Allanite: thorium and light rare earth element carrier in subducted crust
Allanite: thorium and light rare earth element carrier in subducted crust
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DOI：
10.1016/s0009-2541(02)00222-x
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发表时间：
2002-12-30
期刊：
影响因子：
3.9
通讯作者：
Hermann, J
中科院分区：
文献类型：
--
作者：
Hermann, J
对西阿尔卑斯山多拉-马伊拉山榴辉岩深俯冲带的研究表明，副矿物是微量元素的重要寄主。金红石含有大部分的岩石块体Ti，Nb和Ta，而锆石主机几乎所有的Zr和HE超过90%的岩石块体轻稀土元素（LPEE）和Th和约75%的U被纳入副褐帘石。多硅白云母是最有趣的主要矿物，因为它含有超过95%的Rb，Ba和Cs。在2.0-4.5 GPa、680-1150 ℃范围内的模型地壳成分中，掺杂微量元素的合成活塞缸实验表明，在700 ℃和2.0 GPa以上的温度下，以牺牲主要矿物锆石为代价形成副褐帘石。褐帘石通过掺入轻稀土元素而稳定，并且在高达1050摄氏度的温度和至少4.5 GPa的压力下被发现。褐帘石的消失是由于在共存的含水花岗岩熔体中溶解而引起的，与任何主相的分解无关。实验确定的元素之间的分配褐帘石和含水花岗岩熔体在900 ℃，2.0 GPa产量D-LREE（所有熔体）约200（Th）（所有熔体）的60和D-U（所有熔体）的20。这些结果，结合文献数据，被用来估计轻稀土元素的饱和度作为温度的函数的俯冲带液体。褐帘石是一种残留相，温度至少高达900和1000 ℃的变玄武岩和变沉积物，分别为小于或等于10%的部分熔融。因此，褐帘石能够控制LREE和较小程度的Th含量的临界温度范围内的俯冲带液体提取。与褐帘石共存的低温流体不能输送大量的轻稀土元素，因此，显示这些元素富集的弧熔岩可能源自经历了含水花岗岩熔体交代作用的地幔源，（C）2002 Elsevier Science B.V保留所有权利。
ne investigation of deeply subducted eclogites from the Dora-Maira massif, Western Alps reveals that accessory minerals are important hosts for trace elements. Rutile contains most of the bulk rock Ti, Nb and Ta while zircon hosts nearly all Zr and HE More than 90% of the bulk rock light rare earth elements (LPEE) and Th and about 75% of U are incorporated in accessory allanite. Phengite is the most interesting major mineral because it hosts more than 95% of Rb, Ba and Cs. Synthesis piston cylinder experiments in a model crustal composition in the range 2.0-4.5 GPa, 680-1150 degreesC doped with trace elements demonstrate that accessory allanite forms at the expense of the major mineral zoisite at temperatures above 700 degreesC and 2.0 GPa. Allanite is stabilised by the incorporation of light rare earth elements and was found up to temperatures of 1050 degreesC and to pressures of at least 4.5 GPa. Disappearance of allanite is caused by dissolution in a coexisting hydrous granitic melt and is not related to the breakdown of any major phase. Experimentally determined element partitioning between allanite and a hydrous granitic melt at 900 degreesC, 2.0 GPa yield D-LREE(all melt) of about 200(Th)(all melt) of 60 and D-U(all melt) of 20. These results, combined with literature data, are used to estimate light rare earth element saturation levels of subduction zone liquids as a function of temperature. Allanite is a residual phase up to temperatures of at least 900 and 1000 degreesC for metabasalts and metasediments, respectively, at less than or equal to 10% partial melting. Allanite is therefore capable of controlling LREE and to a lesser extent Th contents for the critical temperature range of subduction zone liquid extraction. Low temperature fluids coexisting with allanite are not capable of transporting significant amounts of light rare earth elements and therefore arc lavas showing enrichment of these elements probably originate from a mantle source that experienced metasomatism by a hydrous granitic melt, (C) 2002 Elsevier Science B.V All rights reserved.