Robert P. Wintsch
Professor of Geological Sciences
Metamorphic Petrology, Structural Petrology, Tectonics, Geochronology
- Ph.D., 1975, Brown University
- B.A., 1969, Beloit College
Research of Wintsch and students working with him spans several aspects of metamorphic geology, from diagenesis and low grade metamorphism in slaty rocks to high grade metamorphism and partial melting. Much of this research focuses on identifying the relationships between deformational and metamorphic processes, from the grain scale and pressure solution to the scale of terranes and terrane assembly.
- Geol G222, Petrology
- Geol G420, Field Geology
In 2001, Bob Wintsch led a 3-credit classroom and field seminar in the structural and petrologic development of the northern Appalachians (Description and Photo Gallery). He led a similar trip in May, 2002, to Ontario, Canada.
Recent Research Projects
Analysis of Suspect Terranes
Much of our most recent work has dealt with the identification of suspect or exotic lithotectonic terranes in the Appalachians, and with the history of terrane accretion.
Our approach is a multidisciplinary one that requires a variety of techniques. It relies on field work, where we try to understand the significance of ductile faults, which mark the boundaries of most terranes.
We sample and analyze metamorphic assemblages within terranes to try to identify discontinuitites in metamorphic grade. This work is done on the IU campus, but we date minerals by 40Ar/39Ar and U-Pb methods by collaborating with isotope geologists at the USGS, again to identify discontinuitites in the time of metamorphism or of cooling from metamorphic conditions. Some of our work is in the southern Appalachians, but we have worked most intensively in southern New England. We have begun work in central New England, where we collaborate with geologists from Massachusetts, New Hampshire and Maine, and again with USGS geochronologists.
Low Grade Rocks and Slaty Cleavage
Wintsch is working on low grade rocks with the goal of identifying the reactions that occur during diagenesis, and determining if these reactions occur in environments closed or open on the scale of a hand specimen. The degree of openness is being inferred through determining whether the progress of these reactions correlates with changes in the bulk composition of the whole rock. A related study is looking at the mudstone to slate transition, to determine if pressure solution of mudstones could release, or "mobilize" major components for recycling in the upper crust. Collaborative work on fission track ages in apatite and zircon helps to inductively reconstruct the loading and unloading history of sedimentary basins.
Mylonites and Fault Rocks
We are exploring the relationships among chemical and mechanical processes in metamorphism, and especially in fault zones, where mechanical processes are relatively important. Chemical processes turn out to have a relatively large role in the evolution of fault rocks, from pressure solution-like dissolution/precipitation reactions in a near closed system, to reaction softening and reaction hardening in relatively open systems. We have identified ductile processes in very shallow fault zones where brittle deformation is expected, and evidence for brittle (seismic?) deformation in rocks as high grade as the sillimanite zone, where ductile deformation is expected. We have been working on fault rocks from the Moine thrust, Scotland, Insubric line southern Swiss Alps, and the northern and central Appalachians.
Graduate Student Projects
Chris Amato, (1998) Metamorphic Differentiation in a Mylonitic Schist in a Contact Aureole, Winnemucca, Nevada, by Pressure Solution Creep.
Mimi Attenoukon, (2003) Multiple cleavage development by repeated dissolution and replacement processes in poly-metamorphosed argillites: A study in the Worcester Formation, eastern Massachusetts.
Goeke, E. R. (2003) A study of Amphibole-Plagioclase Mineral Assemblages in the Bronson Hill Terrane of Connecticut and Massachusetts, 212 pp.
Bridget Mulvey, (2004) 40Ar/39Ar constraints on the age of fabric development in the Westminster terrane, north-central Maryland.
Cory McWilliams, (2005) A grain-scale approach to equilibrium during cleavage formation in chlorite and biotite-grade phyllites, SE Vermont.
Aaron Satkoski, (2005), Potential sources of radionuclides in the Waits River Formation, central Vermont.
Cory McWilliams, (2006), Devonian and Carboniferous ages of multiple cleavages in the Waits River Formation, east Athens dome Area, Vermont.
Martha Growdon, (2006), The East Derby fault: evidence for late Paleozoic dextral motion within the Connecticut valley synclinorium.
Mimi Attenoukon, 2006, Constraining the absolute age of multiple fabric-forming events in polymetamorphic argillites, Merrimack terrane, Massachusetts.
