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The compositional zoning of the major divalent cations in metamorphic garnet is a useful tool in reconstructing the pressure-temperature path. However, trace elements can provide a better-preserved record of petrogenetic evolution due to their strong affinity in garnet and slow diffusion rates. In this study, three high-pressure micaschist samples of varying composition and garnet textures from the Krusné hory Mountains (Saxothuringian zone, Bohemian Massif) were examined. By utilizing electron probe micro-analysis and laser ablation inductively coupled plasma mass spectrometry, three distinct types of compositional zoning in garnet were identified by compositional mapping. The zoning types were classified as continuous core-to-rim change, concentric annular changes, and overprinting of a pre-existing distribution; all three provide information on the original mineral composition and texture before garnet overgrowth. The transition from overprint to annular zoning shows relation to temperature increment. The annular zoning allowed the identification of several coupled substitutions, including alkali (sodium and lithium) + yttrium and the alkali + phosphorus substitution which is typical of high- to ultra-high-pressure conditions. The formation of annuli zoning was interpreted to originate not only from the decomposition of trace element bearing phases, but also to be related to the availability of fluid medium during garnet growth. Two samples contained atoll texture garnets, interpreted to be originated from the dissolution of the garnet central part, chemically distinct from the new garnet growing coevally on the rim or replacing the original central part. This proposed process is evidenced by the mass balance calculation of yttrium and heavy rare earth elements between the dissolved garnet and newly formed parts., Author(s): Jan Kulhánek [sup.1], Shah Wali Faryad [sup.1] Author Affiliations: (1) https://ror.org/024d6js02, grid.4491.8, 0000 0004 1937 116X, Faculty of Science, Institute of Petrology and Structural Geology, Charles University, , Albertov [...]

In order to characterize the [micro]m-to-nm structures related to operation of pressure solution on phase boundaries in naturally deformed rocks, we have performed a detailed focused ion beam/transmission electron microscopy study in ultramylonite samples from South Armorican Shear Zone (France) that focused on grain boundary scale. We have studied phase boundaries between quartz, K-feldspar and white mica in both 2D and 3D and compare our evidences with theoretical dissolution precipitation models in the current literature. The dissolution (re)precipitation processes lead to the development of different features at different phase boundaries. In both quartz-white mica and quartz-K-feldspar phase boundaries, voids were ubiquitously observed. These voids have different shapes, and the development of some of them is crystallographically controlled. In addition, part of these voids might be filled with vermiculite. Amorphous leached layers with kaolinite composition were observed at the boundaries of K-feldspar-quartz and K-feldspar-white mica. The development of different features along the phase boundaries is mainly controlled by the crystallography of the phases sharing a common interface, together with the presence of fluids that either leaches or directly dissolve the mineral phases. In addition, the local dislocation density in quartz may play an important role during pressure solution. We suggest that the nanoscale observations of the quartz-white mica phase boundaries show direct evidence for operation of island-and-channel model as described in Wassmann and Stockhert (Tectonophysics 608:1-29, 2013 (See CR35)), while K-feldspar-quartz phase boundaries represents amorphous layers formed via interface-coupled dissolution reprecipitation as described by Hellmann et al. (Chem Geol 294-295:203-216, 2012 (See CR13)). Electronic supplementary material The online version of this article (doi:10.1007/s00410-015-1186-8) contains supplementary material, which is available to authorized users., Author(s): Zita Bukovska[sup.1] [sup.2] , Richard Wirth[sup.3] , Luiz F. G. Morales[sup.4] Author Affiliations: (1) Faculty of Science, Institute of Petrology and Structural Geology, Charles University in Prague, Albertov 6, [...]

