Plume-related regional prevolcanic uplift in the Deccan Traps: Absence of evidence, evidence of absence
Published:January 01, 2007
H.C. Sheth, 2007. "Plume-related regional prevolcanic uplift in the Deccan Traps: Absence of evidence, evidence of absence", Plates, Plumes and Planetary Processes, Gillian R. Foulger, Donna M. Jurdy
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From the mantle plume model it would be expected that one to a few kilometers of regional, domal lithospheric uplift occurred 5–20 m.y. before the onset of flood basalt volcanism. This uplift resulted from heat conduction out of and dynamic support by the hot, buoyant, rising plume head. Field evidence for such uplift would comprise sedimentary sequences that reflect progressive basin shallowing before volcanism or (in the case of differential uplift along faults) widespread conglomerates derived from the basement rocks and underlying the first lavas. Local uplifts and subsidences cannot be used to invoke or rule out plume-caused uplift. Over large areas of the Late Cretaceous Deccan flood basalt province, the base of the lava pile is in the subsurface. Basalt-basement contacts are observed along the periphery of the province and in central India (the Satpura and Vindhya ranges), where substantial post-Deccan uplift is evident. Here, extensive horizontal Deccan basalt flows directly overlie extensive low-relief planation surfaces cut on various older rocks (Archean through Mesozoic) with different internal structures. Locally, thin, patchy Late Cretaceous clays and limestones (the Lameta Formation) separate the basalts and basement, but some Lameta sediments are known to have been derived from already erupted Deccan basalt flows in nearby areas. Thus, the eruption and flowage of the earliest Deccan basalt lava flows onto extensive flat planation surfaces developed on varied bedrock, and the nearly total absence of basement-derived conglomerates at the base of the lava pile throughout the province, are evidence against prevolcanic lithospheric uplift (both regional and local), and thereby the plume head model. There has been major (∼1 km) post-Deccan, Neogene uplift of the Indian peninsula and the Sahyadri (Western Ghats) Range, which runs along the entire western Indian rifted margin, well beyond the Deccan basalt cover. This uplift has raised the regional Late Cretaceous lateritized surface developed on the Deccan lava pile to a high elevation. This uplift cannot reflect Deccan-related magmatic underplating, but is partly denudational, is aided by a compressive stress regime throughout India since the India-Asia collision, and is possibly also related to active eastward flow of the sublithospheric mantle. The easterly drainage of the Indian peninsula, speculated to be dome-flank drainage caused by the plume head, predates the uplift. Field evidence from the Deccan and India is in conflict with a model of plume-caused regional uplift a few million years before the onset of volcanism.