Multiple mantle melting events for two overlapping ca. 2.21-2.18 Ga mafic dyke swarms in the Dharwar craton, India

Abstract

ABSTRACT Two distinct NW- to WNW-trending mafic dike swarms of the previously dated ca. 2.21 Ga Anantapur-Kunigal and ca. 2.18 Ga Mahbubnagar-Dandeli swarms, emplaced in the Dharwar craton, are studied in greater petrological detail. Petrography classifies these as dolerite, olivine-dolerite, and meta-dolerite. The bulk rock geochemistry of 39 new and 11 published samples of both dike swarms are compared to those of three ca. 2.21 Ga and two ca. 2.18 Ga samples previously dated through baddeleyite U-Pb geochronology. All 50 samples are sub-alkaline tholeiite basalt to basaltic andesite in compositions and both swarms have similar differentiation/crystallization trends. Nonetheless, based on the slightly enriched REE patterns of ca. 2.21 Ga samples, as opposed to practically flat ca. 2.18 Ga REE patterns; we propose that 41 samples constitute the ca. 2.21 Ga Anantapur-Kunigal dike swarm and 9 samples belong to the ca. 2.18 Ga Mahbubnagar-Dandeli swarm. Petrogenetic modelling suggests that each swarm was derived through different degrees and proportions of partial melting of both an ambient asthenospheric and metasomatized sub-continental lithospheric mantle (SCLM) and further differentiated through similar fractional crystallization processes. Both mantle melts segregated within the garnet to garnet-spinel transition zone. Geodynamic conditions suggest that dikes of both swarms were emplaced in a similar tectonic system within a single LIP, which was likely triggered through the heating by the same (pulsating?) mantle plume. Such an indirect influence from a mantle plume, not recorded in geochemical signatures, is supported by ~1576°C potential mantle temperature (Tp) estimates for more magnesian parents within both swarms. Available geochronological data on mafic dikes and Palaeopositions of the Dharwar and North American cratons during ca. 2.21–2.18 Ga are well supportive of their link to the Superia supercraton reconstruction.