Welcome to GeoUnion, the graduate student body of the Department of Earth, Environmental and Planetary Sciences. GeoUnion strives to supplement the overall graduate student experience at Rice and DEEPS. GeoUnion represents DEEPS in the overall Rice grad student community, acts as a liaison between students and faculty and organizes a number of intra- and inter-departmental events throughout the academic year.
Phase relations of a depleted peridotite fluxed by a CO2-H2O fluid – Implications for the stability of partial melts versus volatile-bearing mineral phases in the cratonic mantle
We present phase‐equilibria experiments of a K‐bearing, depleted peridotite (Mg# 92) fluxed with a mixed CO2‐H2O fluid (0.5 wt.% CO2 and 0.94 wt.% H2O in the bulk) to gain insight into the stability of volatile‐bearing partial melts versus volatile‐bearing mineral phases in a depleted peridotite system. Experiments were performed at 850–1150 °C and 2–4 GPa using a piston‐cylinder and a multianvil apparatus. Olivine, orthopyroxene, clinopyroxene, and spinel/garnet are present at all experimental conditions. Textural confirmation of partial melt is made at temperatures as low as 1000 °C at 2 GPa, 950 °C at 3 GPa, and 1000 °C at 4 GPa marking the onset of melting at 900–1000 °C at 2 GPa, 850–950 °C at 3 GPa, and 950–1000 °C at 3 GPa. Phlogopite and magnesite breakdown at 900–1000 °C at 2 GPa, 950–1000 °C at 3 GPa, and 1000–1050 °C at 4 GPa. Comparison with previously published experiments in depleted peridotite system with identical CO2‐H2O content introduced via a silicic melt show that introduction of CO2‐H2O as fluid lowers the temperature of phlogopite breakdown by 150–200 °C at 2–4 GPa and stabilizes partial melts at lower temperatures. Our study thus, shows that the volatile‐bearing phase present in the cratonic mantle is controlled by bulk composition and is affected by the process of volatile addition during craton formation in a subduction zone. In addition, volatile introduction via melt versus aqueous fluid, leads to different proportion of anhydrous phases such as olivine and orthopyroxene. Considering the agent of metasomatism is thus critical to evaluate how the bulk composition of depleted peridotite is modified, leading to potential stability of volatile‐bearing phases as the cause of anomalously low shear wave velocity in mantle domains such as mid lithospheric discontinuities beneath continents.
Saha, S. & Dasgupta, R. (2019). Phase relations of a depleted peridotite fluxed by a CO2-H2O fluid – Implications for the stability of partial melts versus volatile-bearing mineral phases in the cratonic mantle. Journal of Geophysical Research: Solid Earth 124. doi:10.1029/2019JB017653
A Framework for Understanding Whole-Earth Carbon Cycling
This chapter explores how the cycling of carbon in subduction zones and orogenic belts varies with supercontinent cycles and mountain building. It discusses the processes that link short-term and long-term carbon cycling and the timescales of these processes, such as the response times of weathering and atmospheric drawdown at periods of enhanced volcanism. This chapter covers topics of potential fluctuations in the long-term CO2 content of Earth’s atmosphere because of mantle–climate feedback.
Lee, C-T. A., Jiang, H., Dasgupta, R. & Torres, M. (2019). A framework for understanding whole Earth carbon cycling. In Orcutt, B., Daniel, I., and Dasgupta, R. (Eds.) Deep Carbon: Past to Present. Cambridge University Press, Cambridge, pp. 313-357. doi:10.1017/9781108677950.011
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