NWA 7034/7533

Martian Polymict RegolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles).   BrecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material* (enriched, maficOne of the two broad categories of silicate minerals, the other being felsic, based on its magnesium (Mg) and/or iron (Fe) content. Mafic indicates silicate minerals that are predominantly comprised of Mg and/or Fe.The term is derived from those major constituents: Magnesium + Ferrum (Latin for iron) + ic (having, alkali- and water-rich crustal lithology)
Found: 2011, Coordinates: 24° 5.311′ N., 14° 46.671′ W
Rabt Sbayta, Ghredad Sabti region, Western Sahara (Southern Morocco)

Numerous individual stones constituting a single heterogeneous breccia, most covered by a distinctive black fusion crustMelted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of  4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below., were found in Western Sahara (strewn field map) by a nomad known as Bahba (E. Hand, 2014). The 525 g main massLargest fragment of a meteorite, typically at the time of recovery. Meteorites are commonly cut, sliced or sometimes broken thus reducing the size of the main mass and the resulting largest specimen is called the "largest known mass". and numerous smaller stones, including a 319.8 g specimen, were purchased by J. Piatek from a Moroccan dealer. A sample was sent for analysis and classification to the University of New Mexico (C. Agee et al.), and after extended in-depth analyses NWA 7034 was determined to be a unique martian basaltic breccia. A separate 84 g stone was purchased some months later by a meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and collector/dealer and sold to L. Labenne. A sample of this stone was submitted for analysis and classification to the Museum National d’Histoire Naturelle in Paris (R. Hewins et al.), and NWA 7533 was determined to be paired with NWA 7034. Additional paired stones were acquired by L. Labenne (e.g., NWA 7475 weighing 80.2 g), M. Jost (NWA 7906 weighing 47.7 g, NWA 7907 weighing 29.94 g, and NWA 8171 weighing 81.88 g), J. Piatek (NWA 8674 weighing 12 g, NWA 10922 weighing 182 g), the University of Leicester (NWA 8114 weighing 1.9 g), B. Hoefnagels (Rabt Sbayta 003 weighing 20.6 g), M. Goff (NWA 11220 weighing 36.63 g), and the University of Glasgow (NWA 11522 weighing 3.2 g). Additional recoveries from the ~10 km long strewn fieldArea on the surface containing meteorites and fragments from a single fall. Also applied to the area covered by tektites, which are produced by large meteorite impacts. Strewnfields are often oval-shaped with the largest specimens found at one end. Given that the largest specimens go the greatest distance, a meteoroid's continue, with a current combined weight of over 2 kg.

Research results for NWA 7034 have been interpreted by some investigators as indicating the meteorite was once part of a basaltic conglomerate formed through sedimentary processes, implicating volcanicIgneous rock that forms from cooling magma on the surface of a planet or asteroid. and/or impact-generated material (Agee et al., 2013). For a possible volcanic scenario, it was proposed that the hot, sintered, pyroclastic debris incorporated a variety of materials as it flowed over the surface. For a possible impact scenario, it was posited that the resulting melt breccia experienced subsequent impact gardening and mixing with aeolian-distributed soils and dust, including siderophile-enriched meteoritic contaminates (Hewins et al., 2013). In other words, the meteorite was once part of a regolith breccia derived from an extensive impact-melt breccia lens from the near-surface crustOutermost layer of a differentiated planet, asteroid or moon, usually consisting of silicate rock and extending no more than 10s of km from the surface. The term is also applied to icy bodies, in which case it is composed of ices, frozen gases, and accumulated meteoritic material. On Earth, the of Mars. Some who subscribe to the impact-melt/impact-gardening scenario have described the textural characteristics of this meteorite breccia as comparable to that of a howarditeOne type of meteorite in the HED (Howardite, Eucrite, Diogenite) achondrite group. Howardites are named after the English chemist Edward Howard (1774-1816), one of the pioneers of meteoritics. Consisting mostly of eucritic and diogenitic clasts and fragments, howardites are polymict breccias. However, they can also contain dark clasts of carbonaceous, and note the close similarities in all major elementSubstance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of ratios and in Ni and Ca abundances between this meteorite and Gusev soils (Humayun et al. (2013).

 

Ongoing research to determine the exact nature of the NWA 7034/7533 pairing group has involved studies of a broad sampling of clasts by multiple research teams. Although the meteorite was initially described by some as being analogous to a volcanic porphyry, more recent investigations have concluded that this meteorite is best described as a regolith breccia consisting of a wide variety of clastA mineral or rock fragment embedded in another rock. types. Studying a variety of small clasts (0.5–4 mm) in a thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope. from NWA 7475, Wittmann et al. (2013) found that the majority of the clasts are surrounded by thin mantles composed of accreted matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. material, with some being described as accretionary lapilliPellets that form by accretion of fine ash around condensing water droplets or solid particles; particularly common in steam-rich volcanic eruptive columns, but also occurring in the turbulent explosion plume rising above an expanding excavation cavity in an impact cratering event. Accretionary lapilli exhibiting concentric internal structure have been found; i.e., rounded in shape, bearing concentric layers, and formed (besides those known from volcanic eruptions) during condensation from a turbulent explosive plume generated in an impact-cratering event.

