Tectonic and volcanic sequences associated with double type coronae on Venus
K. E. Kauhanen (Univ. of Oulu, Finland)
Double-type coronae are a class of subcircular volcanic structures on Venus, consisting of two equal-size components connected together by continuous rim and/or tectonic annulus. In the study, structural and volcanic characteristics of about 40 features found are compared to each other and regional tectonic trends.
Tectonic and volcanic patterns around components of double coronae show different stages of evolution, and support origin by two separate mantle diapirs in most of the cases. However, a few double coronae seem to have formed as two close-by and contemporaneous mantle diapirs. The three traditional stages in corona formation can be seen in tectonic deformation patterns, but not in a consistent way throughout. Radial fractures or graben are often embayed by lava flows. Concentric tectonism supposed to express the flattening phase in the corona formation can be related to late-stage flexure by the volcanic load or rim-related adjustment of regional stresses rather than horizontal movement of material below. In the context of corona formation by upwelling mantle plumes double coronae present a variety of stratigraphical sequences possibly reflecting complex interaction by mantle diapirs and the lithosphere. Early stage of corona formation seem to have been hidden by late volcanism in many of the cases.
Tectonic and volcanic deformation associated with different double-type coronae reveal many similarities in relation to regional tectonic patterns. Formation of wrinkle ridges and deformational belts mostly postdate corona formation but have in some cases coexisted with the final relaxational phase in the corona formation sequence. Fracture sets connecting double coronae to other regional volcanic centers are usually older than deformational belts, but trends may differ from each other. Formation of deformational belts may thus be related to large-scale stresses in the lithosphere rather than existing zones of weakness connecting nearby coronae and other volcanic centers.