Extrusive upper crust formation at slow-spreading ridges: Fault steering of lava flows

Abstract The mantle is the most voluminous part of the Earth. However, mantle petrologists usually have to rely on indirect geophysical methods or on material found ex situ. In this review paper, we point out the in-situ existence of oceanic core complexes (OCCs), which provide large exposures of mantle and lower crustal rocks on the seafloor on detachment fault footwalls at slow-spreading ridges. OCCs are a common structure in oceanic crust architecture of slow-spreading ridges. At least 172 OCCs have been identified so far and we can expect to discover hundreds of new OCCs as more detailed mapping takes place. Thirty-two of the thirty-nine OCCs that have been sampled to date contain peridotites. Moreover, peridotites dominate in the plutonic footwall of 77% of OCCs. Massive OCC peridotites come from the very top of the melting column beneath ocean ridges. They are typically spinel harzburgites and show 11.3–18.3% partial melting, generally representing a maximum degree of melting along a segment. Another key feature is the lower frequency of plagioclase-bearing peridotites in the mantle rocks and the lower abundance of plagioclase in the plagioclase-bearing peridotites in comparison to transform peridotites. The presence of plagioclase is usually linked to impregnation with late-stage melt. Based on the above, OCC peridotites away from segment ends and transforms can be treated as a new class of abyssal peridotites that differ from transform peridotites by a higher degree of partial melting and lower interaction with subsequent transient melt.

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Asymmetry of thermal structure at slow-spreading ridges: Geodynamics and numerical modeling

Computers & Fluids ◽

10.1016/j.compfluid.2012.07.028 ◽

2012 ◽

Vol 68 ◽

pp. 29-37 ◽

Cited By ~ 3

Author(s):

Marco Cuffaro ◽

Edie Miglio

Keyword(s):

Numerical Modeling ◽

Thermal Structure ◽

Spreading Ridges ◽

Slow Spreading

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The geological record of oceanic crustal accretion and tectonism at slow-spreading ridges

10.1575/1912/5693 ◽

1996 ◽

Cited By ~ 10

Author(s):

Gary E. Jaroslow

Keyword(s):

Crustal Accretion ◽

Geological Record ◽

Spreading Ridges ◽

Slow Spreading

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Unveiling the volcanic evolution of the Mohns Ridge

10.5194/egusphere-egu21-1050 ◽

2021 ◽

Author(s):

Håvard Stubseid ◽

Anders Bjerga ◽

Haflidi Haflidason ◽

Rolf Birger Pedersen

Keyword(s):

Autonomous Underwater Vehicles ◽

Volcanic Eruptions ◽

Integrated Approach ◽

Hydrothermal Systems ◽

Ocean Ridges ◽

Spreading Ridges ◽

Geological Evolution ◽

Fast Spreading ◽

Slow Spreading ◽

Resolution Dataset

Volcanic eruptions are far less common along slow-spreading ridges compared to fast-spreading ridges. Consequently, knowledge of the volcanic rejuvenation along close to 1/3 of the global mid-ocean ridges is poorly constrained. To determine the temporal evolution of the rift valley of one of the slowest spreading-ridges in the world, the Mohns Ridge in the Norwegian-Greenland Sea, we have interpreted more than 3000 km of sub-bottom profiles. Sedimentation rates derived from several core locations along the ridge are used to calculate the age of the underlying volcanic crust. Here we present a framework for understanding the geological evolution of rift valleys of slow-spreading ridges using an integrated approach combining geological and geophysical data. The high-resolution dataset acquired using autonomous underwater vehicles, cover more than 50% of the 575 km long Mohns Ridge. The results unravel large variation in sediment thickness inside the central rift area, from exposed basalts to several meters of sediments, within only a few hundreds of meters. Studied sub-bottom profiles reveal active volcanism in the deepest parts of the ridge, areas thought to be inactive, surrounded by significantly older crust covered in meters of sediments. We find that all axial volcanic ridge systems (AVRs) in our area completely renewed their surface within the last 30-50 ka. Detailed volcanological investigation of the central parts of an AVR reveal at least 72 individual eruptions during the last 20 ka ranging in size from 1.2x103 m2 - 2.6 x105 m2. These estimates have been verified with visual observations and sampling using an ROV. Our estimates indicate that more than 230 eruptions are required to renew the surface of an average AVR. Based on the acquired age assessments a volcanic eruption is anticipated to occur approximately every 200 years. Volcanic renewal is a first order control on the lifetime of magmatically driven hydrothermal systems.

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