Caleta el Cobre 022 Martian meteorite: Increasing nakhlite diversity

Abstract

Caleta el Cobre (CeC) 022 is a Martian meteorite of the nakhlite group, showing an unbrecciated cumulate texture, composed mainly of clinopyroxene and olivine. Augite shows irregular core zoning, euhedral rims, and thin overgrowths enriched in Fe relative to the core. Low‐Ca pyroxene is found adjacent to olivine. Phenocrysts of Fe‐Ti oxides are titanomagnetite with exsolutions of ilmenite/ulvöspinel. Intercumulus material consists of both coarse plagioclase and fine‐grained mesostasis, comprising K‐feldspars, pyroxene, apatite, ilmenite, Fe‐Ti oxides, and silica. CeC 022 shows a high proportion of Martian aqueous alteration products (iddingsite) in olivine (45.1 vol% of olivine) and mesostasis. This meteorite is the youngest nakhlite with a distinct Sm/Nd crystallization age of 1.215 ± 0.067 Ga. Its ejection age of 11.8 ± 1.8 Ma is similar to other nakhlites. CeC 022 reveals contrasted cooling rates with similarities with faster cooled nakhlites, such as Northwest Africa (NWA) 817, NWA 5790, or Miller Range 03346 nakhlites: augite irregular cores, Fe‐rich overgrowths, fine‐grained K‐feldspars, quenched oxides, and high rare earth element content. CeC 022 also shares similarities with slower cooled nakhlites, including Nakhla and NWA 10153: pyroxene modal abundance, pyroxenes crystal size distribution, average pyroxene size, phenocryst mineral compositions, unzoned olivine, and abundant coarse plagioclase. Moreover, CeC 022 is the most magnetic nakhlite and represents an analog source lithology for the strong magnetization of the Martian crust. With its particular features, CeC 022 must originate from a previously unsampled sill or flow in the same volcanic system as the other nakhlites, increasing Martian sample diversity and our knowledge of nakhlites.

What Martian Meteorites Reveal About the Interior and Surface of Mars

“…According to their mineral chemistry, nakhlites represent different degrees of thermal processing, attributed to their relative position in the “cumulate pile” (Day et al., 2006; Jambon et al., 2002; Mikouchi et al., 2003; Sautter et al., 2002; Treiman, 2005; Treiman & Irving, 2008). The recovery and study of new nakhlites and chassignites since 2014 (Balta et al., 2017; Corrigan et al., 2015; Jambon et al., 2010; Krämer Ruggiu et al., 2020; Tomkinson et al., 2015; Udry & Day, 2018), however, show greater variation in mineralogy and composition compared to the previously observed samples, suggesting that these rocks were emplaced as several shallow sills and/or lava flows, and may not represent a singular magmatic body. Textural evidence also suggests that the nakhlites have undergone different emplacement and/or shock histories (Corrigan et al., 2015; Griffin et al., 2019; Krämer Ruggiu et al., 2020; Udry & Day, 2018).…”

“…Through terrestrial alteration, bulk composition can be enriched in Ba, Sr, U, and Ce, and possibly the light REEs (Crozaz et al., 2003). For example, the nakhlite Caleta el Cobre (CeC) 022 shows the highest Ce positive anomaly compared to the other nakhlites, likely due to alteration and oxidation in the Atacama desert (Krämer Ruggiu et al., 2020).…”

“…A recent comprehensive study by Udry and Day (2018) showed that nakhlites and chassignites were likely emplaced as various lava flows and/or hypabyssal sills according to their different mineralogies, cooling rates, and qualitative and quantitative textures, similar in many ways to volcanic emplacement on Earth (Balta et al., 2017; Corrigan et al., 2015; Daly et al., 2019b; Jambon et al., 2016; Udry & Day, 2018). At least five eruptive events for the nakhlites are suggested by their 40 Ar/ 39 Ar ages that vary between 1,415 ± 7 (Y‐000749) to 1,322 ± 9 Ma (Lafayette) (Cohen et al., 2017), with the youngest events at 1,215 ± 67 Ma (Krämer Ruggiu et al., 2020)…”

“…(2017), Kramer Ruiggui et al. (2020), Nyquist et al. (2001), Udry and Day (2018); ALH 84001 from Lapen et al.…”

Raman spectroscopic and geochemical studies of primary and secondary minerals in Martian meteorite Northwest Africa 10720

“…The identified and named nakhlites consist of 22 Martian stones: 11 from NWA and 7 from Antarctica (four stones of Miller Range [MIL] group and three stones of Yamato group), Nakhla, Lafayette, Governador Valadares (GV), and recently approved Caleta el Cobre (CeC) 022. [12] Nakhlite meteorites as olivine-bearing clinopyroxenites are igneous cumulates, composed of phenocrystic augite with minor mineral assemblages including titanomagnetite, fayalite, plagioclase, orthopyroxene, sulfides, phosphates, and alteration phases (i.e., iddingsite and sulfates). [13,14] Ar-Ar, Rb-Sr, Sm-Nd, or Lu-Hf isotopic isochrons indicate that nakhlites share the same crystallization age (mean age of 1,340 ± 40 Ma) and ejection age (mean age of 11 ± 1.5 Ma).…”