کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4680200 1634905 2008 14 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Perovskite U–Pb ages and the Pb isotopic composition of alkaline volcanism initiating the Permo-Carboniferous Oslo Rift
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
پیش نمایش صفحه اول مقاله
Perovskite U–Pb ages and the Pb isotopic composition of alkaline volcanism initiating the Permo-Carboniferous Oslo Rift
چکیده انگلیسی

The Permo-Carboniferous Oslo Rift developed in the foreland of the Variscan orogen over a period of some 50 million years through a process characterized by moderate extension and widespread magmatism. The overall tectonic situation places the Oslo Rift in a post-collisional, dextral transtensional setting related to the convergence between Baltica, Laurentia, Gondwana and Siberia during assembly of Pangea, the location probably reflecting the control by pre-existing lithospheric structures. Although a detailed understanding of these factors and processes relies strongly on having a good age control, the dating of mafic to ultramafic alkalic volcanic units formed during initial rifting has been a very challenging task. In this study we have successfully employed perovskite from melilitic and nephelinitic volcanic rocks, together with magmatic titanite in a more evolved ignimbrite, to obtain ID-TIMS high-precision U–Pb ages. Three samples from various levels of the Brunlanes succession, in the southernmost exposures of the Oslo Graben, yield ages of 300.2 ± 0.9, 300.4 ± 0.7 and 299.9 ± 0.9 Ma. A melililitic tuff at the base of the Skien succession further to the northwest yields a slightly younger age of 298.9 ± 0.7 Ma. The initial Pb compositions derived mainly from coexisting pyroxene, apatite and hornblende are characterized by extremely radiogenic initial 206Pb/204Pb ratios (up to 21.3) that confirm a provenance of these early alkaline basalts from HIMU-type sources. The U–Pb ages coincide with the Gzhelian age inferred from fossils in the upper part of the basal rift sedimentary fill of the Asker Group, and post-date the underlying basal sedimentary sequences by some 10 million years, pointing to a relatively rapid initiation of the rifting process.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 265, Issues 1–2, 15 January 2008, Pages 256–269
نویسندگان
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