HR: 15:30h
AN: T23A-07    [Abstracts]
TI: Crust to Upper Mantle Echoes of the Black Sea Opening and Seismotectonic Consequences on the NW Inland
AU: * Besutiu, L
EM: besutiu@geodin.ro
AF: Institute of Geodynamics of the Romanian Academy, 19-21 Jean-Louis Calderon St., Bucharest, 020032, Romania
AB: The paper aims at revealing some tectonic and geodynamic imprints of the Black Sea opening mainly inferred from the potential fields analysis. DSS lines and seismic tomography are added in order to strengthen the interpretation and/or deepen the depth of investigation. Crust structure and dynamics (1) The presence of the oceanic crust in the central part of the basin is well reflected in the geomagnetic anomaly pattern. (2) Unlike some previous hypotheses postulating the existence of an unique rifting, up to date filtering techniques pointed out an unexpected pattern of the gravity and geomagnetic anomalies, trending almost perpendicular each-other within eastern and western basin, thus advocating for a distinct opening of the W and E Black Sea. (3) Correlation with the magnetostratigraphic scale revealed a geomagnetic reversal and seems to indicate a later opening of the eastern basin; off-shore seismics confirm the model by showing a slight overthrusting of the E Pontides over W Pontides. (4) It seems that the W Black Sea opening split the Moesian Plate into several slivers by creating/reactivating older faults trending north-westward. (5) Crust expelled by the Black Sea opening accommodated in various circumstances: (i) East Carpathians it met the inclined outer flank of the TTZ and came into an oblique subduction to which specific peculiarities of the South Harghita Mts. volcanism might be associated; (ii) South Carpathians, crustal slivers facing the vertical contact of the Intra-alpine sub-plate could not subduct, but went into a lithosphere buckling to which the lowest gravity low on the Romanian territory, located in front and not beneath the highest mountains in Romania, seems to be related; (iii) within the bending area of East Carpathians, where three tectonic plates met each other, the speed excess provided by the W Black Sea opening created an unstable triple junction. Upper mantle echoes Fingerprints of the Black Sea opening are well reflected in some recent seismic tomography. The tomography shows in depth extension of some previously mentioned faults into the upper mantle. It seems that W Black Sea rifting affected not only the lithosphere, but part of the upper mantle has been also expelled towards Carpathians. A higher velocity body extending to about 300 km in depth is associated to the Vrancea active seismic zone. Seismotectonic considerations Looking at the seismicity of the SE Carpathians foreland two aspects should be stressed: (i) the unusual seismicity of the Moesian Platform; (ii) the intermediate-depth earthquakes within the bending area of East Carpathians (Vrancea zone) that might be hardly associated to a subduction process. After the Black Sea opening ended, the drift of the NW inland towards Carpathians went on due to the active rifting within SW Arabian Plate. As a rule, lithosphere slivers within the foreland advance together towards Carpathians kept by friction. However, sometimes, they relatively slip each to other thus generating earthquakes along their wedges. An alternate mechanism for the unusual intermediate-depth seismicity within Vrancea zone was proposed: the unstable triple junction. It seems that the Black Sea opening provided the necessary speed excess to the MoP for generating an unstable transform-transform-compression triple junction within Vrancea area. The penetration of the central lithospheric segment of the triple junction into the hotter upper mantle would be followed by thermo- baric accommodation phenomena (e.g. thermal stress, phase-transform processes, dehydrations) to which intermediate-depth seismicity might be related.
DE: 3005 Marine magnetics and paleomagnetics (1550)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8123 Dynamics: seismotectonics
DE: 8155 Plate motions: general (3040)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Joint Assembly