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 - TY - JOUR A1 - Konrad-Schmolke, Matthias A1 - Zack, Thomas A1 - O'Brien, Patrick J. T1 - Combining thermodynamic and trace element modeling : a tool to quantify mineral reactions and trace element budgets during metamorphism Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00167037 U6 - https://doi.org/10.1016/j.gca.2009.05.009 SN - 0016-7037 ER - TY - JOUR A1 - Zack, Thomas A1 - Konrad-Schmolke, Matthias T1 - Distinguishing trace element redistribution during mineral reactions from fluid-induced trace element mobility in blueschists Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00167037 U6 - https://doi.org/10.1016/j.gca.2009.05.019 SN - 0016-7037 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 - Zack, Thomas A1 - O'Brien, Patrick J. A1 - Barth, Matthias T1 - Fluid migration above a subducted slab - Thermodynamic and trace element modelling of fluid-rock interaction in partially overprinted eclogite-facies rocks (Sesia Zone, Western Alps) JF - Earth & planetary science letters N2 - The amount and composition of subduction zone fluids and the effect of fluid-rock interaction at a slab-mantle interface have been constrained by thermodynamic and trace element modelling of partially overprinted blueschist-facies rocks from the Sesia Zone (Western Alps). Deformation-induced differences in fluid flux led to a partial preservation of pristine mineral cores in weakly deformed samples that were used to quantify Li, B, Stand Pb distribution during mineral growth, -breakdown and modification induced by fluid-rock interaction. Our results show that Li and 13 budgets are fluid-controlled, thus acting as tracers for fluid-rock interaction processes, whereas Stand Pb budgets are mainly controlled by the fluid-induced formation of epidote. Our calculations show that fluid-rock interaction caused significant Li and B depletion in the affected rocks due to leaching effects, which in turn can lead to a drastic enrichment of these elements in the percolating fluid. Depending on available fluid-mineral trace element distribution coefficients modelled fluid rock ratios were up to 0.06 in weakly deformed samples and at least 0.5 to 4 in shear zone mylonites. These amounts lead to time integrated fluid fluxes of up to 1.4-10(2) m(3) m(-2) in the weakly deformed rocks and 1-8-10(3) m(3) m(-2) in the mylonites. Combined thermodynamic and trace element models can be used to quantify metamorphic fluid fluxes and the associated element transfer in complex, reacting rock systems and help to better understand commonly observed fluid-induced trace element trends in rocks and minerals from different geodynamic environments. KW - fluid-rock interaction KW - subduction zone KW - fluid migration KW - slab-mantle interface KW - trace element transport Y1 - 2011 U6 - https://doi.org/10.1016/j.epsl.2011.09.025 SN - 0012-821X VL - 311 IS - 3-4 SP - 287 EP - 298 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Konrad-Schmolke, Matthias A1 - O'Brien, Patrick J. A1 - Zack, Thomas T1 - Fluid Migration above a Subducted Slab-Constraints on Amount, Pathways and Major Element Mobility from Partially Overprinted Eclogite-facies Rocks (Sesia Zone, Western Alps) JF - Journal of petrology N2 - The Western Alpine Sesia-Lanzo Zone (SLZ) is a sliver of eclogite-facies continental crust exhumed from mantle depths in the hanging wall of a subducted oceanic slab. Eclogite-facies felsic and basic rocks sampled across the internal SLZ show different degrees of retrograde metamorphic overprint associated with fluid influx. The weakly deformed samples preserve relict eclogite-facies mineral assemblages that show partial fluid-induced compositional re-equilibration along grain boundaries, brittle fractures and other fluid pathways. Multiple fluid influx stages are indicated by replacement of primary omphacite by phengite, albitic plagioclase and epidote as well as partial re-equilibration and/or overgrowths in phengite and sodic amphibole, producing characteristic step-like compositional zoning patterns. The observed textures, together with the map-scale distribution of the samples, suggest open-system, pervasive and reactive fluid flux across large rock volumes above the subducted slab. Thermodynamic modelling indicates a minimum amount of fluid of 0 center dot 1-0 center dot 5 wt % interacting with the wall-rocks. Phase relations and reaction textures indicate mobility of K, Ca, Fe and Mg, whereas Al is relatively immobile in these medium-temperature-high-pressure fluids. Furthermore, the thermodynamic models show that recycling of previously