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In the polymetamorphic Austroalpine Matsch Unit (European Eastern Alps) Cretaceous upper greenschist facies metamorphism overprinted Variscan and Permian magmatic and metamorphic assemblages. Mineral compositional and (micro-)structural data of metapelites and metapegmatites document different mechanisms of interrelated deformation and (re-)equilibration during Cretaceous overprinting: i) Microfractures in relic garnet represented pathways for material transport, and thus established material exchange between intragranular domains and the matrix. Major element equilibration by fast diffusion along microfractures contrasts with limited volume diffusion in adjacent host garnet. ii) Syn-tectonic breakdown of staurolite initially to paragonite, then chloritoid allows correlating reaction progress with the formation of different fracture sets. iii) Syn-tectonic mineral growth with shape-preferred orientation in foliation domains contrasts with radial growth in microlithons and strain shadows of the mylonitic foliation. iv) Syn-tectonic unmixing of pre-existing oligoclase (an14–16) produced fine-grained aggregates of two supposedly coexisting plagioclase-phases (an3–6 and an20–25) in strain shadows of the oligoclase-clasts. v) Pre-existing deformation-induced heterogeneities in the spatial distribution of phases and their preferred orientation influence the kinetics of phase equilibration. Understanding the mechanisms of the mutual interrelation between deformation and phase equilibration is a prerequisite for deducing PT-constraints from strained metamorphic rocks. New garnet—whole rock Sm-Nd data from metapegmatites indicate their emplacement at 263–280 Ma and provide an important age constraint on the interrelated deformation and re-equilibration processes. 相似文献
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Alexander Proyer Gerlinde Habler Rainer Abart Richard Wirth Kurt Krenn Georg Hoinkes 《Contributions to Mineralogy and Petrology》2013,166(1):211-234
We investigated rutile needles with a clear shape preferred orientation in garnet from (ultra) high-pressure metapelites from the Kimi Complex of the Greek Rhodope by electron microprobe, electron backscatter diffraction and TEM techniques. A definite though complex crystallographic orientation relationship between the garnet host and rutile was identified in that Rt[001] is either parallel to Grt<111> or describes cones with opening angle 27.6° around Grt<111>. Each Rt[001] small circle representing a cone on the pole figure displays six maxima in the density plots. This evidence together with microchemical observations in TEM, when compared to various possible mechanisms of formation, corroborates a precipitate origin. A review of exchange vectors for Ti substitution in garnet indicates that rutile formation from garnet cannot occur in a closed system. It requires that components are exchanged between the garnet interior and the rock matrix by solid-state diffusion, a process we refer to as “open-system precipitation” (OSP). The kinetically most feasible reaction of this type will dominate the overall process. The perhaps most efficient reaction involves internal oxidation of Fe2+ to Fe3+ and transfer from the dodecahedral to the octahedral site just vacated by $ {\text{Ti}}^{ 4+ }: 6\,{\text{M}}^{ 2+ }_{ 3} {\text{TiAl}}\left[ {{\text{AlSi}}_{ 2} } \right]{\text{O}}_{ 1 2} + 6\,{\text{M}}^{ 2+ }_{ 2, 5} {\text{TiAlSi}}_{ 3} {\text{O}}_{ 1 2} = 10\,{\text{M}}^{ 2+ }_{ 3.0} {\text{Al}}_{ 1. 8} {\text{Fe}}_{0. 2} {\text{Si}}_{ 3} {\text{O}}_{ 1 2} + {\text{M}}^{2+} + 2 {\text{e}}^{-} + 1 2\,{\text{TiO}}_{ 2} . $ OSP is likely to occur at conditions where the transition of natural systems to open-system behaviour becomes apparent, as in the granulite and high-temperature eclogite facies. 相似文献
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Lucie?Taj?manováEmail author Rainer?Abart Richard?Wirth Gerlinde?Habler Dieter?Rhede 《Contributions to Mineralogy and Petrology》2012,164(4):715-729
