Cenozoic tectonic lineaments of the Terra Nova Bay region, Ross Embayment, Antarctica

Abstract

The Cenozoic tectonic framework of the Terra Nova Bay region is dominated by NW–SE-trending dextral strike–slip faults that represent the onshore expression of dextral transform shear along the Tasman Fracture Zone and Balleny Fracture Zone in the Southern Ocean. These intraplate faults reactivated inherited, Paleozoic crustal discontinuities established during the Ross Orogeny. Cenozoic, N–S to NNE–SSW transtensional faults developed in the crustal blocks in between the strike–slip faults as a kinematic consequence of the transcurrent motion. These transtensional faults provided a suitable mechanism to accomplish for dextral horizontal throw along the NW–SE strike–slip faults. The complex, strike–slip-induced kinematics controlled the location and the emplacement mechanisms of Cenozoic basic magma in the coastal sector of the Terra Nova Bay region. Sequential restoration of the present-day fault pattern in the Terra Nova Bay region, allowed reconstruction of the geologic framework of the area prior to onset of the strike–slip activity (from 105 Ma to 32 Ma), and also before the opening of the Ross Sea (earlier than 105 Ma). The pre-extensional framework was dominated by a vast, flay-lying plateau, mainly made up by the Jurassic Ferrar Supergroup rocks. Crustal thinning occurred due to movement on NNE–SSW- to NE–SW-trending extensional faults, and the inherited, through-going Paleozoic NW–SE regional-scale discontinuities were reactivated as transfer faults. Main extensional faults in the western side of the Ross Sea dip to the NE, and segmented this region into a series of blocks with minor tilting. Strike–slip tectonics characterises Late Cenozoic time, and is responsible for N–S extensional, rather symmetrical faulting along transfer zones in between major NW–SE transcurrent faults. Intersections between these two trends eased deep magma rise and the development of long-lasting, central volcanoes. The morphological effects of the last tectonic event were the development of NW–SE and N–S depressions and the rapid growth of volcanic edifices, that influenced both location and orientation of the main glaciers in northern Victoria Land and are responsible for their characteristic zig-zagging.