Research

My research on the lower oceanic crust is focused primarily on the construction and accretion of the gabbroic lower portions.  To do this, I have taken a multi-pronged approach using the Oman ophiolite, a paleo-fast spreading ridge.

(1) Quantification of the thermal evolution and cooling rates in the lower oceanic crust.  My work on cooling rates suggests that the entire lower oceanic crust cooled quickly and uniformly, requiring active hydrothermal circulation throughout the lower crust.

VanTongeren et al., EPSL, (2008)

Geochemical and Thermal Evolution of Large Magma Chambers

My research on the evolution of large magma chambers has focused primarily on the Upper Zone of the Bushveld Complex of South Africa.  The Bushveld Complex is the world’s largest layered mafic intrusion and is one of the world’s largest sources of precious metals.  The Upper Zone is thought to represent the final pulse of magma into the Bushveld, and is ideal for investigating the effects of heat loss and extreme differentiation of large magma bodies.

Ultimately...

All magmas undergo some degree of crystallization and geochemical evolution prior to eruption or solidification.  I am particularly interested in understanding the chemical and dynamic links between cumulate rocks and their eruptive products.  Some of the questions that I am working to address include:

  1. (1)What is the nature of extreme differentiation in large magma bodies (Fe-rich or Si-rich residual liquids)?

  2. (2)How do large volume high Si rhyolites form? How do volatiles like Cl and F affect their viscosity and ability to flow?

  3. (3)What can the evolution of parent magma compositions of large layered intrusions tell us about magma source regions and early earth tectonics? How can phase equilibria help us to understand the stability of oceanic and continental crust in the early earth?

  4. (4)How do the processes of magma storage and transport through the continental crust affect the final liquid composition at/near the surface?

  5. (5)Where is magma sourced within the lower crust at mid-ocean ridges? and how does cooling and crystallization affect the inter-eruption variability of MORB?

Comparisons between crystallization and cooling in layered intrusions and mid oceanic ridges will ultimately be important in our understanding of igneous differentiation and magma evolution in a variety of tectonic settings.

Me with layered gabbros in Oman.

Stream through the Main Magnetite Seam in the eastern Bushveld.

Early Earth Tectonics

VanTongeren and Korenaga (2012) IGC Meeting Poster Presentation

The construction of oceanic crust in the modern day can inform our understanding of how the crust might have formed in the Archean, when mantle potential temperatures were hotter, magma compositions were more magnesian, and oceanic crust was much thicker.  My work is focused on how changing magma composition influences the phase equilibria present within the crust.  The results have implications for the density of the Archean crust, the onset of plate tectonics, and possibly the creation of the ‘building blocks’ of continental crust.

Johnson, Brown, Kaus & VanTongeren (2014, Nature Geoscience)                       read the ScienceDaily coverage here:  http://www.sciencedaily.com/releases/2013/12/131230101446.htm

Abbott, Mooney, & VanTongeren (2013, Tectonophysics)

Structure and Accretion of Oceanic Plateaus

The Lower Oceanic Crust at Submarine Spreading Centers

(2) Estimate of the bulk composition of the entire oceanic crust.  It has long been known that the majority of MORB erupted is not in equilibrium with the mantle.  And the mantle derived parent magma is not in equilibrium with the observed phase assemblage of MORB.  My work on the lower crust of Oman is aimed at rectifying these two compositions by providing an estimate of the entire oceanic crust (not just the erupted portions).  This work has implications for global geochemical cycles. 

VanTongeren and Kelemen (2013) Goldschmidt

(3) Strain in the lower oceanic crust.  I am working to understand the way in which the lower crust accommodates strain during on-axis extension by the analysis of the lattice-preferred orientation of plagioclase grains in samples throughout the crustal column.  This work has implications for melt distribution on-axis at spreading centers, as well as for the accretionary mechanisms of the crust. 

VanTongeren et al. (2011) AGU (manuscript in preparation)

Similar to the work on the construction and accretion of the “normal” lower oceanic crust, I am also interested in the processes that give rise to massive oceanic plateaus.  In particular, the ~30 km thick crust at Shatsky Rise, off the coast of Japan, is interesting because of the debate over whether this feature was formed at a ridge-ridge-ridge triple junction, or whether it is the result of a thermal plume intersecting the oceanic crust and causing high degrees of melting.  My research uses the geochemistry of the basalts to infer the composition of the lower crust, and compare that with seismic observations at depth.