2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 270-5
Presentation Time: 9:00 AM

RECONSTRUCTION OF THE MELANESIAN BACK-ARC BASINS: IMPLICATIONS FOR ONTONG JAVA PLATEAU ACCRETION


SETON, Maria1, MORTIMER, Nick2, WILLIAMS, Simon E.3, QUILTY, Patrick4, MEFFRE, Sebastein4, GANS, Phillip B.5, MICKLETHWAITE, Steven6, MOORE, Jarrod7 and ZAHIROVIC, Sabin7, (1)School of Geosciences, The University of Sydney, Sydney, 2006, Australia, (2)GNS Science, Private Bag 1930, Dunedin, 9054, New Zealand, (3)School of Geosciences, University of Sydney, Madsen Building F09, Sydney, 2006, Australia, (4)School of Earth Sciences, University of Tasmania, Sandy Bay Campus, Centenary Building, Hobart, 7001, Australia, (5)Dept. of Earth Science, UC Santa Barbara, Santa Barbara, CA 93106-9630, (6)Centre for Exploration Targeting, University of Western Australia, Perth, 6009, Australia, (7)School of Geosciences, University of Sydney, Madsen Blg F09, Sydney, 2006, Australia

The Melanesian Borderlands is a poorly explored area of the northeastern corner of the Australian plate, where interaction between the Pacific and Australian plates and the accretion of the world’s largest oceanic plateau, the Ontong Java Plateau, has resulted in a complex assemblage of back-arc basins, island arcs and volcanic products. The lack of a clear framework to describe the tectonic evolution and plate boundary configurations in the area stems from the limited amount of offshore geophysical and geological data. We present the results of a research voyage on the RV Southern Surveyor to the eastern Coral Sea in October-November, 2012 where swath bathymetry, magnetic and gravity data were collected as well as igneous and sedimentary samples from 14 seafloor sites. A combination of magnetic anomaly profiles, seafloor fabric from swath bathymetry data, Ar-Ar dating of basalts and paleontological dating of carbonates constrain the opening of the Santa Cruz Basin and South Rennell Trough to between ~43-28 Ma. The timing of basin opening corresponds to the opening of the Solomon Sea further north, where chrons 19-16 have been identified. This suggests that a single > 2,000 km long back-arc basin, with at least one triple junction existed landward of the Melanesian subduction zone from the Eocene-Oligocene. Geochemical analyses of the basalts reveal E-MORB compositions, similar to recently re-analysed and dated dredge samples from a previous voyage to the area (ORSTOM). The cessation of spreading along the South Rennell Trough, Santa Cruz Basin and Solomon Sea at ~28 Ma, constrained by Ar-Ar dating of E-MORB basalt from the ridge flank of the South Rennell Trough, indicates a reorganization of the plate boundaries at this time. We speculate that these plate boundary changes indicate the initial soft collision of the Ontong Java Plateau to the Melanesian Arc and suggest that back-arc basins can be used as markers for both local and global plate boundary changes.

Session No. 270

T3. Ridge to Trench Evolution of Oceanic Lithosphere and Its Accretion Tectonics in the Pacific Rim (Past and Present)
Wednesday, 22 October 2014: 8:00 AM-12:00 PM
119/120 (Vancouver Convention Centre-West)
Geological Society of America Abstracts with Programs. Vol. 46, No. 6, p.656
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