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.

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.

STRUCTURAL FRAMEWORK AND BASIN EVOLUTION OF AUSTRALIA’S SOUTHERN MARGIN

2003 ◽  
Vol 43 (1) ◽  
pp. 13 ◽  
Author(s):  
J.P. Teasdale ◽  
L.L. Pryer ◽  
P.G. Stuart-Smith ◽  
K.K. Romine ◽  
M.A. Etheridge ◽  
...  
Keyword(s):  
Late Cretaceous ◽  
Structural Control ◽  
Structural Evolution ◽  
Shear Zones ◽  
Basin Evolution ◽  
Primary Control ◽  
Fold Belt ◽  
Southern Margin ◽  
Lachlan Fold Belt ◽  
Basement Structures

The structural evolution of all of the Southern Margin Basins can be explained by episodic reactivation of basement structures in respect to a specific sequence of tectonic events. Three geological provinces dominate the basement geology of the Southern Margin basins. The Eyre, Ceduna, Duntroon and Polda Basins overlie basement of the Archean to Proterozoic Gawler-Antarctic Craton. The Otway and Sorell Basins overlie basement of the Neoproterozoic-early Palaeozoic Adelaide- Kanmantoo Fold Belt. The Bass and Gippsland Basins overlie basement of the Palaeozoic Lachlan Fold Belt. The contrasting basement terranes within the three basement provinces and the structures within and between them significantly influenced the evolution and architecture of the Southern Margin basins.The present-day geometry was established during three Mesozoic extensional basin phases:Late Jurassic–Early Cretaceous NW–SE transtension forming deep rift basins to the west and linked pullapart basins and oblique graben east of the Southwest Ceduna Accommodation Zone; Early–Mid Cretaceous NE–SW extension; and Late Cretaceous NNE–SSW extension leading to continental breakup. At least three, potentially trap forming, inversion events have variably influenced the Southern Margin basins; Mid Cretaceous, Eocene, and Miocene-Recent. Volcanism occurred along the margin during the Late Cretaceous and sporadically through the Tertiary.First-order structural control on Mesozoic rifting and breakup were east–west trending basement structures of the southern Australian fracture zone. Second-order controls include:Proterozoic basement shear zones and/or terrane boundaries in the western Gawler Craton, which controlled basin evolution in the Eyre and Ceduna Subbasins; Neoproterozoic structures, which significantly influenced basin evolution in the Ceduna sub-basin; Cambro-Ordovician basement shear zones and/or terrane boundaries, which were a primary control on basin evolution in the Otway and Sorell Basins; and Palaeozoic structures in the Lachlan Fold Belt, which controlled basin evolution in the Bass and Gippsland Basins.A SEEBASE™ (Structurally Enhanced view of Economic Basement) model for the Southern Margin basins has been constructed to show basement topography. When used in combination with a rigorous interpretation of the structural evolution of the margin, it provides a foundation for basin phase and source rock distribution, hydrocarbon fluid focal points and trap type/distribution.

scholarly journals Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

2014 ◽  
Vol 86 (3) ◽  
pp. 1101-1113 ◽  
Author(s):  
FABRÍCIO A. CAXITO ◽  
ALEXANDRE UHLEIN ◽  
LUIZ F.G. MORALES ◽  
MARCOS EGYDIO-SILVA ◽  
JULIO C.D. SANGLARD ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Structural Evolution ◽  
Shear Zones ◽  
Central Compartment ◽  
Strike Slip ◽  
Fold Belt ◽  
Main Structure ◽  
The North ◽  
Brasiliano Orogeny ◽  
Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

scholarly journals Songpan Garze fold belt: New petrological and geochronological data

1970 ◽  
Vol 5 (7) ◽  
pp. 32
Author(s):  
Audrey Billerot ◽  
Julia De Sigoyer ◽  
Stéphanie Duchêne ◽  
Olivier Vanderhaeghe ◽  
Manuel Pubellier
Keyword(s):  
Fold Belt ◽  
Special Issue ◽  
Geochronological Data

DOI = 10.3126/hjs.v5i7.1239 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.32

Extension and transtension associated with strike-slip faults and its relation with aquifer potentials: a case study in Aravalli terrane (North Gujarat), India

2020 ◽  
Author(s):  
Rudra Mohan Pradhan ◽  
Tapas Kumar Biswal
Keyword(s):  
Complex Geometry ◽  
Fractured Rock ◽  
Primary Source ◽  
Structural Data ◽  
Shear Zones ◽  
Structural Features ◽  
Strike Slip ◽  
Normal Faults ◽  
Fold Belt ◽  
North Gujarat

