@misc{10481/62120,
year = {2019},
month = {3},
url = {http://hdl.handle.net/10481/62120},
abstract = {At sub‐arc depths, the release of carbon from subducting slab lithologies is mostly
controlled by fluid released by devolatilization reactions such as dehydration of antigorite (Atg‐) serpentinite to prograde peridotite. Here we investigate carbonate–silicate rocks hosted in Atg‐serpentinite and prograde chlorite (Chl‐) harzburgite in the
Milagrosa and Almirez ultramafic massifs of the palaeo‐subducted Nevado‐Filábride
Complex (NFC, Betic Cordillera, S. Spain). These massifs provide a unique opportunity to study the stability of carbonate during subduction metamorphism at P–T
conditions before and after the dehydration of Atg‐serpentinite in a warm subduction
setting. In the Milagrosa massif, carbonate–silicate rocks occur as lenses of Ti‐clinohumite–diopside–calcite marbles, diopside–dolomite marbles and antigorite–diopside–dolomite rocks hosted in clinopyroxene‐bearing Atg‐serpentinite. In Almirez,
carbonate–silicate rocks are hosted in Chl‐harzburgite and show a high‐grade assemblage composed of olivine, Ti‐clinohumite, diopside, chlorite, dolomite, calcite, Cr‐
bearing magnetite, pentlandite and rare aragonite inclusions. These NFC
carbonate–silicate rocks have variable CaO and CO2 contents at nearly constant Mg/
Si ratio and high Ni and Cr contents, indicating that their protoliths were variable
mixtures of serpentine and Ca‐carbonate (i.e., ophicarbonates). Thermodynamic
modelling shows that the carbonate–silicate rocks attained peak metamorphic conditions similar to those of their host serpentinite (Milagrosa massif; 550–600°C and
1.0–1.4 GPa) and Chl‐harzburgite (Almirez massif; 1.7–1.9 GPa and 680°C).
Microstructures, mineral chemistry and phase relations indicate that the hybrid carbonate–silicate bulk rock compositions formed before prograde metamorphism,
likely during seawater hydrothermal alteration, and subsequently underwent subduction metamorphism. In the CaO–MgO–SiO2 ternary, these processes resulted in a
compositional variability of NFC serpentinite‐hosted carbonate–silicate rocks along
the serpentine‐calcite mixing trend, similar to that observed in serpentinite‐hosted
carbonate‐rocks in other palaeo‐subducted metamorphic terranes. Thermodynamic modelling using classical models of binary H2O–CO2 fluids shows that the compositional variability along this binary determines the temperature of the main devolatilization reactions, the fluid composition and the mineral assemblages of reaction
products during prograde subduction metamorphism. Thermodynamic modelling
considering electrolytic fluids reveals that H2O and molecular CO2 are the main fluid
species and charged carbon‐bearing species occur only in minor amounts in equilibrium with carbonate–silicate rocks in warm subduction settings. Consequently, accounting for electrolytic fluids at these conditions slightly increases the solubility of
carbon in the fluids compared with predictions by classical binary H2O–CO2 fluids,
but does not affect the topology of phase relations in serpentinite‐hosted carbonate‐
rocks. Phase relations, mineral composition and assemblages of Milagrosa and
Almirez (meta)‐serpentinite‐hosted carbonate–silicate rocks are consistent with local
equilibrium between an infiltrating fluid and the bulk rock composition and indicate
a limited role of infiltration‐driven decarbonation. Our study shows natural evidence
for the preservation of carbonates in serpentinite‐hosted carbonate–silicate rocks beyond the Atg‐serpentinite breakdown at sub‐arc depths, demonstrating that carbon
can be recycled into the deep mantle.},
organization = {Funding from the European Union FP7 Marie‐Curie Initial Training Network ABYSS under REA Grant Agreement no. 608001},
organization = {Spanish ‘Agencia Estatal de Investigación’ (AEI) grants no. CGL2016‐75224‐R to V.L.S.‐V and CGL2016‐81085‐R to C.J.G and C.M and grant no. PCIN‐2015‐053 to C.J.G},
organization = {Junta de Andalucía Funding under grants no. RNM‐131, RNM‐374 and P12‐RNM‐3141},
organization = {MINECO for financing a Ramón y Cajal fellowship no. RYC‐2012‐11314 and K.H. for a Juan de la Cierva Fellowship no. FPDI‐2013‐16253 and a research contract under grant no. CGL2016‐81085‐R},
publisher = {Wiley},
keywords = {Carbon cycle},
keywords = {Nevado-Filábride complex},
keywords = {Ophicarbonate},
keywords = {Serpentinite dehydration},
keywords = {Subduction fluids},
title = {Subduction metamorphism of serpentinite‐hosted carbonates beyond antigorite-serpentinite dehydration (Nevado‐Filábride Complex, Spain)},
doi = {10.1111/jmg.12481},
author = {Menzel, Manuel Dominik and Garrido, Carlos J. and López Sánchez-Vizcaíno, Vicente and Hidas, Károly and Marchesi, Claudio},
}