Abstract
Taiwan and the Southern Alps of New Zealand are both young transpressive orogens characterized by rapid uplift and exhumation, high heat flow and vigorous surface processes. However, the distribution of heat flow, hot springs and veins in the two orogens is different. Taiwan has higher heat flow, distributed hot springs and localized veining. The Southern Alps has a narrow heat-flow anomaly, localized warm springs and widespread veining. Both orogens have two fluid-flow systems centred about the drainage divide. Shallow topographically driven meteoric water is restricted to the top 2-4 km. Deep flow is dominated by mineralizing rock-exchanged fluids. Extensional deformation occurs in the divide region of both orogens. At depth, vertical stretching produces subhorizontal veins. At shallower levels, stretching is horizontal and veins are steep. Veins in Taiwan are rare with zones of intense veining where flow has been localized into one site during exhumation from metamorphic to near-surface conditions. Fracturing and veining of the initially weak Slate Belt rocks causes a rheological change, increasing the tensile strength and making it more prone to fracturing, thus focusing fluid flow into the same locale. More uniform rheology in the Southern Alps leads to distributed veining.