Stratigraphy and structure of the Ngatamariki geothermal system from new zircon U–Pb geochronology: Implications for Taupo Volcanic Zone evolution

Chambefort, Isabelle; Lewis, B.; Wilson, C. J. N.; Rae, Andrew; Coutts, C; Bignall, Greg; Ireland, Trevor

doi:10.1016/j.jvolgeores.2014.01.015

Cited by 80 publications

(140 citation statements)

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“…Consistent with Wyering et al (2014) and Chambefort et al (2014) deeper samples showed that a higher proportion of the thin section contained secondary minerals and re-crystallisation by quartz and feldspar in veins, matrix, and clasts. In the deepest samples, this appeared to reduce the porosity and permeability by cementing microfractures (quartz veins in Fig.…”

Section: Effect Of Increased Depth On Physical Propertiessupporting

confidence: 66%

“…2; Table 1) has been described by Bignall (2009), Boseley et al (2012 and Chambefort et al (2014). The Tahorakuri Formation is the unit of primary interest in this study for several reasons.…”

Section: Geological Settingmentioning

confidence: 87%

“…The Tahorakuri Formation is a sequence of deposits between the Whakamaru Group ignimbrites and the Torlesse greywacke basement. At NGF, the Tahorakuri Formation comprises a thick pyroclastic sequence (~ 1000-1500 m thick) of primary tuffs, volcaniclastic (reworked) tuffs, and welded ignimbrites, overlain by sediments and tuffs in the northern and central part of the field (Chambefort et al 2014). In the north to northwest of the field a quartz-phyric tonalite intrusion was encountered in three boreholes.…”

Section: Geological Settingmentioning

confidence: 99%

“…This study also incorporates measurements of samples from this intrusion and the Tahorakuri volcaniclastic tuffs and ignimbrites. Dating of the Tahorakuri Formation (Eastwood 2013;Chambefort et al 2014) indicates the unit was deposited over 1.22 Ma. Figure 2 shows locations of cores used in this study.…”

Section: Geological Settingmentioning

confidence: 99%

“…Figure 2 shows formation thickness variability across the field. For the Tahorakuri pyroclastic succession, this ranges from 740 m in NM3 to 1655 m in NM8a (Chambefort et al 2014). Table 6 in the Appendix contains the stresses applied by the various formations of the NGF.…”

Section: Physical Propertiesmentioning

confidence: 99%

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Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

et al. 2018

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The Taupo Volcanic Zone (TVZ) hosts 23 geothermal fields, seven of which are currently utilised for power generation. Ngatamariki geothermal field (NGF) is one of the latest geothermal power generation developments in New Zealand (commissioned in 2013), located approximately 15 km north of Taupo. Samples of reservoir rocks were taken from the Tahorakuri Formation and Ngatamariki Intrusive Complex, from five wells at the NGF at depths ranging from 1354 to 3284 m. The samples were categorised according to whether their microstructure was pore or microfracture dominated. Image analysis of thin sections impregnated with an epoxy fluorescent dye was used to characterise and quantify the porosity structures and their physical properties were measured in the laboratory. Our results show that the physical properties of the samples correspond to the relative dominance of microfractures compared to pores. Microfracture-dominated samples have low connected porosity and permeability, and the permeability decreases sharply in response to increasing confining pressure. The pore-dominated samples have high connected porosity and permeability, and lower permeability decrease in response to increasing confining pressure. Samples with both microfractures and pores have a wide range of porosity and relatively high permeability that is moderately sensitive to confining pressure. A general trend of decreasing connected porosity and permeability associated with increasing dry bulk density and sonic velocity occurs with depth; however, variations in these parameters are more closely related to changes in lithology and processes such as dissolution and secondary veining and re-crystallisation. This study provides the first broad matrix permeability characterisation of rocks from depth at Ngatamariki, providing inputs for modelling of the geothermal system. We conclude that the complex response of permeability to confining pressure is in part due to the intricate dissolution, veining, and recrystallization textures of many of these rocks that lead to a wide variety of pore shapes and sizes. While the laboratory results are relevant only to similar rocks in the Taupo Volcanic Zone, the relationships they highlight are applicable to other geothermal fields, as well as rock mechanic applications to, for example, aspects of volcanology, landslide stabilisation, mining, and tunnelling at depth.

