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
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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DOI：
10.1016/j.gr.2016.08.010
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发表时间：
2016-12
影响因子：
6.1
通讯作者：
Changle Wang;Hua Huang;Xiaoxue Tong;Mengtian Zheng;Zidong Peng;Jingbo Nan;Lianchang Zhang;M. Zhai
中科院分区：
文献类型：
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作者：
Changle Wang;Hua Huang;Xiaoxue Tong;Mengtian Zheng;Zidong Peng;Jingbo Nan;Lianchang Zhang;M. Zhai
安本地区位于华北板块东北部，是我国最重要的铁矿成矿区。大台沟大型条带状铁矿建造（BIF）有可能成为该地区乃至亚洲最大的铁矿存款。在这里，我们提出了原位锆石U-Pb-Hf-O同位素和全岩地球化学数据的变沉积岩（变岩和变砂岩）和奥长片麻岩与此BIF，以提供限制的存款的设置，地质和勘探模式的影响。西姆斯锆石U-Pb定年结果表明，奥长花岗质片麻岩的结晶年龄为3450 ± 19 Ma，是本溪地区迄今发现的最古老的岩石。变质砂岩样品中最年轻的一组碎屑锆石将其最大沉积年龄限制在~ 2.54 Ga。结合变碎屑岩的早期变质年龄~ 2.51Ga，大台沟BIF的沉积年龄可限定在2.54 ~ 2.51Ga之间。变质沉积物经历了不同程度的源岩风化作用。变泥岩的烃源岩经历了中等至严重的化学风化，而变砂岩的烃源岩经历了相对较弱的化学风化。诊断地球化学特征，如Al 2 O3/TiO 2值，微量元素比值，和稀土元素模式表明，变砂岩主要来自长英质火成岩源，而变岩主要来自镁铁质拉斑玄武岩。晚新太古代碎屑锆石的优势进一步表明，它们最有可能来源于安本地区的近同期火山岩。考虑到岩石地层学，地球化学和年代学数据，大台沟BIF被解释为已沉积在弧后盆地，最有可能在古大陆地壳的边缘。这些变质沉积物在高水位期和海侵期间的连续物源变化可归因于附近火山作用性质的变化。结合安本地区其他表壳岩的锆石Hf同位素数据，我们的Hf-O数据揭示了研究区在3.0 Ga和2.8-2.7 Ga期间的主要年轻地壳生长阶段，以及在~ 2.5 Ga期间的地壳改造事件和少量的年轻添加。
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 ~ 2.54 Ga. In combination with the earlier metamorphic age of ~ 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/TiO2values, 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 ~ 2.5 Ga in the studied area.