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The Mesoarchaean Akia terrane, West Greenland, revisited: New insights based on spatial integration of geophysics, field observation, geochemistry and geochronology
Precambrian Research ( IF 3.2 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.precamres.2020.105958
Agnete Steenfelt , Julie Hollis , Christopher L. Kirkland , Alessandro Sandrin , Nicholas J. Gardiner , Hugo K. H. Olierook , Kristoffer Szilas , Pedro Waterton , Chris Yakymchuk

Abstract The northern part of the North Atlantic Craton (NAC) in southern West Greenland comprises a large tract of exposed Meso-Neoarchaean continental crust, divided into the ca 3300–2900 Ma Akia and ca 2900–2500 Ma Tuno terranes. We combine aeromagnetic, stream sediment geochemical, new litho-chemical and zircon geochronological data with previously published data to re-evaluate the crustal architecture and evolution of the Akia terrane and its boundary towards the Tuno terrane. The previously recognised, but overlooked, Alanngua complex, situated between the Akia and Tuno terranes is bounded by aeromagnetic lineaments interpreted as Neoarchaean shear zones and has a distinct spectrum of Neoarchaean magmatic and metamorphic zircon ages that are rare in the Akia terrane. The Alanngua complex comprises components derived from both the Akia and Tuno terranes and is interpreted as a tectonic melange created during the Neoarchaean assembly of the NAC. Within the Akia terrane, the chemistry of orthogneiss samples indicate that a large percentage is too mafic to classify as TTG s.s., implying that not only partial melting of mafic crust, but also some yet unaddressed mantle involvement is necessary in their formation. Previous models for the generation of the ca. 3015–2990 Ma quartz-dioritic Finnefjeld and Taserssuaq complexes conflict with their geochemical variation. The complexes are spatially associated with strong aeromagnetic responses that are interpreted to reflect a large gabbro-diorite intrusion, and we propose that the protoliths of the Finnefjeld and Taserssuaq complexes are genetically linked to such intrusion. Formed at same time are carbonatite, high-Mg gabbro and tonalite-trondhjemite, and we propose that this wide spectrum of rocks could have formed by lithospheric and crustal melting in response to asthenospheric upwelling possibly in an extensional setting. Periods of extensive magmatism in the Akia terrane were previously recognised at ca. 3220-3180 Ma and 3070-2970 Ma. We now subdivide the latter period into three episodes: juvenile basaltic-andesitic volcanism at 3070–3050 Ma; tonalitic and dioritic plutonism at 3050–3020 Ma, and gabbroic-dioritic plus tonalitic-trondhjemitic plutonism at 3020–2985 Ma. This last episode was immediately followed by crustal reworking during collision at 2980–2950 Ma.

中文翻译:

