首页> 外文期刊>Gondwana research: international geoscience journal >Changing provenance of late Neoarchean metasedimentary rocks in the Anshan-Benxi area, North China Craton: Implications for the tectonic setting of the world-class Dataigou banded iron formation
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Changing provenance of late Neoarchean metasedimentary rocks in the Anshan-Benxi area, North China Craton: Implications for the tectonic setting of the world-class Dataigou banded iron formation

机译:华北克拉通鞍山-本溪地区晚新古生界沉积沉积物源的变化:对世界一流的大断沟带状铁构造的构造环境的启示

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The Anshan-Benxi (AnBen) area is situated in the northeastern part of the North China Craton and is considered to be the most important iron metallogenic province in China. The giant Dataigou banded iron formation (BIF) has the potential to be the largest iron deposit in this area, even in Asia. Here, we present in situ zircon U-Pb-Hf-O isotopic and whole-rock geochemical data for metasedimentary rocks (metapelites and metaarenites) and trondhjemitic gneiss associated with this BIF, in order to provide constraints on the setting of the deposit, with implications for geological and exploration models. SIMS zircon U-Pb dating results indicate that the trondhjemitic gneiss crystallized at 3450 +/- 19 Ma, and thus it is the oldest rock so far indentified in the Benxi area. The youngest group of detrital zircons from the metaarenite samples constrains their maximum-depositional age at similar to 2.54 Ga. In combination with the earlier metamorphic age of similar to 2.51 Ga for the metaarenites, the deposition age of the Dataigou BIF can be constrained between 2.54 and 2.51 Ga. The metasediments have undergone varying degrees of source weathering. Source rocks of the metapelites have undergone moderate to severe chemical weathering, whereas those of the metaarenites have subjected to relatively weak chemical weathering. Diagnostic geochemical features such as the Al2O3/TiO2 values, trace element ratios, and REE patterns suggest that the metaarenites were predominantly derived from felsic igneous sources, whereas the metapelites were sourced mainly from mafic tholeiitic rocks. The dominant late Neoarchean detrital zircons further indicate that they were most likely sourced from almost synchronous volcanic rocks in the AnBen area. Taking into account the lithostratigraphic, geochemical, and geochronological data, the Dataigou BIF is interpreted as having been deposited in a back-arc basin, most probably on the margin of an ancient continental crust. Continuous provenance variations of these metasediments during highstand times and transgression can be ascribed to changes in natures of nearby volcanisms. Integrated with previous zircon Hf isotopic data from other supracrustal rocks in the AnBen area, our Hf-O data reveal major juvenile crustal growth stages at 3.0 Ga and during 2.8-2.7 Ga, and a crustal reworking event with minor juvenile addition at similar to 2.5 Ga in the studied area. (C) 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
机译:鞍山—本溪地区位于华北克拉通的东北部,被认为是中国最重要的铁成矿省。大型Dataigou带状铁矿(BIF)有潜力成为该地区最大的铁矿床,即使在亚洲也是如此。在这里,我们提供了与该BIF相关的准沉积岩(变石和变亚砷铁矿)和白垩系片麻片岩的原位锆石U-Pb-Hf-O同位素和全岩石地球化学数据,对地质和勘探模型的意义。 SIMS锆石U-Pb测年结果​​表明,该盘状片麻岩在3450 +/- 19 Ma处结晶,因此是本溪地区迄今发现的最古老的岩石。来自亚砷铁矿样品的最年轻的碎屑锆石将其最大沉积年龄限制在约2.54 Ga。结合亚砷铁矿的较早变质年龄约2.51 Ga,可以将Dataigou BIF的沉积年龄限制在2.54之间和2.51 Ga。沉积物经历了不同程度的源风化作用。变质岩的烃源岩经历了中度到严重的化学风化,而变质亚砷酸盐的烃源岩经历了相对较弱的化学风化。诊断地球化学特征(例如Al2O3 / TiO2值,微量元素比率和REE模式)表明,亚亚砷酸盐主要来自长英质火成岩来源,而亚变质岩主要来自镁铁质硬质岩。占主导地位的新古宙晚期碎屑锆石进一步表明,它们最有可能来自安本地区几乎同步的火山岩。考虑到岩性地层学,地球化学和年代学数据,将Dataigou BIF解释为沉积在后弧盆地中,很可能在古代大陆壳的边缘。在高温和海侵期间这些沉积物的持续物源变化可归因于附近火山活动的性质变化。结合先前在安本地区其他地壳上的锆石Hf同位素数据,我们的Hf-O数据揭示了3.0 Ga和2.8-2.7 Ga期间主要的幼年地壳生长阶段,以及添加了约2.5的未成年人的地壳返工事件镓在研究区域。 (C)2016国际冈瓦那研究协会。由Elsevier B.V.发布。保留所有权利。

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