Insight into late-Iapetus tectonics from new U–Pb zircon and micropalaeontological data from the Navan area, eastern Ireland

Published on 2019-01-08T12:19:49Z (GMT) by
<p>The Ordovician peri-Laurentian Grangegeeth Terrane in eastern Ireland and the adjacent Katian to Wenlock Rathkenny Tract are together a relic of the closing Iapetus Ocean. The Rathkenny Tract succession is part of the Laurentian Southern Uplands-Down-Longford Terrane accretionary prism, but the contact between the Rathkenny and Grangegeeth terranes is cryptic.</p><p>Two cores of Lower Paleozoic strata along a buried projection of the Rathkenny–Grangegeeth outcrops contain volcaniclastic units within a succession of mudstone and siltstone. LA–ICPMS U–Pb dating of zircon from volcanogenic horizons yielded a maximum depositional age of <i>c</i>. 450 Ma. Nearly 98% of zircon ages are 445 – 480 Ma, indicating a proximal volcanic source. Trace element geochemistry of Ordovician zircon indicates host magma sourced in continental crust. A diverse ostracod fauna in mudstone suggests a Katian age, and includes species with Baltic, Laurentian and Avalonian affinities. </p><p>We propose a paired-subduction-zone model for emplacement of the Grangegeeth/Rathkenny succession, with the Rathkenny strata deposited on an oceanic plate between the Laurentian-margin accretionary prism and the 480–450 Ma Grangegeeth peri-Laurentian micro-continental arc. Volcaniclastic detritus fed into the Rathkenny basin was then incorporated into the accretionary prism. The mixed fauna indicates that the Iapetus Ocean was narrow by Katian time. </p>

Cite this collection

McConnell, B.; Riggs, N.; Sevastopulo, G. (2019): Insight into late-Iapetus tectonics from new U–Pb zircon and micropalaeontological data from the Navan area, eastern Ireland. Geological Society of London. Collection.