Tectonics of small tessera islets on Venus

Abstract

Two orthogonal fracture sets pattern many Venusian bar-like tessera blocks. The fracture pattern consists of parallel main edge faults which may have strike-slip displacements, and pronounced dense surface patterns of parallel and high-angle tessera faults with complex cross-cutting relations. Dimensions and regularity of the complex pattern indicate a certain block-wide uniformity of processes involved. The two orthogonal fracture sets within bar-like tessera blocks can be understood in terms of tensional uppermost crust. The bar-like blocks were first caused by primary parallel faulting which was then followed by formation of two orthogonal high-angle fault sets of more local, multiphase relaxational deformation within the blocks. Complex cross-cutting relations of fractures of the two perpendicular sets can be interpreted as results of chocolate tablet boudinage of surface rocks underlied by a low-viscous intralithospheric, or intracrustal, layer. Progressive or superposed high angle fracturing has characterized this relaxational deformation. Few fractures which connect over block boundaries from or into surrounding terrains indicate connections to wider regional stresses which were less important during orthogonal fracturing.