Petrology of the enriched poikilitic shergottite Northwest Africa 10169: Insight into the martian interior

Petrogenesis of Enriched and Intermediate Poikilitic Shergottites: From Magmatic Source to Emplacement

“…Enriched and intermediate poikilitic shergottites of this study all display characteristic bimodal textures, consisting of both poikilitic and interstitial non-poikilitic textures, similar to what has been previously described in the literature (Fig. 1a and 1b) (e.g., McSween et al, 1979;Harvey et al, 1993;Gleason et al, 1997;Gillet et al, 2005;Mikouchi, 2005;Mikouchi and Kurihara, 2008;Usui et al, 2010;Jiang and Hsu, 2012;Walton et al, 2012;Howarth et al, 2014;Combs et al, 2018). The poikilitic textures are comprised of medium-to coarse-pyroxene oikocrysts that partly or completely enclose multiple olivine and spinel chadacrysts ( Fig.…”

“…Shergottites are petrologically classified into four petrographic subgroups: Basaltic, olivine-phyric, poikilitic, and gabbroic (e.g., McSween and Treiman, 1998;Goodrich, 2002;Bridges and Warren, 2006;Walton et al, 2012;Filiberto et al, 2018;Udry et al, 2017). Basaltic and olivine-phyric shergottites are thought to represent extrusive rocks, whereas poikilitic and gabbroic shergottites are thought to be plutonic in origin (e.g., McSween, 1994;Goodrich et al, 2002;Bridges and Warren, 2006;Gross et al, 2011;Filiberto et al, 2014;Howarth et al, 2014;Udry et al, 2017;Combs et al, 2018). As Mars is predominantly a basaltic planet, systematic study of shergottites can lend insight into the martian interior, including martian crustal formation processes.…”

“…The depleted source is thought to have been derived from the mantle, whereas the location of the enriched source is still highly debated and could be located within the martian mantle, crust, or both (e.g., Herd, 2003; Bridges and Warren, 2006;Symes et al, 2008;Basu Sarbadhikari et al, 2011;Shearer et al, 2013;McSween, 2015;Peters et al, 2015). To date, poikilitic shergottites have only been classified as enriched [(La/Yb)CI = >0.8] and intermediate [(La/Yb) (e.g., Harvey et al, 1993;Treiman et al, 1994;Mikouchi et al, 2005;Usui et al, 2010;Liu et al, 2011;Jiang and Hsu, 2012;Howarth et al, 2014;Walton et al, 2012;Combs et al, 2018), suggesting enriched and intermediate poikilitic shergottites do not originate from a common magmatic source.…”

“…Previously, it was proposed that poikilitic shergottites may have formed from the same magma suite and originated from a common igneous body on Mars (e.g., Mikouchi and Kurihara, 2008). However, this suggestion was based on the investigation of intermediate shergottites only, as enriched poikilitic shergottites were first identified in 2010 (e.g., Usui et al, 2010;Jiang and Hsu, 2012;Howarth et al, 2014;Combs et al, 2018). Enriched and intermediate poikilitic shergottites share similar textural attributes (i.e., bimodal poikilitic textures) and mineral assemblages (e.g., McSween et al, 1979;Harvey et al, 1993;Treiman et al, 1994;Goodrich, 2002;Lin et al, 2005;Mikouchi, 2005;Usui et al, 2010;Lin et al, 2013;Howarth et al, 2014;Combs et al, 2016), supporting the proposal of a common poikilitic igneous crystallization location.…”

Hydrogen Isotopic Variations in the Shergottites

“…Martian meteorites have been classified into regolith breccia (e.g., NWA 7034 [3]), orthopyroxenite (ALH 84001), clinopyroxenites (nakhlites), dunites (chassignites), and the most abundant Martian basalt-the shergottites [2]. The shergottites are subclassified into basaltic (e.g., Shergotty), olivine-phyric (e.g., Tissint), and poikilitic (e.g., ALH 77005) sub-groups based on texture and mineralogy [9][10][11][12][13][14][15][16][17][18][19][20]. They are further divided into depleted, intermediate, and enriched-three geochemical groups based on the relative rare earth elemental (REE) abundances and their isotopic compositions of Sr, Nd, and Hf [1, 12,[21][22][23][24][25][26][27].…”