Byline: JiAi Zak (1,2), Scott R. Paterson (3), VojtAch Janousek (2,4), Petr Kabele (5) Keywords: Emplacement; Granite; Incremental growth; Magma chamber; Pluton; Thermal--mechanical modeling Abstract: The Mammoth Peak sheeted intrusive complex formed in the interior of a ~7--10 km deep magma chamber, specifically in the Half Dome granodiorite of the Tuolumne batholith, central Sierra Nevada, CA (USA). The sheets consist of fractionated melts with accumulated hornblende, biotite, magnetite, titanite, apatite, and zircon. The accumulation, especially of titanite, had a profound effect on minor and trace elements (Nb, Ta, Ti, REE, U, Th, P, Zr, Hf, etc.), increasing their contents up to five to six times. Our thermal--mechanical modeling using the finite element method shows that cooling-generated tensile stresses resulted in the inward propagation of two perpendicular sets of dilational cracks in the host granodiorite. We interpret the sheeted complex to have formed by a crack-seal mechanism in a high strength, crystal-rich mush, whereby outward younging pulses of fractionated magma were injected into these syn-magmatic cracks at the margin of an active magma chamber. Thermal--mechanical instabilities developed after the assembly of the sheeted complex, which was then overprinted by late ~NW--SE magmatic foliation. This case example provides a cautionary note regarding the interpretation that sheeted zones in large granitoid plutons imply a diking mechanism of growth because the sheeted/dike complexes in plutons (1) may display inverse growth directions from the growth of the overall intrusive sequence (2) need not record initial chamber construction and instead may reflect late pulsing of magma within an already constructed magma chamber (3) have an overprinting magmatic fabric indicating the continued presence of melt after construction of sheeted complexes and thus a prolonged thermal history as compared to dikes and (4) because the scale of the observed sheeted complexes may be small ( Author Affiliation: (1) Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, 12843, Prague, Czech Republic (2) Czech Geological Survey, Klarov 3, 11821, Prague, Czech Republic (3) Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, CA, 90089-0740, USA (4) Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, 12843, Prague, Czech Republic (5) Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague, Thakurova 7, 16629, Prague, Czech Republic Article History: Registration Date: 17/02/2009 Received Date: 22/07/2008 Accepted Date: 17/02/2009 Online Date: 13/03/2009 Article note: Communicated by T.L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0391-8) contains supplementary material, which is available to authorized users.

Byline: Lucie Tajcmanova (1,2), JiAi Konopasek (1,2), James A. D. Connolly (3) Keywords: Equilibration volume; Coronal structures; Diffusion; Low-pressure granulites; Perple_X; Bohemian Massif Abstract: Plagioclase rims around metastable kyanite crystals appear during decompression of high-pressure felsic granulites from the high-grade internal zone of the Bohemian Massif (Variscan belt of Central Europe). The development of the plagioclase corona is a manifestation of diffusion-driven transfer of CaO and [Na.sub.2]O from the surrounding matrix and results in isolation of kyanite grains from the quartz- and K-feldspar-bearing matrix. This process establishes Si-undersaturated conditions along the plagioclase--kyanite interface, which allow crystallization of spinel during low-pressure metamorphism. The process of the plagioclase rim development is modeled thermodynamically assuming local equilibrium. The results combined with textural observations enable estimation of equilibration volume and diffusion length for Na and Ca that extends [proportional to]400--450 and [proportional to]450--550 um, respectively, around each kyanite crystal. Low estimated bulk diffusion coefficients suggest that the diffusion rate of Ca and Na is controlled by low diffusivity of Al across the plagioclase rim. Author Affiliation: (1) Institute of Petrology and Structural Geology, Charles University, Albertov 6, 128 43, Prague, Czech Republic (2) Czech Geological Survey, Klarov 3, 118 21, Praha 1, Czech Republic (3) Institut fur Mineralogie und Petrographie, ETH-Zentrum, 8092, Zurich, Switzerland Article History: Registration Date: 19/09/2006 Received Date: 22/05/2006 Accepted Date: 14/09/2006 Online Date: 26/10/2006 Article note: Communicated by T.L. Grove.

Byline: Shah Wali Faryad (1), Sumit Chakraborty (2) Keywords: Plus: cooling-exhumation rate; Multicomponent diffusion in garnet; Austroalpine unit; Eastern Alps Abstract: Rocks from the Micaschist--Marble Complex of the Wolz Tauern, which are part of the middle Austroalpine unit, contain large (up to 2 cm) garnet crystals that show clear evidence of multistage growth. Isotopic dating indicates that a Variscan ([proportional to]270 Ma) garnet core was overgrown by new garnet formed during Eo-Alpine metamorphism at Cretaceous times. P-T paths for the Eo-Alpine metamorphism were obtained using the method of pseudosections (Powell and Holland in Metam Geol 16:309--343, 1998) and are consistent with earlier results from independent thermobarometry. Due to the large size of the garnets, growth zoning was preserved during amphibolite facies metamorphism at both Variscan and Alpine times. Full multicomponent diffusion modeling of compositional zoning at the interface of the Alpine and Pre-Alpine garnets in conjunction with the retrieved P-T paths allow average subduction/exhumation as well as heating/cooling rates to be retrieved. The modeling suggests that a minimum subduction/exhumation rate of [proportional to]4 cm/a and heating/cooling rates on the order of 100--260degC/Ma for a 60degC subduction angle are required to preserve the observed compositional zoning overall while modifying the zoning at the interface between two garnets to the extent observed. Such rapid rates of burial/exhumation are consistent with the results of direct GPS measurements of convergence rates at several orogenic belts as well as with inferred rates from modeling in the Alps and other areas. In combination, this indicates that such rapid rates are commonplace during metamorphism in collisional orogens and places important constraints on the rheological behavior of crustal blocks in such orogens. Author Affiliation: (1) Institute of Petrology and Structural Geology, Charles University, Albertov 2, 128 43, Prague, Czech Republic (2) Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitat Bochum, 44780, Bochum, Germany Article History: Registration Date: 13/07/2005 Received Date: 26/11/2004 Accepted Date: 04/07/2005 Online Date: 15/09/2005 Article note: Communicated by J. Hoefs

