DI027-05
Crustal Structure of the Southern Plate Boundary of the Niuafo’ou Microplate, Lau Basin, Southwest Pacific Ocean

Wednesday, 16 December 2020: 04:16
Virtual
Anouk Beniest1,2, Anke Dannowski1, Michael Schnabel3, Reinhard Werner1, Heidrun Kopp1,4, Ingo Heyde3, Udo Barckhausen3, Michael Riedel1, Florian Schmid1, Florian Petersen1, Bettina Schramm1 and Mark D Hannington1,5, (1)GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany, (2)Vrije Universiteit Amsterdam, Amsterdam, Netherlands, (3)BGR Federal Institute for Geosciences and Natural Resources, Hannover, Germany, (4)University of Kiel, Kiel, Germany, (5)University of Ottawa, Ottawa, ON, Canada
Recorded Presentation
Abstract:
The northern Lau Basin, at the Australian-Pacific plate boundary, is one of the fastest opening back-arc basins on earth. An amalgamation of active rifts and spreading centers accommodates the extension. The current configuration of micro-plates, motions and plate-boundaries within the northern Lau Basin has been studied, but remains complex. Especially in the southern part of the Lau Basin questions remain about the crustal structure. In this area, the Central Lau Spreading Center (CLSC) and the southern tip of the Fonualei Rift and Spreading Center (FRSC) define the diffuse southern boundary of the Niuafo’ou microplate. It remains unclear where the southern plate boundary is located and what kind of boundary it is.

We present seismic refraction and reflection data of a 200-km long transect in the transition zone from the eastern side of the CLSC to the southern tip of the FRSC. The seismic data recording was accompanied by parametric sediment echosounder data, gravimetric and magnetic measurements and dredged samples of the seafloor in the vicinity of the profile. A travel time tomography reveals a pronounced lateral variation in seismic P-wave velocities from west to east, within the 7-8 km thick back-arc-crust. Towards the east the crust gradually thickens to 13 km of arc-crust. The reflection seismic data reveals sediment pockets that vary between 300m to 1000m depth and are located on both the thinner back-arc crust and thicker arc-crust. Rock sampling along the transect retrieved predominantly massive aphyric basalts from the back-arc-crust in the west. Ol-Px-Pl-phyric basalts, andesites, and a broad spectrum of volcaniclastic rocks are the most common rock-type collected from the arc-crust in the east. These rocks are currently analyzed to determine the age and geochemical (major, trace element and Sr-Nd-Pb-Hf isotopic) composition of the sampled structures.

The lack of a thinner crust near the southern tip of the FRSC is located and a wide distribution of normal faults in the sedimentary basins that reach the surface suggest that the southern plate boundary of the Niuafo’ou microplate actively accommodates extension in a wide rift setting.

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