Tracing the effects of high-pressure metasomatic fluids and seawater alteration in blueschist-facies overprinted eclogites: Implications for subduction channel processes

Abstract

Nils, Tracing the effects of high-pressure metasomatic fluids and seawater alteration in blueschist-facies overprinted eclogites: Implications for subduction channel processes, Chemical Geology (2011Geology ( ), doi: 10.1016Geology ( /j.chemgeo.2011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT

Elemental transport upon hydration of basic schists during regional metamorphism: Geochemical evidence from the Sanbagawa metamorphic belt, Japan

“…Mass loss associated with dissolution and removal of major elements by fluid flow as much as several tens of percent has been reported in the regional metamorphic belts (e.g., Ague, 1994;van der Straaten et al, 2012), which can result in rather uniform enrichment of fluidimmobile elements, e.g., a large increase in Yb concentration without significant change in La/Yb ratio as in Fig. 6a.…”

Subduction zone metamorphic pathway for deep carbon cycling: II. Evidence from HP/UHP metabasaltic rocks and ophicarbonates

“…Conspicuously absent in the W. Alps exposures are cm-to m-scale, through-going (i.e., at scales beyond those of individual small outcrops) veins indicating larger-scale fluid mobility (e.g., of the type described for Tianshan localities; see van der Straaten et al, 2008van der Straaten et al, , 2012Beinlich et al, 2010;John et al, 2012).…”

“…The C subduction input in carbonated ultramafic rocks is likely far smaller, but still a significant flux (see Alt et al, 2013; (Platt, 1986;Desmons et al, 1999a,b;Jolivet et al, 2003;Zheng, 2012), affording a more thorough assessment of prograde metamorphic devolatilization history (see Bebout, 2007a;Bebout et al, 2013). In this paper, we provide a smaller dataset for carbonate in veins, and as finely disseminated carbonate, in well-studied eclogites in the Tianshan, including eclogites sampled across the envelopes of veins interpreted to be significant intraslab fluid conduits and eclogites that were rehydrated to blueschist along the plate interface during their exhumation (Zack and John, 2007;van der Straaten et al, 2008van der Straaten et al, , 2012Beinlich et al, 2010;John et al, 2012). We integrate field and petrologic observations, theoretical calculations of devolatilization history (using the Perple_X software; Connolly, 2005), and O and C isotope data for these rocks, largely focusing on carbonate (and decarbonation history) but with some attention paid to the minor reduced C that could reside in the metabasalts.…”

“…Other field and petrologic studies provide descriptions for UHP carbonate rocks at individual localities without detailed work evaluating extents of decarbonation and related isotopic shifts (e.g. Becker and Altherr, 1992;Kato et al, 1997;Zheng et al, 2003;Castelli et al, 2007;van der Straaten et al, 2008van der Straaten et al, , 2012Proyer et al, 2014;Lu et al, 2014). The smaller number of studies of HP/UHP metabasaltic rocks conducted at single localities, or over small ranges in grade (prehnite-pumpellyite to blueschist facies), have similarly indicated retention of C in subducting oceanic crust, with little or no isotopic shift, across metamorphic grades Barnicoat, 1999, 2003;Miller et al, 2001).…”

“…Detailed field and chemical studies (e.g., Gao and Klemd, 2003;John et al, 2008John et al, , 2012 have yielded insights into the prograde dehydration of blueschist to carbonate-bearing eclogite veins and multiple textural carbonate setting within the basalts that have seen relatively little exhumation overprinting (Gao and Klemd, 2003;Klemd et al, 2005;Beinlich et al, 2010). van der Straaten et al (2012) presented a small C and O isotope dataset for HP metabasalts from Tianshan which rehydrated to blueschists during their exhumation along the plate interface and suggested that the low  13 C values of some of the carbonates reflect the influence of fluid from a source containing organic/reduced C.…”