scholarly journals Geologic transect across the Grenville orogen of Ontario and New York

2000 ◽  
Vol 37 (2-3) ◽  
pp. 193-216 ◽  
Author(s):  
S D Carr ◽  
R M Easton ◽  
R A Jamieson ◽  
N G Culshaw
Keyword(s):  
New York ◽  
Cross Sections ◽  
Shear Zones ◽  
Normal Faults ◽  
Grenville Province ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Seismic Reflectivity ◽  
Granitoid Rocks ◽  
Laurentian Margin

Revised cross sections of the western Grenville Province incorporate new geologic results and reprocessed seismic reflection data. The geology is presented in terms of three tectonic elements: (1) "pre-Grenvillian Laurentia and its margin" with ca. 1740 and 1450 Ma continental arc plutons and associated supracrustal rocks; (2) "Composite Arc Belt" of allochthonous ~1300-1250 Ma volcanic arcs and sedimentary rocks; and (3) "Frontenac-Adirondack Belt" characterized by supracrustal and granitoid rocks, and anorthosites, of uncertain affinity, that may represent a distinctive part of the Composite Arc Belt or an offshore (micro)continent. Rocks of the Composite Arc and Frontenac-Adirondack belts were amalgamated with each other by ca. 1160 Ma, were then thrust over Laurentia during ca. 1080-1035 Ma and ca. 1010-980 Ma phases of convergence, and were dissected and exhumed by <1040 Ma normal faults. Penetrative deformation was restricted to that part of the pre-Grenvillian Laurentian margin that lies to the southeast of the Grenville front and parts of the accreted Composite Arc and Frontenac-Adirondack belts. The Laurentian rocks in the Grenville Province are bounded to the northwest and southeast by southeast-dipping ductile thrust and (or) normal shear zones. The Composite Arc and Frontenac-Adirondack belts to the southeast are bounded by ductile and brittle-ductile thrust and (or) normal faults that separate domains with contrasting cooling histories. Despite a long pre-Grenvillian tectonic and plutonic history, the present crustal architecture and much of the seismic reflectivity were acquired during 1080-980 Ma phases of compression and extension.

A seismic-based cross-section of the Grenville Orogen in southern Ontario and western Quebec

2000 ◽  
Vol 37 (2-3) ◽  
pp. 183-192 ◽  
Author(s):  
D J White ◽  
D A Forsyth ◽  
I Asudeh ◽  
S D Carr ◽  
H Wu ◽  
...  
Keyword(s):  
Cross Section ◽  
Seismic Refraction ◽  
Shear Zones ◽  
Tectonic Zone ◽  
Grenville Province ◽  
Crustal Layer ◽  
Seismic Reflection Data ◽  
Velocity Models ◽  
Laurentian Margin ◽  
Structural Boundary

A schematic crustal cross-section is presented for the southwestern Grenville Province based on reprocessed Lithoprobe near-vertical incidence seismic reflection data and compiled seismic refraction - wide-angle velocity models interpreted with geological constraints. The schematic crustal architecture of the southwest Grenville Province from southeast to northwest comprises allochthonous crustal elements (Frontenac-Adirondack Belt and Composite Arc Belt) that were assembled prior to ca. 1160 Ma, and then deformed and transported northwest over reworked rocks of pre-Grenvillian Laurentia and the Laurentian margin primarily between 1120 and 980 Ma. Reworked pre-Grenvillian Laurentia and Laurentian margin rocks are interpreted to extend at least 350 km southeast of the Grenville Front beneath all of the Composite Arc Belt. Three major structural boundary zones (the Grenville Front and adjacent Grenville Front Tectonic Zone, the Central Metasedimentary Belt boundary thrust zone, and the Elzevir-Frontenac boundary zone) have been identified across the region of the cross-section based on their prominent geophysical signatures comprising broad zones of southeast-dipping reflections and shallowing of mid-crustal velocity contours by 12-15 km. The structural boundary zones accommodated southeast over northwest crustal stacking at successively earlier times during orogeny (ca. 1010-980 Ma, 1080-1060 Ma, and 1170-1160 Ma, respectively). These shear zones root within an interpreted gently southeast-dipping regional décollement at a depth of 25-30 km corresponding to the top of a high-velocity lower crustal layer.

