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 - Bartoli, Omar A1 - Acosta-Vigil, Antonio A1 - Ferrero, Silvio A1 - Cesare, Bernardo T1 - Granitoid magmas preserved as melt inclusions in high-grade metamorphic rocks JF - American mineralogist : an international journal of earth and planetary materials N2 - This review presents a compositional database of primary anatectic granitoid magmas, entirely based on melt inclusions (MI) in high-grade metamorphic rocks. Although MI are well known to igneous petrologists and have been extensively studied in intrusive and extrusive rocks, MI in crustal rocks that have undergone anatexis (migmatites and granulites) are a novel subject of research. They are generally trapped along the heating path by peritectic phases produced by incongruent melting reactions. Primary MI in high-grade metamorphic rocks are small, commonly 5-10 pm in diameter, and their most common mineral host is peritectic garnet. In most cases inclusions have crystallized into a cryptocrystalline aggregate and contain a granitoid phase assemblage (nanogranitoid inclusions) with quartz, K-feldspar, plagioclase, and one or two mica depending on the particular circumstances. After their experimental remelting under high-confining pressure, nanogranitoid MI can be analyzed combining several techniques (EMP, LA-ICP-MS, NanoSIMS, Raman). The trapped melt is granitic and metaluminous to peraluminous, and sometimes granodioritic, tonalitic, and trondhjemitic in composition, in agreement with the different P-T-a(H2o) conditions of melting and protolith composition, and overlap the composition of experimental glasses produced at similar conditions. Being trapped along the up-temperature trajectory as opposed to classic MI in igneous rocks formed during down-temperature magma crystallization fundamental information provided by nanogranitoid MI is the pristine composition of the natural primary anatectic melt for the specific rock under investigation. So far similar to 600 nanogranitoid MI, coming from several occurrences from different geologic and geodynamic settings and ages, have been characterized. Although the compiled MI database should be expanded to other potential sources of crustal magmas, MI data collected so far can be already used as natural "starting-point" compositions to track the processes involved in formation and evolution of granitoid magmas. KW - Granitoid magmas KW - melt inclusions KW - nanogranite KW - crustal anatexis KW - peritectic phase Y1 - 2016 U6 - https://doi.org/10.2138/am-2016-5541CCBYNCND SN - 0003-004X SN - 1945-3027 VL - 101 SP - 1543 EP - 1559 PB - Mineralogical Society of America CY - Chantilly ER -