Victor Guevara

I am a PhD candidate at Virginia Tech. My research interests lie in the general fields of continental tectonics, convergent margin processes, and crustal evolution. I integrate field mapping, phase equilibria modeling/thermobarometry, geo/thermochronology, and microstructural analyses to reconstruct tectonic histories and quantify the timescales over which such processes occur. My current work at Virginia Tech is broadly concerned with unraveling the tectonometamorphic evolution of high-temperature to ultrahigh-temperature (HT-UHT) metamorphic terranes, and includes projects on: 1) using small bulk-volume pseudosections to better refine HT-UHT P-T evolution, and 2) deciphering tectonic mechanisms of extreme heat flux recorded in Archean cratons.


  Small bulk-volume pseudosections

  Tectonic mechanisms of extreme crustal heat flux during Archean orogenesis

Victor:    CV   email

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Publications

Dragovic, B., Guevara, V.E., Caddick, M.J., and Baxter, E.F., in review. Neoarchean granulite facies ‘ghost metamorphism’ in the Wyoming Craton.

Guevara, V.E. and Caddick, M.J., 2016, in press. Shooting at a moving target: phase equilibria modeling of high temperature metamorphism. Journal of Metamorphic Geology. DOI: 10.1111/jmg.12179

Couëslan, C.G. and Guevara, V.E., 2015. Preliminary results from bedrock mapping in the south and central Cauchon Lake area, eastern margin of the Pikwitonei granulite domain, central Manitoba (parts of NTS 63P7, 8); in Report of Activities, 2015, Manitoba Mineral Resources, Manitoba Geological Survey, p. 24-37.

Couëslan, C.G. and Guevara, V.E., 2015. Bedrock geology of the south and central Cauchon Lake area, central Manitoba (parts of NTS 63P7, 8); Manitoba Mineral Resources, Manitoba Geological Survey, Preliminary Map, scale 1:20,000.

Guevara, V.E., Ward-Waller, C.B., and Baldwin, J.A., 2012. Geologic Map of the Surveyors Ridge Area, Clearwater and Shoshone Counties, Idaho: Idaho Geological Survey Technical Report 12-7, scale 1:24,000.

Lewis, R.S., Brewer, R.A., Jansen, A.C., Guevara, V.E., Vervoort, J.D, and Baldwin, J.A., 2011, Below the Belt: A Road Log of Archean and Paleoproterozoic Rocks in the Eastern Clearwater Complex, Idaho. Northwest Geology, 40, p. 143-158.

Selected Conference Abstracts

Guevara, V.E., Dragovic, B.D., Caddick, M.J., and Baxter, E.F., 2016. The ghost of a craton’s past. Abstracts with Programs – Geological Society of America Northeastern Section Meeting, Albany, NY.

Guevara, V.E., Dragovic, B.D., and Caddick, M.J., 2015. P-T path of short-lived Neoarchean granulite facies metamorphism of the Wyoming Craton. Abstracts with Programs – Geological Society of America Annual Meeting, Baltimore, MD.

Dragovic, B.D.,Guevara, V.E., and Caddick, M.J., 2015. Limitations and utility of Sm-Nd garnet geochronology of high-temperature metamorphism: an example from the Wyoming Craton. Abstracts with Programs – Geological Society of America Annual Meeting, Baltimore, MD.

Guevara, V., Dragovic, B., Caddick, M.J., Baxter, E.F., 2014. 2.69-2.68 Ga granulite facies metamorphism in the Wyoming Craton revealed by Sm-Nd garnet geochronology and trace element zoning, eastern Beartooth Mountains, Montana and Wyoming, USA. American Geophysical Union Fall Meeting, San Francisco, CA, 2014.

Guevara, V.E., Caddick, M.J., and Tracy, R.J., 2013. Is thermodynamic modeling of local mineral equilibria required to elucidate high temperature P-T evolution? Abstracts with Programs - Geological Society of America annual meeting, Denver, CO, 2013.

Baldwin, J.A., Guevara, V.E., and Foster, D.A., 2013, Constraining the Proterozoic growth and modification of the western North American craton in northern Idaho using monazite and xenotime petrochronology. Abstracts with Programs – Geological Society of America, Annual Meeting, Denver, CO, 2013.

