TY - JOUR A1 - Freundt, A. A1 - Grevemeyer, I. A1 - Rabbel, W. A1 - Hansteen, T. H. A1 - Hensen, C. A1 - Wehrmann, H. A1 - Kutterolf, S. A1 - Halama, Ralf A1 - Frische, M. T1 - Volatile (H2O, CO2, Cl, S) budget of the Central American subduction zone JF - International journal of earth sciences N2 - After more than a decade of multidisciplinary studies of the Central American subduction zone mainly in the framework of two large research programmes, the US MARGINS program and the German Collaborative Research Center SFB 574, we here review and interpret the data pertinent to quantify the cycling of mineral-bound volatiles (H2O, CO2, Cl, S) through this subduction system. For input-flux calculations, we divide the Middle America Trench into four segments differing in convergence rate and slab lithological profiles, use the latest evidence for mantle serpentinization of the Cocos slab approaching the trench, and for the first time explicitly include subduction erosion of forearc basement. Resulting input fluxes are 40-62 (53) Tg/Ma/m H2O, 7.8-11.4 (9.3) Tg/Ma/m CO2, 1.3-1.9 (1.6) Tg/Ma/m Cl, and 1.3-2.1 (1.6) Tg/Ma/m S (bracketed are mean values for entire trench length). Output by cold seeps on the forearc amounts to 0.625-1.25 Tg/Ma/m H2O partly derived from the slab sediments as determined by geochemical analyses of fluids and carbonates. The major volatile output occurs at the Central American volcanic arc that is divided into ten arc segments by dextral strike-slip tectonics. Based on volcanic edifice and widespread tephra volumes as well as calculated parental magma masses needed to form observed evolved compositions, we determine long-term (10(5) years) average magma and K2O fluxes for each of the ten segments as 32-242 (106) Tg/Ma/m magma and 0.28-2.91 (1.38) Tg/Ma/m K2O (bracketed are mean values for entire Central American volcanic arc length). Volatile/K2O concentration ratios derived from melt inclusion analyses and petrologic modelling then allow to calculate volatile fluxes as 1.02-14.3 (6.2) Tg/Ma/m H2O, 0.02-0.45 (0.17) Tg/Ma/m CO2, and 0.07-0.34 (0.22) Tg/Ma/m Cl. The same approach yields long-term sulfur fluxes of 0.12-1.08 (0.54) Tg/Ma/m while present-day open-vent SO2-flux monitoring yields 0.06-2.37 (0.83) Tg/Ma/m S. Input-output comparisons show that the arc water fluxes only account for up to 40 % of the input even if we include an "invisible" plutonic component constrained by crustal growth. With 20-30 % of the H2O input transferred into the deeper mantle as suggested by petrologic modeling, there remains a deficiency of, say, 30-40 % in the water budget. At least some of this water is transferred into two upper-plate regions of low seismic velocity and electrical resistivity whose sizes vary along arc: one region widely envelopes the melt ascent paths from slab top to arc and the other extends obliquely from the slab below the forearc to below the arc. Whether these reservoirs are transient or steady remains unknown. KW - Subduction input KW - Forearc dewatering KW - Arc magmatism KW - Subduction fluids Y1 - 2014 U6 - https://doi.org/10.1007/s00531-014-1001-1 SN - 1437-3254 SN - 1437-3262 VL - 103 IS - 7 SP - 2101 EP - 2127 PB - Springer CY - New York ER - TY - INPR A1 - Freundt, A. A1 - Halama, Ralf A1 - Suess, E. A1 - Voelker, D. T1 - Introduction to the special issue on SFB 574 "Volatiles and fluids in subduction zones: climate feedback and trigger mechanisms for natural disasters" T2 - International journal of earth sciences Y1 - 2014 U6 - https://doi.org/10.1007/s00531-014-1059-9 SN - 1437-3254 SN - 1437-3262 VL - 103 IS - 7 SP - 1729 EP - 1731 PB - Springer CY - New York ER - TY - JOUR A1 - Halama, Ralf A1 - Konrad-Schmolke, Matthias A1 - Sudo, Masafumi A1 - Marschall, Horst R. A1 - Wiedenbeck, Michael T1 - Effects of fluid-rock interaction on Ar-40/Ar-39 geochronology in high-pressure rocks (Sesia-Lanzo Zone, Western Alps) JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - In situ UV laser spot Ar-40/Ar-39 analyses of distinct phengite types in eclogite-facies rocks from the Sesia-Lanzo Zone (Western Alps, Italy) were combined with SIMS boron isotope analyses as well as boron (B) and lithium (Li) concentration data to link geochronological information with constraints on fluid-rock interaction. In weakly deformed samples, apparent Ar-40/Ar-39 ages of phengite cores span a range of similar to 20 Ma, but inverse isochrons define two distinct main high-pressure (HP) phengite core crystallization periods of 88-82 and 77-74 Ma, respectively. The younger cores have on average lower B contents (similar to 36 mu g/g) than the older ones (similar to 43-48 mu g/g), suggesting that loss of B and resetting of the Ar isotopic system were related. Phengite cores have variable delta B-11 values (-18 parts per thousand to -10 parts per thousand), indicating the lack of km scale B homogenization during HP crystallization. Overprinted phengite