New Developments in the Appalachian-Caledonian-Variscan Orogen

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.
Testing petrogenetic models for contemporaneous mafic and felsic to intermediate magmatism within the “Newer Granite” suite of the Scottish and Irish Caledonides
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Published:May 19, 2022
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CiteCitation
Donnelly B. Archibald, J. Brendan Murphy, Mike Fowler, Robin A. Strachan, Robert S. Hildebrand, 2022. "Testing petrogenetic models for contemporaneous mafic and felsic to intermediate magmatism within the “Newer Granite” suite of the Scottish and Irish Caledonides", 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
Granitoid batholiths dominated by felsic to intermediate compositions are commonly associated with mafic plutons and enclaves; however, the genetic relationship between the apparently coeval but compositionally dissimilar magmas is unclear. Here, we reviewed the age and lithogeochemical and Nd-Sr isotopic compositions of some classic plutonic rocks emplaced in the Northern Highlands, Grampian and Connemara terranes of the Caledonide orogen of Scotland and Ireland. The Northern Highlands terrane consists mostly of Neoproterozoic metasedimentary rocks of the Moine Supergroup and is located north of the Great Glen fault. The Grampian terrane also consists of Neoproterozoic metasedimentary rocks (Dalradian Supergroup) and is located south of the Great Glen fault in both Scotland and Ireland. Amphibolite-facies metasedimentary rocks in the Connemara terrane are correlated with the Dalradian Supergroup, and the terrane is bounded by splays of the Highland Boundary and Southern Uplands faults. These three terranes were intruded by Silurian–Devonian mafic and felsic to intermediate plutonic rocks that display field evidence for mingling and mixing and have a similar range (between ca. 437 and 370 Ma) in emplacement ages. This range implies they were intruded during and after the late Caledonian Scandian orogenic event that resulted from the mid- to late Silurian collision of amalgamated Avalonia and Baltica with Laurentia and the final closure of the Iapetus Ocean. Our review supports the contention that the Great Glen fault represents a major compositional boundary in the Silurian lithosphere. Felsic to intermediate plutons that occur north of the Great Glen fault are more enriched in light rare earth elements and Ba-Sr-K compared to those to the south. Isotopic compositions of these late Caledonian plutonic rocks on both sides of the Great Glen fault indicate that metasomatism and enrichment of the subcontinental lithospheric mantle beneath the Northern Highlands terrane occurred just prior to emplacement of late Caledonian plutons. Within the same terrane, mafic and felsic to intermediate rocks display similar trace-element and rare earth element concentrations compatible with models implying that fractionation of a mafic magma played an important role in generating the felsic to intermediate magmas. The onset of slab failure magmatism may have been diachronous along the length of the collision zone. If so, slab failure may have propagated laterally, possibly initiating where promontories collided.
- absolute age
- alkaline earth metals
- amphibolite facies
- batholiths
- Caledonian Orogeny
- Caledonides
- chemical fractionation
- Connemara
- continental lithosphere
- Dalradian
- Devonian
- dikes
- diorites
- Europe
- facies
- felsic composition
- gabbros
- Galway Ireland
- Grampian Highlands
- Grampian Orogeny
- granites
- Great Britain
- Great Glen Fault
- Highland Boundary Fault
- IGCP
- igneous rocks
- inclusions
- intrusions
- Ireland
- isotopes
- lamprophyres
- lithosphere
- mafic composition
- magmas
- magmatism
- major elements
- mantle
- metals
- metamorphic rocks
- metamorphism
- metasedimentary rocks
- metasomatism
- mixing
- Moine Supergroup
- monazite
- mylonites
- neodymium
- Neoproterozoic
- nesosilicates
- Northern Highlands
- oceanic lithosphere
- Ordovician
- orthosilicates
- Paleozoic
- phosphates
- plutonic rocks
- plutons
- post-tectonic processes
- Precambrian
- Proterozoic
- rare earths
- Scandian Orogeny
- Scotland
- Scottish Highlands
- silicates
- Silurian
- slabs
- strontium
- syntectonic processes
- trace elements
- U/Pb
- United Kingdom
- upper Precambrian
- Western Europe
- xenoliths
- zircon
- zircon group
- Southern Uplands Fault
- magmatic arcs