Mathematics – Logic
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997e%26psl.152....1m&link_type=abstract
Earth and Planetary Science Letters, vol. 152, Issue 1-4, pp.1-9
Mathematics
Logic
9
Mid-Ocean Ridge Basalts, Arctic Ocean, Mid-Arctic Ocean Ridge, Mineralogy, Geochemistry, Isotope Ratios
Scientific paper
During the ARCTIC '91 expedition aboard RV Polarstern (ARK VIII/3) to the Central Arctic Ocean, a box corer sample on the Gakkel Ridge at 87°N and 60°E yielded a layer of sand-sized, dark brown volcanic glass shards at the surface of the sediment core. These shards have been investigated by petrographic, mineralogical, geochemical and radiogenic isotope methods. The nearly vesicle-free and aphyric glass shards bear only minute microphenocrysts of magnesiochromite and olivine (Fo 88-89 ). Most glasses are fresh, although some show signs of incipient low-temperature alteration. From their shapes and sizes, the glass shards most likely formed by spalling of glassy rinds of a nearby volcanic outcrop. Geochemically, the glasses are relatively unfractionated tholeiites with E-MORB trace element compositions. Thus, they are quite similar to the previously investigated ARK IV/3-11-370-5 basalts from 86°N [1 ]. The Nd and Sr isotopic ratios of PS 2167-2 glasses are significantly lower than for ARK IV/3-11-370-5 basalts and suggest an isotopically heterogeneous mantle source of Gakkel Ridge MORB between 86° and 87°N. The positive -8/4 Pb value (~16) and high 87 Sr/ 86 Sr ratio (0.70270), found for PS 2167-2 glasses are similar to that of ARK IV/3-11-370-5 basalts and show the influence of the DUPAL isotopic anomaly in the high Arctic mantle. These results argue against the presence of an `anti-DUPAL anomaly' in the mantle below the North Pole region and simple models of whole-mantle convection.
Bohrmann H.
Garbe-Schönberg Dieter
Kassens Heidemarie
Mühe Richard
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