Mineralogy of the Glen Torridon Region as detailed by the Mars Science Laboratory CheMin Instrument

Stratigraphically below the Greenheugh pediment, the Mars Science Laboratory (MSL) Curiosity rover traversed through a succession of ancient fluvio-lacustrine deposits within the Glen Torridon (GT) region of Mount Sharp. The GT has been subdivided into three informal groups known as the Jura member, the Knockfarril Hill member, and the Fractured Intermediate Unit (FIU). The drill fines of 6 GT targets were analyzed by the CheMin X-ray diffractometer for mineralogy. Drilled samples include Aberlady (AL) and Kilmarie (KM) from the Jura member, two different samples of Glen Etive (GE and GE2) from the Knockfarril Hill member, the Glasgow (GG) target from the FIU, and Hutton (HU) from the contact of the FIU and the pediment. HU is discussed in a companion CheMin abstract. GT samples are some of the most phyllosilicate-rich targets explored by Curiosity, with abundances ranging from 23 to 34 wt%. Ferric smectite is the dominant phyllosilicate identified in the suite of GT targets, thus confirming orbital mineral identifications based on near-infrared spectra, and consistent with weathering in an oxidizing, open system environment. In addition to this smectitic phase, a mixed-layer phyllosilicate with a basal spacing of 9.3 Å, identified as Fe-bearing talc-serpentine, was detected in KM for the first time along Curiosity's traverse. This talc-serpentine is likely detrital in origin and the Fe content suggests mafic source material that experienced serpentinization. Sharp quartz reflections, suggesting a discrete and well crystalline phase, in the GG XRD pattern may also provide evidence of detrital input from either an evolved provenance or associated with the higher-temperature alteration that formed the talc-serpentine. The GG target also contains the most hematite in the GT samples with broad XRD peaks, suggesting this phase is very fine-grained. Reflecting on Curiosity's previous campaign in Vera Rubin ridge (VRR), where coarse-grained, gray hematite was linked to diagenetic fluids with elevated temperatures, the fine-grained variety of hematite and higher ferric smectite abundances in the GT may suggest limited diagenesis compared to VRR. These preliminary findings for GT mineralogy suggest a window in the rock record that preserves evidence for open system weathering and a more diverse source rock lithology.