5 years ago

Oldest lamproites from Peninsular India track the onset of Paleoproterozoic plume-induced rifting and the birth of Large Igneous Province

Oldest lamproites from Peninsular India track the onset of Paleoproterozoic plume-induced rifting and the birth of Large Igneous Province
Potassic and ultrapotassic magmatism from deep lithospheric sources in intra-cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of Large Igneous Provinces (LIPs) triggered by mantle plumes. Here we report for the first time, precise zircon U–Pb age data from a suite of lamproites in the Bastar Craton of central India that mark the onset of Paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major LIP events during the Precambrian evolution of the Indian shield. The lamproites from the Nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile, apatite and zircon. The rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite. Geochemical features of the lamproites correlate with their counterparts in Peninsular India and other similar suites elsewhere in the world related to rift settings, and also indicate OIB-like magma source. The associated syenite shows subduction-related features, possibly generated in a post-collisional setting. Magmatic zircon grains with high Th/U ratios in the syenite from the Nuapada lamproite form a coherent group with an upper intercept age of 2473±8Ma representing the timing of emplacement of the magma. Zircon grains in three lamproite samples yield four distinct age groups at ca. 2.4Ga, 2.2Ga, 2.0Ga and 0.8Ga. The 2.4Ga group corresponds to xenocrysts entrained from the syenite whereas the 2.2Ga group is considered to represent the timing of emplacement of the lamproites. The ca. 2.0Ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern Bastar and the adjacent Dharwar Cratons. A few young zircon grains in the syenite and lamproites show a range of early to middle Neoproterozoic ages from 879 to 651Ma corresponding to younger thermal event(s) as also represented by granitic veins cutting across these rocks and extensive silicification. Zircon Lu–Hf isotope data suggest magma derivation from a refertilized Paleo-Mesoarchean sub-continental lithospheric mantle, or OIB-type sources. The differences in Hf-isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale. A combination of the features from geochemical and zircon Hf isotope data is consistent with asthenosphere-lithosphere interaction during the lamproite magma evolution. The timing of lamproite emplacement in central India correlates with the global 2.2Ga record of LIPs. We link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction-accretion history prior to the Neoarchean cratonization, as well as the thermal blanket effect of the Earth's oldest supercontinent. Pulsating plumes and continued rifting generated voluminous dyke swarms across the Bastar and Dharwar Cratons, forming part of a major global rifting and LIP event.

Publisher URL: www.sciencedirect.com/science

DOI: S1342937X17303362

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