Revised U–Pb zircon geochronological data for ‘Newer Granite’ intrusions in the Shetland Islands, Scottish Caledonides indicate that they are mainly Devonian in age. Calculation of emplacement ages is complex because many plutons contain significant antecryst populations. In the previous absence of geochemical and isotopic data, the Devonian plutons were attributed to pulses of localized lithospheric melting during strike-slip displacements along the Walls Boundary Fault, given the prevailing view that the Iapetus Ocean had closed significantly earlier. However, new geochemical evidence indicates that most of these plutons have a subduction-related or crustal melting signature, consistent with recent tectonic models that argue that the Iapetus did not finally close until c. 400–390 Ma. We therefore attribute most Devonian plutonism in the Shetland Islands to subduction of the final vestiges of the Iapetus Ocean, contemporaneous with emplacement of the ‘Trans-Suture Suite’ in southern Scotland and northern England. Plutonism was terminated by the collision of combined Avalonia–Baltica with Laurentia at c. 400–390 Ma. The E-type mid-ocean ridge basalt or ocean island basalt chemistry of the Sandsting Complex diorites is consistent with asthenospheric melting after slab foundering.

The physical, mechanical and fracture properties at Stromboli volcano have been integrated at multiple scales to understand whether the interplay between a presumed NE/SW rift zone and the Sciara del Fuoco (SDF) depression has resulted in a zone of weakness able to promote fracturing prone to flank instability. Multiscale fracture quantification by imaging via FracPaQ toolbox both fractures and sample scale fractures has been integrated with rock physics and rock mechanics experiments on cm-scale samples belonging to the Paleostromboli, Vancori, Neostromboli, Pizzo and Present Deposit volcanic cycles that have been taken from within and outside the rift zone. The structural changes to the edifice have been quantitively assessed by mapping at different scale fracture properties such density and orientation within and outside the rift zone allowing to identify the potential damaged zones that could reduce the edifice strength.Results indicate that basalt textures, microfracture density, porosity, chemical zoning and preferential alignments, despite lithologically dependent, can be related to the NE/SW zone of weakness at the regional scale and to collapsed volumes that have been subject to continuous intrusive activity. Numerical inversion models have been performed to cross correlate fracture density in the basalts at multiple scales.A link between microfracture density and seismic velocities has been also established via numerical modelling, allowing to interpret in terms of degree of fracturing the results of seismic tomographies at the field scale, providing a novel method to image crack damage evolution within the inner structure of the volcano edifice.

High temperatures exert a significant influence on the mechanical and fluid flow properties of rocks and minerals. In crystalline rocks, differential thermal expansion of minerals is known to induce microfracture damage leading to changes in bulk volume and tensile strength. Here we report new data from thermally treated core samples of Devon Granite in order to constrain the interplay between tensile strength and thermally-induced damage with respect to the background mineralogy. A series of core samples was cyclically heated at temperatures ranging from 25 to 800 °C, with P-wave velocity and porosity measured after each cycle. Tensile strength decreased significantly from 9 MPa to less than 3 MPa as thermal treatment increased from 25 to 800 °C. The mechanical data were then compared to fracture density values obtained by optical maps of microfracture damage to assess the quantity and degree of linkage of intergranular and intragranular fractures using the FraqPaQ toolbox. The fracture density increased from 0.02 mm−2 to 2.0 mm−2 which is consistent with results obtained from direct physical parameters as calculated from elastic wave data. We conclude that the combined effects of thermal expansion and the α−β phase transition within quartz crystals has a pronounced effect on tensile strength.

The tectonic significance of the Muness Phyllite, which overlies the Unst–Fetlar ophiolite in Shetland, Scottish Caledonides, is poorly understood. U–Pb analyses of detrital zircons show that it was deposited after c . 469 Ma. Early Paleozoic grains have ε Hf values of −0.3 to +12.3 and were probably derived from the extension of the Midland Valley arc. Psammite clasts and the matrix of the Muness Phyllite contain Proterozoic and Archean detrital zircons with age peaks of c . 1, 1.4–1.5, 1.6–1.7, 1.8–1.9 and 2.7 Ga. These are consistent with ultimate derivation from NE Laurentia sources and were probably recycled from the Neoproterozoic East Mainland Succession that underlies the Mesozoic East Shetland Basin. The Muness Phyllite is interpreted to have been deposited soon after the Grampian I orogeny in a successor basin that overstepped and received detritus from the Midland Valley arc, the East Mainland Succession and the Unst–Fetlar ophiolite. It was then deformed and metamorphosed, probably at c. 450 Ma during the Grampian II orogenic event. The Muness Phyllite therefore provides a record of middle to late Ordovician tectonic events along the Scottish sector of the Laurentian margin following ophiolite obduction. Supplementary material: Analytical details and instrumentation parameters and U–Pb and Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.5324986

