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首页> 外文期刊>Contributions to Mineralogy and Petrology >Autochthonous inheritance of zircon through Cretaceous partial melting of Carboniferous plutons: the Arthur River Complex, Fiordland, New Zealand
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Autochthonous inheritance of zircon through Cretaceous partial melting of Carboniferous plutons: the Arthur River Complex, Fiordland, New Zealand

机译：通过石炭纪白垩纪白垩纪部分融化的锆石自生遗传：新西兰菲奥德兰的亚瑟河综合体

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摘要

TIMS and SHRIMP U–Pb analyses of zircons from Milford Orthogneiss metadiorite (P = 1–1.4 GPa; T ≥ 750°C) of the Arthur River Complex of northern Fiordland reveal a bimodal age pattern. Zircons are predominantly either Paleozoic (357.0 ± 4.2 Ma) and prismatic with oscillatory zoning, or Cretaceous (133.9 ± 1.8 Ma) and ovoid with sector or patchy zoning. The younger age component is not observed overgrowing older grains. Most grains of both ages are overgrown by younger Cretaceous (~120 Ma) metamorphic zircon with very low U and Th/U (0.01). We interpret the bimodal ages as indicating initial igneous emplacement and crystallisation of a dioritic protolith pluton at ~357 Ma, followed by Early Cretaceous granulite-facies metamorphism at ~134 Ma, during which a significant fraction (~60%) of the zircon grains dissolved, and subsequently reprecipitated, effectively in situ, in partial melt pockets. The remaining ~40% of original Paleozoic grains were apparently not in contact with the partial melt, remained intact, and show only slight degrees of Pb loss. Sector zoning of the Cretaceous grains discounts their origin by solid state recrystallisation of Paleozoic grains. The alternative explanation—that the Paleozoic component represents a 40% inherited component in an Early Cretaceous transgressive dioritic magma—is considered less likely given the relatively high solubility of zircon in magma of this composition, the absence of 134 Ma overgrowths, the single discrete age of the older component, equivalent time-integrated 177Hf/176Hf compositions of both age groups, and the absence of the Cambrian-Proterozoic detrital zircon that dominates regional Cambro-Ordovician metasedimentary populations. Similar bimodal Carboniferous-Early Cretaceous age distributions are characteristic of the wider Arthur River Complex; 8 of 12 previously dated dioritic samples have a Paleozoic component averaging 51%. Furthermore, the age and chemical suite affinity of these and several more felsic rocks can be matched with those of the relatively unmetamorphosed Carboniferous plutonic terrane along the strike of the Mesozoic margin in southern Fiordland, also supporting the in situ derivation of the Carboniferous “inherited” component.
机译：TIMS和SHRIMP对北峡湾北部亚瑟河水系中的米尔福德Orthogneiss闪长岩（P = 1–1.4 GPa； T≥750°C）的锆石进行的U–Pb分析揭示了双峰年龄模式。锆石主要为古生界（357.0±4.2 Ma）和棱柱形带振荡带，或白垩纪（133.9±1.8 Ma）和卵形带扇形或斑片带。未观察到年龄较小的成分会长出年龄较大的谷物。两个年龄的大多数晶粒都被年轻的白垩纪（〜120 Ma）变质锆石长满，其U和Th / U非常低（0.01）。我们将双峰时代解释为表明在〜357 Ma时有闪长岩原生质岩体的初始火成岩沉积和结晶，随后在〜134 Ma时出现了早白垩纪的粒状相，在此期间，很大一部分（〜60％）的锆石颗粒溶解了。 ，然后有效地在局部熔体腔中再沉淀。剩余的约40％的原始古生代晶粒显然不与部分熔体接触，保持完好无损，并且仅显示出少量的Pb损失。白垩纪颗粒的区域划分通过古生代颗粒的固态重结晶来打折其起源。考虑到锆石在这种岩浆中相对较高的溶解度，没有134 Ma的过度生长，单一的不连续年龄，替代解释（即古生代成分在早白垩世海侵二闪岩岩浆中占40％的遗传成分）被认为不太可能。两个年龄组的较老组分的等效时间积分 177 Hf / 176 Hf组成，并且不存在以寒武纪-奥陶纪为主的寒武纪-元古代碎屑锆石沉积沉积人口。类似的双峰石炭纪-早白垩纪年龄分布是更宽泛的亚瑟河综合体的特征。 12个先前定日期的闪长岩样品中，有8个的古生成分平均为51％。此外，沿着南峡湾地区中生代边缘的走向，这些以及其他一些长英质岩石的年龄和化学组亲合力可以与相对未变质的石炭纪深成岩地层相匹配，这也支持了石炭纪“继承”的原位推导。零件。

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