Age dating of basalt
I ascribe the rifting itself not to mantle plume heads but to large-scale plate dynamics, possibly aided by long-term thermal insulation beneath a supercontinent which may have surface effects similar to those predicted for “plume incubation” models.Non-plume, plate tectonic models are capable of explaining the Deccan in all its greatness., 1990), hundreds of papers have invoked, or supported, a plume head origin for the Deccan Traps of India.The associated flood basalt lavas are not represented or known in India; there are many Precambrian dyke swarms throughout southern India as well.72-73 Ma ages for Quetta and Zhob rocks and 65 Ma age for Dhandhuka-Botad lavas are from Mahoney et al.These papers are in unanimous agreement on two issues: (i) the Deccan originated from the ancestral Runion hotspot which upwelled beneath India in the late Cretaceous, and (ii) the hotspot, now located on the African plate, is fed by a deep mantle plume.The overall appearance of the Deccan, with its roughly circular outcrop, and the linear Laccadives-Chagos (more correctly, Lakshadweep-Chagos) Ridge to the south of India, looks very much like what is expected for a spherical plume head and a narrow plume tail (Figures 2 & 3).The Deccan flood basalt sequence is best developed in the Western Ghats region with ~3 km of stratigraphic thickness (Figures 1-3), and picritic basalts are found there, but these are enriched in cumulus olivine and clinopyroxene and do not represent liquid compositions.The parental melts of these picrites are estimated to have contained only ~ 9-10% Mg O ( Figure 4. Note the complete absence of compositions other than basalt and basaltic andesite, and the nearly exclusive subalkalic (tholeiitic) nature.
The lithic figure comprises a tuff pebble made of basalt, containing marks suggestive of the head, body, and arms of a female human.For example, there is little petrological evidence as yet that the Deccan source was abnormally hot, and the short (~ 1.0 – 0.5 Myr) duration claimed by some for the eruption of the Deccan is in conflict with recent Ar-Ar age data that suggest that the total duration was at least ~ 8 Myr (, 2005a,b).The interplay of several intersecting continental rift zones in India is apparently responsible for the roughly circular outcrop of the Deccan.WG is the Western Ghats region (ages from Venkatesan et al., 1993 and others).~ 64 Ma age for Rajahmundry basalts is from Baksi (2001a). KK, ~ 90-69 Ma Karnataka-Kerala dykes (e.g., Radhakrishna et al., 1994; Anil Kumar et al., 2001). Mary's Islands volcanics (85.5 Ma, Pande et al., 2001), part of the Indo-Madagascar CFB which in India is otherwise represented by the KK dykes.