T25 Tectonics and Volcanism in the Solar System

Sunday, 19 October 2014
8:00 AM - 12:00 PM
301

SILICIC NONMARE VOLCANISM AT THE MOON’S COMPTON-BELKOVICH VOLCANIC COMPLEX

Paper number: T25-3
Program: Technical Sessions
Time: 8:30 AM – 8:45 AM

Authors

Abstract

The Compton-Belkovich Volcanic Complex (CBVC), a 25x35 km feature located at 100°E and 60°N, has elevated topography, high reflectance, and high thorium and silica contents. Morphologies revealed by LRO’s Narrow Angle Camera (NAC) include volcanic cones and small domes or bulges, and irregular depressions. The overall topographic feature is elevated, has a large, irregular central depression, and coincides with the area of high reflectance. Volcanic construction occurred along the eastern and western flanks of the structure, and a cumulo dome with a 7 km wide base, 2 km wide summit, 1 km height, and a summit crater, occurs in the northern part of the complex. CBVC topography consists of eroded volcanic features, small cones of one to several km bases, irregular depressions, and several degraded impact craters with ~0.5 to 1.5 km diameters.

NAC-derived photometry indicates that areas within the CBVC are more reflective than surroundings by 15-30%. High-reflectance material extends 7-8 km E-SE, beyond the topographically elevated terrain, possibly a result of pyroclastic activity. The surroundings are feldspathic, similar to the Apollo 16 site. Areas within the CBVC have reflectance values that are as high or higher than other suspected silicic volcanic features such as the Gruithuisen Domes and Hansteen Alpha. Diviner data indicate that the CBVC has a silicic composition, thus we infer the mineralogy to be dominated by an SiO2 phase and K-feldspar, and/or Si-K-rich glass.

Analysis of the crater size-frequency distributions of the CBVC using NAC and WAC data yield model ages for the CBVC, surrounding regions, and nearby large craters. The age of Compton Crater (160 km diameter) is well constrained to ~3.6 Ga and is stratigraphically older than the CBVC. The young bounding age constraint is the superposition of secondary impact craters from nearby Hayn (87 km diameter) or Belkovich-K (47 km diameter), both Copernican craters. Our preferred model age for volcanic activity at the CBVC is 3.4-3.5 Ga.

M3 spectra are interpreted to indicate that the CBVC surface may be enriched in endogenic OH, possibly associated with pyroclastics. We infer that the CBVC formed by extrusion of lava from a near-surface magma chamber coupled with local collapse, emplacement of late silicic segregations, and possibly silicic pyroclastics.