Distinct Mineralogy and Age of Individual Lava Flows in Atla Regio, Venus Derived From Magellan Radar Emissivity

NASA's Magellan mission revealed that many Venus highlands exhibit low radar emissivity values at higher altitudes. This phenomenon is ascribed to the presence of minerals having high dielectric constants, produced or stabilized by temperature-dependent chemical weathering between the rocks and the atmosphere. Some large volcanoes on Venus have multiple reductions of radar emissivity at varying altitudes. The authors present morphological maps of major lava flow units at Maat, Ozza, and Sapas montes and compare them to radar emissivity. Sapas has a single reduction in emissivity values at 6,054.6 km, while Maat and Ozza have several reductions at altitudes of 6,052.5-6,056.7 km. Emissivity values are highly spatially correlated to individual lava flows indicating that minerals in the rocks control the emissivity signature. The emissivity patterns at these volcanoes require at least four individual ferroelectric mineral compositions in the rocks that are highly conductive at Curie temperatures of 693-731 K. These temperatures are compatible with chlorapatite and some perovskite oxides. Modeling the minimum volumes of ferroelectrics (10-100s ppm) shows the volume and type of ferroelectric may vary over the lifetime of a single volcano. The modeled volumes of ferroelectrics in Ozza and Sapas are greater than in Maat, consistent with the production of ferroelectrics via weathering over a longer period of time, and supporting the idea that Maat has younger volcanic activity. The stratigraphic relationship of Maat's youngest flows with impact craters may indicate the timeframe of the production of specific ferroelectrics via chemical weathering is over 9-60 Ma.