fractionated material, such as in the cores of garnet porphyroblasts, largely controls the compositional re-equilibration of the exhumed rock body. KW - fluid migration KW - subduction KW - fluid-rock interaction KW - Sesia Zone Y1 - 2011 U6 - https://doi.org/10.1093/petrology/egq087 SN - 0022-3530 VL - 52 IS - 3 SP - 457 EP - 486 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Scott, James M. A1 - Konrad-Schmolke, Matthias A1 - O'Brien, Patrick J. A1 - Günter, Christina T1 - High-T, low-P formation of rare olivine-bearing symplectites in variscan eclogite JF - Journal of petrology N2 - Extremely rare veinlets and reaction textures composed of symplectites of olivine (similar to Fo(43-55)) + plagioclase +/- spinel +/- ilmenite, associated with more common pyroxene + plagioclase and amphibole + plagioclase varieties, are preserved within eclogites and garnet pyroxenites in the Moldanubian Zone of the Bohemian Massif. Thermodynamic modelling integrated with conventional geothermometry conducted on an eclogite reveals that the symplectite-forming stage occurred at high T (similar to 850 degrees C) and low P (< 6 and > 2 center dot 5 kbar). The development of the different symplectite types reflects reactions that took place in micro-scale domains. The breakdown of high-P garnet controlled the formation of olivine-bearing and amphibole + plagioclase symplectites, whereas breakdown of high-P omphacite led to formation of pyroxene + plagioclase symplectites. In addition, post-eclogite facies but pre-symplectite stage porphyroblastic amphibole and phlogopite were also replaced by olivine-bearing symplectites. Material transfer calculations and thermodynamic modelling indicate that the formation of different symplectite types was linked despite their different bulk compositions. For example, the olivine-bearing symplectites gained Fe +/- Mg, whereas adjacent amphibole + plagioclase and pyroxene + plagioclase symplectites show losses in Fe and Mg; Al, Si and Ca were also variably exchanged. The olivine-bearing symplectites were particularly sensitive to Na despite the small concentration of this element. In eclogites where Na was readily available, the plagioclase composition in the olivine-bearing symplectites shifted from pure anorthite to bytownite, with the less calcic feldspar partitioning Si and inhibiting the formation of orthopyroxene. This regional high-T, low-P granulite-facies symplectite overprint may have been caused by advective heat loss from rapidly exhumed high-T, high-P granulitic bodies (Gfohl Unit) that were emplaced into and over the middle crust (Monotonous and Varied Series) during Carboniferous continent-continent collision. KW - olivine KW - symplectite KW - eclogite KW - thermodynamics KW - Variscan Y1 - 2013 U6 - https://doi.org/10.1093/petrology/egt015 SN - 0022-3530 SN - 1460-2415 VL - 54 IS - 7 SP - 1375 EP - 1398 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Wilke, Franziska Daniela Helena A1 - O'Brien, Patrick J. A1 - Altenberger, Uwe A1 - Konrad-Schmolke, Matthias A1 - Khan, M. Ahmed T1 - Multi-stage reaction history in different eclogite types from the Pakistan Himalaya and implications for exhumation processes N2 - Metabasites were sampled from rock series of the subducted margin of the Indian Plate, the so-called Higher Himalayan Crystalline, in the Upper Kaghan Valley, Pakistan. These vary from corona dolerites, cropping out around Saif- ul-Muluk in the south, to coesite-eclogite close to the suture zone against rocks of the Kohistan arc in the north. Bulk rock major- and trace-element chemistry reveals essentially a single protolith as the source for five different eclogite types, which differ in fabric, modal mineralogy as well as in mineral chemistry. The study of newly-collected samples reveals coesite (confirmed by in situ Raman spectroscopy) in both garnet and omphacite. All eclogites show growth of amphiboles during exhumation. Within some coesite-bearing eclogites the presence of glaucophane cores to barroisite is noted whereas in most samples porphyroblastic sodic-calcic amphiboles are rimmed by more aluminous calcic amphibole (pargasite, tschermakite, and edenite). Eclogite facies rutile is replaced by ilmenite which itself is commonly surrounded by titanite. In addition, some eclogite bodies show leucocratic segregations containing phengite, quartz, zoisite and/or kyanite. The important implication is that the complex exhumation path shows stages of initial cooling during decompression (formation of glaucophane) followed by reheating: a very similar situation to that reported for the coesite-bearing eclogite series of the Tso Morari massif, India, 450 km to the south-east. