How has Earth changed through time to become the planet we live on today?
In our research group, we study the development of Earth's modern and ancient mountain belts and how Earth's tectonic processes have changed through time, creating the planet we live on today. To do this, we use rock and mineral chemistry and radiometric dating of rocks from around the world.
I am actively looking for graduate and undergraduate students interested in studying Earth's past. Graduate students in the Department of Earth and Environmental Sciences at the University of Michigan are funded for 2 (MS) or 4 (PhD) years of their program, through a combination of research and teaching assistantships. Graduate students receive a tuition waiver, medical health and dental insurance, and an annual stipend of $33,000 to cover their living costs.
Some examples of possible student research projects are described below. If you are interested in any of these, or similar topics, please get in touch! If you have concerns or questions about the application process, you can contact me or visit the University of Michigan EES graduate program.
3.5 billion-year old Morton Gneiss, Minnesota, USA
When did plate tectonics begin and how has it changed through time?
Currently looking for a student to study the Archean tectonic evolution of the Canadian Shield.
Earth’s mantle convection, which facilitates planetary heat loss, is manifested at the surface as plate tectonics. When plate tectonics began and how it has evolved through time are two of the most fundamental and challenging questions in Earth science. Many have inferred plate tectonics to have operated since at least ~2.5 Ga, based on observations such as change in the composition of sediments and igneous rocks or the transition from Archean dome-and-keel terranes to linear fold–thrust belts (e.g. Cawood et al. 2018 PTRS, and references therein). However, it is unclear whether these data are truly indicative of plate tectonics, or record another transitional tectonic mode (e.g. Lenardic et al. 2018 PTRS). In my work, I address these questions through examination of the metamorphic rock record. On modern Earth, plate tectonics is characterized by metamorphic rocks that show a bimodal distribution of apparent thermal gradients (temperature change with depth [pressure]: T/P) in the form of paired metamorphic belts at convergent margins (Miyashiro 1961 JPet). Paired metamorphism has occurred globally since the Paleoproterozoic (c. 2.2 Ga), but the global distribution of metamorphic T/P has broadened and become more distinctly bimodal since that time, suggesting an evolution in the styles of subduction and collisional orogenesis (Holder et al. 2019 Nature). However, a globally bimodal distribution of metamorphic T/P has not yet been demonstrated for the Archean, raising the question of whether plate tectonics (as we observe and define it today) was occurring. My ongoing work consists of targeted case studies to reconstruct the geodynamic histories of Archean terranes and whether plate tectonics was responsible for their formation.
Extreme pressure–temperature conditions in the crust and their geodynamic significance
Currently looking for a student to study ultrahigh-temperature metamorphism in Madagascar.
Ultrahigh-temperature metamorphism (UHTM: >900°C at normal crustal depths; e.g. Kelsey and Hand, 2015 GF) represents the thermal limit of metamorphism within Earth’s crust. Due to the large volumes of granitic melt that can be generated during UHTM, understanding how UHT terranes form is fundamental to our understanding of how: 1) the crust differentiates into a more felsic upper crust and a more residual/mafic lower crust; and 2) the lithosphere is weakened during orogenesis and is permanently strengthened after orogenesis: processes fundamental to the evolution of the continental crust.
Ultrahigh-pressure metamorphism (UHPM: coesite-stable metamorphism, representing depths greater than ~80 km; e.g. Chopin, 1984 C.M.P.) represents the maximum depths to which continental crust has been subducted and exhumed. Petrological, chronological, and structural data from UHPM terranes provide fundamental constraints for geodynamic models of plate tectonics and lithospheric strength and define our understanding of both subduction and continental collision, particularly in the Phanerozoic.
Together, UHPM and UHTM reveal the radically different geodynamic processes acting on Earth’s crust. Understanding the mechanical and thermal processes that lead to these metamorphic extremes is fundamental to our understanding of secular changes in plate tectonics and the chemical and physical evolution of continents. Understanding the petrologic and structural development of such terranes provides us with analogs for interpreting and understanding the behavior of the middle and lower crust of modern orogenic systems, which we cannot directly observe.
Recent related work has focused on constraining the timing and duration of continental subduction during the Caledonian Orogeny in the UHP Western Gneiss Region, Norway (Holder et al. 2015 CG; Hacker et al. 2015 CG; Hacker et al. 2019 JMG); determining the tectonometamorphic evolution of the Bohemian Massif during the Variscan Orogeny (Štípská et al. 2015 JPet, 2016 JMG; Peřestý et al. 2016 JMG); and studying UHTM in southern Madagascar during the East African Orogeny as an analog for the middle to lower crust of the modern India–Asia collision (Horton et al. 2016 Tectonics; Holder et al. 2018 Geology; Holder et al. 2018 JMG; Holder et al. 2019 CMP; Holder and Hacker 2019 CG).
Currently looking for a student to study the significance of U–Pb carbonate dates in a variety of sedimentary and tectonic environments.
U–Pb geochronology—and the growing field of petrochronology: linking geochronology to rock-forming process through petrology and geochemistry—is one of the most fundamental types of data used to interpret the rock record. While broader questions of my research are concerned with tectonics and the evolution of Earth’s continents and mountain belts, another aspect of my research is developing new analytical approaches and perspectives on U–Pb dating for more rigorous interpretation of the rock record. Recent projects have focused on:
• The development and application of U–Pb carbonate dating.
• Evaluating the limits of zircon’s ability to record complex, high-temperature processes in the crust (Štípská et al. 2016 JMG; Holder et al. 2018 JMG).
• Characterizing the relationships between monazite composition and the conditions at which it grew (Holder et al. 2015 CG; Hacker et al. 2015 CG; Holder et al. 2018 JMG; Hacker et al. 2019 JMG).
