A reappraisal of the tectonic significance of early Tertiary low-angle shear zones exposed in the Vernon map area (82 L), Shuswap metamorphic complex, southeastern Canadian Cordillera

2006 ◽  
Vol 43 (2) ◽  
pp. 245-268 ◽  
Author(s):  
P Glombick ◽  
R I Thompson ◽  
P Erdmer ◽  
K L Daughtry
Keyword(s):  
Middle Eocene ◽  
Shear Zones ◽  
Geological Mapping ◽  
Granitic Rocks ◽  
Normal Faults ◽  
Metamorphic Complex ◽  
Early Tertiary ◽  
Shear Sense ◽  
Tectonic Significance ◽  
Shuswap Metamorphic Complex

Detailed geological mapping across the Shuswap metamorphic complex between latitudes 50°00′N and 50°45′N reveals that superstructure forms a semicontinuous carapace across the complex, with minimal evidence of internal thinning. Near the western margin of the complex, superstructure and infrastructure are juxtaposed across low-angle, ~2 km thick, ductile shear zones spatially associated with Paleocene to Early Eocene syn-kinematic granitic rocks. The shear zones, which yield upper plate to the west shear-sense indicators, are interpreted as the northern extension of the Okanagan Valley fault. Farther east, near the north–south axis of the complex, superstructure and infrastructure are separated by an attenuated metamorphic section, but evidence of noncoaxial strain is lacking. Discrete detachments were not found. Steeply dipping normal faults cut low-angle shear zones and do not merge with them at depth. Middle Eocene volcanic and sedimentary rocks rest unconformably on metamorphic basement. The continuity of superstructure indicates that infrastructure was not exhumed by crustal-scale detachments. The results provide the basis for a complete reinterpretation of the tectonic significance of low-angle shear zones exposed in the Vernon area. It is proposed that Late Cretaceous to early Tertiary partial melting of the middle crust resulted in the development of a zone of channel flow. As the channel was underthrust by a crustal-scale ramp in underlying, more competent Paleo proterozoic basement, it was exhumed from depths of 20–30 km and thinned vertically. Shear zones between infrastructure and superstructure are interpreted as being a transient rheological interface at the upper boundary of the channel.

U–Pb constraints on the thermotectonic evolution of the Vernon antiform and the age of the Aberdeen gneiss complex, southeastern Canadian Cordillera

2006 ◽  
Vol 43 (2) ◽  
pp. 213-244 ◽  
Author(s):  
P Glombick ◽  
R I Thompson ◽  
P Erdmer ◽  
L Heaman ◽  
R M Friedman ◽  
...  
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Ductile Deformation ◽  
Granitic Rocks ◽  
Tectonic Activity ◽  
Canadian Cordillera ◽  
Metamorphic Complex ◽  
Seismic Reflection Data ◽  
Gneiss Complex ◽  
Shuswap Metamorphic Complex

The Aberdeen gneiss complex is composed of complexly deformed migmatitic orthogneiss and paragneiss situated within the core of the Vernon antiform, a structure defined by a series of subparallel reflectors visible at upper to middle crustal depths (6–18 km) in seismic reflection data from the Vernon area of the Shuswap metamorphic complex. The Vernon antiform and the Aberdeen gneiss complex lie within the footwall of the gently west dipping (top to the west) Kalamalka Lake shear zone. Migmatitic gneiss exposed within the antiform records evidence (recorded as age domains in complexly zoned zircon grains) of three metamorphic events, occurring at 155–150, 90, and 66–51 Ma. The timing of magmatic events within the antiform includes emplacement of diorite at ~232 Ma, tonalite at ~151 Ma, granodiorite at 102 Ma, and monzonite at 52 Ma. Middle to Late Jurassic metamorphism resulted in widespread migmatization. Early Tertiary metamorphism (66–51 Ma) was coeval with the emplacement of granitic rocks and exhumation typical of other areas of the Shuswap metamorphic complex. Highly deformed orthogneiss situated within the hanging wall of the Kalamalka Lake shear zone, comprising the superstructure, was emplaced at ~171 Ma. Ductile deformation had ceased by 162 Ma. The complex metamorphic and magmatic evolution of the Vernon antiform, which is similar to other areas of the southern Canadian Cordillera including the Nicola horst, Mount Lytton – Eagle plutonic complex, Cariboo Mountains, and Mica Creek area, may reflect episodic tectonic activity at the plate margin.

scholarly journals Precise Location and Mapping of the Main Central Thrust Zone in Reference to Micro-Structures and Deformation along Khudi-Tal Area of Marsyangdi Valley

