Dorsey Wanless


DOEI Postdoctoral Scholar
September 2010 - April 2012

Dorsey’s research interests lie in understanding magmatic plumbing systems beneath mid-ocean ridges, from mantle melting to the eruption of lavas on the seafloor.  Major outstanding questions regarding mid-ocean ridge magma differentiation revolve around a lack of understanding of melt generation and magma-crystal interaction within the upper mantle and lower crust.  Many of the petrologic processes that occur as magma forms in the mantle and percolates through the lower crust to the axial magma chamber are obscured because melts are efficiently homogenized in shallow crustal magma chambers.  Understanding these cryptic processes and the depths at which they occur is critical to developing accurate models of mantle melting, magma contamination and crustal differentiation, which could ultimately answer larger questions regarding the composition of the primitive mantle, seawater-magma interaction, and the construction of the oceanic crust.

Her postdoctoral research at WHOI focuses on seeing beyond the axial magma chamber into the mantle and lower crust through analyses of melt inclusions trapped in olivine phenocrysts from several mid-ocean ridge xenoliths.  These xenoliths formed at various levels within the crust and were trapped in ascending magmas before erupting on the seafloor, effectively providing a window into sub-axial processes at the time of eruption.  Therefore, they provide an opportunity to examine the composition, physical properties, and reactions that occur in the lower crust and mantle prior to melt homogenization in the crustal magma chamber.

While at WHOI, she will be collaborating with Alison Shaw and Mark Behn to gain insight into processes of melt migration and crystallization beneath both fast and intermediate spreading centers.  Geochemical analyses, including volatile (H2O, CO2, F, S, Cl) and trace element analyses, will be conducted using the 1280 and 3f ion microprobe facilities.  Volatile analyses of olivine melt inclusions can be used to estimate the depth of crystallization during ascent and storage of magma within the crust, while detailed trace element studies can be used to determine the parental melt composition and provide insight into mantle melting parameters.  Additionally, major element analyses of melt inclusions will be collected using an electron microprobe to determine magma differentiation processes in both the mantle and crust.  As a corollary project, I plan to utilize the 1280 ion microprobe to determine boron and sulfur isotope ratios of melt inclusions, which will provide insight into possible contamination of magmas from altered crustal material and/or seawater beneath a fast-spreading mid-ocean ridge.

Understanding the anatomy of mid-ocean ridges is critical to our overall interpretation of whole Earth systems because ridges provide the best window into the interior of the Earth.  Studying these systems allows us to make inferences on a number of important processes including: (1) the overall heat budget of the Earth, (2) hydrothermal processes that moderate mantle-hydrosphere exchanges and sustain life at >2 km depth, (3) the processes involved in the formation of oceanic crust, (4) the overall composition of Earth’s mantle, and (5) elemental exchange between the crust, hydrosphere and deep mantle reservoirs.

Dorsey received a Ph.D. from the Department of Geological Sciences at University of Florida (2010), while working with Michael Perfit.  Her dissertation focused on the role of assimilation in the petrogenesis of dacitic lavas on mid-ocean ridges.  She also received a M.S. from the Department of Geology and Geophysics at the University of Hawai’i (2005) and B.A. from the Department of Geology at Colgate University (2001).