Date of Award
Master of Science
Jasper G. Konter
Geochemical compositions of melts produced in the Earth's mantle provide key data for understanding Earth's internal structure. Particularly, the compositions of unusually large outpourings of basaltic lavas in large igneous provinces involve substantial source volumes, thereby contributing to our understanding of mantle structure and dynamics. Although the origin of such lavas remains enigmatic, geochemically they may originate from Earth's oldest and deepest mantle reservoir, transported by a mantle plume or by entrainment in passive upwelling beneath a fast spreading center. The Pacific Ocean basin hosts several large igneous provinces that formed near a triple junction of three oceanic plates, and we here focus on the coupled Mid-Pacific Mountains-Line Islands system of a large igneous province and a linear volcanic chain. Our new Sr-Nd-Pb isotope and 40Ar/39Ar data show complex age relationships along these volcanic structures, and a Pb isotope anomaly that is found in a cluster of small and distinct volcanoes that are geographically grouped. The geographical distinction relates to the plate tectonic structure of the area, limited to the north and south by fracture zones that bounded a captured Pacific microplate. We argue here that very high mantle flow beneath the triple junctions during the highly active Cretaceous period may have sampled dense material from the top of the Pacific large low shear velocity province. Delamination of this dense material and associated mantle influx could generate later, smaller-scale volcanism with a distinct composition and with complex age relationships.
Received from ProQuest
Storm, Lauren, "Isotope Geochemistry and Geochronology of Lavas from the Line Islands Chain, Central Pacific Basin: Insight into the Origin of the Line Islands" (2012). Open Access Theses & Dissertations. 2200.