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The Rodinia supercontinent broke apart during the Neoproterozoic. Rodinia break-up is associated with widespread intraplate magmatism on many cratons, including the c. 720–719 Ma Franklin large igneous province (LIP) of Laurentia. Coeval magmatism has also been identified recently in Siberia and South China. This extensive magmatism terminates ∼1 myr before the onset of the Sturtian Snowball Earth. However, LIP-scale magmatism and global glaciation are probably related. U–Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) baddeleyite dating herein identifies remnants of a new c. 724–712 Ma LIP on the eastern Kalahari Craton in southern Africa and East Antarctica: the combined Mutare–Fingeren Dyke Swarm. This dyke swarm occurs in northeastern Zimbabwe (Mutare Dyke Swarm) and western Dronning Maud Land (Fingeren Dyke Swarm). It has incompatible element-enriched mid-ocean ridge basalt-like geochemistry, suggesting an asthenospheric mantle source for the LIP. The Mutare–Fingeren LIP probably formed during rifting. This rifting would have occurred almost ∼100 myr earlier than previous estimates in eastern Kalahari. The placement of Kalahari against southeastern Laurentia in Rodinia is also questioned. Proposed alternatives, invoking linking terranes between Kalahari and southwestern Laurentia or close to northwestern Laurentia, also present challenges with no discernible resolution. Nevertheless, LIP-scale magmatism being responsible for the Sturtian Snowball Earth significantly increases.

Although Variscan terranes have been documented from the Balkans to the Caucasus, the southeastern portion of the Variscan Belt is not well understood. The Strandja Zone along the border between Bulgaria and Turkey encompasses one such terrane linking the Balkanides and the Pontides. However, the evolution of this terrane, and the Late Carboniferous to Triassic granitoids within it, is poorly resolved. Here we present laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) U–Pb zircon ages, coupled with petrography and geochemistry from the Izvorovo Pluton within the Sakar Unit (Strandja Zone). This pluton is composed of variably metamorphosed and deformed granites which yield crystallization ages of c. 251–256 Ma. These ages are older than the previously assumed age of the Izvorovo Pluton based on a postulated genetic relationship between the Izvorovo Pluton and Late Jurassic to Early Cretaceous metamorphism. A better understanding of units across the Strandja Zone can now be achieved, revealing two age groups of plutons within it. An extensive magmatic episode occurred c. 312–295 Ma, and a longer-lived episode between c. 275 and 230 Ma. Intrusions associated with both magmatic events were emplaced into pre-Late Carboniferous basement, and were overprinted by Early Alpine metamorphism and deformation. These two stages of magmatism can likely be attributed to changes in tectonic setting in the Strandja Zone. Such a change in tectonic setting is likely related to the collision between Gondwana-derived terranes and Laurussia, followed by either subduction of the Palaeo-Tethys Ocean beneath Laurussia or rifting in the southern margin of Laurussia, with granitoids forming in different tectonic environments.

The 1.87–1.84 Ga Black Hills dike swarm of the Kalahari craton (South Africa) is coeval with several regional magmatic provinces used here to resolve the craton's position during Columbia assembly. We report a new 1850 ± 4 Ma (U-Pb isotope dilution–thermal ionization mass spectrometry [ID-TIMS] on baddeleyite) crystallization age for one dike and new paleomagnetic data for 34 dikes of which 8 have precise U-Pb ages. Results are constrained by positive baked-contact and reversal tests, which combined with existing data produce a 1.87–1.84 Ga mean pole from 63 individual dikes. By integrating paleomagnetic and geochronological data sets, we calculate poles for three magmatic episodes and produce a magnetostratigraphic record. At 1.88 Ga, the Kalahari craton is reconstructed next to the Superior craton so that their ca. 2.0 Ga poles align. As such, magmatism forms part of a radiating pattern with the coeval ca. 1.88 Ga Circum-Superior large igneous province.

