Lower Continental Crust. - UCSB Earth Science
... OF CONTINENTAL CRUST Earth’s continental crust is widely believed to be andesitic to dacitic, with 57 to 66 wt% SiO2 (e.g., Rudnick & Gao 2003, 2014), distinct from mafic oceanic crust, with 48 to 52 wt% SiO2 , and from upper mantle residual peridotites, with <46 wt% SiO2 . Compared with oceanic crus ...
... OF CONTINENTAL CRUST Earth’s continental crust is widely believed to be andesitic to dacitic, with 57 to 66 wt% SiO2 (e.g., Rudnick & Gao 2003, 2014), distinct from mafic oceanic crust, with 48 to 52 wt% SiO2 , and from upper mantle residual peridotites, with <46 wt% SiO2 . Compared with oceanic crus ...
Oxygen-isotope and trace element constraints on the origins of silica
... 2003; Kelemen et al., 2003a], for the chemical budgets of arc magmatism [Plank and Langmuir, 1993; Elliott et al., 1997], for the mechanisms responsible for growth of the continental crust [Rudnick and Fountain, 1995; Wang et al., 2003], and for the composition of deeply subducted lithosphere [Kelle ...
... 2003; Kelemen et al., 2003a], for the chemical budgets of arc magmatism [Plank and Langmuir, 1993; Elliott et al., 1997], for the mechanisms responsible for growth of the continental crust [Rudnick and Fountain, 1995; Wang et al., 2003], and for the composition of deeply subducted lithosphere [Kelle ...
Adakitic Dacites Formed by Intracrustal Crystal Fractionation of
... contents. An origin by partial melting of high-pressure crustal sources seems unlikely from isotopic and trace element considerations. Mafic enclaves quenched into one of the dacites, on the other hand, constitute plausible parental magmas. Dacites and mafic enclaves share several characteristics su ...
... contents. An origin by partial melting of high-pressure crustal sources seems unlikely from isotopic and trace element considerations. Mafic enclaves quenched into one of the dacites, on the other hand, constitute plausible parental magmas. Dacites and mafic enclaves share several characteristics su ...
Origin and models of oceanic transform faults. Tectonophysics, 522
... faults that are often associated with asymmetric accretion is well established along ridges spreading at less than 80 mm/yr (e.g., Allerton et al., 2000; Collier et al., 1997; Escartin et al., 2008 and references therein). On the other hand, transform faults are found in all above mentioned types of ...
... faults that are often associated with asymmetric accretion is well established along ridges spreading at less than 80 mm/yr (e.g., Allerton et al., 2000; Collier et al., 1997; Escartin et al., 2008 and references therein). On the other hand, transform faults are found in all above mentioned types of ...
The life cycle of suprasubduction zone ophiolites
... [1] Abstract: Suprasubduction zone (SSZ) ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites. This sequence includes the following: (1) birth, which entails the formation ...
... [1] Abstract: Suprasubduction zone (SSZ) ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites. This sequence includes the following: (1) birth, which entails the formation ...
Shervais, J.W., 2001, Birth, Death, and Resurrection: The Life Cycle
... [1] Abstract: Suprasubduction zone (SSZ) ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites. This sequence includes the following: (1) birth, which entails the formation ...
... [1] Abstract: Suprasubduction zone (SSZ) ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites. This sequence includes the following: (1) birth, which entails the formation ...
Crustal thickness anomalies in the North Atlantic Ocean Tingting Wang
... [1] Gravity‐derived crustal thickness models were calculated for the North Atlantic Ocean between 76°N and the Chain Fracture Zone and calibrated using seismically determined crustal thickness. About 7% of the ocean crust is <4 km thick (designated as thin crust), and 58% is 4–7 km thick (normal cru ...
... [1] Gravity‐derived crustal thickness models were calculated for the North Atlantic Ocean between 76°N and the Chain Fracture Zone and calibrated using seismically determined crustal thickness. About 7% of the ocean crust is <4 km thick (designated as thin crust), and 58% is 4–7 km thick (normal cru ...
