講演情報
[PPS07-P13]CUMULATES IN VISNIR: A PERSEVERANCE ROVER SUPERCAM ANALOG.
*Conner Lesh1、Linda C Kah1 (1.University of Tennessee, Knoxville)
キーワード：
mars、analog、cumulate、visnir、stillwater、jezero
Introduction: Perseverance uses SuperCam visible to near infrared (VISNIR) reflectance spectroscopy as a rapid reconnaissance tool to characterize outcrops and prioritize targets. Mafic cumulate rocks record crustal differentiation on Earth and Mars, but they are difficult to diagnose from natural, weathered surfaces where coatings and alteration obscure primary igneous textures. We use VISNIR spectra of mafic to ultramafic cumulates from the Stillwater Complex, Montana, to test which cumulate-related signatures are detectable on natural surfaces, and how strongly hydration and oxidation overprint them, as a first step toward an Earth analog framework for interpreting possible cumulates in Jezero crater.
Motivation: Jezero exposes an extensive olivine-rich unit, Séítah, whose origin remains debated. Its mineralogy and apparent layering are consistent with an igneous cumulate interpretation [1], while texture and subsurface stratification have been used to argue for sedimentary or volcaniclastic reworking [2,3,4]. Rover-scale constraints make it essential to understand how diagnostic cumulate properties express themselves in VISNIR data.
Instruments and Methods: SuperCam measures VISNIR reflectance from 0.4 to 0.85 µm and 1.3 to 2.6 µm, with partial bridging to 1.0 µm via Mastcam Z filters [5,6]. We collected analog spectra with a Spectral Evolution OreXpress SM 3500 (0.35 to 2.5 µm). We analyzed six pyroxene-rich cumulates, one norite, and one banded cumulate from the Stillwater Complex near Nye, Montana. For each rock, 30 to 50 points were measured on the natural surface and averaged. Spectra were processed in MATLAB to quantify the ~1 µm mafic absorption, the ~0.4 µm Fe3+ feature, and hydration related bands near 1.4, 1.9, and 2.3 µm, and to compute a hydration to mafic ratio for comparing alteration band strength to primary mafic absorption.
Results and Discussion: All samples show features near ~0.4, ~1.0, ~1.4, ~1.9, and ~2.3 µm, with variable depths. The 0.4 µm feature indicates ferric oxidation or coatings, the 1.0 µm feature tracks Fe2+ in mafic silicates (dominantly pyroxene), and co-occurring 1.4, 1.9, and 2.3 µm absorptions are most consistent with Mg rich phyllosilicates from aqueous alteration of mafic protoliths, such as serpentine or chlorite. In plagioclase-rich norites, the 1.0 µm band is flattened and shifted to longer wavelengths, and high albedo plagioclase can exaggerate apparent hydration band depths, an important caveat for rover interpretation.
Implications: Hydration and oxidation signatures alone do not discriminate igneous cumulates from sedimentary or volcaniclastic materials, because alteration can overprint any protolith. Instead, SuperCam VISNIR provides reconnaissance context that should be integrated with SuperCam LIBS, PIXL, SHERLOC, and imaging, where the 1.0 µm band constrains primary mafic silicates, the 1.4 and 1.9 µm bands constrain hydrated phases, the 2.3 µm band constrains Mg-OH bearing alteration products, and the 0.4 µm feature flags ferric coatings, together generating testable mineralogical predictions for Séítah and other candidate cumulates [1,2,3,4].
Future Work and Acknowledgments: A wider array of Mars 2020 analog instruments will be used to analyze this suite of Stillwater complex cumulate rocks that includes WATSON, Mastcam-Z, SuperCam LIBS, and PIXL, on their natural surface, fresh surface, and cut sections. I will also explore spectral subtraction and unmixing to better isolate protolith signatures. This work was funded by NASA’s Mars 2020 mission, SHERLOC investigation.
References: [1] Liu et al. (2022) Science, 377, 1513-1519. [2] Hamran et al. (2022) Sci. Adv., 8, eabp8564. [3] Nosarzewski et al. (2023) LPSC LIV, Abstract 2999. [4] Clavé et al. (2023) JGR Planets, 128, e2022JE007463. [5] Fouchet et al. (2022) Icarus, 373, 114773. [6] Wiens et al. (2021) Space Sci. Rev., 217, 4.
Motivation: Jezero exposes an extensive olivine-rich unit, Séítah, whose origin remains debated. Its mineralogy and apparent layering are consistent with an igneous cumulate interpretation [1], while texture and subsurface stratification have been used to argue for sedimentary or volcaniclastic reworking [2,3,4]. Rover-scale constraints make it essential to understand how diagnostic cumulate properties express themselves in VISNIR data.
Instruments and Methods: SuperCam measures VISNIR reflectance from 0.4 to 0.85 µm and 1.3 to 2.6 µm, with partial bridging to 1.0 µm via Mastcam Z filters [5,6]. We collected analog spectra with a Spectral Evolution OreXpress SM 3500 (0.35 to 2.5 µm). We analyzed six pyroxene-rich cumulates, one norite, and one banded cumulate from the Stillwater Complex near Nye, Montana. For each rock, 30 to 50 points were measured on the natural surface and averaged. Spectra were processed in MATLAB to quantify the ~1 µm mafic absorption, the ~0.4 µm Fe3+ feature, and hydration related bands near 1.4, 1.9, and 2.3 µm, and to compute a hydration to mafic ratio for comparing alteration band strength to primary mafic absorption.
Results and Discussion: All samples show features near ~0.4, ~1.0, ~1.4, ~1.9, and ~2.3 µm, with variable depths. The 0.4 µm feature indicates ferric oxidation or coatings, the 1.0 µm feature tracks Fe2+ in mafic silicates (dominantly pyroxene), and co-occurring 1.4, 1.9, and 2.3 µm absorptions are most consistent with Mg rich phyllosilicates from aqueous alteration of mafic protoliths, such as serpentine or chlorite. In plagioclase-rich norites, the 1.0 µm band is flattened and shifted to longer wavelengths, and high albedo plagioclase can exaggerate apparent hydration band depths, an important caveat for rover interpretation.
Implications: Hydration and oxidation signatures alone do not discriminate igneous cumulates from sedimentary or volcaniclastic materials, because alteration can overprint any protolith. Instead, SuperCam VISNIR provides reconnaissance context that should be integrated with SuperCam LIBS, PIXL, SHERLOC, and imaging, where the 1.0 µm band constrains primary mafic silicates, the 1.4 and 1.9 µm bands constrain hydrated phases, the 2.3 µm band constrains Mg-OH bearing alteration products, and the 0.4 µm feature flags ferric coatings, together generating testable mineralogical predictions for Séítah and other candidate cumulates [1,2,3,4].
Future Work and Acknowledgments: A wider array of Mars 2020 analog instruments will be used to analyze this suite of Stillwater complex cumulate rocks that includes WATSON, Mastcam-Z, SuperCam LIBS, and PIXL, on their natural surface, fresh surface, and cut sections. I will also explore spectral subtraction and unmixing to better isolate protolith signatures. This work was funded by NASA’s Mars 2020 mission, SHERLOC investigation.
References: [1] Liu et al. (2022) Science, 377, 1513-1519. [2] Hamran et al. (2022) Sci. Adv., 8, eabp8564. [3] Nosarzewski et al. (2023) LPSC LIV, Abstract 2999. [4] Clavé et al. (2023) JGR Planets, 128, e2022JE007463. [5] Fouchet et al. (2022) Icarus, 373, 114773. [6] Wiens et al. (2021) Space Sci. Rev., 217, 4.