Geophysical methods, particularly seismic attribute analysis, are seeing increased usage in studying geothermal resources in order to maximize extraction potential and minimize risks. However, to better understand deep processes it is necessary to calibrate surface seismic data to develop new models. Here, we present a series of controlled laboratory experiments where key rock physics data such as fracture network density and permeability are directly measured as a function of simulated depth. We use a suite of fresh and hydrothermally altered rocks from a Philippine geothermal field (Palinpinon or Southern Negros Geothermal Project) which are deformed using a conventional triaxial cell fitted with sensors for microseismicity, fluid pressure and fluid flow. Samples of 100mm length and 40mm diameter were prepared with small notches and a pair of offset 3mm drill holes such that once fractured, the offset drill holes form an access pathway along the newly generated fault plane. In this way, the formation and evolution of natural fracture and damage zones and resulting permeability can be directly evaluated. The sample assembly was encased in a rubber nitrile jacket to separate the sample from the confining fluid (oil) and fitted with up to 18 ports for Acoustic Emission sensors to monitor microseismicity. This setup allows an experiment to gather seismic data in different ray paths and key attributes (static and dynamic moduli) while fracture permeability develops. Our initial results reveal a significant reduction in all seismic attributes (P/S-wave velocities and elastic moduli) after fracture development, except for Poisson’s ratio, which shows the opposite trend. Further, the reduction in fracture permeability coincides with decreasing Poisson’s ratio and increasing P and S wave velocities, dynamic bulk modulus, Lame’s first coefficient and Young’s modulus. Experiments conducted at elevated temperatures (175 C) show a ‘swarm’ of Acoustic Emission events at the moment of, and shortly after, pore fluid decompression. We postulate that this is due to rapid fluid movement and phase changes from liquid to gas within the damage zone. We correlate the resulting data trends to present new links between fracture permeability and seismic data in the case of the altered andesite of the Southern Negros Geothermal Project, thus allowing for better interpretations of surface seismic models of volcanic geothermal fields in the Philippines.

Granite stocks across southwest England have played a significant role in the genesis of world-class polymetallic mineralisation. This study presents the first geochemical and geochronological dataset for the composite Crownhill stock, placing it into the newly emerging geochronological framework for the Cornubian Batholith. The Crownhill stock comprises kaolinised two-mica granite in the north and variably-grained biotite granite in the south that encloses pods of tourmaline granite. All granites are peraluminous (A/CNK > 1) and the biotite (BG) and tourmaline granites (TG) are related by the replacement of biotite by tourmaline and secondary muscovitization. Integrated LA-ICP-MS and CA-ID-TIMS geochronology indicate two-phase magmatism, where zircon cores yield 288.9 +/- 5 Ma and 286.4 +/- 5 Ma and rims yield 277.74 +/- 0.33 Ma and 278.35 +/- 0.35 Ma, for BG and TG respectively. The zircon cores crystallised during initial magmatism, that formed the two-mica and muscovite granites (e.g., Carnmenellis, Bodmin, and Hemerdon) exposed in the north of the Crownhill stock. The zircon rims crystallised from the second phase of magmatism that formed the biotite and tourmaline granites (e.g., Dartmoor and St. Austell). This indicates that zircon crystals were assimilated from older two-mica and muscovite granites and entrained in the second phase of magmatism. Trace element compositions of zircon grains suggest that the rims crystallised from a more evolved magma, where zircon grains hosted in tourmaline granites are broadly more evolved than those from biotite granites. This is likely a result of elevated volatile concentrations delaying zircon fractionation.Trace cassiterite has been observed within interstitial tourmaline in the tourmaline granites, where crystallisation was likely induced by the removal of boron through tourmaline fractionation, coupled with the addition of Sn sourced from the alteration of biotite. The assimilation and overprinting of older granites by second-stage magmatism suggests that the initial phase of magmatism could be more widespread than initially thought and that tourmalinisation may have been responsible for leaching and remobilising Sn from the biotite-rich granites. (C) 2019 Elsevier B.V. All rights reserved.

