Pub Date : 2022-01-02DOI: 10.1080/00288306.2022.2048032
L. Strachan, J. Bailleul, K. J. Bland, A. Orpin, A. McArthur
ABSTRACT This is the first of a two-part New Zealand Journal of Geology and Geophysics Special Issue that focuses on improving our understanding of sedimentary systems of the Hikurangi Subduction Margin, Aotearoa-New Zealand. It is amongst the world’s youngest and most accessible active subduction margins and its sedimentary basins preserve a rich history of inception and ongoing evolution, spanning trench to back-arc positions. These sediments and sedimentary rocks provide a record of surface processes from the latest Paleogene to today, and reflect the spatio-temporal variability of the effects of subduction, seismicity, volcanism, evolving sediment sources, routing systems and processes, all imprinted upon by glacio-eustatic sea-level changes. The papers in this volume focus on the interplay between controlling mechanisms and the dynamics of these systems, from both onshore and offshore sedimentary environments. This issue is divided into two themes, distinguished by geological age: 1. Miocene Sedimentary Systems and intra-slope basin evolution, and 2. Insights from Quaternary Sedimentary Systems from the trench to the inner margin. Collectively, these papers represent significant advances into our understanding of sedimentary systems within the Hikurangi Subduction Margin, with innovative results that may find applications to other convergent settings.
{"title":"Understanding sedimentary systems and processes of the Hikurangi Subduction Margin; from Trench to Back-Arc. Volume 1","authors":"L. Strachan, J. Bailleul, K. J. Bland, A. Orpin, A. McArthur","doi":"10.1080/00288306.2022.2048032","DOIUrl":"https://doi.org/10.1080/00288306.2022.2048032","url":null,"abstract":"ABSTRACT This is the first of a two-part New Zealand Journal of Geology and Geophysics Special Issue that focuses on improving our understanding of sedimentary systems of the Hikurangi Subduction Margin, Aotearoa-New Zealand. It is amongst the world’s youngest and most accessible active subduction margins and its sedimentary basins preserve a rich history of inception and ongoing evolution, spanning trench to back-arc positions. These sediments and sedimentary rocks provide a record of surface processes from the latest Paleogene to today, and reflect the spatio-temporal variability of the effects of subduction, seismicity, volcanism, evolving sediment sources, routing systems and processes, all imprinted upon by glacio-eustatic sea-level changes. The papers in this volume focus on the interplay between controlling mechanisms and the dynamics of these systems, from both onshore and offshore sedimentary environments. This issue is divided into two themes, distinguished by geological age: 1. Miocene Sedimentary Systems and intra-slope basin evolution, and 2. Insights from Quaternary Sedimentary Systems from the trench to the inner margin. Collectively, these papers represent significant advances into our understanding of sedimentary systems within the Hikurangi Subduction Margin, with innovative results that may find applications to other convergent settings.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2022-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49298913","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-22DOI: 10.1080/00288306.2021.1995007
J. Griffin, M. Stirling, D. Barrell, E. J. van den Berg, E. Todd, Ross Nicolls, Ningsheng Wang
ABSTRACT We present the first paleoseismic investigation of the Hyde Fault, one of a series of north-east striking reverse faults within the Otago range and basin province in southern New Zealand. Surface traces of the fault and associated geomorphology were mapped using a lidar digital elevation model and field investigations. Trenches were excavated at two sites across fault scarps on alluvial fan surfaces. The trenches revealed stratigraphic evidence for four surface-rupturing earthquakes. Optically stimulated luminescence dating constrains the timing of these events to around 47.2 ka (37.5–56.7 ka at 95% confidence), 34.6 ka (24.7–46.4 ka), 23.5 ka (19.7–27.3 ka) and 10.5 ka (7.9–13.1 ka). We obtain a mean inter-event time of 12.4 kyr (2.3–23.9 kyr at 95% confidence) and the slip rate is estimated to be 0.22 mm/yr (0.15–0.3 mm/yr). We do not find evidence to suggest that earthquake recurrence on the Hyde Fault is episodic, in contrast to other well-studied faults within Otago, suggesting diverse recurrence styles may co-exist in the same fault system. This poses challenges for characterising the seismic hazard potential of faults in the region, particularly when paleoearthquake records are limited to the most recent few events.
