Timing of Barrovian metamorphism and ‘Older Granite’ emplacement in relation to Dalradian deformation

Robertson, Steve

doi:10.1144/gsjgs.151.1.0005

Cited by 21 publications

(9 citation statements)

References 17 publications

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“…The Grampian orogenic episode comprised three broad phases of tectonism, manifest as earlyorogenic large-scale folds, middle-orogenic large-scale top-tothe-SE shear-related deformation and late-orogenic large-scale folds (see Harris et al 1976;Krabbendam et al 1997). The Barrovian metamorphism developed during the middle-orogenic top-to-the-SE shearing tectonic phase, but in the higher-grade zones also overlapped with the earliest stages of late folding (see Harte & Johnson 1969;Robertson 1994). Large-scale mafic magmatism was coeval with regional metamorphism, during the middle-orogenic top-to-the-SE deformation phase (Viete et al 2010).…”

mentioning

confidence: 99%

The nature and origin of the Barrovian metamorphism, Scotland: ⁴⁰ Ar/ ³⁹ Ar apparent age patterns and the duration of metamorphism in the biotite zone

Viete

Forster

Lister

2011

JGS

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A geochronological traverse across the Barrovian metamorphic series, Scotland, shows 40 Ar/ 39 Ar apparent age spectra that reflect the influence of progressive metamorphism during the Grampian orogenic episode. The lowest-grade units of the Barrovian metamorphic series retain pre-Grampian detrital ages as components of their white mica 40 Ar/ 39 Ar apparent age spectra. These relict ages are progressively obliterated in the direction of increasing metamorphic grade, with a Grampian-age 40 Ar/ 39 Ar step-heating plateau first occurring in the biotite zone. The microstructure at this point shows only limited recrystallization, suggesting loss of argon mainly by diffusion. Forward modelling of argon diffusion from white mica grains was therefore carried out, for various thermal histories and grain sizes, to match 40 Ar/ 39 Ar step-heating apparent age spectra patterns preserved within the biotite zone of the Barrovian metamorphic series. The results imply a thermal duration of between 1 and 10 Ma for Barrovian metamorphism in the biotite zone. Such short time scales for metamorphism place a limit on length scales for the heat sources responsible. Mid-crustal extensional ductile shear zones that crop out in the NE of the Grampian Terrane once focused narrow, Grampian-age heat sources (e.g. magmas, hot fluids, shear heating) that drove a brief thermal episode, resulting in the Barrovian metamorphism. Supplementary material: 40 Ar/ 39 Ar data tables and plots, including (1) data from analyses on flux monitors and plots used for J -factor determination, and (2) data from analyses on unknowns and 40 Ar/ 39 Ar step-heating spectra and inverse isochron plots for each unknown, are available at http://www.geolsoc.org.uk/SUP18442 .

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confidence: 99%

The nature and origin of the Barrovian metamorphism, Scotland: ⁴⁰ Ar/ ³⁹ Ar apparent age patterns and the duration of metamorphism in the biotite zone

Viete

Forster

Lister

2011

JGS

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“…Metamorphic evidence from the Fetteresso Forest area indicates that regional metamorphism which resulted in the development of the Barrovian and Stonehavian metamorphic zones, similar to the progressive D 2 -D 3 tectonothermal event recognised by Robertson (1994).…”

Section: Discussionmentioning

confidence: 77%

“…Elsewhere within the Southern Highlands peak metamorphism accompanied or slightly post-dated D2, and may locally have overlapped with D3 (Harte et al 1984;Dempster and Harte 1986;Robertson 1994). Metamorphic evidence from the Glen Clova area was used by Robertson (1994) to suggest that regional metamorphism resulting in the development of the classical Barrovian metamorphic zones is the product of a progressive D2-D3 tectonothermal event.…”

Section: Tectono-thermal History Of the Southern Highland Group Rocksmentioning

confidence: 99%

“…Metamorphic evidence from the Glen Clova area was used by Robertson (1994) to suggest that regional metamorphism resulting in the development of the classical Barrovian metamorphic zones is the product of a progressive D2-D3 tectonothermal event. D3 structures are not recognized in the Fetteresso Forest area, attesting to the variable nature of this event (Nell and Treagus 1994).…”

Section: Tectono-thermal History Of the Southern Highland Group Rocksmentioning

confidence: 99%

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Ductile fault rocks and metamorphic zonation in the Dalradian of the Highland Border SW of Stonehaven, Kincardineshire

