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The size of a volcanic eruption, and thus the associated potential hazards, depends partly on the depth, geometry, and size of the source magma chamber. To estimate magma chamber depths and sizes, we apply a newly developed analytical method, based on the aspect ratio (length/thickness) of dikes, to three volcanoes in the Karlıova region of Eastern Turkey, namely Turnadağ, Varto, and Özenç. The results indicate that the depths of the source chambers are between 2 and 4 km at Turnadağ, 2 to 5 km at Varto, both of which are located in transtensional tectonic regimes, but from 22 to 27 km at Özenç, which is located in a convergent tectonic regime. A similar reservoir depth at Özenç is indicated by seismic tomography, and this data also suggests that the reservoir is laterally continuous for more than 40 km. The large volume of ignimbrites (>40 km 3) associated with Varto, a collapse caldera, indicates that caldera subsidence may have maintained the excess magmatic pressure (through tectonic forcing) in the chamber over a longer time than during normal pyroclastic eruptions. The dike aspect ratios further indicate magmatic overpressures of 13-21 MPa for Varto, 13-17 MPa for Turnadağ, and 26-31 MPa for Özenç. The combined results from seismic tomography, analytical models and magma compositions indicate that both Turnadağ and Varto volcanoes, which are typical stratovolcanoes composed of mostly intermediate, and more rarely, acidic magmas, were fed by two very shallow and comparatively small magma chambers (2-5 km depth). Whereas less evolved magmas were erupted from Özenç, which hosts predominantly basaltic and intermediate lavas and dikes that were fed by a deep reservoir at 22-27 km depth. Our tomographic models show that none of the volcanoes are located directly over the centre of a deep magma reservoir. Our data also indicates that the magma in the reservoir has migrated between 34 and 40 km in a right lateral motion (to the east) below Varto and Turnadağ, respectively, and 23 km in a left lateral motion (to the west) at Özenç over the past 3 Ma. This lateral propagation of magma can be explained by tectonic escape of the Anatolian block to the west through the Northern Anatolian Fault and the Varto Fault Zone over the last 6 Ma.
The size of a volcanic eruption, and thus the associated potential hazards, depends partly on the depth, geometry, and size of the source magma chamber. To estimate magma chamber depths and sizes, we apply a newly developed analytical method, based on the aspect ratio (length/thickness) of dikes, to three volcanoes in the Karlıova region of Eastern Turkey, namely Turnadağ, Varto, and Özenç. The results indicate that the depths of the source chambers are between 2 and 4 km at Turnadağ, 2 to 5 km at Varto, both of which are located in transtensional tectonic regimes, but from 22 to 27 km at Özenç, which is located in a convergent tectonic regime. A similar reservoir depth at Özenç is indicated by seismic tomography, and this data also suggests that the reservoir is laterally continuous for more than 40 km. The large volume of ignimbrites (>40 km 3) associated with Varto, a collapse caldera, indicates that caldera subsidence may have maintained the excess magmatic pressure (through tectonic forcing) in the chamber over a longer time than during normal pyroclastic eruptions. The dike aspect ratios further indicate magmatic overpressures of 13-21 MPa for Varto, 13-17 MPa for Turnadağ, and 26-31 MPa for Özenç. The combined results from seismic tomography, analytical models and magma compositions indicate that both Turnadağ and Varto volcanoes, which are typical stratovolcanoes composed of mostly intermediate, and more rarely, acidic magmas, were fed by two very shallow and comparatively small magma chambers (2-5 km depth). Whereas less evolved magmas were erupted from Özenç, which hosts predominantly basaltic and intermediate lavas and dikes that were fed by a deep reservoir at 22-27 km depth. Our tomographic models show that none of the volcanoes are located directly over the centre of a deep magma reservoir. Our data also indicates that the magma in the reservoir has migrated between 34 and 40 km in a right lateral motion (to the east) below Varto and Turnadağ, respectively, and 23 km in a left lateral motion (to the west) at Özenç over the past 3 Ma. This lateral propagation of magma can be explained by tectonic escape of the Anatolian block to the west through the Northern Anatolian Fault and the Varto Fault Zone over the last 6 Ma.
The intersection of the Eurasian and Arabian plates and the smaller Anatolian Scholle created the Karlıova Triple Junction (KTJ) in eastern Turkey. In this study, we present analogue model experiments for this region and compare the results with our field observations and data from remote sensing imagery. Our comparison suggests that the sense of slip along curvilinear faults at the west of the KTJ changes along strike moving away from the principal displacement zones, from strike-slip to oblique normal and then to pure normal slip. Although, the active Prandtl cell model has been proposed to explain the overall regional fault pattern at eastern part of the Anatolian Scholle, the map view orientation of the secondary faults within the Karlıova wedge and performed analogue modelling results suggest that the passive wedgeshaped Prandtl cell model with a normal dip-slip component along slip lines is more appropriate in order to explain not only deformation pattern around the KTJ but also internal deformation of eastern part of the Anatolia. Moreover, these faults accumulate the significant amount of deformation that causes to the irregular earthquake behavior and the relatively lower geologic slip-rates along the main fault branch of boundary faults around the KTJ.
The Albula Pass region lies between the Lower Austroalpine Err Nappe and the Middle Austroalpine Silvretta Nappe. They will be treated here as the frame of the non- to gently metamorphic sedimentary units between the two during the Alpide times. Sedimentation started on a metamorphic Hercynian basement during the latest Carboniferous(?) and continued into the Permian. Then a sequence from the Alpine Buntsandstein to the medial Jurassic to early Cretaceous Aptychenkalk (=Maiolica) and radiolarites were deposited in an environment of rifting and subsidence. The succeeding Palombini clastics were laid down after the Aptychenkalk and mark the onset of shortening in the Alpine realm. The initial structures that formed were at least two north-dipping normal faults which formed before the deposition of the Jurassic sedimentary rocks. When shortening set in, the first structure that came into being was the south-vergent Elalbula Nappe, bending the normal faults into close antiforms. It became further dismembered into two pieces creating parts of the future Ela and Albula nappes in the Albula region. This motion was later reversed, when the entire ensemble became bulldozed by the immense body of the Silvretta Nappe along numerous, closely spaced thrust faults, some of which only very locally followed horizontal bits of the old normal faults, but in principle they determined their own course. No evidence for westerly motion could be identified, although microstructures in the structural fabric were not studied. The reason for this may be the pre-orogenic fabric in the bounding tectonic units.
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