Recognizing detachment-mode seafloor spreading in the deep geological past

Large-offset oceanic detachment faults are a characteristic of slow-and ultraslow-spreading ridges, leading to the formation of oceanic core complexes (OCCs) that expose upper mantle and lower crustal rocks on the seafloor. The lithospheric extension accommodated by these structures is now recognized as a fundamentally distinct ''detachment-mode'' of seafloor spreading compared to classical magmatic accretion. Here we demonstrate a paleomagnetic methodology that allows unequivocal recognition of detachment-mode seafloor spreading in ancient ophiolites and apply this to a potential Jurassic detachment fault system in the Mirdita ophiolite (Albania). We show that footwall and hanging wall blocks either side of an inferred detachment have significantly different magnetizations that can only be explained by relative rotation during seafloor spreading. The style of rotation is shown to be identical to rolling hinge footwall rotation documented recently in OCCs in the Atlantic, confirming that detachment-mode spreading operated at least as far back as the Jurassic. I t is now known that large-offset detachment faulting plays a fundamental role in accommodating plate separation at slow-and ultraslow-spreading mid-ocean ridges We illustrate this approach using an example from the northern Mirdita ophiolite of Albania. This is a slice of Jurassic (c. 165 Ma 15 ) oceanic lithosphere, representing a remnant of the eastern branch of the slow-spreading Tethys Ocean that was obducted during Europe-Adria convergence 17 . The contact between mantle and upper crustal rocks in the region of the Puka Massif is locally marked by mylonitic shear zones in amphibole-bearing peridotite

Palinspastic Reconstruction Versus Cross-Section Balancing: How Complete Is the Central Taurides Fold-Thrust Belt (Turkey)?

In many fold-thrust belts, cross section-derived shortening estimates are significantly lower than predicted based on plate convergence. This has led to controversial hypotheses that shortening may be largely underestimated due to wholesale underthrusting (convergence without shortening) below far-traveled continent or ocean-derived nappes. The Late Cretaceous-Eocene Taurides fold-thrust belt (southern Turkey) may contain a highly incomplete shortening record of convergence likely caused by wholesale underthrusting. To estimate this underthrusting, we calculate convergence across the belt using a map-view palinspastic reconstruction that takes into account major rotations of tectonic units during their accretion. We use paleomagnetic and fault kinematic analysis, timing of accretion, and Africa-Eurasia convergence to constrain our reconstruction. Our paleomagnetic results confirm an ~40 degrees clockwise vertical axis rotation of the Geyikda nappe that forms the core of the belt, which we interpret is accommodated by a lateral gradient in underthrusting on faults structurally above and below the Geyikda nappe. We reconstruct ~400-450km of convergence across the Taurides during their accretion. We compare this predicted convergence to shortening calculated from balanced cross sections, in which we reconstruct a minimum of 154-km shortening: 57km within far-traveled nappes, 70-km thrusting of far-traveled nappes over the Geyikda nappe, and 27-km shortening within the Geyikda nappe. Shortening in the Taurides created a significant nappe stack, but the majority of convergence was accommodated by wholesale underthrusting with barely a trace at the surface, including ~160km of convergence by rotation of the belt, and 90-130km related to missing Africa-Eurasia convergence

Orogenic architecture of the Mediterranean region and kinematic reconstruction of its tectonic evolution since the Triassic

The basins and orogens of the Mediterranean region ultimately result from the opening of oceans during the early break-up of Pangea since the Triassic, and their subsequent destruction by subduction accommodating convergence between the African and Eurasian Plates since the Jurassic. The region has been the cradle for the development of geodynamic concepts that link crustal evolution to continental break-up, oceanic and continental subduction, and mantle dynamics in general. The development of such concepts requires a first-order understanding of the kinematic evolution of the region for which a multitude of reconstructions have previously been proposed. In this paper, we use advances made in kinematic restoration software in the last decade with a systematic reconstruction protocol for developing a more quantitative restoration of the Mediterranean region for the last 240 million years. This restoration is constructed for the first time with the GPlates plate reconstruction software and uses a systematic reconstruction protocol that limits input data to marine magnetic anomaly reconstructions of ocean basins, structural geological constraints quantifying timing, direction, and magnitude of tectonic motion, and tests and iterations against paleomagnetic data. This approach leads to a reconstruction that is reproducible, and updatable with future constraints. We first review constraints on the opening history of the Atlantic (and Red Sea) oceans and the Bay of Biscay. We then provide a comprehensive overview of the architecture of the Mediterranean orogens, from the Pyrenees and Betic-Rif orogen in the west to the Caucasus in the east and identify structural geological constraints on tectonic motions. We subsequently analyze a newly constructed database of some 2300 published paleomagnetic sites from the Mediterranean region and test the reconstruction against these constraints. We provide the reconstruction in the form of 12 maps being snapshots from 240 to 0 Ma, outline the main features in each time-slice, and identify differences from previous reconstructions, which are discussed in the final section

Музейна справа сучасної Франції на прикладі музею Бранлі

The article sums up the results of the first year of operation du quai Braniy. It also sheds light on multicultural image of modern France

Formation of the Xigaze Metamorphic Sole under Tibetan continental lithosphere reveals generic characteristics of subduction initiation

