Research article
May 1976

Geochronology of the Channel Islands and adjacent French mainland

Publication: Journal of the Geological Society
Volume 132
Pages 233 - 250

Abstract

Rb-Sr whole-rock dating of igneous and metamorphic rocks of the Channel Islands region has delineated the following major events: 1) Formation of the Pentevrian basement gneisses c. 2600 Ma ago in the northern Guernsey, Alderney and Cap de la Hague region. 2) Possible isotopic rejuvenation of these gneisses during a second metamorphic episode c. 1950 Ma ago. 3) Formation of Pentevrian gneisses in the southern, St Malo-St Brieuc region, 1000–1100 Ma ago. 4) Deposition of the Brioverian sedimentary series in the interval 650–1000 Ma. 5) Emplacement of igneous rocks 650–690 Ma ago during initial phases of the Cadomian Orogeny (late Precambrian) followed by 6) a main regional metamorphic event 620–650 Ma ago, and 7) a post-metamorphic igneous phase 560–610 Ma ago. 8) On Jersey a further post-tectonic granite phase, 480–520 Ma, can be recognized
Within this framework, nearly 130 K–Ar and Rb–Sr mineral ages from the area are interpreted as reflecting initiation of cooling and uplift of the Cadomian orogen as a whole in late Precambrian or Cambrian times.
Only a very few, young minor intrusions are connected with Variscan orogenic events.
Some preliminary comparisons can be made with late Precambrian igneous and metamorphic rocks elsewhere in the Massif Armoricain, southern Britain, eastern Canada and U.S.A.

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cover image Journal of the Geological Society
Journal of the Geological Society
Volume 132Number 3May 1976
Pages: 233 - 250

History

Received: 2 September 1974
Revision received: 16 June 1975
Published: May 1976

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Christopher John Dorrington Adams, Institute of Nuclear Sciences, D.S.I.R., Private Bag, Lower Hutt, New Zealand.

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Citing Literature

  • U–Pb geochronological constraints on the timing of plutonism, volcanism, and sedimentation, Jersey, Channel Islands, UK, Journal of the Geological Society, 10.1144/jgs.158.2.243, 158, 2, (243-251), (2022).
  • Chronology of granite magmatism and associated mineralization, SW England, Journal of the Geological Society, 10.1144/gsjgs.142.6.1159, 142, 6, (1159-1177), (2022).
  • A gravity and magnetic interpretation of the structure of the Irish Midlands and its relation to ore genesis, Journal of the Geological Society, 10.1144/gsjgs.142.6.1059, 142, 6, (1059-1075), (2022).
  • Dalradian deposition and the late Precambrian–Cambrian history of the N Atlantic region: a review of the early evolution of the Iapetus Ocean, Journal of the Geological Society, 10.1144/gsjgs.139.4.0421, 139, 4, (421-431), (2022).
  • Gravity and magnetic studies in the Channel Islands, Journal of the Geological Society, 10.1144/gsjgs.139.1.0035, 139, 1, (35-48), (2022).

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