Discovery of lanthanide tetrad effect in an oceanic plagiogranite from an Ocean Core Complex at the Central Indian Ridge 25°S
Discovery of lanthanide tetrad effect in an oceanic plagiogranite from an Ocean Core Complex at the Central Indian Ridge 25°S
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DOI：
10.2343/geochemj.41.135
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发表时间：
2007-04
影响因子：
0.8
通讯作者：
Kentaro Nakamura;T. Morishita;Q. Chang;N. Neo;H. Kumagai
中科院分区：
文献类型：
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作者：
Kentaro Nakamura;T. Morishita;Q. Chang;N. Neo;H. Kumagai
本文报道了在中印度洋海脊25°S洋核杂岩中发现的大洋斜长花岗岩中首次发现了稀土元素四元系效应。斜长花岗岩主要由钠基斜长石、石英和角闪石组成，并有绿帘石、钛铁矿、锆石、磷灰石和尿安石等副矿物。研究样品的球粒陨石标准化稀土配分模式显示出明显的高稀土元素丰度和明显的负Eu异常，表明其具有很高的分离结晶程度。此外，凸起(M型)四分体效应在稀土配分模式中清晰可见，这意味着斜长花岗岩具有异常富含挥发性(如H2O、CO2、Li、B、F和/或Cl)的母岩浆。由于MORB源具有极低的挥发分含量，与来自海水的外部流体的相互作用被认为是海洋斜长花岗岩中存在四元效应的原因。
This paper reports the first discovery of lanthanide tetrad effect in an oceanic plagiogranite recovered from an Ocean Core Complex at 25°S along the Central Indian Ridge. The plagiogranite consists mainly of sodic plagioclase, quartz, and amphibole with accessory minerals of epidote, titanite, zircon, apatite, and allanite. The chondrite-normalized REE pattern of the studied sample exhibits noticeably high REE abundances with a conspicuous negative Eu-anomaly, indicative of very high degrees of fractional crystallization. In addition, the convex (M-type) tetrad effect is clearly recognizable in the REE pattern, implying an unusually volatile-rich (e.g., H2O, CO2, Li, B, F, and/or Cl) parent magma for the plagiogranite. Because MORB sources are known to have significantly low volatile content, interaction with an external fluid originating from seawater is suggested to be responsible for the presence of the tetrad effect in the oceanic plagiogranite.