Guevara, V.E., Baldwin, J.A., and Foster, D.A., 2012. Exhumation of the middle crust within a continental-scale strike-slip fault system: insights from the Clearwater metamorphic core complex, Idaho. Abstracts with Programs – Geological Society of America, Annual Meeting, Charlotte, NC., 2012

Baldwin, J.A., Guevara, V.E., Stevens, L.M., Cottle, J., and Hacker, B.R., 2012, Deciphering multiple metamorphic events by laser ablation split stream (LASS) petrochronology of monazite and xenotime in the Clearwater complex, northern Idaho. Abstracts with Programs – Geological Society of America Annual Meeting, Charlotte, NC, 2012.

Baldwin, J.A., and Guevara, V.E., 2012, Reconstruction of P-T paths in polymetamorphic rocks of the Clearwater core complex, northern Idaho. Goldschmidt conference, Montreal, QC, 2012.

Guevara, V., Baldwin, J.A., Crowley, J.C., Lewis, R.S., and Foster, D.A., 2012. U-Pb geochronology of pre-Belt Supergroup rocks in the Clearwater complex, Idaho: Implications for Precambrian basement provinces and stratigraphy of the northern Rockies. Abstracts with Programs – Geological Society of America, Rocky Mountain Section Meeting, Albuquerque, NM, 2012.

Guevara, V.E. and Coish, R.A., 2010. A Geochemical and Petrographic Analysis of the Echo Pond Pluton, VT. Abstracts with Programs – Geological Society of America Northeast/Southeast Joint Section Meeting, Baltimore, MD, 2010.

Small bulk-volume pseudosections

Recent advances in petrologic techniques have resulted in increasingly higher resolution pressure-temperature (P-T) paths of rocks. Such advances can be attributed in part to the advent of quantitative P-T pseudosection modeling. One key assumption involved in constructing and interpreting a P-T pseudosection is that the bulk-rock composition chosen for modeling is representative of the ‘effective’ chemical composition in producing the observed mineral assemblages and textures. HT-UHT rocks have commonly experienced extensive partial melting and dehydration, possibly leading to greatly reduced equilibration volumes and forming mineralogically and chemically distinct domains at the sub-m to μm scale. These local chemical heterogeneities may thus control the equilibrium mineral assemblages, in essence being more “effective” than any given bulk composition. I am currently exploring the utility of domainal compositions derived from distinct metamorphic textures within a rock in elucidating HT-UHT P-T histories.

A single texturally and mineralogically heterogeneous hand sample of UHT granulite can be split into different volumes of equilibration at the hand-sample scale, or "macrodomains."

At some point in the rock's history, equilibration volumes became greatly reduced due to loss of intergranular melt/fluid. Thus, the use of "microdomains" can be more useful in constructing this part of the rock's P-T history than any given bulk composition.

Tectonic mechanisms of extreme crustal heat flux during Archean orogenesis

Collisional orogenesis is a fundamental process of plate tectonics, and can ultimately generate HT-UHT conditions (750-1050 C) in the mid- to lower crust. The Archean was a critical period in the formation of the Earth’s stable cratonic crust, but what was the role of collisional orogenesis in cratonization, when were the first true continental collision events, and how did the durations of resultant HT metamorphism evolve throughout the Archean? This project seeks to elucidate whether recognizably modern orogenic processes occurred as early as the beginning of the Mesoarchean, and to quantify how the tempo of orogenesis changed (if at all) over the subsequent 500 Myrs into the Neoarchean to understand the dominant mechanisms of extreme heat flux required for cratonic stabilization. In collaboration with Besim Dragovic, we aim to constrain the nature, timing, and duration of different parts of the P-T-t paths of rocks from two Archean granulite terranes (the Pikwitonei granulite domain in the Superior Craton, and the eastern Bearototh Mountains in the Wyoming Craton), which will provide a test of mechanisms for high crustal heat flux during Neoarchean HT/UHT metamorphism, and whether these mechanisms are similar to those operating in modern convergent plate boundaries. This project is funded by the National Science Foundation, Earthscope Awards for Geochronology Student Research Program, Geological Society of America Foundation, and the National Geographic Society Young Explorer's Program.