Martian Igneous 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
(enriched, permafric, Oxidation 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)
Found April 2001
no coordinates recorded One large mass of 522 g along with twenty-two additional fragments, all together weighing 576.77 g, were found by a French team in the Maarir region near the border of Morocco and Algeria. This Work 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 was designated Northwest Africa 1068, and a sample was submitted to École Normale Supérieure de Lyon and other institutions for analysis and classification. Unaware of the analyses being conducted by the French institutions, additional paired fragments purchased in Morocco having a combined weight of 118 g were submitted to the University of Washington (Irving and Kuehner, 2002). Since the name NWA 1110 had been previously reserved from the Nomenclature Committee for these additional fragments, this meteorite will be recognized as a pairing under both names. Subsequent to this, other individual fragments were recovered in the strewnfield, some of which were submitted to the NomCom under unique NWA numbers (e.g., NWA 1183, NWA 1775, NWA 2373, NWA 2969).
Northwest Africa 1068 is considered to represent a distinct olivine-phyric subgroup of Igneous 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, characterized by an abundance of Group 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 megacrysts (~22 vol%) embedded within a primarily low-Ca A 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. groundmass (~42 vol%). This subgroup would comprise those meteorites derived from a primary Molten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. associated with an ascending Main 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 plume. They are Term used for silicate minerals with cations predominantly Mg and/or Fe. Mafic minerals are dominated by plagioclase and pyroxene, and also contain smaller amounts of olivine. rocks, enriched in Mg (>12%), Ti, and other incompatibles, and were formed at greater depths under higher pressures than the basaltic subgroup. Despite some important compositional differences, close petrological and geochemical similarities exist between NWA 1068 and both the olivine-phyric shergottite LAR 06319 and the olivine-basaltic shergottite NWA 4468 (Sarbadhikari et al., 2009). According to MELTS program modeling, Marks et al. (2010) found that both NWA 1068 and 4468 have compositions that are consistent with the hypothesized parental melt for LA 001; in particular, the Often 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. patterns and initial Sr–Nd isotopic compositions are consistent with such a relationship, and the major Substance 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 compositions reflect a mantle-associated Concentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process.. The Physical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. ages for both NWA 1068 and Los Angeles are concordant at ~180 m.y., and they might be derived from a common primary magma source—with Los Angeles crystallizing after ~40% fractionation, and NWA 1068 after addition of 22% olivine (Treiman and Filiberto, 2014).
The occurrence of Also 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 in the form of Natural glass composed of isotropic plagioclase produced during shock metamorphism (not melting) at pressures of ~30 GPa. Maskelynite is commonly found in shergottites though also found in some ordinary chondrites, HED and lunar meteorites. It is also found in association with meteorite impact craters and crater ejecta. Named after British (~15 vol%), undulose In astronomy, the dimming of starlight as it passes through the interstellar medium. Dust scatters some of the light, causing the total intensity of the light to diminish. It is important to take this effect into account when measuring the apparent brightness of stars. The dark bands running across portions of pyroxene and olivine, impact-melt pockets, and shock veins attest to high Metamorphism produced by hypervelocity impact between objects of substantial size moving at cosmic velocity (at least several kilometers per second). Kinetic energy is converted into seismic and heat energy almost instantaneously, yielding pressures and temperatures far in excess those in normal terrestrial metamorphism. On planetary bodies with no atmosphere, smaller (29–55 GPa) for this meteorite. Minor amounts of Ca-phosphates, K-feldspar, FeS, ulvöspinel, and Brownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups. are also present. Despite its lack of Melted 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., NWA 1068 is relatively fresh, with only minor calcite and clay minerals present in cracks and along grain boundaries. Using the typical increases in the Sr, Ba, and Pb abundances observed in hot desert meteorites as a barometer, NWA 1068 has not been greatly affected by weathering (Barrat et al., 2002).
Similar to other highly shocked martian meteorites, NWA 1068 contains a significant concentration of martian atmospheric Ar within melt pockets (ave. 8.6 Parts per billion (109).), with a minor component present within shock veins (ave. 0.9 ppb). The favored scenario for the existence of this trapped gas component within melt pockets is based on the argument that martian atmospheric gas was initially introduced into pre-existing cracks and pores. Following the passage of a Abrupt perturbation in the temperature, pressure and density of a solid, liquid or gas, that propagates faster than the speed of sound., sudden decompression and pressure release created bubbles within sub-mm- to mm-sized localized melt pockets. Thereafter, as pressures became equilibrated, the trapped atmospheric gases migrated into the vesicles of the melt phase from the surrounding cracks and pores (Walton et al., 2007).
