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

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

May 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55.1467s&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 55, Issue 5, pp.1467-1481

Computer Science

16

Scientific paper

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 87 Sr / 86 Sr (0.7032 to 0.7034), -Nd- (+7.4 to +9.2), and Pb-isotopic compositions ( 206 Pb / 204 Pb = 18.4 to 18.9, 207 Pb / 204 Pb = 15.45 to 15.55, 208 Pb / 204 Pb = 37.92 to 38.45; 7/4 = -4 to +1.6; 8/4 = -10 to +12) 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.

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