Absolute plate motions and regional subduction evolution
... boundary parallel leading to the present-day Rif-Gibraltar-Betic slab [Rosenbaum et al., 2002; Spakman and Wortel, 2004; van Hinsbergen et al., 2014; Chertova et al., 2014]. In Chertova et al. [2014], hereafter called Chert14, we modeled various subduction evolution scenarios for the region with a f ...
... boundary parallel leading to the present-day Rif-Gibraltar-Betic slab [Rosenbaum et al., 2002; Spakman and Wortel, 2004; van Hinsbergen et al., 2014; Chertova et al., 2014]. In Chertova et al. [2014], hereafter called Chert14, we modeled various subduction evolution scenarios for the region with a f ...
1. LEG 209 SUMMARY: PROCESSES IN A 20-KM
... Microstructures show that most residual peridotites were not ductilely deformed at temperatures less than ~1200°C. Structural and paleomagnetic data require tectonic rotations of relatively undeformed blocks; some rotations probably exceeded 60° around nearly horizontal axes parallel to the rift axi ...
... Microstructures show that most residual peridotites were not ductilely deformed at temperatures less than ~1200°C. Structural and paleomagnetic data require tectonic rotations of relatively undeformed blocks; some rotations probably exceeded 60° around nearly horizontal axes parallel to the rift axi ...
Silurian-Early Devonian mafic rocks of the Piscataquis volcanic belt
... are composed of mafic and felsic rocks with rare intermediate types. The mafic rocks are mainly basalts that are commonly strongly fractionated and have the characteristics of intraplate continental tholeiites. The mantlenormalized incompatible trace element patterns of the rocks display negative Nb ...
... are composed of mafic and felsic rocks with rare intermediate types. The mafic rocks are mainly basalts that are commonly strongly fractionated and have the characteristics of intraplate continental tholeiites. The mantlenormalized incompatible trace element patterns of the rocks display negative Nb ...
Plate generation and two-phase damage theory in a model of
... to add another level of sophistication to previous work, but is still obviously a simplification of fully variable viscosity convection and hence convection in Earth. Our goal though is to ascertain the general plate behaviours (i.e. narrow boundary zones separated by rigid plate interiors) of two-p ...
... to add another level of sophistication to previous work, but is still obviously a simplification of fully variable viscosity convection and hence convection in Earth. Our goal though is to ascertain the general plate behaviours (i.e. narrow boundary zones separated by rigid plate interiors) of two-p ...
IODP Proposal Cover Sheet
... ocean drilling (e.g., the "Road to the Moho" chapter in Murray et al., 2000). The Moho (Mohorovii Discontinuity) is a seismically imaged, primary acoustic interface that represents the transition between the Earth’s crust and the underlying mantle. Whereas oceanic crust is formed by a variety of i ...
... ocean drilling (e.g., the "Road to the Moho" chapter in Murray et al., 2000). The Moho (Mohorovii Discontinuity) is a seismically imaged, primary acoustic interface that represents the transition between the Earth’s crust and the underlying mantle. Whereas oceanic crust is formed by a variety of i ...
Plate Tectonics
... ■ Hands-on Activities ■ Meeting Individual Needs (Extension and Intervention) ■ Transparency Activities A teacher support and planning section including ■ Content Outline of the chapter ...
... ■ Hands-on Activities ■ Meeting Individual Needs (Extension and Intervention) ■ Transparency Activities A teacher support and planning section including ■ Content Outline of the chapter ...
Arthur Holmes` paper of 1929 on convection currents within the
... nearly uniform intervals between successive orogenic periods, but only at the expense of discrepancy which becomes still greater. (4) The improbability that compression dispersed through [p. 564] a layer 150 km. thick could produce relatively superficial nappe structures like those of the Alps. (5) ...
... nearly uniform intervals between successive orogenic periods, but only at the expense of discrepancy which becomes still greater. (4) The improbability that compression dispersed through [p. 564] a layer 150 km. thick could produce relatively superficial nappe structures like those of the Alps. (5) ...
Tomography of the 2011 Iwaki earthquake (M 7.0) and Fukushima
... subduction-induced convection in the mantle wedge and dehydration reactions in the subducting slab (Hasegawa and Zhao, 1994; Iwamori and Zhao, 2000; Zhao et al., 1992, 2010). In the forearc region, the temperature is low; hence magma cannot be produced and the low-V and high-σ zones mainly indicate ...
... subduction-induced convection in the mantle wedge and dehydration reactions in the subducting slab (Hasegawa and Zhao, 1994; Iwamori and Zhao, 2000; Zhao et al., 1992, 2010). In the forearc region, the temperature is low; hence magma cannot be produced and the low-V and high-σ zones mainly indicate ...
