Journal of Metamorphic Geology
© 2014 John Wiley & Sons Ltd
Edited By: Michael Brown, Geoff Clarke, Doug Robinson, Richard White and Donna Whitney
Impact Factor: 4.374
ISI Journal Citation Reports © Ranking: 2013: 2/43 (Geology)
Online ISSN: 1525-1314
Geochronology in partially melted rocks
An important goal in studies of crustal melting is to link P–T determinations with time, particularly to understand rates of heating, lengths of melting episodes and rates of cooling and exhumation. Although accessory minerals with a high closure temperature for diffusion of Pb, for example monazite and zircon, are most suitable for dating close to peak P–T conditions for partially melted rocks, linking to a P–T point or range along the P–T path presents challenges since these minerals may survive from the precursors, recrystallize around peak conditions or exhibit new growth as melt crystallizes along the retrograde path. Nowadays these alternatives potentially may be discriminated using microstructural characterization, micro-beam chemical analysis, accessory phase thermometry and trace element distributions between accessory minerals and associated rock-forming minerals to provide constraints on whether grains are relict from the precursor or record the timing of recrystallization and/or new growth in relation to the P–T evolution.
To read the complete commentary, click here
Dirks, P. & Hand, M., 1991. Structural and metamorphic controls on the distribution of zircon in an evolving quartzofeldspathic migmatite: an example from the Reynolds Range, central Australia. Journal of Metamorphic Geology, 9, 191–201.
Suzuki, K. & Adachi, M., 1998. Denudation history of the high T/P Ryoke metamorphic belt, southwest Japan: constraints from CHIME monazite ages of gneisses and granitoids. Journal of Metamorphic Geology, 16, 23–37.
Jung, S. & Mezger, K., 2001. Geochronology in migmatites—a Sm–Nd, U–Pb and Rb–Sr study from the Proterozoic Damara belt (Namibia): implications for polyphase development of migmatites in high-grade terranes. Journal of Metamorphic Geology, 19, 77–97
Moller, A., O'Brien, P.J., Kennedy, A. & Kroner, A., 2002. Polyphase zircon in ultrahigh-temperature granulites (Rogaland, SW Norway): constraints for Pb diffusion in zircon. Journal of Metamorphic Geology, 20, 727–740.
Tomkins, H.S., Williams, I.S. & Ellis, D.J., 2005. In situ U-Pb dating of zircon formed from retrograde garnet breakdown during decompression in Rogaland, SW Norway. Journal of Metamorphic Geology, 23, 201–215.
Hermann, J. & Rubatto, D., 2003. Relating zircon and monazite domains to garnet growth zones: age and duration of granulite facies metamorphism in the Val Malenco lower crust. Journal of Metamorphic Geology, 21, 833–852.
Baldwin, J. A. & Brown, M., 2008. Age and duration of ultrahigh-temperature metamorphism in the Anapolis-Itaucu Complex, Southern Brasilia Belt, central Brazil - constraints from U-Pb geochronology, mineral rare earth element chemistry and trace-element thermometry. Journal of Metamorphic Geology, 26, 213–233.
Kelsey, D.E., Clark, C. & Hand, M., 2008. Thermobarometric modelling of zircon and monazite growth in melt-bearing systems: examples using model metapelitic and metapsammitic granulites. Journal of Metamorphic Geology, 26, 199–212.
Kelsey, D.E. & Powell, R., 2011. Progress in linking accessory mineral growth and breakdown to major mineral evolution in metamorphic rocks: a thermodynamic approach in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–ZrO2 system. Journal of Metamorphic Geology, 29, 151–166.