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The Centre for Exploration Targeting (CET) is pleased to invite you to a Guest Lecture in the CET Seminar Series given by Vicki Hansen.
Abstract
The origins of Archean cratons are debated. Archean cratons consist of crustal granite-greenstone terrains and associated gneiss (GGTs) coupled to roots of strong, buoyant cratonic lithospheric mantle (CLM). I propose that crustal plateaus, quasi-circular craton-like features (~1400–2400 km diameter, 0.5–4 km high), on Earth’s sister planet Venus might serve as analogs for Archean cratons. Crustal plateaus host distinctive surfaces called ribbon-tessera terrain, which are isostatically supported by a compositionally controlled low-density root. Ribbon-tessera also occurs as arcuate-shaped inliers in the Venus lowlands, widely interpreted as remnants of rootless crustal plateaus. Within each crustal plateau, surface ribbon-tessera terrain comprises a vast igneous province analogous to terrestrial GGTs, and the plateau root is analogous to CLM. Crustal plateaus and ribbon-tessera terrain collectively represent Venus’ oldest preserved features and surfaces, and they formed during an ancient period of globally thin lithosphere. To explain the linked features of crustal plateaus, a bolide impact hypothesis has been proposed in which a large bolide pierces ancient thin lithosphere, leading to massive partial melting in the sublithospheric mantle. In this model, melt escapes to the surface, forming an enormous lava pond, which evolves to form ribbon-tessera terrain; mantle melt residue forms a strong, resilient buoyant root, leading to plateau support and long-term stability of an individual crustal plateau. Building on the similarity of GGT–CLM and Venus crustal plateaus, I propose an exogenic hypothesis for Archean craton formation in which a large bolide pierces thin Archean lithosphere, causing localized high-temperature, high- fraction partial melting in the sublithospheric mantle; melt rises, forming an igneous province that evolves to form a GGT, and melt residue develops a complementary CLM. By this mechanism, Archean cratons may have formed in a punctuated fashion at a time when large bolides showered Archean Earth.
About the Speaker
Vicki Hansen is the McKnight Presidential Professor of Earth & Planetary Science at the University of Minnesota, Duluth. Vicki is a structural geologist interested in the dynamic evolution of planets; her work focuses on Earth and Venus, but draws on insights from the Moon, Mars, Mercury, and Jupiter’s and Saturn’s moons. Most planetary geologists use Earth analogs to understand other planets. Vicki flips this around, using the geologic record we can read from Venus’ intricate surface to discover the nature of tectonic processes once active on Venus; these ideas may in turn provide critical clues about Earth’s Archean Eon. Vicki is a 2015 Gledden Visiting Fellow at The University of Western Australia.
Attendees are invited to join CET staff and students afterwards for refreshments provided by our local SEG Student Charter in the Resource Room, Robert Street Building.
