title: Southwest Pacific Absolute Plate Kinematic Reconstruction Reveals Major Cenozoic Tonga-Kermadec Slab Dragging

authors: van de Lagemaat, Suzanna H.A.

subjects: Science & Technology

abstract: Tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench‐parallel slab motion through the mantle, recently defined as a form of “slab dragging.” We investigate here long‐term slab‐dragging components of the Tonga‐Kermadec subduction system driven by absolute Pacific plate motion. To this end we develop a kinematic restoration of Tonga‐Kermadec Trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle. Estimating Tonga‐Kermadec subduction initiation is challenging because another (New Caledonia) subduction zone existed during the Paleogene between the Australia and Pacific plates. We test partitioning of plate convergence across the Paleogene New Caledonia and Tonga‐Kermadec subduction zones against resulting mantle structure and show that most, if not all, Tonga‐Kermadec subduction occurred after ca. 30 Ma. Since then, Tonga‐Kermadec subduction has accommodated 1,700 to 3,500 km of subduction along the southern and northern ends of the trench, respectively. When placed in a mantle reference frame, the predominantly westward directed subduction evolved while the Tonga‐Kermadec Trench underwent ~1,200 km of northward absolute motion. We infer that the entire Tonga‐Kermadec slab was laterally transported through the mantle over 1,200 km. Such slab dragging by the Pacific plate may explain observed deep‐slab deformation and may also have significant effects on surface tectonics, both resulting from the resistance to slab dragging by the viscous mantle.

Plain Language Summary
In studying subduction zones, where one plate dives below another back into the mantle, we tend to focus on the relative motion between the two plates, normally by assuming that the upper plate is fixed relative to the underlying mantle. Plate reconstructions in an “absolute” mantle frame of reference show, however, that trenches often migrate parallel to their trend relative to the mantle. In this paper, we study the southwestern Pacific Tonga‐Kermadec Trench and demonstrate (1) that it is likely much younger than often assumed, and accommodated most if not all of its subduction after ~30 million years ago and (2) that even in this short time period, it moved as much as 1,200 km northward relative to the mantle, parallel to its strike. By comparing this history with the subducted plate that is seismically imaged in the mantle, we show that the subducted Pacific lithosphere underwent major northward slab dragging through the mantle. This dragging explains enigmatic deep earthquakes and seismological observations of mantle structure. Realizing the role of slab dragging may provide novel constraints for deep‐time geological reconstructions as well as natural hazards assessment.

text: Southwest Pacific Absolute Plate Kinematic Reconstruction Reveals Major Cenozoic Tonga-Kermadec Slab Dragging Tectonic plates subducting at trenches having strikes oblique to the absolute subducting plate motion undergo trench‐parallel slab motion through the mantle, recently defined as a form of “slab dragging.” We investigate here long‐term slab‐dragging components of the Tonga‐Kermadec subduction system driven by absolute Pacific plate motion. To this end we develop a kinematic restoration of Tonga‐Kermadec Trench motion placed in a mantle reference frame and compare it to tomographically imaged slabs in the mantle. Estimating Tonga‐Kermadec subduction initiation is challenging because another (New Caledonia) subduction zone existed during the Paleogene between the Australia and Pacific plates. We test partitioning of plate convergence across the Paleogene New Caledonia and Tonga‐Kermadec subduction zones against resulting mantle structure and show that most, if not all, Tonga‐Kermadec subduction occurred after ca. 30 Ma. Since then, Tonga‐Kermadec subduction has accommodated 1,700 to 3,500 km of subduction along the southern and northern ends of the trench, respectively. When placed in a mantle reference frame, the predominantly westward directed subduction evolved while the Tonga‐Kermadec Trench underwent ~1,200 km of northward absolute motion. We infer that the entire Tonga‐Kermadec slab was laterally transported through the mantle over 1,200 km. Such slab dragging by the Pacific plate may explain observed deep‐slab deformation and may also have significant effects on surface tectonics, both resulting from the resistance to slab dragging by the viscous mantle.

Plain Language Summary
In studying subduction zones, where one plate dives below another back into the mantle, we tend to focus on the relative motion between the two plates, normally by assuming that the upper plate is fixed relative to the underlying mantle. Plate reconstructions in an “absolute” mantle frame of reference show, however, that trenches often migrate parallel to their trend relative to the mantle. In this paper, we study the southwestern Pacific Tonga‐Kermadec Trench and demonstrate (1) that it is likely much younger than often assumed, and accommodated most if not all of its subduction after ~30 million years ago and (2) that even in this short time period, it moved as much as 1,200 km northward relative to the mantle, parallel to its strike. By comparing this history with the subducted plate that is seismically imaged in the mantle, we show that the subducted Pacific lithosphere underwent major northward slab dragging through the mantle. This dragging explains enigmatic deep earthquakes and seismological observations of mantle structure. Realizing the role of slab dragging may provide novel constraints for deep‐time geological reconstructions as well as natural hazards assessment.

