The stability of subducted glaucophane with the Earth's secular cooling

The blueschist to eclogite transition is one of the major geochemical-metamorphic processes typifying the subduction zone, which releases fluids triggering earthquakes and arc volcanism. Although glaucophane is an index hydrous mineral for the blueschist facies, its stability at mantle depths in diverse subduction regimes of contemporary and early Earth has not been experimentally determined. Here, we show that the maximum depth of glaucophane stability increases with decreasing thermal gradients of the subduction system. Along cold subduction geotherm, glaucophane remains stable down ca. 240km depth, whereas it dehydrates and breaks down at as shallow as ca. 40km depth under warm subduction geotherm or the Proterozoic tectonic setting. Our results imply that secular cooling of the Earth has extended the stability of glaucophane and consequently enabled the transportation of water into deeper interior of the Earth, suppressing arc magmatism, volcanism, and seismic activities along subduction zones. Along the cold subduction geotherm, glaucophane remains stable down to pressure and temperature (P-T) conditions of ca. 240km depth, whereas under the warm subduction geotherm, it dehydrates and breaks down into pyroxenes and silica between ca. 50 and 100km depths.

Automated summary

The transition from blueschist to eclogite is a major geochemical-metamorphic process in subduction zones, releasing fluids triggering earthquakes and arc volcanism. The stability of glaucophane at mantle depths increases with decreasing thermal gradients in the subduction system, suggesting that the secular cooling of the Earth has extended water transportation into deeper parts of the Earth.