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21 results on '"Antonelli, Michael A."'

2. Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems

Author

Antonelli, Michael A, Mittal, Tushar, McCarthy, Anders, Tripoli, Barbara, Watkins, James M, and DePaolo, Donald J

Subjects
Earth Sciences, Geochemistry, Geology, Geophysics, Ca isotopes, volcanic eruptions, magma recharge, crystal growth, timescales
Abstract

Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2‰) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10-3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

Published
2019

3. Effect of paleoseawater composition on hydrothermal exchange in midocean ridges

Author

Antonelli, Michael A, Pester, Nicholas J, Brown, Shaun T, and DePaolo, Donald J

Subjects
Earth Sciences, Geochemistry, Geology, Geophysics, Life Below Water, paleoseawater, Sr isotopes, hydrothermal systems, midocean ridges
Abstract

Variations in the Mg, Ca, Sr, and SO4 concentrations of paleoseawater can affect the chemical exchange between seawater and oceanic basalt in hydrothermal systems at midocean ridges (MOR). We present a model for evaluating the nature and magnitude of these previously unappreciated effects, using available estimates of paleoseawater composition over Phanerozoic time as inputs and 87Sr/86Sr of ophiolite epidosites and epidote-quartz veins as constraints. The results suggest that modern hydrothermal fluids are not typical due to low Ca and Sr relative to Mg and SO4 in modern seawater. At other times during the last 500 million years, particularly during the Cretaceous and Ordovician, hydrothermal fluids had more seawater-derived Sr and Ca, a prediction that is supported by Sr isotope data. The predicted 87Sr/86Sr of vent fluids varies cyclically in concert with ocean chemistry, with some values much higher than the modern value of ∼0.7037. The seawater chemistry effects can be expressed in terms of the transfer efficiency of basaltic Ca and Sr to seawater in hydrothermal systems, which varies by a factor of ∼1.6 over the Phanerozoic, with minima when seawater Mg and SO4 are low. This effect provides a modest negative feedback on seawater composition and 87Sr/86Sr changes. For the mid-Cretaceous, the low 87Sr/86Sr of seawater requires either exceptionally large amounts of low-temperature exchange with oceanic crust or that the weathering flux of continentally derived Sr was especially small. The model also has implications for MOR hydrothermal systems in the Precambrian, when low-seawater SO4 could help explain low seawater 87Sr/86Sr.

Published
2017

6. Granite petrogenesis and the δ44Ca of continental crust

Author

Antonelli, Michael A., primary, Yakymchuk, Chris, additional, Schauble, Edwin A., additional, Foden, John, additional, Janoušek, Vojtěch, additional, Moyen, Jean-François, additional, Hoffmann, Jan, additional, Moynier, Frédéric, additional, and Bachmann, Olivier, additional

Published
2023
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8. Ca Isotopes in Igneous and High-Temperature Metamorphic Systems and the Hydrothermal Chemistry of Paleoseawater

Author

Antonelli, Michael A

Subjects
Geochemistry, Petrology, Geology, Ca isotopes, disequilibrium, granulite, lower crust, radiogenic, Sr isotopes
Abstract

In the last two decades it has been increasingly recognized that Ca isotope fractionation at high-temperatures can greatly exceed fractionation at surface conditions. These effects have been used to trace recycling of crustal materials into the mantle, to estimate equilibration temperatures in mantle rocks, and to understand kinetic isotope fractionation during diffusion in experimental melts. However, little is known about the competition between kinetic and equilibrium Ca isotope effects in natural samples, which suggests that the use of stable Ca isotope variations as a proxy for carbonate recycling (or for mantle temperature) is significantly underdetermined.The Ca isotope evolution of continental crust, which is currently understudied, is intimately linked to the geochemical evolution of Earth’s mantle, oceans, and atmosphere. As such, this dissertation focuses dominantly on understanding radiogenic, kinetic, and equilibrium Ca isotope variations in igneous and metamorphic rocks from the continental crust, but also includes radiogenic Sr isotope models of hydrothermal circulation at mid-ocean ridges, which are critical to understanding continental weathering rates and the geochemical evolution of seawater over time.Chapter 2 explores the potential feed-back between the chemical and isotopic composition of paleoseawater and high-temperature hydrothermal fluids, which has been implied by Sr-isotope measurements in hydrothermal minerals over time (Antonelli et al., 2017). Chapter 3 presents results from radiogenic Ca isotope measurements in lower-crustal rocks and minerals, confirming that K is effectively lost from the lower crust during high-T metamorphism (Antonelli et al., 2018). Chapter 4 focuses on stable Ca isotope measurements in lower-crustal rocks and minerals, demonstrating that kinetic Ca effects are abundant in nature, both at the whole-rock and inter-mineral scales, and that they can be used to understand paragenesis and Ca diffusion in lower-crustal rocks (Antonelli et al., 2019b). Chapter 5 presents stable Ca isotope results from volcanic and sub-volcanic rocks and minerals, which imply that Ca isotopes can be used to estimate crystal growth-rates in igneous crystals (e.g. phenocrysts, comb-layers, and orbicules) and that associated volcanic eruption/recharge events are generally short-lived (Antonelli et al., 2019a).

