| Abstract: | The Taupo Volcanic Zone (TVZ) is a 200-km-long volcanic arc segment which developed ≤2 Ma ago within the continental crust of the North Island of New Zealand and lies at the southern end of the much larger Tonga-Kermadec arc system. The total crustal heat transfer of the TVZ is at present c. 2600 MW/100 km, most of the heat being transferred by convective geothermal systems. The rate of transfer is anomalously high in comparison to that of other active arcs, and arguably the highest world wide for such a setting. Heat transfer of other active arcs appear to vary almost linearly with subduction speed (about 150 MW/100 km for 10 mm/yr). The mass rate of common type arc extrusions (basalts, andesites, dacites) also increases almost linearly with subduction speed. This allows separation of the TVZ heat transfer into a “normal” component, associated with extrusions and intrusions of andesites and dacites (about 600 MW/100 km), and an “anomalous” component of about 2000 MW/100 km, related to extrusions and intrusions of rhyolitic melts whose generation is not directly controlled by subduction processes.Rhyolitic melts in the TVZ are partial melts of dominantly crustal origin. Comparison with other arcs indicates that the long-term extrusion rate of TVZ rhyolites (about 400 kg/s per 100 km) is also the highest world wide for this setting. The occurrence of voluminous Quaternary rhyolitic pyroclastics is a rare phenomenon and appears to be associated with a few arc segments (TVZ, Sumatra, Kyushu) that undergo significant crustal deformation.Various models have been proposed to explain the phenomenon of the anomalously high heat transfer within the TVZ. Models which require only heat transfer from plumes and subcrustal melts, either ponded at the crust/mantle boundary or intruding a spreading crust, are not suitable because the associated heat transfer at the contact is too low by a factor 2 to explain the required transfer rate of about 0.8 W/m2 representing the “anomalous” crustal heat component of the TVZ. Heat generation by focussed plastic deformation within the ductile lithosphere is an alternative mechanism to explain “endogenous crustal heating” which yields heating rates that are also too low by a factor of two, although important parameters (average yield strength of lithosphere and opening rate of the TVZ) are not well known. A further search for a suitable combination of heat source models is required. |