海德断裂是新西兰南部奥塔哥山脉和盆地省一系列东北走向逆断层之一，我们对其进行了首次古地震调查。利用激光雷达数字高程模型和实地调查绘制了断层和相关地貌的表面轨迹。在冲积扇表面断层陡坡上的两个地点开挖了沟槽。这些海沟揭示了四次地表破裂地震的地层证据。光激发发光测年将这些事件的时间限制在47.2 ka(95%置信度37.5-56.7 ka)、34.6 ka (24.7-46.4 ka)、23.5 ka (19.7-27.3 ka)和10.5 ka (7.9-13.1 ka)左右。我们得到的平均事件间时间为12.4 kyr(95%置信度为2.3-23.9 kyr)，滑移率估计为0.22 mm/yr (0.15-0.3 mm/yr)。我们没有发现证据表明Hyde断层的地震复发是幕式的，与奥塔哥其他研究充分的断层相反，这表明不同的地震复发类型可能在同一断层系统中共存。这对描述该地区断层的潜在地震危险性提出了挑战，特别是当古地震记录仅限于最近的几个事件时。
{"title":"Paleoseismology of the Hyde Fault, Otago, New Zealand","authors":"J. Griffin, M. Stirling, D. Barrell, E. J. van den Berg, E. Todd, Ross Nicolls, Ningsheng Wang","doi":"10.1080/00288306.2021.1995007","DOIUrl":"https://doi.org/10.1080/00288306.2021.1995007","url":null,"abstract":"ABSTRACT We present the first paleoseismic investigation of the Hyde Fault, one of a series of north-east striking reverse faults within the Otago range and basin province in southern New Zealand. Surface traces of the fault and associated geomorphology were mapped using a lidar digital elevation model and field investigations. Trenches were excavated at two sites across fault scarps on alluvial fan surfaces. The trenches revealed stratigraphic evidence for four surface-rupturing earthquakes. Optically stimulated luminescence dating constrains the timing of these events to around 47.2 ka (37.5–56.7 ka at 95% confidence), 34.6 ka (24.7–46.4 ka), 23.5 ka (19.7–27.3 ka) and 10.5 ka (7.9–13.1 ka). We obtain a mean inter-event time of 12.4 kyr (2.3–23.9 kyr at 95% confidence) and the slip rate is estimated to be 0.22 mm/yr (0.15–0.3 mm/yr). We do not find evidence to suggest that earthquake recurrence on the Hyde Fault is episodic, in contrast to other well-studied faults within Otago, suggesting diverse recurrence styles may co-exist in the same fault system. This poses challenges for characterising the seismic hazard potential of faults in the region, particularly when paleoearthquake records are limited to the most recent few events.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2021-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44450630","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-14DOI: 10.1080/00288306.2021.1996401
P. Williams
ABSTRACT The hill country of west central North Island, west of Te Kuiti and Otorohanga, is recognised to be slowly uplifting and relatively stable. The New Zealand national seismic hazard model shows the area to be in a low-risk zone and the New Zealand active faults database recognises no active faults in the region. However, dated evidence provided by speleothems in a cave near Waitomo indicates the intermittent movement of the Okohua fault from before the Last Interglacial until around 38 kyrs ago. Evidence of older movement along the Waipa Fault near Te Kuiti is also apparent from the vertical displacement of the Ngaroma ignimbrite (1.55 Myrs) by about 150 m in the interval prior to the deposition of the Ongatiti ignimbrite at 1.21 Myrs. Net uplift in the West Waikato Hills and Ranges, by about 0.1 mm/yr in the Late Quaternary, is accommodated in a series of NNE-trending faults and transverse faults, resulting in a staircase of fault-bound blocks rising westwards from Waitomo to the western watershed of the Waipa basin. Geomorphologically fresh cliffed lineaments on the Okohua and Hikurangi faults convey evidence of mid to late Quaternary fault activity.
