The Slide Mountain Terrane and the structural evolution of the Finlayson Lake Fault Zone, southeastern Yukon

1997 ◽  
Vol 34 (2) ◽  
pp. 105-126 ◽  
Author(s):  
Heather E. Plint ◽  
Terence M. Gordon
Keyword(s):  
Fault Zone ◽  
Thermal Evolution ◽  
Structural Evolution ◽  
Ocean Basin ◽  
Greenschist Facies ◽  
Reverse Fault ◽  
Metasedimentary Rocks ◽  
Petrologic Study ◽  
Tectonic Boundary ◽  
Finlayson Lake

The Finlayson Lake Fault Zone forms a fundamental, but little studied, tectonic boundary between strata of autochthonous North America and the accreted Slide Mountain and Yukon–Tanana terranes in southeastern Yukon. A structural and petrologic study was undertaken to examine the depositional environment of the Slide Mountain Terrane, its tectono-thermal evolution in the fault zone, and its relationship with the Yukon–Tanana Terrane. The Slide Mountain and Yukon–Tanana terranes are divisible into units dominated by metavolcanic and metasedimentary rocks. Field observations and whole-rock geochemistry indicate that Slide Mountain greenstone is ocean-floor basalt deposited in a deep submarine basin with a proximal terrigenous sediment influx. Either a marginal- or ocean-basin setting is supported by the data. Slide Mountain greenstone is thrust northeastward over metasedimentary rocks of Slide Mountain Terrane and southwestward over rocks of the Yukon–Tanana Terrane. Regional metamorphic grade ranges from subgreenschist to greenschist facies. Pressure–temperature estimates for the subgreenschist–greenschist facies transition are 270–310 °C and 2.1–3.6 kbar (1 kbar = 100 MPa), based on assumed geothermal gradients and the reaction isograd Pmp + Chl = Act + Ep + H2O. Metamorphic peak postdates motion along the westernmost reverse fault that juxtaposes the Slide Mountain and Yukon–Tanana terranes. We interpret the Finlayson Lake Fault Zone as a northeasterly directed thrust sequence disrupted by synmetamorphic back thrusts. The back thrusting may be the consequence of shortening in the upper crust, or larger scale processes such as "tectonic wedging" of Yukon–Tanana Terrane under Slide Mountain Terrane.

Influence of Boundary Conditions on Response of Pipelines Crossing Reverse Fault Zone

2021 ◽  
Author(s):  
Hamid Rostami ◽  
Abdolreza Osouli ◽  
Brent Vaughn ◽  
Hamed Gholizadeh Touchaei
Keyword(s):  
Boundary Conditions ◽  
Fault Zone ◽  
Reverse Fault

scholarly journals Petrogenesis of the 91-Mile peridotite in the Grand Canyon: Ophiolite or deep-arc fragment?

Geosphere ◽  
2021 ◽  
Author(s):  
S.J. Seaman ◽  
M.L. Williams ◽  
K.E. Karlstrom ◽  
P.C. Low
Keyword(s):  
High Pressures ◽  
Grand Canyon ◽  
Mafic Magma ◽  
Ocean Basin ◽  
Partial Melt ◽  
Rock Types ◽  
Tectonic Boundaries ◽  
Tectonic Boundary ◽  
Lower Crustal ◽  
Plagioclase Textures

Recognition of fundamental tectonic boundaries has been extremely difficult in the (>1000-km-wide) Proterozoic accretionary orogen of southwestern North America, where the main rock types are similar over large areas, and where the region has experienced multiple postaccretionary deformation events. Discrete ultramafic bodies are present in a number of areas that may mark important boundaries, especially if they can be shown to represent tectonic fragments of ophiolite complexes. However, most ultramafic bodies are small and intensely altered, precluding petrogenetic analysis. The 91-Mile peridotite in the Grand Canyon is the largest and best preserved ultramafic body known in the southwest United States. It presents a special opportunity for tectonic analysis that may illuminate the significance of ultramafic rocks in other parts of the orogen. The 91-Mile peridotite exhibits spectacular cumulate layering. Contacts with the surrounding Vishnu Schist are interpreted to be tectonic, except along one margin, where intrusive relations have been interpreted. Assemblages include olivine, clinopyroxene, orthopyroxene, magnetite, and phlogopite, with very rare plagioclase. Textures suggest that phlogopite is the result of late intercumulus crystallization. Whole-rock compositions and especially mineral modes and compositions support derivation from an arc-related mafic magma. K-enriched subduction-related fluid in the mantle wedge is interpreted to have given rise to a K-rich, hydrous, high-pressure partial melt that produced early magnetite, Al-rich diopside, and primary phlogopite. The modes of silicate minerals, all with high Mg#, the sequence of crystallization, and the lack of early plagioclase are all consistent with crystallization at relatively high pressures. Thus, the 91-Mile peridotite body is not an ophiolite fragment that represents the closure of a former ocean basin. It does, however, mark a significant tectonic boundary where lower-crustal arc cumulates have been juxtaposed against middle-crustal schists and granitoids.

scholarly journals The thrust contact between the Canastra and Vazante groups in the Southern Brasília Belt: structural evolution, white mica crystallinity and implications for the Brasiliano orogeny

2016 ◽  
Vol 46 (4) ◽  
pp. 567-583 ◽  
Author(s):  
Manuela de Oliveira Carvalho ◽  
◽  
Claudio de Morisson Valeriano ◽  
Pamela Alejandra Aparicio González ◽  
Gustavo Diniz Oliveira ◽  
...  
Keyword(s):  
Structural Evolution ◽  
White Mica ◽  
Low Grade ◽  
Kink Bands ◽  
Metasedimentary Rocks ◽  
Kübler Index ◽  
Crenulation Cleavage ◽  
Thrust Sheets ◽  
Brasiliano Orogeny ◽  
Carbonaceous Phyllite

ABSTRACT: Two regional thrust-sheets of Neoproterozoic metasedimentary rocks occur in the Southern Brasília Belt, northwest Minas Gerais. The lower one comprises the Vazante Group, that is formed in the studied area, from base to top, by the Serra do Garrote (metapelites interlayered with carbonaceous phyllite), Serra do Poço Verde (beige to pink stromatolitic metadolomite with interlayered greenish slates), Morro do Calcário (gray stromatolitic metadolomite interlayered with gray slates) and Serra da Lapa (phyllite with dolarenitic lenses interlayered with slates) formations. The upper thrust sheet consists of the Canastra Group (Paracatu formation): laminated sericite phyllites and carbonaceous phyllites interlayered with quartzite. The Braziliano orogeny resulted in four phases of contractional deformation, associated with low-grade metamorphism. The first two (D1 and D2) are ductile, while the third and fourth ones (D3 and D4) are brittle-ductile. D1 developed a slaty S1 cleavage subparallel to the primary layering, with shallow to steep dips to NW. D2 developed a crenulation cleavage (S2) that dips moderately to NW and is associated with tight to isoclinal folds. D3 and D4 phases developed crenulations and open folds and kink bands. S3 dips steeply to NW, while S4 has moderate to steep dips to NE and SW. White mica crystallinity (Kübler index) measurements in metapelites indicate that both the Canastra and Vazante groups reached anchizone/epizone conditions, and metamorphic discontinuities along thrusts indicate that the peak of metamorphism is pre or syn-thrusting.