The Singhbhum Craton in eastern India is host to at least seven sets of mafic dyke swarms. Four previously dated swarms (studied here) include the NNE-trending Keshargaria (ca. 2.80 Ga) and Ghatgaon (ca. 2.76 - 2.75 Ga) swarms, the ENE-trending Kaptipada swarm (ca. 2.26 Ga), and the ESE-trending Pipilia swarm (ca.1.76 Ga). The dykes range in composition from basalt to andesite and have transitional tholeiitic to calc-alkaline affinities. They show intra- and inter-swarm geochemical and Sr-Nd isotopic heterogeneities and have SiO2 content ranging from 47 to 60 wt.%. The chondrite normalized REE patterns show enrichment in LREE and the Primitive-Mantle normalized multi-element patterns show elevated U, Th, Cs, Rb, K, and Pb; and depletion in Nb, Ta, and Ti. These characteristics indicate involvement of crustal component in the petrogenesis of these dykes. The dykes of different swarms have variable 87Sr/86Sri and eNd(i) values, which define a crust-like isotopic growth trajectory with time from a common chondritic to depleted source that was enriched contemporaneously with the formation of the crustal rocks of the Singhbhum Craton. The isotope data indicate involvement of older enriched crustal material in the petrogenesis of these dykes. Variable but mostly high (compared to similarly evolved magmas) Ni (40 - 590 ppm), Cr (40 - 1110 ppm), and V (120 - 434 ppm) contents particularly of the most primitive dykes indicate that parental melts were in equilibrium with mantle peridotite and experienced only minor fractional crystallization of olivine, pyroxene, and magnetite. The Sr-Nd isotope ratios do not show any correlation with differentiation indices which indicates that the melts were not modified significantly by crustal assimilation during ascent and emplacement. The crust-like secular trend of the Sr and Nd isotopic compositions suggests that the enriched crustal material was incubated in the mantle (i.e., metasomatized lithospheric mantle) for a long time and this source was periodically tapped leading to multiple dyke emplacement events over at least 1 Gyr. The recycled crustal material played a role in metasomatizing the subcontinental lithospheric mantle prior to ca. 2.80 Ga. Mantle plume activity triggered melting of the metasomatized lithospheric mantle many times, leading to the emplacement of mafic dykes of different generations across the craton.

U-Pb geochronology on baddeleyite is a powerful technique that can be applied effectively to chronostratigraphy. In southern Africa, the Kaapvaal Craton hosts a well-preserved Mesoarchean to Paleoproterozoic geological record, including the Neoarchean Ventersdorp Supergroup. It overlies the Witwatersrand Supergroup and its world-class gold deposits. The Ventersdorp Supergroup comprises the Klipriviersberg Group, Platberg Group, and Pniel Group. However, the exact timing of formation of the Ventersdorp Supergroup is controversial. Here we present 2789 ± 4 Ma and 2787 ± 2 Ma U-Pb isotope dilution-thermal ionization mass spectrometry (ID-TIMS) baddeleyite ages and geochemistry on mafic sills intruding the Witwatersrand Supergroup, and we interpret these sills as feeders to the overlying Klipriviersberg Group flood basalts. This constrains the age of the Witwatersrand Supergroup and gold mineralization to at least ca. 2.79 Ga. We also report 2729 ± 5 Ma and 2724 ± 7 Ma U-Pb ID-TIMS baddeleyite ages and geochemistry from a mafic sill intruding the Pongola Supergroup and on an east-northeast–trending mafic dike, respectively. These new ages distinguish two of the Ventersdorp Supergroup magmatic events: the Klipriviersberg and Platberg. The Ventersdorp Supergroup can now be shown to initiate and terminate with two large igneous provinces (LIPs), the Klipriviersberg and Allanridge, which are separated by Platberg volcanism and sedimentation. The age of the Klipriviersberg LIP is 2791–2779 Ma, and Platberg volcanism occurred at 2754–2709 Ma. The Allanridge LIP occurred between 2709–2683 Ma. Klipriviersberg, Platberg, and Allanridge magmatism may be genetically related to mantle plume(s). Higher heat flow and crustal melting resulted as a mantle plume impinged below the Kaapvaal Craton lithosphere, and this was associated with rifting and the formation of LIPs.

