Equilibration and disequilibration between monazite and garnet: indication from phase-composition and quantitative texture analysis

Berger, Alfons; Scherrer, Nadim; Bussy, Francois (2005). Equilibration and disequilibration between monazite and garnet: indication from phase-composition and quantitative texture analysis Journal of Metamorphic Geology, 23(9), pp. 865-880. Wiley 10.1111/j.1525-1314.2005.00614.x

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The integration of information which can be gained from accessory [i.e. age (t)] and rock-forming minerals [i.e. temperature (T) and pressure (P)] requires a more profound understanding of the equilibration kinetics during metamorphic processes. This paper presents an approach comparing conventional P-T estimate from equilibrated assemblages of rock-forming minerals with temperature data derived from yttrium-garnet-monazite (YGM) and yttrium-garnet-xenotime (YGX) geothermometry. Such a comparison provides an initial indication on differences between equilibration of major and trace elements. Regarding this purpose, two migmatites, two polycyclic and one monocyclic gneiss from the Central Alps (Switzerland, northern Italy) were investigated. While the polycyclic samples exhibit trace-element equilibration between monazite and garnet grains assigned to the same metamorphic event, there are relics of monazite and garnet obviously surviving independent of their textural position. These observations suggest that surface processes dominate transport processes during equilibration of those samples. The monocyclic gneiss, on the contrary, displays rare isolated monazite with equilibration of all elements, despite comparably large transport distances. With a nearly linear crystal-size distribution of the garnet grain population, growth kinetics, related to the major elements, were likely surface-controlled in this sample. In contrast to these completely equilibrated examples, the migmatites indicate disequilibrium between garnet and monazite with a change in REE patterns on garnet transects. The cause for this disequilibrium may be related to a potential disequilibrium initiated by a changing bulk chemistry during melt segregation. While migmatite environments are expected to support high transport rates (i.e. high temperatures and melt presence), the evolution of equilibration in migmatites is additionaly related to change in chemistry. As a key finding, surface-controlled equilibration kinetics seem to dominate transport-controlled processes in the investigated samples. This may be decisive information towards the understanding of age data derived from monazite.

Item Type:	Journal Article (Original Article)
Division/Institute:	Bern Academy of the Arts Bern Academy of the Arts > Institute Materiality in Art and Culture Bern Academy of the Arts > HKB Teaching
Name:	Berger, Alfons; Scherrer, Nadim0000-0002-6576-885X and Bussy, Francois
Subjects:	Q Science > QE Geology
ISSN:	0263-4929
Publisher:	Wiley
Funders:	[UNSPECIFIED] Swiss National Science Foundation
Projects:	[UNSPECIFIED] Project 21- 22889.01
Language:	English
Submitter:	Nadim Scherrer
Date Deposited:	10 Feb 2021 15:29
Last Modified:	20 Apr 2021 14:40
Publisher DOI:	10.1111/j.1525-1314.2005.00614.x
Related URLs:	Publisher
Web of Science ID:	000233529800005
Uncontrolled Keywords:	Alps equilibration kinetics monazite thermometry quantitative textures granulite-facies metamorphism trace-element abundances hydrothermal alteration electron-microprobe lower crust age th growth rocks geochronology
ARBOR DOI:	10.24451/arbor.13537
URI:	https://arbor.bfh.ch/id/eprint/13537