Tessera terrain, a major tectonic unit on Venus, comprises ∼8% of the planet's surface and occurs as large (>10 3 km across) high-standing (∼1-4 km above mean planetary radius) plateaus and small (<100 km across) outcrops scattered among the global volcanic plains (Ivanov & Head, 1996). Stratigraphic studies of tesserae establish that they are embayed by, and thus older than, volcanic plains that cover most of the planet's surface (e.g., Ivanov & Head, 1996, in agreement with a tessera crater retention age of 1 (Strom et al., 1994) to 1.4 (Ivanov & Basilevsky, 1993) times the average planetary surface age of ∼300 Ma (Strom et al., 1994) to ∼1 Ga (McKinnon et al., 1997). Tesserae contain the oldest rocks on the surface of Venus and are the only rock record of the planet's history prior to production of the presumably basaltic plains. The composition of tesserae remains unknown. Their plateau shape (Nikolayeva, 1990), dielectric permittivity (Kreslavsky et al., 2000), and infrared emissivity (M. S. Gilmore et al., 2015;Hashimoto et al., 2008) suggest that tesserae are more silica rich than the plains. A felsic tesserae composition would require formation in an extinct era via either voluminous partial melting of basalt or crustal recycling in the presence of abundant water (M.