Search results for "Gondwana"
showing 10 items of 76 documents
Comment on “Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications”. Tectonophysics, 662, 219–242…
2017
Abstract Determining the possible tectonic regimes active during the Neoproterozoic is crucial for the knowledge of the evolution of the super-continent Gondwana. In Madagascar, that occupies a key position in Gondwana, there is an on-going debate regarding the location of possible suture zones and the implications in terms of paleo-geography. Recognizing high-pressure to ultra-high pressure conditions in mafic rocks is commonly viewed as a strong argument for paleo-subduction zones. Ishwar-Kumar et al. (2015) report unusual high pressure conditions (24 kbar) in Neoproterozoic to Cambrian rocks from North-Central Madagascar (Andriamena Complex). They propose a geodynamic model in which exhu…
Tectono-metamorphic evolution of the internal zone of the Pan-African Lufilian orogenic belt (Zambia): Implications for crustal reworking and syn-oro…
2016
Abstract The internal zone of the Pan-African Lufilian orogenic belt (Zambia) hosts a dozen uranium occurrences mostly located within kyanite micaschists in a shear zone marking the contact between metasedimentary rocks attributed to the Katanga Neoproterozoic sedimentary sequence and migmatites coring domes developed dominantly at the expense of the pre-Neoproterozoic basement. The P–T–t–d paths reconstructed for these rocks combining field observations, microstructural analysis, metamorphic petrology and thermobarometry and geochronology indicate that they have recorded burial and exhumation during the Pan-African orogeny. Both units of the Katanga metasedimentary sequence and pre-Katanga…
Carboniferous granites on the northern margin of Gondwana, Anatolide-Tauride Block, Turkey - Evidence for southward subduction of Paleotethys
2016
Carboniferous metagranites with U-Pb zircon crystallization ages of 331-315 Ma crop out in the Afyon zone in the northern margin of the Anatolide-Tauride Block, which is commonly regarded as part of Gondwana during the Late Palaeozoic. They are peraluminous, calc-alkaline and are characterized by increase in Rb and Ba, decrease in Nb-Ta, and enrichment in Sr and high LILE/HFSE ratios compatible with a continental arc setting. The metagranites intrude a metasedimentary sequence of phyllite, metaquartzite and marble; both the Carboniferous metagranites and metasedimentary rocks are overlain unconformably by Lower Triassic metaconglomerates, metavolcanics and Upper Triassic to Cretaceous recry…
Single zircon U–Pb ages and geochemistry of granitoid gneisses from SW Poland: evidence for an Avalonian affinity of the Brunian microcontinent
2010
AbstractSeven granitoid gneisses from the contact zone between the eastern margin of the Variscan belt and the Brunian microcontinent in SW Poland have been dated by ion-microprobe and207Pb/206Pb single zircon evaporation methods. The zircons define two age groups for the gneiss protoliths: (1) late Neoproterozoicc.576–560 Ma and (2) early Palaeozoicc.488–503 Ma granites. The granitoid gneisses belonging to the basement of the Brunian microcontinent contain abundant Mesoproterozoic to latest Palaeoproterozoic inherited material in the range of 1200–1750 Ma. The gneisses of the Variscan crustal domain lack Mesoproterozoic inherited zircon cores. Trace element geochemistry of Proterozoic gnei…
Trilobites from the Red Fauna (latest Emsian, Devonian) of Hamar Laghdad, Morocco and their biodiversity
2018
36 pages; International audience; Trilobites are widespread in Early Devonian deposits of north Gondwana; some of the most emblematic ones were collected from the famous latest Emsian (Early Devonian) mudmound locality Hamar Laghdad in south-eastern Morocco. This locality is famous for its trilobites, especially for the conspicuous red-coloured remains of phacopid trilobites with often greenish eyes. Here, we present a taxonomic revision of the previously described trilobites from the so-called Red Fauna of Hamar Laghdad. We introduce the new taxa Harpes hamarlaghdadensis n. sp. and Morocops davidbrutoni n. sp. Phacopids dominate the trilobite assemblage from the Red Cliff at Hamar Laghdad …
