Dr. Barbara E. John

Barbara John

Professor

structural geology/tectonics, igneous processes

Office Phone: 307-766-4232
Fax Phone: (307) 766-6679

P.O. Box 3006
Laramie, Wyoming 82071-3006
Email: bjohn@uwyo.edu

Education

Geology, PhD, UC - Santa Barbara, 1987
Geology, BA, University of CA - Berkeley, 1978

Research Projects

'Spatial and temporal scales of crustal accretion in slow spreading crust -30° and 23° N MAR'

'Construction and evolution of slow spreading crust - Atlantis Bank, SWIR'

‘Cooling history of denuded oceanic crust and upper mantle near the 15° 20’ Fracture Zone, mid-Atlantic Ridge (ODP Leg 209)’

'Intrusive history of the bimodal Listino ring dike, Adamello Italy'

Publications

* indicates graduate student first author

*Grimes, C.B., John, B.E., Cheadle, M.J., Mazdab, F.K., Wooden, J., Swapp, S., and Schwartz, J., 2009, On the occurrence, trace element geochemistry, and crystallization history of zircon from in situ ocean lithosphere; Contrib. Mineral. Petrol., DOI 10.1007/s00410-009-0409-2.

*Schwartz, J.J., John, B.E., Cheadle, M.J., Reiners, P., and Baines, A.G., 2009, The cooling history of Atlantis Bank oceanic core complex: evidence for hydrothermal activity 2.6 Myr off-axis; G3, v. 10, doi:10.1029/2009GC002466.

*Baines, A.G., Cheadle, M.J., John, B.E., Grimes, C.B., and Schwartz, J.J., 2009, SHRIMP Pb/U zircon ages constrain gabbroic crustal accretion at Atlantis Bank on the ultraslow-spreading Southwest Indian Ridge; Earth and Planetary Science Letters, doi: 10.1016/j.epsl.2009.09.002.

Morris, A., J.S. Gee, N. Pressling, B.E. John, C.J. MacLeod, C.B. Grimes, and R.C. Searle, R.C. 2009, Footwall rotation in an oceanic core complex quantified using reoriented Integrated Ocean Drilling Program core samples; Earth and Planetary Science Letters, doi:10.1016/j.epsl.2009.08.007/.

John B.E., Cheadle, M.J., Gee, J.S., Grimes, C.B., Morris, A., and Pressling, N., 2009, Spatial and temporal evolution of slow spread oceanic crust - graphic sections of core recovered from IODP Hole U1309D, Atlantis Massif, 30°N, MAR (including Pb/U zircon geochronology and magnetic remanence data); Proc. IODP, Sci. Res, 304/305.

*Grimes, C.B., John, B.E., Cheadle, M.J., and Wooden, J.L., 2008, Evolution and timescales for accretion of slow-spreading oceanic crust: constraints from high resolution U-Pb zircon dating of a gabbroic crustal section at Atlantis Massif, 30º N, MAR; G3, v. 9, doi:10.1029/2008GC002063.

*Grimes, C.B., John, B.E., Kelemen, P.B., Mazdab, F.K., Wooden, J.L., Cheadle, M.J., K. Hanghøj, K, and Schwartz, J.J, 2007, Trace element chemistry of zircons from oceanic crust: A method for distinguishing detrital zircon provenance, Geology, v. 35, no. 7, p. 643–646; doi: 10.1130/G23603A.1.

*Baines, A. G., M. J. Cheadle, H. J. B. Dick, A. H. Scheirer, B. E. John, N. J. Kusznir, and T. Matsumoto, 2007, Evolution of the Southwest Indian Ridge from 55°45’E to 62°E: Changes in plate-boundary geometry since 26 Ma, G3, v. 8, Q06022, doi:10.1029/2006GC001559.

Ildefonse, B., Blackman, D.K., B., John, B.E., Ohara, Y., Miller, D.J., MacLeod, C.J., and the Integrated Ocean Drilling Program Expeditions 304/305 Science Party, 2007, Oceanic core complexes and crustal accretion at slow-spreading ridges, Geology, v. 35, no. 7, p.p. 623–626; doi: 10.1130/G23531A.1.

Graduate Students

Christian Christofferson - MS Candidate
Elizabeth Cole - MS Candidate
Jennifer Goyette - MS Candidate
Nicole Schoolmeesters - MS Candidate

Courses

GEOL4610 - Structural Geology and Tectonics
GEOL4820 - Capstone
GEOL5020 - Fundamentals of Research
GEOL5211 - Seminar in Structural Geology and Tectonics

Research Statement

My primary research interest is to understand processes of lithospheric deformation, both on the continents and in the oceans. The majority of this research to date has focused on processes of lithospheric extension, using geologic field projects (both continent and marine-based) with petrologic, geochemical, sedimentologic, microstructural and geophysical studies, to constrain the nature of extension processes (both magmatic and structural). This integrated approach typically includes geochronologic and thermochronologic studies that allow determination of the absolute age of events, rates of geologic/tectonic processes, and the space-time distribution of deformation and/or magmatism. The aim of my approach is use well-placed field studies as natural examples of structural and petrologic processes.

My previous and ongoing research can be divided into three general areas, including deformation of the continental lithosphere, deformation of oceanic lithosphere, and magmatism and deformation.

Deformation of the continental lithosphere:

Controversy still surrounds the processes that form metamorphic core complexes and low-angle normal ('detachment') fault systems in both continental and oceanic settings. Specifically, questions remain regarding the angle(s) at which such faults originate and slip, the capacity of such faults to generate significant earthquakes, characteristics of the transition from plastic to 'brittle' deformation along the faults, the extent to which such faults and their footwalls are deformed by isostatic forces, and the mechanics of any such isostatically driven deformation.

My research on the extensional deformation of continental lithosphere has concentrated on the following: geometry and evolution of large magnitude extensional fault systems; the role of plutonism in extreme crustal extension; the temporal and geochemical evolution of magmatism associated with large-scale crustal extension in the southern Basin and Range; structural and sedimentary history of hanging wall basins to major low-angle normal faults; and constraints on the development of natural fault-related folds in an extensional environment. These projects have been focused in the southern North America Cordillera, with lesser time in Greece, Turkey, and Egypt (Zabargad). In each case, I have tried to concentrate on the timing and rates of the processes involved.

Deformation of the oceanic lithosphere

My interest in deformation processes in the oceanic lithosphere is more recent, and has concentrated on the thermal/mechanical history of oceanic metamorphic core complexes, and tectonic and magmatic accretion processes, both as a shipboard and shore based scientist. Specifically I have been involved in research along slow spreading segments of the SW Indian and northern mid-Atlantic ridges. My work on gabbroic rocks from the SW Indian Ridge emphasizes important T-t aspects in an ultra-slow spreading environment, that include;

  • magnetic anomaly ages in lower oceanic (gabbroic) crust not replicating crustal ages
  • cooling apparently follows an exponential curve, with rates > 800°C/m.y. for the first 500,000 years (from *850°C to *350°C), decreasing gradually to 60-70°C/m.y. for up to 4 million years off-axis,
  • significant heat (~70%) is lost at the axis and within the rift valley, and
  • pure conductive cooling may be the dominant mechanism of heat loss in slow spreading environments.

These conclusions have important implications for estimates of plate spreading rates, the heat budget associated with mid-ocean ridges, and rheology of oceanic crust.

Magmatism and deformation

My interests in magmatism and deformation ranges from emplacement mechanisms of silicic magmas, the geometry of magma bodies, the influence of magmatism in regions of compressional deformation, magmatic to amagmatic spreading at mid-ocean ridges, and the imagine.