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首页> 外文期刊>Contributions to Mineralogy and Petrology >Rare earth element evolution and migration in plagiogranites: a record preserved in epidote and allanite of the Troodos ophiolite
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Rare earth element evolution and migration in plagiogranites: a record preserved in epidote and allanite of the Troodos ophiolite

机译：斜长花岗岩中稀土元素的演化和迁移：Troodos蛇绿岩的附子和尿囊石中保存的记录

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Plagiogranites from the Troodos ophiolite in Cyprus are occasionally epidotised, either partially or completely. Epidotisation phenomena include replacement of pre-existing minerals and filling of miarolitic cavities. In addition to epidote, miarolites in one plagiogranite body (located near the village of Spilia) contain coexisting ferriallanite-(Ce) and allanite-(Y). Textural and geochemical evidence indicates that late-stage REE-enriched granitic melt facilitated crystallisation of magmatic ferriallanite-(Ce). High REE contents persisted after fluid exsolution, causing crystallisation of allanite-(Y) from hydrothermal fluids in the miarolites. The REE pattern of the hydrothermal allanite-(Y) is characterised by LREE and Eu depletion, similar to the parent plagiogranitic magma. As allanite had sequestered most of the REE in the fluid, epidote took over as the principle hydrothermal mineral. Epidote in Troodos plagiogranites records a fluid evolutionary trend beginning with REE-rich-Eu-depleted similar to allanite-(Y) and gradually transforming into the REE-depleted-Eu-enriched pattern prevalent throughout 'conventional' sub-seafloor fluids. A comparison of allanite-bearing and allanite-absent plagiogranites from the same locality suggests that REE-bearing fluids migrated from the plagiogranites. Similar fluid evolution trends observed in diabase-hosted epidote, located adjacent to a large plagiogranite body, suggest influx of plagiogranite-derived REE-bearing fluids. Epidotisation in oceanic settings is usually considered to be the result of alteration by high fluxes of seawater-derived hydrothermal fluids. Although epidotisation by magmatic fluids has been suggested to occur in plagiogranites, our study shows that this autometasomatic process is the dominant mechanism by which epidosites form in plagiogranites. Furthermore, epidotisation of diabase has been attributed solely to seawater-derived fluids, but we show that it is possible for diabase-hosted epidosites to form by migration of plagiogranite-derived fluids.
机译：来自塞浦路斯Troodos蛇绿岩的斜长花岗岩偶尔会部分或全部被石化。岩化现象包括替换先前存在的矿物质和填满微孔洞。除附子外，在一个斜长花岗岩体（位于斯皮利亚村附近）中的辉石岩还含有同时存在的亚铁辉石-（Ce）和尿囊石-（Y）。结构和地球化学证据表明，晚期富集稀土的花岗岩熔体促进了岩浆性铁铝榴石-（Ce）的结晶。流体释放后高REE含量仍然存在，从而导致镁铝石中热液中的尿石-（Y）结晶。地热斜长石-（Y）的REE模式以LREE和Eu耗尽为特征，类似于母体斜纹石岩浆。由于尿囊石封存了流体中的大部分稀土元素，因此，附子成为主要的热液矿物。 Troodos斜长花岗岩中的Epidote记录了一种流体演化趋势，其始于类似于ananite-（Y）的富REE-Eu贫化，并逐渐转变为在“常规”海底地下流体中普遍存在的REE-贫化-Eu富集模式。比较来自相同位置的含尿石和不含尿石的斜长花岗岩，表明含稀土元素的流体从斜长花岗岩中迁移出来。在与大型斜长花岗岩体相邻的辉绿岩寄主的附子中观察到类似的流体演化趋势，表明大量斜长花岗岩衍生的含REE流体涌入。通常认为海洋环境中的岩化作用是海水衍生的热液的高通量改变的结果。尽管已经有人认为斜岩花岗岩中会发生岩浆流体的岩化作用，但我们的研究表明，这种自动变岩过程是斜岩花岗岩中岩岩形成的主要机制。此外，辉绿岩的岩溶作用仅归因于海水衍生的流体，但我们表明，辉绿岩衍生的流体的迁移有可能形成辉绿岩基质的岩岩。

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