Tectonic significance of changes in post-subduction Pliocene-Quaternary magmatism in the south east part of the Carpathian-Pannonian Region

The south-eastern part of the Carpathian–Pannonian region records the cessation of convergence between the European platform/Moesia and the Tisza–Dacia microplate. Plio-Quaternary magmatic activity in this area, in close proximity to the ‘Vrancea zone’, shows a shift from normal calc-alkaline to much more diverse compositions (adakite-like calc-alkaline, K-alkalic, mafic Na-alkalic and ultrapotassic), suggesting a significant change in geodynamic processes at approximately 3 Ma. We review the tectonic setting, timing, petrology and geochemistry of the post-collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration. The calc-alkaline volcanism (5.3–3.9 Ma) marks the end of normal subduction-related magmatism along the post-collisional Călimani–Gurghiu–Harghita volcanic chain in front of the European convergent plate margin. At ca. 3 Ma in South Harghita magma compositions changed to adakite-like calc-alkaline and continued until recent times (< 0.03 Ma) interrupted at 1.6–1.2 Ma by generation of Na and K-alkalic magmas, signifying changes in the source and melting mechanism. We attribute the changes in magma composition in front of the Moesian platform to two main geodynamic events: (1) slab-pull and steepening with opening of a tear window (adakite-like calc-alkaline magmas) and (2) renewed contraction associated with deep mantle processes such as slab steepening during post-collisional times (Na and K-alkalic magmas). Contemporaneous post-collisional volcanism at the eastern edge of the Pannonian Basin at 2.6–1.3 Ma was dominated by Na-alkalic and ultrapotassic magmas, suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the Adriatic indentation. Similar timing, magma chamber processes and volume for K-alkalic (shoshonitic) magmas in the South Apuseni Mountains (1.6 Ma) and South Harghita area at a distance of ca. 200 km imply a regional connection with the inversion tectonics

Post-collisional Tertiary–Quaternary mafic alkalic magmatism in the Carpathian–Pannonian region: a review

Mafic alkalic volcanism was widespread in the Carpathian–Pannonian region (CPR) between 11 and 0.2 Ma. It followed the Miocene continental collision of the Alcapa and Tisia blocks with the European plate, as subduction-related calc-alkaline magmatism was waning. Several groups of mafic alkalic rocks from different regions within the CPR have been distinguished on the basis of ages and/or trace-element compositions. Their trace element and Sr–Nd–Pb isotope systematics are consistent with derivation from complex mantle-source regions, which included both depleted asthenosphere and metasomatized lithosphere. The mixing of DMM-HIMU-EMII mantle components within asthenosphere-derived magmas indicates variable contamination of the shallow asthenosphere and/or thermal boundary layer of the lithosphere by a HIMU-like component prior to and following the introduction of subduction components. Various mantle sources have been identified: Lower lithospheric mantle modified by several ancient asthenospheric enrichments (source A); Young asthenospheric plumes with OIB-like trace element signatures that are either isotopically enriched (source B) or variably depleted (source C); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII-EMI components and slightly influenced by Miocene subduction-related enrichment (source D); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII components and significantly influenced by Miocene subduction-related enrichment (source E). Melt generation was initiated either by: (i) finger-like young asthenospheric plumes rising to and heating up the base of the lithosphere (below the Alcapa block), or (ii) decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs (the Tisia block)

Geochemistry and tectonic development of Cenozoic magmatism in the Carpathian–Pannonian region

This review considers the magmatic processes in the Carpathian–Pannonian Region (CPR) from Early Miocene to Recent times, as well as the contemporaneous magmatism at its southern boundary in the Dinaride and Balkans regions. This geodynamic system was controlled by the Cretaceous to Neogene subduction and collision of Africa with Eurasia, especially by Adria that generated the Alps to the north, the Dinaride–Hellenide belt to the east and caused extrusion, collision and inversion tectonics in the CPR. This long-lived subduction system supplied the mantle lithosphere with various subduction components. The CPR contains magmatic rocks of highly diverse compositions (calc-alkaline, K-alkalic, ultrapotassic and Na-alkalic), all generated in response to complex post-collisional tectonic processes. These processes formed extensional basins in response to an interplay of compression and extension within two microplates: ALCAPA and Tisza–Dacia. Competition between the different tectonic processes at both local and regional scales caused variations in the associated magmatism, mainly as a result of extension and differences in the rheological properties and composition of the lithosphere. Extension led to disintegration of the microplates that finally developed into two basin systems: the Pannonian and Transylvanian basins. The southern border of the CPR is edged by the Adria microplate via Sava and Vardar zones that acted as regional transcurrent tectonic areas during Miocene–Recent times. Major, trace element and isotopic data of post-Early Miocene magmatic rocks from the CPR suggest that subduction components were preserved in the lithospheric mantle after the Cretaceous–Miocene subduction and were reactivated especially by extensional tectonic processes that allowed uprise of the asthenosphere. Changes in the composition of the mantle through time support geodynamic scenarios of post-collision and extension processes linked to the evolution of the main blocks and their boundary relations. Weak lithospheric blocks (i.e. ALCAPA and western Tisza) generated the Pannonian basin and the adjacent Styrian, Transdanubian and Zărand basins which show high rates of vertical movement accompanied by a range of magmatic compositions. Strong lithospheric blocks (i.e. Dacia) were only marginally deformed, where strike–slip faulting was associated with magmatism and extension. At the boundary of Adria and Tisza–Dacia strike–slip tectonics and core complex extension were associated with small volume Miocene magmatism in narrow extensional sedimentary basins or granitoids in core-complex detachment systems along older suture zones (Sava and Vardar) accommodating the extension in the Pannonian basin and afterward Pliocene–Quaternary inversion. Magmas of various compositions appear to have acted as lubricants in a range of tectonic processes