2020 ◽  
Vol 22 ◽  
pp. 33-40
Author(s):  
Lokendra Pandeya ◽  
Kabi Raj Paudyal
Keyword(s):  
Regional Metamorphism ◽  
Static Condition ◽  
Shear Zones ◽  
Geological Mapping ◽  
Lesser Himalaya ◽  
Main Central Thrust ◽  
Thin Sections ◽  
Ductile Shearing ◽  
Shear Sense ◽  
Micro Structures

Geological mapping was carried out along Marsyangdi valley in the Khudi - Dahare -Tal area on a scale of 1: 50,000 covering about 142 square kilometers. Recent study aims to locate the Main Central Thrust (MCT) precisely based on lithostratigraphy, micro-structures, deformation, and metamorphism. Several thin sections were observed to study the metamorphism, deformation, and micro-structures developed in the rocks. The rocks sequences in both the Higher Himalaya and the Lesser Himalaya have undergone polyphase metamorphism and deformation. The Lesser Himalaya experienced first burial metamorphism (M1) followed by garnet grade inverted metamorphism related to the MCT activity (M2) followed by retrograde metamorphism (M3) whereas the Higher Himalaya has undergone regional high-pressure/ high-temperature kyanite/ sillimanite- grade prograde regional metamorphism (M1) followed by the (M2) related to ductile sharing which in turn is overprinted by the later post-tectonic retrograde garnet to chlorite grade metamorphism during exhumation. The polyphase deformation is indicated by the cross-cutting foliation and many other features. The deformation phase D1 is associated with the development of the bedding parallel foliation due to burial in both the Higher Himalaya and the Lesser Himalaya. Isoclinal folds and crenulation cleavage were developed before the collision is categorized as D2. Development of nearly N- S trending mineral and stretching lineation, south vergent drag folds, folded S2 cleavage and microscopic shear sense indicators, rotated syn- tectonic garnet grains, etc. were developed during the deformation D3 related to the ductile shearing through the MCT. Various brittle faults and shear zones cross-cutting all earlier features were developed during D4 during the upheaval. The rocks in the MCT zone are affected by intense sharing and mylonitization as indicated by the presence of many mylonitic structures in the thin sections throughout the Lesser Himalaya in the area. Features like polygonization and ribbon quartz with evidence of sub-grain rotation, mica fish, syn-tectonic rotated garnet grains indicate the ductile shearing in the MCT area suggesting the dynamic recrystallization in the MCT zone whereas rocks of the Higher Himalaya show the evidence of recrystallization under static condition. The MCT zone was mapped precisely based on the microstructures and deformation.

Early Tertiary Anaconda Metamorphic Core Complex, southwestern Montana

2004 ◽  
Vol 41 (1) ◽  
pp. 63-72 ◽  
Author(s):  
J Michael O'Neill ◽  
Jeff D Lonn ◽  
David R Lageson ◽  
Michael J Kunk
Keyword(s):  
Sedimentary Rocks ◽  
Shear Zones ◽  
Detachment Fault ◽  
Integrated System ◽  
Metamorphic Core Complex ◽  
Granitic Rocks ◽  
Core Complex ◽  
Early Tertiary ◽  
Late Tertiary ◽  
Metamorphic Core

A sinuous zone of gently southeast-dipping low-angle Tertiary normal faults is exposed for 100 km along the eastern margins of the Anaconda and Flint Creek ranges in southwest Montana. Faults in the zone variously place Mesoproterozoic through Paleozoic sedimentary rocks on younger Tertiary granitic rocks or on sedimentary rocks older than the overlying detached rocks. Lower plate rocks are lineated and mylonitic at the main fault and, below the mylonitic front, are cut by mylonitic mesoscopic to microscopic shear zones. The upper plate consists of an imbricate stack of younger-on-older sedimentary rocks that are locally mylonitic at the main, lowermost detachment fault but are characteristically strongly brecciated or broken. Kinematic indicators in the lineated mylonite indicate tectonic transport to the east-southeast. Syntectonic sedimentary breccia and coarse conglomerate derived solely from upper plate rocks were deposited locally on top of hanging-wall rocks in low-lying areas between fault blocks and breccia zones. Muscovite occurs locally as mica fish in mylonitic quartzites at or near the main detachment. The 40Ar/39Ar age spectrum obtained from muscovite in one mylonitic quartzite yielded an age of 47.2 + 0.14 Ma, interpreted to be the age of mylonitization. The fault zone is interpreted as a detachment fault that bounds a metamorphic core complex, here termed the Anaconda metamorphic core complex, similar in age and character to the Bitterroot mylonite that bounds the Bitterroot metamorphic core complex along the Idaho-Montana state line 100 km to the west. The Bitterroot and Anaconda core complexes are likely components of a continuous, tectonically integrated system. Recognition of this core complex expands the region of known early Tertiary brittle-ductile crustal extension eastward into areas of profound Late Cretaceous contractile deformation characterized by complex structural interactions between the overthrust belt and Laramide basement uplifts, overprinted by late Tertiary Basin and Range faulting.