Metamorphic soles found under allochthonous oceanic lithosphere, or ophiolites, are interpreted as derived from lower plate oceanic crust material accreted to upper plate mantle during intraoceanic subduction initiation. Their metamorphic evolution is inferred to reflect the thermal structure at the site of subduction nucleation, with granulite-bearing soles linked to initiation at hot spreading centers. Here we present garnet Lu-Hf geochronology for the granulite-bearing sole of the Xigaze ophiolite in South Tibet, whose oceanic crust formed ∼130 Ma through continental forearc extension. Our study shows that sole metamorphism was ongoing by 144 Ma, implying that north-directed subduction began at least 14 million years before oceanic forearc spreading. The upper plate at the time of subduction initiation was thus continental, not oceanic. Our results demonstrate that metamorphic characteristics of soles are independent of the specific tectonic setting at the subduction nucleation site and rather provide generic constraints on the subduction initiation process

ARCFIRE : experimentation with the recursive InterNetwork Architecture

European funded research into the Recursive Inter-Network Architecture (RINA) started with IRATI, which developed an initial prototype implementation for OS/Linux. IRATI was quickly succeeded by the PRISTINE project, which developed different policies, each tailored to specific use cases. Both projects were development-driven, where most experimentation was limited to unit testing and smaller scale integration testing. In order to assess the viability of RINA as an alternative to current network technologies, larger scale experimental deployments are needed. The opportunity arose for a project that shifted focus from development towards experimentation, leveraging Europe's investment in Future Internet Research and Experimentation (FIRE+) infrastructures. The ARCFIRE project took this next step, developing a user-friendly framework for automating RINA experiments. This paper reports and discusses the implications of the experimental results achieved by the ARCFIRE project, using open source RINA implementations deployed on FIRE+ Testbeds. Experiments analyze the properties of RINA relevant to fast network recovery, network renumbering, Quality of Service, distributed mobility management, and network management. Results highlight RINA properties that can greatly simplify the deployment and management of real-world networks; hence, the next steps should be focused on addressing very specific use cases with complete network RINA-based networking solutions that can be transferred to the market

Formation of the Xigaze Metamorphic Sole under Tibetan continental lithosphere reveals generic characteristics of subduction initiation

Metamorphic soles found under allochthonous oceanic lithosphere, or ophiolites, are interpreted as derived from lower plate oceanic crust material accreted to upper plate mantle during intraoceanic subduction initiation. Their metamorphic evolution is inferred to reflect the thermal structure at the site of subduction nucleation, with granulite-bearing soles linked to initiation at hot spreading centers. Here we present garnet Lu-Hf geochronology for the granulite-bearing sole of the Xigaze ophiolite in South Tibet, whose oceanic crust formed ∼130 Ma through continental forearc extension. Our study shows that sole metamorphism was ongoing by 144 Ma, implying that north-directed subduction began at least 14 million years before oceanic forearc spreading. The upper plate at the time of subduction initiation was thus continental, not oceanic. Our results demonstrate that metamorphic characteristics of soles are independent of the specific tectonic setting at the subduction nucleation site and rather provide generic constraints on the subduction initiation process

Kinematics of Late Cretaceous subduction initiation in the Neo-Tethys Ocean reconstructed from ophiolites of Turkey, Cyprus, and Syria

Formation of new subduction zones represents one of the cornerstones of plate tectonics, yet both the kinematics and geodynamics governing this process remain enigmatic. A major subduction initiation event occurred in the Late Cretaceous, within the Neo-Tethys Ocean between Gondwana and Eurasia. Supra-subduction zone ophiolites (i.e., emerged fragments of ancient oceanic lithosphere formed at supra-subduction spreading centers) were generated during this subduction event, and are today distributed in the eastern Mediterranean region along three ~E-W trending ophiolitic belts. Several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra-Neo-Tethyan subduction zone.Here we present new paleospreading directions from six Upper Cretaceous ophiolites of Turkey, Cyprus, and Syria, calculated using new and published paleomagnetic data from sheeted dyke complexes. Our results show that ~NNE-SSW subduction zones were formed within the Neo-Tethys during Late Cretaceous, which we propose were part of a major step-shaped subduction system composed of ~NNE-SSW and ~WNW-ESE segments. We infer that this subduction system developed within old lithosphere, along fracture zones and perpendicular weakness zones, since any Neo-Tethyan spreading ridge formed upon Triassic-Jurassic Gondwana fragmentation would have subducted to the north at the Pontides subduction zone by the Late Cretaceous.Our new results provide and alternative kinematic model of Cretaceous Neo-Tethyan subduction initiation, and calls for future research on the mechanisms of subduction inception within old (and cold) lithosphere, and the formation of metamorphic soles below supra-subduction zone ophiolites in the absence of active spreading ridges.<br/

Mutual Guarantee Institutions (MGIs) and small business credit during the crisis

The recent economic and financial crisis has drawn attention to how mutual guarantee institutions (MGIs) facilitate small and medium enterprises in accessing bank financing. The aim of this paper is twofold. First, we describe the structural features of the Italian market for mutual guarantees and its significance for small business credit. To this end, we use extensive databases (the Central Credit Register and the Central Balance Sheet Register) as well as specific surveys, which allow us to fill information gaps about this industry and to quantify regional diversity. Second, we investigate whether MGIs’ support to small firms continued to be effective in 2008-09, when credit constraints to Italian firms peaked. We find that MGIs played a role in avoiding a break-up in credit flows to affiliated firms, which also benefited from a lower cost of credit. However, this came at the cost of a deterioration in credit quality, which was more intense for customers with guarantees from MGIs.microfinance, peer monitoring, small business finance

The onset of fabric development in deep marine sediments

publisher: Elsevier articletitle: The onset of fabric development in deep marine sediments journaltitle: Earth and Planetary Science Letters articlelink: http://dx.doi.org/10.1016/j.epsl.2017.06.018 content_type: article copyright: © 2017 Elsevier B.V. All rights reserved