Saturday, April 27, 2013

Ancient Rocks of the Isidis Basin and Libya Montes Exposed and Preserved by Hashir Crater

The focus of this HiRISE observation is the inner portion of the approximately 9-kilometer diameter Hashir Crater.

Hashir is located at 84.56 degrees east, 3.63 degrees north within the transition from the vast Isidis Basin plains (Isidis Planitia) to the great circumferential mountains of Libya Montes (i.e., the ancient and dissected mountains raised-up from the Isidis-forming event).

Hashir is of particular interest to scientists because there are several spectral units that are characteristic of the Isidis Basin/Libya Montes region that are exposed or preserved within it. Hashir and its surroundings have been spectrally characterized by multiple orbiting spectrometers spanning almost 25 years, including: Phobos 2-ISM, MGS-TES, MO-THEMIS, MEx-OMEGA and most recently by MRO-CRISM. The results from the analysis of these data indicate the presence of surface materials rich in olivine, pyroxene, clays (Fe/Mg-smectites) and carbonate. The latter two are of particular interest as they were likely formed by alteration of the ancient basaltic rocks through interactions with water. The Fe/Mg-phyllosilicates and carbonate are often associated with olivine in CRISM and HiRISE images because these alteration minerals are observed where the olivine-rich lavas have been eroded away.

This 3D perspective image of Hashir Crater was generated by combining color from CRISM with the high-resolution of a gray-scale HiRISE RED image draped over a HiRISE stereo derived digital terrain model (DTM) with a 3x vertical enhancement. This close-up view from the south (looking north) illustrates the occurrence of the pyroxene-bearing caprock in blue on top of olivine-bearing layered bedrock in green, which in turn overlies a Fe/Mg-smectite-bearing unit in red. The hilly red unit is interpreted to be the central uplift of Hashir Crater, which are rocks uplifted and exposed by the crater-forming event. The blue and green units are more recent lava flows or impact melt deposits from Isidis that filled in Hashir after it formed and have been since eroded back by the high winds in the Libya Montes region.

Image credit: NASA/JPL/University of Arizona/USGS

No comments: