Monterey Bay Aquarium Research Institute


Melt segregation in the Earth’s crust:
Physical processes and
 geochemical signatures

Tracy Rushmer, Ph.D.
University of Vermont

Wednesday, August 1, 2001
3:00 p.m.–Pacific Forum

Successful melt segregation relies on the interplay between two main variables:
(1) The melting reaction and subsequent grain-scale melt distribution and
(2) the tectonic environment. Both variables determine the melt fraction at which interconnectivity is achieved and the rate at which melt can segregate. Melting reactions which have a large positive volume change can produce interconnected crack networks with sufficient permeability for segregation. Deformation associated with external tectonic processes can also induce melt segregation. Deformation-assisted segregation is common in active tectonic environments and trace element geochemistry of low-melt fraction leucocratic granites provide useful constraints on extraction rates during partial melting. As a complement to the natural studies, we have experimentally investigated the partial melting behavior of a typical crustal rock, under both static and dynamic conditions. We compare the trace element signatures of melt which segregates via a crack network with those produced by partial melting in a dynamic environment.