A Likely Formation Mechanism for the Hematite-rich Spherules in the Equatorial Region of Western Mars

Introduction: The gray crystalline hematite on Mars was detected in three regions, Sinus Meridiani, Aram Chaos and Valles Marineris by the thermal emission spectrometer (TES) onboard the Mars Global Surveyor (MGS) orbiter [e.g.1, 2]. The Mars Exploration Rover (MER) Opportunity confirmed that hematite-rich spherules (~ 4.2 mm) are embedded in sulfur-rich layered outcrops and accumulated on the surface as lag deposits of whole and broken spherules at Sinus Me-ridiani [e.g. 3-5]. The formation mechanism of hema-tite-rich spherules has been discussed in a wide range of possible processes since then. Here, we argue for an alternative mechanism that the spherules were originally formed in Valles Marineris and transported to Meridiani Planum (named Sinus Meridiani as well) accompanied with accretion of finer volcanic materials , abrasion of basaltic fragments and break down of whole crystalline spherules during the wash-out flows from Valles Marineris to Meridiani Planum. This is consistent with the hypothesis of the origin and redistribution of sulfates in the equatorial region of western Mars [6]. The proposed formation of the sulphates and associated hematite-rich spherules in the Equatorial Region of Western Mars: Sulfates were detected in situ by the lander Opportunity in surface sands and underlying sulfate-rich sedimentary deposits in Merid-iani Planum. The OMEGA/MEX identified massive sulfate outcrops alternating with layered volcanic deposits in Valles Marineris. It was proposed [6] that sulfates formed as evaporites in enclosed standing bodies of water in the Valles Marineris area following the early alteration of Martian basaltic crust, were then elevated by the Tharsis uplift, and transported together with rock materials to Meridiani Planum by periodic outbursts of water, where they were deposited as sediments. The model comprehensively addresses all forms of sulfate occurrences near the equator in the western Martian hemisphere and relates it to physi-ographic processes (volcanic, tectonic and sedimen-tary) affecting the Martian surface and reasonably explains the occurrences of sulfates, and the fate and source of sulfates in the region. During the precipitation of massive sulfate evaporites, volcanic materials erupted and were deposited alternately to form the dark layers in Valles Marineris before Tharsis was uplifted. The oxidation and crystallization of volcanic materials in the dark layers due to hydrothermal fluids produced crystalline