Abstract

Our understanding of the Yellowstone hotspot and its connection to flood basalts of the Columbia River Basalt province (western and northwestern USA) has grown tremendously over the past decades since the model was first proposed in 1972. Despite strong support for a plume origin of the entire Yellowstone–Columbia River Basalt magmatic province, new non-plume models have emerged to explain early flood basalt volcanism. Unresolved issues of the early flood basalt stage include the location of crustal magma reservoirs feeding these voluminous eruptions and to what extent these were associated with contemporaneous silicic reservoirs.

This study focuses on the newly defined ca. 16–15 Ma Dinner Creek Tuff Eruptive Center that overlaps in time and space with flood basalt volcanism of the Columbia River Basalt Group. New work on distribution, lithologic variations, geochemical compositions, and eruption ages indicate that the extensive Dinner Creek Welded Tuff (herein Dinner Creek Tuff) and associated mapped and unmapped ignimbrites include a minimum of 4 discrete cooling units that spread out over an area of ∼25,000 km2. Widespread fallout deposits in northeast Oregon and the neighboring states of Nevada, Idaho, and Washington have now been compositionally correlated with the redefined Dinner Creek Tuff. Compositional coherence between the ignimbrite sheets and fallout deposits indicate a common source, herein referred to as the Dinner Creek Tuff eruptive center (DITEC).

Cognate mafic components (glass shards, pumice shards, and mafic globules) that range from dacite (∼68 wt% SiO2) to Fe-rich basaltic andesite (∼56 wt% SiO2) in composition are found in two of the cooling units. Major and trace element compositions of the more mafic components match the compositions of nearby Grande Ronde Basalt flows and dikes. Compositional similarities between cognate mafic components and Grande Ronde Basalt flows are direct evidence for coeval mafic and silicic magmatism linking DITEC and Grande Ronde Basalt eruptions. Furthermore, finding Grande Ronde Basalt magmas as coeruptive component in Dinner Creek Tuff suggests that Grande Ronde Basalt magmas were stored beneath Dinner Creek Tuff rhyolites, thereby providing the first direct evidence for the location of a storage site of Columbia River Basalt magmas. Shallow crustal rhyolitic reservoirs active during ca. 16–15 Ma that yielded tuffs of the DITEC and other surrounding contemporaneous and widespread rhyolites of the area likely imposed control on timing and place of eruption of Columbia River Basalt Group lava flows.

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