Undergraduate Projects and Opportunities
There is much opportunity for student participation in field, analytical, and in some cases geochronologic work, and we are flexible about what kinds of problems to approach and where field relations can most effectively be addressed.
Dorais, M.J., Wintsch, R.P., Kunk, M.J., Aleinikoff, J.N., Burton, W., Underdown, C., and Kerwin, C.M., 2013, P-T-t conditions, Nd and Pb isotopic compositions and detrital zircon geochronology of the Massabesic Gneiss Complex, New Hampshire: Isotopic and metamorphic evidence or the identification of Gander Basement, Central New England: American Journal of Science, v. 312, 1049-1097.
Proctor, B. P., McAleer, R., Wintsch, R.P.,Kunk, M.J. 2013. Post Taconic Tilting and an Acadian Structural Overprint of the Classic Barrovian Sequence in Dutchess County, New York, , Am. Jour. Science 313, 649-682.
Growdon, M. L., R., Wintsch, R.P., and Kunk, M.J., 2013 Telescoping metamorphic isograds: Evidence from 40Ar/39Ar dating in the Orange-Milford complex, southern Connecticut : American Journal of Science 313, 1017-1053.
McWilliams, C. K., Kunk, M.J., Wintsch, R.P., and Bish, D.L., 2013, Determining ages of multiple muscovite-bearing foliations in phyllonites using the 40Ar/39Ar step heating method: Applications to the Alleghanian Orogeny in Central New England:, American Journal of Science 313, 996-1016.
Wintsch, R.P., and Yeh, Meng-Wan. 2013, Oscillating brittle and viscous behavior through the earthquake cycle in the Red River Shear Zone: Reaction and textural softening and hardening: Tectonophysics, 587. DOI
Ghanem H., Kunk M., Ludman A., Bish D., Wintsch R. and Biasi, J. 2013, 40Ar/39Ar Evidence for Late Devonian Deformation in the Chester shear zone, East Central Maine in 2013 NEIGC Guidebook for Field Trips in North Central Maine, in, Hanson, L.S., ed. 105th Annual Meeting, Mellinocket, ME, p. 99-124.
Wintsch, R.P., Yi, Keewook, and Dorais, M. J., submitted, Crustal Thickening by Tectonic Wedging in Southern New England, USA: Evidence from Cataclastic Zircon Microstructures and U-Pb ages: Journal of Structural Geology.
Yeh, M-W, R.P. Wintsch, R.P., Liu Y-C., Lo C-H., Chung, S-L., Lin, Y-L., Lee, T-Y., Wang, Y-C., and Stokes, M.R., Evidence for Cool Extrusion of the North Indochina Block Along the Ailao Shan Red River Shear Zone, a Diancang Shan prospective: in review, J. Geology. submitted 10/2013.
., Kelsheimer, K. L., Kunk, M. J., and Aleinikoff, J. N., (2001) A new look at the Alleghanian overprint of Acadian metamorphic rocks in southern New England: Evidence from structure, petrology and thermochronology: in, West, D. P., and Bailey, R. H., Guide-book for geological field trips in New England: GSA Annual Meeting, Boston, p V1-V26.
, Roden-Tice, M,., Kunk, M. J., and Aleinikoff, J. N., (2003), Ductile to brittle Mesozoic overprint of Alleghanian structures, Bronson Hill terrane, Rockville area, Connecticut: in, Brady, J. B., and Cheney, J. T., Guide-book for geological field trips in the five college region:. 95th Annual Meeting of the New England Intercollegiate Geol. Conference, Department of Geology, Smith College, Trip A3, A1-A31.
Kunk,M.J.,, Southworth, S Naeser, C.W., Naeser, N.D., and Mulvey, B. K., 2004,. Multiple Paleozoic metamorphic histories and faulting in the Westminster and Potomac terranes, central Appalachian Piedmont, northern VA and southern MD: in, Southworth, S., and Burton, W., eds. Geology of the National Capital Region - Field Trip Guidebook U. S. Geol. Survey, Circ. 1264, p. 163-188.
, Aleinikoff, J.N., Webster, J.R., and Unruh, D.M., (2005), The Killingworth Complex: A middle and late Paleozoic magmatic and structural dome: Guidebook for Field Trips in Connecticut, State Geological and Natural History Survey of Connecticut, Guidebook No. 8, p. 305-32.