Refertilization of depleted mantle peridotite in the Nagaland–Manipur ophiolite, north‐east India: Constraints from PGE, mineral, and whole‐rock geochemistry

Abstract

This paper discusses whole‐rock geochemistry, mineral chemistry, and platinum group element (PGE) systematics of depleted mantle rocks (harzburgite and dunite) from the northern part of Nagaland–Manipur Ophiolite (NMO), north‐east India, to comprehend their source features, fractionation behaviour of PGE during magmatic evolution, and its tectonic origin. The studied ultramafic rocks are characterized by a low concentration of CaO (0.57–0.71 wt%), Al2O3 (0.18–0.92 wt%) with ∑REE of 1.135–2.702 ppm and high concentrations of MgO (38.70–44.21 wt%), Cr (1,843–4,572 ppm), and Ni (894–4,138 ppm). They show U‐shaped REE patterns [LREE and HREE enrichment (La/Sm)N = 1.85–4.11, (Dy/Yb)N = 0.51–0.85]. Olivine ranges Fo 88.18 to Fo92.23, whereas Cpx and Opx range En44.84 to En47.89 and En86.37 to En93.37 respectively. The chrome spinel Cr# [Cr/(Cr + Al)] and Mg# [Mg/(Mg + Fe2+)] are 0.47–0.83 and 0.31–0.60, respectively, which indicates recrystallization from a boninitic magma in a Supra‐Subduction Zone setting. Conventional thermometry indicates the equilibration temperatures of the dunite sample yielded high temperatures of ~850°C, suggesting their formation due to later interaction with high‐temperature percolating melts. The PGE contents in harzburgite are low (125.6–142.8 ppb) as compared to the dunite (248–360 ppb). They have high PPGE/IPGE and negative Pt* (Pt/Pt* = 0.73) anomaly, which is characteristic of re‐entry of PPGE into the system via reaction with percolating basaltic melt in the mantle wedge. Significantly higher concentration of PPGEs than IPGEs in the samples, indicating recrystallization of PPGEs with early sulphide fractionation. The presence of significant Rh and Pd enhancements relative to Pt in all samples suggests that Pt was removed during PGE fractionation. This could be one of the reasons for both harzburgite and dunite's sulphide undersaturation. PGE distribution in NMO ultramafic rocks was therefore validated as being governed by sulphide saturation in parental magma and altered not only by partial melting but also by fractionation during their production in the Supra‐Subduction Zone environment.

Source characterisation of the residual lherzolite and harzburgite ultramafics of Manipur Ophiolite Belt in the Indo–Myanmar Hill ranges, NE India

“…It is reported that the rocks of the MOMZ formed during forearc‐backarc magmatism in a supra‐subduction zone, probably when the Indian Plate was subducting underneath the Myanmar Plate (Ao & Bhowmik, 2014; Chaubey et al, 2022; Kingson et al, 2019; Singh et al, 2016; Singh et al, 2021; Zaccarini et al, 2016). However, it is also proposed that this ophiolite was formed in a mid‐oceanic ridge spreading center (Ningthoujam et al, 2012; Singh, 2009; Zaccarini et al, 2016), or plume‐ridge interaction as one event and subduction magmatism as another event (Imtisunep et al, 2022; Khogenkumar et al, 2016, 2020).…”

Stable isotope geochemistry and microfossil assemblages of carbonate rocks in the ophiolite mélange zone of the Indo–Myanmar orogenic Belt, NE India: Implications on age and depositional environment

“…The ophiolite sequences occurring all along the Tuting‐Tidding Suture Zone, which runs east of the Siang Antiform have been considered as the south‐eastern extension of the ITSZ (Dutt, Singh, Oinam, & Srivastava, 2021; Dutt, Singh, Srivastava, & Oinam, 2021; Dutt, Singh, Srivastava, Oinam, & Bikramaditya, 2021; Singh et al, 2021; Singh & Singh, 2011, 2013). The suture zone further extends south to the IMOB and the Andaman‐Nicobar Island Arc (Chaubey et al, 2022; Imtisunep et al, 2022; Khogenkumar et al, 2016, 2021; Premi et al, 2022; Singh, 2009; Singh, 2013; Singh et al, 2012; Singh et al, 2013; Singh, Nayak, et al, 2017).…”

Introduction, Part 2—Geodynamic evolution of Eastern Himalaya and Indo‐Myanmar orogenic belts: Advances through interdisciplinary studies

“…Chaubey et al (2022) give a detailed account of the depleted mantle peridotites from the northern part of the Nagaland–Manipur Ophiolites and discussed the characteristics of bulk‐rock and PGE data along with the mineral chemistry to explain the fractionation behaviour of PGE during magmatic evolution and their genetic implications. They argue that depleted mantle rocks (harzburgite, dunite) are residual products of extensive partial melting.…”

“…Geological map of Eastern Himalaya, Indo‐Myanmar orogenic belt, northern, Central Myanmar, and adjacent areas (modified after Mitchell et al, 2007; Searle et al, 2007; Y. R. Singh, Singh, Singh, et al, 2022). Locations of study area presented in the issue include 1/S2: Kundu and Hazarika (2022); 2/S2: Y. R. Singh, Singh, Singh, et al (2022); 3/S2: Rawat and Luirei (2022); 4/S2: Kayal et al (2022); 5/S2: Choudhury et al (2022); 6/S2: N. M. Sharma et al (2022); 7/S2: Goswami, Gogoi, et al (2022); 8/S2: Bikramaditya et al (2022); 9/S2: Goswami, Kalita, et al (2022); 10/S2: Joshi (2022); 11/S2: Jha and Sharma (2022); 12/S2: Shukla et al (2022); 13/S2: Khonglah et al (2022); 14/S2: Ali and Duarah (2022); 15/S2: Mohanty et al (2022); 16/S2: Chanu et al (2022); 17/S2: Majumdar, Gogoi, and Ghatak (2022); Majumdar, Gogoi, Ghatak, Saikia, et al (2022); 18/S2: Ding et al (2022); 19/S2: Ghose et al (2022); 20/S2: Hussain and Dey (2022); 21/S2: Ozukum et al (2022); 22/S2: Jamir et al (2022); 23/S2: Chaubey et al (2022); 24/S2: Bora, Borah, et al (2022); Bora, Mukherjee, et al (2022); 25/S2: Khuman and Ibotombi (2022); 26/S2: Y. R. Singh, Singh, Singh, et al (2022); 27/S2: Thokchom and Kshetrimayum (2021); 28/S2: Barman et al (2022); 29/S2: V. Sharma and Biswas (2022)…”