Abstract:A new 3D lithospheric model has been constructed using high-resolution gravity data from the Irish National Seabed Survey. The sedimentary component of the model incorporated density variations due to laterally varying overcompaction associated with Cenozoic denudation. After optimisation based on gravity inversion, regional crustal thickness variations were defined which are in reasonable agreement with the results of wide-angle seismic experiments. High crustal extension factors (β>5) characterise the deeper… Show more
“…The volcanic province is shown and highlighted with a yellow dotted line. Volcanic features in Rockall Basin are shown, based on the location of strong positive magnetic anomalies [after Kimbell et al , ], and those which appear to be conjugate to the CGVP are indicated by a dotted yellow line. The Barra Volcanic Ridges are shown, one of which aligns with the southern branch of the CGVP, along the trend indicated by the solid red line.…”
“…The volcanic province is shown and highlighted with a yellow dotted line. Volcanic features in Rockall Basin are shown, based on the location of strong positive magnetic anomalies [after Kimbell et al , ], and those which appear to be conjugate to the CGVP are indicated by a dotted yellow line. The Barra Volcanic Ridges are shown, one of which aligns with the southern branch of the CGVP, along the trend indicated by the solid red line.…”
“…In some cases, extension proceeded far enough in the failed rifts separating continental fragments from the interior that exhumed and serpentinized mantle directly underlies the basin sediments. Exhumed mantle is inferred from seismic and potential field studies for the Porcupine Basin (Kimbell et al, 2010), Phu Khanh Basin (Savva et al, 2013), and the Santos Basin (Zalán et al, 2011). Microcontinents, such as Jan Mayen and the Seychelles, are surrounded by oceanic crust.…”
Section: Continental Fragments and Microcontinents: General Settingmentioning
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.
“…However, it appears likely that these lavas are underlain by Mesozoic rifts that contain rocks with relatively high velocities, because of either overcompaction or a high concentration of sills. Magnetic anomalies over the Hatton Basin suggest substantial volumes of magmatic rocks (Kimbell et al 2010).…”
The NE Atlantic region evolved through several rift episodes, leading to break-up in the Eocene that was associated with voluminous magmatism along the conjugate margins of East Greenland and NW Europe. Existing seismic refraction data provide good constraints on the overall tectonic development of the margins, despite data gaps at the NE Greenland shear margin and the southern Jan Mayen microcontinent. The maximum thickness of the initial oceanic crust is 40 km at the Greenland-Iceland-Faroe Ridge, but decreases with increasing distance to the Iceland plume. High-velocity lower crust interpreted as magmatic underplating or sill intrusions is observed along most margins but disappears north of the East Greenland Ridge and the Lofoten margin, with the exception of the Vestbakken Volcanic Province at the SW Barents Sea margin. South of the narrow Lofoten margin, the European side is characterized by wide margins. The opposite trend is seen in Greenland, with a wide margin in the NE and narrow margins elsewhere. The thin crust beneath the basins is generally underlain by rocks with velocities of .7 km s 21 interpreted as serpentinized mantle in the Porcupine and southern Rockall basins; while off Norway, alternative interpretations such as eclogite bodies and underplating are also discussed.Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.
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