Northwest Africa 1068 is composed of abundant olivine megacrysts up to 2 mm in size that have magnesian cores (up to Fo72), and rims (as well as other smaller phenocrysts) that are more ferroan (Fo49). These olivine grains usually occur as single crystals, but many are polycrystalline and contain magmatic inclusions. They show almost identical chemical compositions to the olivines in martian poikilitic (formerly lherzolitic) shergottites, and it is considered by many investigators, based on the disparate Oxidation 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 conditions under which In the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. and rim crystallized (i.e., increasing Oxidation 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 from core to rim) as well as on textural and other petrographic evidence, that the megacrysts are in fact xenocrysts that were accumulated into the magma flow from different melt reservoirs (Herd, 2006; Shearer et al., 2012). The zoning in the rims of these olivine megacrysts could be attributed to Movement of particles from higher chemical potential to lower chemical potential (chemical potential can in most cases of diffusion be represented by a change in concentration). Diffusion, the spontaneous spreading of matter (particles), heat, or momentum, is one type of transport phenomena. Because diffusion is thermally activated, coefficients for diffusion between the olivine and the magma that ensued following their incorporation. In keeping with this diffusion process is the fact that these large olivines appear to have only equilibrated with the groundmass along their rims, a feature which further supports a xenocrystic origin. Moreover, they are enriched in Co and incompatible elements compared to the groundmass, and evidence indicates that they crystallized under more Oxidation 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 conditions.
In an alternative view, it has been argued that the olivine megacrysts represent phenocrysts (co-genetic), as demonstrated by the Term used to describe physical or chemical stasis. Physical equilibrium may be divided into two types: static and dynamic. Static equilibrium occurs when the components of forces and torques acting in one direction are balanced by components of forces and torques acting in the opposite direction. A system in static between Igneous rock composed of crystals that have grown and accumulated (often by gravitational settling) in a cooling magma chamber. olivine and the olivine megacryst cores (Filiberto et al., 2010). Another observation in support of a phenocrystic origin for the olivine megacrysts is that the olivine appears to be in isotopic equilibrium with the other Inorganic 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 components of the rock. The observed zoning in NWA 1068 olivine megacrysts could be interpreted as reworked phenocrysts that were subjected to a short period of gravitational settling and/or convective transport before accumulation (Shearer et al., 2008).
In further support of a phenocrystic origin, it was argued that the melt inclusions within the olivine megacrysts of NWA 1068, as well as in other olivine-phyric shergottites, have a similar composition to that of the bulk rock, indicating a derivation from a common parental source magma. Since the olivine megacrysts and the bulk rock are in chemical equilibrium, there is a high likelihood that the megacrysts represent phenocrysts derived from a common parental source melt. Moreover, the formation of Mg-Al oxide, MgAl2O4, found in CAIs. and high-Ca pyroxene in both the megacrysts and the Fine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. was concurrent. As such, it was undertaken by Filiberto et al. (2013) to compare the composition of the primary trapped melt in the magnesian megacrysts to that of the calculated parental melt prior to incorporation of excess olivine; their results were most consistent with a xenocrystic origin for the megacrysts.
Cooling rate studies place the crystallization of the low-Ti/Al pyroxene in NWA 1068 at a depth of ~85 km (~10 kbar), near the base of the Outermost 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, whereas the pyroxenes with a higher Ti/Al crystallized near the surface (<4.3 kbar), possibly upon eruption. in contrast, geochemical modeling conducted by Filiberto and Dasgupta (2012) suggest that formation occurred at a depth of ~150 km at a temperature of ~1520°C. This temperature is within the range of the calculated average mantle temperature of 1450 (±80) °C for Basalt 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 formation during the Noachian period, 4.5–3.6 b.y. ago. A scenario for the complex petrogenesis of this meteorite was constructed as follows:
Following their crystallization at depth, the cumulate olivine megacrysts were incorporated into an ascending, enriched, oxidized magma plume that originated at the upper-mantle (at depths of ~250–400 km; Kiefer, 2003), envisioned to be similar to lunar ur-KREEP that crystallized as a late-stage residual liquid of the martian Completely 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 (Borg et al., 2012). The magma ponded in or near the base of the crust where olivine crystallized and accumulated from either the same (phenocrysts or antecrysts) or neighboring (xenocrysts) magma plumes. Low-Ti/Al pyroxene then crystallized and erupted onto or near the surface together with the olivine megacrysts. Cooling occurred rapidly close to the surface where shock Rocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. effects became significant. This scenario is consistent with the finding that NWA 1068 has a REE pattern that is similar to other basaltic shergottites, while other olivine-containing shergottites such as DaG 476, Dhofar 019, and SaU 005 do not. Xenocrystic olivines in EETA79001A might have a similar origin. Northwest Africa 1068 is a relatively primitive shergottite with a magnesian bulk composition, but is not as magnesian as experiments indicate it should be if it represented a primary liquid composition. Because it has incorporated a high abundance of olivine megacrysts it no longer represents a primary magma composition (Bunch et al., 2009).
