Systematic and Temporal Geochemical Changes in the Upper Deccan Lavas: Implications for the Magma Plumbing System of Flood Basalt Provinces
Abstract
Large Igneous Provinces (LIPs) are unusual volcanic events in which massive amounts of melt
(∼10^6 km^3) erupt in relatively short time periods (<10^6 years). Most LIP magmas have undergone extensive
fractional crystallization and crustal contamination, but the crustal magmatic plumbing systems and the
processes triggering eruptions are poorly understood. We present new major and trace element and radiogenic
isotope data for 43 individual lava flows from a continuous 1,200 m thick stratigraphic profile through the
upper, most voluminous part of the Deccan LIP (Bushe to Mahabaleshwar Formations). Eruption rates for
this section are constrained by published paleomagnetic directions and absolute U-Pb ages for zircons from
weathered flow tops exposed in the profile. We find four magmatic sequences each lasting ∼10^4 – ∼10^5 years
during which major and trace element compositions change systematically, followed by an abrupt change
in geochemistry at the start of a new sequence. Within each sequence, the MgO content and proportion of
crustal contamination decrease progressively, indicating a continuous replenishment of the associated magma
reservoirs with less contaminated but more evolved melts. These geochemical signatures are best explained
by repeated episodes of melt recharge, mixing, and eruption of variably evolved magmas originating from
relatively small magma reservoir located in different crustal levels.
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