Santos et al. (2015, 2016) described a wide diversity of clast types, the most prevalent of which are igneous clasts, along with melt clasts (spherules of impact or volcanic origin) and proto-breccia clasts. Proto-breccia clasts, representing breccia fragments in existence prior to the assembly of the NWA 7034 breccia, range in size up to ~12 mm and contain very fine-grained matrix material compositionally and/or texturally distinct from the typical fine-grained meteorite bulk matrix. The rounded, layered appearance of some proto-beccia clasts attest to a sedimentary origin (Jacobs et al. (2016). Santos et al. (2015) recognized four sub-types of igneous clasts based on the IUGS classification scheme: basaltBasalt is the most common extrusive igneous rock on the terrestrial planets. For example, more than 90% of all volcanic rock on Earth is basalt. The term basalt is applied to most low viscosity dark silicate lavas, regardless of composition. Basalt is a mafic, extrusive and fine grained igneous rock clasts (the most prevalent igneous clast type; image), basaltic andesite clasts, trachyandesite clasts, and a unique Fe–Ti oxide-, P-rich (FTP) lithological clast type exhibiting a basaltic texture. The relatively small (<1 mm²) FTP clasts consist of highly variable abundances of plagioclaseAlso referred to as the plagioclase feldspar series. Plagioclase is a common rock-forming series of feldspar minerals containing a continuous solid solution of calcium and sodium: (Na1-x,Cax)(Alx+1,Si1-x)Si2O8 where x = 0 to 1. The Ca-rich end-member is called anorthite (pure anorthite has formula: CaAl2Si2O8) and the Na-rich end-member is albite (±alkali feldsparVariety of feldspar containing alkali metals potassium and sodium in a solid solution. A more complete explanation can be found on the feldspar group page that also includes the plagioclase feldspars as part of the feldspar ternary diagram.), Cl-apatite, low-Ca pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category., and Fe–Ti oxides (primarily ilmeniteTi-Fe oxide, TiFeO3, found in achondrites, lunar mare basalts, and shergottites. Ilmenite forms as a primary mineral in mafic igneous rocks. It crystallizes relatively early out of a magma before most of the other minerals, and as a result, the heavier crystals of ilmenite precipitate to the bottom of the magma and magnetiteFe oxide, Fe²⁺Fe³⁺2O4, containing oxidized iron (Fe³⁺) found in the matrix of carbonaceous chondrites and as diagnostic component in CK chondrites. In CK chondrites, magnetite is typically chromian, containing several wt. % Cr2O3.), and are most similar to terrestrial nelsonites and oxide-apatite gabbronorites. In a study of FTP clasts conducted by Santos et al. (2016), no genetic link was found to exist between the FTP clasts and the basalt clasts through either silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the liquid immiscibility or fractional crystallizationA crystallization process in which minerals crystallizing from a magma are isolated from contact with the liquid. It is a key process in the formation of igneous rocks during the process of magmatic differentiation. Also known as crystal fractionation. processes, although both clast groups might represent highly evolved (after 98–99.5% parental melt crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals.) crustal material.

The predominant clast type found by Wittmann et al. (2013) in NWA 7475 is a glassy melt phase that experienced rapid cooling, some of which were cooled after mixing with matrix material. These vitrophyre clasts contain sub-mm-sized phenocrysts of pyroxene, plagioclase, chlorapatite, and opaques, along with a significant Ni contaminant from an exogenous impactor. Specifically, based on the increased Ni and Ir ratios observed in these components of NWA 7533 compared to basaltic shergottitesIgneous stony meteorite with a Martian origin consisting mainly of plagioclase (or a shocked glass of plagioclase composition) and pyroxene. They are the most abundant type of SNC meteorites and the type member is the Shergotty meteorite, which fell in India in 1865. Shergottites are igneous rocks of volcanic or, it was concluded by Flynn et al. (2014) and others that ~5 wt% of an exogenous chondritic component (largely carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than material comparable to interplanetary dust particlesExtremely small (~10 μm in diameter) particles found on Earth (or collected during high altitude flights) that are probably from outer space. Their small size poses a problem for most common chemical and petrographic analytical techniques and thus research into IDPs is marked by the application of new analytical procedures) has been added to the martian regolith, which is consistent with a previous modeled regolith production rate of 1 m/b.y. (Flynn and McKay, 1990). Other melt clasts show evidence for slower crystallization rates, demonstrating that this breccia represents lithologies from multiple impact events. A study of the HSE record in NWA 7034 was undertaken by Goderis et al. (2016), which included the first Os-isotopic analysis. They determined that the bulk meteorite reflects an enrichment in HSE comparable to that of the lunar regolith, and that the HSE patterns are unfractionated and occupy ranges similar to those of chondritic meteorites. An admixture of ~3 wt% CI chondriteRare meteorite class named after the Ivuna meteorite that fell in Tanzania in 1938. They are among the most primitive, friable (crumbly), and interesting of all meteorites, having undergone extensive aqueous alteration. They lack chondrules and CAIs as a result of this alteration, but contain up to 20% water, as equivalent material to the martian regolith would provide this HSE excess; however, since significant alteration of the rock and redistribution of HSEs has occurred through impact melting, weathering, metasomatism, etc., it is now impossible to identify specific chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such group(s) (e.g., carbonaceous, enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3)., Rumuruti) which would satisfy all of the observed HSE ratios. From their Os-isotopic analysis, Goderis et al. (2016) revealed that Re/Os fractionationConcentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process. (with Re losses of ~50%) of the chondritic impactor material occurred ~4.4 b.y. ago and prior to lithification of the NWA 7034 breccia. Furthermore, they demonstrated that a component of this impactor material reflects possible hydrothermal sulfurization associated with a major impact event, the dating of which is consistent with an event recorded by other isotopic chronometers at ~1.1–1.4 b.y. ago.

