Ductile thrusting at mid-crustal level, southwestern Grenville Province

1988 ◽  
Vol 25 (7) ◽  
pp. 1049-1059 ◽  
Author(s):  
Simon Hanmer
Keyword(s):  
Shear Zones ◽  
Wall Rock ◽  
Grenville Province ◽  
Low Viscosity ◽  
Ductile Shear Zones ◽  
Thrust Sheets ◽  
Grenvillian Orogeny ◽  
Central Gneiss Belt ◽  
Viscosity Fluid ◽  
Extensional Structures

The northwestern boundary zone of the Central Metasedimentary Belt (Grenville Province) in the Haliburton area (Ontario) is a stack of alternating tonalitic and syenitic crystalline thrust sheets, transported toward the northwest on out-of-sequence, upper amphibolite facies, ductile thrust zones during the Grenvillian Orogeny, at 1060 Ma, approximately 100 Ma after the initiation of thrusting in the underlying Central Gneiss Belt. Kinematics of the deformation are complex. Predominant northwestward thrusting was, at least partly, coeval with subordinate northeastward thrusting. Late synmetamorphic extensional shears cut both thrusts and thrust sheets. Minor late thrusting on discrete ductile shear zones postdates the extensional structures. Belts of mechanically weak pelite(?) appear to have localised the thrust sheets. Highly mobile marble behaved as a relatively low viscosity fluid during transport, able to intrude and erode more competent wall rock.

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.

A test of detailed Nd isotope mapping in the Grenville Province: delineating a duplex thrust sheet in the Kipawa–Mattawa region

2006 ◽  
Vol 43 (4) ◽  
pp. 421-432 ◽  
Author(s):  
M K Herrell ◽  
A P Dickin ◽  
W A Morris
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Data Sets ◽  
Aeromagnetic Data ◽  
Thrust Sheet ◽  
Grenville Province ◽  
Nd Isotope ◽  
Tectonic Model ◽  
Thrust Sheets ◽  
Archean Crust

Over sixty new neodymium model ages were determined on orthogneisses from the Kipawa–Mattawa region of the Grenville Province to refine previous Nd isotope mapping work in this area. The combined Nd data sets support a tectonic model involving three major thrust sheets in the Kipawa area, separated by major shear zones. The uppermost sheet is correlated with the Allochthonous Polycyclic Belt, represented in the study area by the Lac Watson nappe, along with two allochthonous klippen. These have Nd model ages < 1.8 Ga, consistent with previous work. Within the underlying Parautochthonous Belt, previous workers identified a second major shear zone, separating rocks with Archean and Proterozoic crystallization ages, respectively. These two thrust sheets also have distinct Nd isotope signatures. The lowermost sheet consists of metamorphosed but otherwise relatively pristine Archean crust with Nd model ages > 2.6 Ga, whereas the overlying sheet consists of magmatically reworked Archean parautochthon with model ages from 1.8–2.6 Ga. A residual magnetic-field map developed from aeromagnetic data was compared with the terrane boundaries determined from isotopic data. The aeromagnetic data accurately reflect the margin of relatively pristine Archean crust in the study area, but this boundary does not correspond to the Allochthon Boundary Thrust. Instead, this boundary resulted from downcutting of the basal shear zone of the allochthon. This caused décollement of the strongly reworked Archean parautochthon to generate a duplex thrust sheet that was transported northwestwards over pristine Archean crust.

Coeval migmatites and granulites, Muskoka domain, southwestern Grenville Province, Ontario

2002 ◽  
Vol 39 (2) ◽  
pp. 239-258 ◽  
Author(s):  
Hilke Timmermann ◽  
Rebecca A Jamieson ◽  
Randall R Parrish ◽  
Nicholas G Culshaw
Keyword(s):  
Granulite Facies ◽  
Amphibolite Facies ◽  
Geochronological Data ◽  
Grenville Province ◽  
Mafic Enclaves ◽  
High Grade Metamorphism ◽  
Granitoid Gneisses ◽  
Central Gneiss Belt ◽  
The Relationship ◽  
Extensional Structures

