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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 Krušné hory/Erzgebirge granite pluton
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Textural evidence of magma decompression, devolatilization and disequilibrium quenching: an example from the Western Krušné 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：来自西部克鲁斯内霍里/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 Krušné 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 fine-grained 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 fine-grained 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%) but proportions of phenocrysts to medium-grained matrix vary significantly. Thermodynamic modeling of liquidus equilibria and experimental data in the hydrous haplogranite system require: (1) ascent of a granitic suspension (15–25% phenocrysts) under H2O-undersaturated conditions at 25–45 bar/°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°C was inferred from the presence of micrographic intergrowths of quartz and K-feldspar. The two-phase granites in the Western Krušné 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：我们报告了来自西克鲁斯内厄里/厄尔士山脉的中子（中欧）新出现的“两相”花岗岩质地，并使用晶体尺寸分布数据和热力学模型解释了它们的结晶条件。两相织构由（1）石英，斜长石，钾长石和黑云母的早期斑晶，（2）相同相的中粒基质和（3）后期的非常精细的间隙通道和斑块组成粒度矩阵。拥有两相织构的斑状两云母微花岗岩发生在早期低氟黑云母花岗岩中的少量侵入，或作为演化的高氟锂云母花岗岩的边缘部分。石英晶体尺寸分布的测量显示出三个晶粒群：（1）早期的隐晶（0.5–3.0 mm）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部分（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相线平衡的热力学模型和实验数据要求：（1）在H 2 O-不饱和条件下，在25-45 bar / h的条件下，花岗岩悬浮液（15-25％的表晶）上升。 °C和40 J /（g kbar）的冷却速率以使石英细晶部分吸收并长石细晶继续生长，然后（2）沿着岩体顶部沿着离散的侵入体或体安置，并伴有突然的脱挥发分。在基体成核开始时，由石英和钾长石的显微共生体推断出70-85°C的不平衡过冷。西部克鲁斯内厄里/厄尔士山脉的岩体和东南亚基岩中的两相花岗岩形成了具有高二氧化硅含量和中等挥发性富集的窄组群，但它们的过铝铝酸盐含量和磷含量不同。

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