The source of the subduction component in convergent margin magmas: Trace element and radiogenic isotope evidence from Eocene boninites, Mariana forearc

Journal Article · Wed May 01 00:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90321-U· OSTI ID:6140217

Stern, R J ^[1]; Morris, J ^[2]; Bloomer, S H ^[3]; Hawkins, Jr, J W ^[4]

---

1. Univ. of Texas, Richardson (United States)
2. Dept. of Terrestrial Magnetism, Washington, DC (United States)
3. Boston Univ., MA (United States)
4. Scripps Inst. of Oceanography, La Jolla, CA (United States)

Boninites are generally accepted as being melts from mixtures of depleted harzburgite and a water- and incompatible element-enriched component thought to be derived from the subducted plate (the subduction component). From calculations in this study, Mariana boninites are inferred to obtain 70-90% of Sr, 60-95% of Pb, and 0-80% of Nd from the subduction component, and so provide unique insights into the composition and source of this material as sampled early in the development of the arc. Nd-, Pb-, and Sr-isotopic compositions of Eocene boninites from three dredge sites in the Mariana forearc indicate that this subduction component is isotopically indistinguishable from mantle sources responsible for the generation of typical, northern hemisphere ocean-island basalt. Initial {sup 87}Sr/{sup 86}Sr {epsilon}-Nd-, and Pb-isotopic compositions fall within the Sr-Nd mantle array and along the NHRL for Pb-isotopic compositions. The values for the Eocene boninites are very similar to those of modern Mariana arc lavas, indicating that the subduction component is isotopically homogeneous in time and space. If the depleted endmember in boninite petrogenesis is assumed to be a MORB-source, subducted sediments cannot be significant sources of the subduction component. Instead, the subduction component identified for these boninites must have been derived from dehydration of subducted basaltic crust or via re-equilibration of fluids - and cations - released from the dehydrating slab with the overlying mantle wedge.

• OSTI ID: 6140217
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:5; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
ANDESITES
CENOZOIC ERA
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPED COUNTRIES
EARTH CRUST
EOCENE EPOCH
GEOCHEMISTRY
GEOLOGIC AGES
IGNEOUS ROCKS
ISLANDS
ISOTOPE RATIO
ISOTOPES
LEAD ISOTOPES
MAGMA
MARIANA ISLANDS
NEODYMIUM ISOTOPES
NORTH AMERICA
OCEANIC CRUST
PETROCHEMISTRY
PETROGENESIS
ROCKS
STRONTIUM ISOTOPES
SUBDUCTION ZONES
TERTIARY PERIOD
TRUST TERRITORY OF THE PACIFIC ISLANDS
USA
VOLCANIC ROCKS