Petrology and geochemistry of ultramafic rocks in the Mogok belt, Myanmar: Cumulates from high‐pressure crystallization of hydrous arc melts

Abstract

The Mogok metamorphic belt (MMB) in central Myanmar is well known for its complex tectonics, magmatism, and metamorphism in the framework of Tethyan subduction and India-Asia collision. It is also world renowned due to the gemstone-class rubies and sapphires. Identification and discrimination of those petrological units in this region therefore are important for understanding the gemstone mineralization. Ultramafic massifs also crop out together with the gemstone-bearing metamorphic rocks in the MMB. It is still poorly constrained about their origin (i.e., mantle peridotites of Jurassic-Cretaceous ophiolites or cumulate rocks) and their relationship with the gemstone generation. Here, we report petrological and geochemical data for the Mogok ultramafic rocks. Petrographic observations show that they have typical cumulate textures, with a crystallization order of olivine/spinel-orthopyroxene-clinopyroxene. They have low whole-rock Al 2 O 3 and CaO, and extremely high spinel Cr# (=Cr/[Cr + Al]; up to 0.86). Clinopyroxenes of these rocks show light rare earth element enriched patterns when normalized to CI chondrite. The results suggest that the Mogok ultramafic rocks have different compositions, both whole-rock and mineral, from mantle peridotites of Myanmar ophiolites, such as the Kalaymyo andMyitkyina ophiolites, but resemble typical Alaskan-type ultramafic cumulates. Therefore, the Mogok ultramafic rocks are cumulates generated by high-pressure crystallization of hydrous arc melts, probably during the subduction of the Tethyan oceanic slab. We argue that the emplacement of these arc melts may have provided additional heat for the earlier magmatic rocks and regional high-temperature metamorphism, although there is a need to further constrain the ages of these rocks. This, along with magmatism and metamorphism during post-collisional extension, probably collectively contributed to the generation of world-class coloured gemstone mineralization.

Unexpected Expansion of Rare-Earth Element Mining Activities in the Myanmar–China Border Region

“…The area is endowed with mineral resources such rare earth elements and precious metals, including jadeite and "Burmese Amber" (bu mite) [48]. These precious stones were formed due to the metasomatic alteration of pe dotites in a subduction zone [49,50].…”

“…The area is endowed with mineral resources such as rare earth elements and precious metals, including jadeite and "Burmese Amber" (burmite) [48]. These precious stones were formed due to the metasomatic alteration of peridotites in a subduction zone [49,50]. Detailed geological and mineralogical survey data are not freely available in China and Myanmar; therefore, it is necessary to verify the type of mining activity in the study area to confirm that the mining is indeed for rare earth elements.…”

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

“…This Special Issue‐ Part 2 is a continuation of earlier Special Issue‐ Part 1 published in vol. 57 (2), of Geological Journal , which contained 26 research articles (Ao & Satyanarayanan, 2022; Baral et al, 2022; Bhowmik et al, 2022; Bora, Borah, et al, 2022; Bora, Mukherjee, et al, 2022; Deb & Ray, 2022; Devi & Singh, 2022; Devrani et al, 2022; Doley et al, 2022; Gogoi et al, 2022; Gupta et al, 2022; Hazarika & Kayal, 2021; Imtisunep et al, 2022; Liu et al, 2022; Luirei et al, 2022; Lukram & Tandon, 2022; Bidyananda et al, 2022; Majumdar, Gogoi, & Ghatak, 2022; Majumdar, Gogoi, Ghatak, Saikia, et al, 2022; Mukherjee et al, 2022; Pebam et al, 2021; Rashid et al, 2022; Saikia et al, 2022; Singh and Kshetrimayum, 2021; Singh, Guruaribam, Singh et al, 2022; Singh, Singh, Singh, et al, 2022; Srivastava, 2021; Srivastava & Kichu, 2021). Figure 2 displays the area of study of 29 papers included in this Special Issue 2.…”

“…This Special Issue-Part 2 is a continuation of earlier Special Issue-Part 1 published in vol. 57 (2), of Geological Journal, which contained 26 research articles (Ao & Satyanarayanan, 2022;Baral et al, 2022;Bhowmik et al, 2022;Bora, Mukherjee, et al, 2022;Deb & Ray, 2022;Devrani et al, 2022;Doley et al, 2022;Gogoi et al, 2022;Gupta et al, 2022;Hazarika & Kayal, 2021;Imtisunep et al, 2022;Liu et al, 2022;Luirei et al, 2022;Lukram & Tandon, 2022;Bidyananda et al, 2022;Majumdar, Gogoi, Ghatak, Saikia, et al, 2022;Mukherjee et al, 2022;Pebam et al, 2021;Rashid et al, 2022;Saikia et al, 2022;Singh and Kshetrimayum, 2021; F I G U R E 1 (a) Tectonic map of the peri-Indian region, showing the current plate boundaries and plate distributions, major continental blocks, suture zones, and salient fault systems. (b) Simplified regional geologic map of the Himalayan Orogen, Indo-Myanmar orogenic belt and adjoining areas (modified after Mitchell et al, 2007;Singh, 2013;Yin, 2006) Singh Srivastava, 2021;Srivastava & Kichu, 2021).…”