Earth Sciences 240A – Lecture 6
Meteor Crater / Barringer Crater
Near
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 (
21-24km diameter (1-1.5km object); ~
15 mya
Suevite in breccia
Similarity to
Tektites: Moldavite
Next:
Lecture 7
Other impact events