Research in Accessory Minerals
Texture Development, Geochemistry & Geochronology
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Accessory mineral stability and trace element mobility – the role of bulk rock composition, chemistry and fluid-mineral reactivity.
Experimental work demonstrated that monazite was particularly susceptible to dissolution in the presence of fluids with hard-ligand species present, but would participate in dissolution-reprecipitation reactions in the presence of alkaline fluids. An NSF sponsored project (EAR 1119454) applied the predictions to a natural system in the thermal aureole of the Ballachulish Igneous Complex, Scotland.
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Dissolution-reprecipitation reactions in phosphate minerals: Implications for total U-Th-Pb geochronology to dating metamorphic and alteration processes.
Dissolution-reprecipitation reactions cause changes in the composition of sub-domains in accessory minerals, including the common petrochronometers monazite, xenotime and zircon. If the age of the dissolution-reprecipitation reaction is to be accurately dated and placed into the metamorphic framework of a rocks history, then it is necessary to understand the fate of accumulated radiogenic Pb during the reaction.
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Improving precision for peraluminous magmatism in the Ruby Mountains - East Humboldt Range of the Great Basin Region, western United States.
The Ruby Mountains - East Humboldt Range exposes an attenuated crustal section that includes the roots of a metamorphic core complex. Three periods of magmatism in the complex are well constrained (Late Jurassic, Cenomanian-Turonian in Late Cretaceous and Eocene and Oligocene magmatism associated with core complex exhumation). A fourth period of magmatism is loosely constrained to late Cretaceious to early Paleocene and corresponds with exmplacement of a batholith-sized body of granite in the structurally lower parts of Lamoille Canyon and discrete dikes, sills and sheets of low-temperature, water-rich granites with pegmatitic textures in the mid- to structurally-higher levels of the complex. The zircons are challenging to date because of exceptionally high U abundances, and grains have been over-printed by reaction textures during younger deformation.
The Hetherington group has been experimenting with the application of chemical-abrasion techniques prior to in situ analysis so as to reduce discordancy and improve accuracy of analyses. The outcomes point towards two periods of magmatism - one at ~75 Ma related to crustal thickening and development of a high-standing crustal plateau - the so-called Nevadaplano, and a second event at ~65 Ma, perhaps related to thermal relaxation.