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首页> 外文期刊>Geochemistry, geophysics, geosystems >Large-scale tectonic cycles in Europe revealed by distinct Pb isotope provinces
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Large-scale tectonic cycles in Europe revealed by distinct Pb isotope provinces

机译：不同铅同位素省份揭示的欧洲大规模构造周期

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Lead isotopic systematics of U-poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals "freeze in" the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time-integrated U/Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using similar to 6800 Pb isotope measurements of primarily lead ores and minor K-feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time-integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most of southern Europe. Magmatic influx, followed by segregation of dense sulfide-rich mafic cumulates, resulted in foundering of U- and Th-poor lower crust, thereby changing the bulk composition of the continental crust and leading to distinct time-integrated U-Th/Pb provinces. We show that the tectonic assembly of small crustal fragments leaves the crust largely undifferentiated, whereas the formation of supercontinents results in fundamental changes in the composition of the crust, identifiable in time and space by means of Pb isotope systematics. Observations based on Pb isotopes open up a new perspective on possible relationships between crustal thickness and geodynamic processes, in particular the role of crustal foundering into the mantle and the mechanisms responsible for the existence of cratons.
机译：贫铀矿物（如硫化物和长石）的铅同位素系统可以提供有关大陆起源和演化的独特见解，因为这些矿物在重大构造热事件中会“冻结”地壳的铅同位素组成，从而使该地区的历史成为可能。通过铅同位素告诉非洲大陆。铅模型年龄限制了地壳形成的时间，而时间积分的U / Pb，Th / Pb和Th / U比率揭示了与大陆形成有关的关键地球化学过程。使用类似于铅矿石和次要钾长石的6800 Pb同位素测量方法，我们绘制了整个欧洲和地中海的Pb同位素系统图。铅模型年龄定义了空间上不同的年龄省份，与从古生代到元古代和最新的太古宙的主要构造事件一致。但是，由时间积分的U / Pb和Th / Pb比率定义的区域跨越了年龄省份的边界，高的U / Pb系统性是南欧大部分地区的特征。岩浆涌入，然后富集致密的富含硫化物的铁镁质堆积物分离，导致U和Th贫乏的下地壳倾覆，从而改变了大陆壳的整体组成，并导致了时间整合的U-Th / Pb省。我们表明，小地壳碎片的构造组装使地壳基本未分化，而超大陆的形成导致地壳组成的根本变化，可通过铅同位素系统在时间和空间上加以识别。基于铅同位素的观测为地壳厚度与地球动力学过程之间可能的关系，特别是地壳沉入地幔中的作用以及导致克拉通存在的机理开辟了新的视角。

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