A portion of the clasts (~20%) examined by Wittmann et al. (2013) in NWA 7475 are mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous fragments consisting of plagioclase and alkali feldspars together with pyroxenes; some exhibit features indicative of formation in an igneous, plutonicGeology: Igneous intrusive body that forms when magma is injected into host rocks and solidifies. Plutons occur in the crust of asteroids undergoing differentiation or planets. Named after Pluto, the Roman god of the underworld. Plutonic rocks are the rocks found within a pluton. Astronomy: Category of planet including all environment and reveal a history involving a low degree of shock (S2/3). However, a study of pyroxene grains from many different components (e.g., igneous clasts, phosphate clasts, isolated pyroxene matrix grains) in NWA 7034 indicates that no fractional crystallization occurred, which is contrary to expectations of slow cooling within an extensive melt sheet or a plutonGeology: Igneous intrusive body that forms when magma is injected into host rocks and solidifies. Plutons occur in the crust of asteroids undergoing differentiation or planets. Named after Pluto, the Roman god of the underworld. Plutonic rocks are the rocks found within a pluton. Astronomy: Category of planet including all (Santos et al., 2014). One exceptionally large vitrophyric clast exhibiting a unique fine-grained quench texture has been described in NWA 7034 by Udry et al. (2014). This vitrophyre is an impact melt composed primarily of glass (75 vol%) with skeletal crystals of pyroxene (18 vol%) and olivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion (7 vol%) along with mesostasisLast material to crystallize/solidify from a melt. Mesostasis can be found in both chondrules, in the matrix around chondrules, and in achondrites as interstitial fine-grained material such as plagioclase, and/or as glass between crystalline minerals.  . Its uniquely high Ni content of 1,020 ppmParts per million (10⁶). attests to the incorporation of 5.3–7.7% exogenous chondritic material in the rock. This vitrophyre is both chemically and mineralogically very similar to the Gusev basalt ‘Humphrey’ and associated soils, and is thought to have been derived from a similar igneous lithology. Besides that, new alkali-rich igneous clast types not previously sampled from other martian meteorites have been identified in NWA 7034, including trachyandesite, monzonite, mugearite, and an Fe-, Ti-, and P- rich (FTP) lithology, while still other clasts, notably a siltstone, appear to have a sedimentary origin (Santos et al., 2013, 2015; Wittmann et al., 2013, 2015; Tartèse et al., 2014). The elemental abundances for a 3-mm diameter, fine-grained, aqueously altered spherule discovered in NWA 7533 were ascertained by Humayun et al. (2014), and it was concluded that this phyllosilicate-rich spherule was likely formed through sedimentary deposition underwater during the early Noachian period (phyllosian era) 4.6–4.1 b.y. ago. Some alkali-rich mugearitic clasts show close compositional similarities to the mineralogically evolved ‘Jake Matijevic’ basalt rock analyzed in situ on Mars by the APXS instrument on Curiosity (Stolper et al., 2013).