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Section: Effect Of Increased Depth On Physical Propertiessupporting

confidence: 66%

Section: Geological Settingmentioning

confidence: 87%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Physical Propertiesmentioning

confidence: 99%

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Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

et al. 2018

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Evidence for tectonic, lithologic, and thermal controls on fracture system geometries in an andesitic high‐temperature geothermal field

et al. 2017

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Analysis of fracture orientation, spacing, and thickness from acoustic borehole televiewer (BHTV) logs and cores in the andesite‐hosted Rotokawa geothermal reservoir (New Zealand) highlights potential controls on the geometry of the fracture system. Cluster analysis of fracture orientations indicates four fracture sets. Probability distributions of fracture spacing and thickness measured on BHTV logs are estimated for each fracture set, using maximum likelihood estimations applied to truncated size distributions to account for sampling bias. Fracture spacing is dominantly lognormal, though two subordinate fracture sets have a power law spacing. This difference in spacing distributions may reflect the influence of the andesitic sequence stratification (lognormal) and tectonic faults (power law). Fracture thicknesses of 9–30 mm observed in BHTV logs, and 1–3 mm in cores, are interpreted to follow a power law. Fractures in thin sections (∼5 μm thick) do not fit this power law distribution, which, together with their orientation, reflect a change of controls on fracture thickness from uniform (such as thermal) controls at thin section scale to anisotropic (tectonic) at core and BHTV scales of observation. However, the ∼5% volumetric percentage of fractures within the rock at all three scales suggests a self‐similar behavior in 3‐D. Power law thickness distributions potentially associated with power law fluid flow rates, and increased connectivity where fracture sets intersect, may cause the large permeability variations that occur at hundred meter scales in the reservoir. The described fracture geometries can be incorporated into fracture and flow models to explore the roles of fracture connectivity, stress, and mineral precipitation/dissolution on permeability in such andesite‐hosted geothermal systems.

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Rapid Evolution of Subduction‐Related Continental Intraarc Rifts: The Taupo Rift, New Zealand

et al. 2017

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The evolution of the continental intraarc Taupo Rift in the North Island, New Zealand, is rapid, significantly faster than comparative intracontinental rifts such as the African Rifts. Based on our faulting data and published geological, geophysical, and borehole data, we show that activity in the ~2 Ma Taupo Rift has rapidly and asymmetrically narrowed via inward and eastward migration of faulting (at rates of approximately 30 km Myr−1 and 15 km Myr−1, respectively) and has propagated southward along its axis ~70 km in 350 kyr. The loci of voluminous volcanic eruptions and active faulting are correlated in time and space, suggesting that a controlling factor in the rapid rift narrowing is the presence of large shallow heterogeneities in the crust, such as large rhyolitic magma bodies generated by subduction processes, which weaken the crust and localize deformation. Eastward migration of faulting also follows the eastward migration of the volcanic arc which may be related to rollback of the Pacific crust slab at the Hikurangi subduction zone. Southward propagation of the rift is linked with southward migration of the Hikurangi Plateau/Chatham Rise subduction point and occurs episodically aided by stress changes associated with voluminous local volcanism. The large magma supply during early continental intraarc rift stages explains faster evolution (from tectonic to magmatic) than intracontinental rifts. However, the fast changes in magma supply from the subduction zone can also lead to evolution reversals (more evolved magmatic stages reverting to less evolved tectonic stages), rift cessation, and thus failed continental breakup.

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Stratigraphy and structure of the Ngatamariki geothermal system from new zircon U–Pb geochronology: Implications for Taupo Volcanic Zone evolution

Cited by 80 publications

References 50 publications

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

Matrix permeability of reservoir rocks, Ngatamariki geothermal field, Taupo Volcanic Zone, New Zealand

Evidence for tectonic, lithologic, and thermal controls on fracture system geometries in an andesitic high‐temperature geothermal field

Rapid Evolution of Subduction‐Related Continental Intraarc Rifts: The Taupo Rift, New Zealand

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