Hicks Dome

from Wikipedia, the free encyclopedia

The Hicks Dome is an enigmatic dome-like bulge in the Paleozoic layers of Hardin County in the US state of Illinois .

location

Topology of the Hicks Dome in Hardin County, Illinois

The Hicks Dome, named after the small settlement Hicks, located in Hardin County, Illinois, about 13 kilometers north-west of the Ohio River nearby Elizabethtown .

description

The dome structure, which is elongated slightly to the southeast-northwest ( anticline dipping on both sides ) measures around 14.5 kilometers in diameter and thus follows the Tolu Arch , a bulge in the basement in southern Illinois , which strikes in the same direction .

geology

In the Hicks Dome, the otherwise more or less flat paleozoic sediments of the Illinois Basin are pressed out up to 1200 meters. The sequence of layers extends from the Lower Devonian in the center of the cathedral ( Clear Creek Chert ) to the deep Upper Carboniferous ( Ste. Genevieve Limestone ). The lower carbon ( Mississippium ) lies in an oval belt around the core of the structure. A hole drilled in the center of the dome encountered a mineralized explosive breccia that is at least 400 meters thick at a depth of 490 meters . In the periphery of the dome there are magmatic intrusives of the Permian age , which have penetrated as passages, thin storage passages or diatrems. Usually these are ultra- mafic , calcareous lamprophyres , which can be referred to as minette .

origin

The origin of the cathedral is still controversial. It has recently been viewed as part of the 38th parallel impact crater - a chain of impact craters and other circular structures that continues into Kansas and that may have been caused by a breaking meteorite .

However, most geologists disagree with this theory, since ultramafite , diatrems and breccia vents are located in the center of the bulge . Rather, this points to deep-seated endogenous magmatic processes.

Hardin County fluorite

This is also supported by the widespread fluorite deposits in the Illinois-Kentucky Fluorspar District in the immediate vicinity, which were still mined into the early 1990s. The fluorine in fluorospate is very likely igneous. In addition to fluorite, rare earth minerals are also encountered, which indicate a possible carbonatite stock below the dome structure. In the mineralized breccia, in addition to fluorite, the minerals calcite , quartz , pyrite , as well as subordinate sphalerite and galena were found . In addition to the rare earths, thorium is also present in Monazite . Less common are barite , Bertrandit and Brockit .

Age

Fifarek and colleagues (2001) were able to determine radiometrically a hypopermic age of 270 million years ( Guadalupium / Roadium ) for the Hicks Dome.

Individual evidence

  1. ^ Baxter, JW, GA Desborough and CW Shaw: Areal geology of the Illinois fluorspar district: Part 3, Herod and Shetlerville Quadrangles . In: Circular . tape 413 . Illinois State Geological Survey, 1967, p. 41 .
  2. ^ Nelson, WJ: Structural features in Illinois . In: Illinois State Geological Survey, Bulletin . tape 100 , 1995, pp. 144 .
  3. ^ Moorehead AJ: Igneous Intrusions at Hicks Dome, Southern Illinois, and their relationship to fluorine-base metal rare-earth element mineralization (diploma thesis) . Southern Illinois University-Carbondale, 2013, pp. 226 .
  4. ↑ Rampino, M. R and Volk, T .: Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids? In: Geophys. Res. Lett. tape 23 , 1996, pp. 49-52 .
  5. ↑ Bradbury, JC and Baxter, JW: Intrusive breccias at Hicks Dome . In: Illinois Geological Survey Circular . Vol. 550, 1992, pp. 23 .
  6. ↑ Fifarek, RH, Denny, FB, Snee, LW and Miggins, DP: Permian igneous activity in southeastern Illinois and Western Kentucky: implications for tectonism and economic resources . In: Geological Society of America Abstracts with Programs . Vol. 33, No. 6 , 2001, p. A-420 .

Coordinates: 37 ° 31 '48 "  N , 88 ° 21' 48"  W.