Origin of basaltic magmas of Perşani volcanic field, Romania: A combined whole 6 rock and mineral scale investigation

The Perşani volcanic field is a low-volume flux monogenetic volcanic field in the Carpathian–Pannonian region, 24 eastern-central Europe. Volcanic activity occurred intermittently from1200 ka to 600 ka, forming lava flow fields, 25 scoria cones andmaars. Selected basalts fromthe initial and younger active phaseswere investigated for major and 26 trace element contents and mineral compositions. Bulk compositions are close to those of the primitive magmas; 27 only 5–12% olivine and minor spinel fractionation occurred at 1300–1350 °C, followed by clinopyroxenes at about 28 1250 °C and 0.8–1.2 GPa. Melt generation occurred in the depth range from 85–90 km to 60 km. The estimated 29 mantle potential temperature, 1350–1420 °C, is the lowest in the Pannonian Basin. It suggests that no thermal 30 anomaly exists in the uppermantle beneath the Perşani area and that themaficmagmas were formed by decom- 31 pressionmelting under relatively thin continental lithosphere. Themantle source of themagmas could be slightly 32 heterogeneous, but is dominantly variously depleted MORB-source peridotite, as suggested by the olivine and 33 spinel composition. Based on the Cr-numbers of the spinels, two coherent compositional groups (0.38–0.45 and 34 0.23–0.32, respectively) can be distinguished that correspond to the older and younger volcanic products. This in- 35 dicates a change in themantle source region during the volcanic activity as also inferred from the bulk rockmajor 36 and trace element data. The younger basaltic magmas were generated by lower degree of melting, from a deeper 37 and compositionally slightly different mantle source compared to the older ones. The mantle source character of 38 the Perşanimagmas is akin to that ofmany other alkaline basalt volcanic fields in theMediterranean close to oro- 39 genic areas. The magma ascent rate is estimated based on compositional traverses across olivine xenocrysts using 40 variations of Ca content. Two heating events are recognized; the first one lasted about 1.3 years implying heating 41 of the lower lithosphere by the uprisingmagma,whereas the second one lasted only 4–5 days,whichcorresponds 42 to the time of magma ascent through the continental crust. The alkaline mafic volcanismin the Perşani volcanic 43 field could have occurred as a response to the formation of a narrow rupture in the lower lithosphere, possibly 44 as a far-field effect of the dripping of dense continental lithospheric material beneath the Vrancea zone. Upper 45 crustal extensional stress-field with reactivation of normal faults at the eastern margin of the Transylvanian 46 basin could enhance the rapid ascent of the mafic magmas

Assessment of demountable steel-concrete composite flooring systems

Sustainability concerns steer the construction sector towards adopting a circular economy philosophy. Steel-concrete composite beams are extensively used in multi-story buildings and bridges due to their competitive construction and efficient material use. Currently the composite action is mainly achieved by headed shear connectors welded to the top flange of the beam, obstructing the non-destructive demountability. Demountable shear connectors can be used in order to open up the composite con-struction for reusability. Demountable shear connectors can take the form of a bolted connection which requires a tight control of construction tolerances. This thesis is fo-cused on studying a bolt coupler connector which is seen as a valuable alternative to the more conventional embedded bolt. The proposed shear connector consists of a bolt and coupler embedded in prefabricated concrete decks which are connected through the top flange of the steel section by an injection bolt. Full-scale experiments have been performed to investigate the feasibility of construc-tion of a demountable car park. The demountable flooring was obtained by large pre-fabricated concrete decks in combination with tapered beams. Experimental research has confirmed the possibility of assembly and disassembly of the system if construction tolerances are appropriately designed. The most influential factors were quantified based on experimental observations, measurements and finite element models. The hole clearance should be designed keeping in mind the deformability of the system during construction, the manufacturing tolerances and the speed of construction. Experiments show that resin injection can be reliably and labour efficiently used for large oversized holes which allow for higher fabrication imperfections and reduced construction while at the same time enabling composite action of the connectors under live load.The reusability of the structure was confirmed by a set of eight four-point bending tests considering uniform and non-uniform connector arrangements. Finite element models closely match the experimental results in terms of deflection, stresses and curva-ture. However, the end slip is overpredicted which is in line with research performed by other authors. The efficiency of the non-uniform connector arrangements was studied experimentally and numerically to reduce the construction costs. Concentrating the shear connectors toward the supports will bring the highest benefit in terms of beam bending stiffness without the need of a large number of connectors to prevent uplift. An extensive cost analysis was performed based on a database of 15500 beam solu-tions generated by a design algorithm develop as part of this thesis. The case study provides a preliminary cost assessment of two demountable steel-concrete composite floorings in order to quantify their economic viability. It was shown that the system constructed with prefabricated solid slabs is more viable compared to the demountable profiled sheeting slab. The most influential contribution to the final cost of the struc-ture comes from the steel work and the labour intensive manufacturing.<br/

