Category: Achondrite (Primitive)

Winonaitea partially differentiated asteroid that was disrupted just as it began to form an Fe core and a silicate-rich crust. This disrupting impact mixed silicates into molten Ni-Fe metal forming the silicated IAB irons, and mixed olivine-rich residues of partial melts into unmelted silicates, forming the winonaites. A few winonaites Click on Term to Read More (evolved)*
Found Before 1965, 34° 56′ N., 102° 01′ W.

An 860 g stone covered 80% by weathered 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. Click on Term to Read More was found by a local rancher near Tierra Blanca Creek (translated: white earth creek), about 10 km SW of Canyon, Texas. It was brought to the Department of Geology, West Texas State University, where it was identified by F. Daugherty as 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 Click on Term to Read More. To date only a small number of winonaites have been identified; some of those found outside Antarctica include Pontlyfni, which is the only fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If Click on Term to Read More of the group, Winona, Tierra Blanca, Mount Morris, HaH 193, NWA 516, NWA 1457, NWA 1463 and pairing group, and NWA 1617. Pontlyfni, Mount Morris, and the NWA 725 pairing group contain relict chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at  ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More (porphyritic 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 Click on Term to Read More and radial pyroxene in Pontlyfni).

*Previously, Floss (2000) and Patzer et al. (2003) proposed that the acapulcoitePrimitive achondrite that belongs to a small group named after the Acapulco meteorite that was observed to fall in Mexico in 1976. Acapulcoites are made mostly of fine-grained olivine (Fo3-14), orthopyroxene(En86-97), Ca-rich pyroxene (En51Wo44), plagioclase (An12-31), Ni-Fe metal, and troilite. They are transitional between primordial chondritic matter and more differentiated Click on Term to Read More/lodranite meteorites should be divided based on metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. Click on Term to Read More stage:

1. primitive acapulcoitesPrimitive achondrite that belongs to a small group named after the Acapulco meteorite that was observed to fall in Mexico in 1976. Acapulcoites are made mostly of fine-grained olivine (Fo3-14), orthopyroxene(En86-97), Ca-rich pyroxene (En51Wo44), plagioclase (An12-31), Ni-Fe metal, and troilite. They are transitional between primordial chondritic matter and more differentiated Click on Term to Read More: near-chondritic (Se >12–13 ppmParts per million (10⁶). Click on Term to Read More [degree of sulfide extraction])
2. typical acapulcoites: Fe–Ni–FeS melting and some loss of sulfide (Se ~5–12 ppm)
3. transitional acapulcoites: sulfide depletion and some loss 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 Click on Term to Read More (Se <5 ppm)
4. lodranites: sulfide, metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn Click on Term to Read More, and plagioclase depletion (K <200 ppm [degree of plagioclase extraction])
5. enriched acapulcoites (addition of feldspar-rich melt component)

A similar distinction could be made among the winonaites in our collections, although there is not yet an analog of the IAB complex irons for the acapulcoite/lodranite PB. Northwest Africa 1463 (and pairing group) ranks as the most primitive member of the winonaites, containing intact chondrules comparable to a petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes. 5 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 Click on Term to Read More (Benedix et al., 2003). However, most winonaites experienced extensive thermal metamorphism involving incipient sulfide melting and exhibit highly recrystallized textures, characteristics analogous to the ‘typical’ acapulcoites. Metamorphic progression in other winonaites led to partial loss of the low-melting phases FeS and plagioclase, and these are designated as a ‘transitional’ stage in the acapulcoite/lodranite metamorphic continuum. Those winonaites which experienced the highest temperatures ultimately crystallized from residual melt material, and they exhibit significant depletions in FeS, FeNi-metal, and plagioclase (including plagiophile trace elements). Samples representing this advanced metamorphic stage are known as lodranites in the acapulcoite/lodranite metamorphic sequence, while the term ‘evolved’ could be used to represent a similar metamorphic stage in the winonaite group (e.g., Tierra Blanca; Hunt et al., 2017).

