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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Two distinct origins for Archean greenstone belts
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Two distinct origins for Archean greenstone belts

机译：Archean Greenstone Belts的两个不同的起源

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Applying the Th/Yb-Nb/Yb plot of Pearce (2008) to the well-studied Archean greenstone sequences of Western Australia shows that individual volcanic sequences evolved through one of two distinct processes reflecting different modes of crust-mantle interaction. In the Yilgarn Craton, the volcanic stratigraphy of the 2.99-2.71 Ga Youanmi Terrane mainly evolved through processes leading to Th/YbNb/Yb trends with a narrow range of Th/Nb ('constant-Th/Nb' greenstones). In contrast, the 2.71-2.66 Ga volcanic stratigraphy of the Eastern Goldfields Superterrane evolved through processes leading to Th/Yb-Nb/Yb trends showing a continuous range in Th/Nb ('variable-Th/Nb' greenstones). Greenstone sequences of the Pilbara Craton show a similar evolution, with constant-Th/Nb greenstone evolution between 3.13 and 2.95 Ga and variable-Th/Nb greenstone evolution between 3.49 and 3.23 Ga and between 2.77 and 2.68 Ga. The variable-Th/Nb trends dominate greenstone sequences in Australia and worldwide, and are temporally associated with peaks in granite magmatism, which promoted crustal preservation. The increasing Th/Nb in basalts correlates with decreasing epsilon Nd, reflecting variable amounts of crustal assimilation during emplacement of mantle-derived magmas. These greenstones are typically accompanied in the early stages by komatiite, and can probably be linked to mantle plume activity. Thus, regions such as the Eastern Goldfields Superterrane simply developed as plume-related rifts over existing granite-greenstone crust - in this case the Youanmi Terrane. Their Th/Nb trends are difficult to reconcile with modern-style subduction processes. The constant-Th/Nb trends may reflect derivation from a mantle source already with a high and constant Th/Nb ratio. This, and a lithological association including boninite-like lavas, basalts, and calc-alkaline andesites, all within a narrow Th/Nb range, resembles compositions typical of modern-style subduction settings. These greenstones are
机译：将Pearce（2008）的TH / YB-NB / YB剧集应用于西澳大利亚西澳大利亚的良好的Archean Greenstone序列表明，各个火山序列通过反射不同方式的外壳界面相互作用的不同方法之一演变。在伊莱克纳·克拉顿，2.99-2.71 Ga Youanmi Terrane的火山地层主要通过导致TH / YBNB / YB趋势的流程演变，具有窄范围的TH / NB（'恒定的-TH / NB'Greenstones）。相比之下，东部金菲尔德的2.71-2.66 Ga火山层层通过导致TH / YB-NB / YB趋势的流程演变，显示了TH / NB（'变量-TH / NB'Greenstones）的连续范围。 Pilbara Craton的Greenstone序列显示出类似的演进，在3.49和3.23 Ga和2.77和2.68 Ga之间的3.13和2.95 Ga和可变-Th / Nb Greenstone演变之间的恒定-TH / NB Greenstone演变。变量-TH / NB趋势在澳大利亚和全球范围内占主导地位的绿石序列，并且在促进地壳保存的花岗岩岩浆广场中的峰值与峰值相关。沼气中的增加的Th / Nb与减少εnsilonnd相关，反映了在岩石衍生的岩浆的施加过程中的可变地壳同化。这些绿色岩石通常伴随着Komatiite的早期阶段，并且可能与披露羽流量相关联。因此，诸如东部金菲尔德超恒的地区简单地发展成为现有的花岗岩 - 绿石地壳与羽毛相关的裂缝 - 在这种情况下，Youanmi Terrane。他们的TH / NB趋势很难与现代浏览过程调和。恒定-TH / NB趋势可以反映已经具有高且恒定的TH / NB比的地幔源的推导。这和岩性协会，包括Boninite的熔岩，沼气和钙碱性和钙碱和钙质，所有内容在窄的Th / Nb范围内，类似于现代俯冲设置的典型组成。这些绿石是

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