Did the Orientale impact melt sheet undergo large‐scale igneous differentiation by crystal settling?. Issue 21 (8th November 2016)

• Record Type: Journal Article
• Authors: Cassanelli, James P.; Head, James W.
• Is Part Of: Geophysical research letters. Volume 43:Issue 21(2016)
• Page Start: 11, 156
• Page End: 11, 165
• Publication Date: 2016-11-08
• Subjects: Moon -- impact melt -- lunar basin -- Orientale -- differentiation -- crystallization; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2016GL070425
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Significant quantities of shock‐induced melt are predicted to form during basin‐scale impact events and may contribute substantially to compositional variation in the lunar crust through differentiation processes. Knowledge of the evolution of impact melt sheets and the cooling and crystallization processes involved is therefore important to understanding the geology and petrology of the Moon. Here we perform a case study on the Orientale basin and investigate the possibility of differentiation of the impact melt sheet by assessing the thermal and physical processes that drive cooling and crystallization, focusing on crystal settling. Results predict that convective processes within the impact melt sheet enhance cooling and solidification and inhibit settling of crystals ~1.5 mm in diameter and smaller, preventing differentiation at or below this size. Impact melt sheet thickness is predicted to have minimal influence on crystallization history, suggesting that crystal size is the primary factor controlling lunar impact melt sheet differentiation. Key Points: Rapid convective cooling is predicted to cause solidification of the Orientale melt sheet in ~10 kyr Convection inhibits settling of crystals ~1.5 mm in diameter and smaller, preventing fractional crystallization and differentiation Dominant crystal size is predicted to be the primary factor controlling impact melt sheet crystallization and differentiation