Physical volcanology and geochemistry of Palaeoarchaean komatiite lava flows from the western Dharwar craton, southern India: implications for Archaean mantle evolution and crustal growth

Abstract

Palaeoarchaean (3.38-3.35 Ga) komatiites from the Jayachamaraja Pura (J.C. Pura) and Banasandra greenstone belts of the western Dharwar craton, southern India were erupted as submarine lava flows. These high-temperature (1450-1550°C), low-viscosity lavas produced thick, massive, polygonal jointed sheet flows with sporadic flow top breccias. Thick olivine cumulate zones within differentiated komatiites suggest channel/conduit facies. Compound, undifferentiated flow fields developed marginal-lobate thin flows with several spinifex-textured lobes. Individual lobes experienced two distinct vesiculation episodes and grew by inflation. Occasionally komatiite flows form pillows and quench fragmented hyaloclastites. J.C. Pura komatiite lavas represent massive coherent facies with minor channel facies, whilst the Bansandra komatiites correspond to compound flow fields interspersed with pillow facies. The komatiites are metamorphosed to greenschist facies and consist of serpentine-talc ± carbonate, actinolite-tremolite with remnants of primary olivine, chromite, and pyroxene. The majority of the studied samples are komatiites (22.46-42.41 wt.% MgO) whilst a few are komatiitic basalts (12.94-16.18 wt.% MgO) extending into basaltic (7.71 -10.80 wt.% MgO) composition. The studied komatiites are Al-depleted Barberton type whilst komatiite basalts belong to the Al-undepleted Munro type. Trace element data suggest variable fractionation of garnet, olivine, pyroxene, and chromite. Incompatible element ratios (Nb/Th, Nb/U, Zr/Y Nb/Y) show that the komatiites were derived from heterogeneous sources ranging from depleted to primitive mantle. CaO/Al 2 O 3 and (Gd/Yb) N ratios show that the Al-depleted komatiite magmas were generated at great depth (350-400 km) by 40-50% partial melting of deep mantle with or without garnet (majorite?) in residue whilst komatiite basalts and basalts were generated at shallow depth in an ascending plume. The widespread Palaeoarchaean deep depleted mantle-derived komatiite volcanism and sub-contemporaneous TTG accretion implies a major earlier episode of mantle differentiation and crustal growth during ca. 3.6-3.8 Ga.ARTICLE HISTORY

Geochemistry of Layered Ultramafic Rocks in J.C. Pura Schist Belt, Dharwar Craton, Karnataka, India

“…The contact between layers is distinct, and interaction between dunite and pyroxenite and peridotite and pyroxenite are visible. The sharp contacts may be primarily the result of episodic injection of undifferentiated to slightly differentiated magma pulses that cooled and solidified without undergoing significant fractional crystallization [19]. Magnetite bands associated with chromite are also noticed in the layered sequences (Figure 2(b)).…”

Geochronology, paleomagnetic signature and tectonic models of cratonic basins of India in the backdrop of Supercontinent amalgamation and fragmentation

“…Whereas, the Southern Indian Block (SIB) comprises the Dharwar-(including Southern Granulite Terrain), the Bastar-Singhbhum cratonic nuclei and the Eastern Ghats Belt (EGB) French et al, 2008) (Fig.2). These cratons are composed mostly of granites, gneisses and remnants of greenstone/schist belts of the Archaean age and the cratonic basins (Purana basins) of Proterozoic age (Jayananda et al, 2018(Jayananda et al, , 2016(Jayananda et al, , 2015Manikyamba et al, 2017;Saha and Mazumder, 2012;Chakraborty et al, 2010;Ramakrishna and Vaidyanadhan, 2008;Radhakrishna and Naqvi, 1986). Seismic studies and gravity modelling indicate the general crustal thickness of the Indian peninsular region to be about 35 km (Verma and Subrahmanyam, 1984;Kaila et al, 1979).…”

Annals of Precambrian Lithospheric Evolution and Metallogeny in the Dharwar Craton, India: Recent Paradigms and Perspectives

“…Based on zircon Lu-Hf data with positive and negative εHf(t) values from ~3.9 to 1.5 and Hf depleted model ages (T DM ) of 3041-3366 Ma for the serpentinised dunite and ~0.2 to 2.0 and 2833-2995 Ma for the pyroxenite, the authors suggest that the magma was sourced from a depleted mantle and was contaminated with the ancient continental crust which is supported by the whole rock geochemistry. Based on the petrographic and geochemical characteristics, mantle plume emplacement in a marine environment was been suggested as a possible source for the genesis of J.C. Pura and Banasandra komatiites (Jayananda et al, 2016). To understand the evolution of Archean mantle, age and petrogenesis, Maya et al (2017) studied the major, trace and Sm-Nd isotopic systematics of the spinifex-textured komatiites from Mesoarchean Banasandra greenstone belt of the Sargur Group in the Dharwar Craton.…”