1Zircon is an important host mineral for many high-field strength elements (HFSE), 2 particularly Zr and Hf. Thus, its solubility in geologic fluids at high pressure and 3 temperature plays an important role in terrestrial cycling of these elements during 4 processes in the Earth's crust and mantle. We performed in-situ high-pressure, high-5 with zircon provide evidence for strong differences in the Zr complexation between 22 these fluids. Comparison of XANES spectra to those of model compounds and ab-23 initio simulation of XANES spectra revealed [8] Zr for the HCl solution, [7] Zr for the 24 NaOH solution, and [6] Zr for the Na-Al-silicate-bearing solutions. For the latter 25 3 solutions, formation of alkali zircono-silicate complexes is indicated by the strong 26 dependence of zircon solubility on Na/Al and the similarity of the XANES spectra to 27 spectra simulated based on the local structure around Zr in the alkali zircono-silicates 28 vlasovite and catapleite. Alkali zircono-silicate complexes are responsible for the 29 enhancement of Zr concentrations in Na-Al-silicate-bearing solutions and very likely 30 play an important role for mobilization of HFSE in during fluid-rock interaction. 31Because high alkali/Al can be expected in aqueous fluids at high pressure and 32 temperature due to incongruent dissolution of feldspar and mica, the increase of 33 zircon solubility along the NaAlSi 3 O 8 -Na 2 Si 3 O 7 join points to potentially considerable 34

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Trace element concentrations in aqueous fluids in equilibrium with haplogranitic melt were determined in situ at elevated P-T conditions using hydrothermal diamond-anvil cells and synchrotron-radiation XRF microanalyses. Time-resolved analyses showed that the Rb and Sr concentrations in the fluids became constant in less than 2000 s at all temperatures (500 to 780°C). Although fluid-melt equilibration was very rapid, the change in the concentration of both elements in the fluid with temperature was fairly small (a slight increase for Rb and a slight decrease for Sr). This permitted partitioning data for Rb and Sr between haplogranitic melt and H 2 O or NaCl + KCl + HCl aqueous solutions at 750°C and 200 to 700 MPa to be obtained from EMP analyses of the quenched melt and the in situ SR-XRF analyses of the equilibrated fluid.

SynopsisA confocal setup for micro-XRF and XAFS for in-situ high-pressure and temperature experiments is presented. AbstractA confocal setup is presented that improves micro-XRF and XAFS experiments with highpressure diamond anvil cells (DAC). In this experiment, a probing volume is defined by the focus of the incoming synchrotron radiation beam and that of a polycapillary X-ray half-lens with a very long working distance, which is placed in front of the fluorescence detector. This setup enhances the quality of the fluorescence and XAFS spectra, and thus the sensitivity for detecting elements at low concentrations. It efficiently suppresses signal from outside the sample chamber, which stems from elastic and inelastic scattering of the incoming beam by the diamond anvils as well as from excitation of fluorescence from the body of the DAC.