EAPS Department Lecture
Dr. Julia Baldwin
Mineralogical Society of America Distinguished Lecturer
Department of Geosciences
University of Montana
“Metamorphic Phase Diagrams and Geochronology: You can’t have one without the other”
Monday, Feb 25, 2013
4:00 to 5:00 p.m.
Building 54, Room 915
Comprehensive understanding of tectonometamorphic processes requires an integrated approach to investigating pressure-temperature-time histories. Many metamorphic terranes preserve both complex mineral microstructures and assemblages as well as dateable accessory phases that provide an opportunity to piece together the tectonic evolution and timescales of geologic processes for a given region. However, the typical approach of obtaining geochronologic data from mineral separates is commonly hampered by the absence of petrographic context and the uncertainty in knowing exactly what event is being dated. How accessory phase growth links to major phase reactions such as the growth of garnet or the Al2SiO5 polymorphs is a promising area of future research. Metamorphic core complexes of the northern U.S. Cordillera contain rocks that record a wide variety of metamorphic, magmatic, and fluid-flow processes. Using isochemical phase diagrams, or pseudosections, integrated with in situ laser ablation split stream (LASS) petrochronology of monazite and xenotime in thin section, these complex tectonic histories may be explored. The Clearwater metamorphic core complex in northern Idaho records a polymetamorphic history, with both Proterozoic and Cretaceous-Eocene tectonism. In contrast, the Priest River complex further to the north preserves only Cretaceous-Eocene metamorphism, but rocks have undergone extensive partial melting and thus preserve geochronologic and geochemical signatures linked to crustal anatexis. Because monazite and xenotime are reactive across a broad range of pressure, temperature, and fluid conditions, they are ideal recorders of a range of geologic processes. Coupled with geochemical and P-T data, the LASS method is proving to be a valuable tool for resolving complex metamorphic histories.
Refreshments precede the talk in Building 54, Room 923.
All are welcome.
If you have any questions regarding the lecture, please contact Jacqui Taylor at 617.253.3127 or jtaylor [at] mit [dot] edu. Reservations not required.
Faculty hosts: Sam Bowring and Oliver Jagoutz
Sponsored by the Department of Earth, Atmospheric and Planetary Science.