IVB meteorite

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IVB meteorites
—  Group  —
Tlacotepec meteorite.jpg
Tlacotepec is one of 14 known IVB specimens; in contrast to most IVBs it is an octahedrite instead of an ataxite
Type Iron
Structural classification Most are ataxites (without structure) but show microscopic Widmanstätten patterns
Class Magmatic
Subgroups
  • None?
Parent body IVB
Composition Meteoric iron (kamacite, taenite & tetrataenite); low in volatile elements, high in nickel & refractory elements
Total known specimens14

IVB meteorites are a group of ataxite iron meteorites classified as achondrites. [1] The IVB group has the most extreme chemical compositions of all iron meteorites, meaning that examples of the group are depleted in volatile elements and enriched in refractory elements compared to other iron meteorites. [2]

Contents

Description

The IVB meteorites are composed of meteoric iron (kamacite, taenite and tetrataenite). The chemical composition is low in volatile elements and high in nickel and refractory elements. Although most IVB meteorites are ataxites ("without structure"), they do show microscopic Widmanstätten patterns. The lamellae are smaller than 20 μm wide and lie in a matrix of plessite. [3] The Tlacotepec meteorite is an octahedrite, making a notable exception, as most IVBs are ataxites. [4]

Classification

Iron meteorites were originally divided into four groups designated by Roman numerals (I, II, III, IV). When more chemical data became available some groups were split. Group IV was split into IVA and IVB meteorites. [5] The chemical classification is based on diagrams that plot nickel content against different trace elements (e.g. gallium, germanium and iridium). The different iron meteorite groups appear as data point clusters. [1] [6]

Parent body

IVB meteorites formed the core of a parent body that was later destroyed, some of the fragments falling on Earth as meteorites. [3] Modeling the IVB parent body has to take into account the extreme chemical composition, especially the depletion of volatile elements (gallium, germanium) and the enrichment in refractory elements (iridium) compared to other iron meteorites. [2]

The history of the parent body has been reconstructed in detail. The IVB parent body will have formed from material that condensed at the highest temperatures while the solar nebula cooled off. The enrichment in refractory elements was caused by less than 10 % of the condensible material going into the parent body. [2] Thermal models suggest that the IVB parent body formed 0.3 million years after the formation of the calcium-aluminium-rich inclusions, and at a distance from the sun of 0.9  Astronomical units. [7] [8]

Differentiation of the planet body into a core and mantle was most likely driven by the heat produced by the decay of 26Al and 60Fe. [9] [10] The high nickel concentrations were caused by oxidizing physical conditions. The chemical variation of IVB specimens can be explained as different stages of the fractional crystallization of the convecting core of the parent body. [3] The exact size of the parent body is still debated. Modelling of cooling rates suggest that it had a 140 ± 30 km radius with a 70 ± 15 km radius core. The fast cooling rates are explained by a grazing-shot collision of the parent body with a larger asteroid. This removed the mantle from the parent body, leaving the shattered iron core behind to rapidly cool. [3]

Notable specimens

The Hoba meteorite is the largest meteorite specimen ever found. The Hoba Meteorite near Grootfontein.jpg
The Hoba meteorite is the largest meteorite specimen ever found.

As of December 2012, 14 specimens of IVB meteorites are known. [11] A notable specimen is the Hoba meteorite, the largest known intact meteorite. There has never been an observed fall of an IVB meteorite. [11]

See also

Related Research Articles

Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the entire Solar System, and has made important contributions to the understanding of a number of processes including mantle convection, the formation of planets and the origins of granite and basalt. It is an integrated field of chemistry and geology.

<span class="mw-page-title-main">Earth's outer core</span> Fluid layer composed of mostly iron and nickel between Earths solid inner core and its mantle

Earth's outer core is a fluid layer about 2,260 km (1,400 mi) thick, composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle. The outer core begins approximately 2,889 km (1,795 mi) beneath Earth's surface at the core-mantle boundary and ends 5,150 km (3,200 mi) beneath Earth's surface at the inner core boundary.

<span class="mw-page-title-main">Meteorite classification</span> Systems of grouping meteorites based on shared characteristics

In meteoritics, a meteorite classification system attempts to group similar meteorites and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics, especially mineralogical, petrological, chemical, and isotopic properties.

