Pre-Grenvillian evolution and Grenvillian overprinting of the Parautochthonous Belt in Key Harbour, Ontario: U–Pb and field constraints

1994 ◽  
Vol 31 (3) ◽  
pp. 583-596 ◽  
Author(s):  
David Corrigan ◽  
Nicholas G. Culshaw ◽  
Jim K. Mortensen
Keyword(s):  
High Strain ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Grenville Orogeny ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
High Metamorphic Grade ◽  
Harbour Area ◽  
East West

The Parautochthonous Belt in the region of Key Harbour, Ontario, is composed of Early Proterozoic migmatitic para- and orthogneiss and Mid-Proterozoic granitoids, which were reworked during the Grenville orogeny. Grenvillian deformation is localized into anastomosing arrays of high-strain shear zones enclosing elongate bands and lozenges of rock subjected to lower and near-coaxial strain. Crosscutting relationships preserved in the low-strain domains document two pre-Grenvillian plutonic and tectonometamorphic events, which are bracketed in age by U–Pb zircon geochronology. A 1694 Ma leucogranite intrudes, and provides a minimum age for, high metamorphic grade gneisses formed during an earlier tectonometamorphic event (D1–M1). The leucogranite was intruded by mafic dykes, deformed, and metamorphosed at uppermost amphibolite facies during D2–M2, before the emplacement of Mid-Proterozoic granitoids at ca. 1450 Ma. Following the emplacement of gabbro dykes and pods at ca. 1238 Ma, the area was overprinted by granulite to uppermost amphibolite facies metamorphism (Grenvillian), for which monazites provide a minimum age of ca. 1035 Ma. Titanite U–Pb ages of 1003 – 1004 Ma record cooling through 600 °C. A regionally important swarm of east–west-trending posttectonic pegmatite dykes dated by U–Pb zircon at 990 Ma provides a minimum age for Grenvillian ductile deformation. The present data support the contention that the Parautochthonous Belt in the Key Harbour area consists in part of reworked midcontinental crust of Early to Mid-Proterozoic age.

scholarly journals Mid amphibolite facies metamorphism of harzburgites in the Neoproterozoic Cerro Mantiqueiras Ophiolite, southernmost Brazil

2003 ◽  
Vol 75 (1) ◽  
pp. 109-128 ◽  
Author(s):  
LÉO A. HARTMANN ◽  
FARID CHEMALE-JÚNIOR
Keyword(s):  
Mineral Assemblage ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Metamorphic Event ◽  
Mineral Equilibria ◽  
Facies Metamorphism ◽  
Geological Evolution ◽  
Mineral Compositions

Valuable information is retrieved from the integrated investigation of the field relationships, microstructure and mineral compositions of harzburgites from the Neoproterozoic Cerro Mantiqueiras Ophiolite. This important tectonic marker of the geological evolution of southernmost Brazilian Shield was thoroughly serpentinized during progressive metamorphism, because the oldest mineral assemblage is: olivine + orthopyroxene + tremolite + chlorite + chromite. This M1 was stabilized in mid amphibolite facies - 550-600ºC as calculated from mineral equilibria. No microstructural (e.g. ductile deformation of olivine or chromite) or compositional (e.g. mantle spinel) remnant of mantle history was identified. A metamorphic event M2 occurred in the low amphibolite facies along 100 m-wide shear zones, followed by intense serpentinization (M3) and narrow 1-3 m-wide shear zones (M4) containing asbestos.

Penetrative ductile deformation and amphibolite-facies metamorphism prior to 1851Ma in the western part of the Svecofennian orogen, Fennoscandian Shield

2007 ◽  
Vol 153 (1-2) ◽  
pp. 29-45 ◽  
Author(s):  
Tobias Hermansson ◽  
Michael B. Stephens ◽  
Fernando Corfu ◽  
Jenny Andersson ◽  
Laurence Page
Keyword(s):  
Fennoscandian Shield ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Facies Metamorphism

scholarly journals Compressional and extensional tectonics in low-medium pressure granulites from the Larsemann Hills, East Antarctica

1995 ◽  
Vol 132 (2) ◽  
pp. 151-170 ◽  
Author(s):  
C. J. Carson ◽  
P. G. H. M. Dirks ◽  
M. Hand ◽  
J. P. Sims ◽  
C. J. L. Wilson
Keyword(s):  
High Strain ◽  
Shear Bands ◽  
Shear Zones ◽  
The South ◽  
Medium Pressure ◽  
Larsemann Hills ◽  
The North ◽  
Shear Sense ◽  
Low Pressures ◽  
East West