Background Lateral flow device (LFD) viral antigen immunoassays have been developed around the world as diagnostic tests for SARS-CoV-2 infection. They have been proposed to deliver an infrastructure-light, cost-economical solution giving results within half an hour. Methods LFDs were initially reviewed by a Department of Health and Social Care team, part of the UK government, from which 64 were selected for further evaluation from 1st August to 15th December 2020. Standardised laboratory evaluations, and for those that met the published criteria, field testing in the Falcon-C19 research study and UK pilots were performed (UK COVID-19 testing centres, hospital, schools, armed forces). Findings 4/64 LFDs so far have desirable performance characteristics (orient Gene, Deepblue, Abbott and Innova SARS-CoV-2 Antigen Rapid Qualitative Test). All these LFDs have a viral antigen detection of >90% at 100,000 RNA copies/ml. 8951 Innova LFD tests were performed with a kit failure rate of 5.6% (502/8951, 95% CI: 5.1–6.1), false positive rate of 0.32% (22/6954, 95% CI: 0.20–0.48). Viral antigen detection/sensitivity across the sampling cohort when performed by laboratory scientists was 78.8% (156/198, 95% CI 72.4–84.3). Interpretation Our results suggest LFDs have promising performance characteristics for mass population testing and can be used to identify infectious positive individuals. The Innova LFD shows good viral antigen detection/sensitivity with excellent specificity, although kit failure rates and the impact of training are potential issues. These results support the expanded evaluation of LFDs, and assessment of greater access to testing on COVID-19 transmission. Funding Department of Health and Social Care. University of Oxford. Public Health England Porton Down, Manchester University NHS Foundation Trust, National Institute of Health Research.

The final fragmentation of Rodinia occurred during the Ediacaran period as the continental blocks of Baltica and Laurentia, as well as Amazonia and West Africa, rifted and drifted apart. It was along this progressively rifted margin that the Iapetus Ocean opened and subsequently closed, creating the Caledonian orogeny (sensu lato), some 100 and 200 million years later. The 0.62–0.54 Ga Central Iapetus Magmatic Province (CIMP), accompanying this break-up, is variously manifested in northern Europe and north-eastern North America as mafic dykes and sills, volcanic rocks, as well as carbonatites. This magmatism is interpreted to be broadly coincident with the so-called Marinoan and Gaskiers glaciations, and the subsequent evolution of metazoans. While the various Precambrian basement blocks of Svalbard are known to carry a Caledonian overprint, the proximity of various parts of Svalbard to either Baltica or Laurentia during final Rodinia breakup in the Ediacaran has yet to be established. Petrographic, geochronological and geochemical data from the variably deformed and metamorphosed coarse-grained mafic units of Oscar II Land (OIIL) from Spitsbergen, Svalbard, are presented here to determine the source of the magma and to elucidate on their palaeogeographic affinity with adjacent crustal blocks/units. An alkali and OIB-like affinity of the mafic units is confirmed by their whole-rock geochemical composition. An ID-TIMS U-Pb baddeleyite crystallisation age determination of 560 ± 12 Ma, obtained from one such mafic unit, contrasts with the published Caledonian (sensu lato) age determinations. These data for OIIL compare well with the broadly coeval and geochemically similar 570–560 Ma Norwegian Seiland Igneous Province, which may have formed a part of Baltica. Temporally and compositionally similar mafic units also occur within the North American Appalachian Belt, as well as the Sept-Iles intrusion, which is part of Laurentia. However, any links between these intrusions with those of Svalbard are yet to be unequivocally demonstrated.

