Mid-ocean-ridge seismicity reveals extreme types of ocean lithosphere

Nature ◽  
2016 ◽  
Vol 535 (7611) ◽  
pp. 276-279 ◽  
Author(s):  
Vera Schlindwein ◽  
Florian Schmid
Keyword(s):  
Mid Ocean Ridge ◽  
Ocean Lithosphere ◽  
Ocean Ridge

Thrust-related metamorphism beneath the Shetland Islands oceanic fragment, northeast Scotland

1988 ◽  
Vol 25 (11) ◽  
pp. 1760-1776 ◽  
Author(s):  
John G. Spray
Keyword(s):  
High Pressures ◽  
Hanging Wall ◽  
Crust And Upper Mantle ◽  
Thermal Inversion ◽  
Shetland Islands ◽  
Suprasubduction Zone ◽  
Mid Ocean Ridge ◽  
Close Proximity ◽  
Ocean Lithosphere ◽  
Ocean Ridge

A ≤400 m thick metamorphic sequence showing thermal inversion is present beneath a dismembered ultrabasic–basic complex in the Shetland Islands of northeast Scotland. The metamorphic grade changes from upper amphibolite facies in metabasites at the top of the sequence to low greenschist facies in metasediments at the base. Garnet–clinopyroxene thermometry yields temperatures of ~ 750 °C (at 300 MPa) for the highest grade assemblage. There is no evidence for high pressures of metamorphism, and maximum overburden may never have exceeded the original thickness of the overlying ultrabasic–basic complex, which is estimated to have been ~ 10 km.The internal structure and field relations of the ultrabasic–basic complex reveal that it is a displaced fragment of oceanic crust and upper mantle of Ordovician age. The chemistry of its basic lithologies suggests low-K tholeiite, suprasubduction zone, pre-arc affinities. In contrast, the underlying meteamorphic sequence possesses a mid-ocean ridge basalt (MORB) signature.Four K–Ar age determinations from amphibole mineral separates of the metamorphic sequence range from 479 ± 6 to 465 ± 6 Ma. The highest age is interpreted as the date of the onset of metamorphic sole formation and the initial tectonic displacement of the oceanic fragment.It is concluded that the metamorphic sequence was generated during intraoceanic thrusting during the destruction of a young, marginal oceanic basin located between a continental margin and the ocean lithosphère of Iapetus. Certain MORB lithologies were metamorphosed and transferred to the marginal basin hanging wall during the subduction of Iapetus. Apparent thermal inversion was caused during overthrusting by the gradual underplating of the hanging wall in close proximity to a suprasubduction zone spreading centre.

PETROGENESIS OF GABBRO FROM ARCTIC GAKKEL MID-OCEAN RIDGE

2019 ◽  
Author(s):  
Yung Ping Lee ◽  
◽  
Jonathan E. Snow ◽  
Yongjun Gao
Keyword(s):  
Mid Ocean Ridge ◽  
Ocean Ridge

scholarly journals Melt addition to mid-ocean ridge peridotites increases spinel Cr# with no significant effect on recorded oxygen fugacity

2021 ◽  
Vol 566 ◽  
pp. 116951
Author(s):  
Suzanne K. Birner ◽  
Elizabeth Cottrell ◽  
Jessica M. Warren ◽  
Katherine A. Kelley ◽  
Fred A. Davis
Keyword(s):  
Oxygen Fugacity ◽  
Mid Ocean Ridge ◽  
Ocean Ridge

scholarly journals Sunda arc mantle source δ18O value revealed by intracrystal isotope analysis

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Frances M. Deegan ◽  
Martin J. Whitehouse ◽  
Valentin R. Troll ◽  
Harri Geiger ◽  
Heejin Jeon ◽  
...  
Keyword(s):  
Mantle Source ◽  
Secondary Ion Mass Spectrometry ◽  
Isotope Composition ◽  
Isotope Analysis ◽  
Sunda Arc ◽  
Mid Ocean Ridge ◽  
Plumbing Systems ◽  
Ocean Ridge ◽  
Secondary Ion ◽  
Magma Plumbing

AbstractMagma plumbing systems underlying subduction zone volcanoes extend from the mantle through the overlying crust and facilitate protracted fractional crystallisation, assimilation, and mixing, which frequently obscures a clear view of mantle source compositions. In order to see through this crustal noise, we present intracrystal Secondary Ion Mass Spectrometry (SIMS) δ18O values in clinopyroxene from Merapi, Kelut, Batur, and Agung volcanoes in the Sunda arc, Indonesia, under which the thickness of the crust decreases from ca. 30 km at Merapi to ≤20 km at Agung. Here we show that mean clinopyroxene δ18O values decrease concomitantly with crustal thickness and that lavas from Agung possess mantle-like He-Sr-Nd-Pb isotope ratios and clinopyroxene mean equilibrium melt δ18O values of 5.7 ‰ (±0.2 1 SD) indistinguishable from the δ18O range for Mid Ocean Ridge Basalt (MORB). The oxygen isotope composition of the mantle underlying the East Sunda Arc is therefore largely unaffected by subduction-driven metasomatism and may thus represent a sediment-poor arc end-member.

scholarly journals A subduction influence on ocean ridge basalts outside the Pacific subduction shield

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Y. Yang ◽  
C. H. Langmuir ◽  
Y. Cai ◽  
P. Michael ◽  
S. L. Goldstein ◽  
...  
Keyword(s):  
Upper Mantle ◽  
The Arctic ◽  
Mantle Flow ◽  
Mantle Heterogeneity ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

Primary magmas of mid-ocean ridge basalts 2. Applications

1992 ◽  
Vol 97 (B5) ◽  
pp. 6907 ◽  
Author(s):  
Rosamond J. Kinzler ◽  
Timothy L. Grove
Keyword(s):  
Mid Ocean Ridge ◽  
Ocean Ridge ◽  
Primary Magmas
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