Tectonic Evolution of the Eastern Black Sea and Caucasus : An introduction

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New P-T-t data on the metamorphic sole of the Amasia ophiolites and implications for the geodynamical process, NW of the Sevan-Akera suture zone, Lesser Caucasus (Armenia)

International audienceThe ophiolites of the Lesser Caucasus belong to the Tethyan Ophiolitic Belt. In the northwestern part of the Sevan Akera suture zone (Lesser Caucasus, Armenia) ophiolites correspond to a major obduction of oceanic crust over the South Armenian continental block. Near the locality of Amasia (NW Armenia), our mapping evidenced a series of (1) unmetamorphosed gabbroic oceanic crust, resting on (2) serpentinites and a greenschist grade tectonic mélange composed of deformed pillow-basalts, radiolarites and cherts, and (3) a basal slice of garnet amphibolites bearing similar compositional features as the ophiolite. They are sliced by post Eocene thrusts related to the shortening of the suture after the collision of the South Armenian Block (Sosson et al., 2010). Structural observations allow us to consider these metamorphic rocks (garnet amphibolites and quartz-garnet-oligoclase-amphibole-chlorite schistes) to be the sole of the obducted ophiolite. The metamorphic rocks allow the evaluation of pressure-temperature-time conditions endured by the base of the oceanic crust during the obduction of the Armenian ophiolite series. Pressure and temperature estimations were obtained by calculating equilibrium conditions between different mineral phases which coexist in the sample coupled with whole rock geochemistry using the software PERPLEX. The P-T data show a counterclockwise path with (1) a HT-LP peak of P = 6-7 kbar and T > 630_C, followed by MP-MT peak at P = 8-10 kbar and T = 600_C. In order to further constrain the evolution of the amphibolites and build a P-T-t path using 40Ar/39Ar dating on amphiboles and white micas (phengite). The ages obtained on both HT and MT peaks are similar within error (90.8 Ma ± 3.0 (2σ), and 90.8 Ma ± 1.2 (2 σ), respectively), which suggests a very rapid cooling of the metamorphic sole during its stacking in the subduction zone. The counterclockwise path determined confirms the observations made below the Oman ophiolite by Goffé et al. (1988). This path is also in agreement with a scaling process of oceanic crust during the obduction. In this scenario slices of oceanic crust would have been dragged under the obduction front below a relatively hot oceanic crust. Afterwards, these slices would then have been amphibolitized along a HT-MP geothermal gradient. Rapidly, a thickening of the system at c. 91-90 Ma, and underthrusting of amphibolites would have caused the conditions to change to MP-MT. This infers that the South Armenian Block enters the subduction zone at this date. A recent study has shown metamorphic rocks in the same structural setting were affected by a HP metamorphism in the Blue Schist facies (Rolland et al., 2009). The age of this blue schist of Stepanavan, Armenia is slightly older (95-91 Ma) (Galoyan et al., 2009) than the amphibolites of Amasia (91-90 Ma). This assumes the occurrence of an active subduction just before the development of the HT-MP metamorphism of Amasia. References: Galoyan, G., Rolland, Y., Sosson, M., Corsini, M., Billo, S., Verati, C., Melkonyan, R., 2009. Geology, geochemistry and 40Ar/39Ar dating of the Sevan ophiolites (Lesser Caucasus, Armenia): Evidence for Jurassic Back-arc opening and hot spot event between the South Armenian Block and Eurasia. Journal of Asian Earth Science, 34, 135-153. Goffé, B., Michard, A., Kienast, J.R., Le Mer, O., 1988. A case of obduction-related high-pressure, lowtemperature metamorphism in upper crustal nappes, Arabian continental margin, Oman: P-T paths and kinematic interpretation. Tectonophysics, 151, 363-386. Rolland, Y., Billo, S., Corsini, M., Sosson, M., Galoyan, G., 2009. Blueschists of the Amassia-Stepanavan Suture Zone (Armenia): linking Tethys subduction history from E-Turkey toW-Iran. International Journal of Earth Science, 98, 533-550. Sosson, M., Rolland, Y., Müller, C., Danelian, T., Melkonyan, R., Kekelia, S., Adamia, S., Badazadeh, V., Kangarli, T., Avagyan, A., Galoyan, G., Mosar, J., 2010. Subduction, obduction and collision in the Lesser Caucasus (Armenia, Azernaijan, Georgia), new insights. Geological Society, London, Special Publications, 340, 329-352

