HR: 14:10h
AN: T53E-03    [Abstracts]
TI: Extensional Strain Partitioning in the Eastern Black Sea From Wide-Angle Seismic Data and Subsidence Analysis
AU: * Shillington, D J
EM: djshill@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO14 3ZH United Kingdom
AU: Minshull, T A
EM: tmin@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO14 3ZH United Kingdom
AU: White, N
EM: nwhite@esc.cam.ac.uk
AF: Bullard Laboratories, University of Cambridge, Madingley Road, Cambridge, CB3 0EZ United Kingdom
AU: Edwards, R A
EM: rae@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO14 3ZH United Kingdom
AU: Scott, C
EM: cls203@noc.soton.ac.uk
AF: National Oceanography Centre, Southampton, University of Southampton, European Way, Southampton, SO14 3ZH United Kingdom
AB: The eastern Black Sea is a deep, extensional basin that most likely opened in the late Cretaceous and early Tertiary as a back-arc basin during the subduction of the Tethys Ocean. This area provides an excellent natural laboratory for the study of extensional basins due to the thick sequence of sediments, which host a record of the subsidence history, and the proximity of the conjugate margins, which reduce uncertainties in reconstructions. Additionally, unraveling the timing and style of opening of the Black Sea, which has been the subject of considerable controversy, is critical for studying both past and present day tectonics in this active region. To this end, we employ a two-part study that includes both subsidence analysis and crustal seismology. A new onshore-offshore wide-angle seismic refraction dataset was acquired in February-March 2005 along lines coincident with industry reflection profiles. Both four-component ocean-bottom seismometers and three-component land seismometers were deployed along four transects that survey thin crust in the center of the eastern Black Sea, the Mid Black Sea High (a continental crustal ridge that separates the eastern and western basins), Sinop Trough (a basin at the edge of the eastern Black Sea), and the southern margin. Subsidence analysis has also been conducted on coincident lines by flexurally back-stripping stratigraphic horizons identified in reflection profiles and using them to invert for temporal and spatial variations in strain rate. In this presentation, we show velocity models of two 160-km-long, SW-NE oriented refraction profiles, Lines 3 and 4, obtained by first arrival tomography and coincident strain rate inversion results. Velocity models of these transects show the following new features: 1) significant, asymmetric crustal thinning beneath Sinop trough, 2) a rapid decrease in crustal thickness from ~35 km beneath the Mid Black Sea High to ~8 km in the center of the basin over a lateral distance of ~30 km, 3) a thickness of ~9 km of sediments in the center of the basin, which includes a low velocity zone at its base. The significant reduction in crustal thickness beneath Sinop trough suggests that strain was not merely concentrated in the center of this deep basin, but was partitioned over a broader area prior to localization in the basin center. Crustal thickness variations in velocity model along Line 3 imply extensional factors of ~2 beneath Sinop Trough and ~4 in the basin center. Similar degrees of extension are inferred from subsidence analysis based on stratigraphic horizons identified in the coincident reflection profiles if reasonable assumptions of paleowater depth are made. Furthermore, the shallowest occurrence of mantle velocities beneath Sinop Trough is offset laterally from the deepest part of the basin, implying an element of depth-dependent stretching. Eight-km-thick crust in the center of the basin could correspond either to oceanic crust produced in a back-arc setting or thinned continental crust; continuing work will seek to differentiate between these two possibilities. We use these observations together with subsidence analysis to present a model for the evolution of eastern Black Sea and gain generic insights into extensional basin formation.
DE: 3001 Back-arc basin processes
DE: 3025 Marine seismics (0935, 7294)
DE: 7270 Tomography (6982, 8180)
DE: 8105 Continental margins: divergent (1212, 8124)
SC: Tectonophysics [T]
MN: Fall Meeting 2005