{"title":"Quaternary uplift and fault movement near Waitomo, North Island, New Zealand","authors":"P. Williams","doi":"10.1080/00288306.2021.1996401","DOIUrl":"https://doi.org/10.1080/00288306.2021.1996401","url":null,"abstract":"ABSTRACT The hill country of west central North Island, west of Te Kuiti and Otorohanga, is recognised to be slowly uplifting and relatively stable. The New Zealand national seismic hazard model shows the area to be in a low-risk zone and the New Zealand active faults database recognises no active faults in the region. However, dated evidence provided by speleothems in a cave near Waitomo indicates the intermittent movement of the Okohua fault from before the Last Interglacial until around 38 kyrs ago. Evidence of older movement along the Waipa Fault near Te Kuiti is also apparent from the vertical displacement of the Ngaroma ignimbrite (1.55 Myrs) by about 150 m in the interval prior to the deposition of the Ongatiti ignimbrite at 1.21 Myrs. Net uplift in the West Waikato Hills and Ranges, by about 0.1 mm/yr in the Late Quaternary, is accommodated in a series of NNE-trending faults and transverse faults, resulting in a staircase of fault-bound blocks rising westwards from Waitomo to the western watershed of the Waipa basin. Geomorphologically fresh cliffed lineaments on the Okohua and Hikurangi faults convey evidence of mid to late Quaternary fault activity.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2021-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42384057","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-12DOI: 10.1080/00288306.2021.1994425
Kate E. MacDonald, D. Hart, Sebastian J. Pitman
ABSTRACT Along the northeast coast of New Zealand’s South Island, a 7.8 Mw earthquake on the 14th of November 2016 induced instantaneous uplift of approximately 1 m around the Kaikōura Peninsula. This paper documents a unique field study examining short-term responses in the Mixed Sand and Gravel (MSG) beaches of Kaikōura to a relative sea level fall as a result of this event. We present two conceptual response pathway models which consider the pre-earthquake trends of 18 coastal sites, and two surveys taken over a 22 month period following the earthquake to define the short-term response of MSG beaches to instantaneous relative sea level fall. This study found MSG beach responses vary strongly according to their pre-quake sediment supply, source connectivity and open coast exposure characteristics. Overall, there were two predominant trends in which the beaches were responding in the short-term post-earthquake environment: accretionary profiles and erosional profiles. The difference between these two profile response types can be summarised as pre-earthquake erosional profiles were found to be retreating to pre-earthquake extents 22 months post-earthquake, whilst pre-earthquake accretional and dynamic beaches had an increased or stable trend which promoted stability or growth in beach volume post relative sea level fall.
{"title":"Geomorphic responses of uplifted mixed sand and gravel beaches: combining short-term observations from Kaikōura, New Zealand with longer-term evidence","authors":"Kate E. MacDonald, D. Hart, Sebastian J. Pitman","doi":"10.1080/00288306.2021.1994425","DOIUrl":"https://doi.org/10.1080/00288306.2021.1994425","url":null,"abstract":"ABSTRACT Along the northeast coast of New Zealand’s South Island, a 7.8 Mw earthquake on the 14th of November 2016 induced instantaneous uplift of approximately 1 m around the Kaikōura Peninsula. This paper documents a unique field study examining short-term responses in the Mixed Sand and Gravel (MSG) beaches of Kaikōura to a relative sea level fall as a result of this event. We present two conceptual response pathway models which consider the pre-earthquake trends of 18 coastal sites, and two surveys taken over a 22 month period following the earthquake to define the short-term response of MSG beaches to instantaneous relative sea level fall. This study found MSG beach responses vary strongly according to their pre-quake sediment supply, source connectivity and open coast exposure characteristics. Overall, there were two predominant trends in which the beaches were responding in the short-term post-earthquake environment: accretionary profiles and erosional profiles. The difference between these two profile response types can be summarised as pre-earthquake erosional profiles were found to be retreating to pre-earthquake extents 22 months post-earthquake, whilst pre-earthquake accretional and dynamic beaches had an increased or stable trend which promoted stability or growth in beach volume post relative sea level fall.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2021-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43222901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-08DOI: 10.1080/00288306.2021.1996402
Jamie Cudby, J. Scott, D. Craw, Mark Hesson, C. Rufaut
ABSTRACT The historic Come-In-Time gold mine was developed in a ∼100*100 m area of the >7 km long orogenic Rise and Shine Shear Zone in Otago Schist. The oxidation of hydrothermal ankeritic and auriferous arsenopyrite and pyrite-bearing Otago Schist beneath a regional Miocene unconformity resulted in replacement of sulphides and ankerite by arsenic (As)-bearing ferric oxyhydroxide. The As-bearing ferric oxyhydroxide is mainly concentrated in and near the original mineralisation sites, especially shears, but mobilisation into post-mineralisation joints and fractures has redistributed As on a metre scale. Gold was liberated from sulphides during oxidation and aggregated by supergene oxidation processes into a smaller number of larger particles (mm scale) that are intimately intergrown with As-bearing ferric oxyhydroxide, especially in shears. Eluvial gold in proximal immature debris includes variably rounded supergene particles eroded from nearby, and some externally derived detrital flakes from previously overlying Miocene sediments. Some eluvial gold is trapped in fine sediments by lichen on outcrops. The hydrothermal As-Au relationship has therefore been broadly maintained through oxidation of rocks at the metre scale but Au concentrations have been locally enhanced in the surficial environment.
