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Dresden, Germany

Gartner A.,GeoPlasma Laboratory | Villeneuve M.,Aix - Marseille University | Linnemann U.,GeoPlasma Laboratory | Gerdes A.,Goethe University Frankfurt | And 4 more authors.
Tectonophysics | Year: 2015

The Adrar Souttouf Massif is located at the western margin of the West African Craton and consists of several NNE-SSW trending units. Of them, the two westernmost have been interpreted to be linked with the Avalonian terrane assemblage and Meguma, respectively. New Hf isotopic data corroborates the Avalon correlation but has no impact one way or another on the possible Meguma connection, as there is no Hf data available from the latter. The obtained pattern of εHf(t) values vs. zircon age of the likely Avalonia related Oued Togba unit is similar to published data from Avalonia. Zircons of this unit show characteristic patterns of crustal mixing at 0.7 to 1.3Ga and 1.75 to 2.25Ga, while juvenile crust was likely formed around 0.6 to 0.75Ga, from 1.2 to 2.2Ga, and between 2.5 and 3.2Ga. The zircons of the Sebkha Gezmayet unit reveal crustal mixing for the entire Palaeozoic and Neoproterozoic, from 2.05 to 2.11Ga, and 2.8 to 2.9Ga. Juvenile crust formation is interpreted to have occurred from 0.5 to 0.7Ga, at around 2.1Ga, and at ca. 2.9Ga. As Mesoproterozoic zircons are abundant in the likely Avalonia-like Oued Togba unit, but uncommon at the West African Craton, their origin has to be found elsewhere. A comparison of available Hf data from Amazonia and Baltica, the two potential source cratons of Avalonia, shows similarities but is hampered by the lack of available data from Amazonia. Finally, a few grains from both units have Eoarchaean model ages. Among similar grains from other peri-Gondwanan terranes, they give indication of partial recycling of Eoarchaean crust in the vicinity of the northwestern West African Craton. © 2015 Elsevier B.V.

Gartner A.,GeoPlasma Laboratory | Villeneuve M.,Aix - Marseille University | Linnemann U.,GeoPlasma Laboratory | El Archi A.,Chouaib Doukkali University | Bellon H.,CNRS Oceanic Domains Laboratory
Gondwana Research | Year: 2013

The Moroccan Sahara includes the Dhlou and Adrar Souttouf Massifs, both of which belong to the Souttoufide belt and are located on the western margin of the Archean Reguibat Shield. The Adrar Souttouf Massif has previously been assumed to be part of the Variscan Mauritanian-Appalachian system. New zircon ages from the two units of the Adrar Souttouf Massif have nevertheless allowed us to hypothesise a complex polyphased history. The Massif comprises four NNE-SSW trending units (listed here from east to west). The Sebkha Matallah unit represents the eastern margin of the Adrar Souttouf Massif and is thrust over the Ordovician to Devonian sedimentary Dhloat Ensour Group to the east. A central (Dayet Lawda) unit consisting of mafic and ultramafic rocks is interpreted as a possible remnant of Neoproterozoic oceanic crust or mafic terranes. The western Sebkha Gezmayet and Oued Togba units are mainly composed of granitoids and orthogneisses. Tonian-Stenian (1400-1000. Ma) zircon ages recorded in the Oued Togba and Sebkha Gezmayet units suggest an Avalonian-Meguman-like relationship. The other three age groups obtained in these two units are 610 to 570. Ma (Pan-African), 530 to 490. Ma (Cambrian) and 440 to 270. Ma. The latter population cannot result from Variscan orogeny alone, and is possibly linked to the Salinic and Acadian orogenies of Laurentia. Zircon ages of ~. 3000. Ma and ~. 2650. Ma determined for two granite samples from the Archean foreland corroborate data already published. Lower intercept ages of between 226. Ma (Upper Triassic) and 158. Ma (Upper Jurassic) identified for discordia lines are interpreted as a Mesozoic thermal overprint of the area attributed to the break-up of Pangaea and the initial rifting of the Atlantic Ocean. The ages obtained support a new tectonic model describing the formation of the units of the Adrar Souttouf Massif. © 2013 International Association for Gondwana Research.

