Meter-Scale Chemical and Isotopic Heterogeneities in the Oceanic Mantle, Leka Ophiolite Complex, Norway

Abstract Mantle peridotites from three 3 × 3-meter grids sampled at kilometer distances one another in the ca. 497 Ma Leka Ophiolite Complex (LOC), Norway, are examined to investigate chemical and isotopic nature of oceanic mantle domains centimeter scale. The lithology each grid locality is predominantly harzburgite, but includes layers lenses dunite pyroxenite. Major lithophile trace element compositions indicate a history prior melting pressures or slightly below garnet stability field. common presence orthopyroxenite veins likely reflects infiltration silicic melts associated with supra-subduction zone processes. Osmium isotopes highly siderophile (HSE) abundance data for centimeter-scale sampling traverses pyroxenites into harzburgites reveal that formation had little effect on Os compositions, Os, Ir, Ru Re abundances harzburgites. Adjacent studied, however, Pt Pd appear have been strongly modified by interactions vein-forming fluids as much 4–6 cm pyroxenite-harzburgite contact. initial γOs values (% deviation chondritic reference) range −4.7 +2.2 (6.9% variation), individual uncertainties ±0.2 units. Averaged sites separated 6 km, contrast, differ only maximum 2.6%. Isotopic heterogeneity meter scale is, therefore, larger than kilometer-scale heterogeneity, indicating least some commonly observed globally among result processes acted local general uniformity these suggests portion LOC was homogenous respect long-term Re/Os ratio. projected similar average required modern abyssal peridotites. This observation strengthens previous interpretations, based largely peridotites, state evolution consistent 187Re/188Os ∼0.38. present ∼3 4% difference between composition estimates primitive ∼6% mass has removed it form Re-enriched, mafic crust. Despite recycling this crust back mantle, most evidently not mixed accessible portions upper peridotite mantle. Compared median HSE moderately depleted Re, corresponding evidence 20–30% melt depletion. As values, given characterized greater variations absolute relative differences locales. indicates isotopes, centimeter- meter-scale remobilization effects. Except Ru, ∼30% lower Ru/Ir compared ratio may be more variable generally thought.