Ordovician ocean plate stratigraphy and thrust duplexes of the Ballantrae Complex, SW Scotland: Implications for the pelagic deposition rate and forearc accretion in the closing Iapetus Ocean
Ordovician ocean plate stratigraphy and thrust duplexes of the Ballantrae Complex, SW Scotland: Implications for the pelagic deposition rate and forearc accretion in the closing Iapetus Ocean
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DOI：
10.1016/j.tecto.2015.04.014
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发表时间：
2015-11
期刊：
影响因子：
2.9
通讯作者：
W. Fujisaki;H. Asanuma;Kazue Suzuki;Y. Sawaki;S. Sakata;T. Hirata;S. Maruyama;B. Windley
中科院分区：
文献类型：
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作者：
W. Fujisaki;H. Asanuma;Kazue Suzuki;Y. Sawaki;S. Sakata;T. Hirata;S. Maruyama;B. Windley
Ballantrae杂岩（位于苏格兰西南部的Bennane莱亚）在一个与经典奥陶纪蛇绿岩有关的增生棱柱体中含有重要的海洋板块地层（玄武岩、燧石、泥岩、砂岩）。我们用大洋板块地层学的方法将该棱柱体划分为11个构造单元。为了确定层状硅质岩的沉积时代，从6个不同单元的9个凝灰岩层中分离了锆石。所有的凝灰岩都有早至中奥陶世的时代，尽管它们现在的位置相互距离很远。这些年龄与放射虫和笔石的微体化石记录一致。地层-构造关系表明，大洋板块地层已重复的顺层逆冲断层，这是一个典型的现代加积双重。根据从几个凝灰岩层中获得的锆石U-Pb年龄，我们计算了Bennane莱亚早中奥陶世层状硅质岩的沉积速率;数据表明，沉积速率（0.6-3 m/myr）与放射虫定义的中新生代相当。Ballantrae砂岩中碎屑锆石的年龄谱显示出明显的单峰。467和478 Ma，缺乏前寒武纪锆石。我们的新锆石年龄与已发表的同位素数据和古地理图的整合表明，砂岩沉积在洋内弧附近，远离任何含有前寒武纪岩石的大陆。Bennane莱亚的浮游-碎屑沉积物是在约1000年左右的封闭的Iapetus洋中沉积的。第477章我来了464 Ma时，它们与Ballantrae的洋内弧增生。
The Ballantrae Complex (at Bennane Lea in SW Scotland) contains important ocean plate stratigraphy (basalt, chert, mudstone, sandstone) in an accretionary prism that is associated with a classic Ordovician ophiolite. We used the ocean plate stratigraphy to sub-divide the prism into 11 tectonic units. To determine the depositional age of bedded cherts, zircons were separated from 9 tuff beds from 6 different units. All the tuffs have early to middle Ordovician ages, even though their present positions are mutually distant. These ages are consistent with microfossil records of radiolaria and graptolites. The stratigraphic–structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding-parallel thrusts; this is typical of a modern accretionary duplex. We calculated the sedimentation rate of Early to Middle Ordovician bedded cherts at Bennane Lea on the basis of U–Pb zircon ages obtained from several tuff beds; the data indicate that the depositional rate (0.6–3 m/myr) was as slow as that of Mesozoic–Cenozoic equivalents defined by radiolaria. The age spectra of detrital zircons from Ballantrae sandstones show prominent single peaks at ca. 467 and 478 Ma, and a lack of Precambrian zircons. Integration of our new zircon ages with published isotopic data and palaeo-geographic maps indicates that the sandstones were deposited near an intra-oceanic arc and far from any continent containing Precambrian rocks. The pelagic-to-clastic sediments at Bennane Lea were deposited in the closing Iapetus Ocean from ca. 477 Ma to ca. 464 Ma, when they were accreted with the intra-oceanic arc of Ballantrae.