Age of basement rocks from the Maurice Ewing Bank and the Falkland/Malvinas Plateau

The Maurice Ewing Bank is located east of the Falkland/Malvinas Islands and is one of the most intriguing regions of southern Gondwana. The interaction of several microplates with major cratonic areas resulted in complex displacements between Paleozoic and Cretaceous times. Here, we present combined U-Pb and Lu-Hf zircon isotopic analyses of the Maurice Ewing Bank basement to constrain the age and tectonic setting to aid in paleogeographic reconstruction. The high-grade paragneisses in the bank present dominant Late Mesoproterozoic detrital zircon age distributions with populations at 1032 ± 12 Ma, 1068 ± 16 Ma and 1233 ± 8 Ma and juvenile signature (positive εHf[t] values). The gneisses are cutting by anatectic pink granite crystallized at 1006 ± 13 Ma which formed after syn-collisional high-grade metamorphism and shows juvenile and some crustal component (εHf[t] = +1.6 to −3). The Maurice Ewing Bank basement rocks have same Stenian age and dominant juvenile signature as the arc-related basement rocks from the Falkland/Malvinas Islands and are probably part of the same continental plateau of the South America continent. This new finding enables future reconstructions in paleogeographic models where the basement of the Falkland/Malvinas Islands and the Maurice Ewing Bank formed a single block during the Mesoproterozoic and were partly separated by crustal stretching during the opening of the Atlantic Ocean in the Late Jurassic-Cretaceous. The block played a major role in the deformation of the Cape Fold Belt from the Late Paleozoic through the Mesozoic.Fil: Chemale, Farid. Universidade do Vale do Rio dos Sinos. Programa de Pós-Graduação em Geologia; BrasilFil: Ramos, Victor Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Girelli, Tiago J.. Universidade do Vale do Rio dos Sinos. Programa de Pós-Graduação em Geologia; BrasilFil: Vargas, Mateus. Universidade do Vale do Rio dos Sinos. Programa de Pós-Graduação em Geologia; Brasi

Provenance and paleogeography of the Southern Paran? Basin : geochemistry and U\\Pb zircon geochronology of the Carboniferous-Permian transition.

The Carboniferous-Permian transition of the intracratonic Paran? Basin (S Brazil) includes important evidence of the climate change, tectonics, and paleogeographic configuration of SW Gondwana. During this period, the Late Paleozoic Ice Age (LPIA) was in its final phase in the Paran? Basin, producing a temperate-tropical climate through the transition to the Permian. UPb laser ablation ICP-MS detrital zircon dates and whole-rock geochemistry of rocks from the upper Itarar? Group (Carboniferous) and the lowermost Rio Bonito Formation (Early Permian) in the southern Paran? Basin are determined to characterize the sedimentary-dispersal patterns of the source area and glacial paleoflow. Geochemistry proxies suggest that the studied units experienced different degrees of weathering, with the Itarar? Group's units forming in an arid environment. The overlying Rio Bonito Formation's units were deposited under hotter and more humid climate conditions. The Late Carboniferous to Early Permian units showed similar zircon-age distribution patterns, with a Neoproterozoic main peak from the Uruguayan Sul-Riograndese Shield. A lack of Mesoproterozoic sources in the studied samples indicates that this area of the Paran? Basin probably did not receive sediments from the African side during the Late Carboniferous as previously described. This result suggests a more complex system in which ice caps and small ice sheets dominated the glacial environment during the Late Carboniferous in this segment of SW Gondwana

Granulite accretion to Rio de la Plata Craton, based on zircon U-Pb-Hf isotopes : tectonic implications for Columbia Supercontinent reconstruction.

The paleogeographic reconstruction of the Rio de la Plata involved either allocthonous or autochthonous process reflecting directly the Paleoproterozoic connection of the craton to Columbia Supercontinent. Santa Maria Chico Granulite Complex is a significant fragment of Rio de la Plata intensely affected by the Brasiliano Orogeny. Zircon U-Pb-Hf isotopes by LA-ICP-MS, mineral and whole-rock chemistry and a pseudo-section are presently interpreted. U-Pb-Hf isotopes characterize two main accretionary and metamorphic events: oceanic juvenile crustal accretion (i) 2430?2290?Ma (?Hf(t)?=??3.17 to +7.00), with arc related metamorphism (830?870??C, 6.7?7.2?kbar) at ~2.3?Ga; and continental arc accretion (ii) 2240?2120?Ma (?Hf(t)?=??4 to +2.4), with continental collision metamorphism (770?790??C, 8.7?9.1?kbar) at 2.1?2.0?Ga. Alkaline granitic dikes related to crustal extension at 1.8?Ga cut the granulitic rocks after the stabilization of this crustal segment. The present data point to formation of Paleoproterozoic granulitic rocks of the Santa Maria Chico Granulite Complex and adjacent Nico P?rez and Rivera terranes in multi-stage volcanic arcs to continental collision environment over 370?Ma (2430 to 2060?Ma). These terranes were amalgamated in the Paleoproterozoic to the core of the Rio de la Plata Craton as part of Columbia Supercontinent and intensely reworked during the amalgamation of Western Gondwana in the Neoproterozoic

