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Gartner A.,GeoPlasma Laboratory | Youbi N.,Cadi Ayyad University | Youbi N.,University of Lisbon | Villeneuve M.,Aix - Marseille University | And 5 more authors.
International Journal of Earth Sciences | Year: 2017

Detrital zircon provenance studies are an established tool to develop palaeogeographic models, mostly based on zircon of siliciclastic rocks and isotope data. But zircon is more than just istopes and features well definable morphological characteristics. The latter may indicate single grain transport histories independent of the individual grade of concordance. This additional tool for palaeogeoraphic reconstructions was tested on zircon from siliciclastic and carbonate sedimentary rocks of Palaeozoic age from the Aoucert and Smara areas of the Souttoufides, while findings of zircon in limestone generally open new archives for sedimentary provenance analysis. The morphologies—length, width, roundness, grain surfaces—of 834 detrital zircons from sediments of allochthonous Cambrian, and (par-)autochthonous Ordovician, and Devonian units were studied, while 772 of them were analysed for their U–Th–Pb isotopes by LA-ICP-MS. Mesoproterozoic zircon contents of more than 10% in the Cambrian sediments exclude the West African Craton (WAC) as exclusive source area. Thus, at least one additional external source is suggested. This is likely the western Adrar Souttouf Massif with its significant Mesoproterozoic zircon inheritance, or comparable, yet unknown sources. Decreasing Mesoproterozoic zircon age populations in Ordovician sediments are thought to be linked to the rifting of the terranes in the course of the Rheic Ocean opening and a predominant supply of WAC detritus. The Devonian sediments likely contain reworked material from the Cambrian siliciclastics, which is shown by the zircon age distribution pattern and the zircon morphologies. Therefore, multiple shifts in the direction of sedimentary transport are indicated. © 2017 Springer-Verlag Berlin Heidelberg

Abubaker A.,TU Bergakademie Freiberg | Hofmann M.,GeoPlasma Laboratory | Gartner A.,GeoPlasma Laboratory | Linnemann U.,GeoPlasma Laboratory | Elicki O.,TU Bergakademie Freiberg
International Journal of Earth Sciences | Year: 2017

LA-ICP-MS U–Pb data from detrital zircons of the Ediacaran to Cambrian siliciclastic sequence of the Torgau-Doberlug Syncline (TDS, Saxo-Thuringia, Germany) are reported for the first time. The majority of 203 analysed zircon grains is Proterozoic with minor amount of Archean and Palaeozoic grains. The U–Pb ages fall into three groups: 2.8–2.4 Ga (3%), Neoarchean to earliest Palaeoproterozoic; 2.3–1.6 Ga (46%), early to late Palaeoproterozoic; 1.0–0.5 Ga (47%), Neoproterozoic to Cambrian. This age distribution is typical for the West African Craton as the source area and for Cadomian orogenic events in northwestern Gondwana. The samples show an age gap between 1.6 and 1.0 Ga, which is characteristic for West African provenance and diagnostic in distinguishing this unit from East Avalonia and Baltica. The dataset shows clusters of Palaeoproterozoic ages at 2.2–1.7 Ga, that is typical for western Gondwana, which was affected by abundant magmatic intrusions (ca. 2.2–1.8 Ga) during the Eburnean orogeny (West African craton). Neoarchean zircon ages (3%) point to recycling of magmatic rocks formed during the Liberian and Leonian orogenies. Ediacaran to earliest Cambrian rocks of the TDS originated in an active margin regime of the Gondwanan shelf. The following early Palaeozoic overstep sequence was deposited within rift settings that reflects instability of the West-Gondwanan shelf and the separation of terranes from Ordovician onward. The results of this study demonstrate distinct northwestern African provenance of the Cambrian siliciclastics of the TDS. Due to Th–U ratios from concordant zircon analysis, igneous origin from felsic melts is concluded as the source of these grains. © 2017 Springer-Verlag Berlin Heidelberg

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.

Eckelmann K.,GeoPlasma Laboratory | Nesbor H.-D.,Hessisches Landesamt fur Umwelt und Geologie | Konigshof P.,Senckenberg Naturmuseen und Forschungsinstitute | Linnemann U.,GeoPlasma Laboratory | And 3 more authors.
Gondwana Research | Year: 2014

