Evidence for a Locally Thinned Lithosphere Associated With Recent Volcanism at Aramaiti Corona, Venus

摘要

Heat flow estimates of terrestrial planets and icy satellites are important for exploring their thermal evolution. Topographic signatures of flexure can be used to estimate the effective elastic lithospheric thickness, h(e), and heat flow. Here, we use high resolution stereo topography and axisymmetric elastic flexure models to investigate lithospheric flexure around Narina Tholus, a steep-sided volcanic dome similar to 40 km across that superposes the tectonic annulus of Aramaiti Corona. Our results indicate a best-fit elastic thickness h(e) = 3.9-9.1 km, for values of Young's modulus, E, ranging from 65 to 5 GPa respectively. This suggests a thinned lithosphere locally around Narina Tholus, compared to regional estimates for h(e). The lower values of E are appropriate to the heavily fractured environment of the corona annulus, and we find that they predict flexural stresses compatible with the limited fracturing observed around Narina Tholus. A global survey yielded 13 additional tholi (or tholi groups) at coronae and with stereo coverage, none of which showed evidence for flexure. We find, that locally at Narina Tholus, the heat flow is elevated by a factor of 2-4 relative to that inferred from a previous study of flexure at Aramaiti, consistent with late-stage, possibly recent, volcanism focused at, and facilitated by, the fracture annulus. Our results further strengthen arguments for a currently volcanically active planet and demonstrate the role that high-resolution stereo topography can play in elucidating the current thermal state of Venus.