<span class="mw-page-title-main">Chondrite</span> Class of stony meteorites made of round grains

A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primitive asteroids. Some such bodies that are captured in the planet's gravity well become the most common type of meteorite by arriving on a trajectory toward the planet's surface. Estimates for their contribution to the total meteorite population vary between 85.7% and 86.2%.

<span class="mw-page-title-main">Planetary core</span> Innermost layer(s) of a planet

A planetary core consists of the innermost layers of a planet. Cores may be entirely solid or entirely liquid, or a mixture of solid and liquid layers as is the case in the Earth. In the Solar System, core sizes range from about 20% to 85% of a planet's radius (Mercury).

<span class="mw-page-title-main">Micrometeorite</span> Meteoroid that survives Earths atmosphere

A micrometeorite is a micrometeoroid that has survived entry through the Earth's atmosphere. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. The IAU officially defines meteoroids as 30 micrometers to 1 meter; micrometeorites are the small end of the range (~submillimeter). They are a subset of cosmic dust, which also includes the smaller interplanetary dust particles (IDPs).

<span class="mw-page-title-main">Meteoric iron</span> Iron originating from a meteorite rather than from the Earth since formation

Meteoric iron, sometimes meteoritic iron, is a native metal and early-universe protoplanetary-disk remnant found in meteorites and made from the elements iron and nickel, mainly in the form of the mineral phases kamacite and taenite. Meteoric iron makes up the bulk of iron meteorites but is also found in other meteorites. Apart from minor amounts of telluric iron, meteoric iron is the only naturally occurring native metal of the element iron on the Earth's surface.

Meteoritics is the science that deals with meteors, meteorites, and meteoroids. It is closely connected to cosmochemistry, mineralogy and geochemistry. A specialist who studies meteoritics is known as a meteoriticist.

<span class="mw-page-title-main">Iron meteorite</span> Meteorite composed of iron-nickel alloy called meteoric iron

Iron meteorites, also called siderites or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most iron meteorites originate from cores of planetesimals, with the exception of the IIE iron meteorite group

<span class="mw-page-title-main">Primitive mantle</span> Layer in a newly formed planet

In geochemistry, the primitive mantle is the chemical composition of the Earth's mantle during the developmental stage between core-mantle differentiation and the formation of early continental crust. The chemical composition of the primitive mantle contains characteristics of both the crust and the mantle.

CI chondrites, also called C1 chondrites or Ivuna-type carbonaceous chondrites, are a group of rare carbonaceous chondrite, a type of stony meteorite. They are named after the Ivuna meteorite, the type specimen. CI chondrites have been recovered in France, Canada, India, and Tanzania. Their overall chemical composition closely resembles the elemental composition of the Sun, more so than any other type of meteorite.

Winonaites are a group of primitive achondrite meteorites. Like all primitive achondrites, winonaites share similarities with chondrites and achondrites. They show signs of metamorphism, partial melting, brecciation and relic chondrules. Their chemical and mineralogical composition lies between H and E chondrites.

<span class="mw-page-title-main">IAB meteorite</span> Group of iron meteorites

IAB meteorites are a group of iron meteorites according to their overall composition and a group of primitive achondrites because of silicate inclusions that show a strong affinity to winonaites and chondrites.

IIG meteorites are a group of iron meteorites. The group currently has six members. They are hexahedrites with large amounts of schreibersite. The meteoric iron is composed of kamacite.

<span class="mw-page-title-main">Nonmagmatic meteorite</span> Deprecated term formerly used in meteoritics

Nonmagmatic meteorite is a deprecated term formerly used in meteoritics to describe iron meteorites that were originally thought to have not formed by igneous processes, to differentiate them from the magmatic meteorites, produced by the crystallization of a metal melt. The concept behind this was developed in the 1970s, but it was quickly realized that igneous processes actually play a vital role in the formation of the so-called "nonmagmatic" meteorites. Today, the terms are still sometimes used, but usage is discouraged because of the ambiguous meanings of the terms magmatic and nonmagmatic. The meteorites that were described to be nonmagmatic are now understood to be the product of partial melting and impact events and are grouped with the primitive achondrites and the achondrites.

This is a glossary of terms used in meteoritics, the science of meteorites.

<span class="mw-page-title-main">IIAB meteorites</span> Type of iron meteorite

IIAB meteorites are a group of iron meteorites. Their structural classification ranges from hexahedrites to octahedrites. IIABs have the lowest concentration of nickel of all iron meteorite groups. Most iron meteorites are derived from the metallic planetary cores of their respective parent bodies, but in the case of the IIABs the metallic magma separated to form not only this meteorite group but also the IIG group.

