Characterization of transpressive deformation in shear zones of the Archean North Caribou greenstone belt (NW Superior Province) and the relationship with regional metamorphism

2016 ◽  
Vol 693 ◽  
pp. 261-276 ◽  
Author(s):  
Émilie Gagnon ◽  
David A. Schneider ◽  
Tash Kalbfleisch ◽  
Gerlinde Habler ◽  
John Biczok
Keyword(s):  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Shear Zones ◽  
Superior Province ◽  
The Relationship

Rb–Sr whole-rock geochronology of the Gamitagama area, north central Ontario

1981 ◽  
Vol 18 (2) ◽  
pp. 323-329 ◽  
Author(s):  
A. Turek ◽  
T. E. Smith ◽  
C. H. Huang
Keyword(s):  
Greenstone Belt ◽  
Complex Terrain ◽  
Regional Metamorphism ◽  
Superior Province ◽  
The South ◽  
Stratigraphic Sequence ◽  
North Central ◽  
Metasedimentary Rocks ◽  
Area North ◽  
Radiometric Ages

The Gamitagama greenstone belt is situated to the south of the Archean Wawa belt of the Superior Province, and is about 50 km south of Wawa, Ontario. The Rb–Sr ages being reported here show that the metavolcanic and associated metasedimentary rocks are older than 2665 ± 45 Ma, which is a whole-rock isochron age of the pretectonic or syntectonic trondhjemitic plutons. The Gamitagama Lake complex, a calcalkalic differentiated and multiple diorite pluton, postdates the regional metamorphism and gives an age of 2645 ± 100 Ma. Potassic granitoid stocks, which are considered to be coeval with the Gamitagama Lake complex, define an isochron age of 2590 ± 80 Ma. The greenstone belt and associated intrusives are adjacent to the Southern batholith, a complex terrain of gneisses and migmatites, for which an isochron age of 2570 ± 90 Ma has been obtained. The radiometric ages reported here support the established stratigraphic sequence and prove that the rocks are Archean in age.

The origin and history of the Kapuskasing structural zone, Ontario, Canada

1980 ◽  
Vol 17 (7) ◽  
pp. 866-875 ◽  
Author(s):  
Janet Watson
Keyword(s):  
Lower Crust ◽  
Bouguer Anomaly ◽  
Shear Zones ◽  
Superior Province ◽  
Dike Swarm ◽  
History Of ◽  
Dike Swarms ◽  
Relationship Of ◽  
The Relationship ◽  
Geochronological Evidence

Reexamination of geological, geophysical, and geochronological evidence suggests three principal conclusions. Firstly, the Kapuskasing line came into existence very shortly after the stabilization of the Superior Province. The upfaulting of strips of granulites and associated rocks, and probably the redistribution of densities in the lower crust responsible for the regional positive Bouguer anomaly, took place before the emplacement of the Matachewan dike swarm at ~2690 Ma. Secondly, relative movements along the line during this tectonic stage had an important sinistral transcurrent component and sinistral movements continued during the emplacement of the Matachewan swarm. Thirdly, displacements of various kinds took place on the Kapuskasing line during a number of later events spaced out over a period of more than 2000 Ma; some of their effects can be deduced from the relationship of regional dike swarms and of cratonic cover formations. These findings suggest that the Kapuskasing line did not originate as a rift structure. Analogies are seen with deep transcurrent shear zones of other continents.

The Kapuskasing uplift: a geological and geophysical synthesis

1994 ◽  
Vol 31 (7) ◽  
pp. 1256-1286 ◽  
Author(s):  
John A. Percival ◽  
Gordon F. West
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Gravity Anomalies ◽  
Shear Zones ◽  
Local Deformation ◽  
Gold Deposition ◽  
Superior Province ◽  
Low Grade ◽  
Geophysical Investigation ◽  
Complex Deformation