We present new field observations and petrologic and geochronological data from the Muskoka domain in the southwestern Grenville Province of Ontario in an attempt to constrain the relationship between amphibolite-facies and granulite-facies gneisses in areas of transitional metamorphic grade, and to examine their implication for tectonometamorphic models for the Grenville Province of Ontario. The predominant medium-grained amphibolite-facies migmatitic orthogneisses of the Muskoka domain contain several generations of leucosome, some of which are related to southeast-directed extensional structures. The amphibolite-facies granitoid gneisses contain numerous mafic enclaves with granulite-facies assemblages recrystallized from anhydrous precursors during Grenvillian metamorphism. Other associated granulites are characterized by their patchy occurrence and gradational contacts, similar to the charnockites in southern India. Patchy granulites, leucocratic vein networks in mafic enclaves, and crosscutting leucocratic granulite veins are interpreted to have formed as a result of local differences in reaction sequences and (or) fluid compositions. The U–Pb zircon lower intercept age of the patchy granulites overlaps with the previously determined range of 1080–1060 Ma for high-grade metamorphism in the Muskoka domain, while zircon and titanite from a crosscutting granulite vein crystallized at about 1065–1045 Ma, supporting a Grenvillian age for granulite formation. Peak metamorphic conditions of 750–850°C and 10–11.5 kbar (1 kbar = 100 MPa) were determined from the mafic enclaves, whereas the more felsic migmatites reequilibrated at somewhat lower temperatures. The high temperatures caused extensive migmatization and facilitated rheological weakening of the Muskoka domain 10–25 million years after the start of the Ottawan orogeny in the Central Gneiss Belt.

Wall-rock structure at the present contact surfaces between repeatedly deformed thrust sheets, Grenville Orogen of central Ontario, Canada

2010 ◽  
Vol 47 (6) ◽  
pp. 875-899 ◽  
Author(s):  
Walfried M. Schwerdtner ◽  
Sheng J. Lu ◽  
Jack F. Yang
Keyword(s):  
Granite Gneiss ◽  
Wall Rock ◽  
Geological Structure ◽  
Transverse Strain ◽  
Rock Structure ◽  
Thrust Sheets ◽  
Transverse Gradient ◽  
Central Gneiss Belt ◽  
In Situ Deformation

In the Central Gneiss Belt of the Grenville Orogen (Ontario), ca. 1020 Ma, extensional shearing, disharmonic buckle folding, and seismic faulting at middle to upper crustal levels affected the geological structure of pre-1040 Ma, ductile-thrust sheets. Because much of the repeated in situ deformation was mechanically discontinuous, the present contacts between thrust sheets may not coincide at all localities with the original thrust surfaces. We focused special attention on the basal contact of the Parry Sound domain, whose synformal structure may have resulted from gravitational subsidence of its dense rocks immediately after ductile thrusting. East of Wahwashkesh Lake, a transverse gradient of total strain is absent on horizontal scales of 100–1000 m in lithologically uniform granite gneiss comprising the uppermost western footwall of the northern Parry Sound domain. This contrasts with the steep transverse-strain gradients documented by others, on the same scale, in the wall rocks of Phanerozoic ductile thrusts. We hypothesize that ductile or brittle extension faulting may have removed a 10–20 km long sole-thrust segment at the western flank of the northern Parry Sound domain, together with severely strained rocks of the original uppermost footwall, from the level of the current erosion surface. Within the Parry Sound domain, by contrast, most if not all of the original footwall of the 1160 Ma Mill Lake thrust seems to be preserved at the presently exposed contact surface between the allochthonous basal and interior Parry Sound assemblages.

Structure of the Lac Nominingue – Mont-Laurier region, Central Metasedimentary Belt, Quebec Grenville Province

2001 ◽  
Vol 38 (5) ◽  
pp. 787-802
Author(s):  
L B Harris ◽  
B Rivard ◽  
L Corriveau
Keyword(s):  
Regional Scale ◽  
Shear Zones ◽  
Granulite Facies ◽  
Crustal Thickening ◽  
Gneiss Dome ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Ductile Shear Zones ◽  
Ductile Shear ◽  
East West

The Lac Nominingue – Mont-Laurier region of the Central Metasedimentary Belt, Grenville Province of Quebec, comprises the granulite-facies Bondy gneiss complex (core of the Bondy gneiss dome) and overlying Sourd group metasedimentary rocks. A metamorphic foliation – transposed compositional layering (S1; host to peak-pressure parageneses) has been folded by isoclinal folds (F2 and F3) crosscut by leucosomes that host peak-temperature assemblages. The orthopyroxene isograd cuts obliquely across F3 folds, indicating that 1.20–1.18 Ga granulite-facies metamorphism post-dated D3. D3 structures are cut by ductile shear zones and boudinaged in D4 and are folded by regional-scale, open, upright north–south folds (F5). Folds with shallowly dipping axial surfaces (F6) are subsequently developed in the Sourd group. F5 (and probably F6) developed prior to intrusion of the ca. 1165 Ma Chevreuil suite. In the Nominingue–Chénéville deformation zone (NCDZ) east of the Bondy gneiss dome, Chevreuil intrusions contain north-striking magmatic and tectonic foliations. These, along with host gneisses and metasedimentary rocks, are displaced by conjugate ductile shear zones (northeast dextral and south-southeast sinistral) and north-northeast-striking thrusts. Late open folds (F8) with east-northeast-striking axial surfaces produce dome and basin interference patterns. F2 to F5 folds may have formed during either subhorizontal, east–west contraction or east–west extension resulting from orogenic collapse or convective lithospheric thinning following crustal thickening during terrane assembly in the Elzevirian orogeny. Structures in the NCDZ imply ESE–WNW contraction and NNE–SSW (orogen-parallel) extension in D7 syn- to post-intrusion of the Chevreuil suite. F8 folds imply a late, Grenvillian SSE–NNW contraction.

