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Crustal differentiation driven by long-lived UHT metamorphism in Central Gondwana: A review and synthesis of new data
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DOI：10.1016/j.earscirev.2026.105625.png)
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Abstract
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During the final amalgamation of the Gondwana supercontinent, the East African and Kuunga orogens imparted contrasting thermal regimes that reflect fundamentally different styles of continental collision and deep-crustal evolution. High- to ultrahigh-temperature (HT–UHT) metamorphism, classically explained as resulting from continental collisional orogens, is increasingly recognized as a key process in crustal differentiation, yet its duration and long-term consequences on crustal growth remain debated. This review synthesizes global advances in understanding HT–UHT metamorphism during Gondwana assembly, with new high-resolution zircon petrochronological data from the Highland Complex of Sri Lanka as a benchmark case while drawing emphasis on other classic UHT terranes in the world. Sri Lanka preserves an exceptional exposure of deep continental crust with a unique tectonic position within central Gondwana at the intersection of the East African and Kuunga orogens. Zircons from the Highland Complex of Sri Lanka display inherited magmatic cores as old as ~2.4 Ga overgrown by low-Th/U metamorphic rims that record the HT-UHT metamorphism, followed by intensified zircon recrystallization during a major thermal climax at ~570–540 Ma. A spread of concordant U-Pb ages from ~637 to 490 Ma defines a metamorphic zircon record spanning ~147 Ma, within which a sustained lower-crustal UHT thermal plateau lasting ~80 Ma (from ~570 to 490 Ma) can be implied. In contrast, zircons associated with melt-related growth from the adjacent Wanni Complex which represent relatively shallower crustal levels, yield tightly clustered Cambrian ages. This feature provides a comparative reference that make a purely analytical explanation or short-lived heating events are less likely. These datasets reveal a vertically heterogeneous thermal architecture within the Kuunga Orogen, in which a thermally buffered lower crust may have remained at UHT for several tens of millions of years. We suggest that as melting and melt extraction progressed throughout the UHT plateau, the deep crust likely lost significant quantities of heat-producing elements (U, Th, K) into melts that migrated upward. This may have caused a shift from heat generated mainly by radioactive decay during the main thermal climax (~570–540 Ma) to a prolonged plateau phase (~540–490 Ma), evidenced by our Zircon U-Pb isotope data. A quantitative thermal and mass-balance modelling can test this hypothesis, along with more descriptive petrological and thermal data in future. The continuous zircon age spectrum thus records not only sustained high temperatures but also the gradual cooling driven by the loss of heat-producing elements through anataxis. This review demonstrates that Sri Lanka, with its exceptionally fertile Paleoproterozoic and Grenvillian basement, represents a near-optimal case for long-lived UHT, whereas less radiogenically enriched crust would experience shorter thermal lifetimes. This identifies Sri Lanka as a benchmark natural laboratory for elucidating the linkage among other global long-lived thermal regimes, vertically heterogeneous orogenic architecture, and active crustal differentiation.
Keywords:
Ultrahigh-temperature metamorphism
Central Gondwana
Sri Lanka
Zircon geochronology
Crustal differentiation
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