Composition of the Oceanic Crust - DukeSpace
... 8 cm year1, such as the EPR, have smoother topography and generally lack a prominent axial valley. Instead, there is typically a comparatively narrow axial summit trough or graben. Fornari et al. (1998) recognized two summit types: narrow axial troughs, ≲200 m wide and ≲ 15 m deep, formed by collap ...
... 8 cm year1, such as the EPR, have smoother topography and generally lack a prominent axial valley. Instead, there is typically a comparatively narrow axial summit trough or graben. Fornari et al. (1998) recognized two summit types: narrow axial troughs, ≲200 m wide and ≲ 15 m deep, formed by collap ...
Ophiolite concept and its evolution
... older? in age) and crustal rocks (Jurassic) in these ophiolites do not have a simple melt-residue genetic relationship as expected from modern oceanic lithosphere evolved at mid-ocean ridges. Finally, Steinmann’s observations of the northern Apennine ophiolites and associated deep-sea sedimentary ro ...
... older? in age) and crustal rocks (Jurassic) in these ophiolites do not have a simple melt-residue genetic relationship as expected from modern oceanic lithosphere evolved at mid-ocean ridges. Finally, Steinmann’s observations of the northern Apennine ophiolites and associated deep-sea sedimentary ro ...
Trace Element and Isotope Geochemistry of the Volcanic Rocks of
... are higher and Nd ratios are lower than those of the IHS. The the Lesser Antillean arc (Fig. 1), which formed along IDS is also characterized by high dla0 values, up to 7-6 in the eastern edge of the Caribbean Plate as a result of clinopyroxene. The Sr and Pb isotope ratios are too high, and the sub ...
... are higher and Nd ratios are lower than those of the IHS. The the Lesser Antillean arc (Fig. 1), which formed along IDS is also characterized by high dla0 values, up to 7-6 in the eastern edge of the Caribbean Plate as a result of clinopyroxene. The Sr and Pb isotope ratios are too high, and the sub ...
Rudnick and Lee.fm - Cin
... events (hence lithosphere formation) in the uppermost mantle. Here we review application of the ReOs isotopic system to dating melt depletion in peridotites. In particular, we highlight examples of how this system, when applied to mantle xenolith studies, provides information on the timing of lithos ...
... events (hence lithosphere formation) in the uppermost mantle. Here we review application of the ReOs isotopic system to dating melt depletion in peridotites. In particular, we highlight examples of how this system, when applied to mantle xenolith studies, provides information on the timing of lithos ...
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... coefficients. The results of these models clearly demonstrate that the JTA and the Eoarchaean TTG can be generated by partial melting of plagioclase- and garnet-bearing amphibolite source regions with oceanic plateau-like compositions. Further modelling shows that the JTA and Eoarchaean TTG low MgO ...
... coefficients. The results of these models clearly demonstrate that the JTA and the Eoarchaean TTG can be generated by partial melting of plagioclase- and garnet-bearing amphibolite source regions with oceanic plateau-like compositions. Further modelling shows that the JTA and Eoarchaean TTG low MgO ...
nature ano evolution of the subcontinental mantle lithosphere below
... Ultramafic xenoliths found in the Pleistocene Pali-Aike alkali basalts, the southernmost outcropping of the Patagonian Plateau lavas of southern South America, inelude both garnet-bearing and garnet-free Iherzolites, harzburgites, and orthopyroxenites. Mineral geothermometry and geobarometry indicat ...
... Ultramafic xenoliths found in the Pleistocene Pali-Aike alkali basalts, the southernmost outcropping of the Patagonian Plateau lavas of southern South America, inelude both garnet-bearing and garnet-free Iherzolites, harzburgites, and orthopyroxenites. Mineral geothermometry and geobarometry indicat ...
High-Mg# andesitic lavas of the Shisheisky Complex, Northern
... There are, however, primitive andesitic lavas with relatively high MgO, Mg#, Ni, and Cr that could be in equilibrium with mantle peridotite. These rocks, which are commonly referred to as magnesian or high-Mg# andesites, are common in some modern arcs (Hughes and Taylor 1986; Straub et al. 2008) and ...
... There are, however, primitive andesitic lavas with relatively high MgO, Mg#, Ni, and Cr that could be in equilibrium with mantle peridotite. These rocks, which are commonly referred to as magnesian or high-Mg# andesites, are common in some modern arcs (Hughes and Taylor 1986; Straub et al. 2008) and ...
