Mantle Source Components and Magmatic Evolution for the Comei Large Igneous Province: Evidence from the Early Cretaceous Niangzhong Mafic Magmatism in Tethyan Himalaya

Abstract

The Niangzhong diabase dikes, dated at 138.1 ± 0.4 Ma, are located within the outcrop area of the Comei large igneous province (LIP). These diabase samples can be divided into two groups: samples in Group 1 show varying MgO (1.50 wt.%–10.25 wt.%) and TiO₂(0.85 wt.%–4.63 wt.%) contents, and enriched initial isotope compositions (⁸⁷Sr/⁸⁶Sr(t) = 0.705 6–0.711 2, ε _KNd(t) = −0.3− +3.8), with OIB-like REEs and trace elements patterns, resulting from low degree melting of garnet-bearing lherzolite mantle sources; in contrast, samples in Group 2 show limited MgO (4.14 wt.%–7.75 wt.%) and TiO₂(0.98 wt.%–1.69 wt.%) contents, and depleted initial isotope compositions (⁸⁷Sr/⁸⁶Sr(t) = 0.707 5–0.711 2, ε _Nd(0 = +5.5− +6.2), with N-MORB-like REEs and trace elements patterns, resulting from relatively high degree melting of spinel-bearing lherzolite mantle source. Combined with the published representative data about Comei LIP, we summarize that the source components for Comei LIP products include OIB end-member, enriched OIB end-member, and N-MORB end-member, respectively. Melts modeling suggests that magmas in the Comei LIP evolve in a relatively high oxygen fugacity condition, which influenced their fractionation sequences and led to systematic changes of TiO₂ contents, Ti/Y and Ti/Ti* ratios. From the spatial and temporal distribution of above three end-member samples, deep process of Kerguelen plume during the Comei LIP formation can be interpreted as the interaction among the Kerguelen plume, the overlying lithospheric mantle, and the upwelling asthenosphere. The magmatism of Comei LIP began at ∼140 Ma and then lasted and peaked at ∼132 Ma with the progressively lithospheric thinning of eastern Gondwana upon the impact of Kerguelen plume.

Keywords

Comei large igneous province / mafic magmatic evolution / low-Ti and high-Ti mafic rocks / Kerguelen plume / geochemistry / tectonics

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