Physics
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....12993s&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #12993
Physics
Scientific paper
Jan Mayen is a volcanic island located 650 km NW of Island, just south of the Jan Mayen Fracture Zone (JMFZ), which separates the Kolbeinsey Ridge from the Mohns Ridge. Trace element and Nd-Sr-Pb isotope systematics suggest that the magmas formed from an enriched mantle source, but low ^3He/^4He isotope ratios do not favor a mantle plume origin of the magmatism [1], which is in accordance with geophysical data. An enriched mantle source is also present below the Jan Mayen Platform, just north of the JMFZ, and below the northern parts of the Kolbeinsey Ridge, 160 km west of Jan Mayen. The northern, submarine parts of Jan Mayen and the neo-volcanic zone of the southernmost segment of the Mohns Ridge, which crosses the Jan Mayen Platform, was mapped and sampled during two cruises in 2001. Mapping and sampling of the northern, submarine parts of Jan Mayen show that a volcanic ridge extends across the central parts of the Jan Mayen fracture zone. No tectonic lineaments seem to truncate this ridge. Basalt samples from the northern part of Jan Mayen have an alkali basalt composition, with an isotope signature characterized by high 87Sr/86Sr ratios (0.703589-0.7033913) and low 143Nd/144Nd ratios (0.512877-0.52910). The isotopic composition of volcanic rocks from the northern part of the island is similar to the composition of volcanic rocks from the southern part. Samples from the neo-volcanic zone of the Mohns Ridge across the Jan Mayen Platform have basaltic compositions with 87Sr/86Sr ratios ranging from 0.703505 to 0.703178, and 143Nd/144Nd ratios between 0.512955 to 0.513031. Together basalt from the middle and northern parts of the Mohns Ridge and the Knipovich Ridge, the basalts from the Jan Mayen Platform define a linear array in Sr-Nd isotope space. The Jan Mayen volcanics plot slightly below the enriched end-point of this array. Seismic data suggest that a continental fragment is present just south of Jan Mayen [2]. We see no evidences for an interaction between continental crust and mantle-derived magmas in our data. We suggest that the enriched nature of the basalts from the Jan Mayen area is related to the presence of a more fertile, sub-continental mantel in the region. This is supported by new Sr-Nd isotopic data of mantle xenolites from quaternary volcanic centers on Spitzbergen, which show that the sub-continental mantle in the Arctic region partly have similar Nd-Sr isotopic composition as the basalts in the Jan Mayen area. We furthermore propose that the volcanic activity at Jan Mayen is related to the interaction between a ridge-transform system and a continental fragment, which represent zone of lithospheric weakness and a nucleus for rifting. [1] Stuart, F. M., R. M. Ellam, et al. (2000). "Constraints on mantle plumes from the helium isotopic composition of basalts from the British Tertiary igneous province." Earth and Planetary Science Letters 177(3-4): 273-285. [2] Skogseid, J. and O. Eldholm (1987). "Early Cenozoic crust at the Norwegian continental margin and the conjugate Jan Mayen Ridge." Journal of Geophysical Research, B, Solid Earth and Planets 92(11): 11,471-11,491.
Pedersen Rolf-Birger
Svellingen W.
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