The Hewett Field, Blocks 48/28a, 48/29a, 48/30a, 52/4a and 52/5a, UK North Sea

2020 ◽  
Vol 52 (1) ◽  
pp. 189-202 ◽  
Author(s):  
J. A. Hook
Keyword(s):  
Fault Zone ◽  
North Sea ◽  
Structural Evolution ◽  
Field Development ◽  
Southern North Sea ◽  
Sandstone Formation ◽  
The Uk ◽  
Basin Margin ◽  
Sour Gas

AbstractThe Hewett Field has been in production for some 50 years. Unusually for a Southern North Sea field in the UK Sector, there has been production from several different reservoirs and almost entirely from intervals younger than the principal Leman Sandstone Formation (LSF) reservoir in the basin. Some of these reservoirs are particular to the Hewett area. This reflects the location of the field at the basin margin bound by the Dowsing Fault Zone, which has influenced structural evolution, deposition and the migration of hydrocarbons. The principal reservoirs are the Permo-Triassic Hewett Sandstone (Lower Bunter), Triassic Bunter Sandstone Formation (BSF) (Upper Bunter) and Permian Zechsteinkalk Formation. There has also been minor production from the Permian Plattendolomit Formation and the LSF. Sour gas is present in the BSF only. Several phases of field development are recognized, ultimately comprising three wellhead platforms with production from 35 wells. Gas is exported onshore to Bacton, where the sour gas was also processed. Peak production was in 1976 and c. 3.5 tcf of gas has been recovered. Hewett has also provided the hub for six satellite fields which have produced a further 0.9 tcf of gas. It is expected that the asset will cease production in 2020.

Structural evolution of a major fault zone: the Cape Ray Fault Zone, southwestern Newfoundland, Canada

1996 ◽  
Vol 33 (2) ◽  
pp. 199-215 ◽  
Author(s):  
Benoît Dubé ◽  
Kathleen Lauzière
Keyword(s):  
Fault Zone ◽  
Large Scale ◽  
Regional Scale ◽  
Point Group ◽  
Structural Evolution ◽  
Strain Partitioning ◽  
Two Phase ◽  
Detailed Structural Analysis ◽  
Grand Bay ◽  
Geodynamic Processes

The Cape Ray Fault Zone is a major Paleozoic structure in southwestern Newfoundland, and occurs at or close to the boundary between two major continental blocks, Laurentia and Avalonia. A detailed structural analysis demonstrates that the fault records early reverse-sinistral thrusting of the Grand Bay Complex at amphibolite grade (D2), followed by a protracted event (D3) characterized by reverse-dextral thrusting of the Grand Bay Complex rocks on top of the supracrustal rocks of the Windsor Point Group and retrogression to greenschist facies, as well as a pre-384 Ma orogen-parallel dextral transcurrent mylonite (D4) during the later stages of the collision. Regional-scale strain partitioning induced heterogeneity of strain both along and across the strike of the Cape Ray Fault Zone. The east–west-oriented segment of the Cape Ray Fault Zone is a tear fault that accommodated differential displacement along the length of the fault. Later stages of the deformation include post-384 Ma sinistral transcurrent reactivation of the dextral mylonite and extension. The reverse-sinistral thrusting and the reverse-dextral motion occurred between 415 and 386 Ma and correspond to the two-phase Acadian orogeny recognized at the scale of the orogen and believed to be related to collision between Laurentia and Avalonia. The Cape Ray Fault Zone preserves evidence of large-scale geodynamic processes affecting rocks where the kinematics and the timing are well constrained.

Age and origin of the Dover Fault: tectonic boundary between the Gander and Avalon Zones of the northeastern Newfoundland Appalachians

1981 ◽  
Vol 18 (9) ◽  
pp. 1431-1442 ◽  
Author(s):  
R. D. Dallmeyer ◽  
R. F. Blackwood ◽  
L. Odom
Keyword(s):  
Fault Zone ◽  
Country Rock ◽  
Regional Metamorphism ◽  
Tectonic Activity ◽  
Small Scale ◽  
Present Position ◽  
History Of ◽  
Scale Structures ◽  
Tectonic Boundary ◽  
Small Scale Structures

