The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform
Arthur W Snoke - One of the best experts on this subject based on the ideXlab platform.
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tertiary magmatism and Mylonitization in the ruby east humboldt metamorphic core complex northeastern nevada u pb geochronology and sr nd and pb isotope geochemistry
Geological Society of America Bulletin, 1993Co-Authors: James E Wright, Arthur W SnokeAbstract:U-Pb analyses of 48 zircon and/or monazite fractions from ten intrusive rocks that range in composition from quartz diorite to leucogranite yield crystallization ages between 40 and 29 Ma. The new data indicate that Tertiary intrusive rocks constitute a widespread and significant magmatic component of the Ruby-East Humboldt metamorphic core complex. Some of the intrusive rocks are gneissic to mylonitic and have been penetratively deformed in a shear zone that can be traced for >100 km along the west flank of the core complex. These data, when coupled with previously published geochronologic data, indicate that an important episode of Mylonitization occurred between ∼29 and 23 Ma (late Oligocene). Some field relations and geochronologic data, however, also suggest an earlier history of Mylonitization in parts of the core complex. This earlier mylonitic history may have occurred in the Eocene or even late Mesozoic time, although more-detailed geochronologic data are needed to clearly define the exact time interval. Sr, Nd, and Pb isotopic data from the dated intrusive units indicate that a relatively sharp, approximately east-west-striking crustal boundary separating predominantly Archean basement in the north from Proterozoic basement in the south transects the complex. We speculate that the crustal boundary represents the continuation of the Cheyenne belt into this part of northeastern Nevada. These new data cast doubt on the existence of the proposed 2.0-2.3 Ga crustal province in this part of the northern Great Basin. The isotopic data from the plutonic rocks coupled with published data from at least in part coeval volcanic rocks indicate that mantle-derived magmas were important in their genesis. Collectively, these data indicate that significant crustal growth, via the addition of mantle-derived magmas, occurred during large-magnitude extension in this part of the northern Great Basin.
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temperature and pressure of Mylonitization in a tertiary extensional shear zone ruby mountains east humboldt range nevada tectonic implications
Geology, 1991Co-Authors: Hugh A Hurlow, Arthur W Snoke, K V HodgesAbstract:In the northern Ruby Mountains-East Humboldt Range metamorphic core complex, a kinematically coupled mylonitic shear zone and brittle-plastic detachment fault compose a low-angle extensional fault system that is mid-Tertiary in age. Geothermobarometry of pelitic schists from the mylonitic shear zone yields a temperature and pressure estimate of 820-900 K (580-620 °C) and 310-370 MPa (3.1-3.7 kbar) for mylonite petrogenesis. The shear-zone-detachment-fault system excised 11-12 km of crustal section and accommodated at least 15-17 km of normal-sense dip slip.
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differential stress strain rate and temperatures of Mylonitization in the ruby mountains nevada implications for the rate and duration of uplift
Journal of Geophysical Research, 1990Co-Authors: Bradley R Hacker, J M Christie, Arthur W SnokeAbstract:Kno~ledge of the m.agnitude of the differential stress during the formation of mylonitic rocks provides constramts on mechanical and thermal models for the exhumation of the metamorphosed footwalls of major low-angle detachment faults. We have analyzed the differential flow stress during the Mylonitization of quartzose rocks in the Ruby Mountains, Nevada, using grain-size piezometers and kinetic laws for grain g!owth. Quartzites from mylonitic shear zones in Lamoille Canyon and Secret Creek gorge have grain SizeS of 91-151 ~m and 42-64 ~m, respectively. The peak temperature during Mylonitization was 630°:i:50°C, and analysis of grain-growth kinetics indicates that Mylonitization continued during cooling to temperatures S450°C. Quartz grain-size piezometers suggest that the Mylonitization occurred under differential stresses (crl-cr3) of 38-64 MPa, or maximum shear stresses of 19-32 MPa. Extrapolation of quartzite flow laws indicates that the Mylonitization occurred at strain rates between 10-10 and 10-13.-1. . ' arguments presented m the paper suggest that the likely range of strain rates is 10-11 to 10-12.-1. These strain rates are compatible with displacement rates of the order of 23 mm yr-l along a 1.5-km-thick simple shear zone. Such a shear zone dipping 15° would produce an uplift rate of 5.8 km m.y:1 and a horizontal extensioo rate of 22 km m.y:l. This uplift rate indicates that midcrustal mylonitic rocks could have been lifted up along a 1.5-km-thick simple shear zone dipping 15° in 2.6 m.y.