AbstractMeta-sediments in the Larsemann Hills that preserve a coherent stratigraphy, form a cover sequence deposited upon basement of mafic–felsic granulite. Their outcrop pattern defines a 10 kilometre wide east–west trending synclinal trough structure in which basement–cover contacts differ in the north and the south, suggesting tectonic interleaving during a prograde, D1 thickening event. Subsequent conditions reached low-medium pressure granulite grade, and structures can be divided into two groups, D2 and D3, each defined by a unique lineation direction and shear sense. D2 structures which are associated with the dominant gneissic foliation in much of the Larsemann Hills, contain a moderately east-plunging lineation indicative of west-directed thrusting. D2 comprises a colinear fold sequence that evolved from early intrafolial folds to late upright folds. D3 structures are associated with a high-strain zone, to the south of the Larsemann Hills, where S3 is the dominant gneissic layering and folds sequences resemble D2 folding. Outside the D3 high-strain zone occurs a low-strain D3 window, preserving low-strain D3 structures (minor shear bands and upright folds) that partly re-orient D2 structures. All structures are truncated by a series of planar pegmatites and parallel D4 mylonite zones, recording extensional dextral displacements.D2 assemblages include coexisting garnet–orthopyroxene pairs recording peak conditions of ∼ 7 kbar and ∼ 780°C. Subsequent retrograde decompression textures partly evolved during both D2 and D3 when conditions of ∼ 4–5 kbar and ∼ 750°C were attained. This is followed by D4 shear zones which formed around 3 kbar and ∼ 550°C.It is tempting to combine D2–4 structures in one tectonic cycle involving prograde thrusting and thickening followed by retrograde extension and uplift. The available geochronological data, however, present a number of interpretations. For example, D2 was possibly associated with a clockwise P–T path at medium pressures around ∼ 1000 Ma, by correlation with similar structures developed in the Rauer Group, whilst D3 and D4 events occurred in response to extension and heating at low pressures at ∼ 550 Ma, associated with the emplacement of numerous granitoid bodies. Thus, decompression textures typical for the Larsemann Hills granulites maybe the combined effect of two separate events.

Ductile transpression and localization of deformation along tectonic boundaries in the Caledonides of northwestern Ireland

1998 ◽  
Vol 135 (5) ◽  
pp. 699-718 ◽  
Author(s):  
G. I. ALSOP ◽  
R. BRYSON ◽  
D. H. W. HUTTON
Keyword(s):  
Tectonic Evolution ◽  
Structural Investigation ◽  
High Strain ◽  
Ductile Deformation ◽  
Crustal Thickening ◽  
Regional Deformation ◽  
Facies Metamorphism ◽  
Tectonic Framework ◽  
Heterogeneous Deformation ◽  
Tectonic Boundaries

Orogenesis is increasingly interpreted in terms of strain focusing, localization and partitioning processes. Such heterogeneous deformation is considered a consequence of the tectonic framework, with pre-existing structural and stratigraphic variability providing inherent zones of crustal weakness. Detailed structural investigation of Neoproterozoic Dalradian metasediments in the Glencolumbkille region, northwest Ireland, enables patterns of reworking and strain localization to be assessed in terms of four overprinting ductile deformation episodes. A well-defined and intricate Dalradian stratigraphy provides readily distinguishable markers which not only focus deformation along marked rheological boundaries, but also aid in the definition and identification of resultant geometries. Overall structural and stratigraphic relationships show that whilst D1 was not associated with major structures, D2 is related to north–northeast directed folding and ductile thrusting resulting in a major phase of crustal thickening and almandine-amphibolite facies metamorphism. Structures generated during D2 deformation subsequently became the locus of intense D3 strain and were reactivated in an oblique sense associated with south or southwest directed translations. Local overprinting relationships clearly demonstrate S2 fabrics being transposed by S3 resulting in a composite foliation over large areas. Similarly, the L2 mineral lineation is abruptly transposed by L3 over relatively small distances indicating high D3 strain gradients and the susceptibility of lineations to reworking. The final stage of ductile deformation (D4) which was increasingly localized and focused into earlier (D2−D3) high strain zones, is marked by a pronounced phase of sinistral transpression associated with clockwise cleavage and minor fold transection of northwest verging upright folds. Sinistral shear is strongly partitioned in to the steep limbs of mesoscopic F4 folds. The detailed investigation of structures generated within such multiply deformed and reworked zones provides evidence of both the kinematic and tectonic evolution of regional deformation systems.