Trace element data confirm that Northwest Africa 1068/1110 is unpaired with any previously found martian meteorites. In contrast to the depleted LREE evident in most all other olivine-phyric shergottites, NWA 1068 is enriched in incompatible elements similar to that which is found in the basaltic shergottites Shergotty, Zagami, and Los Angeles; incompatible element ratios are consistent with these basaltic shergottites as well. This suggests a parental magma for NWA 1068 of basaltic shergottite composition which had assimilated a late-stage, enriched, and more-oxidized cumulate component close to lherzolitic composition. Thereafter, olivine crystallized and was accumulated, perhaps as phenocrysts (Shearer et al., 2008).
Studies of NWA 1068 have continued in an effort to characterize the true nature of the olivine megacrysts and to better resolve the petrogenesis of the meteorite. Through advanced Fe–Mg One 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. and major, minor, and trace element analyses of NWA 1068 bulk rock and olivine megacrysts, Collinet et al., (2017) determined that the meteorite is most consistent with a near-primary magma composition. In their formation model the olivine megacrysts and the groundmass of the meteorite are co-genetic. Subsequent to olivine megacryst formation, which they ascertained occurred over a time period of ~2–6 years under relatively slow cooling conditions within a deep Geology: 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 (the final span of ~100 days involved rim and groundmass crystallization at much faster cooling rates during/after magma ascent), the megacryst cores experienced simultaneous diffusion and growth of outer rims along with crystallization of the groundmass pyroxene and olivine, as evidenced by the fractionated Fe–Mg isotope and element profiles which are observed. This diffusion process Oxidation 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 the Fo content by ~3.2 mol% from its original value to values as magnesian as Fo77; these current Fo values had previously been attributed to Fe–Mg equilibrium conditions attained through olivine accumulation. Therefore, the bulk rock composition of NWA 1068, and in a similar way that of LAR 06319, is likely representative of a primary magma, derived from a refractory mantle source, having an intermediate composition of at least ~Fo80 (see diagram below).
Diagram credit: Collinet et al., GCA, vol. 207, p. 294 (2017)
‘Crystallization history of enriched shergottites from Fe and Mg isotope fractionation in olivine megacrysts’
(https://doi.org/10.1016/j.gca.2017.03.029) Isotopic analyses using Sm–Nd and Rb–Sr data have determined a crystallization age for this shergottite of 185 (±11) m.y., and its CRE age has been calculated to be 2.2 (±0.2) m.y. (2.5–3.1 m.y. based on 10Be [Nishiizumi and Caffee, 2006] and 2.0 ±0.5 m.y. based on Ar systematics [Walton et al., 2007]). This CRE age is similar to several other martian meteorites, including NWA 2646, LAR 06319, and NWA 480/1460. Cosmic ray exposure ages have now been determined for many martian meteorites, and Mahajan (2015, #1166) 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 1068/1110 was launched from Mars during the 2.12 m.y.-old impact event. 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 suggest that NWA 1068/1110 might have been ejected with the large group of at least 26 enriched shergottites, or alternatively, it could represent a unique ejection event because of its disparate texture.
Interestingly, a determination of the Pb-isotopic composition of the original source of the olivine-phyric shergottites shows a similar plot to that of the nakhlites, and these diverse martian meteorites may have originated from the same mantle reservoir (Emil et al., 2006). The specimen of NWA 1068 pictured above is a 1.19 g partial slice with a thin black impact-shock vein along the left side and a natural edge along two sides. The photo below shows the Largest 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". of NWA 1068.
∗ Recent geochemical research on the martian basalts has led to new petrogenetic models and classification schemes.read more >>
Photo courtesy of B. Fectay and C. Bidaut—Meteorite.fr