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Emplacement of Hybrid Continental-Oceanic Arc Terranes Without Collision: The Devonian Calliope Arc (New England Orogen, Australia)
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DOI：10.1029/2025TC009022.png)
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Abstract
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The accretion of allochthonous provinces, derived from oceanic plates, has traditionally been considered an important contributor to continental growth. However, increasing evidence shows that some oceanic terranes (e.g., island arcs) are not “exotic,” as suggested by the presence of continental-derived sedimentary provenance. Here we present new data from Devonian arc-related rocks (Calliope Province) in the New England Orogen (eastern Australia), which display an intra-oceanic arc geochemical affinity and evidence of continental detrital material. To better understand the origin and evolution of the Calliope Province, we determined the age and composition of igneous and detrital apatite and zircon grains. Most grains yielded Early to Middle Devonian (399–381 Ma) U-Pb ages and continental to oceanic trace-element geochemical signatures. The rocks also contain older detrital grains, with abundant Silurian, Ordovician, and Cambrian ages, and a minor Precambrian contribution. The presence of inherited detrital material in the Calliope Province, including continental Ordovician and Precambrian grains, indicates that the Devonian Calliope arc was not an allochthonous oceanic terrane. Instead, we propose that its hybrid continental-oceanic geochemical affinity resulted from a continental crustal substrate that experienced hyperextension during the Early Devonian in response to trench retreat. This hybrid continental-oceanic arc was subsequently emplaced within the supra-subduction orogen via thickening and contraction of the forearc region, without involving collision. These results highlight how arc systems are evolving features that may, over time, exhibit hybrid characteristics in between oceanic and continental end members. Recognizing such transitional behaviors in arcs provides important constraints for reconstructing convergent plate boundary zones.
Keywords:
hybrid continental-oceanic arc
Calliope province
New England orogen
Devonian
U-Pb geochronology
tectonics
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