Irving Formation

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Irving Formation
Stratigraphic range: Statherian
Type Formation
Underlies Vallecito Conglomerate
Overlies Twilight Gneiss
ThicknessOver 10,000 feet (3,000 m)
Lithology
Primary Metavolcanic rock
Other Metasedimentary rock
Location
Coordinates 37°35′42″N107°30′32″W / 37.595°N 107.509°W / 37.595; -107.509
Region San Juan Mountains, Colorado
Country United States
Type section
Named forIrving Peak
Named byErnest Howe
Year defined1904
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Irving Formation (the United States)
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Irving Formation (Colorado)

The Irving Formation is a Precambrian geologic formation found in the San Juan Mountains of southwest Colorado, US. It is thought to be Statherian in age (1800 to 1790 million years old.) [1]

Contents

Description

The formation consists of a variety of lithologies (rock varieties) including amphibolite, various schists and gneisses of intermediate to felsic composition, quartzite, metasiltstone, and banded iron formation. A bed of conglomerate is found near the base of the formation in some locations. The beds show indications of mild retrograde metamorphism and dip steeply to the north. [2] It was intruded by the Twilight Gneiss between 1780 and 1770 million years ago (Mya). [1] The complex is older than the Vallecito Conglomerate. [2]

The formation underlies Irving Peak in the San Juan Mountains of Colorado [3] and is exposed across the western and northern Needle Mountains. It is at least a few thousand meters (several thousand feet) thick. [2]

The unit is interpreted as a portion of an island arc accreted to the southern margin of Laurentia as part of the Yavapai Province between 1.8 and 1.755 Gya. [1] Metasedimentary rocks of the formation are interpreted as turbidites derived from the island arc. [4]

Economic resources

The formation was surveyed in 1969 for iron ore. Magnetite-rich beds were found in a few locations but were not judged economical to exploit. [5]

History of investigation

The unit was first named as the Irving Greenstone by Ernest Howe in 1904. [6] The definition was expanded by Fred Barker in 1969, who also renamed the formation as the Irving Formation. [2]

References

  1. 1 2 3 Whitmeyer, Steven; Karlstrom, Karl E. (2007). "Tectonic model for the Proterozoic growth of North America". Geosphere. 3 (4): 220. doi: 10.1130/GES00055.1 .
  2. 1 2 3 4 Barker, Fred (1969). "Precambrian geology of the Needle mountains, southwestern Colorado". U.S. Geological Survey Professional Paper. 644-A. doi: 10.3133/pp644A .
  3. ↑ Cross, Whitman; Howe, Ernest (1905). "Description of Needle Mountains quadrangle [Colorado]". U.S. Geological Survey Geologic Atlas of the United States Folio, Needle Mountains folio. Vol. 131. Retrieved 19 April 2022.
  4. ↑ McLennan, S.M.; Hemming, S.R.; Taylor, S.R.; Eriksson, K.A. (March 1995). "Early Proterozoic crustal evolution: Geochemical and NdPb isotopic evidence from metasedimentary rocks, southwestern North America". Geochimica et Cosmochimica Acta. 59 (6): 1153–1177. doi:10.1016/0016-7037(95)00032-U.
  5. ↑ Steven, T.A.; Schmitt, L.J.; Sheridan, M.J.; Williams, F.E.; Gair, J.E.; Klemic, H. (1969). "Mineral resources of the San Juan primitive area, Colorado, with a section on iron resources in the Irving Formation". U.S. Geological Survey Bulletin. 1261-F. doi: 10.3133/b1261F .
  6. ↑ Howe, Ernest (September 1904). "An Occurrence of Greenstone Schists in the San Juan Mountains, Colorado". The Journal of Geology. 12 (6): 501–509. doi:10.1086/621173.
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