ORIGINAL PAPER Diffusion of divalent cations in garnet: multi-couple experiments A. L. Perchuk Æ M. Burchard Æ H.-P. Schertl Æ W. V. Maresch Æ T. V. Gerya Æ H.-J. Bernhardt Æ O. Vidal Received: 3 April 2008 / Accepted: 13 October 2008 / Published online: 23 November 2008 Ó Springer-Verlag 2008 Abstract We demonstrate the possibility of studying several diffusion couples in a single run, i.e. under almost similar P–T–t–f O 2 conditions, allowing direct comparison of the diffusion rates in different diffusion couples. Thus the duration of experimental study and the risk of failure of expensive experimental equipment can be decreased con- siderably. The diffusion experiments were carried out in piston-cylinder apparatus. Gem-quality garnets of alman- dine, spessartine and grossular compositions together with inclusion-rich eclogitic garnets were embedded in a pow- der of natural pyrope and annealed together under dry conditions at P = 1.9–3.2 GPa and T = 1,070–1,400°C. Diffusion profiles were measured by electron microprobe and fitted numerically on the basis of multicomponent diffusion theory. The datasets derived from different dif- fusion couples yields parameters of the Arrhenius equation for Ca, Mg and Fe in natural eclogitic garnets and Mg, Mn and Fe in gem-quality garnets. We have also studied the effect of grain-boundary diffusion in the sintered pyrope matrix on interdiffusion on the basis of 2D modeling. Under conditions analogous to those of our experimental runs, we show that observed irregularities in some mea- sured diffusion profiles (not applied for the diffusion modeling) can be directly related to the superposition of local grain-boundary diffusion on dominant volume diffusion. Keywords Diffusion  Diffusion coefficient  Garnet  Experiment  Piston-cylinder  Mineral inclusion  Grain-boundary diffusion Introduction Garnet is an important rock-forming mineral of various magmatic, metamorphic and metasomatic rocks. Because of the flexibility provided by many possible end-member compositions, garnets are formed in many different lithologies and at various P–T conditions of the Earth’s crust and mantle. The composition of garnet is very sen- sitive to these parameters and thus variations often lead to the formation of zoned crystals. A variety of zoning pat- terns in metamorphic garnets have been summarized in a number of publications (e.g. Tracy 1982; Chakraborty and Ganguly 1991; Perchuk and Philippot 2000). Garnet zoning is of particular interest, because it can be used to recon- struct rates of temperature and/or pressure variation of rocks from different geodynamic settings (e.g. Lasaga Communicated by T.L. Grove. A. L. Perchuk (&) IGEM, Russian Academy of Sciences, Staromonetny 35, 119017 Moscow, Russia e-mail: alp@igem.ru A. L. Perchuk IEM, Russian Academy of Sciences, Chernogolovka 142432, Russia M. Burchard Mineralogical Institute, University Heidelberg, 69120 Heidelberg, Germany H.-P. Schertl  W. V. Maresch  H.-J. Bernhardt Institute of Mineralogy, Geology and Geophysics, Ruhr-University Bochum, 44780 Bochum, Germany T. V. Gerya ETH Zu ¨rich, Zurich, Switzerland O. Vidal Laboratoire de Geodynamique des Chaines Alpines, C.N.R.S, UMR 5025, Grenoble, France 123 Contrib Mineral Petrol (2009) 157:573–592 DOI 10.1007/s00410-008-0353-6