Southeastern Bulgaria is composed of a variety of rocks from pre-Variscan (ca. 0.3 Ga) to pre-Alpine sensu lato (ca. 0.15 Ga) time. The Sakar Unit in this region comprises a series of granitoids and gneisses formed or metamorphosed during these events. It is cut by a series of post-Variscan hydrothermal veins, yet lacks pervasive Alpine deformation. It thus represents a key unit for detecting potential tectonism associated with the enigmatic Cimmerian Orogenic episode, but limited geochronology has been undertaken on this unit. Here we report age constraints on hydrothermal activity in the Sakar Pluton. The investigated veins contain mainly albite&ndash, actinolite&ndash, chlorite&ndash, apatite&ndash, titanite&ndash, quartz&ndash, tourmaline&ndash, epidote and accessory minerals. The most common accessory minerals are rutile and molybdenite. Apatite and titanite from the same vein were dated by U&ndash, Pb LA&ndash, ICP-MS geochronology. These dates are interpreted as crystallization ages and are 149 &plusmn, 7 Ma on apatite and 114 &plusmn, 1 Ma on titanite, respectively. These crystallization ages are the first to document two stages of hydrothermal activity during the late Jurassic to early Cretaceous, using U&ndash, Pb geochronology, and its association with the Cimmerian orogenesis. The Cimmerian tectono-thermal episode is well-documented further to the east in the Eastern Strandja Massif granitoids. However, these are the first documented ages from the western parts of the Strandja Massif, in the Sakar Unit. These ages also temporally overlap with previously published Ar&ndash, Ar and K&ndash, Ar cooling ages, and firmly establish that the Cimmerian orogeny in the studied area included both tectonic and hydrothermal activity. Such hydrothermal activity likely accounted for the intense albitization found in the Sakar Unit.

Mobilistic plate-tectonic interpretation of Precambrian orogens requires that two conjoined crustal blocks may derive from distant portions of the globe. Nonetheless, many proposed Precambrian cratonic juxtapositions are broadly similar to those of younger times (socalled "strange attractors"), raising the specter of bias in their construction. We evaluated the possibility that the Congo and Kalahari cratons (Africa) were joined together prior to their amalgamation along the Damara-Lufilian-Zambezi orogen in Cambrian time by studying diabase dikes of the Huila-Epembe swarm and sills in the southern part of the Congo craton in Angola and in Namibia. We present geologic, U-Pb geochronologic, and paleomagnetic evidence showing that these two cratons were directly juxtaposed at ca. 1.1 Ga, but in a slightly modified relative orientation compared to today. Recurring persistence in cratonic connections, with slight variations from one supercontinent to the next, may signify a style of supercontinental transition similar to the northward motion of Gondwana fragments across the Tethys-Indian oceanic tract, reuniting in Eurasia. (Less)