Over the past decade, the Kapuskasing uplift has been the subject of intense geological and geophysical investigation as Lithoprobe's window on the deep-crustal structure of the Archean Superior Province. Enigmatic since its recognition as a positive gravity anomaly in 1950, the structure has been variably interpreted as a suture, rift, transcurrent shear zone, or intracratonic thrust. Diverse studies, including geochronology, geothermobarometry, and various geophysical probes, provide a comprehensive three-dimensional image of Archean (2.75–2.50 Ga) crustal evolution and Proterozoic (2.5–1.1 Ga) cooling and uplift. The data favour an interpretation of the structure as an intracratonic uplift related to Hudsonian collision.Eastward across the southern Kapuskasing uplift, erosion levels increase from < 10 km in the Michipicoten greenstone belt, through the Wawa gneiss domain (10–20 km), into granulites (20–30 km) of the Kapuskasing structural zone, juxtaposed against the low-grade Swayze greenstone belt along the Ivanhoe Lake fault zone. Most volcanic rocks in the greenstone belts erupted in the interval 2750–2700 Ma and were thrust, folded, and cut by late plutons and transcurrent faults before 2670 Ma. Wawa gneisses include major 2750–2660 and minor 2920 Ma tonalitic components, deformed in several events including prominent late subhorizontal extensional shear zones prior to 2645 Ma. Supracrustal rocks of the Kapuskasing zone have model Nd ages of 2750–2700 Ma, metamorphic zircon ages of 2696–2584 Ma, and titanite ages of 2600–2493 Ma, reflecting deposition, intrusion, complex deformation, recrystallization, and cooling during prolonged deep-crustal residence. Postorogenic unroofing rapidly cooled shallow (10–20 km) parts of the Superior Province, but metamorphism and local deformation continued in the ductile deep crust, overlapping the time of late gold deposition in shear zones in the shallow brittle regime.Elevation of granulites, expressed geophysically as positive gravity anomalies and a west-dipping zone of high refraction velocities, dates from a major episode of transpressive faulting. Analysis of deformation effects in Matachewan (2454 Ma), Biscotasing (2167 Ma), and Kapuskasing (2040 Ma) dykes, as well as the brittle nature of fault rocks and cooling patterns of granulites, constrains the time of uplift to ca, 1.9 Ga. Approximately 27 km of shortening was accommodated through brittle upper crustal thrusting and ductile growth of an 8 km thick root in the lower crust that has been maintained by relatively cool, strong mantle lithosphere. The present configuration of the uplift results from overall dextral displacement in which the block was broken and deformed by dextral, normal, and sinistral faults, and modified by later isostatic adjustment. Seismic reflection profiles display prominent northwest-dipping reflectors believed to image lithological contacts and ductile strain zones of Archean age; the indistinct reflection character of the Ivanhoe Lake fault is probably related to its brittle nature formed through brecciation and cataclasis at temperatures < 300 °C. The style and orientation of Proterozoic structures may have been influenced by the Archean crustal configuration.

Polymetamorphism in the Archean Hemlo – Heron Bay greenstone belt, Superior Province: P–T variations and implications for tectonic evolution

1993 ◽  
Vol 30 (5) ◽  
pp. 985-996 ◽  
Author(s):  
Yuanming Pan ◽  
Michael E. Fleet
Keyword(s):  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Mineral Chemistry ◽  
Superior Province ◽  
Low Grade ◽  
Garnet Porphyroblasts ◽  
Metamorphic History ◽  
Tectonic Environment ◽  
History Of ◽  
Archean Greenstone Belt

The tectono-metamorphic history of the late Archean (2800–2600 Ma) Hemlo – Heron Bay greenstone belt in the Superior Province has been delineated from textural relationships, mineral chemistry, and P–T paths in metapelites, cordierite–orthoamphibole rocks, and metabasites from the White River exploration property, Hemlo area, Ontario. An early low-temperature, medium-pressure metamorphism (about 500 °C and 6–6.5 kbar (1 kbar = 100 MPa)) is indicated by the occurrence of relict kyanite and staurolite porphyroblasts and zoned garnet porphyroblasts in metapelites and the presence of zoned calcic amphiboles in metabasites. This early metamorphism appears to have been coeval with the previously documented D1 deformation that is associated with, for example, low-angle thrusts. A second regional metamorphism predominates in the Hemlo – Heron Bay greenstone belt and is generally of relatively low grade, at about 510–530 °C and 3.2–3.5 kbar, over most of the study area and increases to medium grade (550–650 °C and 4–5 kbar) towards the southern margin with the Pukaskwa Gneissic Complex and along the central axis enclosing the Hemlo Shear Zone. The second regional metamorphism was contemporaneous with the D3 deformation and was probably related to plutonism. This type of polymetamorphism in the Hemlo – Heron Bay greenstone belt may be equivalent to those in Phanerozoic subduction complexes and therefore supports the arc–arc accretion model for the development of the southern Superior Province. Although the Hemlo – Heron Bay greenstone belt most likely represents a single tectonic environment (an oceanic island arc), the restricted occurrence of the relict kyanite and staurolite indicates that the central portion of this Archean greenstone belt probably was at a deeper crustal level at the time of the first metamorphic event.

