Different Directions

Different Directions

Cat Mountain

L Impact Melt Breccia
Found 1980/81, stayed on a mantel piece until it was confirmed by reflectance spectra tests in 1993

This meteorite was named after the southern-most peak of the Tucson Mountains, located about 2 miles NW from the site of the find, and it has a wonderful story of its find.


Cat Mountain

Photo by Russell Kempton, New England Meteoritical Services.

The importance of this meteorite can not be underestimated for its a history of early solar system formation, its processes, and events. As Grier, Swindle, and Kring have published,  "Cat Mountain provides a rare opportunity to examine the collisional evolution of an asteroid."

Here's part of the story: In its complex history, Cat Mountain underwent at least six impact and heating events:

  1. It's an impact melt breccia that contains chondrule-bearing clasts, which preserve shock veins from an early impact on its parent body (perhaps 2.7 b.y. Ago).

  2. Another impact metamorphosed the chondrule-bearing clasts to type L5.

  3. About 880 m.y. Ago, a major impact created a melt breccia lens at the bottom of a crater, perhaps a km in diameter.

  4. The clasts were surrounded by the swirls of an Fe-Ni metal melt matrix and then underwent cooling.

  5. Roughly 500 m.y. ago, another impact ejected this impact melt breccia from the surface of its parent where it drifted in space until 20 m.y. ago when it was inserted into an Earth crossing orbit.

  6. The final collision reduced the object to a meter-size prior to its impact on Earth.

What you need to visualize is the extreme pressure and heat generated by a meteorite or asteroid impact in space – Impact Melt Meteorites or Impact Melt Breccias (IMB) have formed from material that was liquefied or partially liquefied from such impacts.

Crash
Image from www.research.ufl.edu/.../v10n1/extract3.html

When two bodies in space collide with enough force (due to their mass and velocity) they create massive instantaneous pressures. This pressure affects these meteoroids (later to become meteorites) in different ways. For example, lightly shocked meteorites may just display dark shock veins running through them while the Impact Melts will display a melted and deformed matrix, like Cat Mountain.

Besides this history of heat and impact, Cat Mountain also contained vesicles concentrated near the boundary interface between the melt and the clasts.
Vesicles are rare in meteorites. But in Cat Mountain you can see where the gas-filled vesicles were moving along with the melt.

All in all, this meteorite is a classroom all by itself, and being so, underscores the importance of meteorites and what they can tell us.

Links

Here's a scientific article with a wider range of time lines and information about how samples were dated:
http://adsabs.harvard.edu/full/1994LPI....25..475G

 

 

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