The Eidsfjord shear zone, Lofoten–Vesterålen, north Norway: An Early Devonian, paleoseismogenic low-angle normal fault

2011 ◽  
Vol 33 (5) ◽  
pp. 1023-1043 ◽  
Author(s):  
Mark G. Steltenpohl ◽  
David Moecher ◽  
Arild Andresen ◽  
Jacob Ball ◽  
Stephanie Mager ◽  
...  
Keyword(s):  
Shear Zone ◽  
Normal Fault ◽  
Early Devonian ◽  
North Norway

U-Pb Isotope Geochronology and Granitic Gneisses Nanoparticles from the Xiaomei Shear Zone: Implication for Caledonian Tectonic in the Hainan Island, China

2020 ◽  
Vol 12 (1) ◽  
pp. 39-47
Author(s):  
Zhou Yang ◽  
Shen Baoyun ◽  
Liu Hailing ◽  
Yan Yi ◽  
Yan Yan
Keyword(s):  
Shear Zone ◽  
Tectonic Evolution ◽  
Frictional Heating ◽  
Hainan Island ◽  
Ductile Shear Zone ◽  
Spherical Nanoparticles ◽  
Pb Isotope ◽  
Tectonic Event ◽  
Isotope Geochronology ◽  
Early Devonian

U-Pb ages of zircons from the granitic gneisses in the Xiaomei shear zone, Hainan Island, provide constraints on the age of granitic gneisses and tectonic evolution of Caledonian orogeny in Hainan Island. Zircons extracted from granitic gneisses are rounded and subrounded and characterized by oscillatory overgrowths enclosing inherited cores. The Early Devonian (414–411 Ma) ages of inherited zircons from the Xiaomei granitic gneisses are consistent with tectonic event that uplifted the Hainan island, resulting in the absence of Devonian strata. Meanwhile, nanoparticles are found in the granitic gneisses, including agglomerated nanoparticles and spherical nanoparticles in the ductile shear zone. The spherical nanoparticles in the shear zone are believed to have experienced a two-stage formation, from the linear spherical nanoparticles to planar spherical nanoparticles. With rise in temperature due to frictional heating during the shearing, spherical nanoparticles are deformed to agglomerated nanoparticles and the inherited zircons probably are recrystallized at 411 Ma.

scholarly journals Middle to Late Devonian–Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

Solid Earth ◽  
2018 ◽  
Vol 9 (2) ◽  
pp. 341-372 ◽  
Author(s):  
Jean-Baptiste P. Koehl ◽  
Steffen G. Bergh ◽  
Tormod Henningsen ◽  
Jan Inge Faleide
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Large Scale ◽  
Barents Sea ◽  
Normal Fault ◽  
Early Carboniferous ◽  
Normal Displacement ◽  
Late Devonian ◽  
The North ◽  
Caledonian Orogeny

Abstract. The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle–Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, (i) the Måsøy Fault Complex, (ii) the Rolvsøya fault, and (iii) the Troms–Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE–SW-trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya–Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top–NW normal displacement in Middle to Late Devonian–Carboniferous times. The Troms–Finnmark Fault Complex displays a zigzag-shaped pattern of NNE–SSW- and ENE–WSW-trending extensional faults before it terminates to the north as a WNW–ESE-trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the western Finnmark Platform and the Gjesvær Low in the southwest. The WNW–ESE-trending, margin-oblique segment of the Troms–Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjorden–Komagelva Fault Zone, which is made of WNW–ESE-trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjorden–Komagelva Fault Zone dies out to the northwest before reaching the western Finnmark Platform. We propose an alternative model for the origin of the WNW–ESE-trending segment of the Troms–Finnmark Fault Complex as a possible hard-linked, accommodation cross fault that developed along the Sørøy–Ingøya shear zone. This brittle fault decoupled the western Finnmark Platform from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Middle to Upper Devonian sedimentary units resembling those in Middle Devonian, spoon-shaped, late- to post-orogenic collapse basins in western and mid-Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE–WSW- to NE–SW-trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Middle to Late Devonian–early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya–Ingøya shear zone truncated and decapitated the Trollfjorden–Komagelva Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjorden–Komagelva Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea.

scholarly journals Mineralogy of the Silver King deposit, Omeo, Victoria

2017 ◽  
Vol 129 (1) ◽  
pp. 41
Author(s):  
William D. Birch
Keyword(s):  
Shear Zone ◽  
Phase Assemblage ◽  
Hydrothermal Solutions ◽  
Early Devonian ◽  
Quartz Reef ◽  
Sphalerite Phase

The Silver King mine (also known as Forsyths) operated very intermittently between about 1911 and the late 1940s on Livingstone Creek, near Omeo, in northeastern Victoria. The deposit consists of six thin and discontinuous quartz lodes that are variably mineralised. Assays of up to 410 ounces of silver per ton were obtained but there are only a few recorded production figures. Examination of representative ore samples shows that the main silver-bearing minerals in the primary ore are pyrargyrite, freibergite, andorite and the rare sulphosalt zoubekite, which occur irregularly with pyrite, arsenopyrite, galena and sphalerite. Phase assemblage data indicate that crystallisation occurred over an interval from about 450°C to less than 250°C, with the silver-bearing minerals crystallising at the lowest temperatures. The lodes were formed by the emplacement of hydrothermal solutions into fractures within the Ensay Shear Zone during the Early Devonian Bindian Orogeny. There are similarities in mineralisation and timing of emplacement between the Silver King lodes and the quartz-reef-hosted Glen Wills and Sunnyside goldfields 35‒40 km north of Omeo.

