Research
Subduction zone deformation and metamorphism
Ancient subduction zones provide important information on the physical and chemical evolution of the crust, the history and correlation of past tectonic events, and the timescales of subduction zone processes. Despite the importance of subduction zones to a broad range of geological problems, the mechanisms by which subduction zones initiate and evolve towards steady state are not fully understood. We are working to test models for subduction zone evolution to understand how subduction zones initiate, how subduction systems thermally evolve in space and time, and how material is accreted and ultimately exhumed. Our group is addressing these questions through an NSF-funded investigation of the Easton Metamorphic Suite in the Northwest Cascades of Washington using combined field mapping, structural and microstructural analysis, metamorphic petrology, and geochronology to establish a detailed reconstruction of the subduction history and test the proposed models for early subduction zone evolution.
Related references:
- Cordova, J.L., Mulcahy, S.R., Schermer, E., and Webb, L.E., 2019, Subduction initiation and early evolution of the Easton Metamorphic Suite, Northwest Cascades, Washington, Lithosphere, v. 11, p. 44-58, 10.1130/L1009.1.
- Mulcahy, S.R., Starnes, J.K., Day, H.W., Coble, M.A., and Vervoort, J.D., 2018, Early onset of Franciscan subduction, Tectonics, vol. 37, 10.1029/2017TC004753.
Origin and evolution of large-scale lower-crustal shear zones
The presence of major fault zones within continental crust that are reactivated over 100s of millions of years defies models for continuum deformation of the continents. Large-scale faults occur on every continent and many long-lived intracontinental fault systems record complex histories of reactivation that localized convergent and strike-slip deformation. We are testing competing models for the origin of persistent large-scale faults by studying the tectonic history of exhumed crustal sections of the Valle Fertil fault zone in western Argentina, an approximately 1200-kilometer-long major crustal lineament that records at least 400 million years of intermittent deformation. Through an NSF-funded grant, we are using combined field mapping, structural analysis, metamorphic petrology, and geochronology to determine how this zone originated and evolved during and after the Famatina orogeny. The results will address what factors determine the origin of major structures within complex orogens and the processes by which they ultimately become large-scale faults with prolonged histories of continued reactivation.
Related references:
- Tholt, A.J., Mulcahy, S.R., McClelland, W.C., Roekse, S.M., Meira, V.T., Webber, P., Houlihan, E., Coble, M.A., and Vervoort, J.D., 2021, Metamorphism of the Sierra de Maz and implications for the tectonic evolution of the MARA terrane, Geosphere, 10.1130/GES02268.1.
- Mulcahy, S.R., Roeske, S.M., McClelland, W.C., Ellis, J.R., Jourdan, F., Renne, P.R., Vervoort, J.D., Vujovich, G.I., 2014, Multiple migmatite events and cooling from granulite facies metamorphism within the Famatina arc margin of northwest Argentina, Tectonics, v. 33, p. 1-25, 10.1002/2013TC003398.
- Mulcahy, S.R., Roeske, S.M., McClelland, W.C., Jourdan, F., Iriondo, A., Renne, P.R., Vervoort, J.D., and Vujovich, G.I., 2011, Structural evolution of a composite middle to lower crustal section: The Sierra de Pie de Palo, northwest Argentina, Tectonics, v. 30, p. TC1005, 10.1029/2009TC002656.