Mesozoic tectonics of the Indo-Burmese wedge: a record from the high-pressure metamorphic rocks of the Nagaland-Manipur Ophiolite Belt, NE India

In this study, we make a review of the recent developments on the metamorphic and tectonic evolution of the Nagaland-Manipur Ophiolite Belt (NMOB) in the Indo-Myanmar Ranges. We collate key metamorphic findings and chronological constraints in the NMOB to demonstrate an exceptional record of the full life cycle of the thermal and dynamic history of the Early Mesozoic intra-oceanic subduction system within the eastern arm of the Neo-Tethys from its infancy to its cold-mature stage. The earliest stage of an Early Jurassic-aged oceanic subduction under warm thermal conditions (apparent peak thermal gradient of ~ 20 °C/km), and within the first 1–2 Myrs since subduction initiation is recorded in the newly discovered high- and low-temperature metamorphic sole rocks of the Tusom CV area in the Manipur segment of the ophiolite belt. The metamorphic sole sequence, comprising a package of ultra-high temperature mafic granulites → high-temperature mafic granulite → garnet + clinopyroxene-bearing amphibolite → garnetiferous amphibolite → non-garnetiferous amphibolite → epidote amphibolite and low greenschist facies metasediments, and structurally downward, constitutes an inverted metamorphic sequence. Tectonic slices of hornblende eclogite facies metasediments and metabasites from diffrrent locations in the Nagaland segment of the Ophiolite Belt, on the other hand, reveal an apparent peak thermal gradient of ~ 12–15 ℃/km, indicating an intermediate subduction cooling stage. The structurally upward metamorphic sequence of greenschist facies → pumpellyite-diopside facies → lawsonite blueschist facies and epidote eclogite facies, the latter locally reaching ultra-high pressure metamorphic conditions in metabasalts of the structurally lowermost unit of the Nagaland ophiolite mélange together record a cooler apparent peak thermal gradient of ~ 7–8 ℃/km. We relate this metamorphism with the end stage of the Early Jurassic-aged intra-oceanic subduction, when the Neo-Tethys evolved into a cold-mature stage of subduction.