Stratigraphy, structure, and geochronology of the 3.0–2.7 Ga Wallace Lake greenstone belt, western Superior Province, southeast Manitoba, Canada

2006 ◽  
Vol 43 (7) ◽  
pp. 929-945 ◽  
Author(s):  
C Sasseville ◽  
K Y Tomlinson ◽  
A Hynes ◽  
V McNicoll
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Shear Zones ◽  
Iron Formation ◽  
Superior Province ◽  
Lake Winnipeg ◽  
The North ◽  
Southern Margin ◽  
Plume Magmatism

In western Superior province, the North Caribou terrane (NCT) constitutes a Mesoarchean proto-continent heavily overprinted by Neoarchean magmatism and deformation resulting from the western Superior Province accretion. Locally, along the southern margin of the NCT, Mesoarchean (~3.0 Ga) rift sequences are preserved. These sequences are of key importance to our understanding of the early tectonic evolution of continental crust. The Wallace Lake greenstone belt is located at the southern margin of the NCT and includes the Wallace Lake assemblage, the Big Island assemblage, the Siderock Lake assemblage, and the French Man Bay assemblage. The Wallace Lake assemblage exposes one of the best-preserved Mesoarchean rift sequences along the southern margin of the NCT. The volcano-sedimentary assemblage (3.0–2.92 Ga) exposes arkoses derived from the uplift of a tonalite basement in a subaqueous environment, capped by carbonate and iron formation. Mafic to ultramafic volcanic rocks exhibiting crustal contamination and derived from plume magmatism cap this rift sequence. The Wallace Lake assemblage exhibits D1 Mesoarchean deformation. The Big Island assemblage comprises mafic volcanic rocks of oceanic affinity that were docked to the Wallace Lake assemblage along northwest-trending D2 shear zones. The timing of volcanism and docking of the Big Island assemblage remain uncertain. The Siderock Lake and French Man Bay assemblages were deposited in strike-slip basins related to D3 and D4 stages of movement of the transcurrent Wanipigow fault (<2.709 Ga). Regionally, the Wallace Lake assemblage correlates with the Lewis–Story Rift assemblage observed in Lake Winnipeg, whereas the Big Island assemblage appears to correlate with the Black Island assemblage observed in the Lake Winnipeg area. Thus, the North Caribou terrane appears to preserve vestiges of a Mesoarchean rifted succession together with overlying Neoarchean allochthonous, juvenile, volcanic successions over a considerable distance along its present-day southern margin.

scholarly journals The role of enigmatic deep crustal and upper mantle structures on Au and magmatic Ni-Cu-PGE-Cr mineralization in the Superior Province

2021 ◽  
Author(s):  
L B Harris ◽  
P Adiban ◽  
E Gloaguen
Keyword(s):  
Machine Learning ◽  
Fluid Flow ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
Numerical Models ◽  
Regional Metamorphism ◽  
Shear Zones ◽  
Superior Province ◽  
Upper Crust ◽  
Pge Mineralization

