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We report new petrological and geochronological data of garnet‐cordierite (Grt‐Crd) gneiss as well as two types of leucocratic rocks (garnet‐bearing and cordierite‐bearing leucosomes) crystallized during prograde and near‐peak metamorphisms of the Wanni Complex (WC) in Sri Lanka, and investigate the pressure–temperature–time evolution of granulite‐facies metamorphism for unravelling the timing and tectonics of the Neoproterozoic collisional processes related to Gondwana amalgamation. Grt‐Crd gneiss, garnet‐biotite (Grt‐Bt) gneiss, garnet‐bearing leucocratic rock (Grt‐L), and cordierite‐bearing leucocratic rock (Crd‐L) discussed in this study were collected from Walpita in the margin of the WC along the boundary with the Highland Complex (HC). Grt‐L occurs as thin layers parallel to the foliation of matrix Grt‐Bt and Grt‐Crd gneisses. The occurrences of porphyroblastic garnet in quartzo‐feldspathic matrix and crystallised melt inclusions within the garnet suggest that the Grt‐L could have formed by partial melting of host Grt‐Bt gneiss during prograde to peak metamorphism. Crd‐L is coarse‐grained and massive, lacks obvious foliation, and crosscuts the foliation of host Grt‐Bt gneiss. These observations suggest that the Crd‐L could have intruded after the crystallization of the Grt‐L. Application of phase equilibria modelling in the system NCKFMASHTO for the rocks yielded three discrete thermal events: 600–800°C/4.0–6.0 kbar (Stage 1 from Grt‐L), 700–840°C/5.5–7.0 kbar (Stage 2 from Grt‐Crd gneiss), and 840–880°C/4.5–5.5 kbar (Stage 3 from Crd‐L), suggesting a clockwise P–T evolution. LA‐ICP‐MS zircon U–Pb dating of the leucosomes yielded several metamorphic events: >577 Ma (partial melting of Grt‐L), ~562 Ma (crystallization of Grt‐L), 537 ± 14 Ma (peak metamorphism and crystallization of Crd‐L), and 507–503 Ma (post‐peak cooling event). The results of this study therefore confirmed prolonged (>70 Myr) high‐grade metamorphism of the WC, although the duration might be shorter than that of the HC (>100 Ma). The continuous heat supply necessary for such long‐lived high‐grade metamorphism is explained by a recent tectonic model of Sri Lanka. The model suggests double‐sided subduction and continent‐continent collision, which could have given rise to subsequent slab delamination and differential heating of lower to middle crust. Such complex subduction–collision processes possibly controlled the difference in the style of P–T path and the duration of high‐grade metamorphism between the HC and the WC. [ABSTRACT FROM AUTHOR]

Earth's deep crustal granulites, in particular, metamorphosed clastic sedimentary rocks, are important to decode the composition of the pelitic lower crust. General understanding is that granulite-facies metamorphism extensively removes trace elements from the protolith sediments, resulting their high depletion in newly generated granulites. However, there has been no systematic appraisal on the budget of the trace elements in newly-born granulites compared against that of their pre-metamorphic sediments. A demonstrative example taken from the Highland Complex of Sri Lanka, showing the trace element budget including highly incompatibles of pelitic-granulites remain unmodified, attesting that even ultra-high temperature metamorphism does not cause large-scale removal of trace elements from the sedimentary protoliths, is presented here. Our results reveal that a regional-scale chemical modification during granulite generation in some parts of the mid-lower crust does not enhance the mobility of trace elements in whole rock scale. This finding may impart an important message to researchers that high/ultra-high temperature metamorphism of deep crustal granulites does not necessarily disturb inherited trace element characteristics from their source sediments. • No significant alkaline, HFSE and REE fractionations in granulite formation. • Trace element budget of pelitic-granulites remain unmodified at UHT metamorphism. • Pelitic lower crust is chemically analogous to their sedimentary protoliths. [ABSTRACT FROM AUTHOR]