Origin of Archean subcontinental lithospheric mantle: Some
... progressively depleted in easily fusible components. This process results in progressive change in the composition of the residue, from fertile lherzolite at the first, high-pressure stage of melting, to highly refractory dunite at the final low-pressure stage. As a result of a process that is not wel ...
... progressively depleted in easily fusible components. This process results in progressive change in the composition of the residue, from fertile lherzolite at the first, high-pressure stage of melting, to highly refractory dunite at the final low-pressure stage. As a result of a process that is not wel ...
Geochemistry of mafic rocks and melt inclusions and their
... degree of mantle partial melting. Instead, several small-scale magma intrusions commonly occurred within the crust (Mccaig and Harris, 2012). The lack of a steady-state magma chamber makes it difficult to form corresponding hydrothermal systems. However, once a hydrothermal system was formed in this ...
... degree of mantle partial melting. Instead, several small-scale magma intrusions commonly occurred within the crust (Mccaig and Harris, 2012). The lack of a steady-state magma chamber makes it difficult to form corresponding hydrothermal systems. However, once a hydrothermal system was formed in this ...
Crystal Fractionation processes at Baru Volcano from the Deep to
... transported as cumulates to shallow crustal levels. Commonly in arcs, these cumulates are best represented by two major groups: gabbroic cumulates or olivine gabbros (calcic plagioclase and Fe-rich olivine) and amphibole rich cumulates (hornblende gabbros). The occurrence of these cumulates and the ...
... transported as cumulates to shallow crustal levels. Commonly in arcs, these cumulates are best represented by two major groups: gabbroic cumulates or olivine gabbros (calcic plagioclase and Fe-rich olivine) and amphibole rich cumulates (hornblende gabbros). The occurrence of these cumulates and the ...
Incipient shortening of a passive margin: the mechanical roles of
... adjustments. Models with various strength profiles represented oceanic lithospheres of different ages. The continental lithosphere reacted to an applied boundary velocity according to the strength and density of oceanic lithosphere. Where oceanic lithosphere was stronger and heavier than continental ...
... adjustments. Models with various strength profiles represented oceanic lithospheres of different ages. The continental lithosphere reacted to an applied boundary velocity according to the strength and density of oceanic lithosphere. Where oceanic lithosphere was stronger and heavier than continental ...
Subducting slabs: Jellyfishes in the Earth`s mantle
... i.e., the element size is 1/256 of the size of the unit cube. Free slip is assumed on all boundaries. The experiment is initiated by placing a vertical (unless otherwise specified) plate of length, l = 0.066 (∼182 km) and thickness h = 0.03 (∼83 km) in the mantle between depths of 0.03 and 0.096 (∼8 ...
... i.e., the element size is 1/256 of the size of the unit cube. Free slip is assumed on all boundaries. The experiment is initiated by placing a vertical (unless otherwise specified) plate of length, l = 0.066 (∼182 km) and thickness h = 0.03 (∼83 km) in the mantle between depths of 0.03 and 0.096 (∼8 ...
1 Imaging the transition from flat to normal subduction: Variations in
... result of vertical smearing of low velocity anomalies in the crust down into the mantle, resulting ...
... result of vertical smearing of low velocity anomalies in the crust down into the mantle, resulting ...
Reconstructing the Alps–Carpathians–Dinarides as a key to
... been galvanized in the past decade by teleseismic tomographic images of two positive compressive-wave velocity (+Vp) slab anomalies with contrasting orientations beneath the Alps (Fig. 4a–c): one beneath the Central and Western Alps that dips to the southeast to a depth of about 200 km and is consis ...
... been galvanized in the past decade by teleseismic tomographic images of two positive compressive-wave velocity (+Vp) slab anomalies with contrasting orientations beneath the Alps (Fig. 4a–c): one beneath the Central and Western Alps that dips to the southeast to a depth of about 200 km and is consis ...
Fulltext - ETH E-Collection
... formed as a result of NE-dipping subduction of the Neotethys ocean beneath the European continental margin during the Late Cretaceous. This magmatic arc is associated with some of Europe’s largest porphyry Cu-Au and epithermal Cu-Au deposits. However, the ore deposits are not evenly distributed with ...
