TY - JOUR A1 - Wunder, Bernd A1 - Kutzschbach, Martin A1 - Hosse, Luisa A1 - Wilke, Franziska Daniela Helena A1 - Schertl, Hans-Peter A1 - Chopin, Christian T1 - Synthetic B-[4]-bearing dumortierite and natural B-[4]-free magnesiodumortierite from the Dora-Maira Massif BT - differences in boron coordination in response to ultrahigh pressure JF - European journal of mineralogy N2 - Dumortierite was synthesized in piston-cylinder experiments at 2.5-4.0 GPa, 650-700 degrees C in the Al2O3 -B2O3-SiO2-H2O (ABSH) system. Electron-microprobe (EMP) analyses reveal significant boron-excess (up to 0.26 B-[4] per formula unit, pfu) and silicon-deficiency relative to the ideal anhydrous dumortierite stoichiometry Al7BSi3O18 . The EMP data in conjunction with results from single-crystal Raman spectroscopy and powder X-ray diffraction provide evidence that silicon at the tetrahedral site is replaced by excess boron via the substitution Si-[4] <--> B-[4] + H. The Raman spectrum of synthetic dumortierite in the frequency region 2000 4000 cm(-1) comprises eight bands, of which six are located at frequencies below 3400 cm(-1). This points to strong hydrogen bonding, most likely O2-H center dot center dot center dot O7 and O7-H center dot center dot center dot O2, arising from a high number of octahedral vacancies at the All site and substitution of trivalent Al3+ and B3+ for Si4+ at Si1 and Si2 sites, causing decreasing acceptor-donor distances and lower incident valence at the acceptor oxygen. Contrary to the synthetic high-pressure ABSH-dumortierite, magnesiodumortierite from the Dora-Maira Massif, which is assumed to have formed at similar conditions (2.5-3.0 GPa, 700 degrees C), does not show any B-excess. Tourmaline shows an analogous behaviour in that magnesium-rich (e.g., dravitic) tourmaline formed at high pressure shows no or only minor amounts of tetrahedral boron, whereas natural aluminum-rich tourmaline and synthetic olenitic tourmaline formed at high pressures can incorporate significant amounts of tetrahedral boron. Two mechanisms might account for this discrepancy: (i) Structural avoidance of Mg-[6]-(OR3+)-R-[4] configurations in magnesiodumortierite due to charge deficieny at the oxygens O2 and O7 and strong local distortion of M1 due to decreased O2-O7 bond length, and/or (ii) decreasing fluid mobility of boron in Al-rich systems at high pressures. KW - dumortierite KW - magnesiodumortierite KW - Dora-Maira KW - ultrahigh-pressure (UHP) KW - ABSH-system KW - synthesis KW - tetrahedral boron KW - Raman spectroscopy Y1 - 2018 U6 - https://doi.org/10.1127/ejm/2018/0030-2742 SN - 0935-1221 SN - 1617-4011 VL - 30 IS - 3 SP - 471 EP - 483 PB - Schweizerbart CY - Stuttgart ER - TY - JOUR A1 - Schultze, Dina A1 - Wirth, Richard A1 - Wunder, Bernd A1 - Loges, Anselm A1 - Wilke, Max A1 - Franz, Gerhard T1 - Corundum-quartz metastability BT - the influence of a nanometer-sized phase on mineral equilibria in the system Al2O3-SiO2-H2O JF - Contributions to mineralogy and petrology N2 - The metastable paragenesis of corundum and quartz is rare in nature but common in laboratory experiments where according to thermodynamic predictions aluminum-silicate polymorphs should form. We demonstrate here that the existence of a hydrous, silicon-bearing, nanometer-thick layer (called "HSNL") on the corundum surface can explain this metastability in experimental studies without invoking unspecific kinetic inhibition. We investigated experimentally formed corundum reaction products synthesized during hydrothermal and piston-cylinder experiments at 500-800 degrees C and 0.25-1.8 GPa and found that this HSNL formed inside and on the corundum crystals, thereby controlling the growth behavior of its host. The HSNL represents a substitution of Al with Si and H along the basal plane of corundum. Along the interface of corundum and quartz, the HSNL effectively isolates the bulk phases corundum and quartz from each other, thus apparently preventing their reaction to the stable aluminum silicate. High temperatures and prolonged