Os and highly siderophile element abundance systematics of Earth ’ s upper mantle

Content Provider	Semantic Scholar
Author	Warren Walker Nilam Mattielli
Copyright Year	2011
Abstract	Osmium isotope and highly siderophile element (HSE) abundance systematics of abyssal peridotites may provide new constraints for interpreting isotopic and elemental signatures preserved in terrestrial lavas, as well as for deciphering melt depletion and recycling in the convecting mantle. Here we report new high-precision 186,187Os/188Os isotope and HSE abundance data for bulk samples of abyssal peridotites from the Arctic (Gakkel), Indian (central [CIR] and southwest [SWIR]), and Atlantic (Kane) ridges. Peridotites from the global suite range from relatively fresh to serpentinized harzburgites and lherzolites, with no systematic variation observed for HSE abundances or 186,187Os/188Os with alteration. Average HSE abundances of different ridge segments are broadly similar (0.007±2 " CIchondrite). The HSE are in approximately chondritic-relative abundances, although all ridges studied have supra-chondritic Ru/Ir (Kane = 1.4±0.2; Gakkel = 1.6±0.6; SWIR = 1.5±0.3; CIR = 1.4±0.1), similar to estimates for primitive upper mantle (PUM). Unlike PUM, there is no systematic suprachondritic Pd/Os in SWIR, CIR, or the majority of Gakkel peridotites. There is greater HSE abundance variability in ultra-slow spreading Gakkel, versus Indian or Atlantic peridotites. Abyssal peridotites analyzed in this study have 187Os/188Os ratios ranging from 0.1217 to 0.1587. The 186Os/188Os of SWIR peridotites (0.1198385±4), which were affected by the Bouvet hotspot at ~20Ma, are, on average, higher than for CIR (0.1198360±5), Kane (0.1198353±7 [1]), and Gakkel peridotites (0.1198332±6). SWIR show a general positive correlation for 187Os/188Os-186Os/188Os, but no other correlations are observed between these ratios in the dataset. If CIR, Kane and Gakkel peridotites are representive of convecting upper mantle, then this reservoir has evolved with a long-term Pt/Os that is well within the range of chondrites. In contrast, SWIR peridotites derive from a mantle source with higher Pt/Os. If SWIR 186Os/188Os values relate to high time-integrated Pt/Os, how this signature is transferred from the hotspot to the peridotites is unclear. Lack of correlation between Pt/Os and 186Os/188Os for the suites suggests abyssal peridotites do not record absolute and relative abundances of the HSE in the convecting upper mantle with high fidelity. Metasomatism beneath the Kerguelen Plateau associated with heterogeneous mantle plume V. DEBAILLE1*, G. HUBLET1, N. MATTIELLI1 AND D. WEIS2 1DSTE, Université Libre de Bruxelles, Brussels, Belgium. (*correspondence: vinciane.debaille@ulb.ac.be) 2PCIGR, University of British Columbia, Vancouver, Canada
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Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Synopsis