Oceanic core complex

Saint Peter Saint Paul Megamullion, Equatorial Atlantic Ocean

Seabed geologic feature that forms a long ridge perpendicular to a mid-ocean ridge.

- Oceanic core complex
Saint Peter Saint Paul Megamullion, Equatorial Atlantic Ocean

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Chart of 1839 by HMS Erebus

Saint Peter and Saint Paul Archipelago

Group of 15 small islets and rocks in the central equatorial Atlantic Ocean.

Group of 15 small islets and rocks in the central equatorial Atlantic Ocean.

Chart of 1839 by HMS Erebus
Periscope eyeview from USS Triton (1960)

The islets expose serpentinized abyssal mantle peridotite and kaersutite-bearing ultramafic mylonite atop the world's highest and yet only second largest megamullion (after the Parece Vela megamullion under Okinotorishima in the Pacific Ocean).

View of Doso Doyabi, Snake Range, Nevada, which was formed by detachment faulting.

Detachment fault

Detachment faults have been found on the sea floor close to divergent plate boundaries characterised by a limited supply of upwelling magma, such as the Southwest Indian Ridge.

Detachment faults have been found on the sea floor close to divergent plate boundaries characterised by a limited supply of upwelling magma, such as the Southwest Indian Ridge.

View of Doso Doyabi, Snake Range, Nevada, which was formed by detachment faulting.

These detachment faults are associated with the development of oceanic core complex structures.

Separating the African (or Nubian-Somali plates) and Antarctic plates, the Southwest Indian Ridge (SWIR) stretches 7700 km from the Atlantic Ocean to the Indian Ocean. With an average spreading rate of 14 - 15 mm/yr, the SWIR is one of the slowest-spreading mid-ocean ridges on Earth. Characterised by numerous large transform offsets, most of the SWIR is highly segmented and oblique relative to the spreading direction.

Southwest Indian Ridge

Mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean.

Mid-ocean ridge located along the floors of the south-west Indian Ocean and south-east Atlantic Ocean.

Separating the African (or Nubian-Somali plates) and Antarctic plates, the Southwest Indian Ridge (SWIR) stretches 7700 km from the Atlantic Ocean to the Indian Ocean. With an average spreading rate of 14 - 15 mm/yr, the SWIR is one of the slowest-spreading mid-ocean ridges on Earth. Characterised by numerous large transform offsets, most of the SWIR is highly segmented and oblique relative to the spreading direction.
Topography of the SWIR. White dots are hotspots, dashed lines are fracture zones.

These flanks are rounded and smooth and lack the corrugated pattern associated with oceanic core complexes.

Godzilla Megamullion marked on an elevation map

Godzilla Megamullion

Godzilla Megamullion marked on an elevation map
Map of the Izu–Bonin–Mariana Arc system, with the Godzilla Megamullion in the Parece Vela Basin
Godzilla depicted in Godzilla, King of the Monsters! (1956)

The Godzilla Megamullion (ゴジラ・メガムリオン) is an undersea Japanese megamullion, or oceanic core complex, 600 km south-east of the island of Okinotorishima in the Philippine Sea.

Map of Okinotorishima

Okinotorishima

Coral reef with two rocks enlarged with tetrapod-cement structures.

Coral reef with two rocks enlarged with tetrapod-cement structures.

Map of Okinotorishima
Location of Okinotorishima and details of the island
Satellite Image
Exclusive economic zone of Japan. The lowermost purple near-circle is the area around Okinotorishima

The Parece Vela Basin contains the longest megamullion in the world.

Official English logo

Godzilla (franchise)

Japanese media franchise created and owned by Toho Co., Ltd, centered on the fictional kaiju character Godzilla.

Japanese media franchise created and owned by Toho Co., Ltd, centered on the fictional kaiju character Godzilla.

Official English logo
Every film incarnation of Godzilla between 1954 and 2017
The Reiwa iterations of Godzilla
Storyboard by William Stout for Steve Miner's unproduced 3D Godzilla film
TriStar's Godzilla in Godzilla (1998)
Legendary's Godzilla in Godzilla (2014)

The largest megamullion, located 600 kilometres to the south-east of Okinotorishima, the southernmost Japanese island, is named the Godzilla Megamullion.

Aerial view of Mont Blanc massif, an example of a massif and also the highest summit in the Alps.

Atlantis Massif

Prominent undersea massif in the North Atlantic Ocean.

Prominent undersea massif in the North Atlantic Ocean.

Aerial view of Mont Blanc massif, an example of a massif and also the highest summit in the Alps.

The central dome is corrugated and striated in a way that is representative of an exposed ultramafic oceanic core complex.

Hercules diving at the Lost City in 2005

Lost City Hydrothermal Field

Area of marine alkaline hydrothermal vents located on the Atlantis Massif at the intersection between the Mid-Atlantic Ridge and the Atlantis Transform Fault, in the Atlantic Ocean.

Area of marine alkaline hydrothermal vents located on the Atlantis Massif at the intersection between the Mid-Atlantic Ridge and the Atlantis Transform Fault, in the Atlantic Ocean.

Hercules diving at the Lost City in 2005
Instruments on the ROV Jason in 2018
Map of the Lost City on the Atlantis Massif
The Mid-Atlantic Ridge spreading center pulls the lithosphere apart, creating normal faults which expose sub-surface rocks to seawater.
Olivine, the mineral responsible for Lost City's serpentinization.
Desmophyllum have been observed at the Lost City field
A visiting shark at the Lost City field

The massif itself may have originated in a similar manner to many other ocean core complexes.

Location of the Fifteen-Twenty Fracture Zone and the triple junction between the North American, South American, and African (Nubian) plates. The Azores–Gibraltar Transform Fault is in the top right corner.

Fifteen-Twenty Fracture Zone

Fracture zone located on the Mid-Atlantic Ridge (MAR) in the central Atlantic Ocean between 14–16°N.

Fracture zone located on the Mid-Atlantic Ridge (MAR) in the central Atlantic Ocean between 14–16°N.

Location of the Fifteen-Twenty Fracture Zone and the triple junction between the North American, South American, and African (Nubian) plates. The Azores–Gibraltar Transform Fault is in the top right corner.

Corrugated surfaces known as megamullions or oceanic core complexes measure 25 km along-axis and 10–15 km across.

Diagram showing a transform fault with two plates moving in opposite directions

Kane Fracture Zone

Medium-offset transform fault zone located on the Mid-Atlantic Ridge .

Medium-offset transform fault zone located on the Mid-Atlantic Ridge .

Diagram showing a transform fault with two plates moving in opposite directions

It lies just to the north of the Kane Megamullion, an oceanic core complex that forms the footwall of a long-lived low-angle detachment fault.