Copper isotope evidence for Cu transfer during oceanic crust subduction: insights from the (ultra)high-pressure metamorphic belt of Southwestern Tianshan, China
Abstract
Constraining the behavior of Cu during subduction is the key to decipher processes leading to the porphyry Cu deposit formation at convergent margins, while also shedding light on S cycling owing to the chalcophile affinity of Cu. This study reported δ⁶⁵Cu values for bulk-rock and chalcopyrite from a metamafic rock from the (ultra-)high pressure metamorphic belt of Southwestern Tianshan, China. The rock consists of abundant glaucophane-dominated breccias (part A) crosscut by a large-scale omphacite-rich vein system (part B) with sharp boundaries. The glaucophanedominated breccias are interpreted as partially dehydrated metabasalts, while the omphacite-rich vein system reflects the main fluid pathways in the subduction channel. Part A exhibits elevated δ⁶⁵Cu values (0.07‰ to 0.36‰) and low Cu contents (52 ppm on average) compared to MORB (δ⁶⁵Cu=0.04‰ to 0.14‰; Cu=90 ppm). Together with heavier δ⁶⁵Cu values of chalcopyrite (-0.17‰ to 0.23‰) in part A compared to magmatic sulfide, these suggest that dehydration preferentially releases isotopically light Cu and leaves residues with heavier Cu isotope compositions. Part B shows complementary light δ⁶⁵Cu values both in bulk rock and chalcopyrite. The negative correlation between S and δ⁶⁵Cu indicates that precipitated sulfides complexed with light Cu isotopes may result in lowered δ⁶⁵Cu values in the rock during fluid-rock interactions. Overall, the data point to the mobilization of isotopically light Cu-bearing fluids during the dehydration of mafic crust in subduction environments. However, the absence of commonly high Cu contents in arc magmas suggests that the released copper may be buffered by sulfides in the sub-arc mantle, resulting in Cu-rich sulfide
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BibTeX
@article{chen2026copper,
title = {{Copper isotope evidence for Cu transfer during oceanic crust subduction: insights from the (ultra)high-pressure metamorphic belt of Southwestern Tianshan, China}},
author = {Yu Chen and Yuanyuan Xiao and Yongxiang Yao and Baptiste Debret and Ziwei Sun and Hongmei Gong and Yao Liu and Kaiyun Chen},
journal = {Chemical Geology},
year = {2026},
month = oct,
doi = {10.1016/j.chemgeo.2026.123661},
url = {https://hal.science/hal-05785320v1},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Copper isotope evidence for Cu transfer during oceanic crust subduction: insights from the (ultra)high-pressure metamorphic belt of Southwestern Tianshan, China
AU - Yu Chen
AU - Yuanyuan Xiao
AU - Yongxiang Yao
AU - Baptiste Debret
AU - Ziwei Sun
AU - Hongmei Gong
AU - Yao Liu
AU - Kaiyun Chen
PY - 2026
DA - 2026/10/08
JO - Chemical Geology
DO - 10.1016/j.chemgeo.2026.123661
UR - https://hal.science/hal-05785320v1
AB - Constraining the behavior of Cu during subduction is the key to decipher processes leading to the porphyry Cu deposit formation at convergent margins, while also shedding light on S cycling owing to the chalcophile affinity of Cu. This study reported δ⁶⁵Cu values for bulk-rock and chalcopyrite from a metamafic rock from the (ultra-)high pressure metamorphic belt of Southwestern Tianshan, China. The rock consists of abundant glaucophane-dominated breccias (part A) crosscut by a large-scale omphacite-rich vein system (part B) with sharp boundaries. The glaucophanedominated breccias are interpreted as partially dehydrated metabasalts, while the omphacite-rich vein system reflects the main fluid pathways in the subduction channel. Part A exhibits elevated δ⁶⁵Cu values (0.07‰ to 0.36‰) and low Cu contents (52 ppm on average) compared to MORB (δ⁶⁵Cu=0.04‰ to 0.14‰; Cu=90 ppm). Together with heavier δ⁶⁵Cu values of chalcopyrite (-0.17‰ to 0.23‰) in part A compared to magmatic sulfide, these suggest that dehydration preferentially releases isotopically light Cu and leaves residues with heavier Cu isotope compositions. Part B shows complementary light δ⁶⁵Cu values both in bulk rock and chalcopyrite. The negative correlation between S and δ⁶⁵Cu indicates that precipitated sulfides complexed with light Cu isotopes may result in lowered δ⁶⁵Cu values in the rock during fluid-rock interactions. Overall, the data point to the mobilization of isotopically light Cu-bearing fluids during the dehydration of mafic crust in subduction environments. However, the absence of commonly high Cu contents in arc magmas suggests that the released copper may be buffered by sulfides in the sub-arc mantle, resulting in Cu-rich sulfide
SN - 0009-2541
ER -