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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. E7, 5069, doi:10.1029/2002JE002013, 2003

Hansteen Alpha: A volcanic construct in the lunar highlands

B. Ray Hawke

Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii, USA

D. J. Lawrence

Los Alamos National Laboratory, Los Alamos, New Mexico, USA

D. T. Blewett

NovaSol, Honolulu, Hawaii, USA

P. G. Lucey

Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii, USA

G. A. Smith

Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii, USA

P. D. Spudis

Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA

G. J. Taylor

Hawaii Institute of Geophysics and Planetology, University of Hawaii, Honolulu, Hawaii, USA

Abstract

We have used data from the Clementine and Lunar Prospector spacecraft in conjunction with near-IR reflectance spectra collected with Earth-based telescopes to study the composition and origin of Hansteen Alpha, an arrowhead-shaped highlands feature located on the southern margin of Oceanus Procellarum. Hansteen Alpha is a member of a class of lunar spectral anomalies (Red Spots) that are characterized by a relatively high albedo and a strong absorption in the UV. It has been suggested that at least some of these spectral anomalies were produced by nonmare volcanism. The stratigraphic relationships among the geologic and compositional units in the region show that Hansteen Alpha was emplaced by extrusive igneous processes. The Imbrian-aged craters Hansteen and Billy emplaced relatively FeO- and TiO₂-rich ejecta. Hansteen Alpha exhibits much lower FeO and TiO₂ values. If Hansteen Alpha was present prior to the Billy and Hansteen impact events, it should have been covered with FeO- and TiO₂-rich ejecta because it is located within one crater diameter of the rim crest of each crater. Since it is not, Hansteen Alpha was superposed on these ejecta units. Nonmare volcanism is the only viable process for the formation of Hansteen Alpha. The morphology and surface texture of Hansteen Alpha is similar to many terrestrial features of dacitic and rhyolitic composition formed by extrusions of relatively viscous lavas. Such highly evolved compositions should be very enriched in Th, but Hansteen Alpha exhibits Th abundances of ∼6 ppm. Hence Hansteen Alpha is not composed of a highly evolved highlands lithology.

Received 19 November 2002; accepted 29 April 2003; published 5 July 2003.

Index Terms: 8450 Volcanology: Planetary volcanism (5480); 6250 Planetology: Solar System Objects: Moon (1221); 5410 Planetology: Solid Surface Planets: Composition; 1060 Geochemistry: Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008); 5464 Planetology: Solid Surface Planets: Remote sensing.

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Citation: Hawke, B. R., D. J. Lawrence, D. T. Blewett, P. G. Lucey, G. A. Smith, P. D. Spudis, and G. J. Taylor (2003), Hansteen Alpha: A volcanic construct in the lunar highlands, J. Geophys. Res., 108(E7), 5069, doi:10.1029/2002JE002013.

Copyright 2003 by the American Geophysical Union.