The K/U Ratio is the ratio of a slightly volatile element, potassium (K), to a highly refractory element, uranium (U). It is a useful way to measure the presence of volatile elements on planetary surfaces. The K/U ratio helps explain the evolution of the planetary system and the origin of Earth's moon.

CM chondrites are a group of chondritic meteorites which resemble their type specimen, the Mighei meteorite. The CM is the most commonly recovered group of the 'carbonaceous chondrite' class of meteorites, though all are rarer in collections than ordinary chondrites.

Gas-rich meteorites are meteorites with high levels of primordial gases, such as helium, neon, argon, krypton, xenon and sometimes other elements. Though these gases are present "in virtually all meteorites," the Fayetteville meteorite has ~2,000,000 x10−8 ccSTP/g helium, or ~2% helium by volume equivalent. In comparison, background level is a few ppm.

References

  1. 1 2 M. K. Weisberg; T. J. McCoy, A. N. Krot (2006). "Systematics and Evaluation of Meteorite Classification" (PDF). In D. S. Lauretta; H. Y. McSween, Jr. (eds.). Meteorites and the early solar system II. Tucson: University of Arizona Press. pp. 19–52. ISBN   978-0816525621 . Retrieved 15 December 2012.
  2. 1 2 3 Campbell, Andrew J.; Humayun, Munir (1 October 2005). "Compositions of group IVB iron meteorites and their parent melt". Geochimica et Cosmochimica Acta. 69 (19): 4733–4744. Bibcode:2005GeCoA..69.4733C. CiteSeerX   10.1.1.573.5611 . doi:10.1016/j.gca.2005.06.004.
  3. 1 2 3 4 Yang, Jijin; Goldstein, Joseph I.; Michael, Joseph R.; Kotula, Paul G.; Scott, Edward R.D. (31 July 2010). "Thermal history and origin of the IVB iron meteorites and their parent body". Geochimica et Cosmochimica Acta. 74 (15): 4493–4506. Bibcode:2010GeCoA..74.4493Y. doi:10.1016/j.gca.2010.04.011.
  4. ↑ "The Catalogue of Meteorites". nhm.ac.uk.
  5. ↑ McSween, Harry Y. (1999). Meteorites and their parent planets (Sec. ed.). Cambridge: Cambridge Univ. Press. ISBN   978-0521587518.
  6. ↑ Scott, Edward R. D.; Wasson, John T. (1 January 1975). "Classification and properties of iron meteorites". Reviews of Geophysics. 13 (4): 527. Bibcode:1975RvGSP..13..527S. doi:10.1029/RG013i004p00527.
  7. ↑ Bland, P. A.; F. J. Ciesla (2010). "The Impact of Nebular Evolution on Volatile Depletion Trends Observed in Differentiated Objects" (PDF). 41st Lunar and Planetary Science Conference. Retrieved 23 December 2012.
  8. ↑ Haghighipour, Nader; Scott, Edward R. D. (20 April 2012). "On the Effect of Giant Planets on the Scattering of Parent Bodies of Iron Meteorite from the Terrestrial Planet Region into the Asteroid Belt: A Concept Study". The Astrophysical Journal. 749 (2): 113. arXiv: 1202.2975 . Bibcode:2012ApJ...749..113H. doi:10.1088/0004-637X/749/2/113.
  9. ↑ Moskovitz, Nicholas; Eric Gaidos (2011). "Differentiation of Planetesimals and the Thermal Consequences of Melt Migration". Meteoritics and Planetary Science. 46 (6): 903–918. arXiv: 1101.4165 . Bibcode:2011M&PS...46..903M. doi:10.1111/j.1945-5100.2011.01201.x.
  10. ↑ Moskovitz, Nicholas A.; Walker, Richard J. (31 July 2011). "Size of the group IVA iron meteorite core: Constraints from the age and composition of Muonionalusta". Earth and Planetary Science Letters. 308 (3–4): 410–416. arXiv: 1106.2479 . Bibcode:2011E&PSL.308..410M. doi:10.1016/j.epsl.2011.06.010.
  11. 1 2 "Meteoritical Bulletin Database". Meteoritical Society. Retrieved 17 December 2012.
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