Pre-metamorphic carbon, oxygen and strontium isotope signature of high-grade marbles from the Lützow-Holm Complex, East Antarctica: apparent age constraints of carbonate deposition
Pre-metamorphic carbon, oxygen and strontium isotope signature of high-grade marbles from the Lützow-Holm Complex, East Antarctica: apparent age constraints of carbonate deposition
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DOI：
10.1144/sp308.7
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
M. Satish‐Kumar;T. Miyamoto;J. Hermann;H. Kagami;Y. Osanai;Y. Motoyoshi
中科院分区：
文献类型：
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作者：
M. Satish‐Kumar;T. Miyamoto;J. Hermann;H. Kagami;Y. Osanai;Y. Motoyoshi
摘要东南极Lützow-Holm杂岩高级大理岩的C、O、Sr同位素地球化学研究为研究其沉积时代和沉积后蚀变提供了线索。白云质和方解石大理石以不同厚度（高达100米）的薄层出现在德龙宁毛德地东部的几个露头中，其中大部分经历了沉积后的地球化学蚀变。特别是Sr和O同位素变化广泛，87 Sr/86 Sr（550 Ma）比值高达0.758，δ 18 O值低至−5‰。这些数据表明，成岩作用期间多阶段的流体-岩石相互作用过程、进变质至峰期和退变质事件改变了沉积同位素特征。然而，一些大理岩层，例外地，保存变质前的地球化学特征，如低Sr同位素比值，高δ 18 O和δ 13 C值，以及平衡良好的未蚀变的微量和稀土元素模式。最低的87 Sr/86 Sr同位素比值为0.7066和0.7053，δ 13 C和δ 18 O值较高，表明沉积年龄约为730-830 Ma，但不能排除该年龄段海水对碳酸盐岩的总地球化学重置。表观沉积年龄是一致的碳酸盐沉积在“莫桑比克海洋”，东，西冈瓦纳分离。
Abstract C, O and Sr isotope geochemistry of high-grade marbles from the Lützow-Holm Complex, East Antarctica, has given clues on the depositional ages and post-depositional alterations. Dolomitic and calcitic marbles occur as thin layers with varying thickness (up to 100 m) in several outcrops in eastern Dronning Maud Land, most of which underwent post-depositional geochemical alterations. In particular, the Sr and O isotope alterations are extensive, with 87Sr/86Sr(550 Ma) ratios as high as 0.758 and δ18O values as low as −5‰. These data suggest that multiple stages of fluid–rock interaction processes during diagenesis, prograde to peak and retrograde metamorphic events have altered the depositional isotopic signatures. However, some of the marble layers, exceptionally, preserve pre-metamorphic geochemical characteristics, such as low Sr isotope ratios, high δ18O and δ13C values, and well-equilibrated unaltered trace and rare earth element patterns. Lowest 87Sr/86Sr isotopic ratios of 0.7066 and 0.7053 with high δ13C and δ18O values suggest an apparent age of deposition around 730–830 Ma, although total geochemical resetting of carbonates by seawater of this age cannot be ruled out. The apparent depositional ages are consistent with carbonate deposition in the ‘Mozambique Ocean’ that separated East and West Gondwana.