ABSTRACT Thirsty Creek Norite is a small, undeformed, mafic intrusion intruding gneisses of the Granite Hill Complex in the Buller Terrane. An age of 107.1 ± 4.1 Ma has been obtained using Rb-Sr geochronology. A relatively high MSWD of 4.5 is attributed to sericitization and alteration of plagioclase. This date is consistent with other ages for the timing of high-grade metamorphism in the Granite Hill Complex and may represent a metamorphic age, thus providing a minimum age for metamorphism and emplacement of the norite. However, the relatively undeformed nature of the Thirsty Creek Norite suggests it may postdate metamorphism and we speculate that the date could represent a crystallisation age which is contemporaneous with Rahu Suite granitic magmatism in the adjacent Hohonu Batholith. Several geochemical characteristics, including overlapping initial Sr and Nd isotope compositions, suggest the Thirsty Creek Norite could be a relatively mafic yet contaminated melt that is petrogenetically related to Rahu Suite magmatism. Overlaps in the isotopic compositions of the Thirsty Creek Norite and Rahu Suite granitoids therefore imply that any mafic components involved during granitic magmatism must have had relatively enriched isotopic compositions, and that evolution to more felsic compositions occurred without significant interactions with upper crustal components.

中文翻译：

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新西兰韦斯特兰 Thirsty Creek Norite 的年代学和地球化学

摘要 Thirsty Creek Norite 是一个小的、未变形的、镁铁质侵入体，侵入 Buller Terrane 花岗岩山复合体的片麻岩。使用 Rb-Sr 年代学已经获得了 107.1 ± 4.1 Ma 的年龄。相对较高的 4.5 MSWD 归因于斜长石的绢云母化和改变。该日期与花岗岩山复合体中高级变质作用时间的其他时代一致，可能代表变质时代，从而提供了变质作用和紫砂岩就位的最小年龄。然而，Thirsty Creek Norite 相对未变形的性质表明它可能发生后期变质作用，我们推测该日期可能代表一个结晶时代，它与相邻的 Hohonu 基岩中的 Rahu Suite 花岗岩岩浆作用同时期。几个地球化学特征，包括重叠的初始 Sr 和 Nd 同位素组成，表明 Thirsty Creek Norite 可能是一种相对镁铁质但受污染的熔体，在岩石成因上与 Rahu Suite 岩浆作用有关。因此，Thirsty Creek Norite 和 Rahu Suite 花岗岩的同位素组成重叠意味着在花岗质岩浆作用过程中所涉及的任何基性成分都必须具有相对丰富的同位素成分，并且在没有与上地壳成分发生显着相互作用的情况下演化为更多的长英质成分。