The fine-grained (0.1–5 µm; ave. 0.2–0.3 µm) crystalline matrix in NWA 7034 is comprised of µm-sized plagioclase together with sub-µm-sized pyroxene, and hosts polymineralic clasts (brecciated lithic clasts of McCubbin et al., 2014) of basaltic (i.e., shergottite-like) and gabbroic orthopyroxeniteA rock composed primarily of orthopyroxene. Non-terrestrial orthopyoxenites include diogenites and a single martian meteorite, ALH 84001, that was found in the Allan Hills region of Antarctica in 1984. ALH 84001 is a cumulate rock consisting of 97% coarse-grained, Mg-rich orthopyroxene, with small amounts of plagioclase, chromite, and carbonate. It, basaltic andesite, noriteIgneous rock composed of 90% plagioclase, 95% orthopyroxene (low-Ca pyroxene) and less than 10% olivine. Norite is most commonly found in the lunar (highlands) meteorites but has also been found in about a dozen diogenites, a few shergottites, and a very small number of other achondrite types. Gabbro is very, and monzonite source rock types, along with quenched melt clasts as small as ~5 µm, all embedded together with accessory oxides (primarily magnetite and maghemite), chlorapatite, chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups., sulfides, and other rare phases (Agee et al., 2012; Hewins et al., 2013; Santos et al., 2013). The very fine-grained matrix component in NWA 7533 has the appearance of annealed windblown dust exhibiting an equigranular texture (Lorand et al., 2015 and references therein). Very weakly shocked (<15 GPa) pyrite crystals of sub-mm-size were identified in all breccia components in NWA 7533, and when taken together with Fe-oxyhydroxide replacement products, accounts for ~0.3 vol% of the meteorite (Lorand et al., 2014, 2015). The pyrite, associated with µm-sized magnetite/maghemite grains which served as nucleation sites, crystallized slowly in a late impact heating event (~1.4 b.y. ago) in which hot (up to 500°C) sulfur-bearing metasomatic fluids pervaded the breccia. This late-stage impact-heating event might be responsible for both the pyrite crystallization and the equigranular texture (prevalent 120° triple junctions) of the fine-grained matrix (Muttik et al., 2014; Lorand et al., 2015). The persistence of elevated temperatures >700°C for an extended time period (weeks to months) is attributed to slow cooling at a depth of at least 5 m under an ejecta blanketGenerally symmetrical apron of ejecta surrounding a crater; it is thick at the crater's rim and thin to discontinuous at the blanket's outer edge. (MacArthur et al., 2019).

In their analysis of the NWA 7034 matrix component, Hu et al. (2018) identified assemblages of pyrite-pyrrhotite associated with silicates. They suggest that formation of these assemblages may have occurred during a late impact-heating event, or alternatively, that the pyrite is a replacement product of pyrrhotiteIron sulfide group of minerals whose composition ranges widely between its end members pyrrhotite (Fe7S8) whose crystal structure is monoclinic, and troilite (FeS) whose crystal structure is hexagonal. Its general formula is Fe1−xS (where x = 0 to 0.17). The troilite phase is found mainly in meteorites and in the formed in an earlier period of low-temperature hydrothermal alteration. Some of these pyrite-pyrrhotite assemblages coexist with the late-stage alteration product goethite, which MacArthur et al. (2019) suggest is likely a product of terrestrial alteration. In their atomic-scale investigation of the matrix component in the paired stone NWA 11522, Daly et al. (2018) identified Ca-Al–silicate associated with stishoviteDense, high-pressure phase of quartz; so far identified only in shock-metamorphosed, quartz-bearing rocks from meteorite impact craters. Stishovite was synthesized in 1961 before it was discovered at Meteor Crater, Arizona. Its structure consists of parallel chains of single SiO6 octahedra. The octahedra are on their sides, sharing opposing edges. Image, while Cox et al. (2018) reported twinning in baddeleyiteA rare zirconium oxide (ZrO2) mineral, often formed as a shock-induced breakdown product of zircon. This mineral can be found in some lunar and martian meteorites. grains; both of these mineralogies attest to moderate shock pressures (>25 GPa).

Fine-grained phyllosilicatesClass of hydroxyl-bearing silicate minerals with a sheet-like structure. They result from aqueous alteration are dominantly serpentine and smectite in meteorites; found in the matrixes of carbonaceous chondrites. Phyllosilicates consist of repeating sequences of sheets of linked tetrahedra (T) and sheets of linked octahedra (O). The T sheet consists of (saponite) associated with orthopyroxeneOrthorhombic, low-Ca pyroxene common in chondrites. Its compositional range runs from all Mg-rich enstatite, MgSiO3 to Fe-rich ferrosilite, FeSiO3. These end-members form an almost complete solid solution where Mg2+ substitutes for Fe2+ up to about 90 mol. % and Ca substitutes no more than ~5 mol. % (higher Ca2+ contents occur grain boundaries were also identified in NWA 7034 (Muttik et al., 2014). Studies of the matrix component of NWA 7533 show that it is enriched in siderophile elements consistent with ~5% impactor contamination, and is enriched in incompatible elements consistent with crystallization from a low degree (~4%) partial melt (Humayun et al., 2013). The ~5% enrichment in highly siderophile elements was similarly observed in a sample of NWA 7034, with the associated Os-rich compounds being indicative of contamination primarily from carbonaceous chondrite (CI-like) impactors as opposed to other chondrite types (Goderis et al., 2014). It is notable that spectral analyses of soluble organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. material in NWA 7533 revealed only low-complexity compounds lacking N bonds, possibly a result of subsequent heat modification on Mars (Lorand et al., 2014). Ni-poor magnesian orthopyroxenite clasts akin to ALH 84001 have been characterized through microprobe analyses of noritic clasts in NWA 7533; this breccia component is thought to represent a pristine early crustal lithology (Hewins et al., 2014).

