Bermuda hotspot

The Bermuda hotspot is a supposed midplate hotspot swell in the Atlantic Ocean 500-1000 km southeast of Bermuda,[1] proposed to explain the extinct volcanoes of the Bermuda Rise as well as the Mississippi Embayment[2][3][4] and the Sabine Uplift southwest of the Mississippi Embayment.[5]

A 2002 paper by Roy B. Van Arsdale and Randel Cox of the University of Memphis proposes that the Bermuda hotspot generated the Mississippi Embayment in the Early Cretaceous period, when the hotspot strengthened and uplifted the present-day Mississippi Valley. The resulting highland eroded over time, and when North American plate motion moved the valley away from the hotspot the resulting thinned lithosphere subsided forming a trough.[4] As evidence, Van Arsdale and Cox cite the seismic zones centered on New Madrid, Missouri and Charleston, South Carolina, and the volcanic kimberlite pipes in Arkansas.

Other papers[6][7] argue that the lack of a chain of age-progressive seamounts (as in the Hawaiian-Emperor seamount chain), the absence of present-day volcanism, and the elongation of the Bermuda Rise oblique to plate motion are evidence against a hotspot origin for the Bermuda Rise. Peter R. Vogt and Woo-Yeol Jung[6] alternatively attribute the Bermuda Rise to a reorganization of mantle convection associated with the closing of the Tethys Sea, though noting that shallow processes may not explain the source of the magmatism. A more recent paper [7] finds a thinning in the mantle transition zone under Bermuda, apparently consistent with mantle upwelling and a hot lower mantle below Bermuda.

See also

References

  1. ^ Vacher, H.L.; Rowe, Mark (1997). Vacher, H.L.; Quinn, T. (eds.). Geology and Hydrogeology of Bermuda, in Geology and Hydrogeology of Carbonate Islands, Developments in Sedimentology 54. Amsterdam: elsevier Science B.V. pp. 35–90. ISBN 9780444516442.
  2. ^ Cox, Randel T.; Roy B. Van Arsdale (Jan 2007). "The Mississippi's Curious Origins". Scientific American. 296 (1): 76–82B. Bibcode:2007SciAm.296a..76V. doi:10.1038/scientificamerican0107-76.
  3. ^ Cox, Randel T.; Roy B. Van Arsdale (1997). "Hotspot origin of the Mississippi embayment and its possible impact on contemporary seismicity". Engineering Geology. 46 (3–4): 201–216. doi:10.1016/S0013-7952(97)00003-3.
  4. ^ a b Cox, Randel T.; Roy B. Van Arsdale (2002). "The Mississippi Embayment North America: A First Order Continental Structure Generated by the Cretaceaous Superplume Mantle Event". Journal of Geodynamics. 34 (2): 163–176. Bibcode:2002JGeo...34..163C. doi:10.1016/S0264-3707(02)00019-4.
  5. ^ Nunn, Jeffrey A. (1990). "Relaxation of Continental Lithosphere: an Explanation for Late Cretaceous Reactivation of the Sabine Uplift of Louisiana-Texas". Tectonics. 9 (2): 341–359. Bibcode:1990Tecto...9..341N. doi:10.1029/TC009i002p00341.
  6. ^ a b Vogt, Peter R.; Woo-Yeol Jung (2007). Origin of the Bermuda volcanoes and the Bermuda Rise: History, observations, models, and puzzles (PDF). Special Paper 430: Plates, Plumes and Planetary Processes. 430. pp. 553–591. CiteSeerX 10.1.1.484.2851. doi:10.1130/2007.2430(27). ISBN 978-0-8137-2430-0. Retrieved 2008-08-12.
  7. ^ a b Benoit, Margaret H.; Maureen D. Long; Scott D. King (2013). "Anomalously thin transition zone and apparently isotropic upper mantle beneath Bermuda: Evidence for upwelling". Geochemistry, Geophysics, Geosystems. 14 (10): 4282. Bibcode:2013GGG....14.4282B. doi:10.1002/ggge.20277.
Bermuda Pedestal

