KINEMATICS OF THE ROUND HEAD THRUST, WESTERN NEWFOUNDLAND: INTEGRATING 2D SEISMIC INTERPRETATION AND 3D MODELING

The Round Head Thrust marks the structural front of the Appalachian orogen in western Newfoundland and may play a pivotal role in understanding the kinematics during orogen formation. The Round Head Thrust exhibits a complex history of normal faulting early in the Ordovician Taconian orogeny, followed by "thin-skinned" emplacement of the Humber Arm Allochthon. Subsequent "thick-skinned" thrusting led to inversion, probably in the Devonian Acadian orogeny. Variably oriented open folds in the hanging wall dominate the map pattern at the topographic surface, and probably resulted from movements of the Round Head Thrust. However, despite its significance, the fault's precise movement direction has remained enigmatic.

We present a provisional 3D model of the Round Head Thrust and associated hanging-wall and footwall stratigraphy using 2D seismic lines, from oil exploration efforts in the area. Our interpretation reveals that three distinct fault-bounded "horses" underlie the Round Head Thrust. Using restoration techniques in plan view, we deduced precise movement directions of these lower thrusts. To do this, we focused on the restoration of a single horizon, whose extent is defined by the cutoff lines in each thrust. Our analysis shows hanging wall movements of the Round Head Thrust towards ~303° NW. Subsequent, in-sequence thrusting drives additional horses beneath the Round Head Thrust footwall displaying variable movement directions. Two horses display northward thrust movement with only minimal displacement while a third horse experienced clockwise rotation. We observe an increased amount of displacement along the major faults towards the SW, which is accommodated by an increased amount of folding towards the SW. This deduction not only resolves the historical uncertainty regarding movement direction on the Round Head Thrust but also provides insight into the resulting flexure of the hanging wall.

Our findings underscore the effectiveness of integrating seismic imaging with 3D modeling and restoration efforts to unravel kinematics. It also exemplifies a methodology applicable to analogous geological settings to solve kinematic questions. The insights we gathered in this study significantly advances our understanding of the regional tectonics within the Appalachian orogen of western Newfoundland.