Initial results for the composition of the igneous basement of the Bowers and Shirshov Ridges (Bering Sea, NW Pacific)

• Main Authors: Wanke, Maren, Portnyagin, Maxim, Werner, Reinhard, Hauff, Folkmar, Hoernle, Kaj
• Format: Conference Object
• Language: English
• Published: Westfälische Wilhelms-Universität 2010
• Subjects: Bering Sea; Bowers; Canada; Gaina; Pacific; Kamchatka
• Online Access: https://oceanrep.geomar.de/id/eprint/10150/; https://oceanrep.geomar.de/id/eprint/10150/1/DMG2010_Abstract_Wanke.pdf; http://www.dmg-home.de/Abstracts/DMG2010_Abstracts.pdf

The Bowers and Shirshov Ridges (hereafter BR and SR, respectively) are two prominent submarine structures of unknown age and provenance in the Bering Sea. So far only a few geochemical data exist on the composition of basement rocks from the SR (Silantyev et al., 1985) and none for the BR. Age and geochemical data are crucial to evaluate if the ridges represent remnant island arcs (Cooper et al. 1981, Scholl 2007), former pieces of Kamchatka rifted away through seafloor spreading (SR: Baranov et al. 1991) or parts of the Mesozoic Hawaiian hot-spot (Steinberger & Gaina, 2007). Here we report the first geochemical data on the composition of the basement rocks from the BR and SR, recovered during KALMAR R/V SONNE cruise 201 (Legs 1b and 2) in 2009. Fresh to moderately altered volcanic rocks were dredged from the northern slope of the BR, from seamounts on the western extension of the BR and from the western slope of the central part of the SR. We studied the petrography of the samples and carried out geochemical analyses of major and trace elements by XRF and ICPMS at ACME Lab (Vancouver, Canada) and CAU (Kiel). The rocks from the northwestern slope of the BR are clinopyroxene (cpx)-phyric basalts with minor amounts of olivine (ol) and plagioclase (plag) microphenocrysts, as well as hbl-plag-cpx-bearing basaltic andesites and trachyandesites. The rocks are strongly enriched in LREE (LaN/YbN = 3.2 – 8.5, N indicates normalization to primitive mantle), fluid-mobile elements (Ba, U, K) relative to NMORB and exhibit clear negative anomalies of HFSE (Nb, Ta and Ti) in primitive mantle-normalized incompatible element diagrams. The BR rocks also have a moderate adakitic signature, as indicated by elevated SrN/YN ratios (6.9 – 12.9). Hbl-cpx-plag trachybasalts from the SR have similar major and trace element compositions (LaN/YbN = 2.1 – 4.9) to the BR rocks. The other magmatic series from the SR comprises massive trachyandesites, trachytes and dacites with rare phenocrysts of plag and cpx. These rocks also have ...