Type of evolved achondrite meteorite that represent some of the earliest stages of asteroidal differentiation and magmatism in our solar system. Angrites are named for the Angra dos Reis meteorite, which fell in Rio de Janeiro, Brazil, in early 1869. They are basaltic (mafic) rocks, often containing porous areas, and Click on Term to Read More
Found July 1979
37° 40′ S., 61° 39′ W. This relatively fresh, 16.55 kg, shield-shaped, regmaglypted 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 Click on Term to Read More is by far the largest of the angrites found so far. The mass was found in Buenos Aires Province, Argentina by a farm worker who struck it with a plow. Thinking he had unearthed an Indian artifact, possibly an old mortar, he gave it to the landowner who set it by his house for the next ~20 years. Not until 1998, after reading an article on meteorites, did the owner seek to have the stone analyzed. In September 2000, Dr. G. Kurat of the Naturhistorisches Museum in Vienna, Austria made the determination that it was an Type of evolved achondrite meteorite that represent some of the earliest stages of asteroidal differentiation and magmatism in our solar system. Angrites are named for the Angra dos Reis meteorite, which fell in Rio de Janeiro, Brazil, in early 1869. They are basaltic (mafic) rocks, often containing porous areas, and Click on Term to Read More.
Diagram credit: Nakashima et al., MAPS, vol. 53, #5, p. 965 (2018)
‘Noble gases in angrites Northwest Africa 1296, 2999/4931, 4590, and 4801: Evolution history inferred from Element 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. Click on Term to Read More signatures’
(http://dx.doi.org/10.1111/maps.13039) Trace 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 Click on Term to Read More data argues for a more complex history for D’Orbigny and most angrites, including a non-igneous formation from a refractory In the solar nebula, product of a chemical condensation reaction where a mineral phase precipitates (condenses) directly from a cooling vapor. Click on Term to Read More of a chondritic nature. Late phases of D’Orbigny are enriched in moderately volatile elements compared to early phases, and the two phases were formed under very different 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 Click on Term to Read More conditions—the early phases grew under highly 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 Click on Term to Read More conditions while the late phases grew under highly oxidizing conditions (Varela et al., 2005). The occurrence within anorthite (with or without olivine) of metal+sulfide arrays having a high Ni content (up to 50%) provides further evidence for a reducing sulfurous environment in the early formation history of D’Orbigny (Varela et al., 2015). Moreover, Hwang et al. (2015) observed FeS–oxide associations hosted by anorthite which indicate an increasing degree of oxidation over time. It is also reported that the highly incompatible elements in all olivine phases are far out of 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 Click on Term to Read More (highly enriched) with the parental melt that formed the bulk rock. Curiously, 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 Click on Term to Read More, which formed together with the olivine, contains very different abundances of incompatible elements, suggesting that the olivine and plagioclase formed from melts of dissimilar compositions. It is also considered that the solid spheres, which are now enriched in Ca and unfractionated trace elements, may have previoulsy been composed of CaS before undergoing decomposition under increasingly high oxidizing conditions. By this process the previously bound trace elements were converted into a vapor phase and became available for late phase metasomatism and augite formation. Angrites are extremely ancient meteorites, with some such as D’Orbigny having accretion ages as early as ~0.5 m.y. after the first nebular condensates (Sub-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) were formed (Sugiura and Fijiya, 2012). Other angrites such as LEW 86010 and Angra dos Reis attest to the fact that basaltic extrusion on the angrite parent body continued for ~7 m.y. longer. The early thermal history of the angrite parent body is most consistent with a relatively large sized planetesimal of at least 100 km in diameter (Sahijpal et al., 2007). One scenario for the formation of angrites involves an igneous history.
