New Developments in the Appalachian-Caledonian-Variscan Orogen
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New analytical and field techniques, as well as increased international communication and collaboration, have resulted in significant new geological discoveries within the Appalachian-Caledonian-Variscan orogen. Cross-Atlantic correlations are more tightly constrained and the database that helps us understand the origins of Gondwanan terranes continues to grow. Special Paper 554 provides a comprehensive overview of our current understanding of the evolution of this orogen. It takes the reader along a clockwise path around the North Atlantic Ocean from the U.S. and Canadian Appalachians, to the Caledonides of Spitsbergen, Scandinavia, Scotland and Ireland, and thence south to the Variscides of Morocco.
Sedimentary provenance of Silurian basins in western Ireland during Iapetus closure
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Published:May 19, 2022
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CiteCitation
Nancy Riggs*, Brian McConnell, John Graham, 2022. "Sedimentary provenance of Silurian basins in western Ireland during Iapetus closure", New Developments in the Appalachian-Caledonian-Variscan Orogen, Yvette D. Kuiper, J. Brendan Murphy, R. Damian Nance, Robin A. Strachan, Margaret D. Thompson
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ABSTRACT
Three Silurian basin fills, the Llandovery–Wenlock Croagh Patrick and Killary Harbour–Joyce Country successions and the Ludlow–Pridoli Louisburgh–Clare Island succession, overstep the tectonic contacts between elements of the Grampian (Taconic) accretionary history of the Caledonian-Appalachian orogeny in western Ireland. New U-Pb detrital zircon data from lower strata of these Silurian rocks provide insight into basin evolution and paleogeography.
The shallow-marine Croagh Patrick succession unconformably overlies the Clew Bay Complex and the northern part of the Ordovician South Mayo Trough. Two samples have zircon populations dominated by Proterozoic grains typical of the Laurentian margin, with few younger grains. Up to 13% of the grains form a cluster at ca. 950–800 Ma, which is younger than known Grenville magmatism on the local Laurentian margin and older than known magmatism from Iapetan rifting; these may be recycled grains from Dalradian strata, derived from distal Tonian intrusions. The Killary Harbour–Joyce Country succession overlies the structural contact between the Lough Nafooey arc and the Connemara Dalradian block and records a transgressive-regressive cycle. Four samples of the Lough Mask Formation show contrasting age spectra. Two samples from east of the Maam Valley fault zone, one each from above Dalradian and Nafooey arc basement, are dominated by Proterozoic grains with ages typical of a Laurentian or Dalradian source, likely in north Mayo. One sample also includes 8% Silurian grains. Two samples from west of the fault overlie Dalradian basement and are dominated by Ordovician grains. Circa 450 Ma ages are younger than any preserved Ordovician rocks in the region and are inferred to represent poorly preserved arc fragments that are exposed in northeastern North America. Cambrian to late Neoproterozoic grains in association with young Ordovician ages suggest derivation from a peri-Gondwanan source in the late stages of Iapetus closure.
The Louisburgh–Clare Island succession comprises terrestrial red beds. It unconformably overlies the Clew Bay Complex on Clare Island and is faulted against the Croagh Patrick succession on the mainland. The Strake Banded Formation yielded an age spectrum dominated by Proterozoic Laurentian as well as Ordovician–Silurian ages. Although the basin formed during strike-slip deformation along the Laurentian margin in Ireland and Scotland, sediment provenance is consistent with local Dalradian sources and contemporaneous volcanism. Our results support ideas that Ganderian continental fragments became part of Laurentia prior to the full closure of the Iapetus Ocean.
- absolute age
- arkose
- basins
- Caledonian Orogeny
- Cambrian
- clastic rocks
- Dalradian
- Europe
- faults
- Grampian Orogeny
- Great Britain
- Iapetus
- intrusions
- Ireland
- Laurentia
- lithostratigraphy
- Llandovery
- Lower Silurian
- Ludlow
- marine environment
- Mayo Ireland
- metaigneous rocks
- metamorphic rocks
- metasedimentary rocks
- Neoproterozoic
- nesosilicates
- Ordovician
- orthosilicates
- paleogeography
- Paleozoic
- plate collision
- plate tectonics
- Precambrian
- Pridoli
- Proterozoic
- provenance
- red beds
- regression
- sandstone
- Scotland
- sea-level changes
- sedimentary rocks
- shallow-water environment
- silicates
- siliciclastics
- siltstone
- Silurian
- strike-slip faults
- Taconic Orogeny
- terrestrial environment
- Tonian
- transcurrent faults
- transgression
- U/Pb
- United Kingdom
- upper Precambrian
- Upper Silurian
- Wenlock
- Western Europe
- zircon
- zircon group
- Clew Bay
- South Mayo Trough
- detrital zircon
- Clare Island
- Ganderia