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New Mineral Chemistry and Oxygen Isotopes from Alkaline Basalts in the Northwest Ross Sea, Antarctica: Insights on Magma Genesis across Rifted Continental and Oceanic Lithosphere

Krans, Susan R
http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1372091914

Abstract Details

2013, Master of Science (MS), Bowling Green State University, Geology.
The West Antarctic Rift system hosts one of the world's most extensive alkaline igneous provinces. Rifting that lead to the breakup of the proto-Pacific margin of Gondwana in the Late Cretaceous was initially amagmatic and not related to mantle plume activity. Mantle heterogeneities and magmatic processes along a continent-ocean transect in the Antarctic Northwest Ross Sea region are deduced from geochemical and isotopic study of alkaline basalts. Specifically, new mineral chemistry and oxygen isotopes from the least differentiated basalts expand upon previous studies that have focused primarily on whole-rock data. Alkali olivine basalt and basanite represent two mafic end-members in the Northwest Ross Sea and are characterized by high whole rock Mg# (59 ± 9), Ni + Cr (> 200 ppm), highly variable CIPW normative (> 20% hypersthene to > 20% nepheline) and trace element contents (e.g., Sr = 400 to 1100 ppm, La/Yb = 11 to 28, Nb/Y = 1.2 to 3.6). Phenocryst phases are primarily olivine (Fo66 to Fo91) and clinopyroxene (diopside) with rare amphibole (kaersutite) and exhibit varying degrees of compositional zoning. Temperature and pressure estimates based on mineral-liquid equilibrium range from 1206-1331°C (olivine), 1220-1284°C and 0.9-1.3 GPa (clinopyoxene), indicating that early crystallization occurred at or below the Moho. Olivine oxygen isotopes measured by SIMS range from 4.71 to 5.44‰ and average 5.15 ± 0.52‰ and encompass values for clinopyroxene (4.97 ± 0.36‰) and (5.17 ± 0.10‰) measured by laser fluorination. Correlation between oxygen isotopes and degree of partial melting (i.e. Nb/Y) suggests that lower degree melts preferentially consume a lower δ18O source interpreted as metasomatic veins in the lithospheric mantle. Temperature and pressure estimates across the continent-ocean transect indicate a region of lithospheric necking previously identified for Northern Victoria Land. Evidence for disequilibrium observed texturally and compositionally in minerals suggests complex crustal processes, mainly in the ocean-continent transition zone. The results of this study support previous suggestions that late Cenozoic alkaline magmatism in the West Antarctic Rift System is controlled by variations in partial melting of a heterogeneous mantle source and highlights future potential to investigate physical controls on volcanism at magma-poor rift margins.
Kurt Panter, Dr. (Advisor)
John Farver, Dr. (Committee Member)
Deering Chad, Dr. (Committee Member)
91 p.
Geology; Petrology
alkaline basalt; Northwest Ross Sea; Antarctica; mineral chemistry; oxygen isotopes; metasomatism

Recommended Citations

Citations

  • Krans, S. R. (2013). New Mineral Chemistry and Oxygen Isotopes from Alkaline Basalts in the Northwest Ross Sea, Antarctica: Insights on Magma Genesis across Rifted Continental and Oceanic Lithosphere [Master's thesis, Bowling Green State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1372091914

    APA Style (7th edition)

  • Krans, Susan. New Mineral Chemistry and Oxygen Isotopes from Alkaline Basalts in the Northwest Ross Sea, Antarctica: Insights on Magma Genesis across Rifted Continental and Oceanic Lithosphere. 2013. Bowling Green State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1372091914.

    MLA Style (8th edition)

  • Krans, Susan. "New Mineral Chemistry and Oxygen Isotopes from Alkaline Basalts in the Northwest Ross Sea, Antarctica: Insights on Magma Genesis across Rifted Continental and Oceanic Lithosphere." Master's thesis, Bowling Green State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1372091914

    Chicago Manual of Style (17th edition)

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© 2013, all rights reserved.
This open access ETD is published by Bowling Green State University and OhioLINK.