PALAEONTOLOGICAL (RADIOLARIAN) LATE JURASSIC AGE CONSTRAINT FOR THE STEPANAVAN OPHIOLITE (LESSER CAUCASUS, ARMENIA)

Η χρονολόγηση με βάση μικροπαλαιοντολογικά δεδομένα, των ιζηματογενών καλυμμάτων των οφιολίθων είναι ιδιαίτερης σημασίας για την κατανόηση της παλαιογεωγραφικής και γεωδυναμικής εξέλιξης των περιοχών της Τηθύος. Η οφιολιθική ακολουθία του Stepanavan στη Βόρεια Αρμενία συνίσταται από περιδοτίτες, γάββρους, πλαγιογρανίτες και λάβες και ιζηματογενή καλύματα ραδιολαριτών. Θεωρείται ως η βόρεια επέκταση της οφιολιθικής ζώνης Sevan Akera και η ανατολική επέκταση της ζώνης Izmir-Ankara. Αντιπροσωπεύει κατάλοιπο μιας βραδέως εκτεινόμενης μεσο-ωκεάνιας ράχης, που ήταν ενεργή μεταξύ της Ευρασίας και του νότιου Αρμενικού τεμάχους γκοντβανικής προέλευσης. Τα ραδιολάρια που εξετάστηκαν από τους ραδιολαρίτες στην περιοχή της οφιολιθικής ακολουθίας του Stepanavan πιστοποιούν για πρώτη φορά ηλικία Ανώτερου Ιουρασικού (ανώτερο Κιμμερίδιο έως κατώτερο Τιθώνιο) προσδίδοντας ηλικία για αυτό το τμήμα του ωκεάνιου φλοιού της Τηθύος που παρατηρείται στο Lesser Caucasus.Micropalaeontological age evidence for the sedimentary cover of ophiolites is important to understand the palaeogeographic and geodynamic evolution of Tethyan realms. The Stepanavan ophiolitic suite of Northern Armenia consists of peridotites, gabbros, plagiogranite and lavas with a radiolarite sedimentary cover. It is regarded as the northern extension of the Sevan Akera ophiolitic zone and may be considered as the eastern extension of the Izmir-Ankara suture zone. It represents the relics of a slow-spreading mid oceanic ridge that was active between Eurasia and the South-Armenian Block of Gondwanian origin. Radiolaria extracted from radiolarites of the Stepanavan ophiolite provide for the first time a Late Jurassic (late Kimmeridgian to early Tithonian) age constraint for this part of Tethyan oceanic crust preserved in Lesser Caucasus

La formation tout au long de la vie des agents des bibliothèques universitaires. Enjeux et perspectives

Mémoire de fin d\u27étude du diplôme de conservateur, promotion 28, portant sur la formation des agents des bibliothèques universitaires

Cenozoic-Recent tectonics and uplift in the Greater Caucasus: a perspective from Azerbaijan

The Greater Caucasus is Europe's highest mountain belt and results from the inversion of the Greater Caucasus back-arc-type basin due to the collision of Arabia and Eurasia. The orogenic processes that led to the present mountain chain started in the Early Cenozoic, accelerated during the Plio-Pleistocene, and are still active as shown from present GPS studies and earthquake distribution. The Greater Caucasus is a doubly verging fold-and-thrust belt, with a pro- and a retro wedge actively propagating into the foreland sedimentary basin of the Kura to the south and the Terek to the north, respectively. Based on tectonic geomorphology – active and abandoned thrust fronts – the mountain range can be subdivided into several zones with different uplift amounts and rates with very heterogeneous strain partitioning. The central part of the mountain range – defined by the Main Caucasus Thrust to the south and backthrusts to the north – forms a triangular-shape zone showing the highest uplift and fastest rates, and is due to thrusting over a steep tectonic ramp system at depth. The meridional orogenic in front of the Greater Caucasus in Azerbaijan lies at the foothills of the Lesser Caucasus, to the south of the Kura foreland basin

