Chipping of cratons and breakup along mobile belts of a supercontinent

Abstract

Probably one of the most significant heterogeneities of a continental lithosphere is the noticeable difference in the thickness and properties of its cratonic and mobile parts. The trans-continental mobile belts (Paleoorogens/paleo-sutures) represent a relatively thinner, warm, wet and weak lithosphere, which makes it more vulnerable to episodic mantle (or plume) upwellings and compressional forces. Here evidence is presented from the Indian continental lithosphere to show that these properties of mobile belts (MB) facilitate channeling of thermomagmatic fluxes (TMF) in both lateral as well as vertical directions. This, to a major extent, can account for the observed concentration (or focusing) of geophysical anomalies, tectonomagmatic features and strain along these MBs. In addition, a closer examination of the three continental breakups of Greater India since the Cretaceous reveals that the combination of a sufficiently weakened MB and mantle plume could become 'fatal' for the supercontinental stability. On the other hand, the thick (>200 km) or deep-rooted continental lithosphere beneath cratons is characterized by a relatively cold and dry lithosphere, which resists remobilization. From this relative impenetrability, TMFs are channeled mostly through the MBs following the long-term stability of the cratonic lithosphere. This difference in cratonic and MB regimes results in strongly heterogeneous thermal blanketing. However, in certain situations, the edge of a cratonic region may also get chipped-off following a number of thermotectonic rejuvenations of adjoining MBs - as exemplified by the breakup of the Antongil and Masora cratonic blocks (now lying on the Madagascar) from the Western Dharwar craton (India) during the India-Madagascar separation. From the study of supercontinental dispersals, it seems that the processes of breakup along pre-existing mobile belts may be globally applicable. This is, at times, also accompanied by chipping of cratons. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.