The Timing, Duration and Conditions of UHT Metamorphism in Remnants of the Former Eastern Gondwana

Abstract

Early Palaeozoic ultrahigh-temperature (UHT) metamorphism in eastern Gondwana was an event that started with Gondwana amalgamation at c. 580 Ma and lasted at least 50 Myr. Sapphirine + quartz, Mg–Al granulites preserve a record of the timing and duration of the event along the metamorphic belt. U–Th–Pb dating of zircon and monazite shows that metamorphism peaked almost simultaneously in Antarctica (554.0 ± 4.7 Ma), Sri Lanka (555.5 ± 4.6 Ma), southern India (548.1 ± 8.1 Ma) and Madagascar (550.6 ± 6.0 Ma), and ended in all locations at the same time, 530–520 Ma. Rare earth element (REE) compositions of the metamorphic zircon zones can be matched to the REE zoning in the associated garnet. Phase-diagram modelling indicates that the peak UHT P–T conditions in Antarctica, Sri Lanka, and India were very similar, 1020–1040 °C at 0.8 GPa. Peak conditions in Madagascar were at higher T and similar P: 1090 °C and 0.8 GPa. The East African Orogeny before 600 Ma preconditioned the crust of the eastern Gondwanan terranes by thickening it and harbouring heat-producing elements, heating the crust over c. 60 Myr; such that UHT conditions were reached when East and West Gondwana collided.

Long‐lived high‐grade metamorphism in southern India: Constraints from charnockites and sapphirine‐bearing semipelitic granulites from the Madurai Block

“…The unimodal age distribution from this study, the Madurai and Trivandrum blocks (Figure 14a–c) with ages clustered around 600–500 Ma, is suggestive of a late Neoproterozoic to Cambrian long‐lived metamorphism in both the blocks (Dev et al, 2022; Kadowaki et al, 2019; Tiwari & Sarkar, 2020). Although, monazite ages from Sri Lanka show bimodal distribution (Figure 14d), the older ages (peaking c. 650 Ma) are associated with prograde evolution, and the younger ages (peaking c. 480 Ma) are associated with retrograde growth (Dharmapriya et al, 2015; Durgalakshmi et al, 2021; Sajeev et al, 2010), further indicating a prolonged late Neoproterozoic to Cambrian metamorphic cycle. Texturally controlled in situ dating of the monazite from SGT strengthens the evidence for such prolonged metamorphic cycles (~ > 100 MYr) where UHT conditions are sustained for >40 MYr (Clark et al, 2015; Dev et al, 2022; Kadowaki et al, 2019; Li et al, 2020; Tiwari & Sarkar, 2020) and are in line with our observations.…”

“…Our data from the semipelites and charnockites of the MB suggest a clockwise P-T evolution with an inferred peak at f). All these findings point to regional UHT metamorphism during late Neoproterozoic to Cambrian with clockwise P-T evolution, characteristic of metamorphism in a convergent plate-boundary setting (Durgalakshmi et al, 2021;Harley, 2016;Kelsey & Hand, 2015). In such a collisional orogenic setting, UHT conditions can be attained through magmatic underplating, post-collisional slab breakoff and delamination, and lithospheric extension, as well as through conductive heating from HPE in an crust (Reviewed in Harley, 2016;Lei & Xu, 2018).…”

“…However, attainment of such UHT conditions through internal heating from HPEs within a timeframe of 40-50 MYr requires a moderately HPE-enriched crust (Clark et al, 2011). The East Africa orogeny prior to 600 Ma most likely preconditioned the crust through thickening and harbouring HPE (Durgalakshmi et al, 2021). The collision of the eastern and western Gondwana fragments during the Gondwana assembly likely led to further thickening of the crust which culminated in the attainment of UHT conditions at mid-lower crustal levels.…”

Recent advances in mineralogy, petrology, geochemistry, and geochronology in East Antarctica

“…Recent study has revealed that transitional-zone rocks also attained higher-T granulite facies conditions at the pressures of ~1.1 GPa (Suzuki and Kawakami, 2019). Furthermore, many geological, petrological and geochemical studies have been conducted recently, especially in the granulite-facies zone, that emphasize long-lived high temperature metamorphism with partial melting and possible magma generation at UHT conditions (e.g., Durgalakshmi et al, 2021;Carvalho et al, 2023). However, data from the amphibolite-facies zone are comparatively scarce.…”

Geochemistry of granulitic rocks from the western Madurai Block, Southern Granulite Terrain, India and its Madagascar linkage

“…The Madurai Block comprises granulite-facies rocks that are mostly metaigneous, with chemistries that vary widely between calcic and alkaline, magnesian and ferroan affinities. Tomson et al (2006Tomson et al ( , 2013 The SGT has been correlated with paleo-continental fragments of the Gondwana assemblage in Sri Lanka, East Antarctica and Madagascar (e.g., Plavsa et al, 2012;Li et al, 2020;Durgalakshmi et al, 2021). The Antananarivo Block of Madagascar, adjacent in Gondwana to the western Madurai Block, is also predominantly composed of Neoarchean granulites.…”