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Magma Mixing and Evolution at Minna Bluff, Antarctica Revealed by Amphibole and Clinopyroxene Analyses

Redner, Ellen R
http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1474028057097791

Abstract Details

2016, Master of Science (MS), Bowling Green State University, Geology.
Lava flows from Minna Bluff, Antarctica, are studied in order to provide insight into magma system dynamics, specifically magma mixing. More than 500 lava/dome and volcaniclastic samples that range in age from ~12 to 4 Ma were collected along the 45 km volcanic peninsula. Lava compositions range from basanite to phonolite. A significant proportion of lavas of all whole rock compositions contain amphibole. This study is focused on the textural and compositional characteristics of amphibole and clinopyroxene as a means to understand open system processes causing fluctuations of temperature, pressure during crystallization. Lavas with amphibole (± clinopyroxenes) phenocrysts are texturally diverse and range from porphyritic to glomeroporphyritic. Other phenocrysts consist of olivine, plagioclase, alkali feldspars, magnetite and apatite in a groundmass that varies from holocrystalline to hypohyaline. The amphibole is mostly kaersutite and clinopyroxene is diopside. Compositional zoning in amphibole includes normal, reverse and oscillatory types. The coexisting clinopyroxene is weakly zoned. Amphiboles also exhibit weakly to strongly developed reaction rims, which are produced by decompression and/or increase in temperature. Amphibole phenocrysts have higher Fe/Mg ratios than predicted for equilibrium conditions in basanitic magma and lower ratios than predicted for phonolitic magma. The rims of amphibole phenocrysts in intermediate compositions are mostly in equilibrium but cores of the same grain are not. Clinopyroxene phenocrysts show similar relationships. The amphibole and clinopyroxene phenocrysts that are out of equilibrium suggest magma mixing or accidental incorporation of pre-existing crystal `debris’. Geothermobarometric results suggest that amphiboles and clinopyroxenes formed at pressures 4 to 9 kbars (˜ 15-32 km) and 3 to 14 kbars (˜ 11-47 km), respectively. The majority of barometric calculations indicate depths = 22 km, which is at or below the crust-mantle boundary. It is likely that rising melt reached neutral buoyancy at this boundary and pooled, cooled and crystallized to produce more evolved compositions that were, in turn, periodically replenishment by less evolved melts from below. A five stage history is conceived that illustrates the complex nature of magma evolution at Minna Bluff.
Kurt Panter, Ph.D. (Advisor)
John Farver, Ph.D. (Committee Member)
Thomas Wilch, Ph.D. (Committee Member)
214 p.
Geology
Volcanology; Magma Mixing; Alkaline Magma; Amphibole; Magma Evolution; Minna Hook; Minna Bluff; Antarctica

Recommended Citations

Citations

  • Redner, E. R. (2016). Magma Mixing and Evolution at Minna Bluff, Antarctica Revealed by Amphibole and Clinopyroxene Analyses [Master's thesis, Bowling Green State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1474028057097791

    APA Style (7th edition)

  • Redner, Ellen. Magma Mixing and Evolution at Minna Bluff, Antarctica Revealed by Amphibole and Clinopyroxene Analyses. 2016. Bowling Green State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1474028057097791.

    MLA Style (8th edition)

  • Redner, Ellen. "Magma Mixing and Evolution at Minna Bluff, Antarctica Revealed by Amphibole and Clinopyroxene Analyses." Master's thesis, Bowling Green State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1474028057097791

    Chicago Manual of Style (17th edition)

bgsu1474028057097791
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This open access ETD is published by Bowling Green State University and OhioLINK.