Abstracts from the 2017–2018 Mineral Deposits Studies Group meetings from the 2017–2018 Mineral Deposits Studies Group meeting Cobalt recovery from Katanga ores (DRC): the importance of mineralogical evaluation L. Santoro, St. Tshipeng Yav, E. Pirard and A. Kaniki Natural History Museum (l.santoro@nhm.ac.uk); University of Lubumbashi (Tshipeng@sgs.com); University of Liege (eric.pirard@ulg.ac. be) ABSTRACT Cobalt in the Congolese Copperbelt mines is commonly recovered from Co-oxi-hydroxides (i.e. heterogenite, asbolane) by acid-leaching under reducing conditions. However, most operations face a limit in the leaching yields of cobalt, which usually do not exceed 80%. The main aim of this work was to investigate the causes of the poor recovery, in order to reconcile the Co recovery with processing techniques. Several concentrate samples from different mine plants of Katanga Copperbelt (Kalukuluku, Mutanda, Mabaya, Kamwali and Fungurume) were selected and subjected to a full mineralogical characterisation by Optical Microscopy (OM), X-Ray Diffraction (XRD), automated mineralogy and Scanning Electron Microscopy by Energy Dispersive Spectroscopy (SEM-EDS) prior and after leaching tests. OM and XRD results were used as background information to build a mineral list for mineral identification during automated mineralogy analyses by Mineralogic Mining System (Zeiss ltd.). Automated mineralogy allowed obtaining mineral maps, modal mineralogy, chemical assays and Co deportment for each specimen prior and after leaching. Mineral maps of the leached samples were useful to observe the occurrences of poorly leached Co-bearing particles which were further investigated by SEM-EDS and X-mapping. The results showed that heterogenite (rarely associated with asbolane) is the main cobalt mineral in Katanga. Mineralogic Mining System was able to discriminate between pure heterogenite, and Si-Al-K-bearing heterogenite, asbolane/heterogenite, Heterogenite+Fe-oxi-hydroxide and Co-bearing mixed phases, which resulted more refractory to leaching. The comparison between modal mineralogy of preand post-leached samples indicates a decrease, but not a full leaching of these Co phases: chemical assays and Codeportment, in fact, still reveal the presence of low Co% within Co phases listed above (Table 1). SEM-EDS and Xmapping on single particles of some specimens corroborated the results obtained by Mineralogic.Cobalt in the Congolese Copperbelt mines is commonly recovered from Co-oxi-hydroxides (i.e. heterogenite, asbolane) by acid-leaching under reducing conditions. However, most operations face a limit in the leaching yields of cobalt, which usually do not exceed 80%. The main aim of this work was to investigate the causes of the poor recovery, in order to reconcile the Co recovery with processing techniques. Several concentrate samples from different mine plants of Katanga Copperbelt (Kalukuluku, Mutanda, Mabaya, Kamwali and Fungurume) were selected and subjected to a full mineralogical characterisation by Optical Microscopy (OM), X-Ray Diffraction (XRD), automated mineralogy and Scanning Electron Microscopy by Energy Dispersive Spectroscopy (SEM-EDS) prior and after leaching tests. OM and XRD results were used as background information to build a mineral list for mineral identification during automated mineralogy analyses by Mineralogic Mining System (Zeiss ltd.). Automated mineralogy allowed obtaining mineral maps, modal mineralogy, chemical assays and Co deportment for each specimen prior and after leaching. Mineral maps of the leached samples were useful to observe the occurrences of poorly leached Co-bearing particles which were further investigated by SEM-EDS and X-mapping. The results showed that heterogenite (rarely associated with asbolane) is the main cobalt mineral in Katanga. Mineralogic Mining System was able to discriminate between pure heterogenite, and Si-Al-K-bearing heterogenite, asbolane/heterogenite, Heterogenite+Fe-oxi-hydroxide and Co-bearing mixed phases, which resulted more refractory to leaching. The comparison between modal mineralogy of preand post-leached samples indicates a decrease, but not a full leaching of these Co phases: chemical assays and Codeportment, in fact, still reveal the presence of low Co% within Co phases listed above (Table 1). SEM-EDS and Xmapping on single particles of some specimens corroborated the results obtained by Mineralogic. The poor recovery of cobalt was ascribed to the mineralogical complexity making the routine processing strategy poorly effective. More attention must hence be placed during the processing stages of Co-ores, in order to avoid inappropriate leaching conditions, inappropriate pulp density and liberation issues caused by the occurrence of Co-bearing phases refractory to leaching treatments. The Cristal mineralisation (Amazonas region, Northern Peru): An example of supergene zinc enrichments in tropical areas G. Arfè, N. Mondillo, M. Boni, M. Joachimski, G. Balassone and A. Mormone Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte S. Angelo, Napoli 80126, Italy; GeoZentrum Nordbayern, University of Erlangen-Nuremberg, Schlossgarten 5, Erlangen 91054, Germany; INGV Osservatorio Vesuviano, Via Diocleziano 328, Napoli 80124, Italy Email address: boni@unina.it Table 1. KALUKULUKU MUTANDA MABAYA KAMWALI FUNGURUME Co content 0.02% 0.22% 5.18% 2.11% 0.05% Co-bearing mixed phases 87.49 16.7 33.12 22.46 85.47 Heterogenite 57.83 32.15 27.18 1.14 Si, Al, K-bearing heterogenite 12.5 18.59 32.68 42.61 12.63 Heterogenite+Fe-oxi-hydroxides 6.88 1.21 4.15 0.76 Asbolane 0.83 3.6 © 2018 Institute of Materials, Minerals and Mining and The AusIMM APPLIED EARTH SCIENCE (TRANS. INST. MIN. METALL. B) 2018, VOL. 127, NO. 2, 46–79 https://doi.org/10.1080/25726838.2018.1487425

