U-Pb zircon geochronology, Hf isotope and trace element geochemistry of a unique lower crustal - upper mantle section of a dying slow-spreading mid-ocean ridge (Macquarie Island, Southern Ocean)

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dc.contributor Stowell, Harold Hilton
dc.contributor Goodliffe, Andrew M.
dc.contributor Saal, Alberto E.
dc.contributor.advisor Schwartz, Joshua
dc.contributor.author Jeffcoat, Charles Ryan
dc.date.accessioned 2017-03-01T16:37:23Z
dc.date.available 2017-03-01T16:37:23Z
dc.date.issued 2012
dc.identifier.other u0015_0000001_0001141
dc.identifier.other Jeffcoat_alatus_0004M_11316
dc.identifier.uri https://ir.ua.edu/handle/123456789/1618
dc.description Electronic Thesis or Dissertation
dc.description.abstract Macquarie Island, located in the Southern Ocean, is a section of subaerially exposed oceanic crust formed at the now extinct proto-Macquarie, slow-spreading, mid-ocean ridge. Macquarie Island is unique among oceanic ophiolite sequences in that it is still located in the basin in which it formed. The northernmost part of Macquarie Island is composed primarily of lower crustal gabbro and upper mantle peridotite, and therefore provides a unique window into lower oceanic crust. Here, we report integrated Pb/U zircon ages and Lu-Hf isotopic and trace element data from six samples of the lower crust-upper mantle sequence. Samples consist of two lower crustal gabbros, and three mantle-hosted gabbro dikes/dikelettes and one phlogopite-bearing vein from the upper mantle sequence. ^206 Pb/^238 U SHRIMP-RG zircon error weighted average ages for the lower crustal gabbros are 8.7 ± 0.3 Ma (N = 9) and 9.0 ± 0.2 Ma (N = 13), whereas the mantle-hosted gabbro dikes/dikelettes yield overlapping error-weighted average ages of 8.7 ± 0.2 Ma (N = 9), 8.7 ± 0.3 Ma (N = 8), and 8.9 ± 0.2 Ma (N = 11) (all errors 2σ). The phlogopite vein yielded a slightly younger error weighted average age of 8.5 ± 0.1 Ma (N = 11). Initial epsilon Hf results for zircons from the same samples show a broad distribution ranging from +9.5 to +13.3 for the lower crustal gabbro (N = 28), +7.0 to +16.4 for the gabbro dikes/dikelettes (N = 24), and +8.4 to +12.2 for the phlogopite vein (N = 12). The wide range in values (particularly from the gabbro dikes/dikelettes) is consistent with a heterogeneous source region composed of depleted- and enriched mantle sources. Zircon trace element concentrations also support a heterogeneous source, displaying enrichment in U/Yb relative to N-MORB zircons from the Mid-Atlantic and Southwest Indian Ridge systems. No pattern of enrichment with time is observed within the resolution of the U-Pb zircon dates. We interpret these results to indicate that magmatic construction of Macquarie Island occurred between 8.7 and 9.0 Ma and involved sampling of at least two distinct mantle sources.
dc.format.extent 96 p.
dc.format.medium electronic
dc.format.mimetype application/pdf
dc.language English
dc.language.iso en_US
dc.publisher University of Alabama Libraries
dc.relation.ispartof The University of Alabama Electronic Theses and Dissertations
dc.relation.ispartof The University of Alabama Libraries Digital Collections
dc.relation.hasversion born digital
dc.rights All rights reserved by the author unless otherwise indicated.
dc.subject.other Geochemistry
dc.subject.other Marine geology
dc.subject.other Plate tectonics
dc.title U-Pb zircon geochronology, Hf isotope and trace element geochemistry of a unique lower crustal - upper mantle section of a dying slow-spreading mid-ocean ridge (Macquarie Island, Southern Ocean)
dc.type thesis
dc.type text
etdms.degree.department University of Alabama. Dept. of Geological Sciences
etdms.degree.discipline Geology
etdms.degree.grantor The University of Alabama
etdms.degree.level master's
etdms.degree.name M.S.

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