Genesis and emplacement of Higher Himalayan Leucogranite in the Arunachal Himalaya, Northeast India: constrains from deformation microstructures and geochemical data

Abstract HKT-ISTP 201

Continental extension of northern Gondwana margin in the Eastern Himalaya: Constraints from geochemistry and U–Pb zircon ages of mafic intrusives in the Siang window, Arunachal Himalaya, India

We report new U–Pb zircon age and whole-rock geochemical data from the Pangin mafic intrusive rocks of the Siang window, eastern Himalayas. These mafic rocks are medium to coarse-grained gabbros, consisting mainly of plagioclase and clinopyroxene with accessory phases (hornblende $+$ Fe–Ti oxides) that retain granular and interlocking texture. Geochemically, they display enriched-mid oceanic ridge basalt (E-MORB) affinity characterized by moderate to slightly fractionated REE patterns marked by $(\mathrm{La}/\mathrm{Yb})_{\mathrm{N}} = 2.65-3.99$. Their geochemical characteristics suggest that the parental magmas of these rocks were formed by medium to higher degrees (∼12–28%) of partial melting similar to that of the asthenospheric mantle in the garnet-spinel transition zone. Magmatic zircons from two gabbros yield U–Pb ages of 521.50 $\sim$ 2.53 Ma and 568 ${\pm }$ 2 Ma. This new age reveals two pulses of Late Neoproterozoic and Early Cambrian mafic magmatism that are inconsistent with the temporal distribution of Paleozoic magmatism in the Siang window of the Eastern Himalayas. However, based on the results of this study and the correlation of continental extensional mafic magmatism in the Northwest Himalaya, we suggest that investigated mafic intrusive rocks might have been generated in an extensional tectonic environment during the long-lasting Pan-African orogenic cycle of the late Neoproterozoic to early Cambrian which ended with the formation of the Gondwana supercontinent

Continental extension of northern Gondwana margin in the Eastern Himalaya: Constraints from geochemistry and U–Pb zircon ages of mafic intrusives in the Siang window, Arunachal Himalaya, India

We report new U–Pb zircon age and whole-rock geochemical data from the Pangin mafic intrusive rocks of the Siang window, eastern Himalayas. These mafic rocks are medium to coarse-grained gabbros, consisting mainly of plagioclase and clinopyroxene with accessory phases (hornblende $+$ Fe–Ti oxides) that retain granular and interlocking texture. Geochemically, they display enriched-mid oceanic ridge basalt (E-MORB) affinity characterized by moderate to slightly fractionated REE patterns marked by $(\mathrm{La}/\mathrm{Yb})_{\mathrm{N}} = 2.65-3.99$. Their geochemical characteristics suggest that the parental magmas of these rocks were formed by medium to higher degrees (∼12–28%) of partial melting similar to that of the asthenospheric mantle in the garnet-spinel transition zone. Magmatic zircons from two gabbros yield U–Pb ages of 521.50 $\sim$ 2.53 Ma and 568 ${\pm }$ 2 Ma. This new age reveals two pulses of Late Neoproterozoic and Early Cambrian mafic magmatism that are inconsistent with the temporal distribution of Paleozoic magmatism in the Siang window of the Eastern Himalayas. However, based on the results of this study and the correlation of continental extensional mafic magmatism in the Northwest Himalaya, we suggest that investigated mafic intrusive rocks might have been generated in an extensional tectonic environment during the long-lasting Pan-African orogenic cycle of the late Neoproterozoic to early Cambrian which ended with the formation of the Gondwana supercontinent

Petrogenetic evolution of the felsic and mafic volcanic suite in the Siang window of Eastern Himalaya, Northeast India

The Abor volcanics outcroping in the core of the Siang window in the Eastern Himalaya comprise voluminous mafic volcanics (47%–56% w(SiO2)), with subordinate felsic volcanics (67%–75% w(SiO2)). The felsic volcanics are dacitic to rhyolitic in composition and are typically enriched in LREE (La/SmN = 3.09–3.90) with high REE contents (256–588 ppm), moderately fractionated REE patterns (CeN/YbN = 6.54–9.52) and pronounced negative Eu anomalies (Eu/Eu* = 0.55–0.72). Wide variations in Rb/Zr, K/Rb and La/Sm ratios suggest that they were derived from magmas which were randomly contaminated with crustal material. Chemical characteristics and petrogenetic modelling indicate that the dacites were generated by ∼15% partial melting of a mafic source leaving a residue with 55% plagioclase, 14% orthoclase, 18% clinopyroxene, 5% orthopyroxene, 8% hornblende. The silica-rich rhyodacites and rhyolites were derived from a dacite magma source by a higher degree (>45%) fractional crystallization of an assemblage consisting of 70% plagioclase, 12% clinopyroxene, 7% amphibole and 11% magnetite. The associated LREE-LILE enrichment and pronounced negative anomalies for HFSE (Nb, P, and Ti) exhibited by these felsic volcanics are characteristic of continental rift volcanism, implying that they were emplaced during lithospheric extension

Mechanism of iron integration into LiMn1.5Ni0.5O₄ for the electrocatalytic oxygen evolution reaction

Abstract Spinel-type LiMn1.5Ni0.5O₄ has been paid temendrous consideration as an electrode material because of its low cost, high voltage, and stabilized electrochemical performance. Here, we demonstrate the mechanism of iron (Fe) integration into LiMn1.5Ni0.5O₄ via solution methods followed by calcination at a high temparature, as an efficient electrocatalyst for water splitting. Various microscopic and structural characterizations of the crystal structure affirmed the integration of Fe into the LiMn1.5Ni0.5O₄ lattice and the constitution of the cubic LiMn1.38Fe0.12Ni0.5O₄ crystal. Local structure analysis around Fe by extended X-ray absorption fine structure (EXAFS) showed Fe3+ ions in a six-coordinated octahedral environment, demonstrating incorporation of Fe as a substitute at the Mn site in the LiMn1.5Ni0.5O₄ host. EXAFS also confirmed that the perfectly ordered LiMn1.5Ni0.5O₄ spinel structure becomes disturbed by the fractional cationic substitution and also stabilizes the LiMn1.5Ni0.5O₄ structure with structural disorder of the Ni²⁺ and Mn⁴⁺ ions in the 16d octahedral sites by Fe²⁺ and Fe³⁺ ions. However, we have found that Mn³⁺ ion production from the redox reaction between Mn⁴⁺ and Fe²⁺ influences the electronic conductivity significantly, resulting in improved electrochemical oxygen evolution reaction (OER) activity for the LiMn1.38Fe0.12Ni0.5O4 structure. Surface-enhanced Fe in LiMn1.38Fe0.12Ni0.5O₄ serves as the electrocatalytic active site for OER, which was verified by the density functional theory study