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/00244937 U6 - https://doi.org/10.1016/j.lithos.2009.07.015 SN - 0024-4937 ER - TY - JOUR A1 - Halama, Ralf A1 - Glodny, Johannes A1 - Konrad-Schmolke, Matthias A1 - Sudo, Masafumi T1 - Rb-Sr and in situ Ar-40/Ar-39 dating of exhumation-related shearing and fluid-induced recrystallization in the Sesia zone (Western Alps, Italy) JF - Geosphere N2 - The Sesia zone in the Italian Western Alps is a piece of continental crust that has been subducted to eclogite-facies conditions and records a complex metamorphic history. The exact timing of events and the significance of geochronological information are debated due to the interplay of tectonic, metamorphic, and metasomatic processes. Here we present new geochronological data using Rb-Sr internal mineral isochrons and in situ Ar-40/Ar-39 laser ablation data to provide constraints on the relative importance of fluid-mediated mineral replacement reactions and diffusion for the interpretation of radiogenic isotope signatures, and on the use of these isotopic systems for dating metamorphic and variably deformed rocks. Our study focuses on the shear zone at the contact between two major lithological units of the Sesia zone, the eclogitic micaschists and the gneiss minuti. Metasedimentary rocks of the eclogitic micaschists unit contain phengite with step-like zoning in major element chemistry as evidence for petrologic disequilibrium. Distinct Ar-40/Ar-39 spot ages of relict phengite cores and over-printed rims demonstrate the preservation of individual age domains in the crystals. The eclogitic micaschists also show systematic Sr isotope disequilibria among different phengite populations, so that minimum ages of relict assemblage crystallization can be differentiated from the timing of late increments of deformation. The preservation of these disequilibrium features shows the lack of diffusive re-equilibration and underpins that fluid-assisted dissolution and recrystallization reactions are the main factors controlling the isotope record in these subduction-related metamorphic rocks. Blueschist-facies mylonites record deformation along the major shear zone that separates the eclogitic micaschists from the gneiss minuti. Two Rb-Sr isochrones that comprise several white mica fractions and glaucophane constrain the timing of this deformation and accompanying near-complete blueschist-facies re-equilibration of the Rb-Sr system to 60.1 +/- 0.9 Ma and 60.9 +/- 2.1 Ma, respectively. Overlapping ages in eclogitic micaschists of 60.1 +/- 1.1 (Rb-Sr isochron of sheared matrix assemblage), 58.6 +/- 0.8, and 60.9 +/- 0.4 Ma (white mica Ar-40/Ar-39 inverse isochron ages) support the significance of this age and show that fluid-rock interaction and partial re-equilibration occurred as much as several kilometers away from the shear zone. An earlier equilibration during high-pressure conditions in the eclogitic mica schists is recorded in minimum Rb-Sr ages for relict assemblages (77.2 +/- 0.8 and 72.4 +/- 1.1 Ma) and an Ar-40/Ar-39 inverse isochron age of 75.4 +/- 0.8 Ma for white mica cores, again demonstrating that the two isotope systems provide mutually supporting geochronological information. Local reactivation and recrystallization along the shear zone lasted >15 m.y., as late increments of deformation are recorded in a greenschist-facies mylonite by a Rb-Sr isochron age of 46.5 +/- 0.7 Ma. Y1 - 2018 U6 - https://doi.org/10.1130/GES01521.1 SN - 1553-040X VL - 14 IS - 4 SP - 1425 EP - 1450 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Halama, Ralf A1 - Konrad-Schmolke, Matthias T1 - Retrograde metasomatic effects on phase assemblages in an interlayered blueschist-greenschist sequence (Coastal Cordillera, Chile) JF - Lithos : an international journal of mineralogy, petrology, and geochemistry N2 - Interlayered blueschists and greenschists of the Coastal Cordillera (Chile) are part of a Late Palaeozoic accretionary complex. They represent metavolcanic rocks with oceanic affinities based on predominantly 01B-type REE patterns and immobile trace element ratios. Both rock types have similar mineralogies, albeit with different mineral modal abundances. Amphibole is the major mafic mineral and varies compositionally from glaucophane to actinolite. The presence of glaucophane relicts as cores in zoned amphiboles in both blueschists and greenschists is evidence for a pervasive high-pressure metamorphic stage, indicating that tectonic juxtaposition is an unlikely explanation for the cm-dm scale interlayering. During