The Lithoprobe Abitibi-Grenville transect: two billion years of crust formation and recycling in the Precambrian Shield of Canada

2000 ◽  
Vol 37 (2-3) ◽  
pp. 459-476 ◽  
Author(s):  
John Ludden ◽  
Andrew Hynes
Keyword(s):  
Cross Sections ◽  
High Pressures ◽  
Significant Proportion ◽  
Superior Province ◽  
Crust Formation ◽  
Entire Cross Section ◽  
Grenville Province ◽  
Seismic Reflection Data ◽  
Precambrian Shield ◽  
Reflection Data

We summarize the results of Lithoprobe studies in the Neoarchean southeastern Superior Province and the Mesoproterozoic Grenville Province, in the southeastern Precambrian Shield of Canada, through two composite cross-sections based on seismic reflection data, which define dramatically different styles of crust formation and tectonic accretion in the Neoarchean and Mesoproterozoic. In the Neoarchean, the structures at the surface are steep, with discontinuous and flatter structures at depth, much of the crust appears to be juvenile, and the predominant process of crustal growth is inferred to have been subduction-accretion of primitive crust in a prograding arc system. In the Mesoproterozoic, surface structures are shallow and the seismic character of the crust is continuous over the entire cross-section. Archean parautochthonous rocks and reworked Archean crust comprise a very significant proportion of the preserved crust in the Mesoproterozoic and provided the backstop to the Grenvillian orogeny, resulting in the exhumation of crustal rocks formed at high pressures. Preservation of Neoarchean crust, including a thickened lithosphere in the Superior Province, in contrast to its general destruction in younger orogens, may well relate to a unique thermal regime at this time on Earth.

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 Mantle-derived helium released through the Japan trench bend-faults

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jin-Oh Park ◽  
Naoto Takahata ◽  
Ehsan Jamali Hondori ◽  
Asuka Yamaguchi ◽  
Takanori Kagoshima ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Large Scale ◽  
Japan Trench ◽  
Helium Isotope ◽  
Normal Faults ◽  
Circulation System ◽  
Deep Penetration ◽  
Oceanic Plate ◽  
Seismic Reflection Data ◽  
Reflection Data

AbstractPlate bending-related normal faults (i.e. bend-faults) develop at the outer trench-slope of the oceanic plate incoming into the subduction zone. Numerous geophysical studies and numerical simulations suggest that bend-faults play a key role by providing pathways for seawater to flow into the oceanic crust and the upper mantle, thereby promoting hydration of the oceanic plate. However, deep penetration of seawater along bend-faults remains controversial because fluids that have percolated down into the mantle are difficult to detect. This report presents anomalously high helium isotope (3He/4He) ratios in sediment pore water and seismic reflection data which suggest fluid infiltration into the upper mantle and subsequent outflow through bend-faults across the outer slope of the Japan trench. The 3He/4He and 4He/20Ne ratios at sites near-trench bend-faults, which are close to the isotopic ratios of bottom seawater, are almost constant with depth, supporting local seawater inflow. Our findings provide the first reported evidence for a potentially large-scale active hydrothermal circulation system through bend-faults across the Moho (crust-mantle boundary) in and out of the oceanic lithospheric mantle.

scholarly journals Late Ottawan orogenic collapse of the Adirondacks in the Grenville province of New York State (USA): Integrated petrologic, geochronologic, and structural analysis of the Diana Complex in the southern Carthage-Colton mylonite zone

Geosphere ◽  
2020 ◽  
Vol 16 (3) ◽  
pp. 844-874
Author(s):  
Graham B. Baird
Keyword(s):  
New York ◽  
Pure Shear ◽  
New York State ◽  
Shear Zones ◽  
Core Complex ◽  
Grenville Province ◽  
York State ◽  
Mylonite Zone ◽  
Ductile Shear Zones ◽  
Metamorphic Core

Abstract Crustal-scale shear zones can be highly important but complicated orogenic structures, therefore they must be studied in detail along their entire length. The Carthage-Colton mylonite zone (CCMZ) is one such shear zone in the northwestern Adirondacks of northern New York State (USA), part of the Mesoproterozoic Grenville province. The southern CCMZ is contained within the Diana Complex, and geochemistry and U-Pb zircon geochronology demonstrate that the Diana Complex is expansive and collectively crystallized at 1164.3 ± 6.2 Ma. Major ductile structures within the CCMZ and Diana Complex include a northwest-dipping penetrative regional mylonitic foliation with north-trending lineation that bisects a conjugate set of mesoscale ductile shear zones. These ductile structures formed from the same 1060–1050 Ma pure shear transitioning to a top-to-the-SSE shearing event at ∼700 °C. Other important structures include a ductile fault and breccia zones. The ductile fault formed immediately following the major ductile structures, while the breccia zones may have formed at ca. 945 Ma in greenschist facies conditions. Two models can explain the studied structures and other regional observations. Model 1 postulates that the CCMZ is an Ottawan orogeny (1090–1035 Ma) thrust, which was later reactivated locally as a tectonic collapse structure. Model 2, the preferred model, postulates that the CCMZ initially formed as a subhorizontal mid-crustal mylonite zone during collapse of the Ottawan orogen. With continued collapse, a metamorphic core complex formed and the CCMZ was rotated into is current orientation and overprinted with other structures.

