The Lada Terra rise and Quetzalpetlatl Corona: A region of long-lived mantle upwelling and recent volcanic activity on Venus

摘要

Quetzalpetlatl Corona (～850 km in diameter) and Boala Corona (～350 km × 250 km in diameter), are both situated within the Lada Terra rise, a prominent ～2000-km-wide circular topographic feature rising ～2.5-3 km above the mean planetary radius in the southern hemisphere of Venus, south of the Lavinia Planitia lowlands. Together these features form a unique configuration that combines the characteristics of corona-dominated rises (e.g., Eistla), rifted volcanic rises (e.g., Beta Regio), and large coronae structures (such as Artemis and Heng-O). Three zones of extension converge on the central part of the rise at Boala Corona, and hundreds of extensive lava flows emerge from the summit region, stream down the sides of the rise, and flood the surrounding topographic annulus and moat. Detailed geological mapping of the region shows that Cocomama Tessera terrain was flexed, uplifted and flooded during the formation of the Lada rise. Stratigraphic relationships show that the rise formed over an extended period of time following tessera formation. Evidence for early uplift includes flexure of the tessera, formation of the Quetzalpetlatl Corona annular ridge, and the radial array of flows originating from the center of the feature (showing the presence of downhill slopes). Early Quetzalpetlatl Corona activity was focused on the formation of the annular ridge, and the outer moat continued to form throughout the extended history of the rise, deforming even after the emplacement of some of the most recent lavas. Central radial flows ponded behind the early-forming annular ridge, concentrating the load inside the ridge, perhaps adding to the evolution of the moat. Late-stage activity includes final radial flows and central shields inside Boala Corona. On the basis of gravity, topography and image data, volcanism has persisted into the most recent geological era. We compare the central Lada rise with other regions of Venus thought to be currently active on the basis of Venus Express VIRTIS emissivity data and we conclude that although the area may have been active in the very recent geological past, stratigraphic evidence favors an endogenic origin for some VIRTIS anomalies. The coaxial combination of the broad rise of Lada Terra with large coronae (Quetzalpetlatl and Boala) suggests that these two types of features are parts of a continuum related to the magnitude and history of mantle thermal upwellings. We see no evidence that the culmination of this process results in tessera formation.