Subduction of pelagic sediments; implications for the origin of Ce-anomalous basalts from the Mariana Islands

• Published in: Journal of the Geological Society Vol. 141; no. 3; pp. 453 - 472
• Main Authors: Hole, M. J, Saunders, Andrew D, Marriner, G. F, Tarney, John
• Format: Journal Article
• Language: English
• Published: London Geological Society of London 01-05-1984; The Geological Society of London; Geological Society
• Subjects: active margins; alkali metals; alkaline earth metals; basalts; cerium; clastic sediments; composition; Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geochemistry; igneous and metamorphic rocks; Igneous and metamorphic rocks petrology, volcanic processes, magmas; igneous rocks; island arcs; isotopes; lead; magmas; mantle; Mariana Islands; Marianna Trench; Marine; metals; Micronesia; Oceania; ooze; Pb-207/Pb-204; Pb-208/Pb-204; pelagic sedimentation; petrology; plate convergence; radioactive isotopes; rare earths; ratios; Rb/Ba; rubidium; sedimentation; sediments; Soil and rock geochemistry; Sr-87/Sr-86; stable isotopes; strontium; subduction; tectonophysics; trace elements; trenches; volcanic rocks; Nazca Plate; ISEW, Pacific, Mariana Trench; ISEW, Pacific, Mariana Arc; Island arcs; Subduction zones; Rare earths; Cerium; Trace elements; Mariana Islands; Basalts; Isotopes; Anomalies
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/gsjgs.141.3.0453

A series of pelagic clays and nannofossil oozes from the Nazca plate have been analysed for REE and other trace elements. A calculated average - Pacific Authigenic Weighted Mean Sediment (PAWMS) - shows light REE-enrichment (Lan/Ybn approx 4.5), high contents of Ba and Sr, but low abundances of Rb, Nb and Ta; large negative Ce anomalies (Ce/Ce* approx 0.2) are also found. An attempt is made to model the contributions of PAWMS-type material to the source of the magmas of the Mariana island arc, an intra-oceanic arc far from the effect of continent-derived detritus. Only small amounts of pelagic sediment (0.3-0.5%) are needed to develop the negative Ce anomalies, high Ba/La ratios, and high LIL/HFS-element ratios which characterize these lavas, though a small fluid contribution from the dehydrating subducted oceanic crust is needed to give the high Rb/Ba found in several Mariana suites. Volumetrically it would appear that much of the sediment approaching the Mariana trench may be recycled into the deeper mantle, but incorporation of such material alone cannot account for the trace-element and isotope chemistry of ocean islands.