{"title":"Surficial redistribution of gold and arsenic from the Rise and Shine Shear Zone, Otago, New Zealand","authors":"Jamie Cudby, J. Scott, D. Craw, Mark Hesson, C. Rufaut","doi":"10.1080/00288306.2021.1996402","DOIUrl":"https://doi.org/10.1080/00288306.2021.1996402","url":null,"abstract":"ABSTRACT\u0000 The historic Come-In-Time gold mine was developed in a ∼100*100 m area of the >7 km long orogenic Rise and Shine Shear Zone in Otago Schist. The oxidation of hydrothermal ankeritic and auriferous arsenopyrite and pyrite-bearing Otago Schist beneath a regional Miocene unconformity resulted in replacement of sulphides and ankerite by arsenic (As)-bearing ferric oxyhydroxide. The As-bearing ferric oxyhydroxide is mainly concentrated in and near the original mineralisation sites, especially shears, but mobilisation into post-mineralisation joints and fractures has redistributed As on a metre scale. Gold was liberated from sulphides during oxidation and aggregated by supergene oxidation processes into a smaller number of larger particles (mm scale) that are intimately intergrown with As-bearing ferric oxyhydroxide, especially in shears. Eluvial gold in proximal immature debris includes variably rounded supergene particles eroded from nearby, and some externally derived detrital flakes from previously overlying Miocene sediments. Some eluvial gold is trapped in fine sediments by lichen on outcrops. The hydrothermal As-Au relationship has therefore been broadly maintained through oxidation of rocks at the metre scale but Au concentrations have been locally enhanced in the surficial environment.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2021-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46905143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-03DOI: 10.1080/00288306.2021.1986727
Thomas Brough, A. Nicol, T. Stahl, J. Pettinga, R. Dissen, D. Clark, N. Khajavi, K. Pedley, R. Langridge, Ningsheng Wang
ABSTRACT The 2016 MW 7.8 Kaikōura Earthquake nucleated on The Humps fault, which ruptured across the Emu Plain in North Canterbury. The paleoearthquake history of the fault was poorly constrained prior to the 2016 earthquake. To determine the timing and single-event displacements (SED) of earthquakes on the fault we use Optically Stimulated Luminescence (OSL) and radiocarbon dates of faulted stratigraphy and analysis of faulting (i.e. geometry and slip) at the McLean-1 trench site. At the trench the fault trace trends east–west and primarily accommodated right-lateral strike-slip in 2016 (2 ± 0.2 m strike slip and 0.35 ± 0.05 m vertical slip northside downthrow). The Humps fault is more seismically active than previously thought and accrued slip during at least six surface rupturing paleoearthquakes. The timing of these earthquakes was: 9.8–15.3 ka BP (Event 1), 8.6–11.5 ka BP (Event 2), 8.1–10.9 ka BP (Event 3), 6.0–8.6 ka BP (Event 4), 1840 AD to 4.5 ka (Event 5), and 2016 AD (Event 6). These earthquakes have a mean recurrence interval of 1.8–3.4 kyr and could have recurrence intervals up to ~9 kyr. Kaikōura-type ruptures could occur as frequently as every ∼2 kyr and maybe longer if The Humps fault rupture geometries are not characteristic.
