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Active Deformation and Recent Tectonic Evolution of the SE Carpathian Foreland: Mechanical Coupling between Crust and Upper Mantle

Dana Mucuta,

Department of Geological Sciences, University of South Carolina,

Columbia, South Carolina;

[email protected]

I evaluate spatial and temporal relationships between crustal and mantle structures and seismicity in order to establish the nature and extent of the mechanical coupling between the SE Carpathian foreland deformation and adjacent Vrancea mantle seismicity.

The relationship between crustal structures related to neotectonic basin evolution with mantle seismicity poses a significant geodynamic problem. The SE Carpathians foreland basin is characterized by a thick Miocene-Quaternary sedimentary cover, late Pleistocene-Quaternary extensional faults and unusually low topography. It bears intensely exploited oil reserves. A better understanding of the recent tectonic evolution and burial history of the sediments (reaching a total thickness of about 18 km at the depocenter) would prove extremely useful in identifying new productive series and oil traps.

This work targets the identification of crustal and upper-most mantle structures on seismic sections, distribution, type and geometry of active crustal faults and their possible continuation in the upper mantle. It will ultimately be finalized by integrating the current active and passive seismological data with surface geology and topography in a comprehensive GIS database for accuracy and easy access. Analysis of offsets within the sedimentary cover can provide an estimate on the duration and timing of foreland deformation. The deeper structure (<60 km) was imaged by processing and interpreting deep seismic lines but the shallow data lacks resolving resolution thus field mapping of faults is considered a necessary undertaking. Relocation of crustal earthquakes and focal mechanisms determination can strengthen the interpretation and provide an integrated image of the basin sedimentary cover.

Project description:

Purpose: Analyze and interpret crustal foreland seismicity in conjunction with seismic profiles and mapping faults to define patterns of associations between crust and mantle to provide a valid explanation tying shallow basin deformation with deep seated earthquakes occurring in the Vrancea Area.

Regional Context: The Vrancea Seismogenic Area, located external to the SE Carpathians, is an area of intermediate depth earthquakes with high magnitudes, confined to a very narrow cylindrical body, atypical of a Wadati-Benioff plane. Existent hypotheses explaining its tectonics entertain variations of subduction, although there is a notable miscorrelation of hypocenters with the proposed suture zone and geologic and geophysical data points towards a continuity of continental crust throughout the entire area. In front of the Vrancea area, a thick (18 km, 10 km of Neogene age) and young sedimentary basin (Focsani) was formed, site of intensely exploited oil reserves. This basin shows signs of recent tectonic deformation and low topography seemingly related to its position adjacent to Vrancea. Hydrocarbons are exploited from the late Miocene formations implying sustained subsidence and burial in a short time interval. Shallow earthquakes of low magnitudes are present in the basin, apparently (?) a readjustment response to the mantle ones.

Methods: Analysis of offsets within the sedimentary cover can provide an estimate on the duration and timing of foreland deformation. The deeper structure (<60 km) was imaged by processing and interpreting deep seismic lines but the shallow data lacks resolving resolution thus field mapping of faults is considered a necessary undertaking. Relocation of crustal earthquakes and focal mechanisms determination can strengthen the interpretation and provide an integrated image of the basin sedimentary cover.

Scientific Importance: Testing of a new hypothesis involving partial delamination of continental lithosphere in the Carpathians involving a remnant lithospheric coupling between the crust and uppermost mantle in the foreland.

One-page Summary Report and a Brief Financial Statement

This project is an essential component in a larger project. Carrying it out to the end will lend strength to my conclusions and will make it compelling for the scientific community to accept a different view on mechanisms that can generate mantle seismicity in the absence of subduction. On a local level, a more integrated image of this area will reveal potential problem areas as well as possible new exploration areas. A better understanding of the tectonic mechanisms governing the area will enable future predictions and preparation that would possibly minimize the impact of destructive earthquakes.

Funds are requested to perform field mapping in the Focsani Basin and to aid in the location of shallow seismicity. These two goals can be accomplished in the same time frame and will be followed by a manuscript. Integration of mapped features with those imaged on deep seismic sections already available and correlation with relocations and focal mechanisms of crustal events has the potential of providing the best possible image without requiring collection of more seismic data.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid