Editing 38th parallel structures

{{short description|American Midwest landscape depressions}}
{{for|the manmade structures along the Korean 38th parallel|Korean Demilitarized Zone}}
{{Infobox
| image = [[File:38th parallel structures loc.svg|right|300px]]
| caption = 
{{aligned table|fullwidth=y|leftright=y|row1header = y
|Structure|Coordinates
|[[Hicks Dome]] |{{coord|37.5|N|88.3|W|name=Hicks Dome}}
|[[Avon crater|Avon]] |{{coord|37.8|N|90.2|W|name=Avon crater}}
|[[Crooked Creek crater|Crooked Creek]] |{{coord|37.8|N|91.4|W|name=Crooked Creek crater}}
|[[Decaturville crater|Decaturville]] |{{coord|37.9|N|92.7|W|name=Decaturville crater}}
|[[Hazelgreen crater|Hazelgreen]] |{{coord|37.7|N|92.4|W|name=Hazelgreen crater}}
|[[Weaubleau structure|Weaubleau-Osceola]] |{{coord|38.0|N|93.6|W|name=Weaubleau-Osceola structure}}
|[[Rose Dome]] |{{coord|37.7|N|95.7|W|name=Rose Dome}}
}} | decat = yes <!-- intentionally no data rows -->}}
{{geoGroup}}
The '''38th parallel structures''', also known as the '''38th parallel lineament''',<ref>Gillman, Joe (ed.), [http://www.missourigeologists.org/Meeting2004/AMGguidebook2004.pdf 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</ref> are a series of seven circular depressions or deformations stretching {{convert|700|km|mi}} across southern [[Illinois]] and [[Missouri]] and into eastern [[Kansas]], in the United States, at a [[latitude]] of roughly [[38th parallel north|38 degrees north]]. Estimated at 300 million years old, three are believed to be [[impact event]]s from meteorites, but other structures are possibly remnants of [[volcano]]s.

==History==
Rampino and Volk (1996) postulated that these structures could be the remains of a serial meteorite strike during the late [[Mississippian age|Mississippian]] or early [[Pennsylvanian (geology)|Pennsylvanian]] periods (320 ± 10 Ma).<ref name=Rampino1996_p49>Rampino & Volk, 1996, p.49</ref> Difficulty in determining the age of many of the structures and doubts about the exogenic origins of several of them leave some [[geologist]]s skeptical of this hypothesis. As of 2016, only two of the structures, [[Crooked Creek crater|Crooked Creek]] (320 ± 80 [[megaannum|Ma]]) and [[Decaturville crater|Decaturville]] (< 300 Ma), both in Missouri, are listed as confirmed impact craters in the [[Earth Impact Database]].<ref>{{cite web
|url = https://www.unb.ca/passc/ImpactDatabase/NorthAmerica.html
|date = 2016-05-20
|access-date = 2016-05-30
|title= North America
|work= Earth Impact Database
|author= John Spray (director)
|publisher= Planetary and Space Science Centre, University of New Brunswick
}}</ref>

There is evidence that at least some of the features, such as [[Hicks Dome]] in Illinois, are volcanic in origin. These features are associated with faults and fractured rock, and are accompanied by igneous rocks and mineral deposits. Hicks Dome is a structural [[dome (geology)|dome]] which has its central [[Devonian]] core displaced upward some {{convert|4000|feet}} in relation to the surrounding [[Stratum|strata]]. The dome has small associated [[igneous]] [[Dike (geology)|dikes]] around its flanks.<ref>Raymond Wiggers, 1997, ''Geology underfoot in Illinois'', Mountain Press, p. 252–256. {{ISBN|0-87842-346-X}}</ref>

Interest in the possibility of serial impacts on Earth was piqued by observations of [[comet Shoemaker&ndash;Levy 9]] impacting on [[Jupiter]] in 1994. It has been estimated, however, that the likelihood of such an event occurring 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]], whose gravitational field is even weaker, can be seen in several [[List of features on the Moon#Catena|chains of craters]] on the lunar surface.

== See also ==
* [[Impact event]]
* [[Roche limit]]
* [[List of possible impact structures on Earth]]

== References ==
{{Reflist}}

=== Bibliography ===
* {{cite journal |last1=Rampino |first1=M.R |last2=Volk |first2=T. |year=1996 |title=Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids? |url=https://pubs.giss.nasa.gov/docs/1996/1996_Rampino_ra05200y.pdf |journal=[[Geophysical Research Letters]] |volume=23 |issue=1 |pages=49–52 |doi=10.1029/95GL03605 |bibcode=1996GeoRL..23...49R |accessdate=2019-04-06}}

== Further reading ==
{{refbegin}}
* 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. [https://web.archive.org/web/20060429213030/http://geosciences.missouristate.edu/geology/RI-75(2003AMGguidebook).pdf PDF]
* Luczaj, J. 1998. Argument supporting explosive igneous activity for the origin of "cryptoexplosion" structures in the midcontinent, United States. ''Geology'' '''26'''(April):295.
{{refend}}

{{DEFAULTSORT:38th Parallel Structures}}
[[Category:Possible impact craters on Earth]]
[[Category:Impact craters of the United States]]
[[Category:Carboniferous impact craters]]
[[Category:Landforms of Missouri]]
[[Category:Landforms of Kansas]]
[[Category:Landforms of Illinois]]
[[Category:Hypothetical volcanoes]]