Isotopic dating of overthrusting, collapse and related granitoid intrusion in the Grampian orogenic belt, northwestern Ireland

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doi: 10.1017/S0016756800004209
Authors:Flowerdew, M. J.; Daly, J. S.; Guise, P. G.; Rex, D. C.
Author Affiliations:Primary:
University College Dublin, Department of Geology, Dublin, Ireland
Other:
Leeds University, United Kingdom
Volume Title:Geological Magazine
Source:Geological Magazine, 137(4), p.419-435. Publisher: Cambridge University Press, London, United Kingdom. ISSN: 0016-7568
Publication Date:2000
Note:In English. 50 refs.; illus., incl. 4 tables, geol. sketch maps
Summary:In the Grampian (Ordovician) orogenic belt in NW Ireland, the Dalradian supergroup abuts and interleaves with an enigmatic psammitic unit with relict latest Precambrian granulite-facies assemblages (the Slishwood division). Using Ar-Ar, Rb-Sr and Sm-Nd methods, 53 new mineral ages have been obtained from both rock units, and from pegmatites intruding them, in an attempt to constrain the timing of their juxtaposition and their subsequent history. The Grampian orogeny is dated as between 479 and 459 m.y. but is most likely to have occurred between 470 and 459 m.y. Shortly after juxtaposition, at ∼ 460 m.y., peak amphibolite-facies Barrovian metamorphic conditions were attained; most of the mineral ages in the range 460-540 m.y. are post-metamorphic cooling ages that support rapid exhumation and cooling of the nappe pile soon after peak metamorphism. Post-orogenic, extension-related granitic pegmatites also record the collapse of the orogen at ∼ 455 m.y.; initial Sr isotopic measurements suggest that Dalradian metasediments may have been the source of the pegmatites. The Grampian orogeny in this part of Ireland was apparently a short-lived event spanning no more than 30 m.y. Intrusion of the Ox Mountains granodiorite occurred between 410 and 400 m.y. [R.A.H.]
Sections:Age determination
Subjects:Absolute age; Ar-40/Ar-39; Argon; Caledonian Orogeny; Chronology; Clastic rocks; Dalradian; Dates; Facies; Faults; Grampian Orogeny; Granitic composition; Granulite facies; Inliers; Intrusions; Isotope ratios; Isotopes; Metals; Metamorphism; Neodymium; Noble gases; Ordovician; Orogenic belts; Overthrust faults; Paleozoic; Radioactive isotopes; Rare earths; Retrograde metamorphism; Samarium; Sandstone; Sedimentary rocks; Sm-147/Nd-144; Sr/Sr; Stable isotopes; Tectonics; Europe; Ireland; Mayo Ireland; Western Europe; Achill Island; Initial neodymium; Ox Mountain Granodiorite
Coordinates:N534000 N550000 W0060000 W0100000
Abstract Numbers:01M/14
Record ID:2000073496
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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