Economic viability of demountable steel-concrete composite beams

Composite beams are commonly used in current design practice due to their efficient material use and competitive execution. The shear connection is mainly achieved by means of headed studs welded on the top flange. However, the welded connectors obstruct the possibility of a non‐destructive disassembly required to reuse the steel beams and concrete slabs. Raised concern regarding sustainability aspects drive the construction sector to introduce a shear connector which enables the demountability of the flooring. Composite action can be enabled by a bolted connection consisting of an embedded bolt and coupler connected by an external injection bolt through the top flange of the steel beam. This paper aims to assess the initial investment costs and economic viability of two demountable steel‐concrete composite beam solutions. The investigated systems comprise of two different concrete flanges: a prefabricated solid deck and an in‐situ casted profiled sheeting slab. The cost inputs of the analysis were defined by industry experts based on assumed labour and material requirements. The unit price of the novel connector is significantly higher (approx. 15 times) compared to the regular headed welded stud. This justifies the need to optimize the connector arrangement in order to keep the cost per square meter as low as possible. Non‐uniform connector arrangements can be used to reduce construction time and costs with minor decrease in beam stiffness. A tool was developed to generate a batch of 13500 composite beam designs which were later analysed in terms of costs

Optimization of a composite (steel-concrete) floor system for fast execution and easy demolition

One of the increasingly important parameters in the construction sector is the time required for the execution and easy demounting of a structure. The goal of this paper is to provide insight into an on-going research focusing on structural performance of large prefabricated concrete decks connected by a demountable shear connectors. A large bolt-to-hole clearance is used to accomplish both requirements. The holes are injected by an epoxy resin to ensure composite action. The demountability and reusability of the composite beam system was successfully tested. Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure

Elastic behaviour of a tapered steel-concrete composite beam optimized for reuse

Steel-concrete composite beams are widely used in practice because of their simple construction sequence and economic cross-section design. Reuse of traditional composite beams is not possible due to the permanent connection between the steel beam and concrete deck established by welded headed studs. To allow for fast construction, demountability and reuse of composite beams, various demountable shear connectors can be used. In this paper the results of experiments carried out on demountable and reusable tapered composite beams, consisting of a tapered steel beam and large-scale prefabricated concrete decks, are presented. The performance of various arrangements of resin-injected bolt-coupler shear connectors was considered to optimize the beneficial effect of composite action whilst minimizing the number of shear connectors. An advantage of resin-injected bolted shear connectors is that composite action is obtained instantaneously and simultaneously for all connectors. Demountability and reusability of the composite beam were successfully demonstrated experimentally. Experimental and numerical results indicated that the number of shear connectors necessary to fulfil deflection and end-slip limits can be reduced by concentrating them near the supports of a simply-supported beam. Results obtained using finite element models closely matched the experimental results in terms of deflection, stresses and curvature.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure

Proof of concept of a demountable steel-concrete flooring system

Environmental concerns steerthe construction industry towards more sustainable developmentssuch asdemountable and reusablestructures. Composite structures are a frequent solution for multi-story buildings and bridges, however the use of welded shear connectors requires labour and energy intensive disassembly. Two bays of a demountable flooring systemfor a multi-storey car park building were erected in the laboratory. The flooring system consists of large prefabricated concrete decks connected to taperedsteelbeams. The feasibility of assembly and disassemblyof the flooring system was tested under laboratory condition. Shear interaction was achieved by an embedded bolt and coupler which areconnected to the top flange of the steel beam by an external injection bolt. Oversized holes are used in thetopflangeof the steel beamto accommodate fabricationand executiondeviationsandthedeformations occurringduring construction. Extensive imperfection measurements and finite element models were used to design the oversized hole diameter to 32 mm. Thehole clearance must be compensated either by pretensioning or injecting the bolt-to-hole clearance with an epoxy resinto enable instantaneous composite action underlive loads.Experimental injection of 150 injection bolts confirmsthat epoxyresin can reliably fill the hole clearance, and that the injectionprocess takes30 seconds per bolt.Various non-uniform shear connector arrangementswere considered to minimizeconstruction costs and maximize the speed of execution. The mechanical behaviour of the demountable composite beam was tested experimentally and numerically.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Steel & Composite Structure