The petrochronological records of eclogites in the Scandinavian Caledonides are investigated using EPMA and LA-ICPMS of zircon and apatite for U-Pb geochronology, combined with major and trace element characteristics. Metamorphic zircon from two eclogites from the Lofoten-Vesterålen Complex (Lofoten Archipelago region) collectively yielded a Concordia age 427.8 ± 5.7 Ma and an upper intercept U-Pb age 425 ± 30 Ma. Apatites from the same eclogites provided U-Pb lower intercepts at 322 ± 28 Ma and 354 ± 33 Ma, with the latter also yielding a younger age of 227 ± 24 Ma. Two eclogites from the Lower Seve Nappe (Northern Jämtland) demonstrate different zircon and apatite age records. Metamorphic zircon provided Concordia ages of 467.2 ± 5.9 Ma and 444.5 ± 5.5 Ma, which resolve the age of prograde metamorphism and zircon growth during retrogression, respectively. The lower intercept U-Pb ages of apatites from the same eclogites are 436 ± 18 and 415 ± 25 Ma, respectively. In combination with their geochemical characteristics, they suggest two separate stages of exhumation of eclogite bodies in the Lower Seve Nappe. Zircons from an eclogite from the Blåhø Nappe (Nordøyane Archipelago) yielded a continuum of concordant U-Pb dates from ca. 435 to 395 Ma, which suggests several cycles of HT metamorphism within short intervals. Distinctive trace element characteristics of apatites from the Blåhø Nappe eclogite suggest formation coeval with zircon and garnet during HT metamorphism, but Pb diffusion behaved as an open system until cooling during exhumation of the nappe at 390 ± 12 Ma (lower intercept U-Pb age of apatite). To summarize, this study presents the high potential of coupled zircon and apatite petrochronology of eclogites in resolving their metamorphic evolution, particularly with respect to using trace element characteristics of apatites to constrain the records of their growth, alterations and the meaning of their U-Pb age record., Author(s): Maciej Jaranowski [sup.1], Bartosz Budzyn [sup.1], Christopher J. Barnes [sup.1], Jaroslaw Majka [sup.2] [sup.3], Jirí Sláma [sup.4], Gabriela A. Kozub-Budzyn [sup.3], Karolina Kosminska [sup.3] Author Affiliations: (1) grid.413454.3, 0000 [...]

Mineral compositions and textures of Late Miocene coesite eclogite from Tomagabuna Island were investigated to constrain P-T conditions during UHP metamorphism and subsequent exhumation. Two stages of garnet growth (core and rim), at eclogite-facies conditions, were documented. In addition to core garnet (I), peak assemblages include omphacite, coesite, phengite, and rutile. Rim garnet (II), amphibole, paragonite, plagioclase, quartz, and accessory biotite and spinel were formed after peak pressure conditions. Although a compositional gradient is present at the core-rim garnet interface, the garnet core has a relatively flat compositional profile, suggesting its crystallization in the coesite stability field. Together with minerals formed subsequent to peak pressure (UHP) conditions, the composition of the garnet rim indicates heating of the eclogite during its decompression into the amphibolite facies mineral stability field. Based on compositional zoning in garnet and application of diffusion modelling, we propose that eclogite-facies metamorphism of the mafic protolith and its host lithologies occurred at, or near, UHP conditions. The core garnet (I) formed at 650 °C at 8 Myr in the coesite stability field and was partially resorbed during the onset of exhumation. We infer that garnet rim growth at < 7.1 Ma occurred at P-T conditions corresponding to the boundary between the eclogite and amphibolite facies fields. Diffusion modelling for the garnet core-rim boundary compositions suggests a transient heating event (0.3 Myr) occurred at 1.5 GPa that we infer resulted from heat transport within the Australian-Woodlark plate boundary zone as the coesite eclogite was exhumed. Results caution that apparent P-T paths documented for many UHP terranes may not result from isothermal decompression corresponding to peak temperatures. Instead, paths may link P-T points' set during transient mineral growth events when the UHP rocks form within the subduction channel, and during subsequent heating events, when UHP rocks are exhumed from mantle depths., Author(s): S. W. Faryad [sup.1] , S. L. Baldwin [sup.2] , R. Jedlicka [sup.1] , J. Jezek [sup.3] Author Affiliations: (Aff1) 0000 0004 1937 116X, grid.4491.8, Faculty of Science, Institute [...]

