VARIATION OF REE-HYDROTHERMAL CIRCULATION IN COMPLEX SHEAR ZONES: THE COBEQUID HIGHLANDS, NOVA SCOTIA

2014 ◽  
Vol 52 (6) ◽  
pp. 943-968 ◽  
Author(s):  
Angeliki Papoutsa ◽  
Georgia Pe-Piper
Keyword(s):  
Nova Scotia ◽  
Shear Zones ◽  
Hydrothermal Circulation ◽  
Complex Shear

The influence of dikes on auriferous shear zone development within granitoid intrusions: the Bourlamaque pluton, Val-d'Or district, Abitibi greenstone belt

1993 ◽  
Vol 30 (9) ◽  
pp. 1924-1933 ◽  
Author(s):  
Abdelhay Belkabir ◽  
François Robert ◽  
L. Vu ◽  
C. Hubert
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Slip Direction ◽  
Principal Stresses ◽  
Quartz Veins ◽  
Profound Influence ◽  
Complex Shear ◽  
Zone Development ◽  
Granitoid Intrusions ◽  
Geometry And Kinematics

Shear-zone-related gold–quartz veins in granitoid intrusions are commonly intimately associated with mafic dikes, which may have a profound influence on the localization, orientation, and kinematics of auriferous shear zones. The Bourlamaque pluton of the Val-d'Or district contains several economic auriferous shear zones, most of which follow and overprint diorite dikes. Mineralization in all deposits consists of quartz–tourmaline–pyrite veins in reverse- oblique orientation with a significant range of strike, dip, and slip direction. The geometry and kinematics of shear zone and vein array within the pluton is more complex than the simple conjugate pattern predicted for a deforming homogeneous intrusion. The stress tensor determined from the auriferous shear zones within the pluton indicates the same northerly-directed compression recorded by similar shear zones outside the pluton. This indicates that the complex shear zone and vein pattern within the pluton reflects the influence of diorite dikes, which acted as weak layers that were activated during subsequent deformation, showing the importance of layer anisotropy in auriferous shear zone development.The plunges of orebodies bear simple geometric relationships to the slip direction along a host shear zone: these are generally perpendicular to, or in some cases parallel to, the slip direction. Knowledge of the slip directions along activated dikes would therefore allow prediction of the possible plunge(s) of orebodies at early stages of exploration programs. Slip direction along an activated layer is controlled by the orientation of the layer with respect to the stress field and by the relative magnitudes of the three principal stresses. Using techniques developed for analysis of fault slip data, both parameters can be determined, provided there is a sufficient database, and slip direction can be predicted for activated layers of any orientations.

U–Pb geochronology of Late Proterozoic rocks of the eastern Cobequid Highlands, Avalon Composite Terrane, Nova Scotia

1991 ◽  
Vol 28 (4) ◽  
pp. 504-511 ◽  
Author(s):  
Ronald Doig ◽  
J. Brendan Murphy ◽  
R. Damian Nance
Keyword(s):  
Nova Scotia ◽  
Shear Zones ◽  
Low Grade ◽  
Geochronological Data ◽  
Magmatic Arc ◽  
Late Precambrian ◽  
Ductile Shear Zones ◽  
Ductile Shear ◽  
Orogenic Cycle ◽  
High Level

In the Cobequid Highlands of Nova Scotia, low-grade late Precambrian arc-related volcano-sedimentry rocks typical of the Avalon Composite Terrane overlie platformal metasedimentry rocks and are spatially associated with gneisses previously considered to be basement to both these units. U–Pb zircon dates of 580–587 Ma from an orthogneiss and an amphibolite are similar to the U–Pb zircon dates of 580–610 Ma from both syntectonic granites in ductile shear zones and high-level posttectonic plutons that intruded the Avalonian successions. Hence, the gneisses do not represent basement but are an integral part of the Avalonian orogenic cycle. The geochronological data indicate that penetrative fabrics in the gneisses, syntectonic granites, and volcano-sedimentary successions are penecontemporaneous (ca. 580–620 Ma) and not sequential, as previously interpreted. The gneisses have a metamorphic fabric (S1a), crystallized under amphibolite-facies conditions, and may represent the deeper roots of a late Precambrian magmatic arc. Fabrics within the deformed granite gneisses (S1b) are interpreted as reflecting crystallization within active ductile shear zones associated with intra-arc transtension and basin development. Fabrics in the volcano-sedimentary successions (S1c) are associated with deformation of the basin.

