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Byline: Ewa SAaby (1), MichaA Amigielski (2), Tomasz Amigielski (3), Andrzej Domonik (4), Klaus Simon (5), Andreas Kronz (5) Keywords: Mixing; Element mobility; Diffusion; Alkali feldspar; 3D-depiction; Cut-off value models; Gradient models; Probabilistic models; Geochemical heterogeneity; Karkonosze granite Abstract: As has been demonstrated in recent years, the heterogeneities of coeval magmas can be more successfully revealed by zoned megacrysts rather than by analysis of the whole rocks hosting them. Here, the geochemical heterogeneities of feldspar megacrysts from the Karkonosze granite, Poland, are investigated by LA-ICP-MS. The crystals are the product of migration and growth in regions of poorly mixed magmas. 3D-modeling of the Ba, Sr, and Rb distributions emphasizes the importance of micro-domain growth morphologies. Two models of element behavior--a relative concentration model and a composition gradient model--provide a potentially effective tool for tracking the mixing process on a microscale. Measured concentrations of elements of different mobilities do not agree with what might be expected from the mixing of two end-member magmas. If mixing was the only process occurring, linear correlations between the concentrations of any two elements should be observed this, however, is not the case. For combinations of any two of the three elements, modeling reveals differing non-linear correlations between concentrations. The megacryst heterogeneities provide an insight into how mixing magmas are chaotically advected to growing crystals and the degree of inter-magma element exchange between the magmas. Author Affiliation: (1) Institute of Geological Sciences, Polish Academy of Sciences, Research Centre in Warsaw, Twarda 51/55, 00-818, Warsaw, Poland (2) Institute of Geology, University of Warsaw, A>>wirki i Wigury 93, 02-089, Warsaw, Poland (3) 'Sofrecom Polska', Grojecka 5, 02-019, Warsaw, Poland (4) Institute of Hydrogeology and Engineering Geology, University of Warsaw, A>>wirki i Wigury 93, 02-089, Warsaw, Poland (5) Department of Geochemistry, GZG of Georg-August-University, Goldschmidtstrasse 1, 37077, Gottingen, Germany Article History: Registration Date: 25/03/2011 Received Date: 09/08/2010 Accepted Date: 25/03/2011 Online Date: 19/04/2011 Article note: Communicated by J. Hoefs . Electronic supplementary material The online version of this article (doi: 10.1007/s00410-011-0631-6) contains supplementary material, which is available to authorized users.

Byline: Yilin Xiao (1,2), Jochen Hoefs (2), Zhenhui Hou (1), Klaus Simon (2), Zeming Zhang (3) Keywords: Fluid/rock interaction; Elemental transfer; Isotopic fractionation; Subduction and exhumation; Sulu Abstract: In order to better understand the role of fluids during subduction and subsequent exhumation, we have investigated whole-rock and mineral chemistry (major and trace elements) and Li, B as well as O, Sr, Nd, Pb isotopes on selected continuous drill-core profiles through contrasting lithological boundaries from the Chinese Continental Scientific Drilling Program (CCSD) in Sulu, China. Four carefully selected sample sets have been chosen to investigate geochemical changes as a result of fluid mobilization during dehydration, peak metamorphism, and exhumation of deeply subducted continental crust. Our data reveal that while O and Sr-Nd-Pb isotopic compositions remain more or less unchanged, significant Li and/or B isotope fractionations occur between different lithologies that are in close contact during various metamorphic stages. Samples that are supposed to represent prograde dehydration as indicated by veins formed at high pressures (HP) are characterized by element patterns of highly fluid-mobile elements in the veins that are complementary to those of the host eclogite. A second sample set represents a UHP metamorphic crustal eclogite that is separated from a garnet peridotite by a thin transitional interface. Garnet peridotite and eclogite are characterized by a >10% difference in MgO, which, together with the presence of abundant hydroxyl-bearing minerals and compositionally different clinopyroxene grains demonstrate that both rocks have been derived from different sources that have been tectonically juxtaposed during subduction, and that hydrous silicate-rich fluids have been added from the subducting slab to the mantle. Two additional sample sets, comprising retrograde amphibolite and relatively fresh eclogite, demonstrate that besides external fluids, internal fluids can be responsible for the formation of amphibolite. Li and B concentrations and isotopic compositions point to losses and isotopic fractionation during progressive dehydration. On the other hand, fluids with isotopically heavier Li and B are added during retrogression. On a small scale, mantle-derived rocks may be significantly metasomatized by fluids derived from the subducted slab. Our study indicates that during high-grade metamorphism, Li and B may show different patterns of enrichment and of isotopic fractionation. Author Affiliation: (1) CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, 230026, Hefei, China (2) Geowissenschaftliches Zentrum der Universitat Gottingen, Goldschmidtstrasse 1, 37077, Gottingen, Germany (3) Institute of Geology, Chinese Academy of Geological Sciences, 100037, Beijing, China Article History: Registration Date: 07/03/2011 Received Date: 23/09/2010 Accepted Date: 07/03/2011 Online Date: 19/04/2011 Article note: Communicated by T. L. Grove. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-011-0625-4) contains supplementary material, which is available to authorized users.

Analyses of igneous xenoliths containing high-iron-oxide melt (HIM) indicated that they resulted from crystal fractionation in a deep-crustal chamber of alkali basalt magma. HIM represented a primary magmatic phase. These findings were observed in globules of oxide melts dominated by iron and titanium. Fluid inclusion and mineral composition data showed immiscible separation of the HIM at magmatic temperatures. The HIM separation occurred during clinopyroxene accumulation in an alkali trachybasalt and continued during crystallization of amphibole and K-feldspar.