Ductile shearing of Apennine allochtonous units and Messinian terrigenous deposits on top of the Inner Apulian Platform (Monte Alpi, Southern Italy)

2020 ◽  
Author(s):  
Giacomo Prosser ◽  
Fabrizio Agosta ◽  
Alessandro Giuffrida ◽  
Claudia Belviso ◽  
Francesco Cavalcante
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Geological Mapping ◽  
Middle Pleistocene ◽  
Low Grade ◽  
Late Pliocene ◽  
X Ray ◽  
Time Space ◽  
Ductile Shearing ◽  
Shear Sense

<p>Mylonites are common structural elements in basement complexes. There, strain localization within shear zones occurs at amphibolite to greenschist facieses. More rarely, it also takes place at low-grade to anchizonal conditions in the external portions of orogenic belts. In the present contribution, we document the large-scale architecture, micro-structure, and mineralogy of a prominent shear zone exposed along the southern flank of the Monte Alpi Unit, southern Apennines, Italy. Deformation localized within the Messinian sedimentary protolith topping the carbonates of the Apulian Platform, and in the lowermost tectonic units of the Apennine allochton. Integration of results achieved after field geological mapping, outcrop structural analyses, optical and SEM micropscopy, and X-Ray diffrattometry permits to assess the time-space evolution of the main deformation mechanisms in the aforementioned shear zone. The shear zone involved Messinian shale, sandstones and conglomerates originally deposited in a foreland basin system, and Mesozoic claystones, limestones, and marls that formed in deep basinal environments. Now days, the mylonitic foliation is sub-parallel to the tectonic contact between the Messinian sedimentary cover of the Apulian carbonates and the overlying allochton. Shear-related deformation produced a foliated mylonitic fabric dipping ca. 20° S, and a well-developed, east-trending stretching lineation defined by aligned quartz and/or calcite grains. The conglomeratic levels were boudinaged, and the individual elongated pebbles re-oriented along slip direction. The microstructure of mylonites is characterized by a fine-grained calcite matrix, which shows an intense foliation due to dark bands made up of oxides, organic matter, and minor phyllosilicates. X-ray diffraction data performed on the Messinian shales and Mesozoic claystones, indicate the presence of mixed layer illite/smectite with 80-90% of illite and R1/R3 ordering thus suggesting an high digenetic grade (temperature: 120-140 °C). The two analyzed lithologies mainly differ in the presence of kaolinite, which occurs in the more proximal Messinian facies. Altogether, outcrop-scale kinematic markers such as shear bands, rootles folds and asymmetric porphyroclasts show a consistent top-to-the-east shear sense. Mineralogical and microstructural data indicate that shearing took place at a depth of 6-7 km during the Early Pliocene emplacement of the Apennine allochton on the Apulian Platform, and then exhumed by Late Pliocene low-angle normal faulting, Lower Pleistocene transpression, and Middle-Pleistocene-Holocene high-angle extensional faulting. In summary, the eastward motion of the allochton produced intense and localized low-temperature shearing in sediments on top of the Apulian Platform and in the overlying allochton. A subsequent reactivation of this shear zones as low-angle normal fault during late Pliocene exhumation is envisioned.</p>

Structural and geological mapping of the Gran Sometta-Tournalin ridge (Aosta Valley, Italy)

2020 ◽  
Author(s):  
Matteo Pozzi ◽  
Gloria Arienti ◽  
Anna Losa ◽  
Andrea Bistacchi
Keyword(s):  
Fault Zone ◽  
Structural Data ◽  
Shear Zones ◽  
Geological Mapping ◽  
Level Of Detail ◽  
Greenschist Facies ◽  
Normal Faults ◽  
High Angle ◽  
Crenulation Cleavage ◽  
High Level