Rapid fluid-driven transformation of lower continental crust associated with thrust-induced shear heating

2020 ◽  
Author(s):  
Bjørn Jamtveit ◽  
Kristina G. Dunkel ◽  
Arianne Petley-Ragan ◽  
Fernando Corfu ◽  
Dani W. Schmid
Keyword(s):  
Regional Metamorphism ◽  
Shear Zones ◽  
Amphibolite Facies ◽  
Source Rocks ◽  
Granitic Rocks ◽  
Time Interval ◽  
Fluid Infiltration ◽  
Facies Metamorphism ◽  
Shear Heating ◽  
Host Rocks

<p>Caledonian eclogite- and amphibolite-facies metamorphism of initially dry Proterozoic granulites in the Lindås Nappe of the Bergen Arcs, Western Norway, is driven by fluid infiltration along faults and shear zones. The granulites are also cut by numerous dykes and pegmatites that are spatially associated with metamorphosed host rocks. U-Pb geochronology was performed to constrain the age of fluid infiltration and metamorphism. The ages obtained demonstrate that eclogite- and amphibolite-facies metamorphism were synchronous within the uncertainties of our results and occurred within a maximum time interval of 5 Myr, with a mean age of ca. 426 Ma.  Caledonian dykes and pegmatites are granitic rocks characterised by a high Na/K-ration, low REE-abundance and positive anomalies of Eu, Ba, Pb, and Sr. The most REE-poor compositions show HREE-enrichment. Melt compositions are consistent with wet melting of plagioclase- and garnet-bearing source rocks. The most likely fluid source is dehydration of Paleozoic metapelites, located immediately below the Lindås part of the Jotun-Lindås microcontinent, during eastward thrusting over the extended margin of Baltica. Melt compositions and thermal modelling suggest that short-lived fluid-driven metamorphism of the Lindås Nappe granulites was related to shear heating at lithostatic pressures in the range 1.0-1.5 GPa. High-P (≈2 GPa) metamorphism within the Nappe was related to weakening-induced pressure perturbations, not to deep burial. Our results emphasize that both prograde and retrograde metamorphism may proceed rapidly during regional metamorphism and that their time-scales may be coupled through local production and consumption of fluids.</p>

scholarly journals Structural setting and U–Pb zircon geochronology of the Glen Scaddle Metagabbro: evidence for polyphase Scandian ductile deformation in the Caledonides of northern Scotland

2008 ◽  
Vol 145 (3) ◽  
pp. 361-371 ◽  
Author(s):  
R. A. STRACHAN ◽  
J. A. EVANS
Keyword(s):  
Regional Metamorphism ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Zircon Geochronology ◽  
Zircon Age ◽  
Structural Setting ◽  
Facies Metamorphism

AbstractWithin the Scottish Caledonides, the Glen Scaddle Metagabbro was intruded into the Moine Supergroup of the Northern Highland Terrane after Grampian D2 folding and prior to regional D3 and D4 upright folding and amphibolite-facies metamorphism. A U–Pb zircon age of 426 ± 3 Ma obtained from the metagabbro is interpreted to date emplacement. D3–D4 folding is constrained to have occurred during the Scandian orogenic event. In contrast, polyphase folding and regional metamorphism of the Dalradian Supergroup southeast of the Great Glen Fault is entirely Grampian. These differences are consistent with published tectonic models that invoke a minimum of 700 km of post-Scandian sinistral displacements across the Great Glen Fault to juxtapose the Grampian and Northern Highland terranes.

scholarly journals From static alteration to mylonitization: a nano- to micrometric study of chloritization in granitoids with implications for equilibrium and fluid percolation length scales

2021 ◽  
Author(s):  
Laura Airaghi ◽  
Benoit Dubacq ◽  
Anne Verlaguet ◽  
Franck Bourdelle ◽  
Nicolas Bellahsen ◽  
...  
Keyword(s):  
Reaction Mechanisms ◽  
High Strain ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Low Grade ◽  
Zone Formation ◽  
Crustal Rocks ◽  
Transmission Electron ◽  
Variable Element ◽  
The Matrix