Aeromagnetic and ground gravity data for the Canadian Superior Province, filtered to extract long wavelength components and converted to pseudo-gravity, highlight deep, N-S trending regional-scale, rectilinear faults and margins to discrete, competent mafic or felsic granulite blocks (i.e. at high angles to most regional mapped structures and sub-province boundaries) with little to no surface expression that are spatially associated with lode ('orogenic') Au and Ni-Cu-PGE-Cr occurrences. Statistical and machine learning analysis of the Red Lake-Stormy Lake region in the W Superior Province confirms visual inspection for a greater correlation between Au deposits and these deep N-S structures than with mapped surface to upper crustal, generally E-W trending, faults and shear zones. Porphyry Au, Ni, Mo and U-Th showings are also located above these deep transverse faults. Several well defined concentric circular to elliptical structures identified in the Oxford Stull and Island Lake domains along the S boundary of the N Superior proto-craton, intersected by N- to NNW striking extensional fractures and/or faults that transect the W Superior Province, again with little to no direct surface or upper crustal expression, are spatially associated with magmatic Ni-Cu-PGE-Cr and related mineralization and Au occurrences. The McFaulds Lake greenstone belt, aka. 'Ring of Fire', constitutes only a small, crescent-shaped belt within one of these concentric features above which 2736-2733 Ma mafic-ultramafic intrusions bodies were intruded. The Big Trout Lake igneous complex that hosts Cr-Pt-Pd-Rh mineralization west of the Ring of Fire lies within a smaller concentrically ringed feature at depth and, near the Ontario-Manitoba border, the Lingman Lake Au deposit, numerous Au occurrences and minor Ni showings, are similarly located on concentric structures. Preliminary magnetotelluric (MT) interpretations suggest that these concentric structures appear to also have an expression in the subcontinental lithospheric mantle (SCLM) and that lithospheric mantle resistivity features trend N-S as well as E-W. With diameters between ca. 90 km to 185 km, elliptical structures are similar in size and internal geometry to coronae on Venus which geomorphological, radar, and gravity interpretations suggest formed above mantle upwellings. Emplacement of mafic-ultramafic bodies hosting Ni-Cr-PGE mineralization along these ringlike structures at their intersection with coeval deep transverse, ca. N-S faults (viz. phi structures), along with their location along the margin to the N Superior proto-craton, are consistent with secondary mantle upwellings portrayed in numerical models of a mantle plume beneath a craton with a deep lithospheric keel within a regional N-S compressional regime. Early, regional ca. N-S faults in the W Superior were reactivated as dilatational antithetic (secondary Riedel/R') sinistral shears during dextral transpression and as extensional fractures and/or normal faults during N-S shortening. The Kapuskasing structural zone or uplift likely represents Proterozoic reactivation of a similar deep transverse structure. Preservation of discrete faults in the deep crust beneath zones of distributed Neoarchean dextral transcurrent to transpressional shear zones in the present-day upper crust suggests a 'millefeuille' lithospheric strength profile, with competent SCLM, mid- to deep, and upper crustal layers. Mechanically strong deep crustal felsic and mafic granulite layers are attributed to dehydration and melt extraction. Intra-crustal decoupling along a ductile décollement in the W Superior led to the preservation of early-formed deep structures that acted as conduits for magma transport into the overlying crust and focussed hydrothermal fluid flow during regional deformation. Increase in the thickness of semi-brittle layers in the lower crust during regional metamorphism would result in an increase in fracturing and faulting in the lower crust, facilitating hydrothermal and carbonic fluid flow in pathways linking SCLM to the upper crust, a factor explaining the late timing for most orogenic Au. Results provide an important new dataset for regional prospectively mapping, especially with machine learning, and exploration targeting for Au and Ni-Cr-Cu-PGE mineralization. Results also furnish evidence for parautochthonous development of the S Superior Province during plume-related rifting and cannot be explained by conventional subduction and arc-accretion models.

Skeletal elements of crinoid echinoderms: High-resolution structural and microanalytical results

1983 ◽  
Vol 41 ◽  
pp. 194-195
Author(s):  
D. F. Blake ◽  
L. F. Allard ◽  
D. R. Peacor
Keyword(s):  
High Resolution ◽  
Marine Invertebrates ◽  
Sea Urchins ◽  
Structural Features ◽  
Sea Stars ◽  
High Resolution Tem ◽  
Relationship Of ◽  
The Relationship ◽  
Insight Into

