Development of the Jemez Volcanic Field, New Mexico
The Jemez Volcanic Field is known for Bob Smith's late 60's to early 70's pioneering ideas of eruption
of large volume ignimbrites and subsequent caldera collapse. At least 2, possibly 3, such events occurred in the
past ~2 Ma in this volcanic field. Ph.D. student Leigh Justet and I are working on a combined petrographic,
geochemical, Sr-Nd isotope and 40Ar/39Ar dating project to understand the long term evolution
(eruptions commenced ~16.5 Ma) of this continental volcanic center.
Isotope Geochemistry of the Cerro Toledo Rhyolite, New Mexico
The Cerro Toledo Rhyolite consists of a sequence of pyroclastic and extrusive rocks which were erupted in
the Jemez Volcanic Field between the first caldera collapse event at 1.6 Ma and the second collapse at 1.2 Ma.
These rhyolites record the transition of the magma system from one large volume ignimbrite eruption to the
next (upper and lower Bandelier Tuff) over an ~400 ka period. We are currently studying the geochemical
and isotopic evolution of the Bandelier magma system during this interval in collaboration with
Philip Kyle.
Evolution of the Solitario laccolith-caldera complex, southwest Texas
The Solitario is a unique Eocene laccolith which underwent caldera collapse. The development of this magmatic
system has been outlined in studies led by Chris Henry during
the past few years. Chris and I are finalizing a combined 40Ar/39Ar, geochemical, and
Sr-Nd-Pb isotopic study of this complex magma system. The results will have implications for the development of
shallow crustal silicic magma systems and caldera collapse events in general.
Extensional collapse of the Sevier Orogeny, Granite Mountains, California
Extensional collapse of major mountain belts due to overthickening of the continental crust during convergent
tectonics is a well known process; in fact it is occurring today in the Himalayas. Ph.D. student Joe Kula and
I are working with Michael Wells on a
thermochronologic study of this tectonic event in order to determine the timing and rates of exhumation of these
mid-crustal granites in the late Cretaceous. This area is of particular interest as it is at the southern limit of the
orogenic belt.
Stewart Island - Cretaceous extension and continental breakup, New Zealand
New Zealand, Australia and Antarctica were joined together as part of the Pacific margin of Gondwana until
the mid Cretaceous when extensional tectonism resulted in their separation. The thermal record of this extensional
event is recorded in rocks of all three continents, but perhaps best on South Island, New Zealand where the
Paparoa Metamorphic Core Complex is preserved. Steward Island, which lies south of New Zealand also
appears to preserve a record of this continental breakup. I am working with
Andy Tulloch on a mapping
and thermochronologic study of Steward Island to delineate the timing and rates of this event.
Intercalibration of the 40Ar/39Ar and U/Th-He dating methods
In collaboration with Peter Reiners we are working
on a comparison of thermal histories generated by 40Ar/39Ar dating, particulary of
K-feldspars, with those determined by U/Th-He dating of apatite, zircon and sphene. The results thusfar
are very promising, showing very good agreement between these independent thermochronometers, thus
confirming the assumptions inherent to both techniques.
Evolution of the Yellowstone Plateau Volcanic Field during the past ~500 ka
We have recently begun a new project designed to enhance our understanding of the most recent volcanism
in the Yellowstone Volcanic Field, working with two M.S. students, Nicole Nastanski and Kristeen Bennett,
and Gene Smith.