experimental duration lead to recrystallization of corundum including the HSNL and to the formation of quartz + fluid inclusions inside the host crystal. This process reduces the phase boundary area between the bulk phases, thereby providing further opportunity to expand their coexistence. In addition to its small size, its transient nature makes it difficult to detect the HSNL in experiments and even more so in natural samples. Our findings emphasize the potential impact of nanometer-sized phases on geochemical reaction pathways and kinetics under metamorphic conditions in one of the most important chemical systems of the Earth's crust. KW - Experimental KW - Metastability KW - Corundum KW - Quartz KW - Nanolayers KW - Aluminium– silicates Y1 - 2021 U6 - https://doi.org/10.1007/s00410-021-01786-5 SN - 0010-7999 SN - 1432-0967 VL - 176 IS - 4 PB - Springer CY - Berlin ; Heidelberg ER - TY - JOUR A1 - Kutzschbach, Martin A1 - Wunder, Bernd A1 - Krstulovic, Marija A1 - Ertl, Andreas A1 - Trumbull, Robert B. A1 - Rocholl, Alexander A1 - Giester, Gerald T1 - First high-pressure synthesis of rossmanitic tourmaline and evidence for the incorporation of Li at the X site JF - Physics and chemistry of minerals / in cooperation with the International Mineralogical Association (IMA) N2 - Lithium is an important component of some tourmalines, especially in chemically evolved granites and pegmatites. All attempts at synthesizing Li-rich tourmaline have so far been unsuccessful. Here we describe the first synthesis of rossmanitic tourmaline at 4 GPa and 700 degrees C in the system Li2OAl2O3SiO2B2O3H2O (LASBH) from seed-free solid starting materials consisting of a homogenous mixture of Li2O, gamma-Al2O3, quartz and H3BO3. The solid run products after 12-day run duration comprise rossmanitic tourmaline (68 wt%), dumortierite (28 wt%) and traces of spodumene (3 wt%) and coesite (1 wt%). Tourmaline forms idiomorphic, large prismatic crystals (30 X 100 mu m), which are inclusion free and chemically unzoned. The refined cell dimensions of the tourmaline are: a = 15.7396(9) angstrom, c = 7.0575(5) angstrom, V = 1514.1(2) angstrom 3. Conventionally, the Li+ ion is assumed to exclusively occupy the octahedral Y site in the tourmaline structure to a maximum of 2 Li per formula unit (pfu). However, the chemical composition of our synthetic tourmaline determined by electron microprobe and secondary ion mass spectroscopy results in the formula: (X)(square Li-0.67(11)(0.33(11)))(Y)(Al2.53(10)Li0.47(10))(Z)(Al-6)T(Si5.42(15)B0.58(15))O-18(B)(BO3)(3)(V+W)[(OH)(2.40(3))O-1.60(3)], wherein a significant amount of Li occupies the X site for charge balance requirements. Reliable assignment of the OH-stretching vibrations in a polarized single-crystal Raman spectrum such as a single-crystal XRD structure refinement, confirms the incorporation of Li at the X site [0.24(9) and 0.15(5) Li-X pfu, respectively]. The SREF data show that the LiO1 distances are shortened significantly in order to compensate for the smaller ionic radius of Li+ compared to Na+, K+ or Ca2+ at the X site, i.e., Li is closer to the Si6O18 ring and to a sevenfold coordination with oxygen. KW - High-pressure synthesis KW - Tourmaline KW - Rossmanite KW - Crystal chemistry KW - X site occupancy KW - SIMS KW - SREF KW - Li isotope fractionation Y1 - 2016 U6 - https://doi.org/10.1007/s00269-016-0863-0 SN - 0342-1791 SN - 1432-2021 VL - 44 SP - 353 EP - 363 PB - Springer CY - New York ER - TY - JOUR A1 - Ferrero, Silvio A1 - Ziemann, Martin Andreas A1 - Angel, Ross J. A1 - Wunder, Bernd T1 - Kumdykolite, kokchetavite, and cristobalite crystallized in nanogranites from felsic granulites, Orlica-Snieznik Dome (Bohemian Massif): not evidence for ultrahigh-pressure conditions JF - Contributions to mineralogy and petrology N2 - A unique assemblage including kumdykolite and kokchetavite, polymorphs of albite and K-feldspar, respectively, together with cristobalite, micas, and calcite has been identified in high-pressure granulites of the Orlica-Snieznik dome (Bohemian