NZ tectonics: SESI  (South East South Island) profile

SESI  (South East South Island) profile

Objectives

The age and nature of New Zealand’s basement rock units and their position of the boundaries have been well defined by surface mapping, but little is known about them at depth or offshore. Important questions include :

• How does crustal thickness and the nature of the Moho change across the terranes, metamorphic belts and batholiths?
• Are the terranes a stack of thin thrust slices, or do they occupy substantial thicknesses within the present day crust? 
• To what extent has the 85-110 Ma extension modified the geometry of the earlier convergent orogen?

 The SESI seismic reflection profile images the geometry of the pre-110 Ma basement units down the south-east coastline of South Island. It sheds light on the geometry of terrane boundaries preserved in approximately their pre-Cenozoic configurations. The profile ran almost basically perpendicular to basement terrane boundaries, enabling ready extrapolation of geological structures exposed onshore to the offshore line.

Caption : SESI line shown in light gray, offshore the south east coastline of South Island. 
Figure from Mortimer et al (2002).

 

Seismic reflection profile showing the seismic reflection image (top), and a line drawing of the major reflectors (bottom). Figure from Mortimer et al (2002). 

 

Geological and tectonic interpretation of the SESI profile. Schist foliation is shown by short lines, interpreted faults by heavy lines, Neogene volcanics by black shading, reflective lower crust (extension-related?) by light and dark grey shading.  Figure from Mortimer et al, 2002.

 

Reference
Mortimer, N., Davey, F.J., Melhuish, A., Yu, J., and Godfrey, N.J., 2002, Geological interpretation of a deep seismic reflection profile across the Eastern Province and Median Batholith, New Zealand: crustal architecture of an extended Phanerozoic convergent orogen, N.Z. J. Geol & Geophys., 45, 349-363.

You can contact
Dr Stephen Bannister
Dr Donna Eberhart-Phillips

Street Address : 1 Fairway Drive, Avalon, 5010.
Postal Address : PO Box 30368, Lower Hutt 5040,
New Zealand
Tel:+64 4 570 1444
Fax:+64 4 570 4600

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November 14, 2006