38th parallel structures

The 38th parallel structures, also known as the 38th parallel lineament,[1] are a series of circular depressions or deformations stretching 700 kilometres (430 mi) across southern Illinois and Missouri into eastern Kansas at a latitude of roughly 38 degrees north.

Structure Coordinates Hicks Dome 37.5°N 88.3°W / 37.5; -88.3 (Hicks Dome) Avon 37.8°N 90.2°W / 37.8; -90.2 (Avon crater) Crooked Creek 37.8°N 91.4°W / 37.8; -91.4 (Crooked Creek crater) Decaturville 37.9°N 92.7°W / 37.9; -92.7 (Decaturville crater) Hazelgreen 37.7°N 92.4°W / 37.7; -92.4 (Hazelgreen crater) Weaubleau-Osceola 38.0°N 93.6°W / 38.0; -93.6 (Weaubleau-Osceola structure) Rose Dome 37.7°N 95.7°W / 37.7; -95.7 (Rose Dome)

Rampino and Volk (1996) postulated that these structures could be the remains of a serial meteorite strike in the late Mississippian or early Pennsylvanian periods (320 ± 10 Ma).[2] Difficulty in determining the age of many of the structures and doubts about the exogenic origins of several of them leave some geologists skeptical of this hypothesis. As of 2016, only two of the structures, Crooked Creek (320 ± 80 Ma) and Decaturville (< 300 Ma), are listed as confirmed in the Earth Impact Database.[3]

There is evidence that at least some of them, such as Hicks Dome, are volcanic in origin. They are associated with faults and fractured rock, and are accompanied by igneous rocks and mineral deposits. Hicks Dome is a structural dome which has its central Devonian core displaced upward some 4,000 feet (1,200 m) in relation to the surrounding strata. The dome has small associated igneous dikes around its flanks.[4]

Interest in the possibility of serial impacts on Earth was piqued by observations of comet Shoemaker–Levy 9 impacting on Jupiter in 1994. It is estimated, however, that the likelihood of such an event on Earth is vanishingly small because the Earth's weaker gravitational field is much less able than Jupiter's to pull a speeding object close enough to be torn apart by tidal forces. However, evidence of serial impacts on the Moon can be seen in several chains of craters.

See also

• Impact event
• Roche limit
• List of possible impact structures on Earth

References

1. Gillman, Joe (ed.), Association of Missouri Geologists Field Trip Guidebook, 51st Annual Meeting, Rolla, Missouri, October 1–2, 2004, 2004, Missouri Department of Natural Resources, Geological Survey and Resource Assessment Division, p. 15
2. Rampino & Volk, 1996, p.49
3. John Spray (director) (2016-05-20). "North America". Earth Impact Database. Planetary and Space Science Centre, University of New Brunswick. Retrieved 2016-05-30.
4. Raymond Wiggers, 1997, Geology underfoot in Illinois, Mountain Press, p. 252-256 ISBN 0-87842-346-X

Bibliography

• Rampino, M.R, and T. Volk. 1996. Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids?. Geophysical Research Letters 23. 49-52. Accessed 2019-04-06.

Further reading

• Evans, Kevin R.; Mickus, Kevin L.; & Rovey, Charles W. III (2003). The Weaubleau Structure: Evidence of a Mississippian Meteorite Impact in Southwestern Missouri. Association of Missouri Geologists Field Trip Guidebook, 50th Annual Meeting. Missouri Department of Natural Resources. PDF
• Luczaj, J. 1998. Argument supporting explosive igneous activity for the origin of "cryptoexplosion" structures in the midcontinent, United States. Geology 26(April):295.