Terrane amalgamation in the Clew Bay region, west of Ireland

Johnston, Joseph; Phillips, W. E. A.

doi:10.1017/s0016756800021154

Cited by 18 publications

(31 citation statements)

References 57 publications

(78 reference statements)

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“…A Middle Cambrian-Tremadoc? These microfossil discoveries have proved highly contentious (Graham, 2001) and have been strongly rejected by Johnston & Phillips (1995) and Dewey & Mange (1999). However, Williams et al (1994) and Williams, Harkin & Higgs (1996) contend that the rocks containing the faunal elements described above are in fact mega-clasts in a mélange, the matrix of which has yielded trilete miospores interpreted to be of Silurian (Wenlock) age (Williams et al 1994;Williams, Harkin & Higgs, 1996).…”

Section: Introductionmentioning

confidence: 99%

Structural and stratigraphic relationships across the continuation of the Highland Boundary Fault in western Ireland

Chew

2003

Geol. Mag.

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The relationship between the Dalradian Supergroup and the Highland Border Complex in Scotland has remained contentious for over a century. In western Ireland, the contact between the Dalradian Supergroup and the Clew Bay Complex (a correlative of the Highland Border Complex) is superbly exposed on the island of Achill Beg on the North Mayo coast. The unfossiliferous South Achill Beg succession has been traditionally assigned to the Clew Bay Complex, and this interpretation is supported by a combination of Sm-Nd model age data, heavy mineral analysis and lithostratigraphic correlation. T DM ages range from 1.99-2.66 Ga (mean = 2.28 Ga, n = 6). Detailed structural mapping shows that both the Dalradian and the Clew Bay Complex share the same structural history. A D1 high strain event is common to both units, and is associated with the development of tectonic slides. The D2 event is responsible for the formation of crustal-scale nappes. In both units, beds are consistently downward facing on the S2 foliation. Later dextral shearing (D3) resulted in the tilting of the originally recumbent, S-facing D2 nappes into this downward-facing orientation. Rb-Sr and 40 Ar-39 Ar radiometric dating of muscovite confirms that both units were deformed contemporaneously as the S2 nappe fabric in each is dated at c. 460 Ma. This Middle Ordovician age for deformation of the Clew Bay Complex is highly significant, not least because published microfossil data suggest a Silurian age.

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Section: Introductionmentioning

confidence: 99%

Structural and stratigraphic relationships across the continuation of the Highland Boundary Fault in western Ireland

Chew

2003

Geol. Mag.

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“…This might suggest that subduction-related volcanism on the northern margin of the Irish Caledonides had effectively ceased by this time (Homerian). Also, there is no indication of any ophiolitic detritus from the geochemical or petrographic evidence, an observation confirmed by Johnston and Phillips (1995), who saw little sign of ultrabasic detritus in these rocks, which they considered to be of Lower Ordovician age.…”

Section: Discussionmentioning

confidence: 70%

Turbidites from the Clew Bay Complex, Ireland: provenance based on petrography, geochemistry and crustal residence values

et al. 1996

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“…The tectonic milieu of the western Ireland Caledonides was one of significant oblique-slip movement (Hutton 1987;Williams and Rice 1989;Johnston and Phillips 1995;Williams et al 1997). The Ordovician evolution of the South Mayo basin has been interpreted by Dewey and Shackleton (1984) and Dewey and Mange (1999) to be the result of subduction flip in the middle Ordovician (470 Ma).…”

Section: Discussionmentioning

confidence: 99%

Buried oblique‐slip faults in the Irish Caledonides

Williams

2002

Geological Journal

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Despite over a century of geological investigation, the Ordovician evolution of South Mayo, western Ireland, is still imperfectly understood. An example of this is the supposed lateral equivalence of two formations within the succession, the Rosroe and Derrylea Formations of Arenig age, exposed on opposite limbs of a major east-west syncline. These formations exhibit characteristics which suggest that they were not deposited in the same basin. Both formations contain tuff horizons. Geochemical analysis of these tuffs shows that each formation contains chemically distinct volcanic signatures suggesting deposition in separate sub-basins. Previously the Rosroe Formation on the south limb of the syncline was considered the coarse-grained proximal equivalent of the finer-grained Derrylea Formation, both being deposited in a deep-water fan environment. Previously published palaeocurrent data together with new data show the Rosroe Formation to have been derived from the northeast and therefore it cannot be the proximal equivalent of the Derrylea Formation. Additionally, the two formations show different and distinct associations of heavy mineral assemblages.It is suggested that one explanation for these data is that both formations were deposited in separate sub-basins controlled by oblique slip sinistral faults, similar in some respects to the Cenozoic basins of the Gulf of California. In the Irish case these faults would have been largely buried by later Ordovician sedimentation. Some models for the Ordovician evolution of this area postulate the presence of an initial oceanic arc situated above a southward directed subduction zone. The presence of thick proximal submarine tuffs derived from an arc environment in the Rosroe Formation suggest that at least by this time the subduction zone was in fact northward directed and outboard of the arc.

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Terrane amalgamation in the Clew Bay region, west of Ireland

Cited by 18 publications

References 57 publications

Structural and stratigraphic relationships across the continuation of the Highland Boundary Fault in western Ireland

Structural and stratigraphic relationships across the continuation of the Highland Boundary Fault in western Ireland

Turbidites from the Clew Bay Complex, Ireland: provenance based on petrography, geochemistry and crustal residence values

Buried oblique‐slip faults in the Irish Caledonides

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