Acadian deformation in the shallow crust: an example from the Siluro-Devonian Arisaig Group, Avalon terrane, mainland Nova Scotia

2006 ◽  
Vol 43 (1) ◽  
pp. 71-81 ◽  
Author(s):  
James A Braid ◽  
J Brendan Murphy
Keyword(s):  
Nova Scotia ◽  
Shear Zones ◽  
Thrust Fault ◽  
Structural Features ◽  
Strike Slip ◽  
Normal Faults ◽  
Progressive Deformation ◽  
Acadian Orogeny ◽  
Shallow Crust ◽  
Dextral Strike Slip

The Silurian – Early Devonian Arisaig Group of the Avalon terrane in northern mainland Nova Scotia consists mainly of thinly bedded sandstones, siltstones, and shales deposited in a near shore environment. These strata were deformed in the middle Devonian to form regional northeast- to NNE-trending folds and record deformation processes in the shallow crust during the Acadian orogeny, one of the most regionally extensive orogenic events in the Canadian Appalachians. Structural features in the Arisaig Group are consistent with fold propagation associated with thrust fault geometry and coeval local extension recorded by a set of conjugate normal faults. Many outcrop-scale folds have sheared limbs and show evidence of a complex progressive deformation. Folding was predominantly accomplished by bulk rotation and flattening above thrust fault tips. Early structures (D1–D2) produced regional cylindrical folds, whereas later (D3a, D3b, D3c) structures produced conical folds. D1–D3 fold orientations show high variability, but are consistent with progressive deformation related to reactivation and coeval dextral strike-slip movement along the Hollow Fault. The style of deformation is compatible with models in which strain is partitioned into preexisting shear zones in the basement, with folds in the overlying Arisaig Group initiated above the tips of upward-propagating thrusts as second-order structures related to movement along those shear zones. Taken together, these data indicate that fold mechanisms and geometry in the shallow crust during the Acadian orogeny in mainland Nova Scotia may be related to dextral strike-slip along major faults in the basement and co-genetic upward-propagating thrusts that rotated and flattened overlying strata.

U–Pb and Rb–Sr geochronology of the Wedgeport granitoid pluton, southwestern Nova Scotia

1988 ◽  
Vol 25 (2) ◽  
pp. 255-261 ◽  
Author(s):  
R. F. Cormier ◽  
J. D. Keppie ◽  
A. L. Odom
Keyword(s):  
Nova Scotia ◽  
Shear Zone ◽  
Large Scale ◽  
Shear Zones ◽  
Potassium Feldspar ◽  
Slow Cooling ◽  
Northwestern Margin ◽  
Meguma Terrane ◽  
Tin Deposit ◽  
Straight Lines

Zircons from biotite monzogranite of the Wedgeport Pluton, intrusive into deformed metasediments of the Cambrian(?) Goldenville Formation in the southwestern Meguma Terrane of Nova Scotia, yield concordant U–Pb ages of 316 ± 5 Ma. This is interpreted as the time of intrusion and crystallization. Within the error limits, the 323 ± 12 Ma Rb–Sr whole-rock isochron age is identical and gives an initial 87Sr/86Sr ratio of 0.7137 ± 0.0056. Rb–Sr analyses of mineral separates of biotite, potassium feldspar, and quartz–plagioclase from several samples yield subparallel, internal isochrons with an average age of 257 ± 8 Ma. Initial ratios of the internal isochrons range from 0.716 to 0.759. A slow-cooling model for these latter data is discarded because the mineral data fall on straight lines. Instead, a reheating event related to plutonism ca. 257 Ma ago, which was sufficient to cause local grain-to-grain migration and reequilibration of strontium and rubidium but not large-scale redistribution, is invoked. This reheating is also inferred to be responsible for the hydrothermal alteration and Sn–U mineralization concentrated along the northwestern margin of the pluton. A dextral northeast–southeast shear zone cutting the pluton is also inferred to be ca. 257 Ma old. It may be related to the last stages of westward obduction of the Meguma Terrane.These results provide a clear example of Permo-Carboniferous plutonism in the southwestern Meguma Terrane and suggest a similar interpretation may apply to other anomalously young ages recorded in this area. In light of these results, the Permo-Carboniferous age of the large East Kemptville tin deposit and its location in a dextral shear zone suggest that the association of younger plutonism and shear zones may be a significant factor for economic mineralization.

