Grade and time of metamorphism in the Caledonide Orogen of Britain and Ireland

Fettes, D. J.; Long, C. B.; Bevins, R. E.; Max, M. D.; Oliver, Graham; Primmer, T. J.; Thomas, L. J.; Yardley, B. W. D.

doi:10.1144/gsl.mem.1985.009.01.03

Cited by 26 publications

(8 citation statements)

References 79 publications

(102 reference statements)

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“…500 °C (e.g. Winchester, ; Fettes et al , ) associated with Caledonian orogenesis. The hardness has increased to R ~ 52, due to pervasive recrystallization.…”

Section: Resultsmentioning

confidence: 99%

Lateral plucking as a mechanism for elongate erosional glacial bedforms: explaining megagrooves in Britain and Canada

Krabbendam

Bradwell

2011

Earth Surf Processes Landf

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Megagrooves are kilometre-scale linear topographic lows carved in bedrock, separated by ridges, typically in areas of largely devoid of till. They have been reported from several areas covered by Pleistocene glaciations, such as Canadian NW Territories, Michigan and NW Scotland. Here we report two previously undocumented megagroove fields from Ungava, Canada, and northern England, and present new analyses of the megagrooves from NW Scotland. This paper seeks to determine the nature of the lithological and structural controls on the occurrence and formation of megagrooves. Analysis of both geomorphological and bedrock properties shows that megagrooves are generally: a) confined to well stratified or layered bedrock, such as (meta)sedimentary rocks with closely spaced joints, and tend not to occur on massive rocks such as gneiss or granite, or thick-bedded sedimentary rocks; b) subparallel to palaeo-ice flow and the strike of the strata; and tend not to occur where palaeo-ice flow is at high angles to the strike of strata; c) produced by significant glacial erosion by sustained unidirectional ice flow.Detailed analysis of megagrooves in NW Scotland shows that neither glacio-fluvial erosion, nor differential abrasion was the dominant mechanism of formation. A mechanism, here termed 'lateral plucking', is suggested that involves block plucking on rock steps parallel to ice flow. Removal of joint-bounded blocks from such rock steps involves a component of rotation along a vertical axis. Block removal may be enhanced by a direct component of shear stress onto the vertical stoss sides. The lateral plucking mechanism results in horizontal erosion at right angles to the ice flow, and enhances the groove/ridge topography. Megagrooves are potentially useful as palaeo-ice flow indicators in areas devoid of till, and can thus complement the palaeo-ice stream datasets which are presently largely based on soft-sediment landform studies.

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“…500 °C (e.g. Winchester, ; Fettes et al , ) associated with Caledonian orogenesis. The hardness has increased to R ~ 52, due to pervasive recrystallization.…”

Section: Resultsmentioning

confidence: 99%

Lateral plucking as a mechanism for elongate erosional glacial bedforms: explaining megagrooves in Britain and Canada

Krabbendam

Bradwell

2011

Earth Surf Processes Landf

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“…5A). The lack of an (Fettes et al, 1985), which might explain the apparent discrepancy between mainland Scotland (Fig. 5A) and the area nearer Shetland (Fig.…”

Section: Thin-skinned Versus Thick-skinned Deformation Regimesmentioning

confidence: 99%

Review of seismic reflector signatures of crustal deformation in the Appalachian-Caledonide orogen with reference to the Spanish Variscides and the Uralides