摘要：2016年凯库拉7.8兆瓦地震以驼峰断层为核，该断层在坎特伯雷北部的埃穆平原断裂。在2016年地震之前，断层的古地震历史受到了很差的约束。为了确定断层上地震的时间和单次事件位移（SED），我们使用了光学激发发光（OSL）和断层地层学的放射性碳年代，以及McLean-1海沟现场断层（即几何结构和滑动）的分析。在海沟处，断层走向为东西走向，主要适应2016年的右侧走滑（2 ± 0.2 m走滑和0.35 ± 0.05 m垂直滑动北侧下降）。Humps断层的地震活动比以前认为的要活跃，在至少六次地表破裂的古地震中发生了滑动。这些地震发生的时间为：9.8–15.3 ka BP（事件1），8.6–11.5 ka BP（事件2），8.1–10.9 ka BP（事件3），6.0–8.6 ka BP（事件4），公元1840年至4.5年 ka（事件5）和2016 AD（事件6）。这些地震的平均重现期为1.8-3.4 kyr，复发间隔可达~9 kyr。Kaikōura型破裂的频率可能高达每2次 kyr，如果驼峰断层破裂几何形状不是特征性的，则可能更长。
{"title":"Paleoseismicity of the western Humps fault on the Emu Plain, North Canterbury, New Zealand","authors":"Thomas Brough, A. Nicol, T. Stahl, J. Pettinga, R. Dissen, D. Clark, N. Khajavi, K. Pedley, R. Langridge, Ningsheng Wang","doi":"10.1080/00288306.2021.1986727","DOIUrl":"https://doi.org/10.1080/00288306.2021.1986727","url":null,"abstract":"ABSTRACT The 2016 MW 7.8 Kaikōura Earthquake nucleated on The Humps fault, which ruptured across the Emu Plain in North Canterbury. The paleoearthquake history of the fault was poorly constrained prior to the 2016 earthquake. To determine the timing and single-event displacements (SED) of earthquakes on the fault we use Optically Stimulated Luminescence (OSL) and radiocarbon dates of faulted stratigraphy and analysis of faulting (i.e. geometry and slip) at the McLean-1 trench site. At the trench the fault trace trends east–west and primarily accommodated right-lateral strike-slip in 2016 (2 ± 0.2 m strike slip and 0.35 ± 0.05 m vertical slip northside downthrow). The Humps fault is more seismically active than previously thought and accrued slip during at least six surface rupturing paleoearthquakes. The timing of these earthquakes was: 9.8–15.3 ka BP (Event 1), 8.6–11.5 ka BP (Event 2), 8.1–10.9 ka BP (Event 3), 6.0–8.6 ka BP (Event 4), 1840 AD to 4.5 ka (Event 5), and 2016 AD (Event 6). These earthquakes have a mean recurrence interval of 1.8–3.4 kyr and could have recurrence intervals up to ~9 kyr. Kaikōura-type ruptures could occur as frequently as every ∼2 kyr and maybe longer if The Humps fault rupture geometries are not characteristic.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2021-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42482945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-11-03DOI: 10.1080/00288306.2021.1987280
D. Craw, C. Rufaut, G. Kerr, Dhanashree Pillai
ABSTRACT Evaporative mineral encrustations have formed on bare substrates at three different sites in the Maniototo basin. Two sites, at Patearoa and Belmont have salts derived primarily from marine aerosols. The Patearoa site has developed on clay-rich pans formed on a terrace eroded by the Taieri River into clay-altered schist basement, and dissolution of albite from altered schist has resulted in precipitation of sodium carbonate with halite, at pH∼10. The Belmont site lies on the flat distal part of an active alluvial fan, and halite-dominated salt encrustations develop on thin dry crusts through capillary action from below. At the nearby Hamiltons historic placer gold mine, excavations exposed clay-altered schist basement beneath Eocene auriferous sediments. Highly fractured and hydrothermally altered fault zones dominate basement, with secondary ankeritic carbonate and pyrite. Water-rock interaction of shallow groundwater in the basement leads to enrichment in dissolved Mg and sulphate that overshadows the marine aerosol components, and evaporative encrustations are dominated by Mg-rich minerals including brucite and epsomite. The halite-dominated sites host rare halophyte ecosystems, but progressive colonisation by adventive species will eventually cover the bare saline substrates. Similar colonisation at the Hamiltons site will result in natural rehabilitation of the abandoned mine site.
