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 - 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 - 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 -