Geology of the Alpha Regio (V-32) Quadrangle, Venus

Abstract

This thesis presents a 1:2,500,000 geological map of the Alpha Regio (V-32) quadrangle, Venus. Nearly 40,000 lineaments and 77 geological units were mapped. Several fracture belts have been identified. Plains material, previously mapped as several global units, was divided into 27 units and some were linked to discrete sources. Several corona-sourced volcanic flows were recognized. Cross-cutting relationships reveal a complex geological history throughout which numerous processes have overlapped. Fatua Corona is associated with a radiating graben-fissure system 1700 km in length that swings in trend from radiating to sub-parallel. The structures are inferred to overly dykes, which represent an estimated 57,000 km^3 of magma. The dyke trends were used to establish the regional stress field orientation (NNE-SSW maximum compressive stress). Two hypotheses are proposed to explain the forces contributing to this stress field: 1) extension in the Derceto-Quetzalpetlatl belt, or 2) ridge push from the Alpha-Lada belt. Giant circumferential dyke swarms on Earth resemble the circumferential graben-fissure systems of coronae. Characteristics of circumferential graben-fissure systems in the V-32 quadrangle are catalogued and compared with terrestrial circumferential dyke swarms. Based on this new mapping of circumferential systems, several coronae are shown to be much larger than previously described, notably Thermuthis Corona (330 km to 1250 km in diameter). The high coverage of stereo-derived topography data in this region has enabled the characterization of wrinkle ridge morphometry. The ridges are ~10 km wide with ~100 m of relief and mostly asymmetric. Modeling of the underlying thrust faults suggests they are planar, dip 30°, reach depths of ≤ 5 km, are blind to depths of ≥ 2 km, and have accommodated ~200 m of dip-slip. These results support thin-skinned deformation. Wrinkle ridge density is negatively correlated with crustal thickness, supporting previous models linking the magnitude of strain to the swell-push body force combined with crustal thickness. The strain appears to be specifically related to mantle downwelling along Eistla Regio. The results of this research have been used to identify landing site targets in the V-32 quadrangle for the Venera-D mission. Five targets are suggested in plains material, digitate volcanic flows, and corona-sourced flows.