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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Australasia
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New Zealand
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Fiordland (8)
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Primary terms
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metals
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metasedimentary rocks (2)
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mylonites (1)
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metamorphism (3)
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North America
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Coast plutonic complex (1)
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Peninsular Ranges Batholith (1)
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oxygen
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Paleozoic
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United States
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Alaska (1)
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California
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Salinian Block (1)
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San Gabriel Mountains (1)
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Sierra Nevada Batholith (1)
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Southern California Batholith (1)
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rock formations
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Coastal Batholith (1)
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Tectonic and magmatic construction of lower crust in the Southern California Batholith
Making sense of shear zone fabrics that record multiple episodes of deformation: Electron backscatter diffraction–derived and crystallographic vorticity axis–enhanced petrochronology
Stable and transient isotopic trends in the crustal evolution of Zealandia Cordillera
Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand
Temporal and spatial variations in magmatism and transpression in a Cretaceous arc, Median Batholith, Fiordland, New Zealand
The tempo of continental arc construction in the Mesozoic Median Batholith, Fiordland, New Zealand
Thermochronology of extensional orogenic collapse in the deep crust of Zealandia
Gneiss domes, vertical and horizontal mass transfer, and the initiation of extension in the hot lower-crustal root of a continental arc, Fiordland, New Zealand
Deformation and magma transport in a crystallizing plutonic complex, Coastal Batholith, central Chile
Mid-Cretaceous–Recent crustal evolution in the central Coast orogen, British Columbia and southeastern Alaska
The Coast orogen of western coastal British Columbia and southeastern Alaska is one of the largest batholithic belts in the world. This paper addresses the structure and composition of the crust in the central part of this orogen, as well as the history of its development since the mid-Cretaceous. The core of the orogen consists of two belts of metamorphic and plutonic rocks: the western metamorphic and thick-skinned thrust belt comprising 105–90-Ma plutons and their metamorphic country rocks, and the Coast Plutonic Complex on the east, with large volumes of mainly Paleogene magmatic rocks and their high-temperature gneissic host rocks. These two belts are separated by the Coast shear zone, which forms the western boundary of a Paleogene magmatic arc. This shear zone is subvertical, up to 5 km wide, and has been seismically imaged to extend to and offset the Moho. Lithologic units west of the Coast shear zone record contractional deformation and crustal thickening by thrusting and magma emplacement in the mid-Cretaceous. To the east, the Coast Plutonic Complex records regional contraction that evolves to regional extension and coeval uplift and exhumation after ca. 65 Ma. Igneous activity in the Complex formed a Paleogene batholith and gave rise to high crustal temperatures, abundant migmatite and, as a result, considerable strain localization during deformation. In both belts, during each stage of the orogeny, crustal-scale deformation enabled and assisted magma transport and emplacement. In turn, the presence of magma, as well as its thermal effects in the crust, facilitated the deformation. After 50 Ma, the style of crustal evolution changed to one dominated by periods of extension oriented approximately perpendicular to the orogen. The extension resulted in tilting of large and small crustal blocks as well as intra-plate type magmatic activity across the orogen. Seismic-reflection and refraction studies show that the crust of this orogen is unusually thin, probably due to the periods of orogen-perpendicular stretching. Magmatic activity west of the Coast shear zone in the Late Oligocene and Miocene was related to one period of orogen-parallel transtension along the margin. Small-scale, mafic, mantle-derived volcanic activity continues in the region today. The change from convergence to translation and extension is related to a major plate reorganization in the Pacific that led to a change from subduction of an oceanic plate to northwestward translation of the Pacific plate along the northwest coast of North America. Although it has been proposed that this orogen is the site of major (up to 4000 km) pre-Eocene northward terrane translation, there is little evidence for such large-scale displacement or for the kind of discontinuity in the geological record that such displacement would entail.
Evolution of the middle and lower crust during the transition from contraction to extension in Fiordland, New Zealand
A deeply eroded orogen in southwest New Zealand preserves a record of changing flow patterns in the middle and lower crust during a transition from contraction and crustal thickening to extension and crustal thinning. The New Zealand exposures show that deformation patterns at mid-lower crustal depths were strongly influenced by local variations in crustal structure, temperature, composition, magmatic activity, and rheology. Kinematic parameters, including the orientation of shear zone boundaries, the degree of non-coaxiality and kinematic partitioning, strain symmetry, and whether shear zones were thickening or thinning in different planes of observation, were extremely variable spatially and changed repeatedly over an 8–10 Ma period. However, despite this variability, several aspects of superposed deformations remained constant and can be assigned to distinctive tectonic settings. All shear zones that formed during the 119–111 Ma period in Northern Fiordland record flow involving bulk horizontal (layer-parallel) shortening, vertical (layer-perpendicular) thickening, and >50% pure shear regardless of shear zone orientation, degree of non-coaxiality, strain symmetry, and temperature conditions. In contrast, all shear zones that formed during the 114–90 Ma period in Central Fiordland record flow involving vertical thinning, subhorizontal stretching, and 40%–50% pure shear. These patterns are correlative with regional contraction and regional extension, respectively. The data suggest that at length scales of ~100 km and time scales of ca. 10 Ma, the effects of changing plate boundary dynamics on deformation patterns in the middle and lower crust can be distinguished from the effects of changing local boundary conditions, including steep temperature gradients and variable rheology.
The evolution of an exposed mid-lower crustal attachment zone in Fiordland, New Zealand
Abstract Studies of convergent margins suggest that large subhorizontal shear zones in the lower crust help regulate how displacements are transferred horizontally and vertically through the lithosphere. We present structural data from the Fiordland belt of SW New Zealand that illustrate the progressive evolution of a 25 km thick section of exhumed, Early Cretaceous middle and lower crust. The data show that the mechanisms by which displacements were relayed through the crust during a 25 Ma cycle of arc-related magmatism, high-grade metamorphism and contraction changed repeatedly. During the period 126–120 Ma, a ≥10 km thick batholith composed of gabbroic-dioritic magma was emplaced into the lower crust. Melt-enhanced shear zones evolved at the upper and lower contacts of the batholith where magma and steep temperature gradients created strength contrasts. By ∼ 120 Ma, partial melting of mafic-intermediate lower crust resulted in the formation of high-pressure (14–16 kbar) migmatite and steep, regionally extensive vein networks up to 10 km below the batholith. Melt segregation and transfer through and out of the lower crust were aided by melt-induced fracture arrays and ductile deformation in shear zones. During the period 116–105 Ma, differential shortening of the crust produced a network of subhorizontal and subvertical shear zones at different crustal depths. Near-vertical shear zones up to 15 km wide formed at the deepest part of the section. These shear zones cut upwards across the entire lower crust to merge with a gently dipping upper amphibolite facies fold-and-thrust zone that formed in the middle crust. A 1 km thick, subhorizontal shear zone underlies this mid-crustal fold-and-thrust zone and physically connected shear zones that formed at different crustal depths. Our data suggest that deformation above and below this mid-lower crustal attachment zone was coupled kinematically and accommodated subhorizontal arc-normal displacements in the middle crust and oblique sinistral displacements on steep shear zones in the lower crust. The steep lower crustal shear zones also record components of subhorizontal arc-normal shortening and vertical thickening. These results strongly suggest that large, kinematically coupled networks of flat and steep shear zones separated the Fiordland crust into distinctive structural domains and relayed displacements vertically and horizontally through the lithosphere during Early Cretaceous oblique convergence.