Oxygen, carbon, and strontium isotopic constraints on timing and sources of crustal fluids in an active orogen: South Island, New Zealand

Abstract

Active deformation on New Zealand's South Island can be divided into four tectonic zones: Inboard, Main Divide, Outboard, and Marlborough strike‐slip. On the basis of stable isotope data (δ¹³C and δ¹⁸O) we suggest that calcite veins are formed from a mixed meteoric and metamorphic water in the Inboard and Main Divide tectonic zones, as well as the Alpine‐Wairau Fault of the Marlborough strike‐slip zone. We suggest that the metamorphic waters are derived from the breakdown of biotite at c. 25 km, a depth which corresponds to a conductive zone identified by a recent magnetotelluric study across central South Island. These metamorphic fluids exit the orogen along the steep faults that border the Southern Alps. ⁸⁷Sr/⁸⁶Sr ratios of vein and fault‐zone calcite suggest that calcite formation is associated with young tectonically driven hydrothermal fluid flow in the Inboard, Main Divide, and Wairau Fault zones. The age of calcite formation in the Outboard, Awatere, and Hope Fault zones could not be explicitly determined.

Keywords:

• calcite
• stable isotopes
• strontium isotopes
• fluid flow
• New Zealand