Winonaites define a group of meteorites that have 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 compositions intermediate between groups E and H chondritesChondrites 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 Click on Term to Read More, with O-isotope compositions that are unique from all other groups except IAB complex irons. They have a metamorphically heterogeneous chondritic composition and a reducedOxidation 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 Click on Term to Read More state (Tierra Blanca is among the most oxidizedOxidation 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 Click on Term to Read More of the winonaites). Winonaites are considered by some to derive from the breakup and reassembly of a hot, partially differentiated body ~60–200 km in diameter on which sulfur-rich molten metal had begun forming a coreIn 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. Click on Term to Read More, and silicates had undergone varying degrees of partial meltingAn igneous process whereby rocks melt and the resulting magma is comprised of the remaining partially melted rock (sometimes called restite) and a liquid whose composition differs from the original rock. Partial melting occurs because nearly all rocks are made up of different minerals, each of which has a different melting Click on Term to Read More forming basaltic melts and olivine-rich residues (Benedix et al., 1995, 1996; Hunt et al., 2017). About 10–14 m.y. after CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More, near the stage of peak temperatures, a catastrophic impact disrupted the winonaite–IAB parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More excavating molten core material and injecting it into cooler silicates, which quickly solidified to form the IAB irons with 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 inclusions. Deep burial of these silicated irons resulted in slow cooling rates and permitted the formation of a Thomson (Widmanstätten) structure.

The reassembly that followed this catastrophic collision also mixed olivine-rich residues into unmelted silicates nearer the surface to form the winonaites, while subsequent impact gardening contributed to the mixing of various lithologies. Varying degrees of thermal metamorphism produced the wide variation of 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 observed within the winonaite group. Schulz et al. (2007, 2010) determined a Hf–W isochron for selected winonaites, reflecting the end of Hf–W redistribution between metal and silicate during progressive cooling. They revealed an age of <4.45 b.y. for Winona, which is somewhat younger than that of Pontlyfni. This suggests either that some winonaites cooled very slowly (~4K/m.y. in the temperature range 1150–550K) while at a significant depth, or that the winonaite Hf–W age reflects a late impact-related re-equilibration event on the parent body. The presence of relict chondrules in Pontlyfni but not in Winona is consistent with the former scenario.

Evidence was presented by Yugami et al. (1998) indicating that local textural and mineralogical variations on a cm-scale are the result of petrological processes rather than the reassembly of heterogeneous clastic material. In a similar argument, Benedix et al. (2005) proposed that this small scale heterogeneity is the result of localized heating and cooling rates of fragments following the reassembly after a catastrophic breakup. Utilizing heliumHelium (He) Second lightest and second most abundant element (after Hydrogen) in the universe. The most abundant isotope is 4He (99.9998%), 3He is very rare. Helium comprises ~8% of the atoms (25% of the mass) of all directly observed matter in the universe. Helium is produced by hydrogen burning inside Click on Term to Read More pycnometry, Consolmagno et al. (2007) determined a 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 Click on Term to Read More for Tierra Blanca of 14% (±4%).

Tierra Blanca is an Fe-rich winonaite and is among the coarsest-grained members of the group (0.1–0.2 mm). It has an equigranular texture with abundant triple junctions, and shows no evidence of mixing with a molten metallic phase. Benedix et al. (1998) concluded that the growth of large, poikilitic, Ca-rich pyroxene grains enclosing 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 More in Tierra Blanca occurred during later metamorphic processes. Similar large poikilitic 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 Click on Term to Read More grains present in HaH 193 have been attributed by Floss et al. (2007) to an extended period of thermal metamorphism and slow cooling at depth. Tierra Blanca contains a lower abundance of Ca-rich materials and a higher abundance of olivine and chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups. Click on Term to Read More than other winonaites. It exhibits Fe/Mg reverse zoning in olivine which is attributed to solid state reductionOxidation 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 Click on Term to Read More. However, another study involving 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 Click on Term to Read More fugacities of winonaites (related to the partial pressure of available oxygen) suggests that most of the reduction observed is an intrinsic property of the chondritic precursor (Benedix et al., 2005).