Natural resources, child mortality and governance quality in African countries

This paper contributes to the literature by investigating the effect of natural resources on under-five mortality in a sample of 50 African countries over the period 1996 to 2018. We also examine the extent to which governance shapes the relationship between natural resources and under-five mortality. Our results show that natural resources have increased under-five mortality. Resource rents also have detrimental effects on child mortality by age, gender, and the three major causes of infant mortality from infectious diseases. However, an extended analysis of different types of natural resources suggests that point resources (such as oil, natural gas and mineral rents) increase under-five mortality, in contrast to the diffuse resources (such as forest rent). We also find that governance mitigates the positive effect of natural resources on child mortality. Corresponding governance policy thresholds that should be attained in order to reverse the positive effects of natural resources on child mortality are provided. We thus suggest an increase in the funds allocated to the health sector from resource rents and encourage efforts to improve governance standards in sampled countries

Offshore Oligo-Miocene volcanic fields within the Corsica-Liguria Basin: Magmatic diversity and slab evolution in the western Mediterranean Sea

International audienceThe European and Corsica-Sardinia margins of the Ligurian Sea (western Mediterranean) have been affected by a geochemically diverse igneous activity, offshore and onshore, since the Eocene. This magmatism occurred in a global subduction-related framework. On the European side, the oldest Tertiary magmatism dated at ca. 35 Ma was mainly calc-alkaline. It included the emplacement of plutonic bodies of adakitic affinity, such as the quartz microdiorite laccolith locally referred to as "esterellite". Younger magmatic events on-land within the whole Ligurian domain were mostly medium-K or K-rich calc-alkaline. Miocene volcanic activity was important in Sardinia, where andesites and ignimbrites were erupted during several magmatic cycles. In Corsica, it was minor although it emplaced lamprophyres near Sisco at 15 Ma. Dredging and diving cruises conducted in the Ligurian Sea during the last thirty years allowed us to collect a number of submarine samples. We discuss here their geochemistry (major and trace elements) and their whole-rock K-Ar ages and mineral 40Ar-39Ar plateau ages. Around 15 Ma, minor amounts of adakitic lavas were emplaced off southwestern Corsica, in the deepest part of the Liguria-Corsica Basin. They rested over the thinnest southwestern Corsica Hercynian continental crust. Closer to the coast, contemporaneous calc-alkaline rocks erupted on a less thinned crust. The adakitic events could be indicative of either the final stages of active subduction, or alternatively of a slab tearing linked to the southeastern retreat and steepening of the slab. The latter event could be connected with the end of the Corsica-Sardinia block drifting and its correlative eastern collision. Younger volcanic effusions, dated at 14-6 Ma, occurred mostly northwest and north of Corsica. K-rich calc-alkaline basalts, shoshonites and K-rich trachytes were emplaced during this period, and alkali basalts erupted as early as 12 Ma in Sardinia. In the Toulon area, alkali basalts dated at 7-6 Ma represent the last onshore activity just before the Messinian crisis, and the Pliocene alkali basaltic outpouring in Sardinia. We propose to link these latter volcanic events to the development of a slab window in a post-collisional tectonic framework

Effects of political institutions on the external debt-economic growth nexus in Africa

The main contribution of this study is the determination of an endogenous threshold of institutional quality, beyond which external debt would affect economic growth differently. The focus is on 14 countries of the African Franc zone over the period 1985-2015. Based on the panel Smooth Threshold Regression model, the results reveal that the relationship between external debt and economic growth is based on institutional quality. It is found that the level of indebtedness at which the effect of external debt on economic growth becomes negative is higher in countries with lower levels of corruption and high levels of democracy. This means that poor institutional quality prevents a country from taking full advantage of its credit opportunities. Thus, the more countries become democratic, the more debt helps finance economic growth. These results are robust to sensitivity analysis and Generalized Method of Moments estimation