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首页> 外文期刊>The American mineralogist >Mineralogical, geochemical, and textural indicators of crystal accumulation in the Adamello Batholith (Northern Italy)
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Mineralogical, geochemical, and textural indicators of crystal accumulation in the Adamello Batholith (Northern Italy)

机译：Adamello Batholith中的矿床，地球化学，地球化学和质地指标（北意大利北部）

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In this study, we quantitatively investigate crystal-melt segregation processes in two upper-crustal, intermediate-to-silicic plutons from the Tertiary Adamello Batholith, Italian Alps, by combining (1) an estimation of the amount of crystallized interstitial liquid using cathodoluminescence images, phase maps, and mass-balance calculations with (2) quantification of crystal preferred orientation using electron backscatter diffraction. Cathodoluminescence images, phase maps, and plagioclase profiles are used together to distinguish early grown primocrysts from overgrowths formed after the rheological "lock-up" of the magma bodies. Mass-balance calculations, taking into account mineral compositions and bulk-rock chemistry, are used as an additional means to quantify the amount of trapped melt. The following features are indicative of crystal accumulation (or melt loss) in some parts of the batholith: (1) The amount of crystallized interstitial liquid can be low and negatively correlated with crystal (and shape) preferred orientations. Locally, up to ca. 27% melt may have been lost. (2) Significant intracrystalline deformation in plagioclase (up to ca. 13 degrees of lattice distortion) is present in strongly foliated samples, resulting from compaction in a highly crystalline mush. These mineralogical and textural features indicative of variability in the degree of crystal accumulation in some areas of the Adamello batholith may explain the highly scattered bulk-rock geochemical patterns (particularly in trace elements). However, the precise quantification of the amount of melt loss remains challenging in felsic plutons, because of the compositional deviation from liquid lines of descent due to multi-scale variations in the degree of crystal-melt segregation and the fact that magmatic textures indicative of crystal accumulation can be subtle.
机译：在这项研究中，我们通过结合（1）使用阴极发光图像、相图、以及，和质量平衡计算（2）使用电子背散射衍射定量晶体择优取向。阴极发光图像、相图和斜长石剖面一起用于区分早期生长的原晶体和岩浆体流变“锁定”后形成的过度生长。考虑到矿物成分和大块岩石化学，质量平衡计算被用作量化滞留熔体量的额外手段。以下特征表明岩基某些部分存在晶体积累（或熔体损失）：（1）结晶间隙液的数量可能较低，且与晶体（和形状）首选方向呈负相关。在当地，高达27%的熔体可能已经流失。（2） 由于在高度结晶的糊状物中压实，强烈叶化样品中存在斜长石的显著晶内变形（高达约13度的晶格畸变）。这些矿物学和结构特征表明，阿达梅洛岩基某些区域的晶体聚集程度存在差异，可以解释高度分散的大块岩石地球化学模式（尤其是微量元素）。然而，在长英质深成岩体中，熔体损失量的精确量化仍然具有挑战性，因为晶体熔体分离程度的多尺度变化导致成分偏离液体下降线，而且指示晶体聚集的岩浆结构可能很微妙。

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