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.
Naming and history
The winonaite group is named after the type specimen, the
Winona meteorite. The name itself derived from
Winona, Arizona
Winona is a small populated place in Coconino County in the northern part of the U.S. state of Arizona. At one time it was also called Walnut, and Winona's railroad station was renamed Darling in honor of an engineer.
History
Winona was once a ...
where the type specimen was said to be found during an archaeological excavation of the
Sinagua
The Sinagua were a pre-Columbian culture that occupied a large area in central Arizona from the Little Colorado River, near Flagstaff, to the Verde River, near Sedona, including the Verde Valley, area around San Francisco Mountain, and signifi ...
village
Elden Pueblo
Elden Pueblo ( Hopi: Pasiwvi) was a prehistoric Native American village located at the foot of Mount Elden near Flagstaff, Arizona. The pueblo is thought to have been part of a major trading system.[cist
A cist ( or ; also kist ;
from grc-gre, κίστη, Middle Welsh ''Kist'' or Germanic ''Kiste'') is a small stone-built coffin-like box or ossuary used to hold the bodies of the dead. Examples can be found across Europe and in the Middle Ea ...]
of one of the rooms.
However, a later study indicates the meteorite was found at another Sinagua site and not in Elden Pueblo.
[A. L. Christenson "J. W. Simmons' account of the discovery of the Winona meteorite."''Meteorite'' 10(3):14–16, 2004.]
As of 2021, 54 meteorites are included in the winonaite group.
Description
Winonaites are
achondrites that have a chemical and mineral composition similar to
chondrites. Their composition lies between H and E chondrites.
Their isotopic ratios are similar to the silicate inclusions in
IAB 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.
Description
The IAB meteorites are ...
. In
thin section
In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron ...
, the mineral grains show microstructures of extensive thermal metamorphism and signs of partial melting.
Some winonaite specimen appear to have relics of chondrules (e.g. Pontlyfni and Mount Morris).
Parent body
Winonaites and the two iron meteorite groups
IAB and
IIICD are thought to be derived from the same parent body. The iron meteorites formed part of the core of the
planetesimal
Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the Solar System a ...
and the winonaites were closer to the surface. The reasoning is that the silicate inclusions in IAB meteorites are similar to winonaites, especially in their oxygen isotope ratios. It is less clear whether IIICD meteorites are also part this parent body.
The winonaites show that the parent body was affected by impacts that formed
breccias
Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix.
The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...
of different lithologies. Later these breccias were heated and
Ar-Ar radiometric ages have constrained the
metamorphism
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...
on the parent body to between 4.40 and 4.54 billion years. The parent body also reached temperatures where partial melting took place.
Cosmic ray
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
exposure ages show that the meteorites took about 20 to 80 million years to reach earth.
Notable winonaite meteorites
* Hammadah al Hamra 193:
Amphibole bearing.
* Pontlyfni: Chondrule relics.
* Mount Morris: Chondrule relics.
*
Winona meteorite
See also
*
Glossary of meteoritics
This is a glossary of terms used in meteoritics, the science of meteorites.
#
* 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites.
* 4 Vesta – second-largest asteroid in the asteroid b ...
References
{{Meteorites
Achondrite meteorites