<p>Strain accommodation in upper crustal rocks is often accompanied by fluid-mediated crystallization of phyllosilicates, which influence rock strength and shear zone formation. The composition of these phyllosilicates is commonly used for pressure-temperature-time constraints of deformation events, although it is often highly heterogeneous. This study investigates the reactions producing a phyllosilicate, chlorite, in and below greenschist-facies conditions and the variations in chlorite composition, along a strain gradient in the Bielsa granitoid (Axial Zone, Pyrenees). Compositional maps of chlorite (including iron speciation) are compared to nanostructures observed by transmission electron microscopy in increasingly-strained samples and related to mechanisms of fluid percolation and scales of compositional homogenisation. In the Bielsa granitoid, altered at the late Variscan, Alpine-age shear zones are found with high strain gradients. The undeformed granitoid exhibits local equilibria, pseudomorphic replacement and high compositional heterogeneities in chlorite. This is attributed to: (i) variable element supply and reaction mechanisms observed at nanoscale and (ii) little interconnected intra- and inter-grain nanoporosity causing isolation of fluid evolving in local reservoirs. In samples with discrete and mm-sized fractures, channelized fluid triggered the precipitation of homogeneous Alpine chlorite in fractures, preserving late-Variscan chlorite within the matrix. In low-grade mylonites, where brittle-ductile deformation is observed, micro-, nano-cracks and defects allows the fluid percolating into the matrix at the scale of hundreds of µm. This results in a more pervasive replacement of late-Variscan chlorite by Alpine chlorite. Local equilibria and high compositional heterogeneities in phyllosilicates as chlorite are therefore preserved according (i) matrix-fracture porosity contrasts at nanoscale and (ii) the location and interconnection of nanoporosity between crystallites of phyllosilicates that control reaction mechanisms and element mobility. In low grade mylonites, mineral and compositional replacement remains incomplete despite the high strain.</p>

P–T conditions of Grenville-age eclogite facies metamorphism and amphibolite facies retrogression of the Glenelg–Attadale Inlier, NW Scotland

2005 ◽  
Vol 142 (5) ◽  
pp. 605-615 ◽  
Author(s):  
C. D. STOREY ◽  
T. S. BREWER ◽  
S. TEMPERLEY
Keyword(s):  
Tectonic Evolution ◽  
Amphibolite Facies ◽  
Geodynamic Evolution ◽  
Broad Agreement ◽  
Grenville Orogeny ◽  
Basement Rocks ◽  
Facies Metamorphism ◽  
Uplift Rates ◽  
Peak Metamorphism ◽  
Eclogite Facies

Peak and retrograde P–T conditions of Grenville-age eclogites from the Glenelg–Attadale Inlier of the northwest Highlands of Scotland are presented. Peak conditions are estimated as c. 20 kbar and 750–780°C, in broad agreement with previous work. The eclogites subsequently followed a steep decompression path to c. 13 kbar and 650–700°C during amphibolite facies retrogression. Peak eclogite facies metamorphism occurred > 1080 Ma and retrogression at c. 995 Ma, suggesting fairly sluggish uplift rates of < 0.3 km/Ma and cooling rates of < 1.25°C/Ma, when compared with other parts of the Grenville orogeny and/or modern orogens. However, current poor constraints on the timing of peak metamorphism mean that these rates cannot be used to interpret the geodynamic evolution of this part of the orogen. The P–T–t data, together with petrology and the field relationships between the basement rocks of the Glenelg–Attadale Inlier and the overlying Moine Supergroup, mean that it is difficult to support the currently held view that an unconformable relationship exists between the two. It is suggested that more data are required in order to re-interpret the Neoproterozic tectonic evolution of the northwest Highlands of Scotland.

