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Jenna Adams Seminar Sept. 20th
September 20 @ 3:00 pm - 5:00 pm MDT
Unusual isotopes and inclusions breathe life into our understanding of sediment recycling in ocean island magma genesis
Colorado School of Mines
Subduction zones are the largest recycling systems on Earth where sediments, oceanic crust, mantle lithosphere, volatiles, and possibly blocks of continental crust return to the mantle. Mantle plumes are thought to ‘sample’ these recycled materials leading to a diverse range of geochemical signatures observed in ocean island lavas erupted at hotspot volcanos. Thus, examining the geochemistry of ocean island lavas, particularly with respect to isotopic constraints, has revealed geochemically distinct mantle domains. However, the scale, origin, and compositions of these domains and/or derivative partial melts (that may ultimately give rise to the erupted lavas) remain important questions. In this talk we’ll focus on a mantle domain that is typified by a mantle source incorporating ancient subducted terrigenous sediments, called Enriched Mantle 2 (EM2)—the understanding of which has seen little advancement over the last decade. The archetypical locality exhibiting the EM2 geochemical signature is the Samoan Islands, a hot spot track located in the South Pacific Ocean. Lavas erupted in the Samoan Islands exhibit the hallmark EM2 signature of high 87Sr/87Sr (>0.706) isotopic compositions. A recent detailed examination of unique mineral and melt inclusion compositions from one of the most geochemically enriched (high 87Sr/86Sr) lavas from Samoa has shed new light on the origin/composition of EM2. These results, presented in this talk, ultimately provide insight into the composition of magmas derived from a sediment-infiltrated mantle source (EM2) and help
document the fate of sediment recycled into Earth’s mantle.
Jenna is from Washington state where she did her undergraduate studies at the University of Washington and Central Washington University. She recently completed her PhD at the University of California Santa Barbara and now works as a post-doctoral researcher at the Colorado School of Mines. The focus of her past and present work is to combine thermodynamic phase equilibria modeling with detailed geochemical and petrological studies to create a complete picture of magma genesis in natural volcanic settings. She is currently studying the thermodynamics of garnet solid solutions for implementation into phase equilibria modeling programs, developing new thermodynamic modeling software and applying it to various natural volcanic systems, in addition to analytical geochemistry work studying ocean island basalts from Samoa, which she will discuss in her talk.