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Identification and Description of a Silicic Volcaniclastic Layer in Gale Crater, Mars, Using Active Neutron Interrogation
Author(s) -
Czarnecki S.,
Hardgrove C.,
Gasda P. J.,
Gabriel T. S. J.,
Starr M.,
Rice M. S.,
Frydenvang J.,
Wiens R. C.,
Rapin W.,
Nikiforov S.,
Lisov D.,
Litvak M.,
Calef F.,
Gengl H.,
Newsom H.,
Thompson L.,
Nowicki S.
Publication year - 2020
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1029/2019je006180
Subject(s) - geology , pyroclastic rock , silicic , impact crater , volcanic glass , tridymite , mars exploration program , magma , mineralogy , lava , scoria , geochemistry , sedimentary rock , volcano , astrobiology , volcanic rock , cristobalite , quartz , paleontology , physics
The Dynamic Albedo of Neutrons instrument aboard the Mars Science Laboratory rover, Curiosity, has been used to map a stratigraphically conformable layer of high‐SiO2material in Gale crater. Previous work has shown that this material contains tridymite, a high‐temperature/low‐pressure felsic mineral, interpreted to have a volcanic source rock. We describe several characteristics including orientation, extent, hydration, and geochemistry, consistent with a volcaniclastic material conformably deposited within a lacustrine mudstone succession. Relationships with widely dispersed alteration features and orbital detections of hydrated SiO2suggest that this high‐SiO2layer extends at least 17 km laterally. Mineralogical abundances previously reported for this high‐SiO2material indicated that hydrous species were restricted to the amorphous (non‐crystalline) fraction, which is dominated by SiO2 . The low mean bulk hydration of this high‐SiO2layer (1.85 ± 0.13 wt.% water‐equivalent hydrogen) is consistent with silicic glass in addition to opal‐A and opal‐CT. Persistent volcanic glass and tridymite in addition to opal in an ancient sedimentary unit indicates that the conversion to more ordered forms of crystalline SiO2has not proceeded to completion and that this material has had only limited exposure to water since it originally erupted, despite having been transported in a fluviolacustrine system. Our results, including the conformable nature, large areal extent, and presence of volcanic glass, indicate that this high‐SiO2material is derived from the product of evolved magma on Mars. This is the first identification of a silicic volcaniclastic layer on another planet and has important implications for magma evolution mechanisms on single‐plate planets.