scholarly journals The Gakkel Ridge: Bathymetry, gravity anomalies, and crustal accretion at extremely slow spreading rates

2003 ◽  
Vol 108 (B2) ◽  
Author(s):  
James R. Cochran ◽  
Gregory J. Kurras ◽  
Margo H. Edwards ◽  
Bernard J. Coakley
Keyword(s):  
Gravity Anomalies ◽  
Crustal Accretion ◽  
Gakkel Ridge ◽  
Slow Spreading ◽  
Spreading Rates

scholarly journals Thermochemical anomalies in the upper mantle control Gakkel Ridge accretion

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
John M. O’Connor ◽  
Wilfried Jokat ◽  
Peter J. Michael ◽  
Mechita C. Schmidt-Aursch ◽  
Daniel P. Miggins ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Temporal Distribution ◽  
Volcanic Eruptions ◽  
Spreading Rate ◽  
Spreading Ridge ◽  
Crustal Accretion ◽  
Gakkel Ridge ◽  
Steady Rate ◽  
Slow Spreading ◽  
Ocean Ridge

AbstractDespite progress in understanding seafloor accretion at ultraslow spreading ridges, the ultimate driving force is still unknown. Here we use 40Ar/39Ar isotopic dating of mid-ocean ridge basalts recovered at variable distances from the axis of the Gakkel Ridge to provide new constraints on the spatial and temporal distribution of volcanic eruptions at various sections of an ultraslow spreading ridge. Our age data show that magmatic-dominated sections of the Gakkel Ridge spread at a steady rate of ~11.1 ± 0.9 mm/yr whereas amagmatic sections have a more widely distributed melt supply yielding ambiguous spreading rate information. These variations in spreading rate and crustal accretion correlate with locations of hotter thermochemical anomalies in the asthenosphere beneath the ridge. We conclude therefore that seafloor generation in ultra-slow spreading centres broadly reflects the distribution of thermochemical anomalies in the upper mantle.

The Heterogeneous Tethyan Oceanic Lithosphere of the Alpine Ophiolites

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 23-28 ◽  
Author(s):  
Elisabetta Rampone ◽  
Alessio Sanfilippo
Keyword(s):  
Oceanic Lithosphere ◽  
Passive Margin ◽  
Crustal Material ◽  
Crustal Accretion ◽  
Mantle Dynamics ◽  
Western Tethys ◽  
Mantle Peridotites ◽  
Slow Spreading ◽  
Tethys Ocean ◽  
Basaltic Crust

The Alpine–Apennine ophiolites are lithospheric remnants of the Jurassic Alpine Tethys Ocean. They predominantly consist of exhumed mantle peridotites with lesser gabbroic and basaltic crust and are locally associated with continental crustal material, indicating formation in an environment transitional from an ultra-slow-spreading seafloor to a hyperextended passive margin. These ophiolites represent a unique window into mantle dynamics and crustal accretion in an ultra-slow-spreading extensional environment. Old, pre-Alpine, lithosphere is locally preserved within the mantle sequences: these have been largely modified by reaction with migrating asthenospheric melts. These reactions were active in both the mantle and the crust and have played a key role in creating the heterogeneous oceanic lithosphere in this branch of the Mesozoic Western Tethys.

scholarly journals In situ lower crustal accretion by melt sill injection revealed by seismic layering

2021 ◽  
Author(s):  
Peng Guo ◽  
Satish Singh ◽  
Venkata Vaddineni ◽  
Ingo Grevemeyer ◽  
Erdinc Saygin
Keyword(s):  
Oceanic Crust ◽  
Lower Crust ◽  
Velocity Variation ◽  
Main Process ◽  
Upper Crust ◽  
Crustal Accretion ◽  
Slow Spreading ◽  
Lower Crustal ◽  
Lower Oceanic Crust

Abstract Oceanic crust is formed at mid-ocean spreading centres by a combination of magmatic, tectonic and hydrothermal processes. The crust formed by magmatic process consists of an upper crust generally composed of basaltic dikes and lava flows and a lower crust presumed to mainly contain homogeneous gabbro whereas that by tectonic process can be very heterogeneous and may even contain mantle rocks. Although the formation and evolution of the upper crust are well known from geophysical and drilling results, those for the lower crust remain a matter of debate. Using a full waveform inversion method applied to wide-angle seismic data, here we report the presence of layering in the lower oceanic crust formed at the slow spreading Mid-Atlantic Ridge, ~7-12 Ma in age, revealing that the lower crust is formed mainly by in situ cooling and crystallisation of melt sills at different depths by the injection of magma from the mantle. These layers are 400-600 m thick with alternate high and low velocities, with ± 100-200 m/s velocity variation, and cover over a million-year old crust, suggesting that the crustal accretion by melt sill intrusions beneath the ridge axis is a stable process. We also find that the upper crust is ~400 m thinner than that from conventional travel-time analysis. Taken together, these discoveries suggest that the magmatism plays more important roles in the crustal accretion process at slow spreading ridges than previously realised, and that in-situ lower crustal accretion is the main process for the formation of lower oceanic crust.

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