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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. [ABSTRACT FROM AUTHOR]

Kiruna-type iron oxide-apatite associations occur in a variety of rock types and their origin has remained controversial. Most of the Kiruna-type deposits are associated with intermediate to felsic rocks, and in rare cases with ultramafic rocks. Here we investigate the Seruwila iron oxide-apatite deposit at the contact between the Highland and Vijayan complexes that has been defined as the "eastern suture" in Sri Lanka, which formed during the late Neoproterozoic assembly of the Gondwana supercontinent. The ore deposit is hosted in an ultramafic intrusion and comprises massive and disseminated mineralization. The ore-bearing rocks are mainly composed of low-Ti magnetite and chlor-fluorapatite. Our petrological and geochemical studies suggest a magmatic-hydrothermal model for the mineralization wherein: (1) the Cl-rich magmatic-hydrothermal fluid scavenged iron and P from the ultramafic magma, transported iron to shallower levels in the crust and deposited along the suture zone to form the massive type magnetite and apatite; and (2) the cooling of the hydrothermal fluids resulted in the growth of disseminated magnetite and the precipitation of sulfide minerals, followed by a calcic metasomatism (scapolitization and actinolitization). This model is in conformity with the genetic relation between Kiruna-type deposits and iron oxide-copper-gold (IOCG) deposits. We also report LA-ICP-MS zircon U-Pb ages from the host ultramafic intrusion suggesting its emplacement at ca. 530 Ma, which is younger than the regional high-grade metamorphism associated with the collisional assembly of the crustal blocks in Sri Lanka at ca. 540 Ma. By analogy with the common occurrence of Kiruna-type deposits in extensional tectonic settings, and the geochemical features of the studied rocks including low silica, high Mg, Fe, Ca with high field strength elements (HFSEs such as Nb, Ta, Zr, Hf, Ti) depletion and strong LREE and F enrichment, we theorize that the ultramafic magmatism occurred in a post-collisional extensional setting derived from a volatile- and LREE-rich metasomatized lithospheric mantle. [ABSTRACT FROM AUTHOR]