Delpomdor F.,Free University of Colombia | Linnemann U.,GeoPlasma Laboratory | Boven A.,Royal Museum for Central Africa | Gartner A.,GeoPlasma Laboratory | And 5 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2013

The late Mesoproterozoic-middle Neoproterozoic period (ca. 1300Ma-800Ma) heralded extraordinary climatic and biological changes related to the tectonic changes that resulted in the assembly (~1.0Ga) and the break-up of Rodinia (880Ma-850Ma). In the Democratic Republic of Congo, these changes are recorded in the Mbuji-Mayi Supergroup which was deposited in the SE-NW trending siliciclastic-carbonate failed-rift Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. New LA-ICP-MS U-Pb laser ablation data on detrital zircon grains retrieved from the lower arenaceous-pelitic sequence (BI group) together with C and Sr isotopic data on carbonates from the upper dolomitic-pelitic sequence (BII group) and an 40Ar/39Ar age determination on a dolerite give a new depositional time frame between 1174±22Ma and ca. 800Ma for the Mbuji-Mayi Supergroup. The upper age limit is based on the assumption that the transition between the BIIb and BIIc subgroups recorded the Bitter Springs anomaly. In terms of tectonic and paleoclimatic settings, the BII group was deposited in the eastern passive margin of the Congo Craton during warm periods interlaced with temporarily dry and wet seasons, suggesting greenhouse conditions during the fragmentation of Rodinia. © 2013 Elsevier B.V.

Gartner A.,GeoPlasma Laboratory | Villeneuve M.,Aix - Marseille University | Linnemann U.,GeoPlasma Laboratory | Gerdes A.,Goethe University Frankfurt | And 5 more authors.
Gondwana Research | Year: 2015

Bordered by the Archaean basement of the Reguibat Shield to the E and S, the Adrar Souttouf Massif is located in the southern regions of the Moroccan Sahara and represents the northern part of the Mauritanide belt. The central areas of this massif comprise the Dayet Lawda and Sebkha Matallah units that are mainly composed of mafic rocks. Ten samples taken from these rocks yielded 531 zircon grains that were analysed with respect to their morphology, U-Th-Pb, and Lu-Hf isotope composition. Additionally, 155 apatite grains from six samples were also dated by the U-Th-Pb method. Mostly well rounded zircon grains commonly showed bright cathodoluminescent (CL) overgrowth domains and leaching zones, indicating metamorphic overprint around unaffected oscillatory zoned core areas. All samples but one yielded two significant zircon age populations: ~. 605 Ma and ~. 634 Ma with some inherited grains in the range of ~. 650-740 Ma and very scarcely up to ~. 1190 Ma. For six samples the Hf isotope composition suggests a major contribution of Neoproterozoic juvenile magmas from depleted mantle source. The zircon Hf data for the remaining samples points to a predominant recycling of older Archaean to Palaeoproterozoic crust. Based on the geochemical composition of the rocks, an island arc setting is assumed at the periphery of the West African Craton close to the Cryogenian-Ediacaran boundary. Subsequent metamorphism during accretion and partial obduction onto the basement rocks took place at about 605 Ma. A minor Variscan overprint could be demonstrated for only one sample. This case study exemplifies the great potential of the widely occurring metamorphosed mafic and ultramafic rocks along the western margin of the West African Craton for palaeogeographic and geodynamic reconstructions including the peri-Gondwanan terranes during the Late Neoproterozoic. © 2014.

Sagawe A.,GeoPlasma Laboratory | Gartner A.,GeoPlasma Laboratory | Linnemann U.,GeoPlasma Laboratory | Hofmann M.,GeoPlasma Laboratory | Gerdes A.,Goethe University Frankfurt
Tectonophysics | Year: 2016

The Saxonian Granulite Massif is located at the northern margin of the Saxo-Thuringian Zone of the peri-Gondwana Bohemian Massif. Eight felsic and mafic granulites were studied with respect to their geochemistry and U. Pb zircon geochronology. The felsic granulites are interpreted to be derived from continental crust of possible granitoid composition. An origin from depleted mantle sources with IAT to MORB composition can be assumed for the mafic granulites. The peak of metamorphism is thought to be timed at about 340. Ma, while several earlier metamorphic events are supposed to have occurred at about 355-360, 370-375, 405, and 450. Ma. They reveal a complex and polyphased geologic evolution of the Saxonian Granulite Massif. Protolith emplacement likely took place at c. 450 and 494. Ma. Hf isotopic data suggest Mesoproterozoic crustal ages at least for parts of the massif. As these crustal ages are exotic for the Bohemian Massif, their origin has to be searched elsewhere. Potential source areas could be Amazonia and Baltica, of which the latter is the one preferred. Furthermore, a composite architecture with at least two components-the felsic granulites with Mesoproterozoic crustal model ages, and the mafic granulites of potential island arc origin-is hypothesised. Their amalgamation to the recent appearance of the Saxonian Granulite Massif is likely bracketed between 375 and 340. Ma. © 2016.

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