Resolving the timing of crustal processes and meteorite impact events is central to understanding the formation, evolution and habitability of planetary bodies. However, identifying multi-stage events from complex planetary materials is highly challenging at the length scales of current isotopic techniques. Here we show that accurate U-Pb isotopic analysis of nanoscale domains of baddeleyite can be achieved by atom probe tomography. Within individual crystals of highly shocked baddeleyite from the Sudbury impact structure, three discrete nanostructural domains have been isolated yielding average 206Pb/238U ages of 2,436±94 Ma (protolith crystallization) from homogenous-Fe domains, 1,852±45 Ma (impact) from clustered-Fe domains and 1,412±56 Ma (tectonic metamorphism) from planar and subgrain boundary structures. Baddeleyite is a common phase in terrestrial, Martian, Lunar and asteroidal materials, meaning this atomic-scale approach holds great potential in establishing a more accurate chronology of the formation and evolution of planetary crusts.

U-Pb zircon ages obtained from the late-to post-tectonic 'Newer Granite' suite in Shetland, northernmost Scottish Caledonides, indicate a significantly more protracted intrusion history than was inferred previously from K-Ar data. Emplacement of the Brae Complex (c. 465 Ma), Graven Complex (c. 440 Ma) and the Muckle Roe Granophyre (c. 438 Ma) followed regional deformation and metamorphism of metasedimentary successions during the Grampian orogenic event, and is attributed to NW-directed subduction beneath Laurentia. The almost complete absence of plutons of this age along-strike in mainland Scotland suggests a change in subduction angle and/or the distance between the subduction zone and the Laurentian margin. Intrusion of the Ronas Hill Granite (c. 427 Ma) was approximately coeval with displacement on the Moine Thrust in mainland Scotland, and therefore probably occurred during Baltica-Laurentia collision. A gap of c. 35 myr followed before emplacement of the Mangaster Voe Intrusion and Eastern Granophyre (c. 390 Ma), and a further gap of c. 20 myr before emplacement of the Sandsting Complex (c. 370 Ma). Both periods of magmatism are attributed to pulses of localized lithospheric melting in the vicinity of the Walls Boundary Fault during Devonian sinistral relative displacements between Laurentia and Baltica.

