Search results for "Mid-ocean ridge"
showing 10 items of 12 documents
Seafloor expression of oceanic detachment faulting reflects gradients in mid-ocean ridge magma supply
2019
International audience; Oceanic detachment faulting is a major mode of seafloor accretion at slow and ultraslow spreading mid-ocean ridges, and is associated with dramatic changes in seafloor morphology. Detachments form expansive dome structures with corrugated surfaces known as oceanic core complexes (OCCs), and often transition to multiple regularly-spaced normal faults that form abyssal hills parallel to the spreading axis. Previous studies have attributed these changes to along-axis gradients in lithospheric strength or magma supply. However, despite the recognition that magma supply can influence fault style and seafloor morphology, the mechanics controlling the transition from oceani…
Geochemical constraints on volatile sources and subsurface conditions at Mount Martin, Mount Mageik, and Trident Volcanoes, Katmai Volcanic Cluster, …
2017
Abstract We use the chemical and isotopic composition of volcanic gases and steam condensate, in situ measurements of plume composition and remote measurements of SO2 flux to constrain volatile sources and characterize subvolcanic conditions at three persistently degassing and seismically active volcanoes within the Katmai Volcanic Cluster (KVC), Alaska: Mount Martin, Mount Mageik and Trident. In situ plume measurements of gas composition were collected at all three volcanoes using MultiGAS instruments to calculate gas ratios (e.g. CO2/H2S, SO2/H2S and H2O/H2S), and remote measurements of SO2 column density were collected from Mount Martin and Mount Mageik by ultraviolet spectrometer system…
Trench-parallel spreading ridge subduction and its consequences for the geological evolution of the overriding plate: Insights from analogue models a…
2018
A series of 3-D asthenospheric-scale analogue models have been conducted in the laboratory in order to simulate the arrival of a spreading ridge at the trench and understand its effect on plate kinematics, slab geometry, and on the deformation of the overriding plate. These models are made of a two-layered linearly viscous system simulating the lithosphere and asthenosphere. We reproduce the progressive decrease in thickness of the oceanic lithosphere at the trench. We measure plate kinematics, slab geometry and upper plate deformation. Our experiments reveal that the subduction of a thinning plate beneath a freely moving overriding continent favors a decrease of the subduction velocity and…
A sequence analyzed from the basin to the platform : the Middle Oxfordian calcareous succession in southeastern France
2004
Abstract Middle Oxfordian sedimentation is very homogeneous in southeastern France. It is characterized by a specific alternation of marls and fine-grained limestones (G. transversarium Zone). This work shows that sets of calcareous beds allow accurate stratigraphic correlations in various paleogeographic areas, from the shallow Jura platform to the deep Dauphinois basin. Following a rifting period, this sedimentation illustrates a doming period with decreasing subsidence and water depth. This corresponds to the establishment of a wide marine area more favourable to carbonate sedimentation. Considering sequence stratigraphy, some slight variations occur in the sediment record and lead to in…
The role of slabs and oceanic plate geometry in the net rotation of the lithosphere, trench motions, and slab return flow
2012
[1] Absolute plate motion models with respect to a deep mantle reference frame (e.g., hot spots) typically contain some net rotation (NR) of the lithosphere. Global mantle flow models for the present-day plate setting reproduce similarly oriented NRs but with amplitudes significantly smaller than those found in some high NR Pacific hot spot reference frames. It is therefore important to understand the mechanisms of NR excitation, which we attempt here with two-dimensional cylindrical models of an idealized Pacific domain. We study the influence of slab properties, oceanic ridge position, continental keels, and a weak asthenospheric layer on NR and trench migration. Fast slab return flow dev…
Stress generation at ridge axes by plate divergence and magma rise
1995
Abstract A model is explored for the rifting process particularly at the divergent plate boundary in Iceland, based on direct observations of the Krafla rifting episode 1975–1984. Magma accumulates near the axial crust-mantle transition as the plates diverge from each other and compression on the boundary decreases. Two-dimensional finite-element modelling is applied to investigate how divergence and buoyant rise of magma interact in triggering rifting. Both processes are found to be important, but long intervals between rifting episodes require the time-average deviatoric stress to be compressible normal to the axis.
On the Mesozoic Ionian Basin
2001
SUMMARY New seismic reflection profiles of the Italian deep crust project CROP provide new insights on the structure of the Ionian sea. In spite of the Apennines and Hellenides Neogene subduction zones, two conjugate passive continental margins are preserved at the margins of the Ionian sea, along the Malta escarpment to the southwest and the Apulian escarpment to the northeast. The Ionian sea is likely to be a remnant of the Mesozoic Tethys Ocean, confined by these two conjugate passive continental margins. The transition from continental to oceanic crust appears sharper to the northeast than to the southwest. The basin between southeast Sicily and southwest Puglia was about 330 km wide an…
A free plate surface and weak oceanic crust produce single-sided subduction on Earth
2012
[1] Earth’s lithosphere is characterized by the relative movement of almost rigid plates as part of global mantle convection. Subduction zones on present-day Earth are strongly asymmetric features composed of an overriding plate above a subducting plate that sinks into the mantle. While global self-consistent numerical models of mantle convection have reproduced some aspects of plate tectonics, the assumptions behind these models do not allow for realistic single-sided subduction. Here we demonstrate that the asymmetry of subduction results from two major features of terrestrial plates: (1) the presence of a free deformable upper surface and (2) the presence of weak hydrated crust atop subd…
On the Rifting Dynamics of Plate Divergence and Magma Accumulation at Oceanic Ridge Axes
1995
Rifting dynamics at spreading axes is governed by two processes: the large-scale plate divergence and the local magma accumulation in the crust-mantle transition layer. Both evolve simultaneously. A model is developed particularly for the situation in Iceland where a well studied rifting episode occurred in the Krafla volcanic system 1975–1984. Both the divergence and the buoyant rise of magma create tensile deviatoric stress in the axial region, but while divergence generates an altogether extensional stress field, uprising of buoyant melt produces tension only near the axis but compression of the sides. The buoyant rise is driven by the differential pressure gradient in rock and melt. The…
The Othris Ophiolite, Greece: A snapshot of subduction initiation at a mid-ocean ridge
2008
The mantle section of the Tethyan-type Othris Ophiolite, Greece, records tectono-magmatic processes characteristic of both mid-ocean ridges and supra-subduction zones. The Othris Ophiolite is a remnant of the Jurassic Neotethys Ocean, which existed between Eurasia and Gondwanaland. Othris peridotites range from fertile plagioclase lherzolites to depleted harzburgites. Abundances of Al2O3 and CaO show well-defined inverse linear correlations with MgO, suggesting that the Othris peridotites formed as residua from variable degrees of partial melting. Peridotites from the Fournos Kaitsa and western Katachloron sub-massifs are similar to abyssal peridotites and can be explained by a multistage m…