Massif) as the product of partial melt crystallization in preserved nanogranites. Previous reports of both kumdykolite and kokchetavite in natural rocks are mainly from samples that passed through the diamond stability field. However, because the maximum pressure recorded in these host rocks is <3 GPa, our observations indicate that high pressure is not required for the formation of kumdykolite and kokchetavite, and their presence is not therefore an indicator of ultrahigh-pressure conditions. Detailed microstructural and microchemical investigation of these inclusions indicates that such phases should instead be regarded as (1) a direct mineralogical criteria to identify former melt inclusions with preserved original compositions, including H2O and CO2 contents and (2) indicators of rapid cooling of the host rocks. Thus, the present study provides novel criteria for the interpretation of melt inclusions in natural rocks and allows a more rigorous characterization of partial melts during deep subduction to mantle depth as well as their behavior on exhumation. KW - Partial melt KW - Polymorphs KW - Deep fluids KW - Nanogranites KW - Kumdykolite KW - Kokchetavite KW - Cristobalite Y1 - 2016 U6 - https://doi.org/10.1007/s00410-015-1220-x SN - 0010-7999 SN - 1432-0967 VL - 171 SP - 61 EP - 65 PB - Springer CY - New York ER - TY - JOUR A1 - Ferrero, Silvio A1 - Wunder, Bernd A1 - Ziemann, Martin Andreas A1 - Waelle, Markus T1 - Carbonatitic and granitic melts produced under conditions of primary immiscibility during anatexis in the lower crust JF - Earth & planetary science letters N2 - Carbonatites are peculiar magmatic rocks with mantle-related genesis, commonly interpreted as the products of melting of CO2-bearing peridotites, or resulting from the chemical evolution of mantle derived magmas, either through extreme "differentiation or secondary immiscibility. Here we report the first finding of anatectic carbonatites of crustal origin, preserved as calcite-rich polycrystalline inclusions in garnet from low-to-medium pressure migmatites of the Oberpfalz area, SW Bohemian Massif (Central Europe). These inclusions originally trapped a melt of calciocarbonatitic composition with a characteristic enrichment in Ba, Sr and LREE. This interpretation is supported by the results of a detailed microstructural and microchemical investigation, as well as re-melting experiments using a piston cylinder apparatus. Carbonatitic inclusions coexist in the same cluster with crystallized silicate melt inclusions (nanogranites) and COH fluid inclusions, suggesting conditions of primary immiscibility between two melts and a fluid during anatexis. The production of both carbonatitic and granitic melts during the same anatectic event requires a suitable heterogeneous protolith. This may be represented by a sedimentary sequence containing marble lenses of limited extension, similar to the one still visible in the adjacent central Moldanubian Zone. The presence of CO2-rich fluid inclusions suggests furthermore that high CO2 activity during anatexis may be required to stabilize a carbonate-rich melt in a silica-dominated, system. This natural occurrence displays a remarkable similarity with experiments on carbonate-silicate melt immiscibility, where CO2 saturation is a condition commonly imposed. In conclusion, this study shows how the investigation of partial melting through melt inclusion studies may unveil unexpected processes whose evidence, while preserved in stiff minerals such as garnet, is completely obliterated in the rest of the rock due to metamorphic re-equilibration. Our results thus provide invaluable new insights into the processes which shape the geochemical evolution of our planet, such as the redistribution of carbon and strategic metals during orogenesis. (C) 2016 Elsevier B.V. All rights reserved. KW - partial melting KW - carbonatites KW - nanogranites KW - garnet KW - melt inclusions; nanocarbonatites Y1 - 2016 U6 - https://doi.org/10.1016/j.epsl.2016.08.043 SN - 0012-821X SN - 1385-013X VL - 