up scenarios affecting similar lithospheres at similar extension rates is the cumulative length of time of the pre-break-up rift events, which is 62 and 115 myr for the East and West Indian margins, respectively.