Genesis of scapolite from granulites (lower-crustal xenoliths from the Pamir diatremes): results of study of melt inclusions
Genesis of scapolite from granulites (lower-crustal xenoliths from the Pamir diatremes): results of study of melt inclusions
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DOI：
10.1016/j.rgg.2011.10.005
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发表时间：
2011-11
影响因子：
1.1
通讯作者：
I. A. Madyukov;V. Chupin;D. Kuzmin
中科院分区：
文献类型：
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作者：
I. A. Madyukov;V. Chupin;D. Kuzmin
本文介绍了帕米尔东南部（塔吉克斯坦）辉绿斑岩双晶岩筒中方柱石麻粒岩下地壳捕虏体的矿物学和热压地球化学研究结果。这些麻粒岩的矿物（包括石榴子石、单斜辉石和方柱石）均含有原生熔融包裹体，并利用电子探针、西姆斯和拉曼光谱等方法对其进行了研究。我们已经确定，它们的成分对应于酸性（从流纹英安岩到流纹岩），基本上是H2O ≤ 4 wt.%的正常和高碱度的钾质熔体，Cl ≤ 0.8重量%，和CO2~ 1重量%。熔体中HREE亏损，Th/U比值高（7.7-9.4）。利用矿物学温压计对熔融包裹体的研究表明，含方柱石麻粒岩在约1000 °C和约15 kbar下结晶。这种岩石的结果，最有可能的，从不一致的熔融含碳酸盐的黑云母-石英-斜长石基板在下地壳，这是伴随着结晶的石榴石，单斜辉石，斜长岩，方柱岩捕获微量的酸性熔体作为包体。这些矿物不是从熔体中结晶出来的，而是在熔体存在时结晶出来的。当熔体中CO2含量达到高水平（~1 wt.%）时，高钙方柱石（Me 67 -69）代替斜长石结晶和Cl（≤ 0.8 wt.%）在富含二氧化碳的流体中。
The results of mineralogical and thermobarogeochemical studies of lower-crustal xenolith of scapolite-bearing granulites from the fergusite-porphyry diatremes pipes in Southeastern Pamir (Tajikistan) are presented. All minerals (including garnet, clinopyroxene, and scapolite) of these granulites contain primary melt inclusions, which were studied using thermometric and microprobe methods (EPMA, SIMS, Raman spectroscopy). We have established that their compositions correspond to acid (from rhyodacites to rhyolites), essentially potassic melts of normal and high alkalinity with H2O ≤ 4 wt.%, Cl ≤ 0.8 wt.%, and CO2~ 1 wt.%. The melts are depleted in HREE and have high Th/U ratios (7.7–9.4). Study of melt inclusions using mineralogical thermobarometers showed that the scapolite-bearing granulite crystallized at ~1000 °C and ~15 kbar. This rock resulted, most likely, from the incongruent melting of carbonate-bearing biotite-quartz-plagioclase substrate in the lower crust, which was accompanied by the crystallization of garnet, clinopyroxene, sphene, plagioclase, and scapolite trapping microportions of acid melts as inclusions. The minerals crystallized not from melt but in its presence. High-Ca scapolite (Me67–69) crystallized instead of plagioclase when the melts reached high contents of CO2(~1 wt.%) and Cl (≤ 0.8 wt.%) in the presence of CO2-rich fluid.