A tectonic model for the emplacement of the Main Donegal Granite, NW Ireland

Abstract

The Main Donegal Granite is shown to lie in a major, late stage, NE-SW trending transcurrent sinistral shear zone in the Caledonides of NW Ireland. The zone, which is bent both laterally and upwards around the pluton, has displacements which diminish SW along its length from a maximum of approximately 20 km at the NE end of the pluton. The granite has also been deformed by this sinistral shear but it has a strain component of its own, the nature and development of which indicate that the pluton was accommodated rather than forcefully emplaced in the shear zone. Strain variations between granite and wall rock, and an early plagioclase fabric associated with the petrographic banding of the granite, suggest that intrusion and deformation were more or less synchronous (at around 400 Ma). It is suggested that unconsolidated granite in the shear zone locally created high strain rates and instability which caused the zone to bend, split lengthwise, and progressively create an internal low pressure zone into which the Main Granite was emplaced. The wide variety of emplacement styles of the other, radiometrically synchronous, plutons of the batholith can be attributed to the progressive development of the shear zone: Thorr and Fanad in tension between the zone and a complimentary structure to the N; Ardara and Toories in local compression at the shear zone termination; Rosses in tension on the outer arc of the bending zone; and Trawenagh Bay, as displaced Main Granite magma, in a similar tensional setting during the final stages of deformation.

Determination of Rock Cleavages Using AMS (Anisotropy of Magnetic Susceptibility): a Case Study on the Geochang Granite Stone, Korea

“…따라서 이들 자기엽리구조와 석재 결의 방향 성의 상관성을 규명할 수 있다면, 석재 결의 파악 및 채굴과 가공의 효율성 향상에 크게 기여할 것으로 판 단된다. 화강암에 발달하는 미세구조는 기원과 메카니즘에 따라 크게 4가지로 분류되어 왔다 (Balk, 1937;Barrire, 1981;Hutton, 1982Hutton, , 1988Abbott, 1989;Paterson et al, 1989;Vigneresse, 1990;Philpotts and Asher, 1994;Tobisch and Cruden, 1995) 한편, BW무역과 MD기업사의 자기미세구조와 석 재 결의 방향성 비교 결과는 앞서 기술한 석산의 결 과와는 뚜렷한 차이를 보인다 (Fig. 11e, f) …”

Gravity inversion, AMS and geochronological investigations of syntectonic granitic plutons in the southern part of the Variscan French Massif Central

“…Hutton 1982Hutton , 1988Castro, 1986;Clemens and Mawer 1992;D'Lemos et al 1992;McCaffrey 1992;Tikoff and Teyssier 1992;Neves andVauchez 1995, Tikoff andSaint Blanquat 1997;Crawford et al 1999;McNulty et al 2000). The collapse of mountain belts is often accommodated by ductile extensional tectonics, crustal melting and syntectonic magma emplacement (e. g. Malavieille 1993;Faure 1995;Vanderhaege and Teyssier 2001).…”

Submagmatic Fabric in the 2.6 Ga Bundelkhand Granitoid, India:Evidence from Microstructure

“…Since the pioneering work on magmatic foliations in the early part of the last century 1,2 , widespread interest was generated on the genesis of the fabric and its implications [3][4][5][6][7][8][9][10][11][12] . Foliation in granitoid rocks can be formed by magmatic flow, submagmatic flow and high-to low-temperature solid-state deformation 13 .…”

“…Foliation in granitoid rocks can be formed by magmatic flow, submagmatic flow and high-to low-temperature solid-state deformation 13 . Deformation of magma is common in syntectonic plutons and has been presented in several works 4,14,15 , where the influence of regional tectonics on the ascent and emplacement of magma, and structures generated at the magmatic or submagmatic stage have been illustrated. Magmatic foliation may result from magmatic flow, defined as deformation by displacement of magmatic melt, with consequent rigid-body rotation of suspended crystals, without sufficient interference between crystals to cause plastic deformation in them [9][10][11][12] .…”