Mathematics – Logic
Scientific paper
May 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agusm.p41b..02l&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #P41B-02
Mathematics
Logic
6250 Moon (1221)
Scientific paper
Introduction: This paper reviews evidence from Apollo missions, returned lunar samples, and earth-based reflection spectroscopy, bearing on the composition, structure, and origin of the "highland" crust (actually the global crust, underlying the maria as well as the nominal highlands). Current views are that the crust is primarily anorthosite, formed in a magma ocean, with a layered structure formed of superimposed impact ejecta blankets. Several lines of independent evidence contradict this concept. Structure: Retrospective analysis of lunar surface photos taken by the astronauts on Apollos 15, 16, and 17 reveal pervasive layering, best exposed on the Apennine Front near the Apollo 15 landing site, at Silver Spur. These layers, more than 90, average 16 meters in thickness. Similar layers were found on photos from Apollo 16, of Stone Mountain, and from Apollo 17, of the Sculptured Hills. In thickness, geometry, and regularity they are similar to basaltic lava flows of the Columbia Plateau, the island of Hawaii, and Kauai. The generally- accepted explanation of these layers as overlapping ejecta blankets from mare basins or craters is contradicted by their number and thickness, and the fact that no such layers were found by seismic methods in the Fra Mauro Formation (Imbrium ejecta). Composition: Remote sensing data, from Apollo orbital X-ray fluorescence surveys and earth-based reflection spectroscopy, show that anorthosite is a subordinate constituent of the lunar crust, not the major one. Returned lunar samples support this, despite the masking effects of pervasive brecciation and impact melting. Dominant highland rock types are basalt, frequently feldspar-rich; norite; troctolite; KREEP; and anorthosite, the bulk surface composition corresponding chemically to a high-Al norite. Five-km resolution reflectance traverses by Pieters and others show that anorthosite is a widespread but subordinate component, occurring in central peaks that probably expose anorthosite intrusions. The "magma ocean" concept is petrologically valid but probably applicable only to these intrusions. Conclusion: It is proposed that the highland crust layers are flows of alumnum-rich noritic lavas, collectively several kilometers thick, and that they represent a "first differentiation" of the Moon by massive global volcanism in the first few hundred million years of the Moon's history,concurrent with intense impact cratering.
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