CurrentResearch:

My research activities center aroundunderstanding large scale fluid-rock interactions within the Earth's crust.Fluid-rock interactions are important in a wide range of geological andenvironmental processes. For instance, geofluids can transport and deposit oreconstituents, can drive metamorphic reactions, can be produced by progrademetamorphic reactions, and can have important effects on the deformation propertiesof rocks. In turn, metamorphic reactions involving carbon dioxide play a majorrole in the long term evolution of carbon dioxide in the atmosphere. Myspecific current areas of research include the origin of large stratiform andstratabound ore deposits, the interaction between fluids and large intrusions,and the origin and behavior of fluids during deformation and regionalmetamorphism. Recently, our research group has developed coupled fluid flow,heat and mass transport, and chemical reaction numerical models. These modelsare giving us new insights into natural systems, and they are providing us ameans to quantify fluid flow processes in the earth.

The general research approach is to carry outintegrated studies that include stable isotope, radiogenic isotope, petrologic,mineralogical, chemical, and field data. The field data provides geologicconstraints. The stable isotope data (the isotopes of oxygen, carbon, hydrogen,sulfur, and nitrogen) are used to trace the fluid behavior. The radiogenicisotopes are used to trace the source of metals. The petrologic, mineralogical,and chemical data are used to put constraints on the temperature and pressurehistory of the rocks and fluids. The petrologic, chemical, and radiogenicisotope data are used to quantify the elemental mobility that took place in ahydrothermal or metamorphic system.

The approach described above has lead to anumber of conclusions. 1. Ore deposits are small parts of very largehydrothermal systems. 2. Fluids circulate to at least 30 kilometers into theearth's crust. 3. Fluids carry a great deal of material from one site toanother within the earth's crust. 4. Any modeling of fluid flow in the crustmust take kinetics into account, because moving fluids are in general not inequilibrium with the rocks (that is why the fluids move material and drivereactions).

Using this approach, our group hasdemonstrated that the metals in the Irish sediment hosted Zn-Pb ore deposits(some of the largest reserves of Zn and Pb in the world) were derived frombasement rocks beneath the ore deposits, whereas the sulfur was derived fromthe local near surface environment. Furthermore, we were able to demonstratethat the hydrothermal system that carried the metals operated over the entireIrish midlands and circulated to depths of at least 5km (Caulfield et. al,1986, Dixon et. al, 1989; LeHuray et al, 1988). The next steps in this ongoingresearch are to characterize the mixing process that produced the ores, and tocharacterize the fluid-rock interactions that took place in the basement rocks(Everett, Rye, and Dixon, 1996; Everett, Wilkinson, and Rye, 1999;Everett, Rye, and Elam, 2003)

Our research on the Bushveld Complex(Schiffries and Skinner, 1987; Schiffries and Rye, 1989a,b) has establishedthat there was an extensive hydrothermal system active in the Bushveld Complexthat operated at depths of at least 15 km and temperatures of up to 700 °C. Wehave been able to demonstrate that although these fluids were derived from thesurrounding metamorphic rocks they have oxygen isotopic signatures completelycontrolled by the plagioclase in the Bushveld Complex. This finding impliesthat the fluid flow system evolved from pervasive flow in the inflow region ofthe system to fracture controlled flow in the outflow region of the system.

Our metamorphic and deformation studies (Ryeet al, 1974, Rye and Bradbury, 1988, van Haren, Ague, and Rye 1996) havedemonstrated that fluid flow in rocks is pervasive and along grain boundariesin low grade rocks but flow becomes channelized along specific reactive unitsand fractures in higher grade rocks. Furthermore, much of the fluid flow thatoccurs along fractures appears to be transitory. As minerals undergo isotopicexchange at different rates, we have been able to use the disequilibriumsystematics to estimate the amount of time fluid was present in a vein system.We have also been able to determine the fluid fluxes in both the metamorphicrocks and in the veins. Importantly, these studies have shown with out doubtthat fluids flow in fractures in the earth's crust to depth of at least 30 km.

As our group as developed an understanding ofthe nature of fluid flow in the earth's crust it has become increasinglyobvious that we need to be able to quantify are results. We have recentlydeveloped a number of reactive fluid flow models that we are applying to bothore deposits, and metamorphic rocks. We have already found a number ofstartling results. As fluids flowing are not in equilibrium with the rocks, themodels are showing that many of the conventional wisdoms about how to interpretdata from rocks that interacted with fluids need to be reconsidered (Bolton,Lasaga, and Rye, 1996, 1997, 1999; Ague, and Rye, 1999; Lasaga, Rye and Lü2000; Lasaga, Lü Rye and Bolton, 2001; and Lü Bolton, and Rye, 2004).This fact has huge implications not only for fluid flow in the crust, but alsofor predicting how things like nuclear and waste depositories will behave.