Using amphibole crystals to reconstruct magma storage temperatures and pressures for the post-caldera collapse volcanism at Okataina volcano

摘要: Abstract At Okataina volcano, a caldera-collapse event at 46 ka followed by frequent intra-caldera eruptions (every 1–5 ka) provides an opportunity to examine the temperature and pressure conditions from amphiboles (and other phases) through life cycle of rhyolite magma system. In each 18 examined, amphibole population is heterogeneous (e.g., Al 2 O 3  = 4.45–10.88 wt.%; MgO = 10.81–16.35 wt.%), lacks trends in space or time with composition volume. The crystals are ‘cargo’ gathered rapidly range T-P-X prior eruption, perhaps due buoyancy instabilities system causing overturn blending. Nearly all compositional variation can be accounted for temperature-sensitive edenite Ti-Tschermak exchange mechanisms, ‘Plagioclase exchange’ that influenced co-crystallizing plagioclase composition. pressure-sensitive Al-Tschermak insignificant. This highlights application Al-in-amphibole barometers would produce erroneous conclusions if atomic mechanisms were not assessed. Variations implied substitutions explained petrographic evidence mafic intrusions. Amphibole estimates based on empirical models supported equilibrium calculations involving melt, indicate some relicts hotter thermal regime than dominant melt. Fast equilibrating melts Fe–Ti oxides show dramatic change high rhyodacitic compositions immediately following (42–36 ka), before returning typical low high-SiO production over last ~ 30 ka. Throughout this cycle, record contiguous thermally zoned (700–900 °C), buffered eruption events, reflecting its large size lack connectivity melt generation zones. Hence, crystallization state has little bearing potential eruption.