The southern Rheinisches Schiefergebirge, which is part of the Rhenohercynian zone of the Central European Variscides, exhibits several allochthonous units: the Gießen-, and the Hörre nappe, and parts of the Frankenbach imbrication zone. These units were thrust over autochthonous and par-autochthonous volcano-sedimentary complexes of the Lahn and Dill-Eder synclines. This paper reports a representative data set of U-Pb LA-SF-ICP-MS ages of 1067 detrital zircon grains from Devonian and Lower Carboniferous siliciclastic sediments of the autochthonous and the allochthonous areas, respectively. The cluster of U-Pb ages from the allochthonous units points to a provenance in the Saxothuringian zone. Zircon populations from the Saxothuringian zone are representative of a Gondwanan hinterland and are characterized by age clusters of ~. 530-700. Ma, ~. 1.8-2.2. Ga, ~. 2.5-2.7. Ga, and ~. 3.0-3.4. Ga. Further samples were taken from the autochthonous and par-autochthonous units of the Lahn-Dill and Kellerwald areas. A Lower Devonian sandstone sample from the Siegen anticline provides a reference for siliciclastic sediments derived from the Old Red Continent. These samples show a provenance representative of Laurussia with debris primarily derived from Baltica and Avalonia. U-Pb zircon age clusters occur at ~. 400-450. Ma, 540-650. Ma, 1.0-1.2. Ga, ~. 1.4-1.5. Ga, ~. 1.7-2.2. Ga, and 2.3-2.9. Ga. Provenance analysis and geochemical data of the Rhenohercynian zone provide new information on the evolution of magmatic arcs in the Mid-Paleozoic. The data set constrains top-SE and top-NW directed subduction of the oceanic crust of the Rheic Ocean. Subduction-related volcanism lasted from the Early Devonian to the Early Carboniferous and thus confirms the existence of the Rheic Ocean until the Early Carboniferous. The tectonic model outlined for the Rhenohercynian zone suggests a wide Rheic Ocean. © 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.

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.

Gartner A.,GeoPlasma Laboratory | Villeneuve M.,Aix - Marseille University | Linnemann U.,GeoPlasma Laboratory | El Archi A.,Chouaïb 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.

Gartner A.,GeoPlasma Laboratory | Linnemann U.,GeoPlasma Laboratory | Hofmann M.,GeoPlasma Laboratory
International Journal of Earth Sciences | Year: 2014

The southern Congo Craton is widely overlain by Meso- to Cenozoic sediments of the northern Kalahari Basin, which hamper any correlation of basement units. The latter are represented by the Archaean Angola and Kasai Blocks, while the southern cratonic margin is framed by several Meso- to Neoproterozoic orogenic belts. For provenance analysis of the sedimentary cover and reconstruction of the main zircon-forming events, we studied zircons from recent sediments of the largest rivers at the southern margin of the Congo Craton. U-Pb zircon ages suggest a major amount of the sediments to originate from E Lufilian and Kibaran Belts, while input from the S Damara Belt seems to increase to the W. Ages related to the Angola Block were only noticed in the westernmost parts of the working area, which is not in accordance with the SE-trending drainage pattern, proposed to have been onset during the Cretaceous. Thus, it is assumed that the Meso- to Cenozoic sedimentary cover extended further west than today prior to the Mesozoic to Neogene uplift of the Angola Block and that subsequent erosion exhumed the basement stepwise from west to east. A recurrent destabilisation of the southern margin of the Congo Craton at ~2.7, 1.9, 1.0 and 0.6 Ga is supposed to be represented by major peaks in the age distribution pattern of the total amount of concordant zircons. This is in accordance with similar studies in adjacent areas. Additionally, the obtained data fit well to several hypothesised major events during the supercontinent cycle. © 2013 Springer-Verlag Berlin Heidelberg.

Linnemann U.,GeoPlasma Laboratory | Ouzegane K.,Université Ibn Tofail | Drareni A.,Université Ibn Tofail | Hofmann M.,GeoPlasma Laboratory | And 3 more authors.
Lithos | Year: 2011

