Short-lived continental magmatic arc at Connemara, western Irish Caledonides

Implications for the age of the Grampian orogeny

Anke M. Friedrich, Samuel A. Bowring, Mark W. Martin, Kip Hodges

Research output: Contribution to journalArticle

123 Citations (Scopus)

Abstract

U-Pb geochronological data from the Connemara region of Ireland indicate that continental arc magmatism along the southern margin of Laurentia was short-lived, lasting only from ca. 475 to 463 Ma. Previous work has demonstrated that intrusive activity in Connemara was broadly synchronous with Grampian mid-crustal deformation and upper amphibolite facies metamorphism of Neoproterozoic-lower Paleozoic Dalradian Supergroup rocks. The two oldest intrusions, the Currywongaun and Cashel-Lough Wheelaun gabbros, have U-Pb zircon ages of 474.5 ± 1.0 and 470.1 ± 1.4 Ma, respectively, whereas the U-Pb xenotime age of the postdeformational Oughterard granite is 462.5 ± 1.2 Ma. Thus, the implied age of the Grampian orogeny in Connemara is substantially younger than generally acknowledged, but consistent with other age constraints from Ireland and Scotland. A revised age for the Grampian orogeny helps to solve a long-standing controversy about the age of contractional deformation and arc magmatism in Dalradian Supergroup rocks of the British Isles. This event now demonstrably postdates Neoproterozoic-lower Paleozoic rift deposits and Laurentian passive margin sediments, a finding consistent with deposition of Dalradian Supergroup rocks in an extensional environment at or near the Laurentian margin. The Grampian orogeny is also now demonstrably synchronous with the Taconian orogeny of the northern Applachians. In Middle Ordovician time, the Laurentia-Iapetus plate boundary was characterized by ophiolite obduction, arc-continent collision, and associated short-lived subduction beneath Laurentia from at least the New England Appalachians to the Irish Caledonides.

Original languageEnglish (US)
Pages (from-to)27-30
Number of pages4
JournalGeology
Volume27
Issue number1
DOIs
StatePublished - Jan 1999
Externally publishedYes

Fingerprint

orogeny
Dalradian
Laurentia
magmatism
Paleozoic
Taconic orogeny
rock
arc-continent collision
xenotime
continental arc
obduction
crustal deformation
passive margin
plate boundary
amphibolite facies
ophiolite
Ordovician
zircon
metamorphism
subduction

ASJC Scopus subject areas

  • Geology

Cite this

Short-lived continental magmatic arc at Connemara, western Irish Caledonides : Implications for the age of the Grampian orogeny. / Friedrich, Anke M.; Bowring, Samuel A.; Martin, Mark W.; Hodges, Kip.

In: Geology, Vol. 27, No. 1, 01.1999, p. 27-30.

Research output: Contribution to journalArticle

Friedrich, Anke M. ; Bowring, Samuel A. ; Martin, Mark W. ; Hodges, Kip. / Short-lived continental magmatic arc at Connemara, western Irish Caledonides : Implications for the age of the Grampian orogeny. In: Geology. 1999 ; Vol. 27, No. 1. pp. 27-30.
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abstract = "U-Pb geochronological data from the Connemara region of Ireland indicate that continental arc magmatism along the southern margin of Laurentia was short-lived, lasting only from ca. 475 to 463 Ma. Previous work has demonstrated that intrusive activity in Connemara was broadly synchronous with Grampian mid-crustal deformation and upper amphibolite facies metamorphism of Neoproterozoic-lower Paleozoic Dalradian Supergroup rocks. The two oldest intrusions, the Currywongaun and Cashel-Lough Wheelaun gabbros, have U-Pb zircon ages of 474.5 ± 1.0 and 470.1 ± 1.4 Ma, respectively, whereas the U-Pb xenotime age of the postdeformational Oughterard granite is 462.5 ± 1.2 Ma. Thus, the implied age of the Grampian orogeny in Connemara is substantially younger than generally acknowledged, but consistent with other age constraints from Ireland and Scotland. A revised age for the Grampian orogeny helps to solve a long-standing controversy about the age of contractional deformation and arc magmatism in Dalradian Supergroup rocks of the British Isles. This event now demonstrably postdates Neoproterozoic-lower Paleozoic rift deposits and Laurentian passive margin sediments, a finding consistent with deposition of Dalradian Supergroup rocks in an extensional environment at or near the Laurentian margin. The Grampian orogeny is also now demonstrably synchronous with the Taconian orogeny of the northern Applachians. In Middle Ordovician time, the Laurentia-Iapetus plate boundary was characterized by ophiolite obduction, arc-continent collision, and associated short-lived subduction beneath Laurentia from at least the New England Appalachians to the Irish Caledonides.",
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