Igneous compositions preserved in Gale crater's geological record

Abstract

Gale crater’s geological record has two stratigraphic groups deposited in an early Hesperian fluviolacustrine system[1, 2]. The Bradbury Group (sols 1-750) is dominated by fluvial conglomerate and sandstone with lacustrine mudstone in Yellowknife Bay[1,2]. The Mt Sharp Group (Murray formation) is mainly well laminated lacustrine mudstone[2]. We have analysed NASA Curiosity rover ChemCam[3] observation point compositions for targets up to sol 1482 that have hit in situ host rock lacking obvious diagenetic features. ChemCam data are plotted on scatter and density contour plots for their associated stratigraphic units to replicate whole rock composition[4]. Our results show that coarse grained (>1 mm) targets are dominated by trachybasalt[5] and subalkaline basalt[5] igneous endmembers. Sandstone (0.062 – 1 mm) targets indicate a mixture of subalkaline basalt[5], trachybasalt[5] and potassic igneous[6] sources. Finally, mudstone units are dominated by the subalkaline basalt[5] at Yellowknife Bay, and a relatively silica-rich, subalkaline basalt endmember in most of the Murray formation[4], with an even more silica-rich volcanic component at Marias Pass[7]. This demonstrates that Gale crater sediments record a variety of igneous compositions, with subalkaline basalts dominant, but also including lesser amounts of alkaline and silica oversaturated igneous components. References: [1] Grotzinger et al. (2014) doi:10.1126/science.1242777, [2] Grotzinger et al. (2015) doi:10.1126/science.aac7575. [3] Wiens et al. (2012) doi:10.1007/s11214-012-9902-4. [4] Bedford et al. (subm.) GCA. [5] Edwards et al., (2017) MAPS, doi:10.1111/maps.12953. [6] Treiman et al. (2016) doi: 10.1002/2015JE004932. [7] Morris et al. (2016) doi: 10.1073/pnas.1607098113