{"title":"Contrasting geology and mineralogy of evaporative encrustations in salt-tolerant ecosystems, Maniototo basin, Central Otago, New Zealand","authors":"D. Craw, C. Rufaut, G. Kerr, Dhanashree Pillai","doi":"10.1080/00288306.2021.1987280","DOIUrl":"https://doi.org/10.1080/00288306.2021.1987280","url":null,"abstract":"ABSTRACT Evaporative mineral encrustations have formed on bare substrates at three different sites in the Maniototo basin. Two sites, at Patearoa and Belmont have salts derived primarily from marine aerosols. The Patearoa site has developed on clay-rich pans formed on a terrace eroded by the Taieri River into clay-altered schist basement, and dissolution of albite from altered schist has resulted in precipitation of sodium carbonate with halite, at pH∼10. The Belmont site lies on the flat distal part of an active alluvial fan, and halite-dominated salt encrustations develop on thin dry crusts through capillary action from below. At the nearby Hamiltons historic placer gold mine, excavations exposed clay-altered schist basement beneath Eocene auriferous sediments. Highly fractured and hydrothermally altered fault zones dominate basement, with secondary ankeritic carbonate and pyrite. Water-rock interaction of shallow groundwater in the basement leads to enrichment in dissolved Mg and sulphate that overshadows the marine aerosol components, and evaporative encrustations are dominated by Mg-rich minerals including brucite and epsomite. The halite-dominated sites host rare halophyte ecosystems, but progressive colonisation by adventive species will eventually cover the bare saline substrates. Similar colonisation at the Hamiltons site will result in natural rehabilitation of the abandoned mine site.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2021-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43901613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-26DOI: 10.1080/00288306.2021.2000438
Alistair Stronach, T. Stern
ABSTRACT A new basin depth map for the Wellington Central Business District shows a maximum depth of 540 m near the Wellington Stadium. Our new basin geometry constraints are from a residual gravity anomaly study, based on ∼600 new gravity observations. Residual gravity anomalies are as large as −6.2 mGal with uncertainties <0.1 mGal. Two-dimensional gravity models constrained by boreholes that intersect basement are used to generate the basin depth map. Our maximum depth is twice that previously estimated from other geological and geophysical criteria. An onshore extension of the recently discovered Aotea Fault on the western side of Mt Victoria, is also interpreted from the gravity data. A maximum basement offset of up to 130 m and gravity anomaly gradients up to 8 mGal/km are observed across the fault. A secondary splay off the main Aotea Fault is identified in the NW corner of Mt Victoria, and a possible extension to the Lambton Fault is identified beneath the Wellington Railway Station. This new basin depth and fault trace data provide valuable constraints to models of seismic hazard assessment for Wellington City.
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Pub Date : 2021-10-25DOI: 10.1080/00288306.2021.1990088
J. Dutilleul, S. Bourlange, Y. Géraud, T. Reuschlé
ABSTRACT Several mechanisms involving excess pore pressure related to gas hydrate have been proposed to explain active creeping at landslides such as the north Hikurangi margin Tuaheni Landslide Complex (TLC). Cores and logging data were retrieved by the International Ocean Discovery Program (IODP) Expeditions 372 and 375 from the South TLC at Site U1517. Here, the evolutions of porosity, pore structure and permeability are determined to assess the compaction state in the landslide and compare it with that of the undeformed sequence at Site U1519. Although no evidence of gas hydrate in the landslide at Site U1517 was identified by the cruise, zones suspected to host gas hydrates below the landslide or at Site U1519 are characterised by higher porosity, pore diameter and permeability. We show that most of the sedimentary section is in hydrostatic conditions, except the base of the TLC at Site U1517 and a zone below the base of the gas hydrate stability zone at Site U1519. These zones might be candidates for excess pore pressure build-up. There is no obvious evidence of the involvement of gas hydrate in active creeping at the TLC, which is more likely induced by hydrogeomechanical processes.