Precise geochronology, combined with paleomagnetism on mafic intrusions, provides first-order information for paleoreconstruction of crustal blocks, revealing the history of supercontinental formation and break-up. These techniques are used here to further constrain the apparent polar wander path of the Kaapvaal Craton across the Neoarchean-Paleoproterozoic boundary. U-Pb baddeleyite ages of 2441 +/- 6 Ma and 2426 +/- 1 Ma for a suite of mafic sills located on the western Kaapvaal Craton in South Africa (herein named the Westerberg Sill Suite), manifests a new event of magmatism within the Kaapvaal Craton of southern Africa. These ages fall within a ca. 450 Myr temporal gap in the paleomagnetic record between 2.66 and 2.22 Ga on the craton. Our older Westerberg Suite age is broadly coeval with the Woongarra magmatic event on the Pilbara Craton in Western Australia. In addition, the Westerberg Suite on the Kaapvaal Craton intrudes a remarkably similar Archean-Proterozoic sedimentary succession to that on the Pilbara Craton, supporting a stratigraphic correlation between Kaapvaal and Pilbara (i.e., Vaalbara). The broadly coeval Westerberg-Woongarra igneous event may represent a Large Igneous Province. The paleomagnetic results are more ambiguous, with several different possibilities existing. A Virtual Geomagnetic Pole obtained from four sites on the Westerberg sills is 18.9 degrees N, 285.0 degrees E, A(95) = 14.1 degrees, K = 43.4 (Sample based VGP, n=34: 16.8 degrees N, 2879.9 degrees E, dp=4.4 degrees, dm=7.7 degrees). If primary (i.e., 2441-2426 Ma), it would provide a further magmatic event within a large temporal gap in the Kaapvaal Craton's Paleoproterozoic apparent polar wander path. It would suggest a relatively stationary Kaapvaal Craton between 2.44 Ga and 2.22 Ga, and ca. 35 degrees of latitudinal drift of the craton between ca. 2.66 Ga and 2.44 Ga. This is not observed for the Pilbara Craton, suggesting breakup of Vaalbara before ca. 2.44 Ga. However, it is likely that the Woongarra paleopole represents a magnetic overprint acquired during the Ophtalmian or Capricorn Orogeny, invalidating a paleomagnetic comparison with the Westerberg Sill Suite. Alternatively, our Westerberg Virtual Geographic Pole manifests a 2.22 Ga magnetic overprint related to Ongeluk volcanism. The similarity between Ongeluk and Westerberg paleopoles however may also infer magmatic connections if both are primary directions, despite the apparent 200 million year age this difference. (C) 2015 Elsevier B.V. All rights reserved.