... formed as a result of NE-dipping subduction of the Neotethys ocean beneath the European continental margin during the Late Cretaceous. This magmatic arc is associated with some of Europe’s largest porphyry Cu-Au and epithermal Cu-Au deposits. However, the ore deposits are not evenly distributed with ...
Possible density segregation of subducted oceanic
... The viscosity ratio between the ambient mantle and the serpentinite layer, ηo / ηS, is probably at least 10 because the addition of ppm levels of water to nominally anhydrous minerals can decrease viscosities by a factor of 10 or more [38], hence the presence of enough water to stabilize hydrous min ...
... The viscosity ratio between the ambient mantle and the serpentinite layer, ηo / ηS, is probably at least 10 because the addition of ppm levels of water to nominally anhydrous minerals can decrease viscosities by a factor of 10 or more [38], hence the presence of enough water to stabilize hydrous min ...
Plate dynamics, mantle structure and tectonic evolution of the
... 1.1 Short overview of the tectonic history of the Caribbean plate The Caribbean plate (Figure 1.1) is an actively deforming region between two major subduction zones: the Lesser Antilles subduction zone in the east and the Central America subduction zone in the west. The northern boundary with the N ...
... 1.1 Short overview of the tectonic history of the Caribbean plate The Caribbean plate (Figure 1.1) is an actively deforming region between two major subduction zones: the Lesser Antilles subduction zone in the east and the Central America subduction zone in the west. The northern boundary with the N ...
Weakness of the lower continental crust: a condition for
... (Meissner, 1989). In this paper, we define delamination as the decoupling process of continental lower crust and upper mantle from the overlying crust. Beneath thick crust, negative buoyancy within the lower crust may be strongly enhanced by the gabbro–eclogite transition (Rey, 1993). However, a wea ...
... (Meissner, 1989). In this paper, we define delamination as the decoupling process of continental lower crust and upper mantle from the overlying crust. Beneath thick crust, negative buoyancy within the lower crust may be strongly enhanced by the gabbro–eclogite transition (Rey, 1993). However, a wea ...
Izu-Bonin-Mariana Arc
The Izu-Bonin-Mariana (IBM) arc system is an outstanding example of a plate tectonic convergent boundary. IBM extends over 2800 km south from Tokyo, Japan, to beyond Guam, and includes the Izu Islands, Bonin Islands, and Mariana Islands; much more of the IBM arc system is submerged below sealevel. The IBM arc system lies along the eastern margin of the Philippine Sea Plate in the Western Pacific Ocean. It is most famous for being the site of the deepest gash in Earth's solid surface, the Challenger Deep in the Mariana Trench. The IBM arc system formed as a result of subduction of the western Pacific plate. The IBM arc system now subducts mid-Jurassic to Early Cretaceous lithosphere, with younger lithosphere in the north and older lithosphere in the south, including the oldest (~170 million years old, or Ma) oceanic crust. Subduction rates vary from ~2 cm (1 inch) per year in the south to 6 cm (~2.5 inches) in the north. The volcanic islands that comprise these island arcs are thought to have been formed from the release of volatiles (steam from trapped water, and other gases) being released from the subducted plate, as it reached sufficient depth for the temperature to cause release of these materials. The associated trenches are formed as the oldest (most western) part of the Pacific plate crust increases in density with age, and because of this process finally reaches its lowest point just as it subducts under the crust to the west of it.The IBM arc system is an excellent example of an intra-oceanic convergent margin (IOCM). IOCMs are built on oceanic crust and contrast fundamentally with island arc built on continental crust, such as Japan or the Andes. Because IOCM crust is thinner, denser, and more refractory than that beneath Andean-type margins, study of IOCM melts and fluids allows more confident assessment of mantle-to-crust fluxes and processes than is possible for Andean-type convergent margins. Because IOCMs are far removed from continents they are not affected by the large volume of alluvial and glacial sediments. The consequent thin sedimentary cover makes it much easier to study arc infrastructure and determine the mass and composition of subducted sediments. Active hydrothermal systems found on the submarine parts of IOCMs give us a chance to study how many of earth's important ore deposits formed.