Shallow slab fluid release across and along the Mariana arc-basin system; insights from geochemistry of serpentinized peridotites from the Mariana fore arc

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doi: 10.1029/2006JB004749
Author(s): Savov, Ivan P.; Ryan, Jeffrey G.; D'Antonio, Massimo; Fryer, Patricia
Author Affiliation(s): Primary:
Carnegie Institution of Washington, Department of Terrestrial Magnetism, Washington, DC, United States
University of South Florida, United States
Universita di Napoli Federico II, Italy
Hawaii Institute of Geophysics and Planetology, United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 112(B9). Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 100 refs.; illus., incl. 5 tables, geol. sketch map
Summary: Shallow slab devolatilization is not only witnessed through fluid expulsion at accretionary prisms, but is also evidenced by active serpentinite seamounts in the shallow fore-arc region of the Mariana convergent margin. Ocean Drilling Program (ODP) Leg 195 recovered serpentinized peridotites that present a unique opportunity to study the products of shallow level exchanges between the upper mantle and slab-derived fluids. Similar to samples recovered during ODP Leg 125, the protoliths of these fore-arc serpentinized peridotites are mantle harzburgites that have suffered large volume melt extraction (up to 25%) prior to interactions with fluids released from the downgoing Pacific Plate. Samples recovered from both ODP legs 125 and 195 show U-shaped rare earth element (REE) patterns and very low REE abundances (0.001-0.1 × chondrites). Relative to global depleted mantle values these rocks typically have 1-2 orders of magnitude lower high field strength elements, REE, Th, and U contents. Interestingly, all fore-arc rocks thus far examined show extreme enrichments of fluid mobile elements (FME: B, As, Cs, Sb, Li). Because the elemental and B, Li, and Sr isotope systematics in these fore-arc serpentinites point to nonseawater-related processes, studies of elemental excesses and anomalous isotopic signatures allow assessment of how much of the subducted inventory is lost during the initial subduction process between 10 and 40 km. On the basis of similar but substantial enrichments of FME in the Mariana fore-arc samples recovered at ODP legs 125 and 195, we report large slab inventory depletions of B (∼75%), Cs (∼25%), As (∼15%), Li (∼15%), and Sb (∼8%); surprisingly low (generally less than 2%) depletions of Rb, Ba, Pb, U, Sr; and no depletions in REE and the high field strength elements (HFSE). Such slab-metasomatized mantle wedge materials may be dragged to depths of arc magma generation, as proposed by Tatsumi (1986) and Straub and Layne (2002) and thus represent an unexplored class of mantle material, different in its origins, physical properties and geochemical fingerprint from mantle rocks traditionally used in modeling a wide range of subduction zone processes. Copyright 2007 by the American Geophysical Union.
Year of Publication: 2007
Research Program: ODP Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; 18 Geophysics, Solid-Earth; Basins; Chemical composition; Fore-arc basins; Gases; Igneous rocks; Leg 195; Mantle; Mantle wedges; Mariana Forearc; Mariana Islands; Metasomatism; Micronesia; North Pacific; Northwest Pacific; ODP Site 1200; Ocean Drilling Program; Ocean floors; Oceania; Pacific Ocean; Peridotites; Plutonic rocks; Seamounts; Serpentinization; Slabs; Ultramafics; West Pacific
Coordinates: N134700 N134800 E1460100 E1460000
Record ID: 2008069573
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.