Milan L A, Daczko N R, Clarke G L
Earth Sciences, School of Environmental and Rural Science, The University of New England, Armidale, NSW, 2351, Australia.
Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Armidale, NSW, 2109, Australia.
Sci Rep. 2017 Mar 21;7(1):261. doi: 10.1038/s41598-017-00347-w.
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 km/my per km of arc to a flare-up involving ~100 km/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.
中生代新西兰科迪勒拉弧在地球化学和时间上的两个不同组分表明，在约130 Ma时，全岩Sr/Y比值从低向高转变。近期的填图工作以及对已发表的Sr-Nd数据的重新评估，结合新的原位锆石Hf同位素分析，支持了这两个弧组分之间的成因关系。对地球物理、地球化学和P-T估算的重新评估表明，在约130 Ma时，弧的厚度增加了一倍，至少达到80 km。同时，岩浆添加速率从每千米弧长约14 km/百万年转变为涉及每千米弧长约100 km/百万年的爆发式增长。爆发式岩石的Sr-Nd-Hf同位素比值的异常变化突出了地壳主导源区的重要性。这种模式类似于美洲的科迪勒拉弧，并突出了俯冲系统上覆大陆板块中发生的过程的重要性，而这些过程与大陆地壳生长的长期模型并不完全相符。
