| Title | TECTONIC STRUCTURE AND PERMEABILITY IN THE TAUPŌ RIFT: NEW INSIGHTS FROM ANALYSIS OF LIDAR DERIVED DEMS |
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| Authors | P. Villamor, A. Nicol, H. Seebeck, J. Rowland, D. Townsend, C. Massiot, D.D. McNamara, S.D. Milicich, W. Ries, and S. Alcaraz |
| Year | 2017 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Tectonic structure, permeability, active normal faults, geothermal system, Taupo Rift, LiDAR |
| Abstract | The bulk permeability of upper crustal rocks in the Taupō Rift, central North Island, New Zealand is a function of the development and intersection of active and inherited faults, caldera collapse structures, and/or lithology. To date, major fault trends within the rift have been described as: 1) 030-045°, the dominant rift trend of north of Lake Taupō; 2) 050-065°, the dominant rift trend north of the Ngakuru Graben; 3) 355-005°, inherited basement trends that may influence caldera collapse structures and; 4) 330°, approximately parallel to the structural trends within the basement and Hauraki Rift. Preliminary LiDAR interpretations within and on the eastern margin of the Taupō Rift indicate that an additional set of active faults trending 070-085° could also play an important role in the crustal permeability of the region. All fault trends identified within the Taupō Rift can be found within basement rocks. In outcrops of Mesozoic basement to the east and west of the central Taupō Rift, predominant 355-005° fault trends are found, while 070-085° (with minor 030-045°) trends are observed to the south. Northwest of the rift, 330° trends are present in the basement along with active and inactive faults of the Hauraki Rift. These trends within the Taupō Rift are supported at various scales by geological mapping, geophysical imaging and borehole analysis. The surface expression of geothermal activity in the TVZ occurs predominantly in the rhyolitic dominant central section. In a few cases, geothermal fields are directly associated with large crustal scale faults (e.g., Te Kopia, Waikite, Orakei Korako). Regions within the rift with high densities of faults and their associated intersections do not often spatially correlate with high temperature geothermal systems. In these highly faulted areas, inferred high crustal permeability most likely facilitate the down-welling of cold ground waters providing recharge to the upwelling geothermal plumes. These observations indicate that the interaction of micro- to macro-scale faults (and associated high and low permeability zones), with the geothermal systems is a complex phenomenon which requires multidisciplinary approaches to understand. |