Alteration of primary Cr-spinel mineral composition from the Suru Valley ophiolitic peridotites, Ladakh Himalaya: Their low-temperature metamorphic implications

Abstract

The present study focuses on the chemical modification of a Cr-spinel from the Suru Valley ophiolitic peridotites exposed near Trespone Village of Kargil district, Ladakh Himalaya. The Suru Valley peridotite is partially serpentinised with the preservation of the spinel and relics of olivine and pyroxene. These peridotites contain characteristic red-brown spinel grains of corroded grain boundaries. While analysing these grains for mineral chemistry, compositional variation was observed with Cr-rich cores rimmed by Cr-poor compositions. Secondary spinel compositions, i.e., ferritchromite and magnetite were observed along the margins and cracks of primary Cr-spinel grains. The primary Cr-spinel cores are identified as Cr-rich and are characterised by higher values of Cr 3+ # (0.5-0.6) and lower values of Al 3+ # (0.42-0.54). From primary spinel cores to altered rims it was observed that Cr 3+ # and Fe 3+ # increase while Mg 2+ # decreases due to Mg 2+-Fe 2+ and Al 3+-Fe 3+ exchange with surrounding silicates of host peridotite during alteration. On the basis of present spinel mineral chemistry, metamorphic alteration conditions were transitional between greenschist and lower amphibolite similar to most of the Neo-Tethyan ophiolite peridotites.

Sedimentary facies and mineral provenance of Upper Triassic sandstones offshore Kvitøya, Svalbard: implications for palaeogeographic interpretations in the northern Barents Shelf area

“…In general, using Cr-spinel as a sediment provenance indicator is complicated, as considerable variations in Cr-spinel compositions may occur within the igneous protolith (Power et al 2000). In addition, Cr-spinel compositions may also be influenced by metamorphic or metasomatic alteration of the source rocks (Kimball 1990;Bhat et al 2019). Possible influences of chemical alteration in the present data are illustrated as a distinct increase in Fe and depletion in Al along intragranular fractures in the Cr-spinel grain displayed in Fig.…”

Link between melt-impregnation and metamorphism of Atlantis Massif peridotite (IODP Expedition 357)

“…In many cases where peridotite is highly serpentinized, as in the case of the Atlantis Massif, Cr-spinel commonly represents the only identifiable phase that retains the primary characteristics. Nonetheless, Cr-spinel is also subject to alteration and many studies have focused on and described the effects of hydrothermal alteration during serpentinization and metamorphism of primary Cr-spinel (e.g., Evans and Frost 1975;Kimball 1990;Burkhard 1993;Absalov 1998;Arai et al 2006;Säntii et al 2006;Khalil and El-Makky 2009;Merlini et al 2009;Aswad et al 2011;Gargiulo et al 2013;Saumur and Hattori 2013;Barra et al 2014;Bhat et al 2019;Khedr and Arai 2013;Khedr et al 2022). Of relevance to this study is the modification of Cr-spinel compositions during melt-rock interaction and metamorphism.…”

The Latowu Ultramafic Rock-Hosted Iron Mineralization in the Southeastern Arm Sulawesi, Indonesia: Characteristics, Origin, and Implication for Beneficiation

“…Based on FE-EPMA analysis, the iron-rich minerals were initially derived from the crystallization of Cr-spinel. During the alteration process (serpentinization or low-grade metamorphism), Fe was introduced into Cr-spinel, whereas Mg, Al, and Cr were diffused outward, leading to Fe mainly at the edges and/or fractures of Cr-spinel [17].…”