Subduction of lithospheric plates at convergent margins leads to transport of materials once close to or at the surface of Earth to great depths. Some of them later return to the surface by magmatism or degassing, whereas others end up being stored in the mantle for long periods of time. The fate of carbon-bearing minerals in subduction is of particular interest because they can arbitrate the long-term availability of CO2 at the surface. However, there are major gaps in the understanding of even the most fundamental processes that modulate carbon pathways at mantle depths. We use geodynamic models to understand carbonate pathways upon subduction in the form of large carbonate platforms, which were common in the Tethys realm of Europe. We conducted a series of geodynamic forward models for a 1-km-thick carbonate platform entering subduction. We show that most of the carbonate load detaches from the subducting slab and rises up diapirically through the mantle wedge and eventually mixes with the mantle lithosphere. A smaller fraction gets accreted under the forearc, whereas an even smaller fraction descends deeper into the mantle. The cold diapiric plume has a significant role in retarding silicate mantle melting above these subduction zones and promoting the formation of small-volume carbonate-rich melts and, in some cases, alkaline silica-undersaturated silicate melts. We propose that large amounts of CO2 can be stored as carbonate in the shallow uppermost lithospheric mantle.
Magmatic arcs and intracontinental extensional domains active in the geological past of the Carpathian-Pannonian region host a wealth of plutonic and volcanic suites, which have been studied in various details over the past decades. Today, the primary geochemical information delivered by different studies-a valuable resource for new regional petrogenetic and tectonic interpretations-is still scattered in well over one hundred papers that are more or less accessible to the interested researchers. In order to facilitate the access of the geoscience community to this information, here we present an up-to-date compilation of geochronologic, geochemical and isotopic data characterizing the region.The area covered in this compilation is shown in Figure 1. The aggregate Carpathian Mountains start in the west from near Vienna (Austria) and form a broad east-west arc (the West and East Carpathians), followed by a sharp bend in the Vrancea region; the east-west oriented South Carpathians complete geographically this segment of the long scar marking the closure of various Alpine and Neotethyan basins, which extends from the Alps in the west, to the Himalayas in its far east. The Carpathians have a complex geologic history, but the present-day mountain ranges and basins formed as a result of Cenozoic compression and crust consumption by subduction and collision (Schmid et al., 2020) of a series of back arc basins, whereas the main Tethyan Ocean was located further to the south. A prominent fold and thrust belt of Miocene and younger ages marks the suture between the Eastern European craton to the east and mobile Europe, represented by several peri-Gondwanan terranes (Balintoni et al., 2014). To the interior of this arc lies the Pannonian-Transylvanian basin, a continental extensional domain most recently related to the rollback of the slab since the early Miocene (Royden & Burchfiel, 1989). A smaller mountain range, the Apuseni Mountains, occupies a less extended area within the eastern part of the Pannonian basin.Magmatic products of this region span an 800 Ma range, from a Neoproterozoic arc preserved in the basement of the South Carpathians (Balintoni et al., 2014) to the youngest volcanoes found in the Carpathian bend region; here, at least one volcanic center, Ciomadul, is documented to be active (e.g., Harangi et al., 2015;Popa et al., 2012). We did not compile data on igneous rocks making up various basement terrains, which are Neoproterozoic to late Paleozoic in age; many of those have been metamorphosed during the Paleozoic (Medaris et al., 2003). We did, however, include the following igneous provinces composed of unmetamorphosed volcanic and/or intrusive rocks of the region; (a) a Jurassic island arc province found in the South Apuseni Mts. and buried under younger rocks of the Transylvanian basin (Gallhofer et al., 2017),
We present new sedimentological, petrographical, palaeontological and detrital zircon U-Pb data on late Oligocene-early Miocene sedimentary rocks of the thinskinned thrust belt of East Carpathians. These data were acquired to reconstruct the sedimentary routing system for two compositionally different turbidite fans made of the regionally extensive Kliwa and Fusaru formations. On the eastern margin of the Moldavides foreland basin, large low-gradient river systems draining the East European Platform provided well-sorted quartz-rich sand forming deltas on wide shallow shelves and thick Kliwa submarine fans. Due to the westward subduction of a thinned continental plate, the western basin margin was characterized by short, steep-gradient routing systems where sediment transport to deep water was mainly through hyperpycnal flows. The Getic and Bucovinian nappes of the East Carpathians and the exhumed Cretaceous-Early Palaeogene orogenic wedge fed Fusaru fans with poorly sorted lithic sand. The Fusaru fans trend northwards in the foredeep basin having an elongate depocentre, interfingering and then overlapping on the distal part of the Kliwa depositional system due to the eastward advance of the Carpathian fold-and-thrust belt. A smaller sediment input is supplied by southern continental areas (i.e. MoesianPlatform, North Dobrogea and potentially the Balkans). In general, the sandstone interfingering between distinct basin floor fan systems is less well documented because the facies would be similar and there are not many systems that have a distinct sediment provenance like Kliwa and Fusaru systems. This case study improves the understanding of regional palaeogeography and sedimentary routing systems and provides observations relevant here or elsewhere on the interfingering turbidite fan systems.
Magnesium (Mg) alloys present a promising alternative to aluminum (Al) alloys in lightweight applications. However, relative to Al alloys, Mg alloys have poor castability. Castability is influenced significantly by the dendrite coherency point (DCP), which represents the temperature, time, and solid fraction at which an interlocking solid network forms during solidification. An increase in the solid fraction at coherency may improve the castability of the alloy and reduce casting defects such as porosity, hot tears and misruns. A successful method for increasing the solid fraction at the DCP in Al alloys involves the use of grain refiners such as titanium (Ti). However, the influence of Ti refiners on the DCP in Mg alloys has not been thoroughly investigated. The objective of this research was to study the effect of Al-5Ti-1B refiner on the dendrite growth mechanism, DCP and porosity of AZ91E magnesium alloy. This thesis is a pioneering effort in relating the grain refinement effect of Ti on the DCP, coherency solid fraction, and porosity development during the solidification of Mg alloy, AZ91E. It represents an important step in improving the castability of Mg alloys. Varying levels of Al-5Ti1B grain refiner (0.005, 0.05, 0.1, 0.2, and 0.3 wt.% Ti) were added to AZ91E. The effect of Al-5Ti-1B grain refiner on the microstructure and dendrite growth mechanism of AZ91E was investigated. Quench experiments were performed to observe transformations in the dendritic morphology that resulted from the refiner additions. The growth rate and DCP were determined using the rheological method. The changes in porosity levels were determined for the grain refiner additions.
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