- From formation models developed by Sahijpal et al. (2007), and from Rb–Sr and Hf–W systematics ascertained by Hans et al. (2009), it can be inferred that the angrite parent body experienced a relatively early onset of accretion, which was associated with volatile loss, within ~2–3 m.y. of Solar Definable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with history, a process which then proceeded rapidly to completion over a timeframe of <10 t.y. Crystallization of the angrites proceeded as a two-stage process, beginning with An 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 from a CV-like chondritic source composed of olivine, Orthorhombic, 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, and clinopyroxene at low pressures and elevated Element 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 levels. The abundance of H2O in the parental magma as calculated by Suzuki et al. (2012) was ~0.003–0.012 wt%. They inferred an APB 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 Click on Term to Read More H2O content of ~0.001–0.003 wt% (= 10–30 ppm) based on ~30–40% partial melting and 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. Click on Term to Read More. Heat generated by the decay of short-lived radiogenic isotopes produced metal–silicate melting, A 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 Click on Term to Read More, and basaltic melt extrusion within ~100 t.y. of the onset of accretion. This 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 Click on Term to Read More was slowly cooled to ~650°C, while some of the melt experienced rapid quenching (7–13°C/hr) during eruption onto the surface and/or through a severe impact event.
Based on a study of highly volatile elements (e.g., H, C, F) in the D’Orbigny and Sahara 99555 angrites, Sarafian et al. (2017) determined that H2O and C are enriched by a factor of one million based on the observed abundances of moderately volatile elements, the latter exhibiting relatively high depletions either inherited from the An immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive Click on Term to Read More or associated with planetesimal accretion. They posit that 0.1–1 wt% of volatile-rich carbonaceous chondrite-type material was added to the APB sometime between the time of 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. Click on Term to Read More formation ~4.5650 ago (consistent with chondritic HSE ratios) and the time of crystallization of the earliest known angrites ~4.5636 b.y. ago. From this amount of Carbonaceous 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 material they infer an APB mantle H2O content of ~230 ppm (= 0.023 wt%).
- Severe outgassing of volatiles occurred during the impact event(s), possibly hastened by the reduced strength of the gravitational field of the fragmented planetesimal.
- A magnetic field with a strength ~20% that of present-day Earth was imparted to the angrite PB during its earliest phase of crystallization (as observed from D’Orbigny); this magnetic field may possibly be attributable to an orbital residence very near to the early T-Tauri phase solar field, or to an internal core-dynamo mechanism (Weiss et al., 2008).
- Based on studies of how kirschsteinite-lamellae profiles relate to cooling rates, as well as results of crystallization experiments, the burial depth of the angrites as they were rapidly crystallized in a thin Hot molten or semifluid rock derived from a volcano or surface fissure from a differentiated and magmatically active parent body. Click on Term to Read More flow is inferred to have been within 1 m of the surface.
Another possible petrogenetic history involves a non-igneous formation:
- Kurat et al. (2004) and Varela et al. (2005) have conducted extensive studies of D’Orbigny and other angrites in which they utilized mutiple sources of data (e.g., structural, textural, chemical, and redox evidence). They concluded that the angrites are most consistent with a non-igneous origin from refractory solar nebula condensates having chondritic abundances—basically an asteroid-sized version of a CAI—which record unusual circumstances (e.g., changing redox conditions) in the early history of the solar system.
Diagrams credit: Rivkin et al., Icarus, vol. 192, #2, (2007)
‘Composition of the L5 Mars Trojans: Neighbors, not siblings’
(https://doi.org/10.1016/j.icarus.2007.06.026; open access link) The number of unique angrites represented in our collections today is limited, and they have been grouped by some as basaltic/quenched, sub-volcanic/metamorphic, or plutonic/metamorphic, along with a single dunitic sample in NWA 8535 (photo courtesy of Habib Naji). Notably, another Meteorite 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 from Antarctica, Y-1154, is an anomalous meteorite containing Al,Ti–diopside-hedenbergite that is compositionally similar to angrites, but it has a unique fine-grained, dendritic texture. An excellent petrographic Thin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope. micrograph of D’Orbigny can be seen on John Kashuba’s webpage. The specimen of D’Orbigny pictured above is a 1.6 g partial slice.