重新审视西格陵兰岛中古宙 Akia 地体:基于地球物理学、野外观测、地球化学和地质年代学空间整合的新见解

摘要 西格陵兰岛南部北大西洋克拉通 (NAC) 的北部包括一大片暴露的中-新太古代大陆地壳,分为约 3300-2900 Ma Akia 和约 2900-2500 Ma Tuno 地体。我们将航磁、河流沉积物地球化学、新的岩石化学和锆石年代学数据与先前发布的数据相结合,重新评估 Akia 地体及其向 Tuno 地体的边界的地壳结构和演化。先前公认但被忽视的 Alanngua 杂岩体位于 Akia 和 Tuno 地体之间,其边界是被解释为新太古代剪切带的航空磁线,并且具有明显的新太古代岩浆和变质锆石年龄谱,这在 Akia 地体中是罕见的。Alanngua 复合体由来自 Akia 和 Tuno 地体的成分组成,被解释为在 NAC 的新太古代组装过程中产生的构造混杂物。在 Akia 地体中,正方麻岩样品的化学成分表明,很大比例的基性岩性太强而无法归类为 TTG ss,这意味着不仅基性地壳部分熔融,而且在它们的形成过程中还需要一些尚未解决的地幔参与。用于生成 ca 的先前模型。3015-2990 Ma 石英闪长岩 Finnefjeld 和 Taserssuaq 复合体与其地球化学变化相冲突。这些复合体在空间上与强烈的航磁响应有关,这些响应被解释为反映了大量辉长闪长岩侵入,我们认为 Finnefjeld 和 Taserssuaq 复合体的原岩与这种入侵在遗传上有关。同时形成的是碳酸岩、高镁辉长岩和辉长岩-长闪长岩,我们认为这种广泛的岩石可能是由岩石圈和地壳熔融形成的,以响应软流圈上涌,可能是在伸展环境中。Akia 地体中广泛的岩浆活动时期以前在大约 10 年被确认。3220-3180 毫安和 3070-2970 毫安。我们现在将后一时期细分为三个时期:3070-3050 Ma 的幼年玄武岩-安山岩火山作用;3050-3020 Ma 的调质和闪长质深成岩作用,以及 3020-2985 Ma 的辉长岩-闪长岩加调质-长闪质岩体作用。最后一集紧随其后的是 2980-2950 Ma 碰撞期间的地壳改造。同时形成的是碳酸岩、高镁辉长岩和辉长岩-长闪长岩,我们认为,这种广泛的岩石可能是由岩石圈和地壳熔化形成的,以响应软流圈上涌,可能是在伸展环境中。Akia 地体中广泛的岩浆活动时期以前在大约 10 年被确认。3220-3180 毫安和 3070-2970 毫安。我们现在将后一时期细分为三个阶段:3070-3050 Ma 的幼年玄武岩-安山岩火山作用;3050-3020 Ma 的调质和闪长质深成岩作用,以及 3020-2985 Ma 的辉长岩-闪长岩加调质-长闪质岩体作用。最后一集紧随其后的是 2980-2950 Ma 碰撞期间的地壳改造。同时形成的是碳酸岩、高镁辉长岩和辉长岩-长闪长岩,我们认为,这种广泛的岩石可能是由岩石圈和地壳熔化形成的,以响应软流圈上涌,可能是在伸展环境中。Akia 地体中广泛的岩浆活动时期以前在大约 10 年被确认。3220-3180 毫安和 3070-2970 毫安。我们现在将后一时期细分为三个时期:3070-3050 Ma 的幼年玄武岩-安山岩火山作用;3050-3020 Ma 的调质和闪长质深成岩作用,以及 3020-2985 Ma 的辉长岩-闪长岩加调质-长闪质岩体作用。最后一集紧随其后的是 2980-2950 Ma 碰撞期间的地壳改造。我们提出,这种广泛的岩石可能是由岩石圈和地壳熔化形成的,以响应软流圈上涌,可能是在伸展环境中。Akia 地体中广泛的岩浆活动时期以前在大约 10 年被确认。3220-3180 毫安和 3070-2970 毫安。我们现在将后一时期细分为三个时期:3070-3050 Ma 的幼年玄武岩-安山岩火山作用;3050-3020 Ma 的调质和闪长质深成岩作用,以及 3020-2985 Ma 的辉长岩-闪长岩加调质-长闪质岩体作用。最后一集紧随其后的是 2980-2950 Ma 碰撞期间的地壳改造。我们提出,这种广泛的岩石可能是由岩石圈和地壳熔化形成的,以响应软流圈上涌,可能是在伸展环境中。Akia 地体中广泛的岩浆活动时期以前在大约 10 年被确认。3220-3180 毫安和 3070-2970 毫安。我们现在将后一时期细分为三个时期:3070-3050 Ma 的幼年玄武岩-安山岩火山作用;3050-3020 Ma 的调质和闪长质深成岩作用,以及 3020-2985 Ma 的辉长岩-闪长岩加调质-长闪质岩体作用。最后一集紧随其后的是 2980-2950 Ma 碰撞期间的地壳改造。我们现在将后一时期细分为三个时期:3070-3050 Ma 的幼年玄武岩-安山岩火山作用;3050-3020 Ma 的调质和闪长质深成岩作用,以及 3020-2985 Ma 的辉长岩-闪长岩加调质-长闪质岩体作用。最后一集紧随其后的是 2980-2950 Ma 碰撞期间的地壳改造。我们现在将后一时期细分为三个时期:3070-3050 Ma 的幼年玄武岩-安山岩火山作用;3050-3020 Ma 的调质和闪长质深成岩作用,以及 3020-2985 Ma 的辉长岩-闪长岩加调质-长闪质岩体作用。最后一集紧随其后的是 2980-2950 Ma 碰撞期间的地壳改造。
更新日期:2021-01-01
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