scholarly journals Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia

2020 ◽  
Author(s):  
Craig Magee ◽  
Christopher A.-L. Jackson
Keyword(s):  
Seismic Reflection ◽  
Surface Deformation ◽  
3D Structure ◽  
Sedimentary Basins ◽  
Dyke Swarm ◽  
Normal Faults ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Dyke Swarms ◽  
Nw Australia

Abstract. Dyke swarms are common on Earth and other planetary bodies, comprising arrays of dykes that can extend for 10's to 1000's of kilometres. The vast extent of such dyke swarms, and their rapid emplacement, means they can significantly influence a variety of planetary processes, including continental break-up, crustal extension, resource accumulation, and volcanism. Determining the mechanisms driving dyke swarm emplacement is thus critical to a range of Earth Science disciplines. However, unravelling dyke swarm emplacement mechanics relies on constraining their 3D structure, which is extremely difficult given we typically cannot access their subsurface geometry at a sufficiently high enough resolution. Here we use high-quality seismic reflection data to identify and examine the 3D geometry of the newly discovered Exmouth Dyke Swarm, and associated structures (i.e. dyke-induced normal faults and pit craters), in unprecedented detail. The latest Jurassic dyke swarm is located on the Gascoyne Margin offshore NW Australia and contains numerous dykes that are > 170 km long, potentially > 500 km long. The mapped dykes are distributed radially across a 39° arc centred on the Cuvier Margin; we infer this focal area marks the source of the dyke swarm, which was likely a mantle plume. We demonstrate seismic reflection data provides unique opportunities to map and quantify dyke swarms in 3D in sedimentary basins, which can allow us to: (i) recognise dyke swarms across continental margins worldwide and incorporate them into models of basin evolution and fluid flow; (ii) test previous models and hypotheses concerning the 3D structure of dyke swarms; (iii) reveal how dyke-induced normal faults and pit craters relate to dyking; and (iv) unravel how dyking translates into surface deformation.

scholarly journals Structural and microstructural analysis of K–Mg salt layers in the Zechstein 3 of the Veendam Pillow, NE Netherlands: development of a tectonic mélange during salt flow

2017 ◽  
Vol 96 (4) ◽  
pp. 331-351 ◽  
Author(s):  
Alexander F. Raith ◽  
Janos L. Urai ◽  
Jacob Visser
Keyword(s):  
Microstructural Analysis ◽  
Shear Zones ◽  
Horizontal Shear ◽  
X Ray Diffraction ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Tectonic History ◽  
Dynamic Recrystallisation ◽  
Bulk Chemical ◽  
Tectonic Mélange

AbstractIn fully developed evaporite cycles, effective viscosity contrasts of up to five orders of magnitude are possible between different layers, but the structures and mechanics in evaporites with such extreme mechanical stratification are not well understood. The Zechstein 3 unit in the Veendam salt pillow in the Netherlands contains anhydrite, halite, carnallite and bischofite, showing this extreme mechanical stratification. The Veendam Pillow has a complex multiphase salt tectonic history as shown by seismic reflection data: salt withdrawal followed by convergent flow into the salt pillow produced ruptures and folds in the underlying Z3-anhydrite–carbonate stringer and deformed the soft Z3-1b layerWe analysed a unique carnallite- and bischofite-rich drill core from the soft Z3-1b layer by macroscale photography, bulk chemical methods, X-ray diffraction and optical microscopy. Results show high strain in the weaker bischofite- and carnallite-rich layers, with associated dynamic recrystallisation at very low differential stress, completely overprinting the original texture. Stronger layers formed by alternating beds of halite and carnallite show complex recumbent folding on different scales commonly interrupted by sub-horizontal shear zones with brittle deformation, veins and boudinage. We attribute this tectonic fragmentation to be associated with a softening of the complete Z3-1b subunit during its deformation. The result is a tectonic mélange with cm- to 10 m-size blocks with frequent folds and boudinage. We infer that these structures and processes are common in deformed, rheologically strongly stratified evaporites.

