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- Title
Electrical Conductivity of Clinochlore Dehydration and Implications for High‐Conductivity Anomalies and the Melting in the Mantle Wedge.
- Authors
Shen, Kewei; Wang, Duojun; Wang, Libing; Yi, Li; Zhang, Zhiqing; Cao, Chunjie
- Abstract
The dehydration of clinochlore may supply water for the creation of high‐conductivity anomalies and melting beneath volcanic arc. However, this process has not yet been constrained even though it is critical to understanding water cycling processes during subduction. The electrical conductivity of clinochlore was measured at pressures of 1.0–4.0 GPa and temperatures of up to 1273 K. The pressure weakly affected the electrical conductivity of clinochlore. In contrast, the electrical conductivity was significantly enhanced when the clinochlore was heated to temperatures beyond 1048 K, which was accompanied by decomposition into spinel, forsterite, enstatite and aqueous fluids. The elevated conductivity associated with the high activation energy may reflect the migration of Mg2+ and Al3+ during dehydration. We suggested that the aqueous fluids were released from both talc‐like and brucite‐like layer in the clinochlore, and the volumes of fluids released by samples post mortem determined using X‐ray computed tomography were 7.9–11.5 vol.%. Our results indicate that the dehydration of clinochlore results in a significant increase in conductivity of up to ∼1 S/m due to the interconnected network formed by the fluids. Combined with the geothermal gradient, the experimental data were used to interpret the high‐conductivity anomalies observed at depths of 75–120 km in hot subduction zones and 150–200 km in cold subduction zones. The updip migration of aqueous liquids liberated by clinochlore may act as a major water source for the melting at depths of 110 ± 20 km above the descending slab beneath a volcanic arc. Plain Language Summary: The origin of high‐conductivity anomalies in subduction zones and the water source for melting beneath volcanic arcs remain unknown, despite that they are related to water storage and cycling processes during subduction. Dehydration of hydrous minerals may be one of the causes of high‐conductivity anomalies. Clinochlore, which contains ∼13 wt.% water is the only hydrous mineral after antigorite decomposition in cold subduction zones. To better understand these issues, we first conducted electrical conductivity measurements of clinochlore, which has a high dehydration temperature, at pressures of 1.0–4.0 GPa and temperatures of up to 1273 K. We proposed a new dehydration model for clinochlore under high pressure and temperature. Our results showed the electrical conductivity was significantly elevated during dehydration, and we interpreted the high‐conductivity anomalies at depths as clinochlore dehydration. A large amount of aqueous liquid liberated from the clinochlore may provide additional liquid for melting of the overlying wedge. Therefore, our results provide strong evidence for interpreting of the high‐conductivity anomalies. Key Points: The electrical conductivity of clinochlore was measured at pressures of 1.0–4.0 GPa and temperatures of up to 1273 KThe volumes of fluids released by samples were identified via X‐ray computed tomographyThe dehydration of clinochlore enhances the electrical conductivity and provides a water source for melting beneath volcanic arcs
- Subjects
ELECTRIC conductivity; ELECTRICAL conductivity measurement; COMPUTED tomography; ISLAND arcs; SUBDUCTION zones; RADIOGRAPHIC contrast media
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 8, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2022JB025722