Geochemical diversity in first rocks examined by the Curiosity Rover in Gale Crater: Evidence for and significance of an alkali and volatile‐rich igneous source

Abstract

[1] The first four rocks examined by the Mars Science Laboratory Alpha Particle X-ray Spectrometer indicate that Curiosity landed in a lithologically diverse region of Mars. These rocks, collectively dubbed the Bradbury assemblage, were studied along an eastward traverse (sols 46-102). Compositions range from Na-and Al-rich mugearite Jake_Matijevic to Fe-, Mg-, and Zn-rich alkali-rich basalt/hawaiite Bathurst_Inlet and span nearly the entire range in FeO* and MnO of the data sets from previous Martian missions and Martian meteorites. The Bradbury assemblage is also enriched in K and moderately volatile metals (Zn and Ge). These elements do not correlate with Cl or S, suggesting that they are associated with the rocks themselves and not with salt-rich coatings. Three out of the four Bradbury rocks plot along a line in elemental variation diagrams, suggesting mixing between Al-rich and Fe-rich components. ChemCam analyses give insight to their degree of chemical heterogeneity and grain size. Variations in trace elements detected by ChemCam suggest chemical weathering (Li) and concentration in mineral phases (e.g., Rb and Sr in feldspars). We interpret the Bradbury assemblage to be broadly volcanic and/or volcaniclastic, derived either from near the Gale crater rim and transported by the Peace Vallis fan network, or from a local volcanic source within Gale Crater. High Fe and Fe/Mn in Et_Then likely reflect secondary precipitation of Fe 3+ oxides as a cement or rind. The K-rich signature of the Bradbury assemblage, if igneous in origin, may have formed by small degrees of partial melting of metasomatized mantle. , et al. (2014), Geochemical diversity in first rocks examined by the Curiosity Rover in Gale Crater: Evidence for and significance of an alkali and volatile-rich igneous source,

Melting of the primitive martian mantle at 0.5–2.2 GPa and the origin of basalts and alkaline rocks on Mars

“…These samples were only analyzed with the ChemCam instrument (laser-induced breakdown spectroscopy), and precise bulk rock compositions are not available. However, chemical analyses highlighted an important compositional diversity ranging from basaltic to evolved and alkali-rich compositions similar to Jake_M (Sautter et al, 2014;Schmidt et al, 2014). Alkalibasalts and tholeiitic basalts might coexist in the same locality, as also observed in Gusev Crater.…”

“…The extreme alkali and Al 2 O 3 contents of Jake_M are easier to produce from a low degree melt (∼10 wt.%) produced at a pressure higher than 1.0 GPa. Metasomatism is often invoked to enrich the source of Jake_M in potassium (Schmidt et al, 2014;Stolper et al, 2013). Alternatively, we suggest that low-degree melts, produced from a mantle not anomalously enriched, can fractionate and eventually crystallize to form rocks similar to Jake_M.…”

Mars: a small terrestrial planet

“…22) (Foley et al 2003;Christensen et al 2005;Bandfield 2006;Wray et al 2013). Felsic and alkali-rich igneous rocks (including mugearite, granodiorite, and trachyte) have been identified on float rocks and conglomerate clasts by the Curiosity rover at Gale crater (Stolper et al 2013;Schmidt et al 2014;Sautter et al 2014Sautter et al , 2015. The meteorite breccia NWA 7034 (paired with NWA 7533 and NWA 7475 of similar origin) is a unique piece of ancient crust with zircon crystals dated at 4.43 Gy and contains differentiated felsic rocks with abundant feldspars showing a more complex mineralogy than any other martian meteorites (Agee et al 2013;Humayun et al 2013;Wittmann et al 2015).…”

Remote detection of past habitability at Mars-analogue hydrothermal alteration terrains using an ExoMars Panoramic Camera emulator

“…Aqueous environments interpreted from these rover datasets range from acid sulfate leaching at Meridiani Planum (Squyres and Knoll, 2005), hydrothermal alteration of volcaniclastic deposits at Home Plate, Gusev Crater (Hurowitz et al, 2006;Morris et al, 2008;Schmidt et al, 2009), and aqueous, potentially hydrothermal alteration of basaltic impact breccias (Arvidson et al, 2014;Squyres et al, 2012). NASA's Mars Science Laboratory rover Curiosity has identified a range of lithologies influenced by aqueous activity, ranging from transported volcaniclastics (Schmidt et al, 2014), fluvial conglomerates (Williams et al, 2013), and the fine-grained sedimentary deposits at Yellowknife Bay comprising primary basaltic minerals and alteration phases. The latter includes amorphous material, smectite clays, and sulfates (Vaniman et al, 2014), potentially indicative of sustained hydrous environments (Grotzinger et al, 2014).…”