scholarly journals Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 579-606 ◽  
Author(s):  
Craig Magee ◽  
Christopher Aiden-Lee Jackson
Keyword(s):  
Seismic Reflection ◽  
Surface Deformation ◽  
3D Structure ◽  
Dyke Swarm ◽  
Normal Faults ◽  
Borehole Data ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Dyke Swarms ◽  
Nw Australia

Abstract. Dyke swarms are common on Earth and other planetary bodies, comprising arrays of dykes that can extend laterally for tens to thousands of kilometres. The vast extent of such dyke swarms, and their presumed rapid emplacement, means they can significantly influence a variety of planetary processes, including continental break-up, crustal extension, resource accumulation, and volcanism. Determining the mechanisms driving dyke swarm emplacement is thus critical to a range of Earth Science disciplines. However, unravelling dyke swarm emplacement mechanics relies on constraining their 3D structure, which is difficult given we typically cannot access their subsurface geometry at a sufficiently high enough resolution. Here we use high-quality seismic reflection data to identify and examine the 3D geometry of the newly discovered Exmouth Dyke Swarm, and associated structures (i.e. dyke-induced normal faults and pit craters). Dykes are expressed in our seismic reflection data as ∼335–68 m wide, vertical zones of disruption (VZD), in which stratal reflections are dimmed and/or deflected from sub-horizontal. Borehole data reveal one ∼130 m wide VZD corresponds to an ∼18 m thick, mafic dyke, highlighting that the true geometry of the inferred dykes may not be fully captured by their seismic expression. The Late Jurassic dyke swarm is located on the Gascoyne Margin, offshore NW Australia, and contains numerous dykes that extend laterally for > 170 km, potentially up to > 500 km, with spacings typically < 10 km. Although limitations in data quality and resolution restrict mapping of the dykes at depth, our data show that they likely have heights of at least 3.5 km. The mapped dykes are distributed radially across a ∼39∘ wide arc centred on the Cuvier Margin; we infer that this focal area marks the source of the dyke swarm. We demonstrate that seismic reflection data provide unique opportunities to map and quantify dyke swarms in 3D. Because of this, we can now (i) recognise dyke swarms across continental margins worldwide and incorporate them into models of basin evolution and fluid flow, (ii) test previous models and hypotheses concerning the 3D structure of dyke swarms, (iii) reveal how dyke-induced normal faults and pit craters relate to dyking, and (iv) unravel how dyking translates into surface deformation.

scholarly journals Hydraulic fracturing in thick shale basins: problems in identifying faults in the Bowland and Weald Basins, UK

2016 ◽  
Author(s):  
David K. Smythe
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Reflection ◽  
Upper Jurassic ◽  
Normal Faults ◽  
Regulatory Regime ◽  
Seismic Line ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Unconventional Resource ◽  
The Uk

Abstract. North American shale basins differ from their European counterparts in that the latter are one to two orders of magnitude smaller in area, but correspondingly thicker, and are cut or bounded by normal faults penetrating from the shale to the surface. There is thus an inherent risk of groundwater resource contamination via these faults during or after unconventional resource appraisal and development. US shale exploration experience cannot simply be transferred to the UK. The Bowland Basin, with 1900 m of Lower Carboniferous shale, is in the vanguard of UK shale gas development. A vertical appraisal well to test the shale by hydraulic fracturing (fracking), the first such in the UK, triggered earthquakes. Re-interpretation of the 3D seismic reflection data, and independently the well casing deformation data, both show that the well was drilled through the earthquake fault, and did not avoid it, as concluded by the exploration operator. Faulting in this thick shale is evidently difficult to recognise. The Weald Basin is a shallower Upper Jurassic unconventional oil play with stratigraphic similarities to the Bakken play of the Williston Basin, USA. Two Weald licensees have drilled, or have applied to drill, horizontal appraisal wells based on inadequate 2D seismic reflection data coverage. I show, using the data from the one horizontal well drilled to date, that one operator failed identify two small but significant through-going normal faults. The other operator portrayed a seismic line as an example of fault-free structure, but faulting had been smeared out by reprocessing. The case histories presented show that: (1) UK shale exploration to date is characterised by a low degree of technical competence, and (2) regulation, which is divided between four separate authorities, is not up to the task. If UK shale is to be exploited safely: (1) more sophisticated seismic imaging methods need to be developed and applied to both basins, to identify faults in shale with throws as small as 4–5 m, and (2) the current lax and inadequate regulatory regime must be overhauled, unified, and tightened up.

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