HR: 1340h
AN: T23B-1423    [Abstracts]
TI: Sediment Gravity Flows in a Mid-Ocean Ridge Environment and Their Relationship to Spreading Related Faults, Macquarie Island
AU: * Portner, R A
EM: rportner@els.mq.edu.au
AF: Macquarie University, GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia
AU: Daczko, N R
EM: ndaczko@els.mq.edu.au
AF: Macquarie University, GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia
AU: Dickinson, J A
EM: julesdickinson@gmail.com
AF: RPS Energy, Goldsworth House, Denton Way, Goldsworth Park, Woking, Surrey, NSW GU21 3LG, United Kingdom
AB: Despite the vast body of work devoted to deep water sedimentary processes, relatively little work has been done on sediment gravity flow deposits (gravites) produced along mid-ocean ridges. This is due to difficult access in modern ocean basins and structural overprinting in obducted ophiolites. Nevertheless, a rugged bathymetry (typically associated with slow-spreading ridges) coupled with ongoing tectonic activity makes the mid-ocean ridge depositional environment a prime location to study deep marine sediment gravity flow processes and their relationship to spreading related faults. Here we present data from a range of syntectonic gravites (turbidites, densites and debrites) that were deposited within the Late Miocene proto Macquarie spreading center, a slow to intermediate rate spreading center. Gravites are interbedded with MORB basalt and now uplifted and well-exposed on Macquarie Island. Geophysical data offshore and structural data onshore has constrained the paleo-tectonic setting of the island and show that it formed close to a ridge-transform intersection. Petrographic data indicate that gravites, which are most prevalent adjacent to major spreading-related faults, were solely derived from oceanic crust. Paleoflow indicators and stratigraphic architecture show a strong influence by major spreading related faults and hence paleobathymetry. A unique disparity exists between: 1) sandy polymict gravites produced by unconfined flow with paleocurrent data transverse to major structures and interbedded with thick tabular basalt flows; 2) sandy polymict gravites produced by confined flow with paleocurrents parallel to major structures and interbedded with pillow lavas; and 3) gravelly oligomict gravites lacking sedimentary structures and juxtaposed against local structures. We propose that these relationships correspond to differences in fault proximity, oceanic faulting style and volcanic center effusivity.
DE: 3022 Marine sediments: processes and transport
DE: 3035 Midocean ridge processes
DE: 3042 Ophiolites (8140)
DE: 3675 Sedimentary petrology
DE: 8169 Sedimentary basin processes
SC: Tectonophysics [T]
MN: 2007 Fall Meeting