Crenulation-slip development in a Caledonian shear zone in NW Ireland: evidence for a multi-stage movement history
9
Citation
38
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract In Scotland and Ireland, a Laurentian passive margin sequence, the Dalradian Supergroup, was deformed during the c. 470–460 Ma Grampian orogeny, resulting in the formation of crustal-scale recumbent nappes. In Ireland, this passive margin sequence is in general bounded to the SE by the Fair Head-Clew Bay Line (FHCBL), a segment of a major lineament within the Caledonides. Adjacent to the FHCBL, Dalradian metasediments in two separate inliers have undergone post-Grampian strike-slip movement, with the initially flat-lying Grampian nappe fabric acting as a décollement-like slip surface in both cases. As the orientation of these foliation slip surfaces was oblique to the local shear plane in both inliers, displacement along these pre-existing foliation surfaces was also accompanied by crenulation slip. However, the crenulation-slip morphologies produced imply the opposite sense of movement in the two inliers. 40 Ar- 39 Ar dating of muscovite defining the crenulation-slip surfaces indicates that post-Grampian dextral displacement took place along the FHCBL at 448 ± 3 Ma. A subsequent phase of sinistral movement along the FHCBL took place at c. 400 Ma, based on previously published Rb-Sr muscovite ages for synkinematic pegmatites. The kinematic information obtained from crenulationslip morphologies combined with geochronology can thus be used to constrain the reactivation history of a major crustal-scale shear zone.Keywords:
Crenulation
Accretionary wedge
Wedge (geometry)
Echelon formation
Shear wave splitting
Cite
Citations (2)
Mylonite
Cite
Citations (68)
Mylonite
Shearing (physics)
Metamorphic core complex
Cite
Citations (23)
Hornblende
Fractional crystallization (geology)
Rare-earth element
Trace element
Cite
Citations (17)
The Achankovil shear belt of the southern Indian Peninsular shield is prominent on Landsat images. It coincides with the boundary between charnockites of the Madurai block to the north and khondalites of the Trivandrum block to the south, and with a major change in the aeromagnetic pattern that can be traced across southern India. Field investigations reveal a major shear zone along the southwestern edge of the Achankovil shear belt, the Tenmala shear zone. Rocks in the Tenmala shear zone include charnockite, garnet‐biotite gneiss, garnet‐sillimanite gneiss, cordierite gneiss, and granite. Kinematic indicators include stretched and asymmetric garnet, feldspar and quartz porphyroclasts, shear bands, asymmetric folds, extensional and contractional composite structures, hook folds on rotated and deformed gash veins, and lineations. Kinematic analysis of these features along 60 km of the shear zone indicates primarily dextral shear, with a minor component of reverse shear. Textures, as well as mineral assemblages, are consistent with deformation under granulite facies conditions. Some overprint by the most recently formed charnockite postdates the shearing. Limited geochronologic data suggest a late Proterozoic (Pan‐African) age of shearing. Dextral shear along the Achankovil shear belt is opposite to the sinistral shear reported for the Bongolava‐Ranotsara shear zone in southerhem Magascar; hence these two shear zones cannot be correlated in reconstructions of these parts of Gondwana.
