title: Possible Jurassic age for part of Rakaia Terrane: implications for tectonic development of the Torlesse accretionary prism

authors: Kamp, Peter J.J.

subjects: Torlesse Complex

abstract: Greywacke sandstone and argillite beds comprising Rakaia Terrane (Torlesse Complex) in mid Canterbury, South Island, New Zealand, are widely regarded as Late Triassic (Norian) in age based on the occurrence of Torlessia trace fossils, Monotis, and other taxa. This paleontological age assignment is tested using published 40Ar/39Ar mica and U-Pb zircon ages for these rocks and published and new zircon fission track (FT) ages. The youngest U-Pb zircon ages in the Rakaia Terrane rocks in mid Canterbury are Norian, whereas 10-20% of the 40Ar/39Ar muscovite ages are younger than Norian. Numerical modelling of these mica ages shows that they cannot have originated from partial thermal overprinting in the Torlesse prism if the thermal maximum was short-lived and early in the prism history (210-190 Ma), as commonly inferred for these rocks. The young component of mica ages could, however, be explained by extended residence (200-100 Ma) at 265-290deg.C in the prism. Early Jurassic (c. 189 Ma) zircon FT ages for sandstone beds from Arthur's Pass, the Rakaia valley, and the Hermitage (Mt Cook) are interpreted not to have experienced maximum temperatures above 210deg.C, and therefore cannot have been reduced as a result of partial annealing in the Torlesse prism. This is based on identification of a fossil Cretaceous, zircon FT, partial annealing zone in low-grade schists to the west, and the characteristics of the age data. The Early Jurassic zircon FT ages and the young component of 40Ar/39Ar mica ages are regarded therefore as detrital ages reflecting cooling in the source area, and constrain the maximum depositional age of parts of the Rakaia Terrane in mid Canterbury. The zircon FT data also show the initiation (c. 100 Ma) of marked and widespread Late Cretaceous cooling of Rakaia Terrane throughout Canterbury, which is attributed to uplift and erosion of inboard parts of the Torlesse prism due to continuing subduction accretion at its toe. 
The critical wedge concept is proposed as a new framework for investigating the development of the Torlesse Complex. The Rakaia Terrane may have formed the core of an accretionary wedge imbricated against the New Zealand margin during the Middle or Late Jurassic. Late Jurassic nonmarine sediments (e.g., Clent Hills Formation) accumulated upon the inner parts of the prism as it enlarged, emerged, and continued to be imbricated. Exhumation of Otago Schist from c. 135 Ma may mark the development of a balance (steady state) between sediments entering the prism at the toe and material exiting at the inboard margin. The enlargement of the area of exhumation to all of Canterbury from c. 100 Ma may reflect a dynamic response to widening of the prism through the accretion of Cretaceous sediments. The model of a dynamic critical wedge may help to explain the various expressions of the Rangitata Orogeny.

text: Possible Jurassic age for part of Rakaia Terrane: implications for tectonic development of the Torlesse accretionary prism Greywacke sandstone and argillite beds comprising Rakaia Terrane (Torlesse Complex) in mid Canterbury, South Island, New Zealand, are widely regarded as Late Triassic (Norian) in age based on the occurrence of Torlessia trace fossils, Monotis, and other taxa. This paleontological age assignment is tested using published 40Ar/39Ar mica and U-Pb zircon ages for these rocks and published and new zircon fission track (FT) ages. The youngest U-Pb zircon ages in the Rakaia Terrane rocks in mid Canterbury are Norian, whereas 10-20% of the 40Ar/39Ar muscovite ages are younger than Norian. Numerical modelling of these mica ages shows that they cannot have originated from partial thermal overprinting in the Torlesse prism if the thermal maximum was short-lived and early in the prism history (210-190 Ma), as commonly inferred for these rocks. The young component of mica ages could, however, be explained by extended residence (200-100 Ma) at 265-290deg.C in the prism. Early Jurassic (c. 189 Ma) zircon FT ages for sandstone beds from Arthur's Pass, the Rakaia valley, and the Hermitage (Mt Cook) are interpreted not to have experienced maximum temperatures above 210deg.C, and therefore cannot have been reduced as a result of partial annealing in the Torlesse prism. This is based on identification of a fossil Cretaceous, zircon FT, partial annealing zone in low-grade schists to the west, and the characteristics of the age data. The Early Jurassic zircon FT ages and the young component of 40Ar/39Ar mica ages are regarded therefore as detrital ages reflecting cooling in the source area, and constrain the maximum depositional age of parts of the Rakaia Terrane in mid Canterbury. The zircon FT data also show the initiation (c. 100 Ma) of marked and widespread Late Cretaceous cooling of Rakaia Terrane throughout Canterbury, which is attributed to uplift and erosion of inboard parts of the Torlesse prism due to continuing subduction accretion at its toe. 
The critical wedge concept is proposed as a new framework for investigating the development of the Torlesse Complex. The Rakaia Terrane may have formed the core of an accretionary wedge imbricated against the New Zealand margin during the Middle or Late Jurassic. Late Jurassic nonmarine sediments (e.g., Clent Hills Formation) accumulated upon the inner parts of the prism as it enlarged, emerged, and continued to be imbricated. Exhumation of Otago Schist from c. 135 Ma may mark the development of a balance (steady state) between sediments entering the prism at the toe and material exiting at the inboard margin. The enlargement of the area of exhumation to all of Canterbury from c. 100 Ma may reflect a dynamic response to widening of the prism through the accretion of Cretaceous sediments. The model of a dynamic critical wedge may help to explain the various expressions of the Rangitata Orogeny.