Late Cenozoic evolution of the Nicobar Fan - Insights from U-Pb-Hf in Zircon

International audienceLate Cenozoic deep-sea deposits of the Bengal – Nicobar Fan recorded the events of Himalayan accretion during the India – Asia collision. IODP Expedition 362 – The Sumatra Subduction Zone – recovered a sedimentary section at the Nicobar Fan that comprises Early Miocene to Holocene strata. This work aims to identified potential sources and the evolution of the fluvial system that fed into the Nicobar Fan during that interval. For this, we analyzed zircon U-Pb-Hf in seven samples from sandy and silty turbidite deposits of U1480 and U1481 Sites. U-Pb zircon ages range from 22 to 3358 Ma and εHf −33.7 to +15, originated from Central and Eastern Himalayan, Lhasa Block, peninsular India and Indo Burma Ranges, the Ganges – Brahmaputra rivers drained areas. Our data suggest a significant reorganization of source areas since the Late Miocene. Rapid uplift of the Himalayan syntaxis in the Late Miocene to Pleistocene exposed distinct source rocks, altering the provenance signature and enhancing sediment delivery towards the sink. This is evidenced by gradually switched in first cycle zircons in the Nicobar Fan from the Lhasa Block and Gangdese Batholith to the Bomi-Chayu and Lohit Batholiths. Sediment provenance shifted since the Pliocene, with an increase in Ganges-derived Archean peninsular India, Cambro-Ordovician granites and Greater Himalaya orthogneisses at the Nicobar Fan. We attribute this shift to the rise of the Shillong Plateau, which projected the Brahmaputra delta to the west towards the Ganges river. This rise of the Shillong Plateau and the sea level fall at the Plio-Pleistocene enabled the merge of the Brahmaputra and Ganges deltas for the first time. Our data suggest that the Nicobar Fan was majorly supplied by the Brahmaputra River during the Tortonian, with an only minor contribution from the Ganges river. Following that, an increase in sediment contribution from the Ganges River is observed

Post-glacial permian debris flow deposits and their paleoclimatic implications (Mariana Pimentel paleovalley, southern Paran? Basin).

The end of the Late Paleozoic Ice Age was followed by a global warming climate. This climate transition is characterized by, beyond other aspects, a decrease in the intensity of physical weathering, characteristic of arid conditions, and an increase in the intensity of chemical weathering. In the southern Parana ? Basin, the post-glacial onset and intense record of ?Pedra-Areia? diamictite within the Mariana Pimentel paleovalley was likely controlled by warming climate conditions and mark a period of intense rainfall and slope instability. To test this hypothesis, we have performed facies and sequence stratigraphy analysis on cores located within the Mariana Pimentel paleovalley, and U?Pb-Hf investigations to acquire sediment provenance information. Diamictite deposits were produced by debris flow processes, which transported regolith from the valley wall to the bottom, eroding and incorporating mud and peat when reaching the bottom of the valley. The local source of sediment is explained by the sedimentological characteristics of the diamictite and zircon provenance studies. These deposits are preserved within the transgressive system tract and the abundant deposition was controlled by increasing temperature and humidity, and thus the increase in chemical weathering on the walls, forming the regolith. The development of more humid and warmer climatic conditions, contrasting with the cold and dry climate of the glacial period, was an important control over diamictite deposition

The oldest record of Ediacaran macrofossils in Gondwana (~563 Ma, Itajaí Basin, Brazil)

International audienceThe Avalon biota (Ediacaran Period, 570–559 Ma) marks the first appearance of macroscopic and complex benthic communities in the fossil record. This assemblage is known from a few localities worldwide, mainly in Canada and England. Here, we report for the first time the presence of Ediacaran macrofossils in deposits of similar age from Gondwana (Itajaí Basin, southern Brazil). Our new radiometric date (~563 Ma) indicates that the Itajaí Basin can be chronocorrelated with the classic Avalonian deposits and thus represents one of the oldest records of the Ediacaran biota in Gondwana. We describe the presence of the Ediacaran genus Palaeopascichnus, as well as discs (Aspidella and Nimbia), and other problematic forms. Contrary to the deep-marine macroorganisms of the Avalon Assemblage, the Itajaí fossils are associated with abundant and exceptionally preserved three-dimensional microbial mats and microbially induced sedimentary structures (MISS) in relatively shallow settings (upper slope and distal delta front deposits). In this sense, the Itajaí biota could represent early adaptations of benthic macrobiota to the shallower and more photic environments that characterize the later White Sea Assemblage