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Petrology of Inclusion-Rich Lavas at Minna Bluff, McMurdo Sound, Antarctica: Implications for Magma Origin, Differentiation, and Eruption Dynamics

Scanlan, Mary K.
http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1217952842

Abstract Details

2008, Master of Science (MS), Bowling Green State University, Geology.
Xeno Ridge, a newly discovered group of inclusion-rich deposits located at the top of the Minna Bluff stratigraphic section, formed as a result of magmatic mixing/mingling and provides insight into magma origins, mixing and eruption dynamics, and the evolution of Minna Bluff. Phonolite to tephriphonolite lavas are contain abundant inclusions which vary in size, shape, and mineralogy. Five inclusion types are identified at Xeno Ridge. The lavas that host the inclusions are dark-gray and porphyritic with a hypocrystalline, vesicular groundmass. Minerals within the host lavas include feldspar (plagioclase = An27-An84, alkali feldspar = Ab41Or57-Ab70Or20), amphibole (kaersutite), diopside (~Wo55En35Fs10), titanomagnetite (Ti# 55), olivine (Fo45, Fo81), and apatite. Type I inclusions are highly vesicular with sinuous forms and crenulate margins with the host indicating magmatic mixing/mingling. The mineral assemblage of Type I includes kaersutite (15-20 vol. %), feldspar (plagioclase = An33-An80, alkali feldspar = ~Ab55Or45), diopside (~Wo55En30Fs6), titanomagnetite (Ti# ~75), olivine (Fo48, Fo85) and apatite. Type II inclusions are kaersutite megacrysts and glomerocrysts dominated by kaersutite with subordinate phenocrysts, microphenocrysts and groundmass composed of plagioclase (An20-An76), titanomagnetite (Ti# 84), diopside (~Wo50En35Fs15), and apatite. Type III is a single porphyritic inclusion with phenocrysts of anorthoclase and is similar in texture and mineralogy to lavas found within the Minna Bluff stratigraphic section. Type IV are "salt and pepper" colored inclusions with granular textures consisting of kaersutite with interstitial plagioclase (An16-An55), diopside (~Wo50En36Fs4), titanomagnetite, apatite, sodalite, titanite and olivine. Type V inclusions are similar in appearance to Type IV but have a different mineral assemblage dominated by alkali feldspar (Ab50Or50), nepheline and plagioclase with subordinate, interstitial minerals of Fe-rich clinopyroxene (hedenbergite ~Wo50En17Fs38), titanomagnetite and leucite. Both Types IV and V have sharp contact margins with the host lava indicating that they were fully solidified when entrained by the host magmas, whereas Types I and II were semi-molten. Semi-quantitative geothermobarometric results for kaersutite and clinopyroxene indicate that some crystallized at P-T conditions in the lower crust to upper mantle (5-9 kbars = 15-27 km). High water contents in the magmas induced early crystallization of amphibole and clinopyroxene and suppressed plagioclase, which crystallized along with magnetite at shallow levels within the crust. Four stages are deduced for the mixing and ascent of magma bodies and the incorporation of inclusion types at Xeno Ridge. Stage I: phonolitic magmas that comprise lava compositions prior to mixing with Type I magma ascend into the upper crust. Stage II: replenishing phonotephritic magmas (Type I) ascend from depth within the same conduit system and incorporate partially solidified material (Type II) that originated from sidewall crystallization of previous magmas. Stage III: the mixing event triggered a second episode of magma ascent. Stage IV: the rapid ascent of mixed magmas entrained crystalline selvages of Type IV and V compositions from conduit walls before eruption.
Kurt Panter (Advisor)
John Farver (Committee Member)
Thom Wilch (Committee Member)
232 p.
Geochemistry; Geology
kaersutite; amphibole; LAVAS; microphenocrysts; phenocrysts; clinopyroxene; groundmass

Recommended Citations

Citations

  • Scanlan, M. K. (2008). Petrology of Inclusion-Rich Lavas at Minna Bluff, McMurdo Sound, Antarctica: Implications for Magma Origin, Differentiation, and Eruption Dynamics [Master's thesis, Bowling Green State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1217952842

    APA Style (7th edition)

  • Scanlan, Mary. Petrology of Inclusion-Rich Lavas at Minna Bluff, McMurdo Sound, Antarctica: Implications for Magma Origin, Differentiation, and Eruption Dynamics. 2008. Bowling Green State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1217952842.

    MLA Style (8th edition)

  • Scanlan, Mary. "Petrology of Inclusion-Rich Lavas at Minna Bluff, McMurdo Sound, Antarctica: Implications for Magma Origin, Differentiation, and Eruption Dynamics." Master's thesis, Bowling Green State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1217952842

    Chicago Manual of Style (17th edition)

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