Abstract: Structure of a complex, transpressive collisional boundary: the Salzburg section at northern margins of the Alps

NEUBAUER, FRANZ, JOHANN GENSER, and JOACHIM SCHWEIGL

Based on new structural, and published seismic and well data the structural evolution of units exposed along the Salzburg sector of the northern margin of the Alps is reinterpreted in order to constrain the polyphase history of this transpressive collisional plate margin. This sector comprises a cover nappe complex of structural units of very different paleogeographic origins. The general structure is that of a northwards emplaced, now S-dipping nappe complex with footwall propagation of thrusts that were formed within a period covering c. 100 Ma. Formation of the nappe complex includes the following sequence of major events: (1) A cover nappe complex including a possible suture has been formed during Middle to early Late Cretaceous tectonic events within the Northern Calcareous Alps (NCA - that are now exposed in a hangingwall structural position). (2) This nappe complex has been overprinted by sinistral wrenching leading to the opening of the Salzburg Gosau basin (Late Cretaceous to Eocene) along an overstep of E-trending strike-slip faults. (3) NNE-directed piggy-back emplacement of the NCA nappe complex onto the Rhenodanubian flysch nappes (RDF) occurred during Middle-Late Eocene. The RDF constitutes a wedge-shaped nappe complex (at the northern front of NCA that acted as a hinterland buttress) which formed by (4) initial N-directed overthrusting of Ultrahelvetic continental slope deposits (UH) and subsequent (5) out-of-sequence thrusting forming the present fold-imbricate fan. The assembled UH/RDF wedge was finally carried northwards onto (6) Helvetic units, and, together with these, (7) onto the peripheral molasse basin during Oligocene-Early Miocene. Further modification of the nappe complex took place by NE-trending sinistral strike-slip faults, and N-trending normal faults.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria