Lunar Mingled 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 Click on Term to Read More (fragmental breccia with clasts of very low-Ti 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 Click on Term to Read MorebasaltBasalt 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 Click on Term to Read More, olivine gabbroWork in progress Coarse-grained igneous rock of basaltic composition that formed at depth and is 90% plagioclase. clinopyroxene, https://www.sandatlas.org/gabbro/ The most important mineral groups that make up this rock type are plagioclase and pyroxene. Plagioclase usually predominates over pyroxene. Plagioclase is sodium-calcium feldspar. It contains more calcium than sodium in gabbro. If there is Click on Term to Read MorecumulateIgneous rock composed of crystals that have grown and accumulated (often by gravitational settling) in a cooling magma chamber. Click on Term to Read More, fragmental breccias, and 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). Click on Term to Read More breccias) click on photo for a magnified view Purchased November 2004 no coordinates reported A stone weighing 26 g was purchased from a dealer in Morocco by N. Oakes. A portion was submitted for classification to Northern Arizona University (T. Bunch and J. Wittke). All together, four stones (11.6, 30.6, 64, and 85 g) having a combined weight of 191.2 g were classified under the NWA 2727 designation. Numerous additional stones (or parts thereof) were classified under different NWA-series designations by different labs (e.g., NWA 3160 and NWA 3333; see following photos). All of these similar stones are considered to be a pairing group, and all are also thought to belong to the previously recognized three-member pairing group composed of NWA 773, NWA 2700, and NWA 2977. Consistent with this finding, cosmogenic nuclideA nuclear species characterized by Z protons and N neutrons. Click on Term to Read More studies conducted on NWA 3160 indicate that it is likely paired with NWA 773 (Nishiizumi and Caffee, 2006). Additional paired stones have been recovered and more information and photos of this lunar pairing group can be found on the website of Randy L. Korotev–WUSL.
A detailed petrogenetic model for mareBroad low plains surrounded by basin-forming mountains, originally thought to be a sea (pl. maria). This term is applied to the basalt-filled impact basins common on the face of the Moon visible from Earth. Click on Term to Read More basalts was been presented by J. Day and L. Taylor (2007), for which a synopsis can be found on the NWA 032 page. This model, which demonstrates that NWA 032/479 is launch paired with the Antarctic LaPaz pairing group, was then expounded upon to explore the possibility that the NWA 773 pairing group might also be derived from the same differentiated stratigraphic magmaMolten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. Click on Term to Read More unit as the NWA 032/479 and LAP samples. Based on chemical compositions, mineralogies, textures, cooling rates, and crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. Click on Term to Read More and CRE ages, it was argued that the lunar pairing group of NWA 773 could represent the more rapidly cooled cumulate-rich base of this magma unit, while the olivine-phyric basalt component (constituting NWA 3160 in its entirity) derives from the lowermost layer adjacent to local pre-existing rock. The uniformly slow-cooled LAP samples are proposed to have crystallized in the middle of the flow, while the more rapidly cooled NWA 032 is consistent with crystallization at the upper margin.
Northwest Africa 2727 comprises three of the five compositionally diverse components identified in different members of the NWA 773 clan. The olivine-phyric basalt is a fragmental breccia of a VLT basalt with a geochemical relationship to Apollo 14 Green Glass B1 and KREEPLunar igneous rock rich in potassium (K), rare-earth elements (REE), phosphorus (P), thorium, and other incompatible elements. These elements are not incorporated into common rock-forming minerals during magma crystallization, and become enriched in the residual magma and the rocks that ultimately crystallize from it. Click on Term to Read More. Although major-element concentrations are consistent with a parental melt composition similar to Apollo 14 Green Glass, the parental melt of NWA 2727 would have had a lower Ni concentration more consistent with that of Apollo 15 Green Glass (Gibson et al., 2010). Large olivine-phyric mare basalt lithic clasts and glass porphyrys are embedded within a fine- to coarse-grained brecciated matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More (Bunch et al., 2006; Jolliff et al., 2007). Zoned olivine phenocrysts are present as spinifex- to dendritic-textured or hopper crystals, along with skeletal 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. Click on Term to Read More and 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 Click on Term to Read More, and the olivine is less evolved than the olivine in the cumulate olivine gabbro lithology.
