An Evolved Crust in Early Mars

Using visible/near infrared and thermal infrared spectroscopy from CRISM, TES, and THEMIS, we located several locations in one of the most ancient regions of Mars, Terra Sirenum/Cimmeria, with feldspar-rich signatures. Based on THEMIS data, their composition is intermediate, suggesting the presence of feldspar-rich evolved rocks with (trachy-)andesitic compositions. This discovery adds up to the occurrence of intermediate igneous rocks and fragments in Gale crater and in the martian meteorite "Black Beauty", and suggest the presence of an evolved crust in one of the most ancient region of Mars.
Such evolved crust could either be primary, coming from the crystallization of an enriched mantle or the crystallization of a partial magma ocean, or secondary, coming from an Icelandic-like setting.

© ESA, NASA and M. Kornmesser

Traces of Explosive Volcanism Hidden in a Mudstone

The surprising detection of monoclinic tridymite in a silica-rich mudstone in Gale crater on Mars raised plenty questions regarding its formation mechanisms as monoclinic tridymite is extremely rare on Earth. Silicic volcanism and hydrothermal alteration are two scenarios that have been suggested in the literature and the debate is still ongoing. Reviewing the formation pathways of tridymite on Earth and running thermodynamic modeling, we propose pros and cons for each possible scenario considering the geological context of Gale crater, and the mineralogy and composition of the tridymite-bearing mudstone and rocks in the vicinity. We suggest that explosive volcanism on Mars was not restricted to basaltic plinian eruptions only, and the occurrence of tridymite suggests felsic explosive eruptions at the time Gale crater was still a lake.

Effects of Phosphorus on Martian Magmas

Phosphorus is 10 times more elevated in Mars primitive mantle than in Earth primitive mantle. Although crystallization experiments on terrestrial Fe-rich basalts showed that several % of P2O5 impacts basaltic crystallization sequence, we do not know how phosphorus influences martian magmas. Running piston-cylinder experiments on martian mantle compositions, we investigate the effects of phosphorus on liquid compositions and on residual mineral assemblage. We show that amounts of P2O5 as small as 0.2 wt.% dramatically influence primary melt compositions and the abundances of residual minerals in the mantle.

 Early Noachian Crust and Alkaline Magmatism

Although Mars was assumed to be basaltic for a long time, recent discoveries disrupt this vision. The martian meteorite Northwest Africa (NWA) 7034 and paired, along with the analyses of igneous rocks by the ChemCam instrument onboard Curiosity, evidenced evolved and alkaline igneous clasts and rocks dated from Noachian time. Yet, the widespread detection of orthopyroxene-rich Noachian terrains highly differs from felsic and alkaline magmatism. Reviewing detections of felsic and alkaline materials throughout the ancient Mars ​surface, we discuss such differentiated magmatism in a stagnant lid context, highlighting the co-occurrence of both orthopyroxene-rich rocks and alkaline-felsic rocks.

Magmatic Sources of Detrital Minerals

Detrital igneous minerals within sedimentary rocks of the Bradbury formation in Gale crater, Mars, provide interesting information regarding the nature of their igneous protoliths and the magmatic processes that could have formed them. Using ChemCam and CheMin instruments, which are onboard the Curiosity rover, MELTS thermodynamic models enable to reproduce the composition of detrital mineral from Bradbury. This study suggests that at least two distinct magmas coming from various degrees of melting of a mantle composition experienced crustal fractional crystallization. Detrital igneous minerals likely crystallized from an alkaline and a subalkaline magmas.

Trace Element Calibrations using the ChemCam Instrument

Onboard the Curiosity rover, the ChemCam suite has a laser induced breakdown spectrometer (LIBS) that allows to quantify elemental abundances of rocks and soils at distance (1.6 - 7 m from the rover) at a micrometer scale (350 - 550 µm). Using a large dataset from Los Alamos National Laboratory (LANL), we re-calibrated Li, Rb, Sr, and Ba and quantified for the first time Cu using univariate calibrations. Li, Rb, Sr, Ba and Cu concentrations can now be measured in all materials analyzed by LIBS since the beginning of Curiosity ​journey.

A Cu-Deposit in the Vicinity of Gale Crater

Elevated Cu concentrations (up to 1110 ppm) have been detected within K-sandstones at the Kimberley formation, Gale crater. We investigated which processes could have concentrated Cu within Kimberley rocks. We suggested the presence of a Cu-deposit at the source of the Kimberley sediments and concluded that at least two processes occurred:
- Within igneous rocks and sandstones, Cu-minerals potentially come from magmatic crystallization associated with hydrothermal circulation.
- In fracture fills, Cu and Zn are found in association with Mn-oxides that appear to have precipitated from highly oxidizing circum-neutral groundwater. 

Li, Rb, Sr, and Ba in Gale crater: Geological Implications

Enrichments of Li, Rb, Sr and Ba in rocks can be related to various igneous and weathering processes. Investigating their host minerals within igneous and sedimentary rocks analyzed by ChemCam within the first 1000 martian days, we explored how Li, Rb, Sr, and Ba concentrations can be that high. Low partial melting or late fractionation stage likely enhanced Rb and Ba concentrations within evolved magmas, and  weathering processes released Rb, Ba, Sr, and Li from their protoliths.