exhumation, a retrograde greenschist-facies overprint stabilized chlorite + albite + winchitic/actinolitic amphibole + phengitic white mica +/- epidote +/- K-feldspar at 0.4 +/- 0.1 GPa. Geochemical variability can be partly ascribed to primary magmatic and partly to secondary metasomatic processes that occurred under greenschist-facies conditions. Isocon diagrams of several adjacent blueschist-greenschist pairs with similar protolith geochemistry were used to evaluate metasomatic changes due to retrograde fluid-rock interaction. The most important geochemical changes are depletion of Si and Na and addition of water in the greenschists compared to the blueschists. Transition metals and LILE are mobilized to varying degrees. The unsystematic deviations from magmatic fractionation trends suggest open system conditions and influx of an external fluid. Pseudosection and water isopleth calculations show that the rocks were dehydrating during most of their exhumation history and remained at water-saturated conditions. The mineralogical changes, in particular breakdown of blue amphibole and replacement by chlorite, albite and calcic/sodic-calcic amphibole, are the prime cause for the distinct coloring. Pseudo-binary phase diagrams were used as a means to link bulk rock geochemical variability to modal and chemical changes in the mineralogy. The geochemical changes induced by fluid-rock interaction are important in two ways: First, the bulk rock chemistry is altered, leading to the stabilization of higher modal proportions of chlorite in the greenschists. Second, the retrograde overprint is a selective, layer-parallel fluid infiltration process, causing more intense greenschist-facies recrystallization in greenschist layers and therefore preferential preservation of blue amphibole in blueschist layers. Hence, the distinct colors were acquired by a combination of compositional variability, both primary magmatic and secondary metasomatic, and the different intensity of retrograde fluid infiltration. (C) 2014 Elsevier B.V. All rights reserved. KW - Fluid-rock interaction KW - Metasomatism KW - Element mobility KW - Pseudo-binary phase diagrams KW - Coastal Cordillera (Chile) Y1 - 2015 U6 - https://doi.org/10.1016/j.lithos.2014.12.004 SN - 0024-4937 SN - 1872-6143 VL - 216 SP - 31 EP - 47 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Konrad-Schmolke, Matthias A1 - Halama, Ralf A1 - Manea, Vlad C. T1 - Slab mantle dehydrates beneath KamchatkaYet recycles water into the deep mantle JF - Geochemistry, geophysics, geosystems N2 - The subduction of hydrated slab mantle is the most important and yet weakly constrained factor in the quantification of the Earth's deep geologic water cycle. The most critical unknowns are the initial hydration state and the dehydration behavior of the subducted oceanic mantle. Here we present a combined thermomechanical, thermodynamic, and geochemical model of the Kamchatka subduction zone that indicates significant dehydration of subducted slab mantle beneath Kamchatka. Evidence for the subduction of hydrated oceanic mantle comes from across-arc trends of boron concentrations and isotopic compositions in arc volcanic rocks. Our thermodynamic-geochemical models successfully predict the complex geochemical patterns and the spatial distribution of arc volcanoes in Kamchatka assuming the subduction of hydrated oceanic mantle. Our results show that water content and dehydration behavior of the slab mantle beneath Kamchatka can be directly linked to compositional features in arc volcanic rocks. Depending on hydration depth of the slab mantle, our models yield water recycling rates between 1.1 × 103 and 7.4 × 103 Tg/Ma/km corresponding to values between 0.75 × 106 and 5.2 × 106 Tg/Ma for the entire Kamchatkan subduction zone. These values are up to one order of magnitude lower than previous estimates for Kamchatka, but clearly show that subducted hydrated slab mantle significantly contributes to the water budget in the Kamchatkan subduction zone. KW - rainfall-runoff KW - scaling KW - heterogeneity in soil hydraulic properties KW - surface sealing KW - run-on KW - patched vegetation cover Y1 - 2016 U6 - https://doi.org/10.1002/2016GC006335 SN - 1525-2027 VL - 17 SP - 2987 EP - 3007 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Konrad-Schmolke, Matthias A1 - Babist, Jochen A1 - Handy, Mark R. A1 - O'brien, Patrick J. T1 - The physico-chemical properties of a subducted slab from garnet zonation patterns (Sesia Zone, Western Alps) JF - Journal of petrology N2 - Garnets in continentally derived high-pressure (HP) rocks of the Sesia