454 SP - 121 EP - 131 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Ferrero, Silvio A1 - Wunder, Bernd A1 - Walczak, Katarzyna A1 - Ziemann, Martin Andreas T1 - Preserved near ultrahigh-pressure melt from continental crust subducted to mantle depths JF - Geology N2 - Remnants of hydrous melt formed at mantle depths have been identified and characterized within high-pressure leucogranulites of the Orlica-Snieznik Dome (Bohemian Massif, central Europe). They occur as nanogranites in garnet formed via partial melting of granitoids during the Variscan orogeny. Melt composition and H2O content have been investigated in situ after experimental re-homogenization of the nanogranites, and are consistent with melts produced experimentally from crustal lithologies at mantle depths. This is the first geochemical study of melt inclusions from natural crustal rocks equilibrated close to the stability field of coesite, shedding light on how continental crust melts during deep subduction. Whereas decompressional melting is commonly invoked for deeply subducted crustal lithologies, melting occurred near or at the metamorphic peak pressure in the Orlica-Snieznik granulites. Melting of deeply subducted crustal rocks significantly modifies the rheology and thus promotes fast exhumation: this process has a critical influence on the geodynamic evolution of subduction-collision orogens as well as crustal differentiation at depth. Y1 - 2015 U6 - https://doi.org/10.1130/G36534.1 SN - 0091-7613 SN - 1943-2682 VL - 43 IS - 5 SP - 447 EP - 450 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Ferrero, Silvio A1 - Godard, Gaston A1 - Palmeri, Rosaria A1 - Wunder, Bernd A1 - Cesare, Bernardo T1 - Partial melting of ultramafic granulites from Dronning Maud Land, Antarctica BT - constraints from melt inclusions and thermodynamic modeling JF - American mineralogist : an international journal of earth and planetary materials N2 - In the Pan-African belt of the Dronning Maud Land, Antarctica, crystallized melt inclusions (nanogranitoids) occur in garnet from ultramafic granulites. The granulites contain the peak assemblage pargasite+garnet+clinopyroxene with rare relict orthopyroxene and biotite, and retrograde symplectites at contacts between garnet and amphibole. Garnet contains two generations of melt inclusions. Type 1 inclusions, interpreted as primary, are isolated, < 10 mu m in size, and generally have negative crystal shapes. They contain kokchetavite, kumdykolite, and phlogopite, with quartz and zoisite as minor phases, and undevitrified glass was identified in one inclusion. Type 2 inclusions are < 30 mu m in size, secondary, and contain amphibole, feldspars, and zoisite. Type 2 inclusions appear to be the crystallization products of a melt that coexisted with an immiscible CO2-rich fluid. The nanogranitoids were re-homogenized after heating in a piston-cylinder in a series of four experiments to investigate their composition. The conditions ranged between 900 and 950 degrees C at 1.5-2.4 GPa. Type 1 inclusions are trachytic and ultrapotassic, whereas type 2 melts are dacitic to rhyolitic. Thermodynamic modeling of the ultramafic composition in the MnNCKFMASHTO system shows that anatexis occurred at the end of the prograde P-T path, between the solidus (at ca. 860 degrees C-1.4 GPa) and the peak conditions (at ca. 960 degrees C-1.7 GPa). The model melt composition is felsic and similar to that of type 1 inclusions, particularly when the melting degree is low (< 1 mol%), close to the solidus. However the modeling fails to reproduce the highly potassic signature of the melt and its low H2O content. The combination of petrology, melt inclusion study, and thermodynamic modeling supports the interpretation that melt was produced by anatexis of the ultramafic boudins near peak P-T conditions, and that type 1 inclusions contain the anatectic melt that was present during garnet growth. The felsic, ultrapotassic composition of the primary anatectic melts is compatible with low melting degrees in the presence of