<p>We present a new geological and structural map of the Gran Sometta -Tournalin ridge (Valle d’Aosta). In this area we have Pennidic ophiolitic units of the Combin (Co) and Zermatt-Saas (ZS) zones. In addition, in this area the continental cover sequence of the Pancherot-Cime Bianche-Bettaforca (PCB) unit crops out, close to the base of the Combin zone. The PCB and Co are characterized by Alpine greenschist facies assemblages, while the ZS is characterized by eclogitic assemblages. The greenschist and HP complexes are juxtaposed along the extensional Combin Fault Zone.</p><p>Our detailed 1:5000 map allowed reconstructing in 3D, and with a high level of detail, the spatial and crosscutting relationships between metamorphic layering (e.g. calcschists and metabasites in the Co), ductile foliations and shear zones, semi-brittle features (e.g. extensional crenulation cleavage – ECC - along the Combin Fault Zone), and post-metamorphic brittle faults.</p><p>The metamorphic layering and foliations are sub-horizontal in this area, and the ECC associated to the Combin Fault results in large components of horizontal stretching. These features are crosscut by two sets of high-angle normal faults, of Oligocene and Miocene age (according to literature), and, thanks to the favourable exposure and numerous structural data, we have been able to reconstruct these structures and their relationships in 3D.</p>

Three crustal zones in the Thor–Odin – Pinnacles area, southern Omineca Belt, British Columbia

1991 ◽  
Vol 28 (12) ◽  
pp. 2003-2023 ◽  
Author(s):  
Sharon D. Carr
Keyword(s):  
Late Cretaceous ◽  
Hanging Wall ◽  
Thermal Quenching ◽  
Shear Zones ◽  
Normal Faults ◽  
Substantial Part ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Early Tertiary ◽  
Late Paleocene

The present crustal architecture of the southern Omineca Belt in the Canadian Cordillera is a product of Eocene extension and crustal thinning superimposed on a crust that was thickened and deformed during Paleozoic and Jurassic to Late Paleocene compression. Amphibolite-facies rocks exposed as gneiss complexes within the Shuswap Metamorphic Complex, in the southern Omineca Belt, were buried during compression and were exhumed in the lower plates of low- to moderate-angle plastic–brittle Eocene extensional faults.In the Thor–Odin – Pinnacles area three crustal zones, which have experienced different deformation and thermal histories, and intervening shear zones can be correlated with Lithoprobe seismic reflection data. The Basement Zone, which comprises crystalline basement and overlying supracrustal gneisses, is bounded above by the Monashee décollement, a deep-seated northeasterly directed Mesozoic–Paleocene thrust fault. In the hanging wall of the décollement, polydeformed gneisses and schists of the Middle Crustal Zone are characterized by Late Cretaceous–early Tertiary ductile strain, plutonism, and thermal quenching. They are bounded at the top by crustal-scale Eocene normal faults that juxtapose Upper Crustal Zone rocks characterized by Jurassic and older structures and a Jura-Cretaceous cooling history.Middle Crustal Zone rocks of the Thor–Odin – Pinnacles area are correlative with part of the Late Proterozoic Horsethief Creek Group and Cambrian to Jurassic strata and host extensive plutons, stocks, and sheets of the syntectonic and posttectonic Late Paleocene – Early Eocene Ladybird granite suite. Field mapping and geochronology indicate that (i) a substantial part of the penetrative compressional polydeformation history and the thermal peak of metamorphism within the Middle Crustal Zone occurred in the Late Cretaceous–Paleocene; (ii) thrusting on the Monashee décollement had ended by 58 Ma; (iii) the onset of extensional deformation either overlapped or closely followed the compressional regime; (iv) Middle Crustal Zone metamorphic and igneous rocks were hot in the Paleocene and cooled rapidly in the early Tertiary because of extensional denudation.

scholarly journals The Dabie Extensional Tectonic System: Structural Framework

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Quanlin Hou ◽  
Hongyuan Zhang ◽  
Qing Liu ◽  
Jun Li ◽  
Yudong Wu
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Ultrahigh Pressure ◽  
Metamorphic Complex ◽  
The South ◽  
Magma Intrusion ◽  
The North ◽  
Extensional Tectonic ◽  
Mechanism Transition ◽  
Tectonic System

A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56 km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12 km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190 Ma and ~124 Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later.

Early Tertiary thermotectonic history of the northern Yukon and adjacent Northwest Territories, Arctic Canada

1997 ◽  
Vol 34 (10) ◽  
pp. 1366-1378 ◽  
Author(s):  
Paul B. O'Sullivan ◽  
Larry S. Lane
Keyword(s):  
Northwest Territories ◽  
Fission Track ◽  
Middle Eocene ◽  
Geothermal Gradient ◽  
Crystalline Rock ◽  
Early Eocene ◽  
Channel Formation ◽  
Rapid Cooling ◽  
Early Tertiary ◽  
History Of

