GLOBAL TECTONOMAGMATIC PROCESSES ON VENUS OVER TIME

Venus preserves an incredible record of globally developed tectonomagmatic systems that became more spatially focused over time. These systems highlight the interdependence of tectonic and magmatic processes, which are unavoidably and intimately linked, driven by the transfer of internal heat to the surface of this one-plate planet. The earliest preserved record (1) encompasses the formation of globally distributed ribbon-tessera terrain, formed as ‘scum’ of individual huge lava ponds (1500-2500 km diameter; and perhaps locally preserved remnants of magma seas/oceans). Subsurface melt leaked to progressively deforming surface scum, itself deformed once solidified, contributed to increasing layer thickness, which in turn influenced deformation; the magma served as a driver, and yet also took part in, and changed the course of, deformation, which in turn focused melt pathways. Later volcanic activity (2) occurred synchronously with the formation of anastomosing to orthogonal deformation belts that cover >10 x 10⁶ km². The belts (10’s of km wide, 1000 km-long) variably record extensional, contractional and transpressive strain, likely rooted in the sublithospheric mantle, and may have served as conduits for mantle-derived melt and volatiles, similar to deep-crustal Precambrian shear zones in Brazil and Madagascar. The Artemis super plume (3) dominated mantle circulation in its time and left a volcanotectonic imprint across ~30% of the surface; it may also be responsible for formation of the Ishtar Terra tectonic province. Chains of coronae (4), tectonomagmatic surface expressions of magma blisters in the crust/lithosphere, likely record cylindrical mantle upwellings, perhaps with small-scale cells evolving to large-scale cells over time. Volcanic rises marked by coronae clusters (5; e.g., Bell & Eastern Eistla regio) represent mantle plumes formed on thinner lithosphere and are slightly older than, rift-zone dominated volcanic rises (6; e.g., Atla & Beta regio). Extensive fracture zones (7; up to 10,000+ km-long, 100’s km-wide), marked by chasma, hybrid fractures/graben/pit chains, canali, and lava lakes, accompanied the development of volcanic rises. Elements 4-7 describe broadly synchronous, yet progressive, processes. In all cases tectonism and volcanism are inseparable processes.