Non‐axial planar cleavage and Caledonian sinistral transpression in eastern Ireland

Murphy, F. C.

doi:10.1002/gj.3350200307

Cited by 48 publications

(1 citation statement)

References 25 publications

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“…Subsidence and sedimentation in southeast Ireland continued through Ordovician time (Briick ef al. 1979), so the D2 and D3 events in the Bray and Ribband Groups of Co. Wexford probably represent the early Devonian (Acadian) deformation which is widely recognized elsewhere in the British paratectonic Caledonides, and which involved sinistral transpression (Soper and Hutton, 1984;Murphy 1985;Soper et al 1987).…”

Section: Conclusion and Discussionmentioning

confidence: 98%

Reappraisal of the ‘Cullenstown Formation’: Implications for the Lower Palaeozoic tectonic history of SE Ireland

1989

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The structurally attenuated greenschist facies metasedimentary succession at Cullenstown Strand in south Co. Wexford comprises three formations which in stratigraphic order are ( I ) the Quartzite Formation, (2) the GreywackeiQuartzite Formation, and (3) the Greywacke Formation. The entire sequence is inverted and lies within the lower limb of a large scale overturned D I anticlinal structure that closes towards the southeast. The three formations are lithologically and sedimentologically similar to the Shelmaliere Quartzite, the Cullentra Greywacke, and Newtown Greywacke Formations of the Bray Group in the Forth Mountain -Ferrycarrig area that probably lie on the normal limb of the DI structure. The Cullenstown strata are therefore considered to be part of the Bray Group in southeast Leinster, and hence Cambrian in age.The rocks were affected by three major phases of deformation. DI produced an overturned anticline containing an important tectonic slide. The DI structures are modified by upright D2 and D3 structures. but from regional considerations it is argued that DI is restricted to strata of Cambrian to Lower Ordovician age in southeast Leinster.A model for the tectonic evolution of the southeastern part of the Leinster Basin during Cambro-Ordovician times is presented and discussed. In this model, the southeast margin of the Leinster Basin was delineated by a mylonite zone along the northwest margin of the Precambrian Rosslare Complex. Bray and Ribband Group sediments close to the margin were deformed during the Llanvirn as aconsequence of basin inversion which caused shortening and thrusting of the basin fill across the Rosslare block. The DI compressional structures were subsequently modified during a period of extension, marked by the resumption of sedimentation and outbreak of voluminous volcanicity near the basin margin during the Llandeilo and Caradoc. The D2 and D3 structures in the Bray and Ribband Groups are an expression of later Caledonian deformation.

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Section: Conclusion and Discussionmentioning

confidence: 98%

Reappraisal of the ‘Cullenstown Formation’: Implications for the Lower Palaeozoic tectonic history of SE Ireland

1989

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Late Caledonian dyke‐swarms in Southern Scotland: New field, petrological and geochemical data for the Wigtown Peninsula, Galloway

1986

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Several hundred, dominantly NE-trending dykes invade Silurian flysch sediments of the Wigtown Peninsula. The most basic dykes are K-rich biotite-lamprophyres, hornblende-lamprophyres and appinites ('diorites' of previous maps). More acidic (qz and cm normative) dykes include restricted andesitic compositions ('porphyritcs', c. 57 per cent SiO,) and a continuum from dacitic to rhyolitic compositions ('acid porphyrites' and 'porphyries', c. 63-71 per cent SiO,). The relative abundance of basic to intermediate -k acidic dykes, based on examination of 180 thin sections and 70 new whole-rock analyses, is approximately 7 : 1. The biotite-and hornblende-lamprophyres are distinct in chemistry and distribution, biotite-lamprophyres being confined to the south of the Peninsula. Neither type has any compositional equivalent among the plutonic rocks of the area. Porphyrite and porphyry dykes do not represent simple lamprophyre fractionates, but may be derived from at least two (intermediate and acidic) parent magmas, which may represent crustally-contaminated lamprophyre or entirely separate crustal melts. Emplacement of all dyke compositions was apparently episodic through Wenlock to early Devonian times (c. . Early dykes post-date the main deformation (D,) but predate minor (D,) folding, both D, and D, being related to thrusting. On the current accretionary model for the Southern Uplands, this implies that dyke emplacement commenced before the end of accretion in a compressional tectonic regime-scarcely consistent with the moderate (up to 6 per cent) crustal extension represented by the dykes. The geochemistry of the lamprophyres requires a deep mantle origin several hundred kilometres behind any subduction zone. This suggests that the 'Iapetus suture', at the time of dyke emplacement, was much farther south than its currently inferred position and places the Southern Uplands in a back-arc situation.

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The structure of the Llangranog Lineament, West Wales: A Caledonian transpression zone

Craig¹

1987

Geol. J.

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The Llangranog Lineament is an important NE to NNE-trending zone of oblique-slip deformation in west Wales.Inland from Aberystwyth the lineament is represented by major NNE-striking faults on the west flank of the Machynlleth inlier and by an important NNE-trending vergence divide, the Glandyfi tract, which separates E-verging structures in most of mid Wales and W-verging structures on the coast of Cardigan Bay. A similar vergence divide, the Sarnau divide, marks the southward continuation of the lineament towards Cardigan.In southwest Ceredigion the lineament coincides with a belt of major NE-striking, oblique-slip faults which dip inwards beneath the Sarnau vergence divide. The lineament forms a distinctive structural zone in which the folds verge outwards from the vergence divide and are transected by the regional cleavage. The geometry, orientation, and relationships of the structures in this zone are indicative of deformation involving both compression and transcurrent shear. Restored sections across the Llangranog Lineament show a positive flower structure which has been disrupted by post-Caledonian extension.The structures developed along the Llangranog Lineament suggest that it is the surface expression of a deep basement fault with a significant strike-slip displacement.

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Non‐axial planar cleavage and Caledonian sinistral transpression in eastern Ireland

Cited by 48 publications

References 25 publications

Reappraisal of the ‘Cullenstown Formation’: Implications for the Lower Palaeozoic tectonic history of SE Ireland

Reappraisal of the ‘Cullenstown Formation’: Implications for the Lower Palaeozoic tectonic history of SE Ireland

Late Caledonian dyke‐swarms in Southern Scotland: New field, petrological and geochemical data for the Wigtown Peninsula, Galloway

The structure of the Llangranog Lineament, West Wales: A Caledonian transpression zone

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