year: 2018

title: Does invasiveness predict competition outcomes between ecologically similar invasive blowflies?

authors: Nunn, Daniel

abstract: Biological invasion is a complex puzzle, and its significance is at an all-time high. Current research highlights that the success of invasive species is partly due to their superior performance in key behavioural traits, such as aggression and boldness, especially when compared to ecologically similar native species. However, less attention has been given to differences in these traits among invasive species themselves. Not all invaders are created equal; they vary in their degree of invasiveness, often characterised by the extent of their global spread. If behavioural traits are crucial for invasiveness, it stands to reason that more invasive species - those with greater success - should outperform less invasive ones.

I tested this hypothesis using larval competition between differentially invasive blowfly species. Calliphora stygia has a limited distribution, found only in Australia and New Zealand, whereas Lucilia sericata and Lucilia cuprina (Lucilia spp.) are invaders with almost global distributions. Under direct laboratory competition, the highly invasive Lucilia spp. exhibited fewer body size reductions than C. stygia, regardless of intra- or interspecific competition levels. These findings suggest that competitive traits may exist along a continuum from native to invasive species, increasing predictably with invasiveness. This insight highlights invasiveness as a potentially reliable metric for predicting competition outcomes between ecologically similar sympatric invaders.

text: Does invasiveness predict competition outcomes between ecologically similar invasive blowflies? Biological invasion is a complex puzzle, and its significance is at an all-time high. Current research highlights that the success of invasive species is partly due to their superior performance in key behavioural traits, such as aggression and boldness, especially when compared to ecologically similar native species. However, less attention has been given to differences in these traits among invasive species themselves. Not all invaders are created equal; they vary in their degree of invasiveness, often characterised by the extent of their global spread. If behavioural traits are crucial for invasiveness, it stands to reason that more invasive species - those with greater success - should outperform less invasive ones.

I tested this hypothesis using larval competition between differentially invasive blowfly species. Calliphora stygia has a limited distribution, found only in Australia and New Zealand, whereas Lucilia sericata and Lucilia cuprina (Lucilia spp.) are invaders with almost global distributions. Under direct laboratory competition, the highly invasive Lucilia spp. exhibited fewer body size reductions than C. stygia, regardless of intra- or interspecific competition levels. These findings suggest that competitive traits may exist along a continuum from native to invasive species, increasing predictably with invasiveness. This insight highlights invasiveness as a potentially reliable metric for predicting competition outcomes between ecologically similar sympatric invaders.

year: 2024

title: Operational forest restoration plan for Kukutaaruhe Gully: Part 2

authors: Elliot Noe, Elizabeth

abstract: Kukutaaruhe Gully is a minor branch of Hamilton’s extensive gully system, and runs from the corner of Bankwood and Clarkin Road, behind Fairfield College, connecting with Donny Park in the north and out into the Waikato River. The Kukutaaruhe Education Trust was established to support the implementation of the Fairfield Project, which is a partnership between Ngati Wairere, local community and Fairfield College. The project’s goals include the establishment of an ecological and environmental education centre on the approximately 12 ha of land behind Fairfield College and restoration of the adjacent Kukutaaruhe Gully. In 2019, the University of Waikato’s Environmental Research Institute was contracted by the Kukutaaruhe Education Trust to create an Operational Forest Restoration plan for Kukutaaruhe Gully. This is one in a three-part series created together under one contract:
• Part 1 of 3 is an Overview of the Kukutaaruhe Gully Restoration Initiative
• Part 2 of 3 is this document, the Operational Forest Restoration plan for Kukutaaruhe Gully
• Part 3 of 3 is an Ecological Restoration Plan Template.

text: Operational forest restoration plan for Kukutaaruhe Gully: Part 2 Kukutaaruhe Gully is a minor branch of Hamilton’s extensive gully system, and runs from the corner of Bankwood and Clarkin Road, behind Fairfield College, connecting with Donny Park in the north and out into the Waikato River. The Kukutaaruhe Education Trust was established to support the implementation of the Fairfield Project, which is a partnership between Ngati Wairere, local community and Fairfield College. The project’s goals include the establishment of an ecological and environmental education centre on the approximately 12 ha of land behind Fairfield College and restoration of the adjacent Kukutaaruhe Gully. In 2019, the University of Waikato’s Environmental Research Institute was contracted by the Kukutaaruhe Education Trust to create an Operational Forest Restoration plan for Kukutaaruhe Gully. This is one in a three-part series created together under one contract:
• Part 1 of 3 is an Overview of the Kukutaaruhe Gully Restoration Initiative
• Part 2 of 3 is this document, the Operational Forest Restoration plan for Kukutaaruhe Gully
• Part 3 of 3 is an Ecological Restoration Plan Template.

year: 2020-10