Dataset Information

Areally Extensive Surface Bedrock Exposures on Mars: Many Are Clastic Rocks, Not Lavas.

ABSTRACT: Areally extensive exposures of intact olivine/pyroxene-enriched rock, as well as feldspar-enriched rock, are found in isolated locations throughout the Martian highlands. The petrogenetic origin(s) of these rock units are not well understood, but some previous studies favored an effusive volcanic origin partly on the basis of distinctive composition and relatively high thermal inertia. Here we show that the regolith development, crater retention, and morphological characteristics for many of these "bedrock plains" are not consistent with competent lavas and reinterpret the high thermal inertia orbital signatures to represent friable materials that are more easily kept free of comminution products through eolian activity. Candidate origins include pyroclastic rocks, impact-generated materials, or detrital sedimentary rocks. Olivine/pyroxene enrichments in bedrock plains relative to surrounding materials could have potentially formed through deflation and preferential removal of plagioclase.

SUBMITTER: Rogers AD

PROVIDER: S-EPMC6310033 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Areally Extensive Surface Bedrock Exposures on Mars: Many Are Clastic Rocks, Not Lavas.

Rogers A Deanne AD Warner Nicholas H NH Golombek Matthew P MP Head James W JW Cowart Justin C JC

Geophysical research letters 20180220 4

Areally extensive exposures of intact olivine/pyroxene-enriched rock, as well as feldspar-enriched rock, are found in isolated locations throughout the Martian highlands. The petrogenetic origin(s) of these rock units are not well understood, but some previous studies favored an effusive volcanic origin partly on the basis of distinctive composition and relatively high thermal inertia. Here we show that the regolith development, crater retention, and morphological characteristics for many of the ...[more]

PMID: 30598561

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Project description:This report summarizes observations of returned Apollo rocks and soils, lunar surface images, orbital observations, and experimental impacts related to the erosion and comminution of rocks exposed at the lunar surface. The objective is to develop rigorous criteria for the recognition of impact processes that assist in distinguishing "impact" from other potential erosional processes, particularly thermal fatigue, which has recently been advocated specifically for asteroids. Impact in rock is a process that is centrally to bilaterally symmetric, resulting in highly crushed, high-albedo, quasicircular depressions surrounded by volumetrically prominent spall zones. Containing central glass-lined pits in many cases, such features provide distinctive evidence of impact that is not duplicated by any other process. Additional evidence of impact can include radial fracture systems in the target that emanate from the impact point and clusters of fragments that attest to the lateral acceleration and displacement of each one. It is also important to note that impact produces a wide variety of fragment shapes that might totally overlap with those produced by thermal fatigue; we consider fragment shape to be an unreliable criterion for either process. The stochastic nature of the impact process will result in exponential survival times of surface rocks; that is, rock destruction initially is relatively efficient, but it is followed by ever increasing surface times for the last rock remnants. Thermal fatigue, however, is essentially a thermal-equilibrium process. The corresponding distribution of survival times should be much more peaked in comparison, presumably Gaussian, and diagnostically different from that due to impact. Given the abundance of evidence that has been gleaned from returned Apollo rocks and soils, it is surprising how little has been learned about the impact process from the photography of rocks and boulders taken by the astronauts on the lunar surface. This suggests that it will require rocks and soils returned from asteroids to evaluate the relative roles of thermal versus impact-triggered rock erosion, particularly when both processes are likely to be operating.

Dataset Information

Areally Extensive Surface Bedrock Exposures on Mars: Many Are Clastic Rocks, Not Lavas.

Publications

Areally Extensive Surface Bedrock Exposures on Mars: Many Are Clastic Rocks, Not Lavas.

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