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Hochstetter Lecture 2004

The 2004 Hochstetter Lecture will be given by Dr Andy Tulloch (GNS, Dunedin) at GSNZ branches and other venues in September and October. The subject of his lecture will be:

The geology of Rakiura (Stewart Island) - magmatic arcs, sedimentary basins and Traps for the unwary

old

new

1968 - NZGS 4-mile
2004 - GNS QMAP

Abstract

Subduction along the Mesozoic margin of southern Gondwana produced voluminous magmatism from the Middle Jurassic to the late Early Cretaceous, forming the bulk of New Zealand's Median Batholith, and adding significantly to the proto-NZ land mass. However, much of this batholith in Nelson, Westland and Fiordland is close to the late Cenozoic plate boundary, and older structures have, to varying degrees, been obliterated. Rakiura, more distant from the Alpine Fault, offers a less deformed window on the pre-Cenozoic geology of New Zealand.

Rakiura sits astride the "Median Tectonic Line/Median Tectonic Zone/Median Batholith" boundary between the Eastern and Western Provinces of New Zealand. A GNS transect across this boundary has produced a map which recognises some 29 individual intrusive bodies (plutons). These plutons can be grouped into three complexes, separated by two c. WNW-ESE trending fault zones; Freshwater Fault to the north and Escarpment Fault to the south. Rakiura is 98% comprised of plutonic rock, and 80% of these plutons formed during a 65 my-long episode of plate convergence between 170 and 105 Ma. Magma production rate increased significantly from ~ 130-115 Ma, coincident with a subtle but significant change in magma chemistry. The chemistry, timing and distribution of the post-130 Ma episode of magmatism forms a similar pattern to that observed in other cordilleran batholiths. This style of magmatism appears to presage the end of, or at least a hiatus in, subduction zone magmatism.

The youngest dated pluton on Rakiura (Gog leucogranodiorite) was emplaced at 105 ±1 Ma, only about 3 my before widespread extension began in the New Zealand region. A major low-angle extensional shear zone which parallels the SE coast of Rakiura likely forms part of the western margin to the Great South Basin, and formed in response to continental extension and rifting of New Zealand from West Antarctica.

Allibone, A.H., & Tulloch, A.J. 2004 Geology of the plutonic basement rocks of Stewart Island, New Zealand. NZ Jl of Geology & Geophysics, 47: 233-256.

Itinerary

Palmerston North

Hoch

Mon 6 Sep

 

SL

Tue 7 Sep

New Plymouth

Hoch

Tue 7 Sep

Taupo

Hoch

Wed 8 Sep

Napier

Hoch

Thu 9 Sep

Dunedin

Hoch

Tue 14 Sep

 

SL

Wed 15 Sep

Wellington

Hoch

Mon 20 Sep

 

SL

Tue 21 Sep

Auckland

Hoch

Tue 21 Sep

 

SL

Wed 22 Sep

Hamilton

Hoch

Wed 22 Sep

 

SL

Thu 23 Sep

Christchurch

Hoch

Thu 23 Sep

 

SL

Fri 24 Sep

Nelson

Hoch

Tue 12 Oct

Masterton

Hoch

Wed 13 Oct

Hoch=Hochstetter Lecture (evening). SL=supporting lecture (usually lunchtime).
Contact
local GSNZ branch people to confirm venues and times.

Lecturer's background

Andy Tulloch is a petrologist in the Mapping Section at Geological and Nuclear Sciences (GNS), and is based in the Dunedin Research Centre. He graduated from the University of Canterbury with a BSc (Hons) in 1974, and completed a PhD from Otago University in 1979 with a study of the Victoria Range segment of the Karamea Batholith. Andy joined the NZ Geological Survey division of DSIR in 1979, and for several years worked on the petrology of the Kawerau geothermal field, before focussing on basement petrology.

Andy is field-based petrologist with emphasis on applications to regional geology and tectonics as well as the origins of granitoid rocks and continental growth. He collaborates with a range of isotope laboratories to apply geochronology (especially U-Pb) and thermochronology to problems in New Zealand, Thailand, California, Mexico, Philippines, Indonesia and Antarctica.

From 1994-2003 he was Programme Leader for the FRST programme Origin and development of NZ continental crust, which included leading a multidisciplinary project on the structure and development of the Mesozoic convergent margin on Stewart Island. Within the last 5 years he has also managed three multidisciplinary commercial projects on basement rocks which form major hydrocarbon resevoirs in Sumatra. He is currently undertaking a UTh-He thermochronological study of Transantarctic Mountains uplift in collaboration with Caltech, providing petrological-geochronological support for Fiordland Qmap, beginning a comparision of Mesozoic magmatism and associated mineralisation in Eastern Australia and New Zealand and is supervising PhD projects in southern Stewart Island and Fiordland.

He is a member of the Geological Society of NZ, NZ Geochemical Group, American Geophysical Union, and was a Fulbright Senior Scholar in California in 1991-92.

A list of previous Hochstetter Lecturers can be found on the Awards page