K V Hodges - One of the best experts on this subject based on the ideXlab platform.
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temperature and pressure of Mylonitization in a tertiary extensional shear zone ruby mountains east humboldt range nevada tectonic implications
Geology, 1991Co-Authors: Hugh A Hurlow, Arthur W Snoke, K V HodgesAbstract:In the northern Ruby Mountains-East Humboldt Range metamorphic core complex, a kinematically coupled mylonitic shear zone and brittle-plastic detachment fault compose a low-angle extensional fault system that is mid-Tertiary in age. Geothermobarometry of pelitic schists from the mylonitic shear zone yields a temperature and pressure estimate of 820-900 K (580-620 °C) and 310-370 MPa (3.1-3.7 kbar) for mylonite petrogenesis. The shear-zone-detachment-fault system excised 11-12 km of crustal section and accommodated at least 15-17 km of normal-sense dip slip.
David M. Wayne - One of the best experts on this subject based on the ideXlab platform.
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Rb-Sr redistribution during amphibolite-grade Mylonitization: An example from the Hope Valley Shear Zone, Massachusetts, U.S.A.
Journal of Geodynamics, 1995Co-Authors: David M. WayneAbstract:The Sr and Pb isotopic systematics of minerals and whole rock slabs cut from three large samples of the Ponaganset Gneiss near the Hope Valley Shear Zone (HVSZ) in south-central Massachussets indicate that isotopic redistribution along a Late Paleozoic mylonitic zone in the gneiss occurred in two distinct episodes, via two discrete mechanisms. The Rb-Sr data also provide additional geochronologic evidence for high-grade Alleghanian metamorphism in SE New England. At the sample locality, the Ponaganset Gneiss was sheared at the contact between two lithologically distinct gneiss units. A narrow (
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rb sr redistribution during amphibolite grade Mylonitization an example from the hope valley shear zone massachusetts u s a
Journal of Geodynamics, 1995Co-Authors: David M. WayneAbstract:The Sr and Pb isotopic systematics of minerals and whole rock slabs cut from three large samples of the Ponaganset Gneiss near the Hope Valley Shear Zone (HVSZ) in south-central Massachussets indicate that isotopic redistribution along a Late Paleozoic mylonitic zone in the gneiss occurred in two distinct episodes, via two discrete mechanisms. The Rb-Sr data also provide additional geochronologic evidence for high-grade Alleghanian metamorphism in SE New England. At the sample locality, the Ponaganset Gneiss was sheared at the contact between two lithologically distinct gneiss units. A narrow (<10 cm) band of mylonitic mafic schist also occurs intermittently at the contact. A whole rock age from thin slabs of the mylonitized gray gneiss (274 ± 14) agrees well with a mineral age from the mylonitic gray gneiss (268 ± 5), and with other published age data on Alleghanian metamorphism in southeastern New England. The mafic schist Rb-Sr mineral age (306 ± 4) is significantly older, and may represent the age of the initial episode of deformation and recrystallization. The age-corrected Sr and Pb isotopic signatures of the mylonitized gray gneiss are consistently more radiogenic than those of the adjacent units. Therefore, it is possible that the isotopic alteration of the mylonitic zone involved Sr and Pb from an outside source. Closer examination of the mylonitic gneiss-mafic schist contact also revealed a zone of less radiogenic Sr within 2–3 cm of the contact. The shapes of Rb-Sr isotopic profiles across the contact are indicative of diffusive redistribution which occurred during, or after, the foliation-parallel alteration of Sr and Pb isotopic signatures in the mylonitized gray gneiss. Nonlinear least-squares fits of the data to a diffusion equation yield Dt of approx. 8 × 105 m2 (D = effective diffusivity of Sr in m2/s, t = time in s). Attempts to use this result to estimate the duration of Rb-Sr diffusion produced results that are not consistent with geochronological data, which indicate that these rocks experienced high temperatures for up to 107 yr.
