Constraints on the emplacement of Martian nakhlite igneous rocks and their source volcano from advanced micro-petrofabric analysis

Abstract

Mars is a planet whose landscape has been created to a large degree by igneous processes (Carr & Head, 2010;Greeley & Spudis, 1981;Grott et al., 2013;Taylor, 2013) and modified by hypervelocity impacts (Carr & Head, 2010;Zuber, 2001). From remote sensing studies of the volcanic provinces present on Mars, it is clear that volcanism on the planet has been long lived, spanning several billions of years (Lapen et al., 2010(Lapen et al., , 2017Werner, 2009). Despite orbital monitoring since 1964, observation of active Martian volcanism has not yet occured. Despite the wealth of knowledge gained from remotely analyzing Martian volcanoes, there is a limit to our understanding of the magmatic processes on Mars that can be gained from remote sensing alone (e.g., constraints on interior volcanic processes, magma chamber evolution, quantitative assessment of magma composition, determination

Can the Magmatic Conditions of the Martian Nakhlites be Discerned via Investigation of Clinopyroxene and Olivine Intracrystalline Misorientations?

“…For augite, 4 out of the 21 EBSD data sets can be considered statistically relevant (>300 phenocryst crystals; Griffin, Daly, et al., 2022). 4 data sets contained <100 crystals (Governador Valadares (BM1975,M16,P8469), NWA 817 (N8‐1), NWA 998 (T1), and Y 000593 (106‐A); Figures 3–5).…”

“…For igneous samples, >50% crystal alignment is considered as strong SPO.CPO (Bunge, 1982; Vollmer, 1990). In the nakhlites, augite exhibits S‐ to LS‐type CPO where crystal alignment ranges from 8% to 26% (Griffin et al., 2022). The higher percentage of random crystal orientations within any given sample coupled with a high dependence on crystal orientation for the activation of slip‐system signatures will naturally result in multiple slip‐system development between crystals.…”

“…The variation observed in mIPF patterns between these “paired” stones implies different deformation parameters for the separate meteorites, which could indicate either a range of deformation environments with each meteorite being sourced from a different section within the same igneous body or could suggest that each individual meteorite represents its own separate flow/intrusion. From rudimentary scaling analysis of nakhlite emplacement mechanisms, the Miller Range nakhlites were indicated to form as larger igneous bodies, while the Yamato nakhlites were suggested to form as smaller igneous bodies (Griffin et al., 2022). Model results of smaller igneous bodies in conjunction with the observed differences in crystallographic deformation, similar recovery position, and geochronological dating (Cohen et al., 2017), currently support the hypothesis that the Yamato nakhlite stones formed as individual igneous units that were located in close proximity to one another on Mars while the model indicated a larger igneous body; current geochronological age resolution in combination with presented crystallographic mIPF patterns would suggest that the Miller Range nakhlites could represent different regions (or lobes) from a single igneous event (Griffin et al., 2022).…”

“…From rudimentary scaling analysis of nakhlite emplacement mechanisms, the Miller Range nakhlites were indicated to form as larger igneous bodies, while the Yamato nakhlites were suggested to form as smaller igneous bodies (Griffin et al., 2022). Model results of smaller igneous bodies in conjunction with the observed differences in crystallographic deformation, similar recovery position, and geochronological dating (Cohen et al., 2017), currently support the hypothesis that the Yamato nakhlite stones formed as individual igneous units that were located in close proximity to one another on Mars while the model indicated a larger igneous body; current geochronological age resolution in combination with presented crystallographic mIPF patterns would suggest that the Miller Range nakhlites could represent different regions (or lobes) from a single igneous event (Griffin et al., 2022). Overall, variation in mIPF patterns observed from presented data, suggests that the suite of nakhlite meteorites heterogeneously sample different igneous units and regions from within their launch crater on Mars.…”

“…The nakhlites are basalts with crystal‐sizes ranging from 0.29 to 1 mm, crystal clustering frameworks (Udry & Day, 2018), and low intensity low‐moderate strength girdle CPO (Griffin et al., 2022). Their mafic composition is dominated by augite (55–71 modal%; Udry and Day (2018)) with low to moderate abundances of olivine (1.7–14.9 modal%).…”