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Palaeomagnetism and 40Ar/39Ar geochronology from the South Taimyr igneous complex, Arctic Russia: a Middle–Late Triassic magmatic pulse after Siberian flood-basalt volcanism

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SUMMARY

New palaeomagnetic results and 40Ar/39Ar ages from mafic sills and extrusive rocks from the South Taimyr igneous complex (75°N, 100°E) document late Middle–Early Late Triassic igneous activity in Arctic Siberia. The palaeomagnetic pole determined from the sills (47°N, 122°E, dp/dm= 5/5 ) plots on the 230–220 Ma portion of the apparent polar wander path for Euramerica, and is statistically different from the mean 250 Ma Siberian Traps pole. 40Ar/39Ar ages from three of the sills yield crystallization ages of ca. 229–227 Ma and confirm the pole age. The Taimyr igneous rocks are folded together with Carboniferous to Lower Triassic continental sedimentary rocks of the northern Siberia margin and are unconformably overlain by Early Jurassic sedimentary units that place an upper limit on the cessation of the Late Triassic folding event. In contrast to the sills, the palaeomagnetic pole obtained from the extrusive volcanic rocks (59°N, 146°E, dp/dm= 14/15 ) overlaps within uncertainty with previous Siberian Traps results, but is consistent with any age between 250 and 220 Ma. The 40Ar/39Ar signatures of the extrusive rocks were largely very disturbed and only one sample yielded a precise and interpretable age of 248 Ma.

The intrusive rocks in the South Taimyr igneous complex post-date eruption of the Siberian Traps flood basalts by about 20–25 Myr and are contemporaneous with reported ages from granitic rocks on Novaya Zemlya and late intrusive and pyroclastic rocks from the margins of the Siberian Traps igneous province. The extrusive rocks in South Taimyr may be age-correlative with the extensive Siberian Traps flood basalts with which they have previously been linked; however, our data alone cannot confirm the comagmatic nature of the extrusive rocks within South Taimyr or their genetic link, if any, to the igneous activity that produced the Siberian Traps flood basalts.
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Keywords: Siberian Traps; Taimyr; Triassic; geochronology; igneous rock; palaeomagnetism

Document Type: Research Article

Affiliations: 1: Department of Earth Science, University of Bergen, Allègaten 41, 5007 Bergen, Norway., Email: [email protected] 2: Center for Geodynamics, Geological Survey of Norway, 7491 Trondheim, Norway 3: CASP, University of Cambridge, West Building, Gravel Hill, Huntingdon Road, Cambridge CB3 0DJ, UK 4: University of Bath, Wessex House, Bath BA2 7AY, UK 5: Aerogeologiya, 35 Leninsky Prospekt, 117071 Moscow, Russia

Publication date: November 1, 2005

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