Dating ductile deformation using U–Pb geochronology: examples from the Gilbert River Belt, Grenville Province, Labrador, Canada

1993 ◽  
Vol 30 (7) ◽  
pp. 1458-1469 ◽  
Author(s):  
D. J. Scott ◽  
N. Machado ◽  
S. Hanmer ◽  
C. Gariépy
Keyword(s):  
Isotopic Analysis ◽  
Shear Zones ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Ductile Deformation ◽  
Grenville Province ◽  
Southern Limit ◽  
Zircon Age ◽  
Intense Deformation ◽  
Host Rocks

The Gilbert River Belt, in the Grenville Province in southeastern Labrador, is a distinctive, west–northwest-trending zone of locally intense deformation and voluminous granitoid plutonism, up to 30 km in width. In an attempt to directly quantify the timing of deformation in ductile shear zones within the belt, rocks interpreted as having been intruded synchronously with ongoing deformation were sampled for U–Pb isotopic analysis. Three of these samples are <2 m wide granitic veins that have sharp intrusive contacts that truncate ductile deformation fabrics, but are themselves deformed at metamorphic conditions similar to their host rocks and are therefore interpreted as having intruded after the initiation of deformation and fabric development, but prior to cessation of this deformation. The first vein is syntectonic with respect to amphibolite-facies deformation and yielded a zircon age of [Formula: see text]. The second vein intruded synchronously with the development of a zone of amphibolite-facies straight gneisses, which defines the southern limit of the Gilbert River belt at [Formula: see text]. The third vein is syntectonic with respect to greenschist-facies deformation and yielded a zircon age of [Formula: see text] and a monazite age of 1078 ± 2 Ma. A sample of the K-feldspar megacrystic granite that underlies much of the belt and is interpreted as having intruded during ongoing amphibolite-facies deformation yielded a zircon age of [Formula: see text]; a mildly deformed granitic vein that crosscuts the megacrystic granite at the same location contained zircon that indicate a [Formula: see text] crystallization age. Monazite from a granodioritic gneiss yielded a concordant age of 1077 ± 3 Ma, interpreted as the time of final cooling during gneiss formation. These results indicate that much of the amphibolite-facies deformation (1664 – 1644 Ma) in the Gilbert River Belt is correlative with the regionally extensive Labradorian orogenic event, whereas greenschist-facies deformation (1113 – 1062 Ma) and monazite growth (1078 Ma) are the result of renewed tectonomagmatic activity during Grenvillian orogenesis.

Deformation at an Archean subprovince boundary, northern Minnesota

1991 ◽  
Vol 28 (2) ◽  
pp. 292-307 ◽  
Author(s):  
John R. Tabor ◽  
Peter J. Hudleston
Keyword(s):  
Shear Zones ◽  
Wall Rock ◽  
Amphibolite Facies ◽  
Lower Grade ◽  
Seine River ◽  
Northern Margin ◽  
Shear Structures ◽  
The North ◽  
Dextral Shear ◽  
East West

Structural analysis in the northern margin of the Quetico subprovince (part of the Archean Superior Province of the Canadian Shield) in Minnesota reveals that the main deformation involved polyphase folding (F1 recumbent and nappe-like, and F2 upright, east–west trending, and tight to isoclinal) during regional ductile transpression and amphibolite-facies metamorphism. A younger deformation, developed during the latter stages of regional transpression, resulted in the generation of localized ultraphyllonites along the steeply dipping Rainy Lake – Seine River fault (RLSRF), the major fault separating the Quetico subprovince from the Rainy Lake wrench zone (a wedge-shaped block between the Quetico and Wabigoon subprovinces). The transpression involved north–south shortening and east–west dextral shear. The presence of shear zones in amphibolite-facies wall rock south of the fault and in lower grade ultraphyllonites within the RLSRF suggests that localization of shear occurred by work and (or) reaction softening, possibly enhanced by the influx of fluids during regional cooling. The youngest structures in the wall rock are conjugate brittle faults oriented similarly to the youngest ductile shear structures in the RLSRF, indicating that the zone of transpression widened following the stage of strain localization, possibly due to work hardening during continued regional cooling. Widening of the zone of deformation was accompanied by an increase in the relative intensity of the north–south shortening component of transpression, revealed by chloritized necks of boudinaged quartz ribbons, quartz and calcite microfabrics, and flattening strains. Protracted ductile flow and localized greenschist-facies conditions in the RLSRF, which occurred during widening of the zone of deformation and rotation of the kinematic frame (to produce north–south shortening structures), are best explained by an influx of fluid phases.Mesostructures and quartz microfabrics in late tectonic (but synkinematic) peraluminous leucogranitoid intrusions and host schist 10 km south of the RLSRF record north–south shortening, but not east–west dextral shear, and further support late north–south shortening across the RLSRF.Tectonic settings for the RLSRF include (i) a suture between distinct lithotectonic terranes or (ii) a zone of localization of deformation within the northern margin of the Quetico subprovince following collision between the Quetico and Wabigoon terranes.

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