Introduction: The early history of the terrestrial planets was strongly shaped by the occurrence of several large meteorite impacts. Such large impacts do not only leave a crater as a mark on the surface of the planet but also penetrate deeply into the planet and deposit a major part of their energy at depth. While in small impacts the energy is quickly transferred to the atmosphere and/or space, the deep burial in large impacts prevents such a rapid loss and facilitates the formation of a large thermal anomaly that may persist for thousands or even millions of years. Moreover, by affecting deeper parts of the planet, the impact heats regions that already are at elevated temperature and thus promotes the formation of large amounts of melt, much of which may be extracted in the aftermath of the impact and form a new crust. The source region in the mantle is left depleted in the more fusible mineral phases and incompatible trace components as is also the case in normal melting processes; however, depending on the depth of penetration and the stage in the planet’s evolution at which it occurs, the impact may affect parts of the mantle that would otherwise be undisturbed or at least melt to a lesser extent. The thermal anomaly is thus accompanied by a compositional anomaly. Several studies on the mantle dynamical effects of giant impacts (e.g., [1, 2, 3, 4]) have been carried out, but most of them ignored the compositional contribution to the density anomaly. Method: We combine fully dynamical numerical mantle convection models that include a detailed representation of mantle mineralogy and chemistry and are coupled with a simple model of core energetics (e.g., [5]) with a parameterization of the effects of a large meteorite impact, in particular shock heating of the mantle. The model accounts for melting and the concomitant changes in material properties, especially density. Melt above a defined retention threshold is extracted from the mantle source region and added to the top to form a basaltic crust. Results: The normal melting processes produce a depleted layer in the mantle beneath the lithosphere, which is characterized by a lower content of incompatible elements and a lower density; these consequences of melting are well known from many geodynamical models of terrestrial planets. Giant impacts such as those that formed the large impact basins on Mars instantaneously produce a large supersolidus region in the mantle that may reach deeper than the normal melting zone in such large events as the Utopia-forming one and attain higher degrees of melting. The massive melt production can result in a thickened crust at the impact site in spite of the erosive action of the impact itself, and a long-lived thermal and compositional anomaly remains in the mantle. The reduced density induces a strong local upwelling that can induce mantle plumes or attract existing ones, and the anomaly rises by its own buoyancy to the base of the lithosphere, where it spreads. The thermal anomaly decays over timescales of tens to hundreds of millions of years, but the compositional anomaly may exist much longer and can become “frozen in” in the growing thermal boundary layer. Its gravity or seismic signature may, in principle, be detectable today, although probably only under very favorable circumstances. References: [1] C. C. Reese, et al. (2002) Journal of Geophysical Research 107(E10):5082. [2] C. C. Reese, et al. (2004) Journal of Geophysical Research 109:E08009. [3] W. A. Watters, et al. (2009) Journal of Geophysical Research 114:E02001. [4] J. H. Roberts, et al. (2012) Icarus 218(1):278. [5] T. Ruedas, et al. (2013) Physics of the Earth and Planetary Interiors.

The detailed petrogenesis of mafic sills occurring throughout southern Africa provides strong support for the development of an Umkondo large igneous province on the eastern margin of the Kalahari craton at 1.1Ga. The sills are most extensively developed in the Waterberg and Middelburg basins in northern South Africa and south-eastern Botswana. They are typical fractionated continental tholeiites with subophitic to ophitic dolerites, gabbros and gabbro-norites, and largely basaltic andesite in composition. The vast majority of the sample set defines one major geochemical subgroup, here referred to as the Mesoproterozoic Post-Waterberg sills A (MPWA sills), which is characteristically LREE enriched with relatively unfractionated HREEs, and with normalised incompatible element profiles similar to modern island arc andesites. A small number from the sample set define a minor subgroup (MPWB sills), which has so far only been recognised in the Middelburg basin, South Africa and which is characterized by fractionated HREEs. Both the major and trace element geochemical signatures of the MPWA sills are indistinguishable from the type Umkondo sills and less common lavas documented from Eastern Zimbabwe and mafic sills on the Grunehogna craton in present day Eastern Antarctica. This provides strong supporting evidence for an Umkondo large igneous province developed on the Kalahari craton at 1.1Ga. Despite crustal-type Sr–Nd isotopic signatures in the MPWA sills, bulk contamination by the continental crust is ruled out in favour of derivation from a primitive mantle-like asthenospheric source with a contribution from the subcontinental lithospheric mantle modified by a previous subduction event. The smaller MPWB magma type could represent a smaller degree melt at greater depth from a modified MORB-like source, although the relationship between the two subgroups remains unclear.

