We characterise the geochemistry, zircon Lu-Hf composition, age and the structure of the Uunimäki gabbro (UGB) in south-western Finland to improve the understanding of i) the early Svecofennian (1.92–1.89 Ga) crustal evolution of the central Fennoscandian Shield, ii) the potential role of rift-related magmatism for the build-up of the Paleoproterozoic accretionary orogens and iii) evaluate, which geological features provide the primary control over the localization of an orogenic gold mineralisation. The zircon U-Pb geochronology defines an age of 1891 ± 5 Ma for the UGB, which is slightly older than most mafic intrusions in south-western Finland. The obtained chondritic initial zircon ɛ_Hf values with E-MORB type geochemical affinity suggest a sub continental lithospheric mantle source for the UGB. The overall geochemistry indicates that the UGB magma as well as other E-MORB type rocks in the Pirkanmaa and Häme belts were formed in a rift-related environment in a fore-arc region at 1.89 Ga, predated by arc-type magmatism at ~1.90 Ga and back-arc magmatism at ~1.92 Ga in the Tampere belt. Slab retreat due to roll-back is suggested to cause the extension and related magmatism in the fore-arc region. Moreover, the timing and compositional and isotopic changes of early-orogenic magmatism are broadly compatible with intervals of extension and contraction, i.e., a tectonic switching model, and may provide a perspective to rapid build-up of Paleoproterozoic crust. Structural characterisation provides a framework where gold mineralisations are preferentially located within the high-strain north-eastern domain of the UGB, within fracture networks adjoining the high-strain zones. Our results indicate that neither the geochemical composition nor age of the intermediate-mafic intrusive host rocks play a major role in controlling the formation of gold mineralisation. By contrast, the localization of orogenic gold is controlled by localised structures (shear zones, fractures), and the variation in lithological composition of the intrusive host may contribute to the style of the mineralisation.

我们对芬兰西南部 Uunimäki 辉长岩 (UGB) 的地球化学、锆石 Lu-Hf 组成、年龄和结构进行了表征，以提高对 i) 中央芬诺斯坎迪亚地盾的早期 Svecofennian (1.92–1.89 Ga) 地壳演化的理解, ii) 裂谷相关岩浆作用对古元古代增生造山带的形成的潜在作用和 iii) 评估哪些地质特征提供了对造山带金矿化定位的主要控制。锆石 U-Pb 年代学定义了 UGB 的年龄为 1891 ± 5 Ma，比芬兰西南部的大多数镁铁质侵入体年龄稍大。得到的球粒陨石初始锆石 ɛ _Hf具有 E-MORB 型地球化学亲和性的数值表明 UGB 存在亚大陆岩石圈地幔源。整体地球化学表明，Pirkanmaa 和 Häme 带中的 UGB 岩浆以及其他 E-MORB 型岩石形成于前弧区域 1.89 Ga 的裂谷相关环境中，早于约 1.90 的弧型岩浆作用坦佩雷带中~1.92 Ga 处的 Ga 和弧后岩浆活动。认为由于回滚引起的板岩后退引起了弧前区的伸展和相关的岩浆活动。此外，早造山岩浆活动的时间、成分和同位素变化与伸展和收缩的间隔（即构造转换模型）广泛兼容，并可能为古元古代地壳的快速形成提供一个视角。结构特征提供了一个框架，其中金矿化优先位于 UGB 的高应变东北区域内，在与高应变区相邻的裂缝网络内。我们的结果表明，中基性侵入主岩的地球化学成分和年龄都不是控制金矿化形成的主要作用。相比之下，造山金的定位受局部结构（剪切带、裂缝）的控制，侵入宿主岩性成分的变化可能会影响成矿的风格。我们的结果表明，中基性侵入主岩的地球化学成分和年龄都不是控制金矿化形成的主要作用。相比之下，造山金的定位受局部结构（剪切带、裂缝）的控制，侵入宿主岩性成分的变化可能会影响成矿的风格。我们的结果表明，中基性侵入主岩的地球化学成分和年龄都不是控制金矿化形成的主要作用。相比之下，造山金的定位受局部结构（剪切带、裂缝）的控制，侵入宿主岩性成分的变化可能会影响成矿的风格。