TROPICS Continent-Building in Costa Rica
... this root is believed to record protracted melt extraction, the volume of extracted melt is much larger then the volume of existing continental crust. Present-day melting at ridges and arcs produces smaller volumes of less depleted, residual mantle peridotite. Some authors have envisioned formation ...
... this root is believed to record protracted melt extraction, the volume of extracted melt is much larger then the volume of existing continental crust. Present-day melting at ridges and arcs produces smaller volumes of less depleted, residual mantle peridotite. Some authors have envisioned formation ...
Layered Mantle Lithosphere in the Lac de Gras
... of garnet types indicate that the shallow layer consists of ~60% (clinopyroxene-free) harzburgite and 40% lherzolite, whereas the deeper layer contains 15–20% harzburgite and 80–85% lherzolite. T estimates on eclogite xenoliths show that all were derived from the deeper layer. Xenolith data and garn ...
... of garnet types indicate that the shallow layer consists of ~60% (clinopyroxene-free) harzburgite and 40% lherzolite, whereas the deeper layer contains 15–20% harzburgite and 80–85% lherzolite. T estimates on eclogite xenoliths show that all were derived from the deeper layer. Xenolith data and garn ...
On the nature of the Moho: Lithospheric-scale
... observed wavefield of the Moho below the Great Bear magmatic are: (1) Prominent PmP phase between 80 and 220 km offsets followed by ~0.5 s long coda, and a very weak amplitude Pn phase observed at offsets > 160 km offset (Fig. 1a). (2) Amplitude behavior of the PmP phase with offset is highly errati ...
... observed wavefield of the Moho below the Great Bear magmatic are: (1) Prominent PmP phase between 80 and 220 km offsets followed by ~0.5 s long coda, and a very weak amplitude Pn phase observed at offsets > 160 km offset (Fig. 1a). (2) Amplitude behavior of the PmP phase with offset is highly errati ...
Negredo et al. Pamir subduction, EPSL, 259, 2007
... the India–Eurasia collision zone, with steep northward subduction of Indian lithosphere beneath the Hindu Kush and southward subduction of Asian lithosphere under the Pamir. We investigate the geometry and the timing of these subduction processes. Seismic tomography images are used to constrain the ...
... the India–Eurasia collision zone, with steep northward subduction of Indian lithosphere beneath the Hindu Kush and southward subduction of Asian lithosphere under the Pamir. We investigate the geometry and the timing of these subduction processes. Seismic tomography images are used to constrain the ...
Distinct Updip Limits to Geodetic Locking and Microseismicity at the
... Rica. Geodetic inversions for interseismic slip on the plate interface reveal locking equal to ~75% of the plate velocity between 8 and 15 km depth below sea level, while shallow interplate microearthquakes begin deeper, between 15 and18 km below sea level, in a region that appears to be freely slip ...
... Rica. Geodetic inversions for interseismic slip on the plate interface reveal locking equal to ~75% of the plate velocity between 8 and 15 km depth below sea level, while shallow interplate microearthquakes begin deeper, between 15 and18 km below sea level, in a region that appears to be freely slip ...
Gabbroic Pegmatite Intrusions, Iberia Abyssal
... of 127 ± 4 Ma, which we interpret as an igneous age. The Site 1070 gabbro pegmatites are the only igneous rocks that are demonstrably coeval with rifting in the southern IAP. As such, they help to document the transition from non-volcanic margin to normal ocean crust formation in this part of the No ...
... of 127 ± 4 Ma, which we interpret as an igneous age. The Site 1070 gabbro pegmatites are the only igneous rocks that are demonstrably coeval with rifting in the southern IAP. As such, they help to document the transition from non-volcanic margin to normal ocean crust formation in this part of the No ...
Nakajima_etal_GRL200.. - Research School of Earth Sciences
... reveal that the depth extent of the low-velocity (hydrated) oceanic crust varies along the arc. The low-velocity oceanic crust is subducting to depths of 120– 150 km beneath Kanto, which is 40– 70 km deeper compared to NE Japan. Such deeper preservation of the low-velocity oceanic crust beneath Kant ...
... reveal that the depth extent of the low-velocity (hydrated) oceanic crust varies along the arc. The low-velocity oceanic crust is subducting to depths of 120– 150 km beneath Kanto, which is 40– 70 km deeper compared to NE Japan. Such deeper preservation of the low-velocity oceanic crust beneath Kant ...
A reassessment of the timing of early Archaean crustal
... of similar gabbroic samples yield an isochron age of 3677 ± 37 Ma, and (3) a volcanogenic Akilia Association schist was dated at 3685 ± 8 Ma with the U-Pb ion-probe method. The combined age of c. 3.67–3.68 Ga is in direct conflict with the interpretation of U-Pb zircon age spectra of younger, cross- ...