The Dover Fault forms a tectonic boundary between northern portions of the Gander and Avalon Zones of the Newfoundland Appalachians. A systematic geochronological investigation across the mylonitic fault zone has been carried out to clarify the origin and history of tectonic activity along this important Appalachian structure.Zircon fractions from the mylonitic Lockers Bay Granite (Gander Zone) record individually discordant U–Pb dates, but yield a well-defined upper concordia intercept age of 460 ± 20 Ma. Hornblende (1 sample) and biotite (11 samples) from variably mylonitic Gander Zone lithologies (plutonic and metamorphic) adjacent to the fault zone record undisturbed 40Ar/39Ar age spectra with plateau ages of 395 and 365–383 Ma, respectively. Together with field and petrographic characteristics, the new geochronologic data suggest that the Lockers Bay Granite originated as an anatectic melt during high-grade regional metamorphism of the country rock terrane at approximately 460 Ma. The crystal-rich magma was subsequently emplaced into its present position thereby producing local discordance with small-scale structures in host gneisses.Following its emplacement, the Lockers Bay Granite and country rock terrane were maintained at elevated postmetamorphic temperatures for a prolonged interval until they underwent rapid strain during Acadian (Devonian) juxtaposing of the northern Gander and Avalon Zones along the Dover Fault. Sudden Acadian uplift along the fault is suggested because of the rapid cooling of the northern Gander Zone through temperatures required for argon retention in hornblende and biotite. Post-mylonite brecciation may have locally affected argon isotopic systems of phyllitic lithologies adjacent to the fault zone in the study area.

Paleoseismology of an active reverse fault in a forearc setting: The Poukawa fault zone, Hikurangi forearc, New Zealand

1998 ◽  
Vol 110 (9) ◽  
pp. 1123-1148 ◽  
Author(s):  
Harvey M. Kelsey ◽  
Alan G. Hull ◽  
Susan M. Cashman ◽  
Kelvin R. Berryman ◽  
Patricia H. Cashman ◽  
...  
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Reverse Fault

Aeromagnetic Interpretations of the Crittenden County Fault Zone

2020 ◽  
Vol 92 (1) ◽  
pp. 494-507
Author(s):  
Christopher Marlow ◽  
Christine Powell ◽  
Randel Cox
Keyword(s):  
Seismic Hazard ◽  
Fault Zone ◽  
Detection Methods ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Reverse Fault ◽  
Maximum Magnitude ◽  
Fault Systems ◽  
Basement Faults ◽  
Seismic Reflection Profiles

Abstract The Crittenden County fault zone (CCFZ) is a potentially active fault zone located within 25 km of Memphis, Tennessee, and poses a significant seismic hazard to the region. Previous research has associated the fault zone with basement faults of the eastern Reelfoot rift margin (ERRM) and described it as a northeast-striking, northwest-dipping reverse fault. However, we suggest that there is an incomplete understanding of the fault geometry of the CCFZ and the ERRM in this region due to significant gaps in seismic reflection profiles used to interpret the fault systems. To improve our understanding of the structure of both fault systems in this region, we apply two processing techniques to gridded aeromagnetic data. We use the horizontal gradient method on reduction-to-pole magnetic data to detect magnetic contacts associated with faults as this technique produces shaper gradients at magnetic contacts than other edge detection methods. For depth to basement estimations, we use the analytic signal as the method does not require knowledge of the remnant magnetization of the source body. We suggest that the CCFZ extends approximately 16 km farther to the southwest than previously mapped and may be composed of three independent faults as opposed to a continuous structure. To the northeast, we interpreted two possible faults associated with the ERRM that intersect the CCFZ, one of which has been previously mapped as the Meeman–Shelby fault. If the CCFZ and the eastern rift margin are composed of isolated fault segments, the maximum magnitude earthquake that each fault segment may generate is reduced, thereby, lowering the existing seismic hazard both fault systems pose to Memphis, Tennessee.

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