Tuesday, February 19, 2013

A fascinating effusive dome in Mare Vaporum

An effusive non-monogenetic volcanic dome super-positioned on a ghost crater near the north boundary of Mare Vaporum. LROC Narrow Angle Camera (NAC) mosaic M18144897LR, LRO orbit 11810, January 14, 2012; 1.29 meters resolution, mid-afternoon illumination incidence angle 66.7° imaged from 128.62 km [NASA/GSFC/Arizona State University].
Raffaello Lena and Barry Fitz-Gerald

We report a volcanic structure located some 40 kilometers west-southwest of the Yangel crater (9 km, 16.957°N, 4.688°E) in Mare Vaporum.

This dome (16.4°N, 3.3°E) lies immediately south of a mare inundated "ghost crater" approximately 7.5 km in diameter and appears to have partially affected part of that craters southern rim.

SELENE-1 (Kaguya), Chang'E-2 and Clementine albedo imagery clearly display dark pyroclastic material distributed upon the inner slope of the ruined ghost crater and adjacent to the north of the prominent dome, suggesting an ash type deposit. On the summit, a shallow depression is located, which likely corresponds to the vent or a collapse feature.

A presumably non-monogenetic mode of formation may be responsible for the peculiar shape of the dome, consisting of two layers, as shown in the derived data.

With a diameter of 5.2 kilometers and a height of 620 meters the dome appears to show evidence of mulch-phased activity modification from regional tectonic movements. Spectral analysis released on the calibrated and normalized Clementine UV/VIS and NIR reflectance data shows a LPD (Lighting Power Density) characteristic of pyroxenes and olivine.

LROC NAC view of the study area showing the 620 meter-high dome (1) with a possible debris apron (1a), partially submerged ghost crater (2) and its rim (3), area of uplift (4), merger of the debris apron of dome with the ghost crater wall (5), possibly an avalanche scar (6) and dark mantle deposits on the inner crater wall (7). (The yellow rectangle encompasses a field of view at considerably higher resolution in the next image.) LROC NAC mosaic M181144987LR [NASA/GSFC/Arizona State University].
Much closer look at the contact zone at the north side of the dome and the presumably older ghost crater, over its rim and wall. A 1.6 km meter field of view from LROC NAC mosaic M168183822LR, spacecraft orbit 9919, August 17, 2011; incidence angle 42.22° at 40 cm per pixel resolution (visible in next image - field of view in yellow rectangle above) from 24.42 km [NASA/GSFC/Arizona State University].
Dark mantle material at area of contact between the dome of interest and the ghost crater rim and wall, possibly affected by an avalanche, visible in this 233 meter-wide field of view at full resolution from LROC NAC mosaic M168183822LR [NASA/GSFC/Arizona State University].
According to its irregular shape, with the presence of two layers, the dome presumably formed during several stages of effusion, a process that may build up steep edifices, like in the Marius hills.

In this scenario we argue that the examined region has undergone an effusive process (in several eruption phases), before forming a steeper construct (average slope around 13°) and a subsequent explosive phase of volcanism forming the dark pyroclastic deposit. 

Representing this thinking the dome resembles some of the steeper domes among the Marius Hills, raising questions about sources of magma on the Moon's surface. A complete work is ongoing reporting our results collected by making use of LRO WAC images, SELENE-1 and Clementine multispectral data, the LOLA digital elevation model and the LROC WAC-based GLD100 DTM.

LROC QuickMap 3D relative elevation demonstration of the roughly 150 sq. km study area (top) Chang'E-3 global 40 meter low incidence albedo photography (center left) LRO WAC-derived surface elevation plot of a west to east cross-section dome (center right) and imagery from SELENE-1 (Kaguya) at bottom center.
The albedo contrast becomes more apparent under a higher Sun. LROC (NAC) mosaic M1098830275LR, LRO orbit 14284, August 5, 2012; 1.28 meters resolution from 126.74 km [NASA/GSFC/Arizona State University].
Results from this study were featured by Charles Wood as Lunar Picture of the Day, February 15, 2012 and discussed in a forum post at Cloudy Nights Telescope Reviews.

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