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Abstract:
Parga Chasma is a discontinuous rift system marking the southern boundary of the BAT region on Venus. Along a 1,500 km section of Parga Chasma, detailed mapping has revealed 5 coronae, 11 local rift segments distinct from a regional extension pattern, and 47 graben-fissure systems. These systems are often centred within coronae or large volcanoes, but many are isolated and indicate cryptic centres. Some of these magmatic centres are further observed as the loci of triple-junction rifting, collectively comprising the 11 local rift segments. Cross-cutting relationships between the corresponding graben-fissures and rift faults reveal synchronous formation, implying a genetic association. Additionally, cross-cutting relationships reveal these local events to postdate the regional extension, further indicating multiple stages of rifting. This provides an explanation for the discontinuous morphology of Parga Chasma, and its result has implications to explain the morphologies of other rift systems, both on Venus and Earth.