year: 2001

title: What’s that bug? Community participation in biosecurity in Mount Maunganui, New Zealand

authors: Payne, Penny R.

abstract: Biosecurity is essential to protect against the negative effects of non-native invasive species. As part of the government’s ‘Biosecurity 2025’ Initiative to enlist all New Zealanders as biosecurity risk managers, Tauranga Moana has been named the ‘biosecurity capital’ of New Zealand. The initiative will involve large-scale citizen science, for reporting and management of pest and disease threats. In this context we measured baseline awareness, perceptions and behaviour around biosecurity among two key groups of respondents, the local community at Mount Maunganui (surrounding Tauranga’s port) and school children. An online survey was completed by 324 members of the local community, while 120 school children completed a survey about their biosecurity knowledge and behaviours after using a biosecurity education kit. Results indicate that while both groups report a relatively high level of understanding about the concept of biosecurity, and acknowledge it as extremely important, knowledge of current pest threats and correct biosecurity behaviours could be improved. Mount Maunganui community members rate their understanding of biosecurity as better than the average New Zealander, but are less likely to have taken regular biosecurity action in the past year. For school children, improved biosecurity efforts could be evidenced by more active pest monitoring, and greater discussion about biosecurity outside of school (e.g. with their family at home). Key enablers for achieving more impactful citizen science for biosecurity among these groups are targeted education, and practical advice about what they can do to help.

text: What’s that bug? Community participation in biosecurity in Mount Maunganui, New Zealand Biosecurity is essential to protect against the negative effects of non-native invasive species. As part of the government’s ‘Biosecurity 2025’ Initiative to enlist all New Zealanders as biosecurity risk managers, Tauranga Moana has been named the ‘biosecurity capital’ of New Zealand. The initiative will involve large-scale citizen science, for reporting and management of pest and disease threats. In this context we measured baseline awareness, perceptions and behaviour around biosecurity among two key groups of respondents, the local community at Mount Maunganui (surrounding Tauranga’s port) and school children. An online survey was completed by 324 members of the local community, while 120 school children completed a survey about their biosecurity knowledge and behaviours after using a biosecurity education kit. Results indicate that while both groups report a relatively high level of understanding about the concept of biosecurity, and acknowledge it as extremely important, knowledge of current pest threats and correct biosecurity behaviours could be improved. Mount Maunganui community members rate their understanding of biosecurity as better than the average New Zealander, but are less likely to have taken regular biosecurity action in the past year. For school children, improved biosecurity efforts could be evidenced by more active pest monitoring, and greater discussion about biosecurity outside of school (e.g. with their family at home). Key enablers for achieving more impactful citizen science for biosecurity among these groups are targeted education, and practical advice about what they can do to help.

year: 2023-02

title: The reform of Maori land tenure and the quest for sustainability in New Zealand

authors: Jay, Grace Mairi M.

subjects: geography

abstract: Many of the countries of the Pacific region (including Australia and New Zealand) have a British colonial legacy. This history has had wide implications for the development of the region: economically, politically and socially. The cadastral (property based) systems in these countries have been influenced by British land conveyance and registration practices, and by colonial history. To date, Australia and new Zealand are still trying to resolve land tenure and information problems which are steeped in historical and ethnic dimensions. Land is the single most important factor for Maori development in New Zealand, and has great implications for the development of this country.

text: The reform of Maori land tenure and the quest for sustainability in New Zealand Many of the countries of the Pacific region (including Australia and New Zealand) have a British colonial legacy. This history has had wide implications for the development of the region: economically, politically and socially. The cadastral (property based) systems in these countries have been influenced by British land conveyance and registration practices, and by colonial history. To date, Australia and new Zealand are still trying to resolve land tenure and information problems which are steeped in historical and ethnic dimensions. Land is the single most important factor for Maori development in New Zealand, and has great implications for the development of this country.

year: 1997