Apatite fission-track data from 16 sedimentary and crystalline rock samples indicate rapid regional Early Eocene denudation within the onshore Beaufort–Mackenzie region of northwestern Canada. Rocks exposed in the area of the Big Fish River, Northwest Territories, cooled rapidly from paleotemperatures of >80–110 °C to <6 0°C at ca. 56 ± 2 Ma, probably in response to kilometre-scale denudation associated with regional structuring. The data suggest the region experienced a geothermal gradient of ~28 °C/km prior to rapid cooling, with ~2.7 km of section having been removed from the top of the exposed section in the Moose Channel Formation and ~3.8 km from the top of the exposed Cuesta Creek Member. Farther to the west, rocks exposed in the headwaters of the Blow River in the Barn Mountains, Yukon Territories, were exposed to paleotemperatures above 110 °C in the Late Paleocene prior to rapid cooling from these elevated paleotemperatures due to kilometre-scale denudation at ca. 56 ± 2 Ma. Exposure of these samples at the surface today requires that a minimum of ~3.8 km of denudation occurred since they began cooling below ~110 °C. The apatite analyses indicate that rocks exposed in the northern Yukon and Northwest Territories experienced rapid cooling during the Early Eocene in response to kilometre-scale denudation, associated with early Tertiary folding and thrusting in the northern Cordillera. Early Eocene cooling–uplift ages for onshore sections are slightly older than the Middle Eocene ages previously documented for the adjacent offshore foldbelt and suggest that the deformation progressed toward the foreland of the foldbelt through time.

scholarly journals Structural setting and tectonic evolution of the Bahariya Depression, Western Desert, Egypt

GeoArabia ◽  
2003 ◽  
Vol 8 (1) ◽  
pp. 91-124 ◽  
Author(s):  
Adel R Moustafa ◽  
Ati Saoudi ◽  
Alaa Moubasher ◽  
Ibrahim M Ibrahim ◽  
Hesham Molokhia ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Tectonic Evolution ◽  
Middle Miocene ◽  
Middle Eocene ◽  
Western Desert ◽  
Normal Faults ◽  
Surface Mapping ◽  
Early Mesozoic ◽  
Hydrocarbon Fields ◽  
Stable Area

ABSTRACT An integrated surface mapping and subsurface study of the Bahariya Depression aided the regional subsurface interpretation. It indicated that four major ENE-oriented structural belts overlie deep-seated faults in this part of the ‘tectonically stable’ area of Egypt. The rocks of the Bahariya area were deformed in the Late Cretaceous, post-Middle Eocene, and Middle Miocene-and subsurface data indicated an early Mesozoic phase of normal faulting. The Late Cretaceous and post-Middle Eocene deformations reactivated the early normal faults by oblique slip and formed a large swell in the Bahariya region. The crest was continuously eroded whereas its peripheries were onlapped by Maastrichtian and Tertiary sediments. The tectonic evolution of the Bahariya region shows great similarity to the deformation of the ‘tectonically unstable’ area of the northern Western Desert where several hydrocarbon fields have been discovered. This similarity may indicate that the same phases of deformation could extend to other basins lying in the ‘tectonically stable’ area, such as the Asyut, Dakhla, Nuqura, and El Misaha basins.

scholarly journals EVOLUTION OF KARAKORAM SEQUENCE, HUNZA VALLEY NE PAKISTAN: EVIDENCES FROM FIELD MAPPING AND MICRO-ANALYTICAL WORK

2020 ◽  
Vol 5 ◽  
pp. 19
Author(s):  
S. S. Baig ◽  
C. Xue ◽  
Masroor Alam ◽  
Naeem Ullah ◽  
M. Alam ◽  
...  
Keyword(s):  
Geological Mapping ◽  
Central Portion ◽  
High Grade ◽  
Metamorphic Complex ◽  
Field Mapping ◽  
The North ◽  
Analytical Work ◽  
History Of ◽  
Micro Analysis ◽  
East West

The Karakoram metamorphic Complex (KMC) in the southern Karakoram block is one of the best examples of Barrovian type metamorphism that comprises numerous exhumed metapelite units where a series of low to high grade (green schist to sillimanite facie) rocks are exposed. This sequence shows a complex polyphase history of metamorphism and deformation which offer deeper understanding of collision orogeny. Karakoram metamorphic Complex contains metapelites, meta-carbonates, meta-igneous and amphibolite layers, cross-cut by granite sheets in the northern part. This complex is bounded to the north by the Hunza plutonic unit which is the central portion of the massive east-west trending Karakoram axial batholith and to the southwest by the Main Karakoram thrust (MKT). In this contribution, we provide detail geological mapping, petrography, geochemistry and micro-analytical work using Electron Prob-micro analysis in the central Hunza Valley.

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