Identification of the EMII-type mantle end-member of the Kerguelen mantle plume and its implications for the initial breakup of eastern Gondwana: New constraints from the Cretaceous diabase in the Tethyan Himalaya

Abstract

The breakup of eastern Gondwana during the Early Cretaceous has been well-documented. However, the relationship between Cretaceous mafic magma and the Kerguelen mantle plume has not been well-constrained. It is also unknown if the Kerguelen mantle plume in the Tethyan Himalaya played a key role in triggering the breakup of eastern Gondwana. The petrogenesis and geodynamic processes of the coeval magmatism in the Tethyan Himalaya might provide value insights into this issue. In this study, we conducted petrological, geochronological, and geochemical investigations on a recently identified diabase from the Yamdrok Lake. The diabase contains zircon grains with a U-Pb age of 138 ± 8 Ma, suggesting the emplacement at the Early Cretaceous. Geochemically, the studied samples display OIB-like trace elemental features that are enriched in light rare earth elements (LREEs) but no significant depletion in high field strength elements (HFSEs), such as Nb, Ta, and Ti. Furthermore, they have relatively uniform Sr-Nd-Pb-Hf-O isotopic compositions with initial ⁸⁷Sr/⁸⁶Sr ratios varying from 0.70563 to 0.70623, ε_Nd(t) and ε_Hf(t) values range from 0.6 to 0.8 and 1.0–2.4, respectively, whole-rock δ¹⁸O values of 6.42 ‰ to 7.50 ‰, and (²⁰⁸Pb/²⁰⁴Pb)_i = 38.995 ∼ 39.285, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.673 ∼ 15.698, and (²⁰⁶Pb/²⁰⁴Pb)_i = 18.689 ∼ 18.914, similar to an EMII-type enriched mantle. And recycled shallow continental crustal materials into the OIB-like mantle source might account for the EMII-type mantle features observed in this study. Considering the Kerguelen mantle plume locating beneath the triple junction of Australia, Antarctica, and Greater India, we propose that the mafic rocks in this study might be genetically related to the early activity or even initiation of the Kerguelen plume during the Early Cretaceous. Our study further indicates that the Kerguelen mantle plume contains EMI- and EMII-type isotopic compositions, which are characterized by geochemical complexity and variation.