A Basin Model for Massive Banded Iron-Formations and its Geophysical Applications
A Basin Model for Massive Banded Iron-Formations and its Geophysical Applications
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块状带状铁矿盆地模型及其地球物理应用
DOI：
10.1086/628887
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发表时间：
1984
期刊：
影响因子：
--
通讯作者：
J. L. Cisne
中科院分区：
文献类型：
--
作者：
J. L. Cisne
由于条带铁形成(BIF)密度随着水深的增加向软流圈上部密度方向明显减小，沉积物密度与水深之间的反馈通过沉积驱动的下沉作用将沉积物的体积密度调制到软流圈上部。这一机制有助于解释为什么在较长波长的块状BIF，陆架盆地具有大致均匀的体积组成，以及为什么它们的体积密度与现代软流圈的体积密度非常接近。短波长盆地的BIF密度与上地幔密度之间的差异给出了岩石圈弯曲刚性的粗略估计。南非威特沃特斯兰德盆地的弹性岩石圈，距今2.7年。其厚度大约是典型的现代大陆岩石圈的一半。与均衡平衡有关的动态效应软流层几百公里深处的动态粘性的估测。澳大利亚哈默斯利盆地之下的流体地幔，公元前2.5年。AGO的粘性与现代低速带差不多。在一定程度上，大量生物信息流中铁的积累和储存在将深海中的溶解铁浓度降低到所需水平方面发挥了关键作用，那里的游离氧积累，如果不是在大气中，必须等待具有被动边缘的大型大陆的增长--因为岩石圈的弯曲刚性实际上应该将厚重的生物信息流限制在广阔的大陆架上。
Because banded iron-formation (BIF) density evidently decreased toward upper asthenosphere density with increasing water depth, feedback between sediment density and water depth by way of sedimentation-driven subsidence should have modulated the sediments' bulk density to the upper asthenosphere's. This mechanism helps explain why massive BIF's in longer wavelength, continental shelf basins have a more or less uniform bulk composition, and why their bulk densities closely correspond to the modern upper asthenosphere's. The difference between BIF and upper mantle densities in a short wavelength basin yields a rough estimate of the lithosphere's flexural rigidity. The elastic lithosphere of the Witwatersrand Basin, South Africa, 2.7 b.y. ago was about half as thick as typical modern continental lithosphere. Dynamic effects associated with isostatic equilibration yield estimates of the asthenosphere's dynamic viscosity to few hundred km depths. The fluid mantle beneath the Hamersley Basin, Australia, 2.5 b.y. ago was about as viscous as the modern low velocity zone. To the extent that accumulation and storage of iron in massive BIF's played a key role in lowering dissolved iron concentrations to required levels in the deep ocean, buildup of free oxygen there, if not in the atmosphere, must have had to await the growth of large continents with passive margins-for the lithosphere's flexural rigidity should effectively have limited thick BIF's to broad continental shelves.