HYBRID FRACTURE/DIKE/GRABEN/PIT-CHAIN/CANALI STRUCTURES ON VENUS: DYNAMIC INTERPLAY BETWEEN SURFACE AND SUBSURFACE COMPONENTS OF VOLCANO-TECTONIC SYSTEMS

We describe a new type of volcanic structure on Venus that represents a hybrid between subsurface fractures and dikes, graben, pit-chains, and surface canali and flows. These hybrid structures record major dynamic interplay between subsurface and surface components of a regionally extensive volcano-tectonic province on Venus (~2000 km-wide, >6000 km-long). The region overlaps spatially with chains of coronae (>200 km-diameter tectonomagmatic blisters) and areas of penetratively developed fracture domains. The coronae and fracture domains form a single wide zone (1500 km) with large coronae and splits into several splays (~500 km-wide) along strike to the west marked by smaller coronae, or lacking coronae. The hybrid lineaments are best developed away from large coronae. Individual hybrid lineaments range in width from 1 to >5 km, with lengths exceeding several 100 kms; lineament spacing ranges from 10’s of km to essentially overlapping and/or coalescing at the scale of the lineaments. The hybrid structures occur dominantly in mesoland/highland regions, perhaps related to preservation or, alternatively, differences in local lithosphere thickness, age and/or composition. Hybrid structures variably change along strike from zones of en echelon fractures, to fractures, pit-chains, graben, leaky dikes, and channels. Lava lakes also occur locally. Hybrid lineaments both pre-date and post-date adjacent flows, evidence that they play a key role in the plumbing of the broad magmatic system. Although these hybrid structures clearly source local surface flows, they likely play a much greater role in transporting surface material to depth as evidenced by widespread occurrence of pit-chains with negative topography and sharply defined topographic troughs formed by coalesced pit-chains. The hybrid structures can form from singular lineaments, but they can also evolve from suites of intersecting lineaments, resulting in a stepped or even sinuous surface pattern. These structures can evolve further into sinuous channels, or canali. These hybrid lineaments might also occur at other major rift regions such as the volcanic rises of Atla and Beta. These types of features might have been important in early Earth volcano-magmatic systems, or perhaps in contemporary divergent plate-boundary environments.