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Solid Earth An interactive open-access journal of the European Geosciences Union

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Solid Earth, 5, 1243-1275, 2014
http://www.solid-earth.net/5/1243/2014/
doi:10.5194/se-5-1243-2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review article
04 Dec 2014
Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments
J. L. Tetreault1 and S. J. H. Buiter1,2 1Geodynamics Team, Geological Survey of Norway (NGU), Trondheim, Norway
2Centre for Earth Evolution and Dynamics, University of Oslo, Oslo, Norway
Abstract. Allochthonous accreted terranes are exotic geologic units that originated from anomalous crustal regions on a subducting oceanic plate and were transferred to the overriding plate by accretionary processes during subduction. The geographical regions that eventually become accreted allochthonous terranes include island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents. These future allochthonous terranes (FATs) contribute to continental crustal growth, subduction dynamics, and crustal recycling in the mantle. We present a review of modern FATs and their accreted counterparts based on available geological, seismic, and gravity studies and discuss their crustal structure, geological origin, and bulk crustal density. Island arcs have an average crustal thickness of 26 km, average bulk crustal density of 2.79 g cm−3, and three distinct crustal units overlying a crust–mantle transition zone. Oceanic plateaus and submarine ridges have an average crustal thickness of 21 km and average bulk crustal density of 2.84 g cm−3. Continental fragments presently on the ocean floor have an average crustal thickness of 25 km and bulk crustal density of 2.81 g cm−3. Accreted allochthonous terranes can be compared to these crustal compilations to better understand which units of crust are accreted or subducted. In general, most accreted terranes are thin crustal units sheared off of FATs and added onto the accretionary prism, with thicknesses on the order of hundreds of meters to a few kilometers. However, many island arcs, oceanic plateaus, and submarine ridges were sheared off in the subduction interface and underplated onto the overlying continent. Other times we find evidence of terrane–continent collision leaving behind accreted terranes 25–40 km thick. We posit that rheologically weak crustal layers or shear zones that were formed when the FATs were produced can be activated as detachments during subduction, allowing parts of the FAT crust to accrete and others to subduct. In many modern FATs on the ocean floor, a sub-crustal layer of high seismic velocities, interpreted as ultramafic material, could serve as a detachment or delaminate during subduction.

Citation: Tetreault, J. L. and Buiter, S. J. H.: Future accreted terranes: a compilation of island arcs, oceanic plateaus, submarine ridges, seamounts, and continental fragments, Solid Earth, 5, 1243-1275, doi:10.5194/se-5-1243-2014, 2014.
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Continents are composed of a collage of accreted terranes: tectonically sutured crustal units of various origins. This review covers the cycle of terrane accretion from the original entity (modern-day oceanic island arcs, oceanic plateaus, submarine ridges, seamounts, continental fragments, and microcontinents) to present-day examples of terrane accretion to finally allochthonous accreted terranes.
Continents are composed of a collage of accreted terranes: tectonically sutured crustal units of...
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