Isotopic evidence for a hotspot origin of the Louisville Seamount Chain
Isotopic evidence for a hotspot origin of the Louisville Seamount Chain
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DOI：
10.1029/gm043p0283
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发表时间：
2013-03
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通讯作者：
Q. Cheng;K. Park;J. Macdougall;A. Zindler;G. Lugmair;H. Staudigel;J. Hawkins;P. Lonsdale
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作者：
Q. Cheng;K. Park;J. Macdougall;A. Zindler;G. Lugmair;H. Staudigel;J. Hawkins;P. Lonsdale
路易斯维尔海山链(LSC)是南太平洋最长的海山链，在许多方面与夏威夷-帝王链相似，暗示着一个热点起源。对横跨LSC全长、时间跨度超过65My的10座LSC海山的15个样品进行了Ndsr和Pb3种同位素组成的分析。由于大多数样品都是陈旧的和蚀变的，为了研究海水的蚀变效应和获得年龄校正的锶和钕同位素组成，进行了系统的淋溶实验。这些实验表明，即使是新出现的样品也由于海水锶的加入而升高了87Sr/86Sr，而且高度蚀变的样品可能含有大量的海水Nd，可能赋存于次生氧化物或磷酸盐相中。然而，经过适当的浸出后，可以获得可靠的、经过年龄校正的87Sr/86Sr和143Nd/144Nd的初始比值。淋滤样品的数据显示，同一海山内不同岩石类型和整个LSC链的锶、钕和铅同位素组成的范围都很窄(87Sr/86Sr从.7032到.7038；143Nd/144Nd从.51282到.51294；206Pb/204Pb从19.128到19.452)。LSC海山记录了不同于MORB源的化学羽流特征，并且在很长一段时间内在大范围内非常均匀。这些数据还暗示了长寿命上升地幔热柱的固定源区，从而有利于摩根[1971,1972a，b]提出的至少部分非对流的地幔结构和热点热柱可能的深地幔起源。LSC和MORB源之间没有明显的混合，这可能对烟羽的传输机制有影响。
The Louisville Seamount Chain (LSC) is the longest seamount chain in the South Pacific and in many ways resembles the Hawaiian‐Emperor chain, suggesting a hotspot origin. Fifteen samples from ten LSC seamounts spanning the length of the LSC and covering a time span of more than 65 My were analyzed for Nd, Sr and Pb isotopic compositions. Since most of the samples are old and altered, systematic leaching experiments were conducted in order to study seawater alteration effects and to obtain age‐corrected Sr and Nd isotopic compositions. These experiments show that even fresh appearing samples have elevated87Sr/86Sr due to seawater Sr addition, and that highly altered samples may contain substantial amounts of seawater Nd, possibly hosted in secondary oxides or phosphate phases. However, after appropriate leaching, reliable, age‐corrected87Sr/86Sr and143Nd/144Nd initial ratios can be obtained. The data for leached samples show very narrow ranges in Sr, Nd and Pb isotopic compositions (87Sr/86Sr from .7032 to .7038;143Nd/144Nd from .51282 to .51294;206Pb/204Pb from 19.128 to 19.452) both for different rock types within the same seamount and for the LSC chain as a whole. The LSC seamounts record a chemical plume signature that is distinct from that of MORB sources and is very homogeneous on a large scale over a long period of time. The data also imply a stationary source region for the long‐lived upwelling mantle plume, thus favoring a mantle structure which is at least partly non‐convective and a likely deep mantle origin for the hotspot plume as proposed by Morgan [1971, 1972a,b]. No appreciable mixing occurred between the LSC and MORB sources, which may have implications for the mechanism of plume transport.