Early Devonian sinistral strike-slip in the Caledonian basement of Oscar II Land advocates for escape tectonics as a major mechanism for Svalbard terranes assembly

2020 ◽  
Author(s):  
Grzegorz Ziemniak ◽  
Jarosław Majka ◽  
Maciej Manecki ◽  
Katarzyna Walczak ◽  
Pauline Jeanneret ◽  
...  
Keyword(s):  
Shear Zone ◽  
Barents Sea ◽  
Weighted Average ◽  
Shear Zones ◽  
Structural Features ◽  
Greenschist Facies ◽  
Western Boundary ◽  
Structural Development ◽  
Early Devonian ◽  
Mylonitic Foliation

<p>The Svalbard’s Southwestern Basement Province in contrary to the Northwestern and Eastern Basement Provinces is commonly correlated with the Pearya Terrane or Timanides and bears a complicated internal structure. Here, we present new data from Oscar II Land supporting the model of Svalbard’s Basement being divided into the Laurentia and Barentsia plates in the late-Caledonian period.</p><p>In Oscar II Land the enigmatic Müllerneset Formation is tectonically juxtaposed against the remaining greenschist facies metamorphosed basement. It consists of Mesoproterozoic to Neoproterozoic metapelites and metapsammites that experienced a polymetamorphic history. The progressive amphibolite facies event M1 of unknown age reached the pressure-temperatures conditions of 5-7 kbar at 500-560 °C. The subsequent greenschist facies overprint (M2) is associated with mylonitization strongly pronounced across the whole Müllerneset Formation. Mylonitic foliation S2 dips steeply to the SW and it is associated with a stretching lineation dipping moderately-to-shallowly to the SE. In the western part of the unit, monazite is growing within the S2 foliation and related shear bands mainly replacing allanite. Th-U-total Pb dating of homogenous monazite population yielded a weighted average age of 410 ± 7 Ma with MSWD = 0.26 and p = 0.997. In the western part, where mylonitic foliation is less prevalent, monazite growths within M1 porphyroblasts and within the S2 foliation. Th-U-total Pb dating revealed an array of ages between 480 – 280 Ma with no correlation of chemical or structural features allowing divisions into subgroups.</p><p>Dating results indicating an early Caledonian signal should be attributed to the progressive M1 event. Uniform monazite age of 410 ± 7 Ma in the western part represents the timing of the M2 greenschist facies overprint. Younger ages obtained in the eastern part suggest fluid related disturbance of Th-U-Pb system during late Caledonian, Ellesmerian and Eurekan events. The timing of monazite growth during the M2 event is identical with the 410 ± 2 Ma <sup>40</sup>Ar/<sup>39</sup>Ar cooling age reported by Dallmeyer (1989). Geochronological evidence combined with structural observations suggests that the Müllerneset Formation in the Early Devonian was tectonically exhumed on the NW-SE trending left-lateral strike- to oblique-slip shear zone. Similarly oriented tectonic zones within the Southwestern Basement Province, in the Berzeliuseggene unit and the Vimsodden-Kosibapasset Shear Zone are also of similar age. This set of anastomosing shear zones is roughly parallel to the proposed orientation of the suture between Barentsia and Laurentia (Gudlaugsson et al. 1998). The documented Early Devonian sinistral displacement may mark the western boundary of the Barentsia microplate laterally extruded during the final Caledonian collision in a style similar to present day Anatolian Plate escape.</p><p>This work is funded by NCN research project no. 2015/17/B/ST10/03114, AGH statutory funds 16.16.140.315 and RCN Arctic Field Grant no. 282546.</p><p>Dallmeyer, R. D. (1989). Partial thermal resetting of<sup> 40</sup>Ar/<sup>39</sup>Ar mineral ages in western Spitsbergen, Svalbard: possible evidence for Tertiary metamorphism. Geological Magazine, 126(5), 587-593.</p><p>Gudlaugsson, S. T., Faleide, J. I., Johansen, S. E., & Breivik, A. J. (1998). Late Palaeozoic structural development of the south-western Barents Sea. Marine and Petroleum Geology, 15(1), 73-102.</p>

