Scheduled Cruises in 2003

Summary of a recent cruise on margins research (D.031)

Location :   Campbell Plateau (SE New Zealand)

Research ship and cruise identifier :   RV Sonne, cruise SO-169

Starts :   18 January 2003, Lyttelton (NZ)

Ends :   24 February 2003, Devonport (NZ)

Principal Scientist/Investigator :   K. Gohl

Laboratory :   Alfred Wegener Institute for Polar and Marine Research (AWI), Bremerhaven, Germany

Other investigators :   G. Uenzelmann-Neben (AWI), K. Hoernle (GEOMAR), F. Davey (GNS, NZ), S. O'Reilly (Macquarie Univ., AUS)

E-mail contact for further information :   kgohl@awi-bremerhaven.de

Scientific objectives :   The Campbell Plateau off New Zealand, as part of the greater New Zealand continent called Zealandia, is one of the world's largest submarine plateaus. Most of its tectonic-magmatic evolution and structural composition is relatively unknown. Existing geophysical and petrological data indicate that at least two major magmatic phases affected the growth and development of the plateau. Mid to Late Cretaceous rift-related magmatic phases and Cenozoic magmatism stemmed from different mantle sources. As existing magnetic, gravity and reflection seismic data indicate, the plateau can be divided in zones of distinct tectonic origin of which the intra-plateau Great South Basin is the best investigated one. The relation between magmatic events and tectonic and structural evolution of the Campbell Plateau is one of the significant remaining questions in the framework of reconstructing the evolution of Zealandia and the southwestern Pacific region.

The major objectives and questions to be addressed include :
(1) Structure and evolution of crustal segments of the Campbell Plateau: Gravity and magnetic data indicate a partitioning of the plateau in several crustal segments with varying crustal thickness. In particular, the westward extension of the Bounty Trough toward the Great South Basin shows a gravity signal that might be indicative for oceanic crustal affinity. Did extension/rifting reach a stage in which oceanic crust was formed? What are the crustal thickness and the composition of the crust-mantle boundary across the plateau? The Stokes and Campbell Magnetic Anomaly Systems are clearly defined and suggest the existence of magmatic crustal provinces. What are the volume, source and timing of this magmatism?

(2) Break-up process of Campbell Plateau from Marie Byrd Land: The timing of the break-up between Campbell Plateau and Marie Byrd Land at around 82 Ma is relatively well documented by magnetic lineations identified off the plateau margin. The process that led to break-up, however, has not been understood. Why is the slope anomalously steep (fast break-up? erosion?)? What was the role of magmatism during break-up? How far did extension evolve before oceanic crust developed? Is a submarine plateau margin different from a passive continental margin?

(3) Volcanism of Campbell Plateau: A dominant magmatic phase occurred during rifting and break-up. Do the Cretaceous volcanics show indications for an origin from shallow asthenospheric or deeper plume-generating sources? Do rift-related volcanics show lithospheric contamination? A second major magmatic phase ocurred in the Cenozoic. What is the mantle source of these volcanics? Are they geochemically related to volcanics of the Hikurangi Plateau, the rift-related volcanics, or the Cenozoic volcanics of Marie Byrd Land and NorthVictoria Land (Antarctica)?

We plan the following data acquisition and sampling :
(1) Ocean-bottom seismograph (OBS) and reflection seismic transect across Campbell Plateau: A deep crustal seismic transect, subdivided in two profiles, will stretch from the vicinity of the South Island coast across the plateau and its southeastern margin. OBS systems will be deployed in intervals of ~10 km to record densely sampled wavefields generated from airgun arrays large enough for wavefields penetrating to returning from the upper mantle. In addition, deep crustal reflection seismics will be shot during OBS deployment. Such a combined dataset allows detailed inversion for seismic structure, velocity and reflection/transmission characteristics for the entire crust and upper lithosphere.

(2) Reflection seismic profiling across southeastern plateau margin: We plan to cross the southeastern margin on three different locations with deep crustal reflection seismic profiles in order to generate a representative dataset on the sediment formations and the basement and crust-mantle boundary structure and characteristics along the plateau margin.

(3) Petrological-geochemical sampling: We plan to dredge basement rocks from suitable sites along the southeastern and western margin and from the plateau centre. Target areas are those where samples from volcanics associated with the break-up magmatism, the Auckland-Campbell hot spot trace, and Cenozoic magmatic activity can be expected.