McBride¹,

Knapp²

2002

Variscan-Appalachian Dynamics: The Building of the Late Paleozoic Basement

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After the µrst images of the crustal structure of the southern Appalachians appeared on seismic re×ection proµles in the 1970s (Cook et al., 1979), thousands of kilometers of deep seismic data were acquired over the greater Appalachian-Caledonide-Variscan orogen on both sides ABSTRACT The availability of thousands of kilometers of deep seismic re×ection proµles from the Paleozoic orogenic belts around the North Atlantic Ocean provides an unparalleled opportunity to synthesize the contrasts and similarities of crustal deformation fabrics of compressional orogens. Dominating re×ector fabrics are (1) shallow crustal sequences of subhorizontal re×ections (décollement levels) that abruptly merge with complex dipping zones (sutures or root zones), (2) broad antiformal re×ector patterns, in places underlain by a dipping planar re×ector and interpreted as asymmetric folding and shearing in the deep crust, (3) complex, subhorizontal re×ectors in the middle to lower crust that can be explained in places as intense ductile shearing related to terrane accretion and continental convergence, and (4) zones of deeply penetrating and mostly planar dipping features, interpreted as reverse-sense brittle faults or ductile shear zones. The structure of re×ectors nearer the Moho discontinuity is more complex and variable relative to planar re×ectors higher in the crust. Re×ectors that curve into the Moho seem to typify orogens where the synorogenic lowermost crust is preserved and imply that the Moho acted as a décollement. In contrast, cases where dipping planar re×ectors are abruptly cut off by a ×at Moho suggest a postorogenic process that has destroyed and reequilibrated lowermost crustal structure. Other variations between the diverse re×ector fabrics can in part be understood (and predicted) in terms of variations between thin-and thick-skinned deformation regimes, which are usually not viewed simultaneously on any one proµle or group of proµles. More recently acquired deep seismic proµles from the Spanish Variscides and the Uralides provide examples of convergent belts where most of the full crustal orogenic structure has been preserved intact. These may serve as analogs for less well preserved or evolving orogenic belts.

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“…These units were affected by Caledonian deformation and metamorphism, the peak of which occurred c.470 Ma, and were the result of a series of collisions between Iapetus crust and associated island arcs, and the Laurentian and Avalonian continents. The Grampian Orogeny (c.470 Ma), an early phase of the Caledonian Orogeny, specifically refers to the collision between an oceanic island arc and the margin of the Laurentian continent (Chew et al, 2010;Cooper et al, 2011;Fettes et al, 1985;Powell and Phillips, 1985). A suite of syn-to post-orogenic intrusions associated with the Grampian Orogeny (dating to c.475-460 Ma) are located in the north and west of Ireland, and includes the Tyrone Igneous Complex plutons and the Oughterard Granite of Connemara (Chew and Stillman, 2009).…”

Section: Lower Palaeozoicmentioning

confidence: 99%

The genesis of gold mineralisation hosted by orogenic belts: A lead isotope investigation of Irish gold deposits

et al. 2014

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Lead isotope analyses have been performed on 109 gold and 23 sulphide samples from 34 Irish gold occurrences, including 27 placers, and used to shed light on the sources of mineralising fluids and metals associated with gold mineralisation hosted by orogenic belts. The Pb isotope ratios of lode and placer gold range from 206 Pb/ 204 Pb = 17. 287-18.679, 207 Pb/ 204 and 208 Pb/ 204 Pb = 37.517-38.635, consistent with the Pb isotopic data on previously reported Irish sulphide mineralisation. There is no evidence that gold mineralisation is associated with distinctive source regions, and it appears to have been derived from similar sources to those responsible for the widespread sulphide mineralisation in Ireland. It is inferred that the principal controls on the Au mineralisation are structural and not related to the distribution of Au in their source rocks. The range of Pb isotope ratios favours the interaction of multiple source reservoirs predominantly during the Caledonian Orogeny (c.475-380 Ma). Underlying basement was the primary control on two key sources of Pb. Gold occurrences located to the south-east of the Iapetus Suture are characterised by Pb compositions that derive predominantly from the Late Proterozoic crustal basement or overlying Lower Palaeozoic sediments, whilst those located north-west of the Iapetus Suture are characterised by less radiogenic Pb signatures derived predominantly from Late Proterozoic or older crustal basement. A third source, relatively enriched in radiogenic Pb, also played a role in the formation of a number of Irish gold occurrences, and may have been associated with syn-to postorogenic intrusives. Magmatic processes may therefore have played an important role in the formation of some gold occurrences located in orogenic settings.

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Grade and time of metamorphism in the Caledonide Orogen of Britain and Ireland

Cited by 26 publications

References 79 publications

Lateral plucking as a mechanism for elongate erosional glacial bedforms: explaining megagrooves in Britain and Canada

Lateral plucking as a mechanism for elongate erosional glacial bedforms: explaining megagrooves in Britain and Canada

Review of seismic reflector signatures of crustal deformation in the Appalachian-Caledonide orogen with reference to the Spanish Variscides and the Uralides

The genesis of gold mineralisation hosted by orogenic belts: A lead isotope investigation of Irish gold deposits

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