Enormous masses of highly mature quartz sands were deposited in Western Gondwana during the Cambrian-Ordovician time, and provide a wide range of information concerning magmatic events through time, provenance, paleoclimate, and basin history. We present a provenance study based on 630 U-Pb (LA-ICP-MS) ages of detrital zircon from the latest Cambrian to Ordovician siliciclastic rocks of the Tassili Ouan Ahaggar basin situated in the Algerian Sahara. Most authors suggest local sources only for the sandstones. Instead, we demonstrate that the detritus is derived from different cratons and terranes which contributed to the deposition of a Cambrian-Ordovician overstep sequence covering western and northern Africa. Most zircon ages (61.0%) fall in the range of ~. 540 to 740. Ma and are interpreted to have been derived from Pan-African orogenic belts such as the Trans-Saharan Belt of NW Africa and previously from the Brazila belt of South America. Other potential sources for this zircon population are terranes of Cadomian affinity situated marginal to West Africa. The second-largest zircon population (20.2%) is 2.0 to 2.2. Ga, and is attributed to sources in the West African craton, such as the Birimian basement and the Eburnean orogenic belt, with possible partial input from the Amazonian craton. A zircon population of 7.1% yields Mesoproterozoic and early Paleoproterozoic ages in the range of ~. 1.3 to ~. 1.8. Ga and was probably derived from source rocks outside of the West African basement, the Tuareg shield and other adjoining areas. The Amazonian craton is a potential source region. A population of 6.7% of all zircon ages scatter from ~. 750. Ma to ~. 980. Ma and may reflect input from latest stages of the formation of Rodinia and its subsequent dispersal. A smaller population (3.2%) of zircon ages lie between ~. 2.3 and 2.65. Ga, and may be derived from late Paleoproterozoic to early Archaean rocks from the West African craton and possibly from Amazonia. Less than 1% of all zircons are Meso- to Paleoarchaean ones and provide evidence for the input of very old cratonic basement, most likely from cratonic inliers of the West African craton (Leonian, Liberian). Because of the potential input of detrital zircon from the Amazonian craton, which is reflected in the Mesoproterozoic and late Paleoproterozoic grains, we speculate that some of the Paleoproterozoic to Neoarchean (2.0. Ga to 2.6. Ga) zircons were also derived from Amazonia. Due to the total lack of 1.0-1.2. Ga old zircon, our data set excludes all crustal domains situated in the Arabian-Nubian shield and the East African belt, as well as the Sunsás belt of Amazonia ("Sunsás-Grenvillian") as potential sediment sources.Sedimentation in the Tassili Ouan Ahaggar basin started in uppermost Cambrian to Ordovician time due to the opening of the Rheic Ocean. This event led to subsidence related to the rift and drift of Avalonia and related terranes from the northwestern Gondwanan margin. The basal Early Tassili quartzite has detrital zircon populations that suggest a local provenance either from West African or from a related terrane in the Tuareg shield. A dramatic change occurs in the deltaic to shallow marine strata of the Lower Ordovician Ajjers Formation and in the overlying marine sandstones of the Middle Ordovician d'In Azaoua Formation. Our data for both formations indicate the Pan-African orogen, and very likely Cadomian terranes as the main source for the detritus. During this time, the region was affected by rift tectonics due to the opening of the Rheic Ocean and therefore amenable to erosion at rift shoulders and escarpments. Our data also indicate that glacial erosion in Upper Ordovician (Hirnantian) time must have affected larger areas of old cratonic surfaces as the populations of Paleoproterozoic to Archaean zircons are significantly higher than in other age clusters.Large parts of highly mature sands of the Cambro-Ordovician section in the Tassili Ouan Ahaggar basin were derived from a peneplain in the interior of Gondwana, that formed during Cambrian times. This peneplain was formed under warm-humid climate on a vegetation-free land surface and in an extreme corrosive environment that was influenced by high atmospheric pCO2 caused by Pan-African and Avalonian-Cadomian volcanism, volcanic activity related to the opening of the Iapetus, and Late Cambrian-Early Ordovician rift volcanism as well. © 2011 Elsevier B.V.

Linnemann U.,GeoPlasma Laboratory | Herbosch A.,Free University of Colombia | Liegeois J.-P.,Royal Museum for Central Africa | Pin C.,CNRS Magmas and Volcanoes Laboratory | And 2 more authors.
Earth-Science Reviews | Year: 2012

This study provides an up-to-date and comprehensive review of the Early Palaeozoic evolution of the Brabant Massif belonging to the Anglo-Brabant Deformation Belt. Situated at the southeastern side of Avalonia microplate, it is the only well-known part of the northern passive margin of the Rheic Ocean. The Cambrian-Silurian sedimentary pile is >13km thick, with >9km for the Cambrian only. The unraveling of this continuous registration reflects the successive rifting and drifting of Avalonia from the Gondwana mainland, followed by soft-collisional processes with Baltica and finally the formation of Laurussia. Based on recently established detailed stratigraphy, sedimentology and basin development, on U-Pb LA-ICP-MS analyses of igneous and detrital zircon grains along with geochemical data including Sm-Nd isotopes, a new geodynamic and palaeogeographic evolution is proposed. Brabant Megasequence 1 (lower Cambrian to lowermost Ordovician, >9km thick) represents an embayment of the peri-Gondwanan rift from which the Rheic Ocean has evolved. Detrital zircon ages demonstrate that the Brabant is a typical peri-Gondwanan terrane with a major Pan-African (Neoproterozoic age) and a mixed West African and Amazonian source (Palaeoproterozoic, Archaean and some Mesoproterozoic age). The transition towards the Avalonia drifting is marked by an unconformity and a short volcanic episode. The northward drift of Avalonia towards Baltica is recorded by the Megasequence 2 (Middle to Upper Ordovician, 1.3km thick). The source for Mesoproterozoic zircons vanished, as the result of the Rheic Ocean opening and the isolation from Amazonian sources. The transition to Megasequence 3 is marked by a drastic change in palaeobathymetry and an important (sub)volcanic episode during a tectonic instability period (460-430Ma), reflecting the Avalonia-Baltica soft docking as also shown by the reappearance of Mesoproterozoic detrital zircons, typical of Baltica. Unradiogenic Nd isotope signature (ε Nd -4/-5) and T DM model ages (1.3-1.7Ga) for Brabant magmatic rocks indicate an old recycled component. Megasequence 3 (uppermost Ordovician to lowermost Devonian; >3.5km thick) includes the onset of a Silurian foreland basin that reflects the tectonic inversion of the core of the massif (Brabantian orogeny) in response to the Baltica-Avalonia-Laurentia collision. Finally, the comparison with the strikingly similar Cambrian successions of the Harlech Dome (Wales, Avalonia) and the Meguma terrane (Nova Scotia, peri-Gondwana) allows the construction of a new Early Cambrian palaeogeographic model for the whole Avalonia microplate, in which the Meguma terrane is included. © 2012 Elsevier B.V.

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