Analyses of the O-isotopic composition of NWA 7034 was conducted at two separate labs—UNM (Sharp et al.) and UC San Diego (Thiemens et al.)—both of which demonstrated higher δ18O, δ17O, and Δ17O values than for any other martian meteoriteOver 30 of the meteorites found on Earth almost certainly came from Mars (see http://www.imca.cc/mars/martian-meteorites.htm and http://www2.jpl.nasa.gov/snc/). All but one belongs to the group known as SNC meteorites, which includes the shergottites, nakhlites, and chassignites. SNC meteorites contain minerals that crystallized within the past 1.35 to 0.15 Ga, making them. Oxygen-isotopic analyses of NWA 7475 (Korotev et al., 2013) and of NWA 7906 and 7907 (Hofmann et al., 2014) resulted in similar values to those of NWA 7034. These higher isotopic values for NWA 7034 have been attributed to either multiple distinct and persistent O-isotopic reservoirs on Mars (inconsistent with a global magma oceanCompletely molten surfaces of terrestrial planets or moons that formed soon after accretion. Samples returned by the Apollo missions provide evidence of a lunar magma ocean, crystallization of which produced a stratified Moon with a low-density crust formed by accumulation of the mineral plagioclase overlying a higher density mantle of), or to photochemical reactions and exchange processes occurring in the near-surface litho/hydro/atmospheric environment (Ziegler et al., 2013). A less likely possibility is that an exotic isotopically heavy projectile pervaded the host rock of NWA 7034, but no such component has been identified. Notably, NWA 7034 has the highest δ37Cl values measured to date, likely caused by a low degree of crustal contamination possibly involving near-surface, low-temp fluid-mediated alteration (Sharp et al., 2016). The high content of 37Cl in the crustal component is due to its early isotopic exchange with the martian atmosphere, which had undergone significant mass-dependent fractionation involving loss of light Cl isotopes to space.

The water in NWA 7034, which is enriched in the heavy H isotopeOne of two or more atoms with the same atomic number (Z), but different mass (A). For example, hydrogen has three isotopes: ¹H, ²H (deuterium), and ³H (tritium). Different isotopes of a given element have different numbers of neutrons in the nucleus. (D), is present at a much higher abundance than in all other martian meteorites—as high as ~0.6 wt% or 6000 ppm. In another study, an even higher water content of ~8000 ppm was measured in the paired meteorite NWA 7533 (Beck et al., 2014), while succeeding analyses of different phases of the same meteorite gave a lower water abundance of <3600 ppm (Remusat et al. (2015). It was revealed that D-rich water occurs in multiple mineral phases, including Fe-hydroxide (ferrihydrite), apatite, and ilmenite. Apatite is identified as a major constituent of the FTP clasts, but is also present in basalt clasts and as ubiquitous grains throughout the matrix (Muttik et al., 2013; Santos et al., 2013). McCubbin et al. (2016) measured the water content and H-isotopic composition in apatites from various clast types (see diagram below). They ascertained that the δD values for all of the clasts are consistent with that of the hypothesized intermediate crustal reservoir (δD = 1000–2000‰) as posited by Usui et al. (2015). However, the possibility that incomplete H exchange has occurred between mantleMain silicate-rich zone within a planet between the crust and metallic core. The mantle accounts for 82% of Earth's volume and is composed of silicate minerals rich in Mg. The temperature of the mantle can be as high as 3,700 °C. Heat generated in the core causes convection currents in (δD = <275‰) and atmosphere (δD = 2500–6100‰) reservoirs has not yet be ruled out.

Utilizing infrared spectometry and electron microscopy, Muttik et al. (2014) observed several hydrous Fe-oxide phases in the groundmass of NWA 7034 including ferrihydrite, magnetite, maghemite, hematiteFe-oxide mineral (Fe2O3) that may be the major cause of the red color on Mars. Coarser-grained gray hematite has the same chemical formula as the red variety, but a different crystalline structure. Deposits of gray hematite found in the Terra Meridiani region of Mars may suggest that water once circulated, and ilmenite, each associated with aqueous/hydrothermal processing. They reported that up to 1100 ppm of the total water is attributable to the ferrihydrite, and ~150 ppm of the water is hosted by the apatite. In addition, it was estimated that the maghemite component in NWA 7034 might contain 1000 ppm of water and the phyllosilicates up to 1900 ppm, while other hosts of water still remain to be determined. Of particular interest is the hypothesis that the missing olivine component in this basaltic breccia lithology is due to its initial conversion by weathering processes to Fe-oxides such as magnetite, along with other secondary phases (Humayun et al., 2014). It is proposed that this stage was followed by the destruction of these secondary phases during subsequent impact melting events, leading to the formation of phases such as orthopyroxene, and that fractional crystallization of the noritic melts ultimately produced the monzonitic clasts. X-ray diffractionAnalytical technique used to determine the structures of crystalline solids. A monochromatic beam of X-rays (usually Cu-Kα) is diffracted off repeating planes of atoms in crystalline samples to produce a diffraction pattern. Through analysis of the diffraction pattern, atomic structures can often be determined. analysis of NWA 8114 pyroxenes conducted by by MacArthur et al. (2016) revealed the presence of hydrationReaction of a substance with water./oxidation products they identified as magnetite and goethite.