Timing and duration of melting in the mid orogenic crust: Constraints from U–Pb (SHRIMP) data, Muskoka and Shawanaga domains, Grenville Province, Ontario

2004 ◽  
Vol 41 (11) ◽  
pp. 1339-1365 ◽  
Author(s):  
Trond Slagstad ◽  
Michael A Hamilton ◽  
Rebecca A Jamieson ◽  
Nicholas G Culshaw
Keyword(s):  
High Grade ◽  
Field Observations ◽  
Ion Microprobe ◽  
Melt Crystallization ◽  
Geochronological Data ◽  
Grenville Province ◽  
Deformational History ◽  
High Grade Metamorphism ◽  
Grenvillian Orogeny ◽  
Central Gneiss Belt

The Central Gneiss Belt in the Grenville Province, Ontario, exposes metaplutonic rocks, orthogneisses, and minor paragneisses that were deformed and metamorphosed at crustal depths of 20–35 km during the Mesoproterozoic Grenvillian orogeny. We present sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon data from eight samples of migmatitic orthogneiss, granite, and pegmatite from the Muskoka and Shawanaga domains that constrain the age and duration of partial melting in the mid orogenic crust. Our results support earlier interpretations that the protoliths to these migmatitic orthogneisses formed at ca. 1450 Ma. Emplacement and crystallization of granite and pegmatite in the Shawanaga domain took place at ca. 1089 Ma, apparently coevally with deformation and high-grade metamorphism. Leucosomes in the Muskoka and Shawanaga domains yield ages of 1067 and 1047 Ma, respectively, interpreted as the ages of melt crystallization. The geochronological data and field observations suggest that melt was present at the mid-crustal level of the Grenville orogen during a significant part of its deformational history, probably at least 20–30 million years. By analogy with modern orogens, the amount and duration of melting observed in the Muskoka and Shawanaga domains may have had an impact on the orogenic evolution of the area.

The timescale of the aseismic to seismic deformation in a cooling pluton: 40Ar-39Ar ages of the solid-state deformation in the Adamello (Southern Italian Alps)

2021 ◽  
Author(s):  
Silvia Mittempergher ◽  
Stefano Zanchetta ◽  
Federico Caldiroli ◽  
Andrea Bistacchi ◽  
Andrea Zanchi ◽  
...  
Keyword(s):  
Thermal Anomaly ◽  
Shear Zones ◽  
Wall Rock ◽  
Deformation Phase ◽  
Ductile Shear Zones ◽  
Ductile Shearing ◽  
Two Samples ◽  
Ductile Shear ◽  
Magma Pulses ◽  
Absolute Age

&lt;p&gt;The northern Adamello is crosscut by ductile shear zones and pseudotachylyte-bearing faults, both compatible with the same stress field, with ductile shear zones crosscut by brittle faults. These relations are coherent with the re-equilibration of the pluton-related thermal anomaly to temperatures typical of the base of the seismogenic continental crust (T = 250 &amp;#8211; 300&amp;#176;). Our new &lt;sup&gt;40&lt;/sup&gt;Ar-&lt;sup&gt;39&lt;/sup&gt;Ar ages help to constrain the absolute age and duration of each deformation phase.&lt;/p&gt;&lt;p&gt;Samples included wall-rock biotite, bulk ultramylonites and pseudotchylytes. Before stepwise heating &lt;sup&gt;40&lt;/sup&gt;Ar-&lt;sup&gt;39&lt;/sup&gt;Ar measurements, samples were characterized by microstructural, geochemical and petrological analyses.&lt;/p&gt;&lt;p&gt;The wall-rock biotite is 33.4&amp;#177;0.1 Ma old, independently of grainsize. Mylonites feature complex age spectra between 28-31 Ma, including biotite and altered feldspar. Four pseudotachylyte matrices are clustered around 30-31.5 Ma, and two samples have 25-26 Ma ages.&lt;/p&gt;&lt;p&gt;Ductile shearing active 2 Ma after wall-rock emplacement indicates either low strain rates, or a long-lasting thermal anomaly, which might be due to high emplacement depth, and/or the progressive assemblage of adjacent plutons through small magma pulses. Seismogenic faulting overlaps with mylonitization around 31 Ma; younger pseudotachylyte ages may be due to late-stage reactivation.&lt;/p&gt;

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