Paleozoic and Grenvillian structures in the southern Appalachians: extended interpretation from seismic reflection data

Abstract

Interpretive reprocessing of seismic reflection data and correlation of the seismic data with gravity data have elucidated Paleozoic and Grenvillian structures in the southern Appalachians. The seismic data include ADCOII, Seisdata, and COCORP reflection profiles which traverse the Blue Ridge and Inner Piedmont geologic provinces of South Carolina, North Carolina, and Georgia. <p>Based on the reprocessed data, all of the major faults within the allochthonous upper crust, including the Brevard fault zone and the Hayesville fault, are interpreted to root in the Blue Ridge master decollément. Reflectors extending beneath the surface location of the Hayesville fault may be a deformational zone that extends in the direction of structural strike and is associated with Alleghanian transpression. Alternatively, the reflectors may actually represent the subsurface location of the J layesvil1e fault, in which case convergent reflector geometry of the Hayesvi1le fault and the Blue Ridge thrust suggest that the Blue Ridge thrust occupied a zone of weakness previously created by the Hayesville fault. Both the Blue Ridge thrust and Brevard fault zone ramps are interpreted to have a genetic re1ation to underlying basement topography. Relative amplitude data enabled the discrimination between Blue Ridge-Inner Piedmont crystalline rocks from underlying Lower Paleozoic shelf strata, thereby allowing the delineation of the Blue Ridge thrust. The revised geometry of the Blue Ridge thrust constrains the top of the shelf sequence beneath the Blue Ridge to depths less than 3 km. This relatively shallow depth of the shelf sequence, and the presence of duplex structures and bright spots within the sequence are auspicious factors for hydrocarbon exploration. <p>Reflectors within the upper-to-lower crust are interpreted to be preserved Grenvillian structures that were reactivated at the basement surface during Late Proterozoic-Early Cambrian extension. The reflectors are cross-cut by proposed post-Grenvillian, pre-Alleghanian low density intrusions that have acoustically transparent bases. Correlation of seismic and gravity data suggests that disturbances in the Douguer gravity field can be attributed to these structures within the autochthonous crust. <p>Discontinuous reflection packages from depths of 36-42 km are interpreted to originate from the Mohorovicic Discontinuity. The reflectors trend about N 15°E with a true dip of approximately 15°NW.