<p>Fractured rock aquifers are one of the most difficult aquifers to characterize due to complex geometry and fracture network. In Aravalli terranes of North Gujarat, communities depend on basement rock aquifers as the primary source of water supply. The hydrogeology of these aquifers is poorly understood and the drinking/irrigation wells are frequently placed in this area with little appreciation of the fracture systems. Increasing water demand puts stress to explore groundwater from less reliable sources of basement rocks and hence, makes it vital to identify potential hydrogeological zones. Lineament studies are commonly used for targeting groundwater bearing zones in hard rock terrane and very often ignore the other important structural settings viz. extension, transtension etc. For the present study, structural data pertaining faults and fractures have been mapped through fieldwork and Electrical resistivity imaging (ERT) technique. The key objective of the study is to correlate the structural features (extensional and transtensional settings) with geophysical profiles and to find out potential hydrogeological zones from where water can be explored economically. The study area comes under the Ambaji basin of Aravalli-Delhi fold belt which is a Proterozoic fold belt running 700-800 km in NE-SW direction and situated in NW India. The Aravalli-Delhi fold belt had undergone multiple phases of deformation. In this area, three major sets of fractures are present and are oriented largely in WNW-ESE, NE-SW, and NW-SE direction. The WNW-ESE fracture is dextral in nature which has interpreted from the displacement of fold limbs. Further, these are right lateral en-echelon normal faults where NE-SW extension has been taken place. There is another set of fracture i.e. NW-SE which is due to stretching of strike-slip fault. The ductile shear zones in the area are also parallel to the NW-SE fracture set. The shear zones are opened-up due to extension and formed potential aquifers. ERT has been carried out along and across the fractures to understand the subsurface fracture geometry. The ERT shows deep sited fractures and low resistivity values at the cross-section of WNW-ESE faults with the shear zone. This concludes a strong correlation between different structural settings with potential aquifers which could be used for pumping as well as artificial recharge sites for long term sustainability.</p><p><strong>Keywords-</strong> Aravalli terrane, Aquifer, Extension, Fracture, ERT</p>

Potassium-argon age studies in West Greenland

1968 ◽  
Vol 5 (3) ◽  
pp. 683-691 ◽  
Author(s):  
Ole Larsen ◽  
Jørgen Møller
Keyword(s):  
Central Region ◽  
Shear Zones ◽  
Fold Belt ◽  
West Greenland ◽  
Basement Rocks ◽  
Igneous Activity ◽  
Basement Gneiss ◽  
Age Studies ◽  
North And South ◽  
Age Determinations

Geochronological units have been established in West Greenland partly on the basis of 34 new K–Ar age determinations, of which 32 were made on biotites.The central part of West Greenland belongs to a single basement gneiss unit more than 2700 m.y. old. Blocks of basement rocks are traversed by rectilinear shear zones tens of kilometers long and several kilometers wide. In these tectonic belts relic slices of supracrustal rocks occur within reworked basement gneisses. The latter give K–Ar ages of 2500–2700 m.y. Ages close to 1800 m.y. are found locally. North and south of the central region of old basement younger orogenic rocks are found: the Nagssutôqidian fold belt in northern West Greenland dated at approximately 1700 to 1750 m.y. and the Ketilidian fold belt in South Greenland of which the late- to post-kinematic granites are about 1500 to 1600 m.y. old. The Gardar non-orogenic igneous activity, 1000 to 1300 m.y., is found only in South Greenland.

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.

scholarly journals Structural framework of rocks of the Lagoa D'anta mine area, iron-manganese Urandi-Caetité-Licínio de Almeida District, Bahia, Brasil

2015 ◽  
Vol 45 (2) ◽  
pp. 173-192 ◽  
Author(s):  
Jofre de Oliveira Borges ◽  
Simone Cerqueira Pereira Cruz ◽  
Johildo Salomão Figueiredo Barbosa ◽  
Edmar da Silva Santos
Keyword(s):  
Meteoric Water ◽  
Shear Zones ◽  
Fold Belt ◽  
Structural Framework ◽  
Iron Mine ◽  
Main Circulation ◽  
Host Rocks ◽  
Iron Manganese ◽  
Araçuaí Orogen ◽  
Western Portion

<p>The Urandi-Caetité-Licínio de Almeida Iron-Manganese District encompasses a total of 35 manganese mines, most of which are already exhausted, and 1 currently active iron mine. The host rocks of these ores are associated with the Paleoproterozoic Caetité-Licínio de Almeida Metavolcanossedimentary Sequence. These units have been deformed by the northern Serra do Espinhaço Thrust and Fold Belt, in the northern section of the Araçuaí Orogen. Interbeddings of itabirite, cummingtonite schist, calcite and manganese-dolomitic marbles, calc-silicate and carbonate-silicate rocks, and amphibolitic metabasalt were found at the Lagoa D'anta mine, in addition to quartz-jacobsite schist, residual manganese-rich soil and manganese lateritic breccia. The main structural framework presents a general NE-SW trend and it consists predominantly of compressional structures. This structural framework is associated with the evolution of two Ediacaran dextral transpressional shear zones, the Carrapato zone, in the western portion, and São Timóteo zone, in the eastern portion. The structural framework of the Lagoa D'anta mine reflects a higher degree of shortening in the southern sector of the northern Serra do Espinhaço Thrust and Fold Belt, in the northern area of the Araçuaí Orogen. The ductile structures related to these deformational phases were nucleated under conditions of progressive metamorphism with minimum temperature of 550°C. Stockwork structures of quartz, calcite, epidote, grunerite and magnetite truncate the mine's ductile structures. Fractures were the main circulation channels for meteoric water, which culminated in the formation of a high-content supergene ore in the mine.</p>

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