Contrasting origins of the upper mantle revealed by hafnium and lead isotopes from the Southeast Indian Ridge
Contrasting origins of the upper mantle revealed by hafnium and lead isotopes from the Southeast Indian Ridge
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DOI：
10.1038/nature03026
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发表时间：
2004-11
期刊：
影响因子：
64.8
通讯作者：
B. Hanan;J. Blichert‐Toft;D. Pyle;D. Christie
中科院分区：
文献类型：
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作者：
B. Hanan;J. Blichert‐Toft;D. Pyle;D. Christie
印度洋中脊玄武岩的同位素特征的起源仍然是个谜，因为这些玄武岩的地球化学成分要么与来自循环的、古老的蚀变洋壳和沉积物的污染相一致，要么与古老的大陆壳或岩石圈相一致。因此，放射性同位素特征可能是上地幔被含有再循环的蚀变古洋壳和沉积物的羽状物污染的结果，在冈瓦纳裂谷和分裂期间大陆物质的分离和分散到浅地幔中，或上地幔被古代俯冲过程污染。确定一个规模大到足以影响印度洋中脊玄武岩源区主要部分的过程是一个长期存在的问题。在这里，我们提出了铪和铅同位素数据从整个印度-太平洋地幔边界在澳大利亚-南极不一致地区的东南印度洋海岭，这表明，太平洋和印度上地幔玄武岩源区分别受到不同的机制。我们推断，在这个地区的印度上地幔同位素签名的影响主要是由下大陆地壳夹带冈瓦纳裂谷，而太平洋上地幔的同位素签名的影响主要是由洋底俯冲相关的过程。
The origin of the isotopic signature of Indian mid-ocean ridge basalts has remained enigmatic, because the geochemical composition of these basalts is consistent either with pollution from recycled, ancient altered oceanic crust and sediments, or with ancient continental crust or lithosphere. The radiogenic isotopic signature may therefore be the result of contamination of the upper mantle by plumes containing recycled altered ancient oceanic crust and sediments, detachment and dispersal of continental material into the shallow mantle during rifting and breakup of Gondwana, or contamination of the upper mantle by ancient subduction processes,. The identification of a process operating on a scale large enough to affect major portions of the Indian mid-ocean ridge basalt source region has been a long-standing problem. Here we present hafnium and lead isotope data from across the Indian–Pacific mantle boundary at the Australian–Antarctic discordance region of the Southeast Indian Ridge, which demonstrate that the Pacific and Indian upper mantle basalt source domains were each affected by different mechanisms. We infer that the Indian upper-mantle isotope signature in this region is affected mainly by lower continental crust entrained during Gondwana rifting, whereas the isotope signature of the Pacific upper mantle is influenced predominantly by ocean floor subduction-related processes.