Geoscience Colloquia for Spring 09 Semester
Thursday February 26, 2009 2 PM
Dr. Bruce A. Brown
Wisconsin Geological and Natural History Survey
Title: “Wisconsin Mineral Industry : Past and Future”
Lapham Hall 262
This colloquium is in conjunction with Dr. Kean’s Geology of Wisconsin class.
Thursday March 26, 2009 4 PM
Mr. Jay Byers (UWM alumnus, MS)
Chevron International E&P Co.
Title: “Techniques for determining reservoir properties, as applied to an oil field in Angola, Africa”
Lapham Hall 262
Refreshments served prior to the colloquium at 3:30 in Lapham 380.
Thursday April 9, 2009 4 PM
Dr. Peter Cook
CSIRO Land and Water
National Ground Water Association Darcy Lecturer
Title: “Environmental Tracers In Modern Hydrogeology: Reducing Uncertainty in Groundwater Flow Estimation”
Lapham Hall 262
Quantitative hydrogeology is often traced back to Henri Darcy in the mid 19th Century, who observed a linear relationship between flow rate and hydraulic gradient, the proportionality constant later becoming known as hydraulic conductivity. Even today, groundwater flow rates are most frequently determined as the product of measured hydraulic gradients and hydraulic conductivities, the latter determined using aquifer tests. However, estimation of aquifer hydraulic conductivity remains a significant source of uncertainty. Although within the past few decades, environmental tracer methods which can provide independent estimates of groundwater flow rates have been developed, these methods are still not widely used outside of the research community.
There are a large number of environmental tracers, all with different properties and hence different potential uses, although those that are most useful for estimating groundwater flow rates are those that provide information on the age of the groundwater (the time that has elapsed since recharge). Tracers which can be used for this purpose include a range of tracers with variable but well-known input history (e.g., chlorofluorocarbons), and radioactive isotopes for which the rate of input to the groundwater has been relatively constant over time, but which decay at a known rate (e.g., 14C).
The potential of environmental tracers is most apparent in heterogeneous systems, where hydraulic conductivity can be highly spatially variable. Because tracers integrate over time and space, they are able to provide regional-scale estimates of groundwater flow rates, often with an accuracy which is much greater than is possible using hydraulic data alone. In fractured rock systems, hydraulic conductivity is extremely variable spatially, and diffusive exchange between young water moving through the fractures and old water stored in the matrix complicates interpretation of environmental tracers. In these systems, joint interpretation of hydraulic and environmental tracer data can correct for the effects of matrix diffusion on apparent tracer ages, and hence provide robust estimates of groundwater flow.
Thursday April 23, 2009 4 PM
Dr. Judith Chester
Texas A&M University
Title: “Structural-Petrologic Characterization of the San Andreas Fault Zone from SAFOD”
Lapham Hall 262
The presentation will outline the drilling and sampling activities at the EarthScope San Andreas Fault Observatory at Depth (SAFOD), and illustrate how we are using observations from the drillhole to interpret: 1) the development of fault zone architecture, 2) the occurrence of seismic and aseismic deformation, 3) the absolute strength of the fault, and 4) the energy budget of earthquakes. Earthquakes are one of our greatest natural hazards, and understanding the fundamental processes of earthquake faulting is one of the most challenging problems in the Earth sciences. Understanding the physics of earthquake rupture requires the study of faulting over a wide range of spatial and temporal scales. The macroscopic characteristics of earthquake rupture nucleation, propagation, and arrest depend in part on processes operating at the mesoscopic and microscopic scales. Geologic observations of active and exhumed faults, rock deformation experiments, geophysical observations of seismic sources, and theoretical models have contributed to our current understanding of these processes. Research has been impeded, however, by our inability to observe active fault zones directly, and to sample earthquake source regions at depth. The overall scientific objective of SAFOD is to drill, sample and monitor the San Andreas Fault at seismogenic depths to understand the physical and chemical processes of deformation and earthquake generation within an active, plate-bounding fault. Collection of rock samples from the active slipping zones of the San Andreas Fault at depth is a major achievement and provides a wonderful opportunity to test hypotheses and constrain earthquake faulting models. Rock samples taken from SAFOD include a complete suite of cuttings from the borehole, tens of small, sidewall core samples from within the fault zone proper, and six continuous, large-diameter spot cores from different locations across the San Andreas fault zone, two of which cross the actively slipping segments identified by geologic and down-hole geophysical observations. As part of our EarthScope research, we are mapping the mesoscale structure and lithology of the cores, and performing optical and electron microscopy, XRF, XRD, and stable isotope analyses to characterize the deformation mechanisms, mineral reactions, and fluid-rock reactions that are important to seismic and aseismic slip in the San Andreas fault zone.
Thurssday April 30, 2009 4 PM
Dr. Adam Kent
ODP Distinguished Lecturer
Oregon State University
Title: “Exploring Oceanic Magmatism Through the Study of Silicate Melt Inclusions.”
Lapham Hall 262
Ocean crust formation is largely controlled by the nature and dynamics of oceanic magmatic systems. In concert with more conventional petrologic studies the examination of silicate melt inclusions – small parcels of melt trapped in igneous phenocryst phases –provides significant insight into the nature of oceanic magma systems. Melt inclusions confer specific advantages as they preserve the composition of magmas present early in the magmatic system prior to crystal fractionation and magma mixing, and can also preserve pre-eruptive volatile abundances. This presentation will review the mechanisms of formation of melt inclusions, and address the possibility that variations in inclusion compositions reflect chemical fractionation during inclusion trapping or subsequent re-equilibration with the host mineral and external melt. I will also discuss recent studies that highlight the potential of melt inclusions for studying oceanic magmas. One example involves assessing the role of subduction-related inputs in magma generation in back arc systems. In the northern portion of the Izu-Bonin-Mariana arc melt inclusion analyses reveal that the influence of subduction extends deep (~200 km) into the back arc in a region of diffuse magmatism. Despite the similarities between mid ocean ridges, where magmatism is related to decompression, and many back arc spreading systems the high water contents of Izu back arc magmas argue against a significant role for decompression melting – even at large distances from the arc front itself.