 

The O-isotopic composition of the water in this meteorite is consistent with its derivation as a volatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). component from a separate reservoir in the interior of Mars, and/or with metasomatic processes after lithification of the host rock. Analyses of the D/H ratio of the water led to the recognition of two distinct components attributable to various possible scenarios, but is most indicative of multiple H-isotope reservoirs. While the water has an O-isotopic composition enriched in the heavy oxygenElement that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only isotopes (corresponding to more negative Δ17O values) compared to the bulk meteorite, it falls near the middle of the compositional range for the water in other martian meteorites (Agee et al., 2013; Nunn et al., 2013). It was posited by Ziegler et al. (2013) that the positive δ18O end-member is associated with plagioclase feldsparAn alumino-silicate mineral containing a solid solution of calcium, sodium and potassium. Over half the Earth’s crust is composed of feldspars and due to their abundance, feldspars are used in the classification of igneous rocks. A more complete explanation can be found on the feldspar group page.. These different oxygen reservoirs (lithosphereRigid outer layer of a planet. The base of the lithopshere is defined by the temperature at which the brittle/ductile transition occurs in the mantle./hydrosphere/atmosphere) have been sustained on Mars over eons as evidenced by the range of Δ17O values from martian zircons that were formed over b.y. timescales (Nemchin et al., 2014). Various Fe- and Fe–Ti oxides are present in all clast types and in the matrix of NWA 7034, attesting to a post-igneous environment more oxidizingOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons,  while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants than that of any other martian meteorite (Agee et al., 2013). Both the similar spectrographic signature and redoxOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons,  while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants state of the martian surface compared to the NWA 7034 meteorite pairing group, which is representative of the martian regolith, suggests that such material is a primary source of the planet-wide distribution of dust (Beck et al., 2014).

Both NWA 7034 and ALH 84001 have REEOften abbreviated as “REE”, these 16 elements include (preceded by their atomic numbers): 21 scandium (Sc), 39 Yttrium (Y) and the 14 elements that comprise the lanthanides excluding 61 Promethium, an extremely rare and radioactive element. These elements show closely related geochemical behaviors associated with their filled 4f atomic orbital. values that are in close agreement with previous estimates for the martian crust (Nyquist and Shih, 2013, and references therein). In analyses of the chemical composition of NWA 7034, Humayun et al. (2013) and Gordon et al. (2013) detected a significant enrichment of the REE compared to all other martian meteorites sampled to date.

The high Th content (~2.65 ppm) in NWA 7034 is another indicator of source magmaMolten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. enrichment, and there remains the possibility that a Th–LREE correlation might exist to serve as a marker for a more specific regional origin. Moreover, data specific to NWA 7533 attests to a significant enrichment in HSE, particularly Ni and Ir, compared to other martian meteorites. Similar compositional measurements conducted by Korotev et al. (2013) for the NWA 7475 stone indicate similarities exist in Ir, Ni, and AuThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The concentrations to mature lunar regolith. It is noteworthy that the Na content of NWA 7475 is significantly less than that measured for NWA 7034. The low Ba content recorded for NWA 7475 indicates that a very low degree of terrestrial contamination has occurred.

Although the geochemistryStudy of the chemical composition of Earth and other planets, chemical processes and reactions that govern the composition of rocks and soils, and the cycles of matter and energy that transport Earth's chemical components in time and space. of the SNC suite of martian meteorites does not closely match that measured by NASA orbiters and surface rovers, the chemical composition of NWA 7034 is a very good match to basaltic rocks and soils analyzed at Gusev CraterBowl-like depression ("crater" means "cup" in Latin) on the surface of a planet, moon, or asteroid. Craters range in size from a few centimeters to over 1,000 km across, and are mostly caused by impact or by volcanic activity, though some are due to cryovolcanism. by the Mars Exploration Rover Spirit (e.g., Ca/Al ratio; Gordon et al., 2013), and to the average martian crust as measured spectroscopically by the Mars Odyssey orbiter (Agee et al., 2013). The geochemical data for NWA 7034 are consistent with the composition of a martian crust that formed as a low degree partial melt (~4–5%) of a garnet-bearing peridotite source mantle (Humayun et al., 2013). The high degree of natural remanent magnetization calculated for this meteorite provides the first archetypal material which would be consistent with the martian magnetic fields documented by the Mars Global Surveyor (Rochette et al., 2013). Given that NWA 7034 does represent a lithology with a high content of ferromagnetic minerals, it would be required that a similar lithology constitute at least a kilometer of the Noachian crust to account for the observed martian magnetic anomalies (Gattacceca et al., 2013). Some investigators suggest a likely source region for such regolith breccias could be the heavily cratered southern highlands, a region that shows smilarities with some compositional and spectral data obtained for these meteorites (Lorand et al., 2015, and references therein).