Phillips¹,

Auton²

1997

SJG

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SynopsisHigh strain zones, characterized by shear fabrics and mylonites, have been identified within lower amphibolite-grade, coarse granular metasandstones of the Glen Lethnot Grit Formation of the Southern Highland Group (Dalradian) along the Highland Border, south-west of Stonehaven. The rocks comprise part of a polydeformed, regionally metamorphosed, Neoproterozoic sequence, bounded to the north by the post-orogenic Mount Battock Granite (Late Caledonian) and to the south-east by the Highland Boundary Fault Zone. Early regional Dl and D2 structures have been rotated by a major monoform, the Highland Border Downbend (D4), to produce a steeply dipping, downward facing succession. The mylonitic metasandstones contain a variety of kinematic indicators, including asymmetrical pressure shadows, S-C fabrics, shear bands and an extensional crenulation cleavage, which yield a sense of shear of top-towards-the SE (present structural position). Regional syn-to post-D2 metamorphism resulted in the development of prograde pelitic mineral assemblages which overgrow earlier Dl structures. Mylonitic fabrics within the high strain zones, developed during D2, both deform and are also overgrown by syn-to post-kinematic biotite porphyroblasts. The high strain zones may represent part of a major ductile structure active during the Dalradian D2-D3 tectonothermal event, which contributed to the development of strong metamorphic gradients and narrowing of mineral assemblage zones within the Highland Border. Introduction and geological setting

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“…This D4 phase of deformation was broadly coeval with uplift of the orogenic belt. Prograde regional metamorphism accompanied or slightly postdated D2, and may locally have overlapped with D3 (Harte et al, 1984;Dempster and Harte, 1986;Robertson, 1994).…”

Section: The Dalradian Supergroup Of Scotland Andmentioning

confidence: 99%

Cummingtonite in the Dalradian of NE Scotland

Smith¹,

Phillips²

2002

Mineral. mag.

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The first recorded occurrence of cummingtonite in the Scottish Dalradian is described. The mineral occurs in thin layers within a psammite-semipelite sequence forming the lower part of the Easdale Subgroup in which it coexists with bytownitic plagioclase, almandine-rich garnet and quartz. Textural and mineral chemical evidence suggest that the cummingtonite developed from hornblende during amphibolite-facies regional metamorphism. The protolith to this cummingtonite-bearing rock is believed to have been a basaltic tuff, possibly alkaline in character, containing a significant proportion of sedimentary detritus. The cummingtonite-bearing rock may provide the earliest record of basic volcanism in the Dalradian of the Ballater district.

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Timing of Barrovian metamorphism and ‘Older Granite’ emplacement in relation to Dalradian deformation

Cited by 21 publications

References 17 publications

The nature and origin of the Barrovian metamorphism, Scotland: ⁴⁰ Ar/ ³⁹ Ar apparent age patterns and the duration of metamorphism in the biotite zone

The nature and origin of the Barrovian metamorphism, Scotland: ⁴⁰ Ar/ ³⁹ Ar apparent age patterns and the duration of metamorphism in the biotite zone

Ductile fault rocks and metamorphic zonation in the Dalradian of the Highland Border SW of Stonehaven, Kincardineshire

Cummingtonite in the Dalradian of NE Scotland

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Timing of Barrovian metamorphism and ‘Older Granite’ emplacement in relation to Dalradian deformation

Cited by 21 publications

References 17 publications

The nature and origin of the Barrovian metamorphism, Scotland: 40 Ar/ 39 Ar apparent age patterns and the duration of metamorphism in the biotite zone

The nature and origin of the Barrovian metamorphism, Scotland: 40 Ar/ 39 Ar apparent age patterns and the duration of metamorphism in the biotite zone

Ductile fault rocks and metamorphic zonation in the Dalradian of the Highland Border SW of Stonehaven, Kincardineshire

Cummingtonite in the Dalradian of NE Scotland

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The nature and origin of the Barrovian metamorphism, Scotland: ⁴⁰ Ar/ ³⁹ Ar apparent age patterns and the duration of metamorphism in the biotite zone

The nature and origin of the Barrovian metamorphism, Scotland: ⁴⁰ Ar/ ³⁹ Ar apparent age patterns and the duration of metamorphism in the biotite zone