Another component of NWA 2727 is a ferroan olivine gabbro cumulate, which along with the olivine-phyric basalt lithology represent the main constituents of this 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 Click on Term to Read More. A fragmental or regolith breccia lithology is present in lesser abundance and is composed of ferroan olivine gabbro cumulate intrusiveRefers to igneous rocks that crystallized underground. Click on Term to Read More material (26 vol%) mixed with surface porphyritic olivine basalt (60 vol%). The gabbro and basalt were derived from a similar parental melt, but the basalt source was less evolved (following 20% olivine crystallization) than that of the gabbro. In addition, a magnesian olivine gabbro lithology likely related to the ferroan olivine gabbro has been identified, and an incompatible-element-rich basaltic lithology derived from trapped intercumulus melt is present in some of the other paired stones (Shaulis et al., 2013).
Investigation of a section of NWA 2727 by North et al. (2013) revealed the presence of a pyroxene-rich clastA mineral or rock fragment embedded in another rock. Click on Term to Read More ~3 mm in size associated with the ferroan gabbro. This clast contains pigeoniteLow-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, found as a major mineral in eucrites and shergottites. In order to be considered pigeonite, the clinopyroxene must contain 5 to 20 mol % of calcium (Wo5 - 20). Chondrites of petrologic types 4 and below contain significant low-Ca clinopyroxene. During metamorphism to higher temperatures, all existing and augiteHigh-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, that occurs in many igneous rocks, particularly those of basaltic composition. In order to be considered augite, the clinopyroxene must contain 20 to 45 mol % of calcium (Wo20 - 45). An important and unique Martian meteorite is NWA 8159, that has been classified as an augite basalt. Click on Term to Read More along with plagioclase and high-Ba K-feldspar with accessory silicaSilicon dioxide, SiO2., 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 Click on Term to Read More, and sulfide. The pyroxene is similar to pyroxenes found in the paired lunaite NWA 7007, including the occurrence in both meteorites of Fe-rich pyroxferroite with its breakdown product symplectite. The presence of these 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 Click on Term to Read More species are consistent with rapid cooling and crystallization near the surface. Furthermore, North-Valencia et al. (2014) recently described a leucogabbro component in NWA 2727 composed primarily of plagioclase (61.8%) and pyroxene (38.2%); this lithology is likely related to that found in the paired NWA 3170 which Shaulis et al. (2017) termed anorthositic gabbro.
Studies of the paired stone NWA 3160 revealed that light-REE abundances and incompatible trace 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 Click on Term to Read More concentrations, especially the highly incompatible element Th, are higher compared to most other basaltic lunar samples, while plagiophile element concentrations (Na, Sr, and Eu) are lower. These characteristics demonstrate the uniqueness of this lunar meteorite and help establish a probable pairing group (Zeigler et al., 2006). The 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. Click on Term to Read More concentrations in the cumulate olivine gabbro lithology show significant variation among the different members of this lunar meteorite clan, with NWA 2727 and NWA 773 showing higher abundances compared to NWA 2977. This variation in REE abundance among the different samples could reflect the respective crystallization stage (Nagaoka et al., 2015).
Components of NWA 2727 and its pairings are compositionally similar to the olivine-phyric basalt and cumulate olivine gabbro components in the previously established NWA 773/2700/2977 pairing group. Still, the much higher abundance of mare basalt clasts in NWA 2727 and pairings, along with significant differences in the gabbro components, initially persuaded investigators that these lunaite groupings were not paired. However, considering the overall compositional and textural similarities that exist among the various stones, as well as their uniqueness compared to all other lunaites, it was ultimately established that they do represent a single diverse pairing group (Zeigler et al., 2006). Further reasons to accept the pairing argument include the reasonably similar CRE ages among different stones (~ 73–154 m.y.; Fernandes et al., 2003), the identical young Ar–Ar ages (2.7–2.8 b.y.) of like components from separate stones (Zeigler et al, 2007; Burgess et al., 2007), and the concordant Pb–Pb ages calculated for the majority of the clan members. A 14C terrestrial age of 17 (±1) t.y. was determined for the paired NWA 773 by Nishiizumi et al. (2004). A possible origin for this lunar pairing group from the nearside Procellarum KREEP Terrane is consistent with petrographic results.
