Abstract
Two geochemically and temporally distinct components of the Mesozoic Zealandia Cordilleran arc indicate a shift from low to high Sr/Y whole rock ratios at c. 130 Ma. Recent mapping and a reappraisal of published Sr-Nd data combined with new in-situ zircon Hf isotope analyses supports a genetic relationship between the two arc components. A reappraisal of geophysical, geochemical and P-T estimates demonstrates a doubling in thickness of the arc to at least 80 km at c. 130 Ma. Contemporaneously, magmatic addition rates shifted from ~14 km3/my per km of arc to a flare-up involving ~100 km3/my per km of arc. Excursions in Sr-Nd-Hf isotopic ratios of flare-up rocks highlight the importance of crust-dominated sources. This pattern mimics Cordilleran arcs of the Americas and highlights the importance of processes occurring in the upper continental plates of subduction systems that are incompletely reconciled with secular models for continental crustal growth.
Highlights
In this contribution, we utilise 1:250,000 scale mapping[20], geochemistry and geochronology[21,22,23,24,25,26,27,28,29,30] to identify a flare-up event in a 200 km long segment of a Mesozoic arc formed along the Pacific margin of Gondwana
New Zealand comprises Permian to Cretaceous forearc terranes (Eastern Province) that had accreted to the Pacific margin of Gondwana (Western Province) by the Triassic (Fig. 1)
There are three volumetrically important Mesozoic components of the Median Batholith (Fig. 1): (i) Triassic– Early Cretaceous (>129 Ma) calc-alkaline rocks of the Darran Suite characterised by dominantly low Sr/Y ratios (Fig. 2; defined as less than 4038); (ii) Early Cretaceous (
Summary
Two geochemically and temporally distinct components of the Mesozoic Zealandia Cordilleran arc indicate a shift from low to high Sr/Y whole rock ratios at c. 130 Ma. Cordilleran arcs form within continental crust above convergent plate margins as trench-parallel belts of voluminous calc-alkaline magmatism They are important locations for continental crustal growth[1], with the bulk of the igneous rocks being emplaced in episodes of short (5–20 my) duration high magmatic flux, called magmatic flare-ups that have a periodicity of 30–70 my[2,3,4,5,6,7,8]. The ensuing influx of asthenosphere returns the arc to background levels of flux and juvenile isotopic compositions In this contribution, we utilise 1:250,000 scale mapping[20], geochemistry and geochronology[21,22,23,24,25,26,27,28,29,30] to identify a flare-up event in a 200 km long segment of a Mesozoic arc formed along the Pacific margin of Gondwana New in-situ zircon Hf isotope data and a reappraisal of published Sr-Nd-Hf data support a relationship between the older and younger arc components
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