Zone (Western Alps) exhibit three different chemical zonation patterns, depending on sample locality. Comparison of observed garnet zonation patterns with thermodynamically modelled patterns shows that the different patterns are caused by differences in the water content of the subducted protoliths during prograde metamorphism. Zonation patterns of garnets in water-saturated host rocks show typical prograde chemical zonations with steadily increasing pyrope content and increasing XMg, together with bell-shaped spessartine patterns. In contrast, garnets in water-undersaturated rocks have more complex zonation patterns with a characteristic decrease in pyrope and XMg between core and inner rim. In some cases, garnets show an abrupt compositional change in core-to-rim profiles, possibly due to water-undersaturation prior to HP metamorphism. Garnets from both water-saturated and water-undersaturated rocks show signs of intervening growth interruptions and core resorption. This growth interruption results from bulk-rock depletion caused by fractional garnet crystallization. The water content during burial influences significantly the physical properties of the subducted rocks. Due to enhanced garnet crystallization, water-undersaturated rocks, i.e. those lacking a free fluid phase, become denser than their water-saturated equivalents, facilitating the subduction of continental material. Although water-bearing phases such as phengite and epidote are stable up to eclogite-facies conditions in these rocks, dehydration reactions during subduction are lacking in water-undersaturated rocks up to the transition to the eclogite facies, due to the thermodynamic stability of such hydrous phases at high P-T conditions. Our calculations show that garnet zonation patterns strongly depend on the mineral parageneses stable during garnet growth and that certain co-genetic mineral assemblages cause distinct garnet zonation patterns. This observation enables interpretation of complex garnet growth zonation patterns in terms of garnet-forming reactions and water content during HP metamorphism, as well determination of detailed P-T paths. KW - dehydration KW - high-pressure metamorphism KW - Sesia Zone KW - subduction KW - thermodynamic modelling Y1 - 2006 U6 - https://doi.org/10.1093/petrology/egl039 SN - 0022-3530 VL - 47 IS - 11 SP - 2123 EP - 2148 PB - Oxford Univ. Press CY - Oxford ER - TY - THES A1 - Konrad-Schmolke, Matthias T1 - Thermodynamic and geochemical modeling in metamorphic geology T1 - Thermodynamische und geochemische Modellierungen in metamorpher Geologie N2 - Quantitative thermodynamic and geochemical modeling is today applied in a variety of geological environments from the petrogenesis of igneous rocks to the oceanic realm. Thermodynamic calculations are used, for example, to get better insight into lithosphere dynamics, to constrain melting processes in crust and mantle as well as to study fluid-rock interaction. The development of thermodynamic databases and computer programs to calculate equilibrium phase diagrams have greatly advanced our ability to model geodynamic processes from subduction to orogenesis. However, a well-known problem is that despite its broad application the use and interpretation of thermodynamic models applied to natural rocks is far from straightforward. For example, chemical disequilibrium and/or unknown rock properties, such as fluid activities, complicate the application of equilibrium thermodynamics. One major aspect of the publications presented in this Habilitationsschrift are new approaches to unravel dynamic and chemical histories of rocks that include applications to chemically open system behaviour. This approach is especially important in rocks that are affected by element fractionation due to fractional crystallisation and fluid loss during dehydration reactions. Furthermore, chemically open system behaviour has also to be considered for studying fluid-rock interaction processes and for extracting information from compositionally zoned metamorphic minerals. In this Habilitationsschrift several publications are presented where I incorporate such open system behaviour in the forward models by incrementing the calculations and considering changing reacting rock compositions during metamorphism. I apply thermodynamic forward modelling incorporating the effects of element fractionation in a variety of geodynamic and geochemical applications in order to better understand lithosphere dynamics and mass transfer in solid rocks. In three of the presented publications I combine thermodynamic forward models with trace element calculations