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First Geochemical Evidences for Existence of Slow-Spreading Ridges in the Pacific Ocean

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  • Chemistry
  • Geography


CONTROL ID: 1460728 TITLE: First Geochemical Evidences for Existence of Slow-Spreading Ridges in the Pacific Ocean AUTHORS (FIRST NAME, LAST NAME): Elizaveta Andreevna Krasnova1, Maxim Portnyagin1, 2, Sergey Silantyev1, Reinhard Werner2, Kaj Hoernle2 INSTITUTIONS (ALL): 1. Sobolev AV laboratory, Vernadsky Institute RAS, Moscow, Russian Federation. 2. Helmholtz Centre for Ocean Research Kiel (GEOMAR), Kiel, Germany. ABSTRACT BODY: Stalemate Fracture Zone (SFZ) is a 500 km long SE-NW trending transverse ridge between the northernmost Emperor Seamounts and the Aleutian Trench which originated by flexural uplift of Cretaceous (?) oceanic lithosphere along a transform fault at the Kula-Pacific plate boundary [1]. Sampling at the SFZ and the fossil Kula-Pacific Rift valley was carried out during the R/V SONNE cruise SO201 Leg 1b in July 2009. These rocks are thought to represent a complete section of oceanic lithosphere formed at the fossil Kula-Pacific Spreading Center. A broad spectrum of mantle peridotites ranging from spinel lherzolites to dunites were dredged at station DR37 at the northern bend of SFZ. Spinel in lherzolites has Mg#=0.65-0.68, NiO=0.26-0.34 wt%, Cr#=0.26-0.33, Fe3+#=0.021-0.030 and TiO2=0.04-0.09 wt%. Clinopyroxene has Mg#=91.7-92.4, Cr#=0.12-0.16, TiO2=0.06- 0.15 wt%, Na2O=0.19-0.41 wt%, NiO=0.06-0.09 wt% and is moderately depleted in HREE and extremely depleted in MREE and Zr (C1-normalized YbN=4.0- 5.6, [Sm/Yb]N=0.05-0.14, [Zr/Y]N=0.001-0.009) [2,3]. In terms of spinel and clinopyroxene Cr# and absolute concentrations of HREE, Ti and Na, these compositions are less depleted than those from the Hess Deep peridotites [4] formed at the fast spreading East-Pacific Rise. The SFZ peridotites are more similar to abyssal peridotites from slow-spreading ridges [e.g., 5]. Geochemical modeling suggests that the SFZ peridotites can be formed by 10-12% of near-fractional partial melting of depleted MORB mantle. We used the correlation between degree of p

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