Thermo-tectonic Implications of Zircon and Apatite FT Data of the Marlborough Region, South Island, New Zealand

Abstract

Zircon and apatite fission track (FT) reveal some of the thermo-tectonic features of the Marlborough Region, South Island, New Zealand. The very young FT ages (< 10 Ma) of zircon and apatite in the vicinity of the Alpine Fault bend and Seaward Kaikoura Range coincide with the recent rapid uplift/erosion. Four samples with reset zircon ages in the Alpine Fault bend reveal that the host rocks in this area cooled below the closure temperature of zircon (~240°C) in the late Miocene. Unlike these four zircon FT ages, most zircon FT ages are consistent with depositional ages. Annealed apatite and unannealed zircon FT ages show that the host rocks in Marlbouough did not experience exposure to the closure temperature fo zircon in the Mesozoic burial, but passed through the partial annealing zone (PAZ) of apatite (~60-110°C). The host rocks in the north rather than those in the south passed through the lower part of apatite PAZ. In addition, most of the zircon samples with low P (Χ2) values (< 5%) show that the samples have been slightly annealed, implying that the host rocks might have experienced the upper part of the partial annealing zone of zircon (~175°C) during the Mesozoic cooling.

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