High-Temperature phase transitions in serpentine

Serpentines are widely used to investigate lithospheric strength, subduction-zone processes, and the cycling of carbon and water in the Earth. In this work we have investigated the high-temperature phase transitions in natural serpentine with respect to the time of heating. The starting material was obtained by grinding natural serpentine sample and verified using powder X-ray diffraction (λ = 1.5406 Å). The powder was heated at temperatures from 300 to 1000 °C in 100 °C increments for durations ranging from 30 minutes to 24 hours, using 1–6 hour intervals. No phase changes were observed up to 400 °C. Two forsterite (Mg₂SiO₄) peaks at 35.993° and 36.857° first appeared in the XRD pattern at 500 °C after 3 hours of heating. The first appearance of enstatite (MgSiO₃), marked by peaks at 28.188⁰ and 31.289⁰ were observed in the XRD pattern at 600⁰C starting at 8 hours of heating. Our work provides a robust temperature-time (T-t) phase diagram. The systematic T-t framework shows that serpentine breakdown and forsterite/enstatite formation depend on both temperature and duration of heating, rather than temperature alone. This can have implications for subducting slabs; where mineral transformations, fluid release, and associated changes in rheology may be governed by slab thermal histories and residence times at depth. These effects can influence interpretations of slab strength, seismic structure, and volatile cycling in subduction zones.