Geochemistry of serpentinized peridotites from the Mariana forearc Conical Seamount, ODP Leg 125; implications for the elemental recycling at subduction zones

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doi: 10.1029/2004GC000777
Author(s): Savov, Ivan P.; Ryan, Jeffrey G.; D'Antonio, Massimo; Kelley, Katherine; Mattie, Patrick
Author Affiliation(s): Primary:
University of South Florida, Geology Department, Tampa, FL, United States
Universita Federico II di Napoli, Italy
Boston University, United States
Volume Title: Geochemistry, Geophysics, Geosystems - G<sup>3</sup>
Source: Geochemistry, Geophysics, Geosystems - G>3`, 6(4), 24p. Publisher: American Geophysical Union and The Geochemical Society, United States. ISSN: 1525-2027
Note: In English. 81 refs.; illus., incl. 7 tables, sketch map
Summary: Recent examinations of the chemical fluxes through convergent plate margins suggest the existence of significant mass imbalances for many key species: only 20-30% of the to-the-trench inventory of large-ion lithophile elements (LILE) can be accounted for by the magmatic outputs of volcanic arcs. Active serpentinite mud volcanism in the shallow forearc region of the Mariana convergent margin presents a unique opportunity to study a new outflux: the products of shallow-level exchanges between the upper mantle and slab-derived fluids. ODP Leg 125 recovered serpentinized harzburgites and dunites from three sites on the crests and flanks of the active Conical Seamount. These serpentinites have U-shaped rare earth element (REE) patterns, resembling those of boninites. U, Th, and the high field strength elements (HFSE) are highly depleted and vary in concentration by up to 2 orders of magnitude. The low U contents and positive Eu anomalies indicate that fluids from the subducting Pacific slab were probably reducing in nature. On the basis of substantial enrichments of fluid-mobile elements in serpentinized peridotites, we calculated very large slab inventory depletions of B (79%), Cs (32%), Li (18%), As (17%), and Sb (12%). Such highly enriched serpentinized peridotites dragged down to depths of arc magma generation may represent an unexplored reservoir that could help balance the input-output deficit of these elements as observed by Plank and Langmuir (1993, 1998) and others. Surprisingly, many species thought to be mobile in fluids, such as U, Ba, Rb, and to a lesser extent Sr and Pb, are not enriched in the rocks relative to the depleted mantle peridotites, and we estimate that only 1-2% of these elements leave the subducting slabs at depths of 10 to 40 km. Enrichments of these elements in volcanic front and behind-the-front arc lavas point to changes in slab fluid composition at greater depths.
Year of Publication: 2005
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; Basins; Conical Seamount; Europium; Fluid phase; Fore-arc basins; Geochemistry; Leg 125; Mantle; Mariana Islands; Metaigneous rocks; Metals; Metamorphic rocks; Metasomatic rocks; Metasomatism; Micronesia; Ocean Drilling Program; Oceania; Plate convergence; Rare earths; Serpentinite; Serpentinization; Slabs; Subduction zones
Coordinates: N120000 N200000 E1480000 E1440000
Record ID: 2006020294
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