Downward-facing fold in the Torlesse accretionary wedge, Titahi Bay, Wellington, New Zealand

Abstract

Late Triassic greywacke and argillite from Titahi Bay, Wellington form part of the Torlesse Complex, interpreted as a subduction-related accretionary wedge. Several mesoscopic folds formed during tectonism, some with accompanying axial-surface cleavage, and others having cleavage oblique to the axial surface. At least two deformational events are clearly recognised. Upward-facing folds and a downward-facing fold, both with accompanying axial-surface cleavage, indicate that parts of the sequence were already overturned prior to formation of the downward-facing fold. The folds with oblique cleavage developed during the earlier event and thus are not transected folds. Groove casts were rotated to their predeformational orientation by unrolling the two fold generations. Based on the orientation of the groove casts and other sedimentary structures, the paleocurrent flowed from southwest to northeast, and reconstructions indicate that the sediment was transported longitudinally in the trench.

Keywords:

• Torlesse Complex
• accretionary wedge
• deformation
• folds
• paleocurrents