The Bermuda Pedestal is an oval geological feature in the northern Atlantic Ocean containing the topographic highs of the Bermuda Platform, the Plantagenet (Argus) Bank, and the Challenger Bank. The pedestal is 50 km (31 mi) long and 25 km (16 mi) wide at the 100 fathom line (-185 m), while the base measures 130 km by 80 km at -4200 m. Surrounding the pedestal is a much larger mid-basin swell known as the Bermuda Rise, measuring 900 km by 600 km at the 5000 m depth contour. The islands of Bermuda are located on the southeastern margin of the Bermuda Pedestal.The oceanic crust surrounding the Bermuda is about 120 Ma, while the initial uplift of the Bermuda Rise occurred in the Middle to Late Eocene. Erosion continued from that time until the Early Oligocene. Volcaniclastic deposition and erosion ended with subsidence below sea level in the Late Oligocene. Volcanic basement is at -75 m across the platform, and -50 m on the island, except for a highpoint near Castle Harbour, at -15 m. These volcanics consist of tholeiitic lavas and intrusive lamprophyric sheets.Scientists have long considered the Bermuda Pedestal to be the remains of a large extinct shield volcano that formed between 45 and 35 million years ago. A number of theories have been established to explain the origin of the Bermuda Pedestal. According to one of these theories, it was formed by the volcanic activity of the Bermuda hotspot. However, a hotspot origin for the Bermuda Pedestal has never been strongly supported and has been largely shut out by a detailed and tightly argued paper by Peter R. Vogt of the University of California and Woo-Yeol Jung of the United States Naval Research Laboratory. In contrast, Vogt and Jung propose that the Bermuda Pedestal possibly formed as a result of a worldwide reorganization of the Earth's tectonic plates due to the closing of the Tethys Ocean when the Indian subcontinent collided with Eurasia.The size of the Bermuda Pedestal combined with knowledge of other mid-ocean volcanoes tells us that the Bermuda volcano originally reached 1,000 m (3,300 ft) above sea level and that it took three to ten million years to reduce it to sea level.

Hotspot (geology)

In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.

Jackson Volcano

Jackson Volcano is an extinct volcano 2,900 feet (880 m) beneath the city of Jackson, Mississippi, under the Mississippi Coliseum. The uplifted terrain around the volcano forms the Jackson Dome, an area of dense rock clearly noticeable in local gravity measurements. E.W. Hilgard published his theory of an anticline beneath Jackson in 1860 due to his observations of surface strata. The dome contains relatively pure carbon dioxide which is used in oil production in Gulf Coast oil fields. The noble gas data suggests mantle origins with a date of 70 million years for the Jackson Dome intrusion. Geologists have evidence of repeated uplifts accompanied by dike intrusions and volcanic extrusions, erosion, and sedimentation with one coral reef having developed during a submergence. Much of the oil at the crest of the dome volatilized during a late uplift, but oil production wells numbered over a hundred in 1934.

Jackson Volcano is believed to have been extinct for at least 66 million years. A hypothesis states that the Jackson Volcano and related igneous activity in Mississippi were a result of the North America Plate's passage over the Bermuda hotspot 66 million years ago. Alternatively, the volcanism may have been part of a worldwide eruption driven by superplumes, similar to the conditions that created the Deccan Traps and the Siberian Traps.The volcano is one of four inside cities in the United States, Diamond Head in Honolulu, Hawaii, Pilot Butte in Bend, Oregon, and Mount Tabor in Portland, Oregon being the others. The volcano was discovered in 1819.

Midnight Volcano

Midnight Volcano is a buried extinct volcano near Midnight, Mississippi in southern Humphreys County. The volcano was last active in the Late Cretaceous period and is associated with the volcanic activity of the Monroe Uplift, which occurred around 80 million years ago. The Jackson Volcano, southeast of Midnight, was active around 10 million years later. Volcanic debris from Midnight or other volcanoes of the Monroe Uplift were found in the "Coffee sand," a Cretaceous sand layer to the north of the volcano.

Mississippi embayment

The Mississippi Embayment is a physiographic feature in the south-central United States, part of the Mississippi Alluvial Plain. It is essentially a northward continuation of the fluvial sediments of the Mississippi River Delta to its confluence with the Ohio River at Cairo, Illinois. The current sedimentary area was formed in the Cretaceous and early Cenozoic by the filling with sediment of a pre-existing basin. An explanation for the embayment's formation was put forward by Van Arsdale and Cox in 2007: movement of the earth's crust brought this region over a volcanic "hotspot" in the Earth's mantle causing an upthrust of magma which formed the Appalachian-Ouachita range. Subsequent erosion caused a deep trough that was flooded by the Gulf of Mexico and eventually filled with sediment from the Mississippi River.

Olympic-Wallowa Lineament

The Olympic-Wallowa lineament (OWL) – first reported by cartographer Erwin Raisz in 1945 on a relief map of the continental United States – is a physiographic feature of unknown origin in the state of Washington (northwestern U.S.) running approximately from the town of Port Angeles, on the Olympic Peninsula to the Wallowa Mountains of eastern Oregon.

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