Lo-En
Lo-En | |
---|---|
Summit depth | 1,080 metres (3,540 ft) |
Height | 4,561 ± 526 metres (14,964 ± 1,726 ft) |
Summit area | 823 square kilometres (318 sq mi) |
Location | |
Coordinates | 10°07′N 162°48′E / 10.117°N 162.800°E[1] |
Country | Marshall Islands |
Geology | |
Type | Guyot |
Lo-En or Hess is an
The seamount is formed by
.Name and research history
The name "Lo-En" is a reference to the
Geography and geology
Local setting
Lo-En lies within the northern
The seamount rises 4,561 ± 526 metres (14,964 ± 1,726 ft) above the seafloor
No
Lo-En shares its volcanic edifice with Eniwetok;[23] a northern spur from Lo-En almost reaches Eniwetok[7] while another spur emerges in south-southeast direction[12] and is about 14.5 kilometres (9.0 mi) long.[24] Another seamount lies 50 kilometres (31 mi) farther west from Lo-En.[7] The seafloor underneath Lo-En is 113[1]–156.9 ± 5 million years old[9] and lies at a depth of more than 5 kilometres (3.1 mi).[7]
Regional setting
The
The formation of many such seamounts
Candidate hotspots responsible for the formation of Lo-En are the
Based on plate motion reconstructions, the region of the Marshall Islands was located in the region of present-day French Polynesia during the time of active volcanism. Both regions display numerous island chains, anomalously shallow ocean floors and the presence of volcanoes.[38] About 8 hotspots have formed a large number of islands and seamounts in that region, with disparate geochemistries,[39] and that geological province has been called the "South Pacific Isotopic and Thermal Anomaly" or DUPAL anomaly.[40]
Composition
Lo-En has erupted
Geologic history
The geologic history of Lo-En seamount is relatively poorly known;
Volcanism and first biotic phenomena
A first phase of volcanic activity occurred 114 million years ago, and was followed by a second episode during the Campanian,[49] separated by as much as 30 million years.[50] The first episode has been dated at 111.6–114.0 million years ago[51] and was contemporaneous with volcanic activity at other western Pacific seamounts. The second episode may be responsible for the cones that emerge from or are embedded in sediments that cover Lo-En. Eniwetok was active 76.9 million years ago[15] and flexural effects from its growth may have influenced the second volcanic phase at Lo-En.[52] Potentially, the first episode was caused by the Macdonald hotspot and the second by the Rarotonga and Rurutu hotspots.[36]
The volcanic rocks encountered in drill cores consist of
Post-volcanic
Lo-En was submerged in the Turonian[22] by about 112.8 ± 1.2 million years ago, long before surrounding seamounts and islands formed.[1] The absence of a barrier reef would have facilitated the erosion of Lo-En's summit.[52] It is possible that flexural loading by Eniwetok pushed Lo-En downward and thus prevented the formation of reefs on Lo-En during the Cretaceous when the seamount was uplifted by a hotspot.[55] It took about 2–7 million years from the end of volcanic activity until sedimentation began.[56]
During the Albian, limestones were emplaced on Lo-En.[18] These appear to reflect the formation of reefs[57] and a shallow carbonate bank, material from which has been dredged on the southern flank.[58] This platform drowned during the late Albian, similar to many other carbonate platforms of similar age,[59] and there is no evidence of mid-Cretaceous platforms.[48]
Starting in the Albian–Cenomanian,[10] pelagic limestone was deposited directly on the volcanic rocks during Santonian–Coniacian times; in light of fossil data it is likely that the seamount was not overly deep at that time.[60] Sediments of Cretaceous–Paleocene age reach thicknesses of less than 1 metre (3 ft 3 in).[23]
Starting in the Oligocene,[58][61] pelagic oozes were deposited on Lo-En. The previously emplaced limestones also underwent phosphate reactions as they were exposed on the seafloor,[60] and some of the sediments underwent reworking.[23]
- Arkangelskiella specillata
- Aspidolithus parcus expansus
- Eiffellithus eximius
- Gephyrorhabdus coronadventis
- Lithastrinus septenarius
- Micula sp.
- Nannoconus farinacciae
- Reinhardtites sp.
- Stoverius sp.
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- ^ Haggerty & Premoli Silva 1995, p. 943.
- ^ a b Larson et al. 1995, p. 924.
- ^ Larson et al. 1995, p. 929.
- ^ a b c Erba, Premoli Silva & Watkins 1995, p. 158.
- ^ Bogdanov et al. 1995, p. 748.
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