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首页> 外文期刊>Contributions to Mineralogy and Petrology >Fractional crystallization of primitive, hydrous arc magmas: an experimental study at 0.7 GPa
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Fractional crystallization of primitive, hydrous arc magmas: an experimental study at 0.7 GPa

机译：原始含水弧形岩浆的部分结晶：0.7 GPa的实验研究

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Differentiation of mantle-derived, hydrous, basaltic magmas is a fundamental process to produce evolved intermediate to SiO_2-rich magmas that form the bulk of the middle to shallow continental and island arc crust. This study reports the results of fractional crystallization experiments conducted in a piston cylinder apparatus at 0.7 GPa for hydrous, calc-alkaline to arc tholeiitic magmas. Fractional crystallization was approached by synthesis of starting materials representing the liquid composition of the previous, higher temperature experiment. Temperatures ranged from near-liquidus at 1,170℃ to near-solidus conditions at 700℃. H_2O contents varied from 3.0 to more than 10 wt%. The liquid line of descent covers the entire compositional range from olivine-tho-leiite (1,170℃) to high-silica rhyolite (700℃) and evolves from metaluminous to peraluminous compositions. The following crystallization sequence has been established: olivine→ clinopyroxene → plagioclase, spinel → orthopyroxene, amphibole, titanomagnetite → apatite → quartz, biotite. Anorthite-rich plagioclase and spinel are responsible for a marked increase in SiO_2-content (from 51 to 53 wt%) at 1,040℃. At lower temperatures, fractionation of amphibole, plagioclase and Fe-Ti oxide over a temperature interval of 280℃ drives the SiO_2 content continuously from 53 to 78 wt%. Largest crystallization steps were recorded around 1,040℃ and at 700℃. About 40 % of ultramafic plutonic rocks have to crystallize to generate basaltic-andesitic liquids, and an additional 40 % of amphibole-gabbroic cumulate to produce granitic melts. Andesitic liquids with a liquidus temperature of 1,010℃ only crystallize 50 % over an 280℃ wide range to 730℃ implying that such liquids form mobile crystal mushes (<50 % crystals) in long-lived magmatic systems in the middle crust, allowing for extensive fractionation, assimilation and hybridization with periodic replenishment of more mafic magmas from deeper magma reservoirs.
机译：地幔衍生，含水，玄武岩浆的分化是产生演化到富SiO_2的岩浆的中间过程的基本过程，这些SiO_2岩浆形成了中，浅大陆和岛弧壳的主体。这项研究报告了在0.7 GPa的活塞缸设备中对含水钙碱至弧形岩浆进行分级结晶实验的结果。通过合成代表先前的较高温度实验的液体组成的原料来实现部分结晶。温度范围从1170℃接近液相线到700℃接近固相线。 H_2O含量从3.0到10 wt％以上不等。下降的液体线涵盖了从橄榄石-黄铁矿（1,170℃）到高硅流纹岩（700℃）的整个成分范围，并且从金属成分转变为高铝成分。已建立以下结晶顺序：橄榄石→斜吡咯烷→斜长石，尖晶石→邻苯二酚，斜闪石，钛磁铁矿→磷灰石→石英，黑云母。富含钙长石的斜长石和尖晶石在1,040℃时导致SiO_2含量显着增加（从51 wt％增至53 wt％）。在较低的温度下，闪石，斜长石和Fe-Ti氧化物在280℃的温度范围内的分馏将SiO_2的含量从53 wt％连续提高到78 wt％。最大的结晶步骤记录在1,040℃和700℃左右。大约40％的超镁铁质深成岩必须结晶才能生成玄武质-安山岩液，另外40％的闪石-闪石堆积形成花岗岩熔体。液相线温度为1,010℃的安第斯液体只能在280℃至730℃的宽范围内结晶50％，这意味着此类液体在中地壳的长寿命岩浆系统中形成了可移动的晶体糊状物（<50％的晶体），从而可以广泛地扩散。较深的岩浆储集层对更多的镁铁质岩浆进行定期补充，分级，同化和杂交。

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