| Abstrakt: |
Mars early crust is more complex than homogenously basaltic with evolved magmatism evidenced by intermediate and felsic igneous rocks found in various locations in the southern hemisphere and martian meteorites. Geophysical constraints argue against a dense thick basaltic crust in the southern hemisphere, rather consistent with a buried light crust (<3,100 kg m−3), possibly evolved, underneath a basaltic surface. One of the oldest crustal components accessible at the surface of Mars, Terra Cimmeria/Sirenum (TSC), presents geochemical anomalies potentially suggesting an evolved crustal component at depth. Using visible/near infrared spectroscopy, we identify nine excavated feldspar‐rich locations in this region, and thermal infrared data suggest a silica concentration corresponding to intermediate compositions. The low density of such terrains compared to basalts supports that TSC crustal component is evolved. Early crusts of planetary bodies in the solar system were thus not restricted to basaltic compositions, and evolved crusts might have been widespread. Plain Language Summary: Despite basaltic terrains widely observed at the surface of Mars, recent missions and a martian meteorite evidenced evolved magmatism (SiO2 > 53 wt.%), highlighting a heterogeneous crust on Mars. Geophysical and seismic constraints suggest the presence of buried evolved crustal components with low density compared to basalts, below subsequent basaltic lava flows. We investigate one of the most ancient region accessible at the surface of Mars using visible/near infrared and thermal infrared spectroscopy to verify that hypothesis. Nine feldspar‐rich terrains excavated by impact, fractures, and erosion are detected with evolved compositions. One of the oldest crustal component on Mars thus presents an evolved crust underneath the surface, in agreement with geophysical/seismic data. Hence, planetary bodies early crusts are not systematically basaltic as generally thought, but could be evolved too as inferred from several rare evolved meteorites (e.g., Erg Chech 002). Key Points: Nine feldspar‐rich regions of intermediate silica compositions were identified in Terra Sirenum/Cimmeria (TSC)The feldspar‐rich terrains are excavated crustal materials supporting a pre‐Noachian evolved crust at TSCAn early evolved crust on Mars suggests that early crusts in the solar system were not restricted to basaltic [ABSTRACT FROM AUTHOR] |
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