A significant discovery was made by Kayama et al. (2018) of abundant (ave. 77 wt%) moganite-bearing silica micrograins in the gabbroic–basaltic breccia martix component of NWA 2727. Moganite is a thermochemically metastable mineral phase that is considered to have formed through precipitation from alkaline fluids under high-pressure (impact-related) conditions on the Moon. Other high-pressure silica phases are also present in this meteorite and associated with moganite, including coesiteHigh-pressure polymorph of silicon dioxide (SiO2). Has the same chemical composition as cristobalite, stishovite, seifertite and tridymite but possesses a different crystal structure. Coesite forms at intense pressures of above about 2.5 GPa (25 kbar) and temperature above about 700 °C, and was first found naturally on Earth in impact Click on Term to Read More, 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 Click on Term to Read More, and cristobaliteHigh temperature polymorph of silicon dioxide (SiO2). Has the same chemical composition as coesite, stishovite, seifertite and tridymite but possesses a different crystal structure. This silica group mineral occurs in terrestrial volcanic rocks, martian and lunar meteorites, chondrites and impact glasses like Libyan Desert Glass. Cristobalite has a very open Click on Term to Read More, all of which were formed as transition minerals from precursor moganite during peak shock pressure; this peak pressure is calculated to have been in the range of 8–22 GPa. Post-shock temperatures are calculated to have been 673–1073 K in the breccia matrix where moganite occurs, and to have reached >1173 K in shock veins where moganite was converted to the other high-pressure phases. Kayama et al. (2018) presented a multi-stage scenario to account for the formation of moganite as follows (also see diagram below):
Alkaline fluids (pH 7.0–12.0) were delivered by 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 Click on Term to Read More meteorites to the lunar surface <2.67 b.y. ago, where the water was trapped as subsurface ice in permanently shadowed regions (PSR) within a stability depth range of 0.1 mm to >100 m.
Impacts into existing basaltic and gabbroic lithologies in the Procellarum KREEP Terrane (PKT) and South Pole–Aitken [SPA] basin regions produced a mixed gabbroic–basaltic breccia and incorporated a component of the subsurface meteoritic water ice.
Moganite-bearing silica micrograins precipitated from the aqueous fluid component within the gabbroic–basaltic breccia matrix at temperatures of 363–399 K and a pH of 9.5–10.5.
The NWA 2727 lithology (sunlit) and adjacent lithologies (773 clan) were ejected from the PKT region of the Moon ~1–30 m.y. ago, during which time the shock-induced conversion of some moganite to high-pressure silica phases occurred. Based on silica solubility equations, Kayama et al. (2018) calculated that a lunar bulk water content of at least 0.6–12.3 wt % would be required to precipitate the volume of moganite present in NWA 2727.
Schematic History of Moganite Precipitation on the Moon click on image for a magnified view
Diagram credit: Kayama et al., Science Advances, vol. 4, #5, eaar4378 (2 May 2018, open accesslink) ‘Discovery of moganite in a lunar meteorite as a trace of H2O ice in the Moon’s regolith’ (https://doi.org/10.1126/sciadv.aar4378) It is generally accepted that the Moon was formed from the debris that resulted from a collision between Earth and a smaller body named ‘Theia’, which created an all-encompassing 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 Click on Term to Read More. It was calculated from isotopic data that the earliest time this event could have occurred is 4.517 b.y. ago (Nemchin et al., 2009), or 30–110 m.y. after the beginning of the Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. (Yin et al., 2002; Kleine et al., 2005). Based on Pb–Pb dating of zirconOrthosilicate mineral, Zr(SiO4), observed in all terrestrial rocks type and in ordinary chondrites, eucrites, mesosiderites, and lunar rocks. crystals, which is a late crystallization product derived from the last dregs of the lunar magma ocean, Nemchin et al. (2009) determined that crystallization of the lunar magma ocean was complete by 4.417 (±0.006) b.y. ago, thus establishing the timeframe for the solidification of the lunar magma ocean at 100 m.y. They also reasoned that formation of an anorthositeA phaneritic, intrusive igneous rock made with a modal composition (i.e. volume%) > 90% plagioclase feldspar of undefined composition (anorthitic to albitic, or combination thereof), and a small mafic component between 0 - 10% such as pyroxene, ilmenite, magnetite, and olivine 1. The name anorthosite is derived from the calcium-rich Click on Term to Read MorecrustOutermost 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 Click on Term to Read More could not begin until 80–85% of the magma ocean had crystallized, which would allow relatively rapid cooling over a time interval of ~50 m.y. The final 25% of crystallization would have taken place under an insulating anorthosite crust over a similar time interval of ~50 m.y.
A transmitted light view of a petrographic thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope. of NWA 2727 can be seen on John Kashuba’s page. The photo of NWA 2727 shown above is a 2.0 g slice sectioned from the original 30.6 g stone. The specimen consists of porphyritic olivine basalt clasts of varying grain size, clasts of ferroan olivine gabbro cumulate, and a regolith breccia component, each sintered into a composite rock by shock-melt veins. The photo below shows the outside appearance of the 30.6 g parent stone. Photo courtesy of N. Classen