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标题：Age, Geochemistry and Origin of the ArdaraAppinite Plutons, Northwest Donegal,Ireland
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作者：J. Brendan Murphy ; R. Damian Nance ; Logan B.Gabler 等
期刊名称：Geoscience Canada
印刷版ISSN：0315-0941
电子版ISSN：1911-4850
出版年度：2019
卷号：46
期号：1
页码：31-48
DOI：10.12789/geocanj.2019.46.144
语种：English
出版社：Geological Association of Canada
摘要：In northwest Donegal, Ireland, a large number of coevalappinitic (hornblende-plagioclase-rich) plutons and lampro-phyre dykes occur around the Ardara pluton, a granitic satellitebody and one of the oldest phases of the ca. 428–400 Macomposite Donegal Batholith. The appinite units form abimodal (mafic–felsic) suite in which hornblende is the domi-nant mafic mineral and typically occurs as large prismatic phe-nocrysts within a finer grained matrix. Lamprophyre dykes aremafic in composition with a geochemistry that is very similarto that of the mafic appinite bodies. Both mafic rocks are sub-alkalic, with calc-alkalic and tholeiitic tendencies, and showtrace element abundances indicating that the mantle sourcewas contaminated by subduction zone fluids. 40Ar/39Ar analysisof hornblende separated from two samples of appinite yieldmid-Silurian (434.2 ± 2.1 Ma and 433.7 ± 5.5 Ma) cooling agesthat are interpreted to closely date the time of intrusion.Hence, according to the available age data, the appinite bodiesslightly predate, or were coeval with, the earliest phases of theDonegal Batholith. Sm–Nd isotopic analyses yield a range ofinitial εNd values (+3.1 to –4.8 at t= 435 Ma) that, togetherwith trace element data, indicate that the appinitic magmaswere likely derived from melting of metasomatized sub-conti-nental lithospheric mantle and/or underplated mafic crust,with only limited crustal contamination during magma ascent.The appinitic intrusions are interpreted to have been emplacedalong deep-seated crustal fractures that allowed for mafic andfelsic magma to mingle. The magmas are thought to be theproducts of collisional asthenospheric upwelling associatedwith the closure of Iapetus and the ensuing Caledonian oroge-ny, either as a result of an orogen-wide delamination event oras a consequence of more localized slab break-off.