Research Article| January 01, 2011 A detrital record of lower oceanic crust exhumation within a Miocene slow-spreading ridge: Macquarie Island, Southern Ocean Ryan A. Portner; Ryan A. Portner † GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia †E-mail: ryan.portner@mq.edu.au Search for other works by this author on: GSW Google Scholar Melissa J. Murphy; Melissa J. Murphy GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia Search for other works by this author on: GSW Google Scholar Nathan R. Daczko Nathan R. Daczko GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney NSW 2109, Australia Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (1-2): 255–273. https://doi.org/10.1130/B30082.1 Article history received: 30 Apr 2009 rev-recd: 25 Jan 2010 accepted: 27 Jan 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Ryan A. Portner, Melissa J. Murphy, Nathan R. Daczko; A detrital record of lower oceanic crust exhumation within a Miocene slow-spreading ridge: Macquarie Island, Southern Ocean. GSA Bulletin 2011;; 123 (1-2): 255–273. doi: https://doi.org/10.1130/B30082.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Uplift, exhumation, and denudation of the lower oceanic crust are recorded by sedimentary rocks of Macquarie Island (54°30′S, 158°54′E), which were deposited within the slow-spreading proto–Macquarie spreading ridge between ca. 9 and 12 Ma. Measured stratigraphic sections typically contain basal basaltic breccia lithofacies that are overlain by a thick sequence of enriched mid-ocean-ridge basalt (E-MORB) with thin intercalations of gabbroic sedimentary lithofacies. Basaltic detritus has zeolite to lower-greenschist metamorphic grades typical of the upper oceanic crust, and gabbroic detritus has upper-greenschist to amphibolite metamorphic grades typical of the lower oceanic crust. Breccia clast counts and sedimentary structures indicate that basaltic lithofacies were locally derived from the footwalls of adjacent spreading-related faults. Sedimentary structures, detrital clinopyroxene major- and trace-element geochemistry, and 206Pb/238U zircon geochronology indicate that the gabbroic lithofacies were more distally derived from a Paleogene-aged tholeiitic MORB source. Detrital zircon populations of ca. 27 and ca. 33 Ma correspond to oceanic magnetic anomalies 8o and 13o, respectively, and exclude ca. 8.5 Ma gabbroic rocks of Macquarie Island as a potential source. Geodynamic reconstructions show that anomaly 8o crust from the Southeast Indian Ridge was juxtaposed against the active proto–Macquarie spreading ridge when sedimentary rocks of Macquarie Island were deposited and was a likely source for the gabbroic lithofacies. The proto–Macquarie spreading ridge and Southeast Indian Ridge were connected by the Jurru long-offset transform, which has undergone significant transpression since 27 Ma. This transpression formed a bathymetric transverse ridge that was composed of structurally isolated blocks of heterogeneously aged Paleogene source crust, which provided the source for Macquarie Island's gabbroic sedimentary lithofacies. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.