Contrasting Modes of Deformation in Cratonic vs Non-cratonic Lithosphere during Early-stage Rifting

Meritxell Colet, Columbia University
Folarin Kolawole, Columbia University
Rasheed Ajala, Lamont-Doherty Earth Observatory
Kaiwen Wang, Institute of Geology and Geophysics, Chinese Academy of Sciences
Obeid S. Lemna, University of Dar es Salaam
Gabriel D. Mulibo, University of Dar es Salaam
Felix Waldhauser, Lamont-Doherty Earth Observatory
W. Roger Buck, Lamont-Doherty Earth Observatory

Abstract

Continental rifts commonly follow orogenic belts but are also observed globally to break the inherently stronger Archean cratons, presenting an intriguing strength paradox. We explore a magma-poor sector of the East African Western Rift where active rifting has initiated across an Archean craton and an adjacent Proterozoic orogenic belt, in which both terranes host incipient and maturing rift segments. Using a new machine learning-enhanced earthquake catalog, we detected and located 5,002 earthquakes that illustrate the distribution of active brittle deformation in each rift. Our results reveal ubiquitously unimodal seismogenic depth zonation that peaks in the lower crust of craton-hosted rifts, contrasting the variable depths of peak seismicity in orogen-hosted rifts. To elucidate these contrasting strain localization patterns, we model the representative lithospheric yield strength envelopes that explain the depth zonation of brittle failure in the rift domains. The results suggest that lower crustal strain focusing is a fundamental mode of rift initiation and temporal persistence of extensional strain localization in cratons. We argue that the breaking of cratons is facilitated by early-stage strain localization in the deep crust.

Session

Large-scale tectonics