Charnockite
Mylonite
Lineation
Shearing (physics)
Sillimanite
Cite
Citations (66)
Research Article| February 01, 1988 Hercynian crustal-scale extensional shear zone in the Pyrenees Bas van den Eeckhout; Bas van den Eeckhout 1Institute for Earth Sciences, State University of Utrecht, Budapestlaan 4, 3584 CD Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Hendrik J. Zwart Hendrik J. Zwart 1Institute for Earth Sciences, State University of Utrecht, Budapestlaan 4, 3584 CD Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Author and Article Information Bas van den Eeckhout 1Institute for Earth Sciences, State University of Utrecht, Budapestlaan 4, 3584 CD Utrecht, Netherlands Hendrik J. Zwart 1Institute for Earth Sciences, State University of Utrecht, Budapestlaan 4, 3584 CD Utrecht, Netherlands Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1988) 16 (2): 135–138. https://doi.org/10.1130/0091-7613(1988)016<0135:HCSESZ>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Bas van den Eeckhout, Hendrik J. Zwart; Hercynian crustal-scale extensional shear zone in the Pyrenees. Geology 1988;; 16 (2): 135–138. doi: https://doi.org/10.1130/0091-7613(1988)016<0135:HCSESZ>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Detailed structural analysis of metasedimentary rocks and gneisses in the Hospitalet massif (Pyrenees) has revealed that upright structures in low-grade rocks are in a structurally higher position and older than gently inclined to flat-lying structures in higher grade rocks. The steep structures were (sub)vertically flattened during formation of the flat-lying structures, indicating that the higher grade rocks formed as part of a shear-zone system. A similar conclusion can be drawn from the relation between deformation and metamorphism in the higher grade rocks. We suggest that the shear zone may have accommodated crustal extension. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Cite
Citations (68)
Pegmatite
Allochthon
Massif
Mylonite
Cite
Citations (29)
The southern Menderes Massif in southwest Turkey consists mainly of orthogneisses and overlying Palaeozoic–Middle Paleocene schists and marbles. The contact between the two distinct rock types is almost everywhere structural, herein named the southern Menderes shear zone: a S-facing, high-angle ductile shear zone that separates metamorphic rocks of differing grade. Although there is a consensus that the shear zone was associated with top-to-the-S–SSW shearing and is of Tertiary age, its origin and nature have been highly debated over the last decade. Some claim the contact is a thrust fault, while others have argued for an extensional shear zone. Integration of field and microstructural data (the identification of different fabrics, associated kinematics and overprinting relationships) with fission-track thermochronology and the P – T paths of the rocks above and below the shear zone, supports the conclusion that the southern Menderes shear zone is an extensional shear zone and not a thrust. The data are consistent with a model that the exhumation and cooling of the southern Menderes Massif occurred after a period of extensional deformation. Pervasive top-to-the-N–NNE high-temperature–medium-pressure ductile shear structures (D 2 deformation) overprint an early HP event (D 1 deformation). The subsequent top-to-the-S–SSW greenschist shear band foliation (D 3 deformation) developed mostly around the orthogniess–schist contact and forms the most characteristic features of the massif. The top-to-the-N–NNE structures are attributed to the main Alpine constructional deformation that developed during back-thrusting of the Lycian nappes during the latest Palaeogene collision between the Sakarya continent and the Anatolide-Tauride platform across the Neotethyan Ocean. The top-to-the-S–SSW structures are interpreted to be the result of the exhumation of the massif during the activity of the southern Menderes shear zone. The presence of these two distinct fabrics with differing kinematics suggests that the southern Menderes shear zone operated as a top-to-the-N–NNE thrust fault during early Alpine contractional deformation but was later reactivated with an opposite sense of movement (top-to-the-S–SSW) during subsequent Oligocene–Miocene extensional collapse.
Massif
Mylonite
Greenschist
Lineation
Overprinting
Cite
Citations (58)
The Acebuches metabasites constitute a slice of oceanic crust located at the Variscan suture between the Ossa Morena and the South Portuguese zones (Iberian Massif). The emplacement of the metabasites onto the accretionary prism was associated with the activity of the southern Iberian shear zone. Careful measurements of the fabrics and structures related to this shear zone show consistent kinematic criteria pointing to the presence of a simple shear component, with an oblique predominantly left‐lateral sense of displacement. The data are consistent with existing models of triclinic or oblique shear zones considering coeval simple shear and pure shear components. These models provide a satisfactory explanation of the observed spatial variations in the foliation, lineation and fold hinge data. The kinematics of other shear deformations, older and younger than the southern Iberian shear zone, have also been established. These results offer new insights into the tectonic evolution of this suture of the Variscan belt, and show how complex transpressional strains can arise during oblique crustal deformation associated with the motions of tectonic plates.
Lineation
Massif
Accretionary wedge
Cite
Citations (41)
Diachronous
Main Central Thrust
Thermochronology
Mylonite
Closure temperature
Cite
Citations (8)