Clare J. Tochilin

Graduation Year


Date of Thesis Acceptance

Fall 5-12-2010

Major Department or Program

Geology - Environmental Studies


Kirsten Nicolaysen; Robert Carson


The Aleutian Islands are a volcanic arc that formed as a result o f the subduction of the Pacific plate beneath the North American plate. The obliquity of the plate convergence has caused separation of the arc crust into five structural blocks that have undergone varying amounts of clockwise rotation. The amount of blo ck rotation varies longitudinally due to the increasing obliquity of convergence moving west along the arc. This study addresses whether there has been rotati on in the eastern portion of the arc du ring the last two million years . For this study, paleomagn etic core samples from young Quaternary and older Tertiary flows on Unalaska Island were analyzed using alternating field and thermal demagnetization techniques to determin e whether rotation has occurred . Bulk geochemical analysi s and mineralogical analys is showed that the presence of pyrrhotite, titanomagnetite, and titanohematite and the degrees of oxidation of these minerals have a significant effect on the magnetic signatures in rocks of the Tertiary Unalaska Formation. The study determined that there has been no rotation on the island since the emplacement of the Lava Ramp flows (~54 ka).

Page Count


Subject Headings

Aleutian Islands (Alaska) -- Geology, Volcanoes -- Research, Island arcs, Volcanic rock, Unalaska Island (Alaska), Plate tectonics -- Pacific Area, Plate tectonics -- North America, Structural Geology, Lava flows, Igneous rocks, Paleomagnetism, Whitman College -- Dissertation collection 2010 -- Geology-Environmental Studies

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Document Type

Whitman Community Accessible Thesis

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