Crystallization of REE minerals and redistribution of U, Th, and REE at contact boundary between granite and gabbro during hydrothermal alteration
Crystallization of REE minerals and redistribution of U, Th, and REE at contact boundary between granite and gabbro during hydrothermal alteration
复制标题
DOI：
10.1016/j.pce.2010.03.035
复制
发表时间：
2010-01-01
影响因子：
3.7
通讯作者：
Hidaka, Hiroshi
中科院分区：
文献类型：
--
作者：
Horie, Kenji;Tsutsumi, Yukiyasu;Hidaka, Hiroshi
在这项研究中，研究了日本西南部宇奈月地区与火成岩活动相关的钍和稀土元素 (REE) 的重新分布行为。在花岗岩和辉长岩的接触边界处。独居石、磷钇矿等稀土矿物，以及钾长石中的铁钛氧化物被辉长岩同化形成的稀土氧化物。 U 富集在磷钇矿 (UO2 > 0.72 wt.%) 和 REE 氧化物 (UO2 > 0.10 wt.%) 中，而 Th 富集在 REE 氧化物中 (ThO2 > 1.32 wt.%)。考虑到U4+和Y3+离子半径的相似性，U与重稀土元素一起并入磷钇矿和稀土元素氧化物中。 Th 掺入磷钇矿（八重配位位点）和独居石（九重配位位点）中分别受到较低含量的 Gd 和 Dy 的限制。接触边界处辉长岩中斜长石的索斯特岩化和花岗岩中黑云母的绿泥石化表明，辉长岩侵入后期发生了低温热液蚀变，发生在 253 +/- 1 Ma。相比之下，绿泥石化花岗岩中的锆石包含蚀变区域，其特征是背散射电子和阴极发光图像之间的暗响应；这是由于 Zr 和 Hf 的释放导致平均原子序数较低造成的；掺入非化学式元素，如 Ca、Fe 和 Al；由于辐射损伤导致结晶度低。改变的区域显示出 Th (ThO2 > 1.50 wt.%) 和轻稀土元素 (LREE) 到中稀土元素 (MREE) 的富集以及正 Eu 异常；这表明Th和LREE-MREE（特别是Eu2+）在热液蚀变过程中优先与Ca结合。 U. Th 的再分配行为。低温热液蚀变过程中的稀土元素和稀土元素强烈依赖于它们的离子半径。锆石中的钍矿可能是由高钍蚀变域的出溶形成的。 (C) 2010 Elsevier Ltd. 保留所有权利。
In this study, redistribution behaviors of U. Th, and rare earth elements (REE) in association with igneous activity in the Unazuki region of southwest Japan were investigated. At the contact boundary between granite and gabbro. REE minerals such as monazite, xenotime, and REE oxides formed with Fe-Ti oxides in K-feldspar assimilated by gabbro. U was enriched in xenotime (UO2 > 0.72 wt.%) and REE oxides (UO2 > 0.10 wt.%), whereas Th was concentrated in REE oxides (ThO2 > 1.32 wt.%). Considering the similarity between the ionic radii of U4+ and Y3+, U was incorporated into xenotime and REE oxides together with heavy REE. Th incorporation into xenotime (eightfold coordinated site) and monazite (ninefold coordinated site) was constrained by the lower contents of Gd and Dy, respectively. Saussuritization of plagioclase in gabbro and chloritization of biotite in granite at the contact boundary suggest low-temperature hydrothermal alteration at late stages of gabbro intrusion that occurred at 253 +/- 1 Ma. In contrast, zircon in the chloritized granite contained altered domains characterized by a dark response between back-scattered electron and cathodoluminescence images; this was caused by a low average atomic number due to the release of Zr and Hf; the incorporation of non-formula elements such as Ca, Fe, and Al; and low crystallinity because of radiation damage. The altered domains showed enrichments of Th (ThO2 > 1.50 wt.%) and light REE (LREE) to middle REE (MREE) as well as positive Eu anomalies; this suggests the preferential incorporation of Th and LREE-MREE (particularly Eu2+) with Ca occurring during the hydrothermal alteration. The redistribution behaviors of U. Th. and REE during low-temperature hydrothermal alteration strongly depend on their ionic radii. Thorite in zircon was probably formed by the exsolution of high-Th altered domains. (C) 2010 Elsevier Ltd. All rights reserved.