Yaocen Pan: Processing and interpretation of marine seismic reflection data from the Baltic Sea area and the Lesser Antilles

Abstract

This dissertation is a comprehensive summary of two case studies using Multichannel seismic (MCS) reflection data in characterizing the fossilized inversion tectonics at the Sorgenfrei–Tornquist Zone (STZ) and ongoing subduction at the Lesser Antilles. 

In the first paper, new seismic profiles acquired within the Bornholm Gat in the SW Baltic Sea area are processed, which image Late Cretaceous- Paleogene inversion and exhumation of a previously poorly characterized narrow crustal zone in the southern end of the STZ. Upper Cretaceous deposition shows predominant contourites and gravity-driven sedimentation were largely controlled by inversion tectonics and influenced by the intensification of bottom currents. The results suggest more than one tectonic pulse during the Late Cretaceous-Cenozoic inversion, resulting from a far-field NE-SW compression transmitted from the Africa- Iberia-Europe convergence and the intraplate stress associated with the enhanced collisional coupling between the Alpine-Carpathian orogen and its foreland.

In the second paper, we present a structural and depositional interpretation of the STZ based on detailed stratigraphic mapping of marginal trough basins. The Hanö Bay and Bornholm Basin contain a sand-rich mounded drift proximal to the northeast of the STZ, and this unit is resolved with high seismic vertical resolution and represents a clear example of a siliciclastic-carbonate mixed depositional system. The comparison of sequence-stratigraphic indicators and the global sea-level curve allows for a refined reconstruction of the inversion history. A major inversion phase is interpreted to start around the Santonian-Campanian. Furthermore, we attribute a penecontemporaneous change in the depositional pattern, i.e., the erosional Campanian-Maastrichtian contourite moat system, to intensified bottom current activity related to significant global cooling, in conjunction with the paleoceanographic modification induced by the inversion tectonics.

The third paper deals with the structure and fluid migration in the Lesser Antilles subduction zone, where a subducting seamount ridge interacts with the upper plate. In this work, we present a reprocessed multichannel seismic (MCS) profile together with bathymetry, earthquake data and tomographic velocity structures in the central Lesser Antilles. Our results suggest that fluids are expelled upward from the band of subducted sediments at the southern flank of the Tiburon ridge, leading to an NW-SE elongated zone of hydrofractured and weakened crust above a serpentinized mantle corner, consistent with a prominent aseismic corridor. We suspect that the high interplate seismic activity offshore Martinique at ~30-65 km depths may correspond to deeply subducted indurated sediments that act as a strong asperity on the plate interface.