In this thesis, the longevity and continuity of the Vaalbara supercraton is addressed in six papers aimed at placing new temporal and spatial constraints onthe supercraton in the Mesoarchean to Paleoproterozoic. It has been speculated since the 1960’s that the Kaapvaal Craton in southern Africa, together withthe Pilbara Craton in Western Australia existed as a single landmass during the Precambrian – the Vaalbara supercraton. Many studies have demonstrated thegeological similarities between the cratons, particularly in terms of their Mesoarchean to Paleoproterozoic unconformity-bounded sequences. These unconformity-bounded sequences have continuously been refined and developed, especially since the 1990’s. The first main stratigraphic similarities lie in the volcanic and sedimentary successions found in the Neoarchean Fortescue Group and Ventersdorp Supergroup basins on the Pilbara and Kaapvaal cratons, respectively, along with other associated basins. The unconformably overlying Hammersley (and Turee Creek) Group and Transvaal Supergroup on the Pilbara and Kaapvaal cratons, respectively, also show many stratigraphic similarities, and both host world-class deposits of hydrothermally-upgraded iron formations. However, no marker beds or precise age matches have yet been made, especially in the extensive Mesoarchean to Paleoproterozoic mafic dyke swarms and sill provinces present in each craton from the time interval discussed in this thesis. Regardless, the geological discussions has been aided by geochronological and paleomagnetic studies, which have both credited and discredited the existence of the Pilbara and Kaapvaal cratons as nearest neighbours for the time interval between ca. 2.87 Ga and ca. 2.65 Ga.In this thesis, the so-called magmatic barcode record of large igneous provinces (LIPs), which are extensive and short-lived volcanic events, of the KaapvaalCraton is presented together with that of the Pilbara Craton in conjunction with previous geochronological and paleomagnetic studies. This magmatic barcoderecord refines temporal, and through paleomagnetism, spatial constraints, and invalidates the existence of Vaalbara as a distinct continuous supercraton. Magmatic and paleomagnetic linkages between the 2.99-2.98 Ga Usushwana Complex on the Kaapvaal Craton and the ca. 2.87 Ga Millindinna Complex on thePilbara Craton are shown to be incorrect with new ages for the Usushwana Complex and Badplaas dyke swarm presented in Gumsley et al. (2015). Extensivemafic dyke swarms associated with Neoarchean Fortescue volcanism on the Pilbara Craton and Ventersdorp volcanism on the Kaapvaal Craton also show lesssimilarities from new paleomagnetic and geochronological constraints. These constraints are presented in Gumsley et al. (2016) and Evans et al. (2017) for thenewly identified White Mfolozi and Black Range mafic dyke swarms, respectively, on the Kaapvaal and Pilbara cratons. Gumsley et al. (2017) and Kampmannet al. (2015) also present a new LIP, the Ongeluk, on the Kaapvaal Craton which has not been identified on the Pilbara Craton. This new LIP is composed ofthe Ongeluk Formation in the Transvaal Supergroup on the western margin of the Kaapvaal Craton, as well as the Westerberg Sill Province and a north-trendingmafic dyke swarm. The Ongeluk LIP appears to break some of the stratigraphic comparison between the upper Transvaal Supergroup on the Kaapvaal Cratonand the Turee Creek Group on the Pilbara Craton. In addition, a new late Paleoproterozoic mafic dyke swarm, the Tsineng swarm, is presented for the western Kaapvaal Craton in Alebouyeh Semami et al. (2016), which is correlated with Hartley Formation volcanism in the Olifantshoek Supergroup. This magmaticevent may also define a new LIP on the western Kaapvaal Craton. This mafic dyke swarm and its associated volcanism has also not been documented on thePilbara Craton.Instead, it is proposed that the Pilbara and Kaapvaal cratons were part of a much larger continent or supercontinent in the Neoarchean to Paleoproterozoic.This large crustal block likely included the Wyoming, Superior and Hearne cratons of North America, together with the Kola-Karelia Craton located between Russia and Finland, as well as possibly the Singhbhum Craton of India and the Samartia terrane of Russia and Ukraine. This continent or supercontinent, termed ‘Supervaalbara’ here, allows for the Kaapvaal and Pilbara cratons to share many geological similarities without being nearest neighbours, along possiblythe same passive margin. The geological evolution of all these cratons is very similar, particularly in the Paleoproterozoic, and which may have been driven byglobal processes. These global processes may include true polar wander, the submergence and subsequent remergence of continents with sea-level rise and fall, as well as atmospheric oxygenation and global glaciation. Paleomagnetic studies provide further continuity supporting the existence of Supervaalbara, which appears geologically distinct from the Rae family of cratons, suggesting perhaps two different continents in the early Paleoproterozoic before the assembly of the supercontinent Columbia (Nuna) in the late Paleoproterozoic.

The first significant buildup in atmospheric oxygen, the Great Oxidation Event (GOE), began in the early Paleoproterozoic in association with global glaciations and continued until the end of the Lomagundi carbon isotope excursion ca. 2,060 Ma. The exact timing of and relationships among these events are debated because of poor age constraints and contradictory stratigraphic correlations. Here, we show that the first Paleoproterozoic global glaciation and the onset of the GOE occurred between ca. 2,460 and 2,426 Ma, ∼100 My earlier than previously estimated, based on an age of 2,426 ± 3 Ma for Ongeluk Formation magmatism from the Kaapvaal Craton of southern Africa. This age helps define a key paleomagnetic pole that positions the Kaapvaal Craton at equatorial latitudes of 11° ± 6° at this time. Furthermore, the rise of atmospheric oxygen was not monotonic, but was instead characterized by oscillations, which together with climatic instabilities may have continued over the next ∼200 My until ≤2,250–2,240 Ma. Ongeluk Formation volcanism at ca. 2,426 Ma was part of a large igneous province (LIP) and represents a waning stage in the emplacement of several temporally discrete LIPs across a large low-latitude continental landmass. These LIPs played critical, albeit complex, roles in the rise of oxygen and in both initiating and terminating global glaciations. This series of events invites comparison with the Neoproterozoic oxygen increase and Sturtian Snowball Earth glaciation, which accompanied emplacement of LIPs across supercontinent Rodinia, also positioned at low latitude.