Reconnaissance thermochronology of southern Zealandia

• Main Authors: Nick Mortimer, Barry Kohn, Diane Seward, Terry Spell, Andy Tulloch
• Format: Dataset
• Language: unknown
• Published: 2016
• Subjects: Geology; Precambrian; Gondwana; Great South Basin; Campbell Plateau; extensional rifting episode; Ma; Hikurangi Plateau collision; Miocene intraplate volcanism; Zealandia; Chatham Rise regions; dredge; borehole cuttings samples; Ar; zircon; thermochronological systems reset; Antarctic; Iselin Bank; Antarc*
• Online Access: https://doi.org/10.6084/m9.figshare.3454127.v1; https://figshare.com/articles/Reconnaissance_thermochronology_of_southern_Zealandia/3454127

We report new fission-track, (U–Th)/He and 40 Ar/ 39 Ar ages for minerals in surface, dredge and borehole cuttings samples from the southern South Island, Campbell Plateau and Chatham Rise regions of the Zealandia continent. Our results indicate that much of southern Zealandia underwent rapid cooling in the interval 105–80 Ma, probably during widespread intracontinental rifting before Zealandia split from Gondwana. The 108 ± 11 Ma rapid exhumation of a zircon He retention zone in the Chatham Schist, however, may record cessation of long-lived subduction at the Gondwana margin owing to Hikurangi Plateau collision and/or the onset of the extensional rifting episode. Locally, basement rocks have been appreciably heated, and thermochronological systems reset, in response to deepening of the Great South Basin and by local Miocene intraplate volcanism. An apatite fission-track age of 179 ± 17 Ma from a dredge sample of Precambrian granite at the southern tip of the Campbell Plateau indicates that it is probably ice-rafted, thus in situ Precambrian crust in Zealandia is still unconfirmed. In contrast, a zircon (U–Th)/He age of 99 ± 9 Ma from a Precambrian metarhyolite from Iselin Bank at the conjugate Antarctic continental margin plausibly indicates an in situ position.