The mechanisms through which the continental crust has been formed are debatable. However, there exist two contrasting models to explain the evolution of continental crust e.g. a) horizontal accretion of island arcs and b) vertical accretion due to differentiation of magmatic material above hotspots. Whether both the processes operated together or separately is hard to ascertain. Also, there is no consensus on the processes that govern secular change in the character of the crust in Archean, as revealed by the seismological and petrological data. We address these key issues using the converted wave data by extracting the bulk crustal properties of the Indian cartons. Our analysis reveals that most of the crust is formed in the early Archean and hen gradually altered, making it mafic-to-intermediate in bulk composition. Further, the present day heat-flow values, which are higher in late-Archaean correspond to regions of thinner crust, implying that the crustal formation prevails at much higher temperatures predominantly through vertical accretion initially and then by slab melting. Subsequently, the horizontal accretion dominants and a large part of the lower crust seems to be degenerated making it thinner and intermediate in composition.
Figure. Clustering and temporal distribution of bulk crustal properties for the Indian cratons. All the available parameters for the single cratons are average out with the error bar as shown by the bar lines. (a) variation of bulk crustal thickness with respect to bulk Vp/Vs, (b and c) temporal variation of crustal thickness and Vp/Vs respectively. The labeling inside the subplots are the abbreviations for the cratons e.g. EDC – Esatern Dharwar craton, WDC – Western Dharwar craton, BC – Bastar craton, SC – Singhbhum craton and BhC- Bundelkhand craton. The dashed line represent the bets fit regression line with regression coefficient of r.
Haldar, C; Kumar, P; Kumar, M. Ravi; Ray, L; Srinagesh, D (2018). Seismic evidence for secular evolution and alteration of Archaean crust in Indian shield, precambrian Research, 304, 12-20, DOI: 10.1016/j.precamres.2017.10.023