Undeformed rhyolite and granophyre in the Coats Land crustal block of East Antarctica, dated as 1112 +/- 4 Ma, are identical in age to both the Umkondo large igneous province (LIP) of the Kalahari craton (southern Africa) and the early Keweenawan LIP of Laurentia (North America). Although marine and satellite data demonstrate that Coats Land was close to Kalahari within the Gondwana supercontinent, the Coats Land rocks yield Pb isotope compositions strikingly distinct from those of the Umkondo province, yet indistinguishable from rocks of the Keweenawan province. The anorogenic Red Bluff granitic suite, along the present-day southern Laurentian margin in the Franklin Mountains (Texas, USA), is of comparable age, general rock type, and Pb isotope composition to rocks of Coats Land and may provide a piercing point for a Coats Land-Laurentia link. Paleomagnetic poles permit the Coats Land block to be close to this part of Laurentia ca. 1100 Ma and allow juxtaposition of Kalahari and southern Laurentia ca. 1000 Ma. The Coats Land crustal block may therefore be a critical tectonic tracer for placing Laurentia within late Mesoproterozoic and Neoproterozoic paleogeographic reconstructions. If this hypothesis is correct, Laurentia collided with the Kalahari craton along Antarctica's Maud orogen, which would represent a continuation of the ca. 1000 Ma Grenville orogen of eastern and southern Laurentia.

The Kalahari Craton was initially stabilized following cessation of Palaeoproterozoic orogenesis in southern Africa at ca. 1.8Ga. Subsequent Mesoproterozoic intraplate magmatism at ca. 1.4–1.35Ga formed a series of alkaline and carbonatitic complexes in the southern part of the craton. Original volcanic structures are partly preserved in some of the complexes, and a variety of intrusive rocks (e.g., quartz syenite, nepheline syenite, pyroxenite, ijolite, carbonatite) are present. The Premier kimberlite cluster was emplaced in the same region at ca. 1.2Ga, but available geochronology indicates that the main alkaline magmatism preceded 1.2–1.0Ga orogenesis in the Namaqua–Natal–Maud Belt along the southern craton margin. Another, more extensive intraplate magmatic event at ca. 1.1Ga formed the Umkondo Igneous Province, which is recognized over an area of ∼2.0×106km2 on the Kalahari Craton, including a detached fragment now located in Antarctica. Much of the province comprises high-level mafic intrusions, but erosional remnants of basalt lava piles and bimodal basalt/rhyolite assemblages are also present. Most of the mafic rocks are continental tholeiites, but trace-element geochemistry reveals distinct subgroups that cannot be related by crustal-level assimilation/fractional crystallization processes or by partial melting of a uniform mantle source. Geochronological and palaeomagnetic data indicate that enormous volumes of tholeiitic magma were emplaced within the province in a narrow time frame at ca. 1112–1106Ma, which is inferred to record uprise of a mantle plume behind the Namaqua–Natal–Maud Belt.

We report U-Pb baddeleyite crystallization ages of similar to1927 and similar to1879 to similar to1872 Ma for dolerite sills intruding the 'Waterberg Group in Botswana and South Africa. These data increase the known extent of similar to1.9 Ga intraplate magmatism in southern Africa and place tighter age constraints on the Waterberg Group than previously available. In South Africa, similar to1.88 Ga dolerite intrudes upper Waterberg strata, constraining most, if not all, of the succession to have accumulated between similar to2.06 Ga (age of the underlying Bushveld Complex) and similar to1.88 Ga. This is consistent with derivation of much of the group from uplifted sources in reactivated segments of the Limpopo Belt. The dolerites are typical continental tholeiites, but their trace-element contents discriminate them from dolerite sills of the 1.1 Ga Umkondo Igneous Province, which occur in the same region. Paleomagnetic samples from dolerite intrusions in the Waterberg Group in South Africa (including one sill with a U-Pb baddeleyite age of similar to1872 Ma), and from dolerite sills and basalt flows in the Soutpansberg Group to the east-northeast, yield antipodal directions with a site mean pole at 15.6degreesnorth, 17.1degreeseast, A(95) = 8.9degrees. These data are interpreted to indicate that the similar to1879 to similar to1872 Ma dolerites were intruded into the Waterberg Group during voluminous magmatism associated with development of the Soutpansberg rift basin. Older, similar to1927 Ma dolerite in Botswana is similar in age and geochemistry to basalts in the craton-margin Olifantshoek Supergroup, suggesting that the mafic magmatism in those two regions is genetically related.