ABSTRACT

We use a recently completed airborne magnetic and gamma-ray spectrometric survey, and new U/Pb and ⁴⁰Ar/³⁹Ar age determinations, to revise and clarify several aspects of Brook Street Terrane geology in the Takitimu Mountains. Steeply dipping and homoclinal Permian Takitimu Subgroup formations defined in the central part of the range can, with moderate confidence, be traced along strike to other parts of the range where they are more complexly folded and faulted. We report intrusion ages for three Brook Street plutonic suites: pyroxene-bearing White Hill Intrusives (306-270 Ma, U/Pb zircon), amphibole-bearing Mackinnon Peak Intrusives (261 ± 1 Ma, ⁴⁰Ar/³⁹Ar amphibole), and shoshonitic Wether Hill Dikes (254 ± 1 Ma, ⁴⁰Ar/³⁹Ar plagioclase). Geological relationships between these intrusions and the host Takitimu Subgroup reinforce the Early Permian age of the latter, which is distinct from the overlying Late Permian Productus Creek Group. The Wether Hill Dikes mark the cessation of igneous activity in the Brook Street Terrane at c. 254 Ma. A large (n = 499) dataset of detrital zircon U/Pb ages from the nonmarine Jurassic Barretts Formation confirms a local Median Batholith-Tuhua Intrusives provenance and supports a post-Permian fore-arc tectonic setting along the Gondwana margin.

摘要

我们使用最近完成的机载磁力和伽马射线光谱测量以及新的 U/Pb 和⁴⁰ Ar/ ³⁹ Ar 年龄测定，来修正和澄清塔基蒂姆山脉布鲁克街地体地质的几个方面。在该山脉中心部分定义的陡倾和同斜二叠纪 Takitimu 亚群地层可以在中等可信度下沿着走向追溯到该山脉的其他部分，在那里它们的褶皱和断层更为复杂。我们报告了三个布鲁克街深成岩套的侵入年龄：含辉石的 White Hill 侵入岩（306-270 Ma，U/Pb 锆石）、含角闪石的 Mackinnon Peak 侵入岩（261 ± 1 Ma、40 Ar/ 39 ^Ar角闪石^）和松玄质 Wether Hill 岩脉 (254 ± 1 Ma, ⁴⁰Ar/ ³⁹ Ar 斜长石）。这些侵入体与所在的塔基蒂姆亚群之间的地质关系强化了后者的早二叠世时代，这与上覆的晚二叠世 Productus Creek 群不同。韦瑟山堤标志着布鲁克街地体火成岩活动的停止。254马。来自陆海侏罗纪 Barretts 组的碎屑锆石 U/Pb 年龄的大型数据集 ( n  = 499) 证实了当地的中基岩-Tuhua 侵入体起源，并支持沿冈瓦纳边缘的二叠纪后弧前构造环境。