Happy Canyon

EL-chondrite, Impact-Melt Rock
(EL6/7 in MetBull 54)
(Primitive Enstatite AchondriteUsed in past as synonym for Aubrites. Present definition from the Meteoritical Bulletin states that this rare class is an "enstatite-rich  achondrite  that has not yet been classified into a group". Click on Term to Read More [Pilski et al., 2011])

Found 1971
34° 48.1′ N., 101° 34′ W. A single mass of ~16.3 kg was plowed up on the R. L. Grigsby farm about 2 km northwest of Wayside, Texas. Current chemical, petrologic, and isotopic studies have classified Happy Canyon as a member of the EL-chondrite 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. It was impact-melted ~4.53 b.y. ago from a metamorphosed rock of 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. 6 or less, cooling rapidly from a temperature of 1425°C due to the incorporation of cold clastic material (fine-grained lithology). During this impact-melt event Ar and other volatile elementsChemical elements that condense (or volatilize) at relatively low temperatures. The opposite of volatile is refractory. Volatile elements can be divided into moderately volatile (Tc = 1230–640 K) and highly volatile (Tc < 640 K). The moderately volatile lithophile elements are: Mn, P, Na, B ,Rb, K, F, Zn. The moderately Click on Term to Read More were degassed. The older I–Xe chronometer referencing an age of ~4.565 b.y. attests to the fact that this chronometer was not reset during metamorphism (Bogard et al., 2010). After solidification, the entire rock was impact-shocked to stage S2, causing undulatory extinctionIn 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 Click on Term to Read More of enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3). Click on Term to Read More.

Studies of Zn isotopes in enstatite 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 by Moynier et al. (2010) led them to conclude that Happy Canyon was derived from either an EH-like, an EL3 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, or possibly an aubriteAubrites are named for the Aubres meteorite that fell in 1836 near Nyons, France. They are an evolved achondrite that is Ca-poor and composed mainly of enstatite (En100) and diopside (En50Wo50) with minor amounts of olivine (Fa0) and traces of plagioclase (An2-8).  They contain large white crystals of enstatite as Click on Term to Read More parent body, and rejects an origin from EL6 material or Shallowater. Boesenberg et al. (2014) found that the feldsparAn alumino-silicate mineral containing a solid solution of calcium, sodium and potassium. Over half the Earth’s crust is composed of feldspars and due to their abundance, feldspars are used in the classification of igneous rocks. A more complete explanation can be found on the feldspar group page. Click on Term to Read More compositions in Happy Canyon overlap those of other EL meteorites.

The convergence of the extremely old ages of both Happy Canyon and 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 has given support to a new theory known as the molten-planetesimal model. This model involves the low-velocity collision of two molten 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 resulting in impact splashing and formation of chondrules and larger blobs of melt. Happy Canyon and other impact-melt rocks (e.g., Ilafegh 009) are said to represent the larger splash material from an impact in which small splash droplets produced chondrules and macrochondrules. High-pressure phases that were formed were likely transformed to low-pressure polymorphs through high-temperature annealing (Rubin and Wasson, 2011). Alternatively, Pilski et al. (2011) propose that this type of 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 exhibiting relict chondrules and triple junctions should more properly be classified as a primitive enstatite achondriteAn achondrite is a type of stony meteorite whose precursor was of chondritic origin and experienced metamorphic and igneous processes. They have a planetary or differentiated asteroidal origin where the chondritic parent body reached a sufficient size that through heating due to radioactive decay of 26Al (aluminum isotope) and gravitational Click on Term to Read More representing the residue from the rapid 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 on an enstatite chondriteType of meteorite high in the mineral enstatite and also referred to as E-chondrites. Although they contain substantial amounts of Fe, it is in the form of Ni-Fe metal or sulfide rather than as oxides in silicates. Their highly reduced nature indicates that they formed in an area of the Click on Term to Read More parent body. The specimen of Happy Canyon shown above is a 0.2 g end piece containing rare free 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.