Andreas G Koestler - One of the best experts on this subject based on the ideXlab platform.
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heterogeneous deformation and Mylonitization of a granulite complex jotun valdres nappe complex central south norway
Geological Journal, 2007Co-Authors: Andreas G KoestlerAbstract:The Helgedal Zone is the Caledonian, heterogeneously deformed base of the Jotun Complex, within the Jotun-Valdres Nappe Complex (Sognefjell, South Norway). It consists of an anastomosing system of shear zones isolating lozengeshaped lenses of less deformed rocks. Structural and geometrical features are described to define the type of deformation and to evaluate the tectonic significance of this zone. Granulitic gabbros and pegmatitic dykes are deformed together in the highly strained mylonitic zones. Microtextural investigations indicate that the quantitative relation between mafic and felsic minerals and the content of quartz determine the different behaviour of the two rock types during deformation.
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Heterogeneous deformation and Mylonitization of a granulite complex, jotun‐valdres nappe complex, Central South Norway
Geological Journal, 2007Co-Authors: Andreas G KoestlerAbstract:The Helgedal Zone is the Caledonian, heterogeneously deformed base of the Jotun Complex, within the Jotun-Valdres Nappe Complex (Sognefjell, South Norway). It consists of an anastomosing system of shear zones isolating lozengeshaped lenses of less deformed rocks. Structural and geometrical features are described to define the type of deformation and to evaluate the tectonic significance of this zone. Granulitic gabbros and pegmatitic dykes are deformed together in the highly strained mylonitic zones. Microtextural investigations indicate that the quantitative relation between mafic and felsic minerals and the content of quartz determine the different behaviour of the two rock types during deformation.
Sharon Mosher - One of the best experts on this subject based on the ideXlab platform.
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Mylonitization in the lower plate of the buckskin rawhide detachment fault west central arizona implications for the geometric evolution of metamorphic core complexes
Journal of Structural Geology, 2012Co-Authors: John S Singleton, Sharon MosherAbstract:Abstract In metamorphic core complexes it is commonly unclear whether lower plate mylonites formed as the down-dip continuation of a detachment fault, or whether they represent a subhorizontal shear zone that was captured by a more steeply dipping detachment fault. Detailed microstructural, fabric, and strain data from mylonites in the Buckskin-Rawhide metamorphic core complex, west-central Arizona, constrain the structural development of the lower plate shear zone. Widespread exposures of ∼22–21 Ma granitoids of the Swansea Plutonic Suite enable us to separate Miocene strain coeval with core complex extension from older deformation. Mylonites across the lower plate consistently record top-to-the-NE-directed shear. Miocene quartz and feldspar deformation/recrystallization mechanisms indicate ∼450–500 °C Mylonitization temperatures that were relatively uniform across a distance of ∼35 km in the extension direction. Quartz dynamically recrystallized grain sizes do not systematically vary in the extension direction. Strain recorded in the Swansea Plutonic Suite is also relatively uniform in the extension direction, which is incompatible with models in which lower plate mylonites form as the ductile root of a major detachment fault. Altogether these data suggest the mylonitic shear zone initiated with a ≤4° dip and was unroofed by a more steeply dipping detachment fault system. Lower plate mylonites in the Buckskin-Rawhide metamorphic core complex thus represent a captured subhorizontal shear zone rather than the down-dip continuation of a detachment fault.
