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

Abstract

Compared segments of East and West Indian passive margins have different evolution and crustal architecture. The East Indian margin is less magmatic. It results from a crust first/mantle second breakup scenario of a continent experiencing two rift events. The West Indian margin is more magmatic. It results from a mantle first/crust second breakup 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 accommodating thinning in the thinning and hyperextension zones and a zone of the exhumed mantle separating continental and oceanic crusts. The West Indian margin in contrast is characterized by landward-dipping listric faults accommodating magma-assisted thinning in the thinning and hyperextension zones and no exhumed mantle. The final breakup affects the lithospheric mantle layer in the East Indian case and the crustal layer in the West Indian case. Although the temperature-dependent rheologies of these two last unbroken layers are rather different, seismic interpretation suggests that they are both broken by upward-convex normal faults, which succeed the development of listric faults. They appear to be the first spontaneously formed faults in the breakup-delivering process, although their nucleation may be magma-assisted. The main difference between controlling factors of the aforementioned breakup scenarios affecting similar lithospheres at similar extension rates is the cumulative time length of pre-breakup rift events, being 62 and 115 Ma at East and West Indian margins.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5912978