We have performed phase equilibrium experiments in the system forsterite-enstatite-pyrope-[H.sub.2]O with Mg[Cl.sub.2] or Mg[F.sub.2] at 1,100 °C and 2.6 GPa to constrain the solubility of halogens in the peridotite mineral assemblage and the fluid-mineral partition coefficients. The chlorine solubility in forsterite, enstatite and in pyrope is very low, 2.1-3.9 and 4.0-11.4 ppm, respectively, and it is independent of the fluid salinity (0.3-30 wt% Cl), suggesting that some intrinsic saturation limit in the crystal is reached already at very low chlorine concentrations. Chlorine is therefore exceedingly incompatible in upper-mantle minerals. The fluorine solubility is 170-336 ppm in enstatite and 510-1,110 ppm in pyrope, again independent of fluid salinity. Forsterite dissolves 1,750-1,900 ppm up to a fluid salinity of 1.6 wt% F. At higher fluorine contents in the system, forsterite is replaced by the minerals of the humite group. The lower solubility of chlorine by three orders of magnitude when compared to fluorine is consistent with increasing lattice strain. Fluid-mineral partition coefficients are [10.sup.0]-[10.sup.2] for fluorine and [1.sup.03]-[10.sup.5] for chlorine. Since the latter values are orders of magnitude higher than those for hydroxyl partitioning, fluid flow from the subducting slab through the mantle wedge will lead to an efficient sequestration of [H.sub.2]O into the nominally anhydrous minerals in the wedge, whereas chlorine becomes enriched in the residual fluid. Simple mass balance calculations reveal that rock-fluid ratios of up to >3,000 are required to produce the elevated Cl/[H.sub.2]O ratios observed in some primitive arc magmas. Accordingly, fluid flow from the subducted slab into the zone of melting in the mantle wedge does not only occur rapidly in narrow channels, but at least in some subduction zones, fluid pervasively infiltrates the mantle peridotite and interacts with a large volume of the mantle wedge. Together with the Cl/[H.sub.2]O ratios of primitive arc magmas, our data therefore constrain the fluid flow regime below volcanic arcs. Keywords Forsterite * Enstatite * Pyrope * Fluorine * Chlorine * Aqueous fluid * Subduction * Metasomatism * Fluid flow, Introduction Fluorine and chlorine are minor constituents in the upper mantle and were traditionally interpreted as hosted by hydrous phosphates or silicates (Smyth 1981; Smyth et al. 1981; Newsom 1995; [...]

Crystallization of natural magmas is inherently a disequilibrium process, which involves nucleation and growth kinetics, melt-crystal mechanical interactions and subsolidus modifications, which are all recorded in the resulting rock texture. We use a new high-resolution three-dimensional numerical model to address the significance and consequences of homogeneous versus heterogeneous crystal nucleation in silicate magmas. With increasing amount of heterogeneous nuclei during crystallization, initially equigranular textures evolve to porphyritic, bimodal and spherulitic types. The corresponding crystal size distributions (CSDs) become concave-up curved, the clustering index progressively decreases, and the grain contact relationships record increased clustering. Concave-up curved CSDs previously interpreted as resulting from multistage crystallization, mixing of crystal populations, grain agglomeration, or size-dependent growth are now predicted, consistently with other size, spatial and clustering parameters, to form by heterogeneous crystal nucleation. Correlation relationships between various textural parameters and the fraction of heterogeneous nuclei are calibrated and used on representative volcanic and plutonic rocks, including cumulate rocks, to deduce the fraction of heterogeneous nuclei. The results indicate that ~60 to ~99 % of all nuclei are heterogeneous. For plutonic and cumulate rocks, the estimate of the heterogeneous nuclei fraction based on the clustering index is significantly lower than other estimates. Such discrepancies, in general, point to the occurrence of other processes, and here, the results imply that crystal-mush compaction and interstitial melt extraction were involved during the magma solidification. Formation of crystals in clusters, implicit for heterogeneous nucleation, implies that greater efficiency of crystal-melt separation is expected in these situations. Keywords Heterogeneous nucleation * CSD * Crystal cluster * Crystallization * Quantitative texture measurement, Introduction Magma chambers are complex systems whose internal dynamics and temporal evolution are determined by rheological properties of crystal mush which forms and evolves as crystallization progresses (e.g., Marsh 1989; [...]