MRO Identification and Characterization of Volatile-rich Impact Melt Bodies on Mars: Implications for Valley Network and Phyllosilicate Formation

Details MRO Identification and Characterization of Volatile-rich Impact Melt Bodies on Mars: Implications for Valley Network and Phyllosilicate Formation MRO Identification and Characterization of Volatile-rich Impact Melt Bodies on Mars: Implications for Valley Network and Phyllosilicate Formation

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.4004t&link_type=abstract

American Astronomical Society, DPS meeting #39, #40.04; Bulletin of the American Astronomical Society, Vol. 39, p.493

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Scientific paper

Recent high-resolution images of geologically young and well-preserved impact craters acquired by HiRISE ( 30 cm-scale) and CTX ( 6 m-scale) have revealed compelling evidence for surficial impact melt-bearing bodies (e.g., ponds and flows) and a strong relationship with channels, alluvial fans, and possible "wet” debris flows. Channels appear to be directly sourced from melt ponds on terraces and ejecta. The 150x125 km diameter fresh crater Hale provides an example of fluvially modified terrain ( 60,000 km2), which we suggest resulted from the emplacement of volatile-rich ejecta. This close association between ejecta and fluvial morphologic features has implications for the formation of Martian valley networks and outflow channels in the Noachian.
Meanwhile, CRISM has mapped new phyllosilicate (e.g., phyllosilicates) occurrences at scales of 18 m. To date, they are all found in well-exposed Noachian highlands, many within reasonable proximity to the largest impact basins on Mars (e.g., Chryse, Isidis, Hellas). We suggest that there may also be a causal relationship between impact cratering (i.e., the heavy bombardment period) and the emplacement of these phyllosilicate-rich lithologies.
Phyllosilicates are quite abundant in terrestrial impactites, especially in the melt-bearing lithologies. Studies of terrestrial structures show that volatile-rich impact melts can produce phyllosilicates by several mechanisms, two of which may have prevailed on Noachian Mars: 1) solid-state devitrification of hydrous impact melts, and 2) impact-induced hydrothermal alteration. The former mechanism requires impact into a volatile-rich terrain, but does not require long-term water-rock interactions. The latter mechanism involves post-impact aqueous fluid movement and interaction for which there is some evidence from HiRISE.
Given the regional context of the Martian phyllosilicates provided by OMEGA and CRISM, the discovery of putative impact melts associated with Martian craters, and terrestrial analogue studies, we suggest that melt-bearing impactites may be a significant source of phyllosilicate bearing lithologies on Mars.

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