Alleghanian reactivation of the Acadian fold belt, Meguma Zone, southwest Nova Scotia

1997 ◽  
Vol 34 (6) ◽  
pp. 833-847 ◽  
Author(s):  
Nicholas Culshaw ◽  
Montserrat Liesa
Keyword(s):  
Nova Scotia ◽  
Shear Zones ◽  
Fold Belt ◽  
Geochronological Data ◽  
Basement Structures

Shear zones and northwest-verging folds define a 30 km wide belt of deformation that overprints the Acadian fold belt and telescopes isograds in the Meguma Zone in southwest Nova Scotia. The shear zones appear to form a linked system that accommodated convergence-dominated transpression of the Meguma Zone against an irregular Avalon boundary. Available geochronological data indicate a Mid-Carboniferous (Alleghanian–Variscan) age for the overprinting deformation. The Mid-Carboniferous basement reactivation in southwest Nova Scotia is likely coeval with deformation of Carboniferous strata and reactivation of basement structures (Meguma Group) in the northern Meguma Zone. Together, these Mid-Carboniferous structures may define a wide belt of Alleghanian–Variscan deformation across the northwest (cratonward) margin of the Meguma Zone.

scholarly journals Interaction between low-angle normal faults and hydrothermal circulation during Early Permian extensional tectonic in the central Southern Alps, N Italy

2021 ◽  
Author(s):  
Sofia Locchi ◽  
Stefano Zanchetta ◽  
Marilena Moroni ◽  
Andrea Zanchi
Keyword(s):  
Coming Out ◽  
Sedimentary Cover ◽  
Shear Zones ◽  
Southern Alps ◽  
Variscan Orogeny ◽  
Normal Faults ◽  
Lower Permian ◽  
Early Permian ◽  
Hydrothermal Circulation ◽  
Northern Border

<p>At the end of the Variscan orogeny, several episodes of crustal extension starting in the Early Permian occurred in central Southern Alps (cSA), affecting the Adria passive margin (Handy et al., 1999). During this period, a megashear zone with dextral kinematics led to the transition from Pangea A to Pangea B configuration (Muttoni et al., 2003). The transtensional to extensional deformation regime led to the development of intra-continental basins infilled by Upper Carboniferous to Lower Permian sedimentary successions (Cadel et al., 1996). Crustal shortening related to Alpine compression was responsible for a partial or complete inversion of favourably oriented normal faults inherited from the Permian tectonics (Blom & Passchier, 1997). Despite this, SSE-dipping Early Permian Low-Angle Normal Faults (LANFs) are well-preserved because they exceptionally escaped most of the Alpine deformations. Their surfaces are within the Lower Permian sedimentary cover, or at the interface between the sedimentary cover and the Variscan basement, passing to intra-basement shear zones.<br>Two major Permian LANFs (Aga-Vedello and Masoni faults) are recorded in the Pizzo del Diavolo Fm. along the northern border of the Permian Orobic Basin (N Italy). They are “non-Andersonian” normal faults whose surfaces are characterized by cataclastic bands usually sealed by centimetric to metric layers of dark grey to black aphanitic tourmalinites (Zanchi et al., 2019). Tourmalinites indicate fluids circulation channelled along high permeability fault zones and are related to magmatic-hydrothermal fluids that produced metasomatic tourmalines with different compositions at different distances from the fluid source, i.e. the crystallizing intrusive bodies. In addition to Aga-Vedello and Masoni faults, further exposures of Permian LANFs occur in other sectors of the cSA and they are always associated with the presence of tourmalinites. Several authors (De Capitani et al., 1999; Slack et al., 1996; Cadel et al., 1996) link the cSA tourmalinites with the U mineralization of Novazza - Vedello district but this correlation could not be so direct and clear, due to the low concentration of Uranium in tourmalinites coming out from our whole-rock analyses.<br>The main purpose of this research is to better characterize the entity and the genesis of this regional hydrothermal event and relate it to the role played by the structural setting on hydrothermal circulation in intracontinental extensional settings. Fieldwork and observations combined with microstructural and geochemical analyses of tourmalinites coming from different sectors of the cSA have been performed to reach this goal.</p><p> </p><p>Blom, J. C., & Passchier, C. W. (1997). Geologische Rundschau, 86, 627-636.<br>Cadel, G., et al. (1996). Memorie di Scienze Geologiche, 48, 1-53.<br>De Capitani, L., et al. (1999). Periodico di Mineralogia, 68, 185-212.<br>Handy, M., R., et al. (1999). Tectonics 18, 1154-1177.<br>Muttoni, G., et al. (2003). Earth Planet Science Letters, 215, 379–394.<br>Slack, J., F., et al. (1996). Schweiz. Mineral. Petrogr. Mitt., 76, 193-207.<br>Zanchi A. et al. (2019). Italian Journal of Geosciences, 138, 184-201</p>

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