Potassium–Argon Age Measurements on Two Igneous Rocks from the Ordovician System of Scotland

Harris, P. M.; Farrar, Edward; Macintyre, R. M.; York, Derek; Miller, John A.

doi:10.1038/205352a0

Cited by 32 publications

(14 citation statements)

References 10 publications

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“…Although it is possible that the Ballantrae Ophiolite Complex is an along-strike equivalent of the Tyrone Igneous Complex, current age constraints are not sufficient for reconstructing the petrochemical evolution of the exposed sequences across tectonic blocks (discussed by Hollis et al 2012). Although graptolite-bearing sedimentary units are Early to Late Arenig in age (Stone & Strachan 1981;Stone & Rushton 1983;Rushton et al 1986), considerably older ages have also been produced from gabbro of within-plate affinity (K-Ar age of 487 ± 8 Ma: Harris et al 1965), and island-arc lavas (e.g. whole-rock Sm-Nd age of 501 ± 12 Ma: Thirlwall & Bluck 1984).…”

Section: Other Potential Correlatives?mentioning

confidence: 99%

Evolution of the Tyrone ophiolite, Northern Ireland, during the Grampian–Taconic orogeny: a correlative of the Annieopsquotch Ophiolite Belt of central Newfoundland?

Hollis

Cooper

Roberts

et al. 2013

JGS

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The Tyrone Plutonic Group of Northern Ireland represents the upper portions of a tectonically dissected suprasubduction-zone ophiolite accreted to the composite Laurentian margin during the Middle Ordovician. Understanding its development and relationship to the Tyrone Central Inlier, an outboard fragment of relatively high-grade, peri-Laurentian continental crust, is essential for reconstructing the closure of the Iapetus Ocean. The Tyrone Plutonic Group is composed of tectonized layered, isotropic and pegmatitic gabbros, sheeted dolerite dykes and rare pillow lavas. New U–Pb zircon thermal ionization mass spectrometry geochronology has yielded an age of 483.68 ± 0.81 Ma from pegmatitic gabbro. Geochemical characteristics, Nd and Sr isotope systematics, and zircon inheritance indicate that the Tyrone Plutonic Group formed above a north-dipping subduction zone, by the propagation of a spreading centre into a microcontinental block. Synkinematic, calc-alkaline tonalitic to granitic material preserved in the contact zone between the Tyrone Plutonic Group and the Tyrone Central Inlier has produced pressure estimates of 2.3–4.0 ± 0.6 kbar and temperatures of 525–610 °C. Coeval arc–ophiolite accretion at c . 470 Ma may explain how sillimanite-grade metamorphic conditions were reached locally in the underlying Tyrone Central Inlier. Strong temporal, geochemical and lithological similarities exist to the Annieopsquotch Ophiolite Belt of Newfoundland. Supplementary materials: Petrographic photographs, whole-rock, isotopic and mineral geochemical data, and U–Th–Pb isotopic data are available at www.geolsoc.org.uk/SUP18646 .

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Section: Other Potential Correlatives?mentioning

confidence: 99%

Evolution of the Tyrone ophiolite, Northern Ireland, during the Grampian–Taconic orogeny: a correlative of the Annieopsquotch Ophiolite Belt of central Newfoundland?

Hollis

Cooper

Roberts

et al. 2013

JGS

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“…The Millenderdale gabbro is also thought to have had a withinplate origin (Smellie & Stone 2001) and has been dated (K-Ar) at 487±8 Ma . Not included in Figure 7 is the first radiometric date recorded from the Ballantrae Complex: ca 475 Ma, K-Ar from biotite in a gabbro "1.5 miles north of Colmonell" (Harris et al 1965). This poorly defined location probably relates to a gabbroic enclave within the Southern Serpentinite Belt that might be either intrusive or a tectonic inclusion related to the beerbachite bodies.…”

Section: Subject To Those Reservations Most Of the Published Resultsmentioning

confidence: 99%

A review of geological origins and relationships in the Ballantrae Complex, SW Scotland

Stone

2014

SJG

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SynopsisA substantial history of research has established the Ballantrae Complex as an ophiolite assemblage, generated within the Iapetus Ocean and accreted at the margin of Laurentia as that ocean began to close. Radiometric dates and graptolite biostratigraphy provide an age range from Neoproterozoic (rarely and questionably) to early Ordovician (commonly and securely). Components of the complex formed in a range of oceanic environments: within-plate oceanic islands, island arcs and backarc spreading zones. Overall, the various lines of evidence point to an early Arenig marginal basin, incorporating some older elements, which was tectonically disrupted and compressed during an obduction event driven by arc-continent collision. Despite the general consensus as to the age and origin of the complex there remain areas of uncertainty. It is highly probable that some components of the complex that are now structurally juxtaposed originated at a considerable distance from each other both horizontally and vertically. Further, the sporadic presence of high-grade metamorphic rocks -notably blueschists -suggests a complicated and probably polyphase structural history, whilst the relative importance of serpentinite diapirism versus compressional and strike-slip tectonics remains unresolved.

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“…2A; Thirlwall and Bluck, 1984). The within-plate gabbro at Millenderdale has a K-Ar age of 487 ± 8 Ma (Harris et al, 1965).…”

Section: Geological Backgroundmentioning

confidence: 99%

Imbricated ocean-plate stratigraphy and U-Pb zircon ages from tuff beds in cherts in the Ballantrae complex, SW Scotland

Sawaki

Shibuya

Kawai

et al. 2009

Geological Society of America Bulletin

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Ocean-plate stratigraphy (basalt, chert, clastics) of the Balcreuchan Group in the Ballantrae complex is repeated by layer-parallel thrusts to form duplex structures south of Bennane Head, ~5 km north of Ballantrae. Five tuff beds, all in chert, have similar U-Pb zircon ages of ca. 470 ± 10 Ma. The geometrical polarity of the duplexes and the zircon ages provide new constraints on the tectonic evolution of the accretionary wedge of the Ballantrae complex. Northwestward thrusting of the duplexes suggests that subduction was from the northwest to the southeast, and this polarity at the leading edge of the main ophiolite body is consistent with the northward younging of the volcanic arc rocks of the Ballantrae complex.

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Potassium–Argon Age Measurements on Two Igneous Rocks from the Ordovician System of Scotland

Cited by 32 publications

References 10 publications

Evolution of the Tyrone ophiolite, Northern Ireland, during the Grampian–Taconic orogeny: a correlative of the Annieopsquotch Ophiolite Belt of central Newfoundland?

Evolution of the Tyrone ophiolite, Northern Ireland, during the Grampian–Taconic orogeny: a correlative of the Annieopsquotch Ophiolite Belt of central Newfoundland?

A review of geological origins and relationships in the Ballantrae Complex, SW Scotland

Imbricated ocean-plate stratigraphy and U-Pb zircon ages from tuff beds in cherts in the Ballantrae complex, SW Scotland

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