J. Daly, M. Flowerdew, Martin J. Whitehouse, E. Badenszki
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引用次数: 0
Abstract
A geochronological and isotopic study grounded by field observations is presented on the southern-most Lewisian orthogneisses of Iona, southwest Scotland. Syenitic orthogneisses in western Iona and granodioritic orthogneisses in the east have yielded indistinguishable SIMS U-Pb zircon
c
. 2710 Ma protolith ages, among the youngest recorded from the Lewisian. Whole-rock Sm-Nd and zircon Lu-Hf data indicate largely juvenile Neoarchaean crustal additions. Based on this evidence, a north-south trending mylonite zone separating eastern and western Iona is unlikely to be a terrane boundary. Extensive reworking during the “late Laxfordian” deformational event between 1779-1753 Ma (bracketed between pre-tectonic migmatisation and post-tectonic granitic pegmatite intrusion) likely corresponds to accretion of the Rhinns Complex to the Nuna/ Columbia supercontinent. Zircon Lu-Hf data indicate that late Laxfordian melts were largely derived from the Neoarchaean orthogneisses. K-feldspar Pb isotope ratios in the orthogneisses have likely been reset during late Laxfordian metamorphism while those in a post-tectonic syenitic pegmatite, with a U-Pb zircon age of 1688 ± 8 Ma are considered to be original and consistent with an exotic source. Correlation of the Iona Lewisian with Coll and Tiree is possible but the younger age of the Iona orthogneisses does not support correlation with the Rona terrane.
期刊介绍:
Although published only since 1965, the Scottish Journal of Geology has a long pedigree. It is the joint publication of the Geological Society of Glasgow and the Edinburgh Geological Society, which prior to 1965 published separate Transactions: from 1860 in the case of Glasgow and 1863 for Edinburgh.
Traditionally, the Journal has acted as the focus for papers on all aspects of Scottish geology and its contiguous areas, including the surrounding seas. The publication policy has always been outward looking, with the Editors encouraging review papers and papers on broader aspects of the Earth sciences that cannot be discussed solely in terms of Scottish geology.
The diverse geology of Scotland continues to provide an important natural laboratory for the study of earth sciences; many seminal studies in geology have been carried out on Scottish rocks, and over the years the results of much of this work had been published in the Journal and its predecessors.
The Journal fully deserves its high reputation worldwide and intends to maintain its status in the front rank of publications in the Earth sciences.