Published
2018

12. Anomalous sulphur isotopes in plume lavas reveal deep mantle storage of Archaean crust

Author

Cabral, Rita A., Jackson, Matthew G., Rose-Koga, Estelle F., Koga, Kenneth T., Whitehouse, Martin J., Antonelli, Michael A., Farquhar, James, Day, James M.D., and Hauri, Erik H.

Subjects
Volcanic plumes -- Observations, Isotopes -- Properties, Lava -- Observations, Sulfur -- Properties, Earth -- Mantle, Environmental issues, Science and technology, Zoology and wildlife conservation
Abstract

Basaltic lavas erupted at some oceanic intraplate hotspot volcanoes are thought to sample ancient subducted crustal materials (1,2). However, the residence time of these subducted materials in the mantle is [...]

Published
2013
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20. Calcium isotope evidence for early Archaean carbonates and subduction of oceanic crust

Author

Antonelli, Michael A., Kendrick, Jillian, Yakymchuk, Chris, Guitreau, Martin, Mittal, Tushar, and Moynier, Frédéric

Subjects
13. Climate action, 14. Life underwater
Abstract

Continents are unique to Earth and played a role in coevolution of the atmosphere, hydrosphere, and biosphere. Debate exists, however, regarding continent formation and the onset of subduction-driven plate tectonics. We present Ca isotope and trace-element data from modern and ancient (4.0 to 2.8 Ga) granitoids and phase equilibrium models indicating that Ca isotope fractionations are dominantly controlled by geothermal gradients. The results require gradients of 500–750 °C/GPa, as found in modern (hot) subduction-zones and consistent with the operation of subduction throughout the Archaean. Two granitoids from the Nuvvuagittuq Supracrustal Belt, Canada, however, cannot be explained through magmatic processes. Their isotopic signatures were likely inherited from carbonate sediments. These samples (> 3.8 Ga) predate the oldest known carbonates preserved in the rock record and confirm that carbonate precipitation in Eoarchaean oceans provided an important sink for atmospheric CO2. Our results suggest that subduction-driven plate tectonic processes started prior to ~3.8 Ga., Nature Communications, 12 (1), ISSN:2041-1723

21. Joe Lovano and Us Five: a study on the development of a unique improvisational voice from within the jazz tradition

Author

Antonelli, Michael Robert

Subjects
Music education, Improvisation, Jazz, Jazz performance, Unique improvisational voice, Communities of practice, Jazz education
Abstract

Both researchers and jazz professionals believe the expansion of jazz performance programs in universities over the last several decades warrants a need for critical research into the processes and experiences by which jazz students develop into professionals. Although the number of colleges offering degrees in jazz performance has risen dramatically during this time, instructional approaches remain relatively standardized throughout the schools. The purpose of this study was to investigate the experiences of five working professional New York City jazz musicians in an attempt to better understand how they learned to improvise and develop their individual voices. These musicians included Joe Lovano, Otis Brown III, Francisco Mela, James Weidman, and Matthew Wilson. In this study I used Wenger's (2008) theory of Communities of Practice as the theoretical framework for an exploration of the meaning, practice, community, and identity of these five professional jazz musicians. Data collected for this case study entailed interviews, observations, and collection of artifacts. The interview data provided by the participants were transcribed and coded for the purpose of identifying emerging themes. The themes were then woven into a narrative based on the participants' responses to a series of open-ended questions. The themes that emerged included auto-biographical recollections of the participants' earliest musical experiences. The musicians spoke openly about their childhoods and various aspects of the context of their learning experiences on the way to becoming jazz professionals. The discussion included the musicians' views on communicating through improvisation, mentoring, and the value of relationships created through involvement in a jazz community on the development of a unique improvisational voice. Two major themes emerged in data analysis. First, Joe Lovano and Us Five experienced university jazz educations but in interviews and observation, the musicians seemed not dependent on, or even utilizing that part of their past. Instead, the musicians strongly emphasized community and community building, professional on-stage experience, and longitudinal exposure and life study that many college jazz majors may never experience. Second, the musicians eschewed certain viewpoints within the music profession, within university music programs, and within the public sector that musicians can simply blend technical prowess with diligent study of a prescribed curriculum to become a professional jazz musician. Here the interviewees uniformly suggested that a unique, individual voice was necessary for acceptance within the field. Finally, I present an example based upon the data from this study of how Wenger's (2008) community of practice could be used to develop a new understanding of the process of jazz improvisation and the development of a unique improvisational voice in an institutional setting.

Published
2015

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