Paleostress and Deformation Patterns in a Collisional Orogeny: Examples from the West Carpathians and the Appalachians

FLEISCHMANN, KARL H., Earth Sciences & Resources Inst., University of South Carolina, Columbia, SC, MICHAL NEMCOK, Geologicky Ustav Dionyza Stura, Bratislava, Czechoslovakia, J. FRANK KEITH, JR., Earth Sciences & Resources Inst., University of South Carolina, Columbia, SC

Results from field analyses of two convergent orogens show the importance of stress analysis techniques in identifying the subtleties of convergent deformation not recorded by the larger scale aspects of regional geology. The northeastern part of the Slovakian West Carpathians is composed of Tertiary and Mesozoic sediments and Tertiary volcanics. Field analysis of brittle faults indicates that initial thrusting and subsequent back-thrusting were orogen-perpendicular through early Badenian time. Subsequent thrusting was accompanied by second-order strike-slip faults, indicating local exchanges of stress field(3) and stress field(2). Strike-slip faulting clearly was dominant in the outer flysch until late Sarmatian time, with stress field(1) and stress field(3) oriented NE and NW, respe tively. In the northern portion of the Champlain Valley, N80W-directed Taconic thrusting produced calcite-mineralized bedding-plane slip surfaces in the sedimentary rocks. Older mineralized faults were reactivated in basement rocks, first as calcite-mineralized high-angle reverse faults and subsequently as oblique slip faults. Stress analysis of fault-slip data suggested that the Taconic stress field was dominated by an N80W horizontal stress field(1), with the vertical stress changing from stress field(3) (Taconian) to stress field(2) (Taconian-Acadian?). For both the West Carpathians and the Appalachians, these analyses showed the change from a classic thrust-dominated stress regime to a strike-slip-dominated stress regime. In neither case is this change recorded by other elements of t e regional geology.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)