Heterogeneous martian mantle: Evidence from petrology, mineral chemistry, and in situ U-Pb chronology of the basaltic shergottite Northwest Africa 8653

Young magmatism and Si‐rich melts on Mars as documented in the enriched gabbroic shergottite NWA 6963

“…Si‐rich mesostasis in NWA 6963 and likely in other enriched shergottites is a product of magmatic differentiation and not of shock. This conclusion is in agreement with conclusions of previous studies (Filiberto et al., 2014; Herd et al., 2018; Leroux & Cordier, 2006; Stolper & McSween, 1979; Wu et al., 2021). Next to magmatic inclusions (Ikeda, 2005) and evolved igneous clasts within the regolith breccia NWA 7034 and paired stones (Humayun et al., 2013; Lindner et al., 2020), these areas are rare samples of highly differentiated melts form Mars, which are accessible in laboratories on Earth.…”

“…Our results-based on rock ages-therefore favor the formation of Si-rich mesostasis in the late stage of source rock crystallization. In view of the geochemical similarities of enriched shergottites (e.g., Udry et al, 2020) and the widespread occurrence of Si-rich mesostasis in these samples (e.g., Leroux & Cordier, 2006;Sheen et al, 2021), our results thus support the conclusion of a late-stage crystallization of Si-rich mesostasis in enriched shergottites as presented by, for example, Stolper and McSween (1979), Leroux and Cordier (2006), and Wu et al (2021.…”

“…2a), Sheen et al (2021) for several enriched shergottites (their figs. 4c, 5d, and 6d), Wu et al (2021) in NWA 8653 (their fig. 1e), Zhou et al (2013) in Zagami (their fig.…”

“…Two exceptions exist with ages of 2.4 Ga (Herd et al, 2017;Lapen et al, 2017). The ages have been determined using either the Sm-Nd, Lu-Hf, or Rb-Sr radiogenic systems by measuring mineral separates and whole rock fractions (e.g., Borg et al, 2005;Combs et al, 2019;Ferdous et al, 2017;Marks et al, 2010;Shafer et al, 2010;Shih et al, 2009), or using the U-Pb radiogenic system and measuring Zr-rich accessory minerals or phosphates with in situ ion beam techniques (e.g., Koike et al, 2016;Moser et al, 2013;Staddon et al, 2021;Wu et al, 2021;Zhou et al, 2013). Herd et al (2007) used in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb measurements of baddeleyite and generated data roughly in accordance with previously published young Sm-Nd and Rb-Sr ages (Borg et al, 2005).…”

“…LA‐MC‐ICP‐MS has so far only recently been used for U–Pb dating of merrillite in Martian meteorites (McFarlane & Spray, 2022; Wilson et al., 2019). Otherwise, ages for Martian meteorites were either determined using other isotopic chronometers and/or techniques (e.g., Borg et al., 2005; Combs et al., 2019; Ferdous et al., 2017; Koike et al., 2014, 2016; Marks et al., 2010; Moser et al., 2013; Shafer et al., 2010; Shih et al., 2009; Terada et al., 2003; Wu et al., 2021; Zhou et al., 2013), or the same isotopic chronometer and technique, but used on a different phase than merrillite, for example, baddeleyite in basaltic Martian meteorites (Herd et al., 2007, 2018; Sheen et al., 2021). Merrillite is a minor but ubiquitous phase in NWA 6963, and part of the coarse‐grained groundmass with grain sizes of 100–1000 μm.…”