rims in the weakly deformed samples generally yield younger apparent Ar-40/Ar-39 ages than the respective cores. They also show variable effects of heterogeneous excess 40 Ar incorporation and Ar loss. One acceptable inverse isochron age of 77.1 +/- 1.1 Ma for rims surrounding older cores (82.6 +/- 0.6 Ma) overlaps with the second period of core crystallization. Compared to the phengite cores, all rims have lower B and Li abundances but similar delta B-11 values (-15 parts per thousand to -9 parts per thousand), reflecting internal redistribution of B and Li and internal fluid buffering of the B isotopic composition during rim growth. The combined observation of younger Ar-40/Ar-39 ages and boron loss, yielding comparable values of both parameters only in cores and rims of different samples, is best explained by a selective metasomatic overprint. In low permeability samples, this overprint caused recrystallization of phengite rims, whereas higher permeability in other samples led to complete recrystallization of phengite grains. Strongly deformed samples from a several km long, blueschist-facies shear zone contain mylonitic phengite that forms a tightly clustered group of relatively young apparent Ar-40/Ar-39 ages (64.7-68.8 Ma), yielding an inverse isochron age of 65.0 +/- 3.0 Ma. Almost complete B and Li removal in mylonitic phengite is due to leaching into a fluid. The B isotopic composition is significantly heavier than in phengites from the weakly deformed samples, indicating an external control by a high-delta B-11 fluid (delta B-11 = + 7 +/- 4 parts per thousand). We interpret this result as reflecting phengite recrystallization related to deformation and associated fluid flow in the shear zone. This event also caused partial resetting of the Ar isotope system and further B loss in more permeable rocks of the adjacent unit. We conclude that geochemical evidence for pervasive or limited fluid flow is crucial for the interpretation of Ar-40/Ar-39 data in partially metasomatized rocks. Y1 - 2014 U6 - https://doi.org/10.1016/j.gca.2013.10.023 SN - 0016-7037 SN - 1872-9533 VL - 126 SP - 475 EP - 494 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Konrad-Schmolke, Matthias A1 - Halama, Ralf T1 - Combined thermodynamic-geochemical modeling in metamorphic geology: Boron as tracer of fluid-rock interaction JF - Lithos : an international journal of mineralogy, petrology, and geochemistry N2 - Quantitative geochemical modeling is today applied in a variety of geological environments from the petrogenesis of igneous rocks to radioactive waste disposal. In addition, the development of thermodynamic databases and computer programs to calculate equilibrium phase diagrams has greatly advanced our ability to model geodynamic processes. Combined with experimental data on elemental partitioning and isotopic fractionation, thermodynamic forward modeling unfolds enormous capacities that are far from exhausted. In metamorphic petrology the combination of thermodynamic and trace element forward modeling can be used to study and to quantify processes at spatial scales from mu m to km. The thermodynamic forward models utilize Gibbs energy minimization to quantify mineralogical changes along a reaction path of a chemically open fluid/rock system. These results are combined with mass balanced trace element calculations to determine the trace element distribution between rock and melt/fluid during the metamorphic evolution. Thus, effects of mineral reactions, fluid-rock interaction and element transport in metamorphic rocks on the trace element and isotopic composition of minerals, rocks and percolating fluids or melts can be predicted. Here we illustrate the capacities of combined thermodynamic-geochemical modeling based on two examples relevant to mass transfer during metamorphism. The first example focuses on fluid-rock interaction in and around a blueschist-facies shear zone in felsic gneisses, where fluid-induced mineral reactions and their effects on boron (B) concentrations and isotopic compositions in white mica are modeled. In the second example, fluid release from a subducted slab, the associated transport of B as well as variations in B concentrations and isotopic compositions in liberated fluids and residual rocks are modeled. We compare the modeled results of both examples to geochemical data of natural minerals and rocks and demonstrate that the combination of thermodynamic and geochemical models enables quantification of metamorphic processes and insights into element cycling that would have been unattainable if only one model approach was chosen. (C) 2014 Elsevier B.V. All rights reserved. KW - Thermodynamic-geochemical modeling KW - Fluid-rock interaction KW - Subduction KW - Dehydration KW - Boron isotopes Y1 - 2014 U6 - https://doi.org/10.1016/j.lithos.2014.09.021 SN - 0024-4937 SN - 1872-6143 VL - 208 SP - 393 EP - 414 PB - Elsevier CY - Amsterdam ER -