ALBERT

Description: New petrological and geochronological data are presemted on high-grade ortho- and paragneisses from north-western Ghana, forming part of the Paleoproterozoic (2.25-2.00 Ga) West African Craton. The study area is located in the interference zone between N-S and NE-SW trending craton-scale shear zones, formed during the Eburnean orogeny (2.15-2.00 Ga). High-grade metamorphic domains are separated from low-grade greenstone belts by high-strain zones, including early thrusts, extensional detachments and late-stage strike-slip shear zones. Paragneisses sporadically preserve high-pressure, low-temperature (HP-LT) relicts, formed at the transition between the blueschist facies and the epidote-amphibolite sub-facies (10.0-14.0 kbar, 520-600°C), and represent a low (~15°C km −1 ) apparent geothermal gradient. Migmatites record metamorphic conditions at the amphibolite-granulite facies transition. They reveal a clockwise pressure-temperature-time ( P–T–t ) path characterised by melting at pressures over 10.0 kbar, followed by decompression and heating to peak temperatures of 750°C at 5.0-8.0 kbar, which fit a 30°C km −1 apparent geotherm. A regional amphibolite-facies metamorphic overprint is recorded by rocks that followed a clockwise P–T–t path, characterised by peak metamorphic conditions of 7.0-10.0 kbar at 550-680°C, which match a 20-25°C km −1 apparent geotherm. These P–T conditions were reached after prograde burial and heating for some rock units, and after decompression and heating for others. The timing of anatexis and of the amphibolite-facies metamorphic overprint is constrained by in-situ U-Pb dating of monazite crystallization at 2138±7 and 2130±7 Ma respectively. The new dataset challenges the interpretation that metamorphic breaks in the West African Craton are due to diachronous Birimian “basins” overlying a gneissic basement. It suggests that the lower crust was exhumed along reverse, normal and transcurrent shear zones and juxtaposed against shallow crustal slices during the Eburnean orogeny. The craton in NW Ghana is made of distinct fragments with contrasting tectono-metamorphic histories. The range of metamorphic conditions and the sharp lateral metamorphic gradients are inconsistent with “hot orogeny” models proposed for many Precambrian provinces. These findings shed new light on the geodynamic setting of craton assembly and stabilisation in the Paleoproterozoic. It is suggested that the metamorphic record of the West African Craton is characteristic of Paleoproterozoic plate tectonics and illustrates a transition between Archean and Phanerozoic orogens. This article is protected by copyright. All rights reserved.

Description: The LEXIS project (Large-scale EXecution for Industry & Society, H2020 GA825532) provides a platform for optimised execution of Cloud-HPC workflows, reducing computation time and increasing energy efficiency. The system will rely on advanced, distributed orchestration solutions (Atos YSTIA Suite, with Alien4Cloud and Yorc, based on TOSCA), the High-End Application Execution Middleware HEAppE, and new hardware capabilities for maximising efficiency in data processing, analysis and transfer (e.g. Burst Buffers with GPU- and FPGA-based data reprocessing). LEXIS handles computation tasks and data from three Pilots, based on representative and demanding HPC/Cloud-Computing use cases in Industry (SMEs) and Science: i) Simulations of complex turbomachinery and gearbox systems in Aeronautics, ii) Tsunami simulations and earthquake loss assessments which are time-constrained to enable immediate warnings and to support well-informed decisions, and iii) Weather and Climate simulations where massive amounts of in-situ data are assimilated to improve forecasts. A user-friendly LEXIS web portal, as a unique entry point, will provide access to data as well as workflow-handling and remote visualisation functionality. As part of its back-end, LEXIS builds an elaborate system for the handling of input, intermediate and result data. At its core, a Distributed Data Infrastructure (DDI) ensures the availability of LEXIS data at all participating HPC sites, which will be federated with a common LEXIS Authentication and Authorisation Infrastructure (with unified security model, user database and policies). The DDI leverages best of breed data-management solutions from EUDAT, such as B2SAFE (based on iRODS) and B2HANDLE. REST APIs on top of it will ensure a smooth interaction with LEXIS workflows and the orchestration layer. Last, but not least, the DDI will provide functionalities for Research Data Management following the FAIR principles (“Findable, Interoperable, Accessible, Reusable”), e.g. DOI acquisition, which helps to publish and disseminate open data products.