... of similar gabbroic samples yield an isochron age of 3677 ± 37 Ma, and (3) a volcanogenic Akilia Association schist was dated at 3685 ± 8 Ma with the U-Pb ion-probe method. The combined age of c. 3.67–3.68 Ga is in direct conflict with the interpretation of U-Pb zircon age spectra of younger, cross- ...
Petrology and Geochemistry of Lavas
... Since the elegant summary of Central American geology by Weyl [1] in 1980, petrological and geochemical studies unveiled large variations in the Tertiary and Quaternary volcanics both along the volcanic chain and across it. The active volcanoes define an abrupt volcanic front, located 165 to 190 km ...
... Since the elegant summary of Central American geology by Weyl [1] in 1980, petrological and geochemical studies unveiled large variations in the Tertiary and Quaternary volcanics both along the volcanic chain and across it. The active volcanoes define an abrupt volcanic front, located 165 to 190 km ...
pegmatites and pegmatites, just like granites and granites
... depending on the proportion of mantlederived and crust-derived components in the source. At the end of an orogeny, however, there is commonly a tendency for the overthickened crust to founder, and to allow hot, asthenospheric mantle to rise relatively quickly, such that a change in tectonic setting ...
... depending on the proportion of mantlederived and crust-derived components in the source. At the end of an orogeny, however, there is commonly a tendency for the overthickened crust to founder, and to allow hot, asthenospheric mantle to rise relatively quickly, such that a change in tectonic setting ...
Geomagnetic Deep Sounding in and around the Kenya Rift Valley
... Congo, the delay is only f 1 s, suggesting that the anomalous zone is less extensive there. The delay at Kaptagat, relative to Bulawayo, is about + 2 s (Backhouse 1972), and can be interpreted as being due to a thickness of about 100 km of material with P velocity 7 km s-'. Fairhead & Girdler (1971) ...
... Congo, the delay is only f 1 s, suggesting that the anomalous zone is less extensive there. The delay at Kaptagat, relative to Bulawayo, is about + 2 s (Backhouse 1972), and can be interpreted as being due to a thickness of about 100 km of material with P velocity 7 km s-'. Fairhead & Girdler (1971) ...
Magmas and Igneous Rocks
... geothermal gradient. Once such mechanism is convection, wherein hot mantle material rises to lower pressure or depth, carrying its heat with it. If the raised geothermal gradient becomes higher than the initial melting temperature at any pressure, then a partial melt will form. Liquid from this part ...
... geothermal gradient. Once such mechanism is convection, wherein hot mantle material rises to lower pressure or depth, carrying its heat with it. If the raised geothermal gradient becomes higher than the initial melting temperature at any pressure, then a partial melt will form. Liquid from this part ...
Tarapacб intermediate-depth earthquake - meteo
... 4. InSAR and GPS Modeling [9] Static surface displacement is modeled combining coseismic displacements, from permanent GPS stations, and interferograms from ENVISAT radar images. Data from 7 continuous GPS stations (Table S3) are processed using the GAMIT software [King and Bock, 2001], together wit ...
... 4. InSAR and GPS Modeling [9] Static surface displacement is modeled combining coseismic displacements, from permanent GPS stations, and interferograms from ENVISAT radar images. Data from 7 continuous GPS stations (Table S3) are processed using the GAMIT software [King and Bock, 2001], together wit ...
Mantle plume
A mantle plume is a mechanism proposed in 1971 to explain volcanic regions of the earth that were not thought to be explicable by the then-new theory of plate tectonics. Some such volcanic regions lie far from tectonic plate boundaries, for example, Hawaii. Others represent unusually large-volume volcanism, whether on plate boundaries, e.g. Iceland, or basalt floods such as the Deccan or Siberian traps.A mantle plume is posited to exist where hot rock nucleates at the core-mantle boundary and rises through the Earth's mantle becoming a diapir in the Earth's crust. The currently active volcanic centers are known as ""hot spots"". In particular, the concept that mantle plumes are fixed relative to one another, and anchored at the core-mantle boundary, was thought to provide a natural explanation for the time-progressive chains of older volcanoes seen extending out from some such hot spots, such as the Hawaiian–Emperor seamount chain.The hypothesis of mantle plumes from depth is not universally accepted as explaining all such volcanism. It has required progressive hypothesis-elaboration leading to variant propositions such as mini-plumes and pulsing plumes. Another hypothesis for unusual volcanic regions is the ""Plate model"". This proposes shallower, passive leakage of magma from the mantle onto the Earth's surface where extension of the lithosphere permits it, attributing most volcanism to plate tectonic processes, with volcanoes far from plate boundaries resulting from intraplate extension.