Concordant pulse in Mn, Y and HREEs concentrations during UHP eclogitic garnet growth: Transient rock dynamics along a cold subduction plate interface

• Published in: Earth and planetary science letters 2020-01, Vol.530, p.115908, Article 115908
• Main Authors: Tan, Zhou, Agard, Philippe, Gao, Jun, Hong, Tao, Wan, Bo
• Format: Article
• Language: English
• Subjects: Chinese SW-Tianshan; cold subduction regime; diffusion modeling; garnet zoning; Sciences of the Universe; UHP oceanic eclogite; Zr-in-rutile thermometry
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2019.115908

•First evidence for concordant Mn, HREE and Y zoning in UHP eclogitic garnet.•Zr-in-rutile thermometry and diffusion modeling suggest a transient T pulse of ∼80°C.•Such thermal pulses reflect changes in rock dynamics along subduction plate interface.•Diffusion-controlled growth should be considered when deriving P–T from garnet zoning. We herein report strikingly concordant Mn, Y, and HREE garnet zoning in ultrahigh-pressure low-temperature oceanic eclogites found in the fossil Devonian-Carboniferous subduction plate interface in SW-Tianshan. Zr-in-rutile thermometry, thermodynamic modeling and diffusion-controlled garnet growth modeling show that this type of zoning can be explained by a short-lived transient, most likely a ∼80°C thermal pulse (from 490 to 570°C). This event could be as transient as ∼300 Ka, assuming a prograde to peak burial duration of 5 Ma. Such garnet zoning is observed for grains sampled meters apart (Fig. 1d) and was detected in other eclogites in the region. This transient event could reflect the short-lived movement of UHP oceanic slices, once detached, towards the hotter mantle wedge, and/or deformation-induced remobilization of fluids enhancing diffusion-controlled garnet growth.