Affiliation:
1. Department of Earth, Atmospheric, and Planetary Sciences Purdue University West Lafayette IN USA
2. Department of Physics and Astronomy Purdue University West Lafayette IN USA
Abstract
AbstractIn contrast to multiring basins, megabasins lack clear ring structures and display crustal profiles characterized by a thin layer of crust at their center that gradually increases in thickness to the surrounding region. The 1,550‐km‐diameter Caloris basin on Mercury is often speculated to be a multiring basin; however, its crustal structure is indicative of a megabasin, perhaps explaining the lack of discernible rings. Here, we model the formation of Caloris basin using iSALE‐2D under a range of preimpact thermal conditions to determine whether the processes responsible for its megabasin crustal structure could lead to the formation of basin rings. We find that thermal gradients between 22 and 30 K/km—hotter than previously inferred—facilitate the reproduction of Caloris basin's crustal structure through crustal flowback, though such preimpact thermal structures preclude its formation as a multiring basin. Instead, repeated thrusting and necking events during transient crater collapse induce instances of fault reactivation, which diminish initial fault offsets and produce a series of discrete crustal blocks. Models assuming cooler thermal gradients lead to overly thin or non‐existent crust at the basin center, in contrast to observations. Even if crustal deficits were made up via a differentiating melt pool, the crust elsewhere would be overly thick, supporting the idea that the crustal structure of megabasins is primarily associated with transient crater collapse. We conclude that the transition to a megabasin morphology on terrestrial planetary surfaces, like the multiring transition, is dependent upon the size of the basin compared to the lithospheric thickness.
Funder
Planetary Science Division
Publisher
American Geophysical Union (AGU)
Subject
Space and Planetary Science,Earth and Planetary Sciences (miscellaneous),Geochemistry and Petrology,Geophysics