Samples of essentially “dry” high-pressure felsic granulites from the Bohemian Massif (Variscan belt of Central Europe) contain up to 2-mm-large perthitic alkali feldspars with several generations of plagioclase precipitates in an orthoclase-rich host. The first generation takes the form of lenses homogeneous in size, whereas the size of a second generation of very thin albite-rich precipitates is more variable with comparatively high aspect ratios. In the vicinity of large kyanite, garnet or quartz inclusions, the first generation of plagioclase precipitates is significantly less abundant, the microstructure is coarser than in the remainder of the perthitic grain and the host is a tweed orthoclase. The first generation of precipitates formed at around 850 °C during the high-pressure stage (16–18 kbar) of metamorphism. Primary exsolution was followed by primary coarsening of the plagioclase precipitates, which still took place at high temperatures (850–700 °C). The coarsening was pronounced due to the access of fluids in the outer portions of the perthitic alkali feldspar and in more internal regions around large inclusions. The second generation of albite-rich precipitates was formed at around 570 °C. TEM investigations revealed that the interfaces between the second-generation plagioclase lamellae and the orthoclase-rich host are coherent or semi-coherent. During late evolutionary stages of the perthite, albite linings were formed at phase boundaries, and the perthitic microstructure was partially replaced by irregularly shaped precipitates of pure albite with incoherent interfaces. The albitization occurred below 400 °C and was linked to fluid infiltration in the course of deuteric alteration. Based on size-distribution analysis, it is inferred that the precipitates of the first generation were most probably formed by spinodal decomposition, whereas the precipitates of the second generation rather were formed by nucleation and growth. 相似文献
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Schuster Roman Habler Gerlinde Schafler Erhard Abart Rainer 《Mineralogy and Petrology》2020,114(2):105-118
Mineralogy and Petrology - Polycrystalline calcite was deformed to high strain at room-temperature and confining pressures of 1–4 GPa using high-pressure torsion. The high confining... 相似文献
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Rainer?AbartEmail author David?Heuser Gerlinde?Habler 《Contributions to Mineralogy and Petrology》2014,168(5):1074
Myrmekites have attracted the attention of petrographers over more than a century, and several genetic models have been proposed. We report on myrmekites from the Weinsberg granite of the Moldanubian zone of Upper Austria. Based on petrographic evidence, fluid-mediated replacement of alkali feldspar by myrmekite during the sub-solidus evolution of the granite is inferred. The replacement was metasomatic on the scale of the myrmekite domains requiring addition of sodium and calcium and removal of potassium from the reaction site. In contrast, silica and aluminum were conserved across the reaction front. Myrmekite formation appears to have been synchronous with and related to the hydration of orthopyroxene and concomitant replacement of primary magmatic plagioclase by biotite at around 500 °C. The evolution of the myrmekite microstructure and a peculiar composition zoning of the plagioclase constituting the myrmekite matrix is qualitatively explained by a model for discontinuous precipitation, which accounts for chemical segregation by diffusion within the reaction front and the propagation of the reaction front with finite mobility as potentially rate limiting processes. Constraints on the underlying reaction rates are derived from the preserved microstructure and chemical pattern. Crystal orientation imaging by electron backscatter diffraction reveals grain-internal deformation, which is primarily concentrated in the quartz and less pronounced in the plagioclase matrix of the myrmekite. This is interpreted as a growth feature related to different transformation strain at the segments of the myrmekite reaction front, where quartz and plagioclase are formed. 相似文献
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P-immobilisation and phosphatase activities in lake sediment following treatment with nitrate and iron 总被引：3，自引：0，他引：3
The influence of a further developed inlake restoration method on the P-immobilisation and microbial activities, especially under anoxic conditions was investigated. The impact of nitrate and iron dosing with a newly developed nitrate storage compound (Depox®Fe) was tested in enclosures in the eutrophic dimictic Lake Dagowsee, Germany. Additions of 50 g m−2 of NO3−–N and 66 g m−2 of Fe3+ ensured availability of nitrate at the sediment surface during a 2-months period.As a result the phosphate release from the anoxic sediments was completely suppressed even 1 year after the application. The hypolimnetic deoxygenation was unaffected by the Depox®Fe addition. However, sulfur reduction and methanogenesis were inhibited and the phosphatase activity increased. 相似文献
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