MIT Experimental Petrology Laboratory

SUBDUCTION ZONE MAGMAS

A focus of our research group has been the study of magmatic processes in subduction zone environments. Our interests in this problem are wide ranging. One recent area of focus is on the conditions and mass transfer processes in the subducted lithosphere and overlying mantle wedge  that lead to the unique major and trace element abundance signatures observed in subduction zone magmas.  Graduate student Christy Till is pursuing experimental and field studies to learn more about these processes.

Quantifying the role of H₂O in the melt generation process is also of central interest. By obtaining estimates of pre-eruptive H₂O contents of primitive arc magmas, we can constrain the pressure and temperature conditions of melting and estimate the trace element and isotopic compositions of components that are added from the slab.

Our work in the Mt.Shasta region of California continues with both laboratory experiments and field work to understand the nature of mantle melt inputs and the processes of crustal level differentiation that have led to the production of the lavas at the Cascade's largest volcano.

Click below for backscattered-electron images and photomicrographs showing interesting textures of subduction-related lavas:

1. 2. 3. 4. 5.
1. Oscillatory zoned plagioclase phenocryst surrounded by a fine-grained groundmass.
2. Olivine and orthopyroxene (lower right) phenocrysts with Fe-rich cores and Mg-rich rims.
3. Oscillatory zoned clinopyroxene showing evidence of magma mixing.
4. Photomicrograph showing reacted amphibole and clinopyroxene.
5. Zoned amphibole from an inclusion in andesitic lava.