Pre-Hirnantian (latest Ordovician) benthic community assemblages: controls and replacements in a siliciclastic-dominated platform of the eastern Anti…
2007
17 pages; International audience; Lower-middle Ashgill sedimentary strata from the Mediterranean region have recorded a key episode of temperate-to-cold water, carbonate productivity predating the onset of the Hirnantian glaciation. The latitudinal position of the Moroccan margin of North Gondwana during Ashgill should have been adequate for the recorded development of carbonate factories. However, carbonate productivity was neither homogeneous nor laterally persistent, as documented in the eastern Anti-Atlas. Whereas in the Erfoud area, the bryozoan-dominated limestones of the Ashgill Khabt-el-Hajar Formation indicate the intensive activity of carbonate factories, these were dramatically r…
The metamorphic rocks of the Nunatak Viedma in the Southern Patagonian Andes: Provenance sources and implications for the early Mesozoic Patagonia-An…
2019
The Nunatak Viedma within the Southern Patagonian Icefield has been considered as a volcanic center based on its geomorphologic features, despite the fact that field explorations by Eric Shipton determined its metamorphic nature 70 years ago. We carried out fieldwork to characterize this isolated outcrop and performed the first U-Pb dating in detrital zircons from the basement rocks located inside the Southern Patagonian Icefield. We recognized very-low grade metamorphic rocks, corresponding principally to metapelites and metapsammites, and scarce metabasites. Detrital zircons in three metapsammitic samples (composite group of 240 grains) yielded prominent age population peaks at ∼1090, ∼96…
Detrital-zircon geochronology and provenance of the El Oro Metamorphic Complex, Ecuador: Geodynamic implications for the evolution of the western Gon…
2019
Abstract The El Oro Metamorphic Complex (EOMC) in SW Ecuador has been the subject of debate for several decades. While previous studies have focused on the metamorphic and deformation history of the complex to determine its geodynamic evolution, the pre-metamorphic history and its association to units in the north-central Andes remains poorly understood. Here we present a U-Pb detrital zircon provenance study to provide insights into the depositional history and the geodynamic setting of the EOMC. Our results imply that the southern portion of the EOMC (the Tahuin division) is composed of an older Palaeozoic (pre-Famatinian) sequence in the south (El Tigre unit; c. 525-510 Ma), and younger …
The migration path of Gondwanian dinosaurs toward Adria: New insights from the Cretaceous of NW Sicily (Italy)
2021
Abstract The increasing dinosaur record from Italy questioned classic palaeogeographic scenarios for the Central Mediterranean area and suggest the proximity of landmass areas and a geographical connection between Gondwana and Laurasia during Cretaceous times. Besides several track-sites and exceptionally-preserved specimens (e.g. Scipionyx samniticus), the Italian dinosaur record also consists of isolated bones, among which the bone fragment of a theropod discovered in north-western Sicily. The bone occurs in a shallow-water carbonate succession (i.e. Pizzo Muletta, Palermo Mountains) pertaining to the Panormide Carbonate Platform (PCP). The bone was previously ascribed to the Cenomanian, …
First Perigondwanan record of actinolepids (Vertebrata: Placodermi: Arthrodira) from the Lochkovian (Early Devonian) of Spain and its palaeobiogeogra…
2011
Different palaeogeographic models have been proposed for the position of Laurussia ( including Baltica) and Gondwana-derived microcontinents ( including Ibero-Armorica) during Ordovician to Late Carboniferous times. Principal differences concern the presence and duration of a large ocean, the Rheic Ocean, acting as a faunal barrier between these areas. The timing of the collision of Laurussia with Gondwana and/or Gondwana-derived terranes continues to be debated. Here we present new faunal data revealing close biogeographical relations between Ibero-Armorica ("Perigondwanan" or Gondwanan derivate terranes) and Podolia (SE margin of Baltica, in Laurussia). The placoderm assemblage found in t…