Spectral evidence for alkaline rocks and compositional diversity among feldspathic light-toned terrains on Mars

Previously reported plagioclase detections in the near-IR (NIR) are associated with crater-exposed subsurface materials as well light-toned bedrock plains poor crater retention. Because Fe-bearing has a weak ~1.25 μm feature that can be easily obscured by stronger absorptions most pyroxenes and olivines, candidate lithologies must dominated (e.g., anorthosite) and/or spectrally neutral quartz, K-spar, some volcanic glasses, Fe2+−poor pyroxenes). To further understand NIR detections, we investigated spectral nature of these THEMIS CRISM data, focused on six exposures Nili Patera caldera Terra Sabaea (~20–25°S, ~40–47°E). Thermal infrared data from discriminate between lithologies; however, it lower spatial resolution (100 m/pix) than (18 thus increasing likelihood subpixel mixing rock sand. We forward modeled range mixtures mafic sands alkaline subalkaline spanning total alkali-silica diagram to identify suite compositions could plausibly fit observations. In Patera, feldspathic likely consist plagioclase-dominated composition silica content below ~60 wt%. However, at least one location Sabaea, significant alkali feldspar (trachyandesitic trachytic) contents up ~60–65% inferred contain straddle boundary intermediate-to-felsic highly silicic or quartz-bearing rhyolites, granite, dacites) not locations studied. Last, results indicate NIR-based differing lithologies.