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)
Electronic Thesis or Dissertation 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...
Main Author: | |
---|---|
Other Authors: | , , , |
Format: | Thesis |
Language: | English |
Published: |
University of Alabama Libraries
2012
|
Subjects: | |
Online Access: | https://ir.ua.edu/handle/123456789/1618 |
id |
ftunivalabama:oai:ir.ua.edu:123456789/1618 |
---|---|
record_format |
openpolar |
spelling |
ftunivalabama:oai:ir.ua.edu:123456789/1618 2023-05-15T17:09:55+02:00 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) Jeffcoat, Charles Ryan Schwartz, Joshua Stowell, Harold Hilton Goodliffe, Andrew M. Saal, Alberto E. 2012 96 p. https://ir.ua.edu/handle/123456789/1618 English eng University of Alabama Libraries The University of Alabama Electronic Theses and Dissertations The University of Alabama Libraries Digital Collections https://ir.ua.edu/handle/123456789/1618 All rights reserved by the author unless otherwise indicated. Geochemistry Marine geology Plate tectonics thesis text 2012 ftunivalabama 2023-01-07T16:40:04Z Electronic Thesis or Dissertation 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 ... Thesis Macquarie Island Southern Ocean University of Alabama Institutional Repository Indian Southern Ocean |
institution |
Open Polar |
collection |
University of Alabama Institutional Repository |
op_collection_id |
ftunivalabama |
language |
English |
topic |
Geochemistry Marine geology Plate tectonics |
spellingShingle |
Geochemistry Marine geology Plate tectonics Jeffcoat, Charles Ryan 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) |
topic_facet |
Geochemistry Marine geology Plate tectonics |
description |
Electronic Thesis or Dissertation 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 ... |
author2 |
Schwartz, Joshua Stowell, Harold Hilton Goodliffe, Andrew M. Saal, Alberto E. |
format |
Thesis |
author |
Jeffcoat, Charles Ryan |
author_facet |
Jeffcoat, Charles Ryan |
author_sort |
Jeffcoat, Charles Ryan |
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) |
title_short |
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) |
title_full |
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) |
title_fullStr |
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) |
title_full_unstemmed |
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) |
title_sort |
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) |
publisher |
University of Alabama Libraries |
publishDate |
2012 |
url |
https://ir.ua.edu/handle/123456789/1618 |
geographic |
Indian Southern Ocean |
geographic_facet |
Indian Southern Ocean |
genre |
Macquarie Island Southern Ocean |
genre_facet |
Macquarie Island Southern Ocean |
op_relation |
The University of Alabama Electronic Theses and Dissertations The University of Alabama Libraries Digital Collections https://ir.ua.edu/handle/123456789/1618 |
op_rights |
All rights reserved by the author unless otherwise indicated. |
_version_ |
1766066279418953728 |