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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.

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.

We report a new paleomagnetic pole for the Black Range Dolerite Suite of dykes, Pilbara craton, Western Australia. We replicate previous paleomagnetic results from the Black Range Dyke itself, but find that its magnetic remanence direction lies at the margin of a distribution of nine dyke mean directions. We also report two new minimum ID-TIMS 207Pb/206Pb baddeleyite ages from the swarm, one from the Black Range Dyke itself (>2769 ± 1 Ma) and another from a parallel dyke whose remanence direction lies near the centre of the dataset (>2764 ± 3 Ma). Both ages are slightly younger than a previous combined SHRIMP 207Pb/206Pb baddeleyite weighted mean date from the same swarm, with slight discordance interpreted as being caused by thin metamorphic zircon overgrowths. The updated Black Range suite mean remanence direction (D = 031.5°, I = 78.7°, k = 40, α95 = 8.3°) corresponds to a paleomagnetic pole calculated from the mean of nine virtual geomagnetic poles at 03.8°S, 130.4°E, K = 13 and A95 = 15.0°. The pole's reliability is bolstered by a positive inverse baked-contact test on a younger Round Hummock dyke, a tentatively positive phreatomagmatic conglomerate test, and dissimilarity to all younger paleomagnetic poles from the Pilbara region and contiguous portions of Australia. The Black Range pole is distinct from that of the Mt Roe Basalt (or so-called ‘Package 1’ of the Fortescue Group), which had previously been correlated with the Black Range dykes based on regional stratigraphy and imprecise SHRIMP U–Pb ages. We suggest that the Mt Roe Basalt is penecontemporaneous to the Black Range dykes, but with a slight age difference resolvable by paleomagnetic directions through a time of rapid drift of the Pilbara craton across the Neoarchean polar circle. (Less)

The volcanic Hartley Formation (part of the Olifantshoek Supergroup, which is dominated by red bed successions) in South Africa recorded depositional and tectonic conditions along the western Kaapvaal Craton during the late Palaeoproterozoic. It formed in association with red bed deposition elsewhere in the cratonic hinterland and along the craton’s northern margin. However, the exact correlation of the Olifantshoek Supergroup with these other red-bed successions is hindered by poor geochronological constraints. Herein, we refine the age and palaeopole of the Hartley Formation, and provide geochronological constraints for large-scale 1.93–1.91 Ga bimodal magmatism on the Kaapvaal Craton (herein named the Hartley large igneous province). We present new age constraints for the mafic and felsic phases of this event at 1923 ± 6 Ma and 1920 ± 4 Ma, respectively, which includes the first reported age dating of the Tsineng Dyke Swarm that has been linked to Hartley volcanism. A mean 1.93–1.91 Ga palaeoma...

On the south-easternmost Kaapvaal Craton, a NE-trending plagioclase-megacrystic dolerite dyke swarm, herein named the White Mfolozi Dyke Swarm (WMDS), has been identified. New U–Pb baddeleyite ages presented here indicate that the WMDS was emplaced within less than 10 million years, with our three most robust results yielding a weighted mean age of 2662 ± 2 Ma. The WMDS is coeval with the youngest dykes of a 2.70–2.66 Ga radiating dyke swarm already identified further north on the eastern side of the Kaapvaal Craton. This dyke swarm radiates out from the eastern lobe of the ca. 2.05 Ga Bushveld Complex. A clustering of ages from the WMDS and the 2.70–2.66 Ga radiating dyke swarm identify potential magmatic peaks at 2701–2692 Ma, 2686–2683 Ma and 2665–2659 Ma. Geochemical signatures of the dykes do not correlate with these age groups, but are rather unique to specific areas. The northern part of the eastern Kaapvaal Craton hosts relatively differentiated 2.70–2.66 Ga dolerite dykes that could have ...

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.

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.