A NEW DISCOVERY OF 3.8 BILLION-YEAR-OLD HYDROTHERMAL VOLCANIC SEAFLOOR DEPOSITS ON MARS PROVIDES A WINDOW INTO EARLY EARTH

On Earth, much of the record of early geological processes in general, and seafloor processes specifically is completely lost to subduction or erosion. What record remains has been metamorphosed, obfuscating important clues to early environmental conditions, as well as seafloor processes that could have played an important role in abiogenesis. By contrast, Mars – a planet without plate tectonics and with much lower erosion rates throughout most of its history contains a more ancient and better preserved geologic record than the Earth.

Remote sensing-based studies have reported the detection of thousands of clay mineral deposits on Mars, but one site appears to be unlike any of the others found to date. Unusual deposits in the Eridania basin appear to correspond to ancient martian seafloor deposits. The Eridania deposits differ from other clay mineral deposits on Mars in terms of geologic context, mineralogy, morphology, texture, color and age.

Eridania basin is composed of a series of interconnected topographic sub-basins, together forming a closed basin 3x larger than the Caspian Sea. As described by previous authors, abundant geomorphological evidence shows that the basin was filled with water to a depth of >1.5 km. The most ancient deposits within these basins correspond to thick (>400 m), massive deposits with mottled color patterns and textures contained striking examples of boxwork and irregular veins. Based on hyperspectral infrared analysis, these deposits contain a combination of minerals analogous to those found in seafloor settings on Earth: saponite, Mg-rich nontronite and Fe-mica, talc/smectite mixed-layer clays, Fe-rich talc, silica, (Fe,Mg,Mn)-carbonates, and probably Fe-sulfides.

The suite of features observed in Eridania deep basin deposits is unlike anything observed elsewhere on Mars. Most ancient, large (40-200 km-diameter) basins on Mars have been resurfaced by subaerial mafic-ultramafic volcanism, and the Eridania basins were no exception. However, in Eridania, there happened to be a deep (>1 km) sea present when that volcanism occurred >3.8 Ga. The result was 10⁴-10⁵ km³ of intensely altered Fe-Mg-rich deposits analogous to those found in seafloor environments on Earth. These well-preserved deposits provide an invaluable window into early Earth processes.