The Zealandia portion of the Pacific–Gondwana margin underwent widespread extension, fragmentation, separation and subsidence during the final stages in the breakup of Gondwana. Although these processes shaped the geology of New Zealand, their timing and the timing of subduction cessation in the region remain unclear. To investigate the timing of these processes, we used Lu–Hf garnet geochronology to date six samples of the Alpine Schist, which represents the metamorphic section of the former Zealandia margin. The garnet dates range from 97.3 ± 0.3 to 75.4 ± 1.3 Ma. Compositional zoning in garnet indicates that the spread in ages results from diachronous metamorphism in the upper plate at the Pacific–Gondwana margin, occurring concurrently with rifting of Zealandia from East Gondwana via opening of the Tasman Sea. Clear spatial trends in the timing of garnet growth throughout the Alpine Schist are absent, indicating that either regional age trends were offset by post‐metamorphic deformation, or that metamorphism did not result from a single regional heat source, and was instead driven by short‐duration, spatially dispersed processes such as episodic fluid‐fluxing or mechanical heating. Diachronous metamorphism of the Alpine Schist can be attributed to heat conduction from the rising upper mantle during widespread extension, progressive burial and heating of accretionary wedge sediments during ongoing horizontal shortening, or fluid‐fluxing sourced from a subducting and dehydrating Hikurangi Plateau. These results indicate that during separation of Zealandia from East Gondwana in the late Cretaceous, the crust at the Pacific–Gondwana margin remained hot, potentially facilitating the extensive thinning of the Zealandia lithosphere during this time.
Granitic pegmatites emplaced within the Alpine Schist of New Zealand provide an opportunity to assess the relationship between metamorphism and melting during the separation of Zealandia from eastern Gondwana. We combined monazite, xenotime, and zircon petrochronology from 12 pegmatite samples with whole-rock geochemistry to link pegmatites to the conditions and mechanisms of partial melting of the Alpine Schist. Monazite dates define a broad range from ca. 85 to ca. 50 Ma, interpreted to represent primary crystallization, remelting of existing pegmatites, and fluid-assisted recrystallization. Xenotime and zircon dates match monazite dates from the same sample, except where recrystallization or sampling of inherited age domains has led to younger or older dates, respectively. The total age range of primary, unmodified igneous monazite is 79.5 ± 0.4-49.8 ± 0.2 Ma, extending the known lower time limit for pegmatite emplacement by 17 m.y., and indicating that the generation and crystallization of melts occurred over a period of 30 m.y. Whole-rock compositions indicate that water-fluxed melting was the dominant melting mechanism, although minor dehydration melting may have contributed to the earliest melts. Partial melting initiated immediately prior to the youngest record of garnet growth in the Mataketake Range region and persisted for 28 m.y. after garnet growth ceased in this region. The timing, duration, and mechanisms of partial melting and their relationship to the timing of metamorphism suggest that short-lived melting events were driven by episodic water fluxing from ca. 80 to 50 Ma in the Alpine Schist. Late Cretaceous to Paleogene intraplate deformation focused between the NW and SE regions of Zealandia is proposed as a potential mechanism for this prolonged period of partial melting and melt emplacement within a geographically restricted area.
<div> <p><span>Geoethics is not just a matter of geoscience, but involves complex transdisciplinary concerns with social, economic and cultural implications. Because of this, both geoethicists within geosciences and those working in social sciences and humanities are increasingly calling for dialogue across disciplinary silos. Drawing from our work on the British Academy funded interdisciplinary project, &#8216;Mining for Meaning: the Geoethics of Extractive Industries,&#8217; we trace out what an interdisciplinary engagement with Geoethics might look like. As an earthly ethics that necessarily stretches beyond geological considerations to consider the socio-natural, cultural-spiritual and political-economic, any engagement with Geoethics demands conversations that bring geoscientific understandings into more explicit dialogue with ideas from the social sciences and the geohumanities (though not exclusively). Acknowledging the very real challenges of doing interdisciplinary work - from distinct understandings about research, knowledge and results, to disciplinary-specific technical terminology - we set out the core ideas underpinning Geoethical approaches in these domains. This lays important groundwork for crafting meaningful and indeed ethical conversations that stretch across these disciplines, but crucially, avoids the mining of other disciplines for useful concepts and metaphors, without due regard for their context, history and technical meaning &#8211; a form of disciplinary extractivism in itself. Animated by this anti-extractivism, the paper presents a reading of how the earth, ethics, knowledge and practices are understood from within the geosciences, social sciences and geohumanities respectively, charting out what we hope to be a useful frame of reference for working across these disciplines. We then use this analysis as the bedrock for discussing the potential of cross-disciplinary conversation. By critically responding to the relative strengths, limitations and offerings of each discipline&#8217;s conceptualisation of geoethics, we bring to the fore important interdisciplinary frictions, overlaps and potential collaborative directions. Taken together, we suggest that this two-part analysis offers scope for crafting meaningful conversations necessary for an interdisciplinary Geoethics.</span><span>&#160;</span></p> </div>
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