High pressure phase relations of subducted volcaniclastic sediments from the West Pacific and their implications for the geochemistry of Mariana Arc magmas

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doi: 10.1016/j.chemgeo.2013.01.015
Author(s): Martindale, Marina; Skora, Susanne; Pickles, Jonathan; Elliott, Tim; Blundy, Jonathan; Avanzinelli, Riccardo
Author Affiliation(s): Primary:
University of Bristol, School of Earth Sciences, Bristol, United Kingdom
Other:
Universita degli Studi di Firenze, Italy
Volume Title: Chemical Geology
Source: Chemical Geology, Vol.342, p.94-109. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541 CODEN: CHGEAD
Note: In English. 120 refs.; illus., incl. 5 tables, sketch map
Summary: The phase relations of natural volcaniclastic sediments from the west Pacific Ocean were investigated experimentally at conditions of 3-6 GPa and 800-900°C with 10 wt.% added H2O (in addition to ∼10 wt.% structurally-bound H2O) to induce hydrous melting. Volcaniclastic sediments are shown to produce a sub-solidus assemblage of garnet, clinopyroxene, biotite, quartz/coesite and the accessory phases rutile±Fe-Ti oxide±apatite±monazite±zircon. Hydrous melt appears at temperatures exceeding 800-850°C, irrespective of pressure. The melt-producing reaction consumes clinopyroxene, biotite and quartz/coesite and produces orthopyroxene. These phase relations differ from those of pelagic clays and K-bearing mid ocean ridge basalts (e.g. altered oceanic crust) that contain phengite, rather than biotite, as a sub-solidus phase. Despite their relatively high melt productivity, the wet solidus for volcaniclastic sediments is found to be higher (825-850°C) than other marine sediments (700-750°C) at 3 GPa. This trend is reversed at high-pressure conditions (6 GPa) where the biotite melting reaction occurs at lower temperatures (800-850°C) than the phengite melting reaction (900-1000°C). Trace element data was obtained from the 3 GPa run products, showing that partial melts are depleted in heavy rare earth elements (REE) and high field strength elements (HFSE), due to the presence of residual garnet and rutile, and are enriched in large ion lithophile elements (LILE), except for Sr and Ba. This is in contrast to previous experimental studies on pelagic sediments at sub-arc depths, where Sr and Ba are among the most enriched trace elements in glasses. This behavior can be partly attributed to the presence of residual apatite, which also host some light REE in our supra-solidus residues. Our new experimental results account for a wide range of trace element and U-series geochemical features of the sedimentary component of the Mariana arc magmas, including imparting a substantial Nb anomaly to melts from an anomaly-free protolith. Abstract Copyright (2013) Elsevier, B.V.
Year of Publication: 2013
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 06 Petrology, Sedimentary; Chemical composition; Clastic sediments; Crystal chemistry; Electron probe data; Geochemical anomalies; High pressure; Hydration; ICP mass spectra; Island arcs; Leg 129; Lithostratigraphy; Major elements; Mariana Islands; Mariana Trench; Mariana Trough; Marine sediments; Mass spectra; Melting; Metals; Micronesia; Mineral composition; Niobium; North Pacific; Northwest Pacific; ODP Site 800; ODP Site 801; ODP Site 802; Ocean Drilling Program; Oceania; P-T conditions; Pacific Ocean; Pelagic sedimentation; Phase equilibria; Phase transitions; Pigafetta Basin; Pressure; Rare earths; SEM data; Sedimentary petrology; Sedimentation; Sediments; Spectra; Stratigraphic units; Subduction zones; Textures; Trace elements; Volcaniclastics; West Pacific
Coordinates: N183831 N183835 E1562136 E1562134
N130000 N210000 E1470000 E1430000
Record ID: 2014000232
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands