Mantle rock exposures at oceanic core complexes along mid-ocean ridges
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Date
2015-12
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Instytut Geologii UAM
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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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Keywords
peridotite, OCC, detachment fault, megamullion, slow-spreading ridge
Citation
Geologos, 2015, 21, 4, pp. 207-231
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ISBN
978-83-232187-4-6
ISSN
1426-8981