A Rb–Sr age of NWA 7034 was calculated to be ~2.1 b.y. by Agee et al. (2013), and ~2.7 b.y. by Nyquist et al. (2016), reflecting a late isotopic disturbance. However, attempts to replicate this age for other breccia samples have not been entirely successful. A Sm–Nd age for some pyroxene grains reflects a much older age of 4.39 (±0.08) b.y. (Nyquist et al., 2013), while a separate Sm–Nd investigation of the bulk matrix material conducted by Nyquist et al. (2016) resulted in a similar age of ~4.42 b.y.; this age is also consistent with previous U–Pb chronometry. It was inferred from their study that all of the igneous matrix components in this breccia, as well as the orthopyroxenite ALH 84001, likely formed contemporaneously as part of an early, evolved, REE-enriched martian crust. Notably, the 147Sm/144Nd ratio (0.171) calculated for NWA 7034 by Agee et al. (2013) matches that estimated for the parental melt of the martian crust (Nyquist and Shih, 2013). This meteorite therefore represents the only sample collected from this geologic time period (early Amazonian epoch) on Mars. It is interesting that the noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. analyses conducted by Cartwright et al. (2013) revealed a U-Th-He age of ~170 m.y., equivalent to the currently debated young formation age of shergottites. A chronology for the primary and secondary components composing the breccia is being developed through Rb–Sr systematics (Charlier et al., 2013).

The first U–Pb dating of martian zirconOrthosilicate mineral, Zr(SiO4), observed in all terrestrial rocks type and in ordinary chondrites, eucrites, mesosiderites, and lunar rocks. micro-xenocrysts, residing for the most part within the matrix, yields a wide range of ages—from 1.5 b.y. to 4.443 (±0.022) b.y. in NWA 7475 (Moser et al., 2013), and 1.712 (±0.085) b.y. to 4.428 (±0.025) b.y. in NWA 7533 (Humayun et al., 2013). The range for NWA 7475 represents the oldest Mars crustal component dated thus far, and it indicates that a resetting event occurred ~1.7 b.y. ago. A similar study of zircons from NWA 7034 yielded a slightly younger U–Pb age as old as 4.37 (±0.07) b.y., and also indicates a probable disturbance occurred ~1.5 b.y. ago (Tartèse et al., 2014). The timing of Os fractionation recorded in NWA 7034 determined by Goderis et al. (2014) is concordant with this late disturbance. Yin et al. (2014) dated zircon, baddeleyite, and various phosphate grains, which revealed a wide range of ages between ~4.4–1.44 b.y., and they contend that the formation of NWA 7034 occurred at 1.44 b.y. An even younger U–Pb age determined for phosphate grains in NWA 7533 of ~1.36 b.y. is considered to reflect a metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. resetting event (Bellucci et al., 2015). Notably, the youngest age of ~800 m.y. was established for a single alkali feldspar grain in NWA 7533 (Lindsay et al., 2014, and references therein). Measurements of REE and Ti concentrations in monzonitic–noritic hosted zircons in NWA 7533 led to the conclusion that the crystallization temperature was in the range of ~700–800°C (Nemchin et al., 2014).

Based on similar observations of a bi-modal U–Pb chronometry preserved in zircon and phosphate grains in monzonite clasts from NWA 7533, Bellucci et al. (2014) proposed a plausible differentiationA process by which a generally homogeneous chondritic body containing mostly metal, silicates and sulfides will melt and form distinct (differentiated) layers of different densities.   When the melting process continues for a long enough period of time, the once chondritic body will re-partition into layers of different composition including history of Mars over the period ~4.5–1.7 b.y. They contend that the monzonite clasts represent an early martian crustal differentiate that was re-melted 4.4 b.y. ago, and that the 1.35 b.y. age represents the event in which all of the components were coalesced into the meteorite source breccia. The meteorite lithology experienced a short-lived thermal event at 1.7 b.y. as a regolith component in which partial resetting of feldspars occurred. They also determined that the U–Pb ratios for early martian basalt source reservoirs were significantly higher than previous estimates based on shergottiteIgneous stony meteorite with a Martian origin consisting mainly of plagioclase (or a shocked glass of plagioclase composition) and pyroxene. They are the most abundant type of SNC meteorites and the type member is the Shergotty meteorite, which fell in India in 1865. Shergottites are igneous rocks of volcanic or models, and derived a value for the regolith of ~7.4 (vs. ~3 previously ascribed to bulk silicate Mars). Based on the U-Th-Sm/He and other chronometric systems, Cassata et al. (2018) determined that impact-related brecciationThe formation of a breccia through a process by which rock fragments of of various types are recemented or fused together. of the source terrain parental to NWA 7034 occurred no earlier than ~225 m.y. ago. (e.g., U-Th-Sm/He age of 135–113 m.y.). Their schematic chronology for NWA 7034 and pairings derived from multiple radioisotope systems is shown below.

A Schematic History of Martian Breccia NWA 7034

 

The primary investigative team for NWA 7034 concluded that the corrected Ar and Xe systematics were a good match to the martian atmosphere as measured by the Viking lander, which indicates that a trapped martian atmospheric component is present in the meteorite like that observed in some other martian meteorites. In a Xe-isotopic analysis of NWA 8114 conducted by Crowther et al. (2014), the origin for the major component of the Xe was also attributed to the martian atmosphere.

