Trace-element zoning patterns in porphyroblastic garnets in low-t eclogites: Parameter optimization of the diffusion-limited ree-uptake model

Ryo Fukushima, Tatsuki Tsujimori, Shogo Aoki, Kazumasa Aoki

Research output: Contribution to journalArticlepeer-review

Abstract

Compositional zoning patterns of the major elements and REEs in prograde-zoned garnets whose Mg/(Mg + Fe) atomic ratios increase rimward have been widely used to understand the metamorphic P–T–t trajectories, and the diffusion-limited REE-uptake model is a promising way to interpret their growth rates and the REE diffusion kinetics in the low-temperature eclogite. In order to elucidate their growth kinetics with Skora et al.'s (2006) diffusion-limited REE uptake model for prograde-zoned garnets, we examine the trace-element zoning patterns of two prograde-zoned porphyroblastic garnets (~6 mm in size) in low-temperature eclogites from two different localities. Core-to-rim trace-element profiles in a garnet (prp5–9-alm61–67 sps1–3 grs24–30 ) of a glaucophane-bearing epidote eclogite of Syros (Cyclades, Greece) are characterized by the presence of Y + HREE peaks in the mantle, which might be attributed to a continuous breakdown of the titanite to form rutile during the garnet growth. In contrast, those in a garnet (prp4–7 alm61–68-sps3–10 grs23–24 ) extracted from a lawsonite-eclogite of the South Motagua Mélange (SMM) (Guatemala) have prominent central peaks of Y + HREEs. Although the REE profiles of both the garnets can be explained by the diffusion-limited uptake, their Mn profiles suggest that their growth-rate laws are different: i.e., diffusion-con-trolled (Syros) and interface-controlled (SMM). Prior to the model application, we optimize the number of the parameters as the garnet grows with the interface-controlled processes based on the growth Péclet number. In particular, we propose the ratio of the REE diffusivity in the eclogitic matrix to the garnet growth rate as the new parameter. Visualizing the values of the new parameters allows to readily understand the relationship between the REE profiles and the REE-diffusion/gar-net-growth kinetics in low-T eclogite. Our model refinement leads to the simple quantitative characterization of core-to-rim REE profiles in garnet in low-temperature eclogites.

Original languageEnglish
Article numbere12394
Pages (from-to)1-17
Number of pages17
JournalIsland Arc
Volume30
Issue number1
DOIs
Publication statusPublished - 2021 Jan 1

Keywords

  • Diffusion-limited REE uptake model
  • Eclogite
  • Growth kinetics
  • Zoned garnet

ASJC Scopus subject areas

  • Geology

Fingerprint Dive into the research topics of 'Trace-element zoning patterns in porphyroblastic garnets in low-t eclogites: Parameter optimization of the diffusion-limited ree-uptake model'. Together they form a unique fingerprint.

Cite this