biotite and amphibole as reactants. KW - Nanogranitoids KW - partial melting KW - thermodynamic modeling KW - Antarctica KW - ultramafic granulites KW - kumdykolite KW - kokchetavite KW - High-Grade Metamorphism KW - Anatexis KW - and Granite Magmatism Y1 - 2018 U6 - https://doi.org/10.2138/am-2018-6214 SN - 0003-004X SN - 1945-3027 VL - 103 IS - 4 SP - 610 EP - 622 PB - Mineralogical Society of America CY - Chantilly ER - TY - JOUR A1 - Ferrero, Silvio A1 - Borghini, Alessia A1 - Wunder, Bernd A1 - Walle, Markus A1 - Günter, Christina A1 - Ziemann, Martin Andreas T1 - A treasure chest full of nanogranitoids BT - an archive to investigate crustal melting in the Bohemian Massif JF - Metamorphic Geology: Microscale to Mountain Belts N2 - The central European Bohemian Massif has undergone over two centuries of scientific investigation which has made it a pivotal area for the development and testing of modern geological theories. The discovery of melt inclusions in high-grade rocks, either crystallized as nanogranitoids or as glassy inclusions, prompted the re-evaluation of the area with an ‘inclusionist’ eye. Melt inclusions have been identified in a wide range of rocks, including felsic/perpotassic granulites, migmatites, eclogites and garnet clinopyroxenites, all the result of melting events albeit over a wide range of pressure/temperature conditions (800–1000°C/0.5–5 GPa). This contribution provides an overview of such inclusions and discusses the qualitative and quantitative constraints they provide for melting processes, and the nature of melts and fluids involved in these processes. In particular, data on trace-element signatures of melt inclusions trapped at mantle depths are presented and discussed. Moreover, experimental re-homogenization of nanogranitoids provided microstructural criteria allowing assessment of the conditions at which melt and host are mutually stable during melting. Overall this work aims to provide guidelines and suggestions for petrologists wishing to explore the fascinating field of melt inclusions in metamorphic terranes worldwide, based on the newest discoveries from the still-enigmatic Bohemian Massif. Y1 - 2018 SN - 978-1-78620-400-4 U6 - https://doi.org/10.1144/SP478.19 SN - 0305-8719 VL - 478 SP - 13 EP - 38 PB - Geological Soc Publishing House CY - Bath ER - TY - JOUR A1 - Borghini, Alessia A1 - Ferrero, Silvio A1 - Wunder, Bernd A1 - Laurent, Oscar A1 - Ziemann, Martin Andreas T1 - Granitoid melt inclusions in orogenic peridotite and the origin of garnet clinopyroxenite JF - Geology N2 - Granitic melt inclusions were found in layers of garnet clinopyroxenites from orogenic peridotites hosted in high-pressure felsic granulites of the Granulitgebirge, central Europe. The inclusions are both glassy and crystallized, and occur as clusters in the garnet. Microstructural features suggest that the inclusions formed while garnet was growing as a peritectic phase, likely alongside clinopyroxene. The chemistry of the melt, in particular its trace element signature, shows a crustal contribution, probably due to the involvement of phengite in the melt-producing reaction, most likely in the presence of a fluid. The presence of a granitoid melt in mantle rocks may be the result of localized melting of a phengite-bearing protolith either already present in the peridotites or, more likely, within the local deeply subducted crustal units. In the latter case, the melt would have infiltrated the peridotites and generated pyroxenite via metasomatism. In either case, the presence of granitoid inclusions in orogenic peridotite provides direct evidence for a genetic connection between a high-pressure crustal melt and garnet pyroxenites. The in situ characterization of these remnants of natural melt provides direct quantitative constraints on (one of) the agents responsible for the interaction between crust and mantle. Y1 - 2018 U6 - https://doi.org/10.1130/G45316.1 SN - 0091-7613 SN - 1943-2682 VL - 46 IS - 11 SP - 1007 EP - 1010 PB - American Institute of Physics CY - Boulder ER -