nick mortimer, barry kohn, diane seward, terry spell, andy ...€¦ · gns science south zealandia...
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GNS Science
South Zealandia thermotectonics
Nick Mortimer, Barry Kohn, Diane Seward, Terry Spell, Andy Tulloch GNS Science, U Melbourne, VUW, UNLV
GNS Science
South Zealandia
Apatite He 70°C Apatite FT 100°C Zircon He 200°C Zircon FT 230°C
FT and (U-Th)/He Thermochronology
Thin section field of view 1 mm
GNS Science
Tectonic framework... to test
Independently date subduction cessation, rifting, other events?
Is dredged 1170 Ma granite in situ?
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Challis et al. (1982)
GNS Science
Data coverage
10 sites: 5xAHe, 11xZHe, 10xAFT, 9xZFT, (4xAr-Ar) samples
GNS Science
Results: Apatite FT and He ages
Canterbury Basin: Kamp (1991, PR1796)
GNS Science
Results: Apatite FT and He ages
Dredged 1170 Ma granite AFT is too old to be in situ
CI basement roasted by Mio volcs (ZHe=8Ma)
Basement burial in
sed basins
No burial in basin (115 Ma volcs)
Quenched 97 Ma granite
‘Expected’ basement
ages
GNS Science
Results: Chathams ZHe
Age vs metamorphic grade reveals partial retention zone
error bars ±2!
High U grain w
radiation damage
GNS Science
Interp: Bounty and Chathams Tt
Very similar 80-100 Ma cooling histories
error bars ±2!
GNS Science
Summary: South Zealandia thermochronology
NIWA map
Neogene reset (burial, volcanism) 97-115 Ma syn- deposition/ intrusion Allochthonous Intra-Zealandia 80-100 Ma rifting related exhumation
!
!
No continent-ocean margin effects (Hikurangi Plateau, SW Pacific Basin rifting)?
Canterbury & Great South Basins
Rifted
Platform
Platform
Plat. Rift
Rifted
Platform Rifted Basins
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