Determination of cooling rates of glasses over four orders of magnitude

Volcanic materials can experience up to eleven orders of magnitude of cooling rate (q) starting from 10 K s. The glassy component of volcanic material is routinely measured via differential scanning calorimeter (DSC) to obtain q through the determination of the glass fictive temperature (T). Conventional DSC (C-DSC), which has been employed for decades, can only access a relatively small range of q (from ~ 10 to ~ 1 K s). Therefore, extrapolations up to six orders of magnitude of C-DSC data are necessary to derive q of glasses quenched both at extremely low and high q. Here, we test the reliability of such extrapolations by combining C-DSC with the recently introduced flash calorimetry (F-DSC). F-DSC enables to extend the q exploration up to 10 K s. We use three synthetic glasses as analogs of volcanic melts. We first apply a normalization procedure of heat flow data for both C-DSC and F-DSC to derive T as a function of experimental q, following the "unified area-matching" approach. The obtained T-q relationship shows that Arrhenius models, widely adopted in previous studies, are only valid for q determination within the calibration range. In contrast, a non-Arrhenius model better captures q values, especially when a significant extrapolation is required. We, therefore, present a practical "how-to" protocol for estimating q using DSC.