Petrology, Geochemistry, and Experimental Studies of Mafic Enclaves and Amphibole at Shiveluch Volcano, Kamchatka

• Main Author: Goltz, Andrea Elizabeth
• Format: Text
• Language: English
• Published: Washington University Open Scholarship 2021
• Subjects: Geochemistry; Geology; Kamchatka
• Online Access: https://openscholarship.wustl.edu/art_sci_etds/2606; https://openscholarship.wustl.edu/cgi/viewcontent.cgi?article=3670&context=art_sci_etds

This thesis connects mineralogical, chemical, and physical observables in quenched mafic inclusions from Shiveluch Volcano in Kamchatka and high pressure and temperature experiments to elucidate the water content of primitive magmas at Shiveluch, the timing of magmatic recharge events relative to eruption, and the petrogenetic history of andesites erupted at Shiveluch. Using the petrology of basaltic andesite mafic inclusions erupted from Shiveluch, in Chapter 2, the water content of primitive magmas at Shiveluch is found to be 8-10 wt%, which is two to three times higher than the global average determined by other methods, and the temperature of primitive magmas was found to be 1062+/-48degrees C, consistent with high magmatic water contents. The high water contents and low temperatures of these magmas are conducive to amphibole crystallization throughout the liquid line of descent. In Chapter 3, the oxidation state of iron in amphibole is developed as a magmatic oxybarometer applicable to hydrous magmas using XAFS analysis of synthetic amphibole in piston cylinder experiments. The oxybarometer is applied to natural amphibole in the mafic inclusions studied in Chapter 2, and only two samples appear to preserve the oxygen fugacity of their equilibrium magmas. The difference between the measured oxidation state of iron in natural amphibole and the expected oxidation state is equated to the timing of mafic recharge events (which led to enclave formation) relative to eruption, and we find that three distinct mafic recharge events within three months of eruption are preserved in the mafic enclaves. Finally, in Chapter 4, the products of high pressure and temperature experiments are compared to the quenched mafic inclusions studied in Chapter 2 and erupted andesites at Shiveluch in order to understand the genesis of andesite erupted at Shiveluch. Only experiments run at high water content reproduce the phase assemblages observed in mafic enclaves, meaning that andesites are at least in part formed through fractional ...