Crustal anatexis in the laboratory: high diffusivities of HFSE and REE in melt reveal very short timescales for granite formation

Date & time

12.30–1.30pm 25 August 2017


Ringwood Room, J4


Antonio Acosta-Vigil


 Michael Anenburg
 0451 406 232

Crustal anatexis produces silicate melts of broadly granitic composition and is fundamental in the generation and differentiation of the continental crust. Major element compositions of granitic melts are largely controlled by dissolution of the major rock-forming minerals at the source, whereas trace element signatures are largely regulated by the dissolution of accessory minerals such as zircon and monazite. Experimental studies have shown that major element compositions are established rapidly upon melting, but acquisition of trace elements is thought to require large timeframes due to the slow dissolution kinetics of accessory phases, related to the sluggish diffusion of their constituents in melt. Hence, to produce crustal granites and maximize crustal differentiation, melts should spend ≥102-105 years in the source to dissolve the accessory minerals. However, physical-mechanical studies have proposed that melt can be produced, segregated and transferred from the source to the upper continental crust or surface of the Earth in 10-1-102 years. To address this paradox, we have conducted novel partial melting experiments on solid macroscopic cylinders of a typical crustal source rock, a metapelite, that allows investigations of melt distribution and major and trace element melt composition to be coupled. We observe that experimental granitic melts become interconnected throughout the metapelite and acquire their major and trace element crustal signature in days, reconciling data from chemical and physical studies.

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