Hochstetter
Lecture 2004Hochstetter
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
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.
email a.tulloch_at_gns.cri.nz |
A list of previous Hochstetter Lecturers can be found on the Awards page
