Geochemical Investigation of Monogenetic Volcanoes from the Pribilof Islands, Bering Sea, Alaska
Small-volume basaltic magmas found at continental intraplate environments have not been as extensively studied compared to their polygenetic counterparts. Specifically, regions such as the Bering Sea basalt province, described as a diffuse igneous province, have commonly been overlooked. Assumptions...
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BearWorks
2021
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| Online Access: | https://bearworks.missouristate.edu/theses/3691 https://bearworks.missouristate.edu/cgi/viewcontent.cgi?article=4731&context=theses |
| Summary: | Small-volume basaltic magmas found at continental intraplate environments have not been as extensively studied compared to their polygenetic counterparts. Specifically, regions such as the Bering Sea basalt province, described as a diffuse igneous province, have commonly been overlooked. Assumptions that these systems are invoked by simple, single batches of magma has subsequently left a gap in understanding the processes responsible for primary magma generation away from plate boundaries with little tectonic influence. The following studies that constitute this thesis focus on an in-depth geochemical investigation at the crystal and sub-crystal scale to evaluate lithospheric mantle heterogeneities, processes that govern primary magma generation, and time scale estimations to constrain subsurface processes at monogenetic volcanic centers. The Pribilof Islands are one of approximately fifteen late Cenozoic (<6 >Ma) monogenetic volcanic fields that are regionally dispersed in the Bering Sea. St. George and St. Paul, two of the principal Pribilof Islands, constitute the youngest volcanic remnants in the Bering Sea basalt province. Here, major and trace element contents of olivine phenocrysts from St. Paul lavas have been investigated to constrain pre-eruptive magmatic conditions and estimate time scales using Fe–Mg interdiffusion. Additionally, lherzolite xenoliths is host alkali basalts from St. George were investigated to constrain melt extraction and metasomatism of the lithospheric mantle underlying the Pribilof Islands. Trace and rare earth element contents were used to decipher and estimate the degree of partial melting and metasomatism prior to xenolith entrainment and transportation to the surface. These data suggest the source of magmatism for the Pribilof Islands, and likely the Bering Sea basalt province as a whole, is not sourced from mantle xenoliths. Instead, these data suggest magma is sourced from melt-extraction of a primitive mantle source likely initiated by lithospheric extension which triggered decompression melting of a metasomatized upper mantle. |
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