Echinodermata is a phylum of marine invertebrates which has been extant since Cambrian time (c.a. 500 m.y. before the present). Modern examples of echinoderms include sea urchins, sea stars, and sea lilies (crinoids). The endoskeletons of echinoderms are composed of plates or ossicles (Fig. 1) which are with few exceptions, porous, single crystals of high-magnesian calcite. Despite their single crystal nature, fracture surfaces do not exhibit the near-perfect {10.4} cleavage characteristic of inorganic calcite. This paradoxical mix of biogenic and inorganic features has prompted much recent work on echinoderm skeletal crystallography. Furthermore, fossil echinoderm hard parts comprise a volumetrically significant portion of some marine limestones sequences. The ultrastructural and microchemical characterization of modern skeletal material should lend insight into: 1). The nature of the biogenic processes involved, for example, the relationship of Mg heterogeneity to morphological and structural features in modern echinoderm material, and 2). The nature of the diagenetic changes undergone by their ancient, fossilized counterparts. In this study, high resolution TEM (HRTEM), high voltage TEM (HVTEM), and STEM microanalysis are used to characterize tha ultrastructural and microchemical composition of skeletal elements of the modern crinoid Neocrinus blakei.

Microstructural Characterization of Au-Ge-Ni based ohmic contacts to GaAs/AlGaAs modfet device

1987 ◽  
Vol 45 ◽  
pp. 326-327
Author(s):  
A.K. Rai ◽  
A.K. Petford-Long ◽  
A. Ezis ◽  
D.W. Langer
Keyword(s):  
Contact Resistance ◽  
Ohmic Contact ◽  
Ohmic Contacts ◽  
Microstructural Characterization ◽  
Almost Everywhere ◽  
Spacer Layer ◽  
Good Contact ◽  
The Relationship ◽  
Lower Contact

Considerable amount of work has been done in studying the relationship between the contact resistance and the microstructure of the Au-Ge-Ni based ohmic contacts to n-GaAs. It has been found that the lower contact resistivity is due to the presence of Ge rich and Au free regions (good contact area) in contact with GaAs. Thus in order to obtain an ohmic contact with lower contact resistance one should obtain a uniformly alloyed region of good contact areas almost everywhere. This can possibly be accomplished by utilizing various alloying schemes. In this work microstructural characterization, employing TEM techniques, of the sequentially deposited Au-Ge-Ni based ohmic contact to the MODFET device is presented.The substrate used in the present work consists of 1 μm thick buffer layer of GaAs grown on a semi-insulating GaAs substrate followed by a 25 Å spacer layer of undoped AlGaAs.

Characterization of Auditory Disability and Its Relation to the Resilience

2018 ◽  
Vol 5 (2) ◽  
pp. 15
Author(s):  
Bibian Bibeca Bumbila García ◽  
Hernán Andrés Cedeño Cedeño ◽  
Tatiana Moreira Chica ◽  
Yaritza Rossana Parrales Ríos
Keyword(s):  
Social Integration ◽  
Conceptual Analysis ◽  
Disabled People ◽  
Disabled Students ◽  
Hearing Disability ◽  
Technical University ◽  
The Relationship ◽  
Made In

The objective of the work is to establish the characterization of the auditory disability and its relationship with resilience at the Technical University of Manabí. The article shows a conceptual analysis related to the inclusion and social integration of disabled students. Based on the fact that the person with disabilities grows and develops in the same way as that of people without disabilities and what usually happens is that disabled people are rejected and discriminated against based on a prefabricated and erroneous conceptualization of these people. The results associated with the application of the SV-RES test prepared by the researchers are shown (Saavedra & Villalta, 2008b). Characterization of the auditory deficit is made in the students, and the limitations that derive from it are pointed out. We analyze the particularities related to communication with students who have a hearing disability and resilience in this type of student, where some personal highlights that in this sense constitute an example of resilience. Finally, the results related to the study of the relationship between students' hearing disability and the level of resilience dimensions are shown.

The Problem of Divine Hiddenness

2018 ◽  
Author(s):  
Michael C. Rea
Keyword(s):  
Problem Of Evil ◽  
Philosophical Discussion ◽  
Detailed Characterization ◽  
The Past ◽  
Divine Hiddenness ◽  
The Problem Of Evil ◽  
The Relationship

This chapter provides a detailed characterization of the various meanings of the term “divine hiddenness,” carefully and rigorously articulates the version of the problem of divine hiddenness that has dominated contemporary philosophical discussion for the past twenty-five years, and then explains the relationship between that problem and the problem of evil.

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