Mylonite-dominated footwall geometry in a shear zone, central Pyrenees

1984 ◽  
Vol 121 (5) ◽  
pp. 429-436 ◽  
Author(s):  
C. W. Passchier
Keyword(s):  
Shear Strain ◽  
Shear Zone ◽  
Fault Zone ◽  
Normal Fault ◽  
Fault System ◽  
Ductile Shear Zone ◽  
Massif Central ◽  
Strain Profile ◽  
Crustal Shortening ◽  
Central Pyrenees

AbstractA major ductile shear zone in the gneissic core of the Saint-Barthélemy Massif, central Pyrenees, is characterized by an asymmetric shear strain profile defined as mylonite-dominated footwall geometry. The shear zone is part of a low angle fault system in the massif which caused thinning of a sequence of lithologic units and isograds. The shear zone is interpreted as a low angle normal fault zone of probably Cretaceous age, predating Alpine crustal shortening in the central Pyrenees.

scholarly journals Mid/Late Devonian-Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

2017 ◽  
Author(s):  
Jean-Baptiste Koehl ◽  
Steffen G. Bergh ◽  
Tormod Henningsen ◽  
Jan-Inge Faleide
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Large Scale ◽  
Barents Sea ◽  
Normal Fault ◽  
Early Carboniferous ◽  
Normal Displacement ◽  
Late Devonian ◽  
The North ◽  
Caledonian Orogeny

Abstract. The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle-Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, i) the Måsøy Fault Complex, ii) the Rolvsøya fault, iii) the Troms-Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE-SW trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya-Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top-to-the-NW normal displacement in Mid/Late Devonian-Carboniferous times. The Troms-Finnmark Fault Complex displays a zigzag-shaped pattern of NNE-SSW and ENE-WSW trending extensional faults before it terminates to the north as a WNW-ESE trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the Finnmark Platform west and the Gjesvær Low in the southwest. The WNW-ESE trending, margin-oblique segment of the Troms-Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjord-Komagelv Fault Zone, which is made of WNW-ESE trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjord-Komagelv Fault Zone dies out to the northwest before reaching the Finnmark Platform west. We propose an alternative model for the origin of the WNW-ESE trending fault segment of the Troms-Finnmark Fault Complex as a possible hard-linked, accommodation cross-fault that developed along the Sørøy-Ingøya shear zone. This brittle fault decoupled the Finnmark Platform west from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Mid/Late Devonian sedimentary units resembling Middle Devonian, spoon-shaped, late/post-orogenic collapse basins in western and mid Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE-WSW to NE-SW trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Mid/Late Devonian-early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya-Ingøya shear zone truncated and decapitated the Trollfjord-Komagelv Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjord-Komagelv Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea.

scholarly journals Tectonostratigraphic record of late Miocene–early Pliocene transtensional faulting in the Eastern California shear zone, southwestern USA

Geosphere ◽  
2021 ◽  
Author(s):  
Rebecca J. Dorsey ◽  
Brennan O’Connell ◽  
Kevin K. Gardner ◽  
Mindy B. Homan ◽  
Scott E.K. Bennett ◽  
...  
Keyword(s):  
North America ◽  
Shear Zone ◽  
Gulf Of California ◽  
Colorado River ◽  
Normal Fault ◽  
River Valley ◽  
Plate Motion ◽  
Fault System ◽  
Eastern California Shear Zone ◽  
Southwestern Usa

The Eastern California shear zone (ECSZ; southwestern USA) accommodates ~20%–25% of Pacific–North America relative plate motion east of the San Andreas fault, yet little is known about its early tectonic evolution. This paper presents a detailed stratigraphic and structural analysis of the uppermost Miocene to lower Pliocene Bouse Formation in the southern Blythe Basin, lower Colorado River valley, where gently dipping and faulted strata provide a record of deformation in the paleo-ECSZ. In the western Trigo Mountains, splaying strands of the Lost Trigo fault zone include a west-dipping normal fault that cuts the Bouse Formation and a steeply NE-dipping oblique dextral-normal fault where an anomalously thick (~140 m) section of Bouse Formation siliciclastic deposits filled a local fault-controlled depocenter. Systematic basinward thickening and stratal wedge geometries in the western Trigo and southeastern Palo Verde Mountains, on opposite sides of the Colorado River valley, record basinward tilting during deposition of the Bouse Formation. We conclude that the southern Blythe Basin formed as a broad transtensional sag basin in a diffuse releasing stepover between the dextral Laguna fault system in the south and the Cibola and Big Maria fault zones in the north. A palinspastic reconstruction at 5 Ma shows that the southern Blythe Basin was part of a diffuse regional network of linked right-step­ping dextral, normal, and oblique-slip faults related to Pacific–North America plate boundary dextral shear. Diffuse transtensional strain linked northward to the Stateline fault system, eastern Garlock fault, and Walker Lane, and southward to the Gulf of California shear zone, which initiated ca. 7–9 Ma, implying a similar age of inception for the paleo-ECSZ.

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