in order to enlarge the application of geochemical numerical forward modeling. In these publications a combination of thermodynamic and trace element forward modeling is used to study and quantify processes in metamorphic petrology at spatial scales from µm to km. In the thermodynamic forward models I 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. One of the included publications shows that trace element growth zonations in metamorphic garnet porphyroblasts can be used to get crucial information about the reaction path of the investigated sample. In order to interpret the major and trace element distribution and zoning patterns in terms of the reaction history of the samples, we combined thermodynamic forward models with mass-balance rare earth element calculations. Such combined thermodynamic and mass-balance calculations of the rare earth element distribution among the modelled stable phases yielded characteristic zonation patterns in garnet that closely resemble those in the natural samples. We can show in that paper that garnet growth and trace element incorporation occurred in near thermodynamic equilibrium with matrix phases during subduction and that the rare earth element patterns in garnet exhibit distinct enrichment zones that fingerprint the minerals involved in the garnet-forming reactions. In two of the presented publications I illustrate the capacities of combined thermodynamic-geochemical modeling based on examples relevant to mass transfer in subduction zones. 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 and associated transport of B and variations in B concentrations and isotopic compositions in liberated fluids and residual rocks are modeled. I show that, combined with experimental data on elemental partitioning and isotopic fractionation, thermodynamic forward modeling unfolds enormous capacities that are far from exhausted. In my publications presented in this Habilitationsschrift I compare the modeled results 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 so far. Thus, the contributions to the science community presented in this Habilitatonsschrift concern the fields of petrology, geochemistry, geochronology but also ore geology that all use thermodynamic and geochemical models to solve various problems related to geo-materials. N2 - Große Teile des Planeten auf dem wir leben sind für direkte Beobachtungen unzugänglich. Dieser Umstand umfasst nicht nur eine räumliche Komponente, so wie dies z.B. in den Tiefseegräben der Ozeane oder im Erdinneren der Fall ist sondern auch eine zeitliche Komponente, da viele für uns lebenswichtigen Prozesse, wie z.B. die Verschiebung der Kontinentalplatten, in für uns kaum beobachtbaren Raten stattfinden. Daher sind sogenannte Proxies, d.h. Archive in denen Informationen über die untersuchten Prozesse aus der längeren Vergangenheit gespeichert sind für die Geowissenschaften von sehr großer Bedeutung. Der wohl bekannteste Proxy ist zur Zeit CO2, dessen Konzentration in der Atmosphäre mit der Lufttemperatur korreliert wird. Als Archive für diesen Proxy dienen in der Regel Luftblasen in den Schichten der Eisschilde. Ist der Prozess bekannt, der den Proxy mit der gesuchten Information verbindet, im Falle von CO2 ist das der weitgehend bekannte sogenannte Treibhaus-Effekt, der die Oberflächentemperatur auf der Erde kontrolliert, kann man aus den Daten der Vergangenheit auf die Zukunft rückschließen. Wichtig ist dabei natürlich, dass der Prozess, der den Proxy kontrolliert genau bekannt ist, denn sonst führen dessen Messungen und die Interpretation der Daten zu falschen Rückschlüssen. In der von mir vorgelegten Habilitationsschrift geht es um Prozesse, die bestimmte Proxies in Gesteinen kontrollieren und darum, aus den Messungen der Proxies Rückschlüsse über Prozesse machen zu können, die weit außerhalb unseres direkt beobachtbaren Raumes liegen. Bei den untersuchten Prozessen handelt es sich um die sogenannte Lithosphärendynamik, die Bewegung der Gesteine in den obersten etwa 100km unseres Planeten. Diese Dynamik und die damit verbundenen Massenbewegungen sind weder räumlich noch zeitlich gut zu beobachten, die Prozesse laufen meist in größeren Tiefen und im Maßstab von Millionen von Jahren ab, sind aber dennoch für die Menschen von größter Bedeutung, da sie für Erdbeben, Vulkanausbrüche aber auch für die Lagerstättenbildung verantwortlich sind. Bewegungen der Gesteine in der Lithosphäre gehen mit Druck- und Temperaturänderungen in den Gesteinen einher. Die Gesteine versuchen sich diesen Änderungen anzupassen, was durch chemische Veränderungen in den Mineralen aus denen die Gesteine