Through a Global Forum initiative at Brown University, Professor Lew Ashwal from Witwatersrand University in South Africa visited the Department of Geological Sciences from July 16 to 27th. The overall goal of the Forum was to initiate long-term research links with prominent universities around the globe. Lew is a world expert on terrestrial anorthosite formation and his visit sparked broad interest and support across Brown/MIT NLSI for discussions on the formation of lunar anorthosite. During Lew’s visit, the current knowledge of the origin of both terrestrial and lunar anorthosites was reviewed and interdisciplinary research directions discussed.
Lew’s visit began with two extended lectures by him on terrestrial anorthosites, followed by a three-day field trip to anorthosite regions in the Adirondacks. This was to bring participants up to speed on the current state of knowledge about terrestrial anorthosites and lay the foundation for comparing to lunar anorthosites. Jim McLelland (Colgate University) led the field trip and lectured on the formation of the Adirondack massif. A few additional photos of the field trip are posted on facebook.
The field trip was followed by a one-day symposium in which both graduate students and faculty focused on the current state of knowledge about lunar anorthosite formation. The formal symposium drew to a close with the final talk given by Prof. Ashwal, summarizing terrestrial anorthosites and making connections to their lunar brethren.
The symposium discussion was very lively and subjects ranged widely from detailed petrology of samples to global dynamics of magma oceans. The consensus among participants was that the new compositional data from remote analysis of lunar mineralogy is most consistent with a global magma ocean (as opposed to serial plutonism). A few people raised questions about how the new-found H2O in the lunar mantle would change our models of anorthosite formation. Also, the issue of how the very pure anorthosite (with scarce mafic minerals) widely observed across the Moon is formed was also discussed. In comparing the lunar anorthosites to terrestrial examples, it was unclear whether they were analogous to Archean anorthosites, which have similarly high An contents, but are thought to be derived from hydrous magmas. Or whether the Proterozoic anorthosite massifs are better analogs for lunar magma ocean evolution, despite having substantially lower An contents. One conclusion was that more experimental work is necessary to quantify fractionation of basaltic liquids at depth, with varying amounts of H2O as well as additional work to identify the type and scale of petrographic relations of other lithologies found with anorthosite across the lunar surface.
“The combination of activities provided a highly productive environment that stimulated thought-provoking interactions among Faculty, students, and visitors about the interconnections of fundamental processes that are common to the Earth and the Moon. Was also great fun!” Said NLSI Team lead Dr. Carle Pieters.
Posted by: Soderman/NLSI Staff
Source: NLSI Team/Brown-MIT