Article

Orbital Identification of Carbonate-Bearing Rocks on Mars

Department of Geological Sciences, Brown University, Providence, RI02912, USA.
Science (Impact Factor: 31.48). 01/2009; 322(5909):1828-32. DOI: 10.1126/science.1164759
Source: PubMed

ABSTRACT Geochemical models for Mars predict carbonate formation during aqueous alteration. Carbonate-bearing rocks had not previously
been detected on Mars' surface, but Mars Reconnaissance Orbiter mapping reveals a regional rock layer with near-infrared spectral
characteristics that are consistent with the presence of magnesium carbonate in the Nili Fossae region. The carbonate is closely
associated with both phyllosilicate-bearing and olivine-rich rock units and probably formed during the Noachian or early Hesperian
era from the alteration of olivine by either hydrothermal fluids or near-surface water. The presence of carbonate as well
as accompanying clays suggests that waters were neutral to alkaline at the time of its formation and that acidic weathering,
proposed to be characteristic of Hesperian Mars, did not destroy these carbonates and thus did not dominate all aqueous environments.

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