• Calculating elemental diffusivities in titanite (Holder et al. 2019 CMP) and assessing mechanisms of titanite recrystallization (Holder and Hacker 2019 CG) to improve understanding of the geological significance of U–Pb titanite dates.
Štípská P, Schulman K, Racek M, Lardeaux JM, Hacker BR, Kylander-Clark ARC, Holder RM, Košuličová M (2019) Finite pattern of Barrovian metamorphic zones: interplay between thermal reequilibration and post-peak deformation during continental collision—insights from the Svratka dome (Bohemian Massif). International Journal of Earth Sciences. doi:10.1007/s00531-019-01788-6
Holder RM, Viete DR, Brown M, Johnson TE (2019) Metamorphism and the evolution of plate tectonics. Nature. doi:10.1038/s41586-019-1462-2
Holder RM, Hacker BR, Seward GGE, Kylander-Clark ARC (2019) Interpreting titanite U–Pb dates and Zr thermobarometry in high-grade rocks: empirical constraints on elemental diffusivities of Pb, Al, Fe, Zr, Nb, and Ce. Contributions to Mineralogy and Petrology. doi:10.1007/s00410-019-1578-2
Hacker BR, Kylander-Clark ARC, Holder RM (2019) REE partitioning between monazite and garnet: Implications for petrochronology. Journal of Metamorphic Geology. doi:10.1111/jmg.12458
Holder RM, Hacker BR (2019) Fluid-driven resetting of titanite following ultrahigh-temperature metamorphism in southern Madagascar. Chemical Geology. doi:10.1016/j.chemgeo.2018.11.017
Holder RM, Sharp ZD, Hacker BR (2018) LinT, a simplified approach to oxygen-isotope thermometry and speedometry of high-grade rocks: An example from ultrahigh-temperature gneisses of southern Madagascar. Geology. doi:10.1130/G40207.1
Holder RM, Hacker BR, Horton F, Rakotondrazafy AFM (2018) Ultrahigh‐temperature osumilite gneisses in southern Madagascar record combined heat advection and high rates of radiogenic heat production in a long‐lived high‐temperature orogen. Journal of metamorphic Geology. doi:10.1111/jmg.12316
Peřestý V, Lexa O, Holder RM, Jerabek P, Racek M, Štípská P, Schulmann K, Hacker B (2016) Metamorphic inheritance of Rheic passive margin evolution and its early Variscan overprint in the Teplá-Barrandian Unit, Bohemian Massif. Journal of Metamorphic Geology. doi:10.1111/jmg.12234
Štípská P, Powell R, Hacker BR, Holder RM, Kylander-Clark ARC (2016) Uncoupled U/Pb and REE response in zircon during the transformation of eclogite to mafic and intermediate granulite (Blanský les, Bohemian Massif). Journal of Metamorphic Geology. doi:10.1111/jmg.12193
Horton F, Hacker BR, Kylander-Clark ARC, Holder RM, Jöns N (2016) Focused radiogenic heating of middle crust caused ultrahigh temperatures in southern Madagascar. Tectonics. doi:10.1002/2015TC004040
Holder RM, Hacker BR, Kylander-Clark ARC, Cottle JM (2015) Monazite trace-element and isotopic signatures of (ultra)high-pressure metamorphism: examples from the Western Gneiss Region, Norway. Chemical Geology. doi:10.1016/j.chemgeo.2015.04.021
Hacker BR, Kylander-Clark ARC, Holder RM, Andersen T, Peterman E, Walsh E, Munnikhuis J (2015) Monazite response to ultrahigh-pressure subduction from U-Pb dating by laser-ablation split-stream ICP-MS. Chemical Geology. doi:10.1016/j.chemgeo.2015.05.008
Štípská P, Hacker BR, Racek M, Holder RM, Kylander-Clark ARC, Schulmann K, Hasalová P (2015) Monazite Dating of Prograde and Retrograde P–T–d paths in the Barrovian Terrane of the Thaya Window, Bohemian Massif. Journal of Petrology. doi:10.1093/petrology/egv026
Broussolle A, Štípská P, Lehmann J, Schulmann K, Hacker BR, Holder RM, Kylander-Clark ARC, Hanžl P, Racek M, Hasalová P, Lexa O, Hrdličková K, Buriánek D (2015) P−T−t−D record of crustal-scale horizontal flow and magma assisted doming in the SW Mongolian Altai. Journal of Metamorphic Petrology. doi:10.1111/jmg.12124
Holder RM, (2018) Book Review: Petrochronology: Methods and Applications, RiMG volume 83. American Mineralogist. doi:10.2138/am-2018-683
Selected conference abstracts
Invited talk: Holder RM, Yakymchuk C (2019) Monazite Eu anomalies: Beyond Feldspar. EGU
Invited talk: Holder RM, Hacker B, Ryb U (2018) Linking high- and low-temperature processes in the crust with U–Pb dating of carbonate rocks and minerals. Goldschmidt
Invited talk: Holder RM, Hacker BR, Kylander-Clark ARC, Nuriel P, Roberts N (2017) Directly Dating Deformation by U-Pb Carbonate LA-ICP-MS. Goldschmidt
EGU 2017 outstanding student poster award: Holder RM, Hacker BR (2017) Titanite petrochronology of ultrahigh-temperature (UHT) calc-silicates from southern Madagascar: laser-ablation split-stream ICP-MS spot analyses, depth profiles, and quantified trace-element x-ray maps. EGU
Strain Analysis of Archean, Metasedimentary Rocks in the Virginia Horn, Northeastern Minnesota. Gustavus Adolphus College, 2012.