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Blueschist metamorphism in an active subduction zone

Maekawa, Hliokazu, Shozul, Masaya, Ishll, Teruaki., Fryer, Patricia B. and Pearce, Julian A. 1993. Blueschist metamorphism in an active subduction zone. Nature 364 (6437) , pp. 520-523. 10.1038/364520a0

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Abstract

The high-pressure, low-temperature metamorphic rocks known as blueschists have long been considered to form in subduction zones, where the descent of a relatively cold slab leads to the occurrence of unusually low temperatures at mantle pressures. Until now, however, the link between blueschist-facies rocks and subduction zones has been indirect, relying on a spatial association of blueschists with old subduction complexes, and estimates of the geothermal gradients likely to exist in subduction zones. Here we strengthen this link, by reporting the discovery of blueschist-facies minerals (lawsonite, aragonite, sodic pyroxene and blue amphibole) in clasts from a serpentinite seamount in the forearc of the active Mariana subduction zone. The metamorphic conditions estimated from the mineral compositions are 150–250 °C and 5–6 kbar (16–20 km depth). The rocks must have been entrained in rising serpentine mud diapirs, and extruded from mud volcanoes onto the sea floor. Further study of these rocks may provide new insight into the tectonics of trench-forearc systems, and in particular, the processes by which blueschist-facies clasts come to be associated with forearc sediments in ancient subduction complexes.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
ISSN: 0028-0836
Last Modified: 04 Jun 2017 02:04
URI: http://orca-mwe.cf.ac.uk/id/eprint/8479

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