Earth Sciences 240A – Lecture 6

Meteor Crater / Barringer Crater

Near Flagstaff, Arizona; (also called ‘Coon Mountain’)

Early theories

Explosive gas-rich volcano; Laccolith; Salt dome

Early exploration

Late 1870s: rumors of silver ‘chunks’; 1891: assay Iron with Pb, Ag, Au

Wrong! Actual: Fe + 7.9% Ni (tr. others)

Called ‘Canyon Diablo’ samples

Important developments:

1906: 1st attempt to rename as Meteor Crater; accomplished in 1910

Philosophy controversy

1930s: ‘Barringer Crater’ for geologist looking for metal mass

1947: acknowledged by some to be impact crater

1963: acknowledged universally to be impact crater

Crater Area Geology

1.1 km wide; circle; uplifted/tilted rim 45m above desert

Recent seds form flat floor 185m below desert; further 265m shattered rock below

            Meteorite; fragments in rim and up to 10 km away

Coesite; stishovite; tektites; shatter cones

Meteoroid

‘Iron’ type; 30m dim.; 300,000 tons; Speed: 15 km/s at impact; Est. 49,000 years ago

Impact Environment (speculative)

100 million tons rock instantly pulverized; Dust darkened sky for …(time)??; Local raging wildfires; All life of Colorado Plateau destroyed

General Impact Characteristics

Kinetic energy = 1/2 mass x (velocity)2

‘Hypervelocity’ = velocity unaffected by Earth’s atmosphere

Ejecta blanket

Simple basin vs. complex basin: Critical size: 4 km diameter; Central peak (rebound)

Meteorite fragments: Critical size: ~1 km

Summary

Circular crater; possible central uplift

Associated breccias; disrupted strata

Meteorite fragments?

Coesite, stishovite, other hi-P forms

Shatter cones

Tektites

Probable evidence of huge fires

Nördlinger Ries Crater (Ger.)

21-24km diameter (1-1.5km object); ~ 15 mya

Suevite in breccia

Similarity to Sudbury geology?

Tektites: Moldavite

Next:

Lecture 7

Other impact events

Tagish Lake meteorite