Abstract The island of Seram, eastern Indonesia, incorporates Miocene ultrahigh-temperature (UHT; >900°C) garnet–sillimanite granulites that formed by extensional exhumation of hot mantle rocks behind the rolling-back Banda Arc. UHT metamorphic conditions are supported by new Zr-in-rutile thermometry results and the Miocene age of the UHT event is confirmed by closely-matched heavy rare earth element (HREE) abundances between garnet and c. 16 Ma zircon. Monazites also record identical U–Pb ages, within uncertainty. However, these geochronometers do not date peak UHT metamorphism; instead, they date retrograde, garnet-consuming (Zr- and rare earth element (REE)-liberating) reactions that produced the granulites’ post-peak cordierite + spinel reaction microstructures. Zircons shielded within garnet did not crystallize c. 16 Ma rims and so were unaffected by the entire UHT event. Miocene UHT metamorphism overprinted a Late Triassic–Early Jurassic upper-amphibolite facies event that grew garnet cores and 216–173 Ma zircon. In the Miocene, these garnet cores were overgrown by peritectic garnet rims during UHT metamorphism, with some rutiles recording c. 900°C Zr-in-rutile temperatures. Garnet Lu–Hf ages of 138 Ma – produced by core–rim mixing – demonstrate that a component of Hf 4+ produced since c. 200 Ma was retained through the c. 16 Ma UHT event. Accordingly, UHT conditions must have been very short-lived and exhumation of the granulite complex very rapid.

Abstract Structural investigations and U–Pb sensitive high-resolution ion microprobe (SHRIMP) dating of rocks from the southwestern Central Zone of the Damara Belt, Namibia, reveal that a major SE-verging deformation event (D2) occurred at between 520 and 508 Ma. During D2, SE-verging simple shear and NE–SW pure shear extension in a constrictional stress field produced recumbent, south- to SE-verging, kilometre-scale folds and ductile shear zones, a NE–SW extensional lineation and conjugate shear bands, and was coeval with granitoid emplacement and high-grade metamorphism. The timing of this event is constrained by anatectic leucosomes in D2 shear zones (511±18 Ma) and extensional shear bands (508.4±8.7 Ma) as well as by syntectonic grey granites (520.4±4.2 Ma), and is similar to ages for high-grade metamorphism in the Central Zone. An upright folding event (D3) occurred at c . 508 Ma, resulting in the formation of basement-cored fold interference domes. The timing of deformation and metamorphism at 520–508 Ma in the mid-crustal SW Central Zone contrasts with ages of 560–540 Ma for shallow crustal NW-verging folding and thrusting elsewhere in the Central Zone that was concomitant with voluminous magmatism. This magmatism led to metamorphism and anatexis of the basement and the emplacement of anatectic red granites at 539±17 to 535.6±7.2 Ma, which contain 1013±21 Ma inherited zircons. The Central Zone therefore contains a record of crustal thickening, heating of the mid-crust, exhumation and orogen-parallel extension over the life of an orogen.

Abstract Analysis of new lithological, structural, metamorphic and geochronological data from extensive mapping in Mozambique permits recognition of two distinct crustal blocks separated by the Lurio Belt shear zone. Extrapolation of the Mozambique data to adjacent areas in Sri Lanka and Dronning Maud Land, Antarctica permits the recognition of similar crustal blocks and allows the interpretation that the various blocks in Mozambique, Sri Lanka and Antarctica were once part of a mega-nappe, forming part of northern Gondwana, which was thrust-faulted c. 600 km over southern Gondwana during amalgamation of Gondwana at c. 590–550 Ma. The data suggest a deeper level of erosion in southern Africa compared with Antarctica. It is possible that this thrust domain extends, through the Zambezi Belt or Valley, as far west as the Damara Orogen in Namibia with the Naukluft nappes in Namibia, the Makuti Group, the Masoso Suite in the Rushinga area and the Urungwe klippen in northern Zimbabwe, fitting the mega-nappe pattern. Erosional products of the mountain belt are now represented by 700–400 Ma age detrital zircons present in the various sandstone formations of the Transantarctic Mountains, their correlatives in Australia, as well as the Urfjell Group (western Dronning Maud Land) and probably the Natal Group in South Africa.

Abstract The rocks of the Kalahari Craton in central western Mozambique have crystallization ages of between c . 2300 and 3400 Ma and comprise dominantly granite–greenstones, peraluminous two-mica granites, subordinate younger mafic and granitic intrusions of uncertain age and cover sedimentary rocks. The rocks of the Mozambique Belt comprise c . 1100 Ma intrusive granitoids as well as mafic intrusives and supracrustal migmatite gneisses of uncertain age. The boundary zone between and including these two crustal provinces is characterized by a strong N–S penetrative planar and migmatitic fabric. Sparse kinematic indicators suggest a sinistral sense of displacement along this shear zone. The metamorphic gradient increases from west to east from low grade on the Kalahari Craton to high-grade in the east, characterized by two generations of anatectic migmatization. 40 Ar/ 39 Ar thermochronology on mica suggests that the Kalahari Craton lithologies have experienced heating above at least c . 300°C during the c . 1100 Ma Grenville age orogeny and again at c . 530 Ma during the Pan-African Orogeny, possibly related to the collisional amalgamation of East and West Gondwana. The Mozambique Belt lithologies record a c. 550 Ma thermal overprint with the lithologies in the vicinity of the N–S shear zone recording thermal reactivation at c . 470 Ma. Comparisons of the new data with that from western Dronning Maud Land, which was adjacent to the study area prior to Gondwana fragmentation, yield many similarities.

The Lebowa Granite Suite of the Bushveld Complex is a large, 2054 Ma old, A-type batholith, characterised by numerous relatively small magmato-hydrothermal, polymetallic ore deposits. The mineralisation is represented by a three-stage paragenetic sequence: early magmatic Sn-W-Mo-F ores (600 °C > T > 400°C), followed by a Cu–Pb–Zn–As–Ag-Au paragenesis (400 °C > T > 200°C) and then late-stage Fe–F–U mineralisation (< 200°C). The first stage of mineralisation (typified by the endogranitic Zaaiplaats tin deposit) is related to incompatible trace element concentration during crystal fractionation and subsequent fluid saturation of the magma. Evolution of the late magmatic fluids as they were channelled along fractures, as well as mingling with externally derived connate or meteoric fluids, resulted in the deposition of the second stage of mineralisation (typified by the fracture-related, endogranitic Spoedwel and Albert deposits and the exogranitic, sediment-hosted Rooiberg mine) which is dominated by polymetallic sulphide ores. As the externally derived fluid component became progressively more dominant, oxidation of the polymetallic sulphide assemblage and precipitation of hematite, pitchblende and fluorite occurred generally along the same fracture systems that hosted the earlier sulphide paragenesis. Small hydrothermal zircons trapped along quartz growth zones from the Spoedwel deposit yield a U–Pb concordia age of 1957 ± 15 Ma. Whole-rock Rb–Sr age determinations from the Lebowa Granite Suite fall in the range 1790 ± 114 Ma to 1604 ± 70 Ma and are interpreted to reflect alkali element mobility and isotopic resetting during exhumation of the Bushveld granite. In contrast to thermal modelling which indicates that hydrothermal activity should have ceased within 4 my of emplacement, isotopic evidence suggests that mineralisation was long-lived, but episodic, and that fluid flow events were linked to major periods of Palaeo- and Mesoproterozoic orogenic activity along the margins of the Kaapvaal Craton. During these orogenic episodes, fluid flow was enhanced by tectonically induced fluid over-pressuring and/or exhumation of the Bushveld Complex.