Textural comparison of four winonaites, L to R: NWA 1463 (with relict chondruleRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at  ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More), Winona, Tierra Blanca, HaH 193
Image credit: Floss et al., MAPS, vol. 43, #4, p. 660 (2008)
‘Evolution of the winonaite parent body: Clues from silicate mineral trace element distributions’
(http://dx.doi.org/10.1111/j.1945-5100.2008.tb00676.x)
Some regions of coarse-grained olivine grains may represent partial melt residues produced by the extraction of a basaltic melt and FeNi–FeS through veins. These features attest to a moderate degree of silicate partial melting on the precursor body at a temperature of 1200°C, which has been confirmed through two-pyroxene geothermometry analysis (900–1100°C estimated by Lindsley, 1983). However, Floss et al. (2008) analyzed the suspected silicate partial melt and melt residue lithologies in Tierra Blanca, Winina, and HaH 193 for expected incompatible element enrichments and depletions, respectively. Despite variable incompatible trace element abundances, they did not findMeteorite not seen to fall, but recovered at some later date. For example, many finds from Antarctica fell 10,000 to 700,000 years ago. Click on Term to Read More differences in plagioclase among winonaites and were unable to unequivocally demonstrate that a silicate partial melt exists. Instead, they propose that the rare fine-grained plagioclse-rich, and coarse-grained olivine lithologies present in some winonaites, as well as the ubiquitous FeNi-metal veining, were produced through impact-induced shock meltingComplete melting of target material produced by the shock of a meteoric impact. Different minerals will experience certain shock effects at different pressures and temperatures. For example, dense target rocks like anorthosite will typically experience whole rock melting above 50 to 60 GPa, while chondritic rocks require more than 70 Click on Term to Read More; they infer that any occurrence of silicate partial melting was not widespread. In a subsequent study of eight winonaites, Hunt et al. (2017) utilized major element and 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 data as well as two-pyroxene thermometry to ascertain that only Tierra Blanca experienced temperatures high enough (1473 [±100] K) to produce silicate melting and extraction. However, previous studies (Benedix et al., 1998, 2005) have revealed that Winona is heterogeneous in both its texture and in its range of peak temperatures, concluding that some portions of this meteorite were likely to have experienced some degree of silicate partial melting. It is interesting that in their trace element study of Winona, Hunt et al. (2017) found that it has a similar positive Ce anomaly to achondrites recovered from Antarctica. They reason that since this Ce anomaly is produced through terrestrial weathering in a cold desert environment, it is likely that Winona was transported south to Arizona from a similar cold desert location.

Based on similar silicate textures, reduced mineral chemistry, and O-isotopes, it is presumed that the winonaites and the IAB complex irons originated on a common parent body. Utilizing a Ge/Ni vs. 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 Click on Term to Read More/Ni coupled diagram, Hidaka et al. (2015) determined that FeNi-metal in the winonaite Y-8005 plots in the field of the sLL subgroup of the IAB complex irons. In addition, the metal in this winonaite retains a near chondritic composition likely representative of the precursor material of the parent body. In view of these findings, they suggest that the sLL subgroup rather than the main group of the IAB complex represents the primitive metal of the IAB–winonaite parent body, with the main group possibly representing a partial melt of the sLL subgroup.

Oxygen 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. Click on Term to Read More data obtained by Hunt et al. (2012) for silicate inclusions in IAB irons, along with the observed volatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). element depletions, led to the inferrence that the winonaite precursor likely had a volatile-depleted carbonaceous chondrite-like composition. From results of their trace element analyses of a broad sampling of winonaites, Hunt et al. (2017) recognized that CM chondrites represent the closest match; however, the important differences that exist indicate that the precursor to winonaites is unlike any meteorite class currently known. Yugami et al. (1999) speculate that these and other primitive achondrites may have been heated early in the Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. by both radiogenic 26Al decay and by slow-speed collisions of planetesimalsHypothetical solid celestial body that accumulated during the last stages of accretion. These bodies, from ~1-100 km in size, formed in the early solar system by accretion of dust (rock) and ice (if present) in the central plane of the solar nebula. Most planetesimals accreted to planets, but many – Click on Term to Read More. The Tierra Blanca 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". Click on Term to Read More of 465 g was traded from the Dr. Elbert A. King Collection to the Natural History Museum, London. The specimen shown above is a 1.1 g cut fragment.