{"title":"Porosity and permeability evolution in the Tuaheni Landslide Complex at Hikurangi margin from IODP Sites U1517 and U1519","authors":"J. Dutilleul, S. Bourlange, Y. Géraud, T. Reuschlé","doi":"10.1080/00288306.2021.1990088","DOIUrl":"https://doi.org/10.1080/00288306.2021.1990088","url":null,"abstract":"ABSTRACT Several mechanisms involving excess pore pressure related to gas hydrate have been proposed to explain active creeping at landslides such as the north Hikurangi margin Tuaheni Landslide Complex (TLC). Cores and logging data were retrieved by the International Ocean Discovery Program (IODP) Expeditions 372 and 375 from the South TLC at Site U1517. Here, the evolutions of porosity, pore structure and permeability are determined to assess the compaction state in the landslide and compare it with that of the undeformed sequence at Site U1519. Although no evidence of gas hydrate in the landslide at Site U1517 was identified by the cruise, zones suspected to host gas hydrates below the landslide or at Site U1519 are characterised by higher porosity, pore diameter and permeability. We show that most of the sedimentary section is in hydrostatic conditions, except the base of the TLC at Site U1517 and a zone below the base of the gas hydrate stability zone at Site U1519. These zones might be candidates for excess pore pressure build-up. There is no obvious evidence of the involvement of gas hydrate in active creeping at the TLC, which is more likely induced by hydrogeomechanical processes.","PeriodicalId":49752,"journal":{"name":"New Zealand Journal of Geology and Geophysics","volume":null,"pages":null},"PeriodicalIF":2.2,"publicationDate":"2021-10-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45233873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-10-11DOI: 10.1080/00288306.2021.1985529
Ruth M. Corkill, G. Turner
ABSTRACT Palaeomagnetic records from three cores of lake sediment have been merged, producing a new Holocene geomagnetic secular variation record for northern New Zealand. The cores are from Lake Pupuke, a maar lake in Auckland Volcanic Field (AVF). They contain tephra from Rangitoto Volcano (530 ± 10 yr BP), Taupō (1718 ± 10 yr BP), Tūhua/Mayor Island (7637 ± 100 yr BP) and Rotomā tephra from Ōkataina Volcanic Centre (9423 ± 120 yr BP). These tephra dates are supplemented by selected radiocarbon age estimates. The cores were correlated using tephra and fine-scale variations in magnetic susceptibility. The natural remanent magnetisation is strong, stable and carried by fine-grained titanomagnetite from AVF’s basaltic volcanoes. The resulting palaeosecular variation (PSV) record spans from 10,000 to 1500 yr BP. It shows well-defined, millennial-scale swings in direction between 10,000 and 8000 yr BP and between 4000 and 1500 yr BP, while between 8000 and 4000 yr BP variations are of higher frequency and lower amplitude and centre on the geocentric axial dipole field direction. This is in excellent agreement with published PSV records from Mavora Lakes, 1000 km further south, indicating the regional nature of PSV – resulting from broad-scale changes in the circulation of conducting iron-rich fluid of Earth’s outer core.
摘要将三个湖泊沉积物核心的古地磁记录合并，为新西兰北部创造了一个新的全新世地磁长期变化记录。岩芯来自奥克兰火山场（AVF）的马尔湖Pupuke湖。它们包含Rangitoto火山的火山灰岩（530 ± 10 年BP），陶（1718年） ± 10 yr BP），图华/马约尔岛（7637 ± 100 yr BP）和来自Ōkataina火山中心的Rotomātephra（9423 ± 120 年BP）。这些tephra日期由选定的放射性碳年龄估计补充。使用tephra和磁化率的精细尺度变化对岩心进行了关联。天然残余磁化强度强、稳定，由AVF玄武岩火山的细粒钛磁铁矿携带。由此产生的古长期变化（PSV）记录跨度从10000到1500 年BP。它显示了明确的千禧一代规模在10000到8000之间的方向波动 年BP介于4000和1500之间 年BP，在8000到4000之间 yr BP变化具有较高的频率和较低的振幅，并且以地心轴向偶极子场方向为中心。这与Mavora Lakes公布的PSV记录非常一致，1000 再往南公里，表明PSV的区域性——这是由地核富含铁的导电流体循环的大范围变化引起的。
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