The pre-atmospheric diameter for the meteoroidSmall rocky or metallic object in orbit around the Sun (or another star). was determined to be <50 cm, and the CRE age based on 3He, 21Ne, and 38Ar was calculated to be 5.1, 11.4, and 5.4 m.y., respectively (Agee et al., 2013). A study of volatile elementsChemical elements that condense (or volatilize) at relatively low temperatures. The opposite of volatile is refractory. Volatile elements can be divided into moderately volatile (Tc = 1230–640 K) and highly volatile (Tc < 640 K). The moderately volatile lithophile elements are: Mn, P, Na, B ,Rb, K, F, Zn. The moderately (C, N, and noble gasesElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive.) in the matrix of NWA 7034 was undertaken to better constrain the CRE age of this meteorite (Grady et al., 2014). Results reveal a complex evolutionary history involving both terrestrial contamination and incorporation of a trapped martian atmosphere component, and the 21Ne-based CRE age was determined to be ~12 m.y. New He-, Ne-, and Ar-based CRE age data for NWA 7034 were interpreted by Cassata et al. (2018) to suggest a meteoroid having a pre-atmospheric diameter of 240 cm and shielding conditions consistent with a depth of ~115 cm. Cosmic ray exposure ages have now been determined for many martian meteorites, and Mahajan (2015) compiled a chart based on the reported CRE ages for 53 of them. He concluded that together these 53 meteorites represent 10 distinct impact events which occurred 0.92 m.y., 2.12 m.y., 2.77 m.y., 4.05 m.y., 7.3 m.y., 9.6 m.y., 11.07 m.y., 12.27 m.y., 15 m.y., and 16.73 m.y.—see his chart here. It was argued that NWA 7034 was launched from Mars in a unique impact event 7.3 m.y. ago. In a noble gas study involving NWA 8114 (paired to NWA 7034), Busemann et al. (2015) reported an average CRE age based on 21Ne and 38Ar of 8.2 m.y. In a subsequent review based on multiple criteria, Irving et al. (2017 [#2068]) made a new determination of the number of separate launch events associated with the known (101 at the time of their study) martian meteorites. They speculate that the number could be as few as twenty, and concur with Mahajan (2015) that the NWA 7034 pairing group represents a unique ejection event.

Macromolecular carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. was identified in feldspar inclusions by Raman spectroscopyTechnique of splitting electromagnetic radiation (light) into its constituent wavelengths (a spectrum), in much the same way as a prism splits light into a rainbow of colors. Spectra are not smooth but punctuated by 'lines' of absorption or emission caused by interaction with matter. The energy levels of electrons in conducted at the Carnegie Institution in Washington D.C. (Steele et al., 2013). The origin of this organic material is so far unknown—it may derive from biogenic or abiogenic processes on Mars, or it may be meteoritic in origin. In addition, the C-isotopic ratios in the meteorite were found to be similar to some shergottites, albeit terrestrial weathering products may have contributed to the results.

Measurements were made by Kiefer et al. (2014) to determine the bulk densityMass of an object divided by its volume. Density is a characteristic property of a substance (rock vs. ice, e.g.). Some substances (like gases) are easily compressible and have different densities depending on how much pressure is exerted upon them. The Sun is composed of compressible gases and is much, grain density, porosityThe volume percentage of a rock that consists of void space. Vesicular porosity is a type of porosity resulting from the presence of vesicles, or gas bubbles, in igneous rock such as the pumice presented here. Vesicular porosity is very rare in meteorites and is often associated with slag, one, and magnetic susceptibility of this regolith breccia; values were reported as 2,900 (±40) kg per m³, 3,160 (±20) kg per m³, 7.4 (±1.5) %, and 4.43 (±0.08), respectively. Based on X-ray tomagraphy and other techniques, Hofmann et al. (2014) determined the bulk density of NWA 7034 pairings (NWA 7906 and NWA 7907), and from the bulk meteorite mode data, the grain density was estimated. In combination with these values, the porosity was determined as follows:

• grain density = 3.26 g/cm³
• bulk density = 2.89 (±0.03) g/cm³
• porosity = 11.4 (±0.9) vol %

The ‘Supplementary Materials’ section accompanying the Science article ‘Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia Northwest Africa 7034’, by Agee et al. (2013), is available here. The 1.37 g complete fragment pictured above is most likely a member of the NWA 7034 pairing group, but it has not yet been submitted for laboratory verification. This specimen appears to have been detached from a larger mass at altitude, and exhibits both primary and secondary fusionProcess in which two lighter atomic nuclei combine to form a heavier atomic nucleus. Very high temperatures are normally required in order for atomic nuclei to collide with sufficient energy to overcome the Coulomb barrier (their mutual electrostatic repulsions). Fusion that occurs under high-temperature conditions is called thermonuclear fusion. Fusion crust features. The actual color of the specimen is somewhat darker in hand sample than the pictures indicate, and its nickname ‘Black Beauty’ does seem an appropriate one.

*See the accepted petition to revise the designation for the meteorite Northwest Africa 7034 and its pairings from ‘martian basaltic breccia’ to ‘martian polymict breccia’.