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首页> 外文期刊>Geologica Carpathica >Vertical zonality of fractionated granite plutons reflected in zircon chemistry: the Cinovec A-type versus the Beauvoir S-type suite
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Vertical zonality of fractionated granite plutons reflected in zircon chemistry: the Cinovec A-type versus the Beauvoir S-type suite

机译：锆石化学反应反映的花岗岩花岗岩分离体的垂直区域性：Cinovec A型与Beauvoir S型套件

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摘要

We studied vertical changes in the chemical composition of zircon from two contrasting Variscan granite systems. The Beauvoir system (Massif Central, France) composed of three successive intrusions (Bl, B2, B3) represents typical peraluminous S-type granite extremely enriched in P, F, Li, Rb, Cs, Be, Sn, Nb, Ta, and poor in Zr, Th, REE and Y. The Cinovec system (Kru?né hory Mts/Erzgebirge, Czech Republic/Germany) composed of two successive intrusions (protolithionite granite, zinnwaldite granite) is only slightly peraluminous, P-poor, F, Li, Rb, Cs, U, Th, REE, Y, Sc, Sn, W, Nb, Ta-rich granite, which may be classified as A-type. In both localities, the most fractionated intrusions are located on the top of the system. Samples from borehole GPF-1 (Beauvoir) represent an 800 m long vertical section through the entire granite stock, while CS-1 borehole (Cinovec) reached a depth of 1600 m. Chemical compositions of zircons from both granite systems show distinct vertical zonality, but their shape and elemental speciation is highly contrasting. At Beauvoir, zircon shows a remarkable increase in Hf-content from 2-4 wt. % Hf0_2 (-0.03 apfu Hf) in the deepest B3-unit to 15-19 wt. % Hf0_2 (up to 0.18 apfu Hf) in the uppermost Bl-unit. The highest contents of F, P, and U were detected in the intermediate unit B2 at a depth of 400-600 m. At Cinovec, Hf shows only moderate enrichment from ca. 2 wt. % Hf0_2 in the deeper protolithionite granite to 5-10 wt. % Hf〇2 in the uppermost part of the zinnwaldite granite.,High contents of Th (3-8 wt. % Th0_2) are entirely bound in the uppermost section of the granite copula to a depth of 200 m, but below this level the contents only sporadically exceed 1 wt. % ThQ2. Concentrations of U, Y, HREE, Sc and Bi also reach their highest values in the uppermost parts of the zinnwaldite granite, but their decrease downward is much gentler. Extreme enrichment of outer zones of zircon crystals from some granites with Hf or high contents of Th, U, REE, Y, Nb and of some other elements in zircons from other localities is not considered to be a specific phenomenon characterizing melts of A- or S-type granite, but reflects a high degree of fractionation of systems rich in Na and F.
机译：我们研究了两个对比的Variscan花岗岩系统中锆石化学成分的垂直变化。 Beauvoir系统（法国马西夫中央）由三个连续的侵入岩（B1，B2，B3）组成，代表了典型的铝质S型花岗岩，富含P，F，Li，Rb，Cs，Be，Sn，Nb，Ta和Cinovec系统（捷克共和国/德国的Kru？néhory Mts / Erzgebirge，捷克共和国/德国）由两个连续的侵入岩（原生锂石花岗岩，zinnwaldite花岗岩）组成，仅略带高铝质，贫P，F， Li，Rb，Cs，U，Th，REE，Y，Sc，Sn，W，Nb，富含Ta的花岗岩可归为A型。在这两个地方，入侵程度最高的入侵都位于系统的顶部。 GPF-1钻孔（Beauvoir）的样品代表整个花岗岩储层的800 m长垂直截面，而CS-1钻孔（Cinovec）的深度达到1600 m。两种花岗岩系统中锆石的化学成分均显示出明显的垂直带状性，但它们的形状和元素形态却形成了鲜明的对比。在波伏娃，锆石的Hf含量从2-4 wt。％显着增加。最深的B3单元中的％Hf0_2（-0.03 apfu Hf）至15-19 wt。最上面的B1单元中的％Hf0_2（最高0.18 apfu Hf）。在400-600 m深度的中间单元B2中检测到F，P和U的最高含量。在Cinovec，Hf仅显示来自ca的中等富集。 2重量较深的原生锂花岗岩中的Hf0_2为5-10 wt。％。高含量的Th（3-8 wt。％Th0_2）在花岗岩石系的最上部达到200 m的深度，但在此水平以下，含量仅偶尔超过1 wt。 ％ThQ2。 U，Y，HREE，Sc和Bi的浓度在zinnwaldite花岗岩的最上部也达到了最高值，但向下的减小要缓和得多。来自某些地方的Hf或高含量的Th，U，REE，Y，Nb和其他位置的锆石中某些其他元素的花岗岩中的锆石晶体的外部区域的极端富集不被认为是表征A-或Or熔体的特殊现象。 S型花岗岩，但反映出富含Na和F的系统的高度分馏。

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