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

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Tectonic framework... to test

Independently date subduction cessation, rifting, other events?

Is dredged 1170 Ma granite in situ?

!"#$%&''(

)'"*&"+(

!,"*,"#(-./&(

((((01&"*(((23+*,(4"/.5(

43+5*6(

)'"731#(

Challis et al. (1982)

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Data coverage

10 sites: 5xAHe, 11xZHe, 10xAFT, 9xZFT, (4xAr-Ar) samples

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Results: Apatite FT and He ages

Canterbury Basin: Kamp (1991, PR1796)

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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

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Results: Chathams ZHe

Age vs metamorphic grade reveals partial retention zone

error bars ±2!

High U grain w

radiation damage

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Interp: Bounty and Chathams Tt

Very similar 80-100 Ma cooling histories

error bars ±2!

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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