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首页> 外文期刊>Contributions to Mineralogy and Petrology >Textural evidence of magma decompression, devolatilization and disequilibrium quenching: an example from the Western Krusne hory/Erzgebirge granite pluton
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Textural evidence of magma decompression, devolatilization and disequilibrium quenching: an example from the Western Krusne hory/Erzgebirge granite pluton

机译：岩浆减压，脱挥发分和不平衡淬火的质地证据：来自西部克鲁斯（Krusne hory）/厄尔士山脉的花岗岩岩体的例子

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We report new occurrences of "two-phase" granitic textures from the Western Krusne hory/Erzgebirge pluton (central Europe) and use crystal-size distribution data and thermodynamic modeling to interpret their crystallization conditions. The two-phase texture consists of (1) early phenocrysts of quartz, plagioclase, K-feldspar and biotite, (2) medium-grained matrix of the same phases and (3) interstitial channels and patches of a late-stage, very finegrained matrix. The porphyritic two-mica microgranites, which host two-phase textures, occur as minor intrusions in early low-F biotite granites or as marginal parts of evolved high-F Li-mica granites. Measurements of the crystal-size distribution of quartz revealed three grain populations: (1) early phenocrysts (0.5-3.0 mm) showing partial resorption by residual melt, (2) a medium-grained population of the equigranular rock matrix (0.05-0.50 mm) that experienced minor coarsening by subsolidus annealing and (3) a finegrained population (<0.03 mm) in the interstitial channels and patches formed during rapid devolatilization; this quartz group shows no or poor grain coarsening. All samples exhibit similar fraction of the fine-grained population (44-52 percent) but proportions of phenocrysts to medium-grained matrix vary significantly. Thermodynamic modeling of liq-uidus equilibria and experimental data in the hydrous hap-logranite system require: (1) ascent of a granitic suspension (15-25 percent phenocrysts) under H_2O-undersaturated conditions at 25-45 bar/ deg C and a cooling rate of 40 J/(g kbar) in order to produce partial resorption of quartz phenocrysts and continued growth of feldspar phenocrysts, followed by (2) emplacement as discrete intrusions or bodies along pluton roof accompanied by sudden devolatilization. At the onset of matrix nucleation, disequilibrium undercooling of 70-85 deg C was inferred from the presence of micrographic intergrowths of quartz and K-feldspar. The two-phase granites in the Western Krusne hory/Erzgebirge pluton and in the Southeast Asian batholith form compositionally narrow groups with high-silica and moderate volatile enrichments but they differ in peraluminosity and phosphorus concentrations.
机译：我们报道了来自西克鲁斯纳霍里/厄尔士山脉厄尔（欧洲中部）的“两相”花岗岩质地的新出现，并使用晶体尺寸分布数据和热力学模型来解释其结晶条件。两相织构由（1）石英，斜长石，钾长石和黑云母的早期斑晶，（2）同一相的中粒基质和（3）后期，非常细粒的间隙通道和斑块组成矩阵。斑岩质的两云母微花岗岩具有两相结构，在早期低氟黑云母花岗岩中少量侵入，或在高氟锂云母花岗岩的边缘部分发育。测量石英的晶体尺寸分布可发现三个晶粒群：（1）早期的隐晶（0.5-3.0 mm），其显示出残余熔体的部分吸收;（2）中粒的等粒岩体（0.05-0.50 mm） ）通过亚固相线退火经历了轻微的粗化，并且（3）在快速脱挥发分期间形成的间隙通道和斑块中有细粒度的粒子（<0.03 mm）;该石英族没有或没有较差的晶粒粗化。所有样品均显示出相似的细粒度种群比例（44-52％），但表晶与中等粒度基质的比例差异很大。液相-白云母体系中液体-uidus平衡的热力学模型和实验数据要求：（1）在H_2O饱和条件下，在25-45 bar /℃和冷却条件下，在H_2O不足的条件下，上升花岗岩悬浮液（15-25％的细晶）。速率为40 J /（g kbar），以产生石英隐晶石的部分吸收和长石隐晶石的持续生长，然后是（2）沿着岩体顶沿着离散的侵入体或岩体安置，并伴有突然的脱挥发分。在基质成核开始时，从石英和钾长石的显微共生体的存在推断出70-85摄氏度的不平衡过冷。西部克鲁斯/赫兹/厄尔士山脉的岩体和东南亚的基岩中的两相花岗岩构成了具有高二氧化硅含量和中等挥发性富集作用的狭窄组群，但它们的钙铝矿化度和磷浓度不同。

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