bestehen, geschieht. Solche Veränderungen infolge der Anpassung an sich ändernde Umweltbedingungen sind uns allen bekannt: Eis schmilzt, wenn die Umgebungstemperatur über dem Gefrierpunkt liegt und die Kraft, die wir im Verbrennungsmotor aus der chemischen Reaktion zwischen Benzin und Luft gewinnen setzen wir in Bewegung um. Die Berechnung solcher chemischer Anpassungen an sich ändernde Umgebungsbedingungen erfolgt mit Hilfe der Thermodynamik. Mit thermodynamischen Modellen können wir voraussagen welche Veränderungen in einem chemischen System auftreten, wenn sich die Umgebungsbedingungen ändern. Im Bezug auf Gesteine bedeutet dies, dass wir die chemische Zusammensetzung der Minerale bei bestimmten Druck und Temperaturbedingungen voraussagen können und umgekehrt auch aus der chemischen Zusammensetzung der Minerale auf die Druck- und Temperaturbedingungen bei ihrer Entstehung rückschließen können. Einige Minerale, wie z.B. Granat oder Feldspat weisen in Gesteinen oft eine chemische Zonierung auf, d.h. wie die Jahresringe in einem Baum haben solche Minerale konzentrische Anwachssäume, die sich in ihrer chemischen Zusammensetzung unterscheiden und so ein Archiv über die erfahrenen Druck- und Temperaturveränderungen in der Geschichte des Gesteins darstellen. Zur Interpretation dieser Zonierungen bedarf es komplexer thermodynamischer Modellierungen mit denen ich mich in den hier zusammengefassten publizierten Arbeiten beschäftigt habe. In den in dieser Habilitationsschrift zusammengefassten Arbeiten arbeite ich vor allem heraus, dass sowohl die Haupt- als auch die Spurenelementzonierungen in den Mineralen Granat und Hellglimmer hervorragende Indikatoren für Elementtransportprozesse in den Gesteinen sind. In Granat können Haupt- und Seltenerdelementzonierungen herangezogen werden um Elementfraktionierungsprozesse während der Gesteinsentwicklung zu detektieren. In den Hellglimmern ist die Konzentration und isotopische Zusammensetzung von Bor indikativ für eine Fluid-Gesteins-Wechselwirkung. Ich zeige, dass mit von mir und meinen Co-Autoren entwickelten thermodynamisch-geochemischen Modellen solche Elementtransportprozesse quantifiziert werden können. In den hier vorgelegten Arbeiten verwende ich solche numerischen Modelle um Prozesse vom µm bis km Maßstab zu quantifizieren. KW - geology KW - petrology KW - thermodynamic modelling KW - Geologie KW - Petrologie KW - thermodynamische Modellierungen Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-101805 ER - TY - JOUR A1 - Konrad-Schmolke, Matthias A1 - Handy, Mark R. A1 - Babist, Jochen A1 - O'Brien, Patrick J. T1 - Thermodynamic modelling of diffusion-controlled garnet growth N2 - Numerical thermodynamic modelling of mineral composition and modes for specified pressure-temperature paths reveals the strong influence of fractional garnet crystallisation, as well as water fractionation, on garnet growth histories in high pressure rocks. Disequilibrium element incorporation in garnet due to the development of chemical inhomogeneities around porphyroblasts leads to pronounced episodic growth and may even cause growth interruptions. Discontinuous growth, together with pressure- and temperature-dependent changes in garnet chemistry, cause zonation patterns that are indicative of different degrees of disequilibrium element incorporation. Chemical inhomogeneities in the matrix surrounding garnet porphyroblasts strongly affect garnet growth and lead to compositional discontinuities and steep compositional gradients in the garnet zonation pattern. Further, intergranular diffusion-controlled calcium incorporation can lead to a characteristic rise in grossular and spessartine contents at lower metamorphic conditions. The observation that garnet zonation patterns diagnostic of large and small fractionation effects coexist within the same sample suggests that garnet growth is often controlled by small-scale variations in the bulk rock chemistry. Therefore, the spatial distribution of garnet grains and their zonation patterns, together with numerical growth models of garnet zonation patterns, yield information about the processes limiting garnet growth. These processes include intercrystalline element transport and dissolution of pre-existing grains. Discontinuities in garnet growth induced by limited element supply can mask traces of the thermobarometric history of the rock. Therefore, thermodynamic modelling that considers fractional disequilibrium crystallisation is required to interpret compositional garnet zonation in terms of a quantitative pressure and temperature path of the host rock Y1 - 2005 SN - 0010-7999 ER -