Crystal Size Distribution of Periclase in Contact Metamorphic Dolomite Marbles from the Southern Adamello Massif, Italy
Crystal Size Distribution of Periclase in Contact Metamorphic Dolomite Marbles from the Southern Adamello Massif, Italy
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意大利阿达梅洛地块南部接触变质白云石大理石方镁石的晶体尺寸分布
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发表时间：
2009
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通讯作者：
J. R. Bowman
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作者：
T. Müller;L. Baumgartner;C. Foster;J. R. Bowman
介绍了意大利阿达梅洛地块南部Cima Uzza峰附近两个剖面接触变质白云岩大理岩中方镁石的粒度分布。该数据库结合地球化学和岩石学信息推断方镁石形成反应的控制。接触变质白云岩大理岩出露于镁铁质侵入岩接触部位，部分被镁铁质侵入岩包围。水镁石是退变质的假球状方镁石晶体。方镁石的前向生长是在6058 ℃附近富水流体有限渗透的结果。稳定同位素数据显示，13 C和18 O在岩浆接触面附近的一个狭窄区域（约40厘米）内耗尽，而方镁石形成反应前沿从接触面延伸至4米。CSD分析沿着两个配置文件显示，方镁石晶体的中值粒度不改变，但有一个渐进的更大的粒度分布，包括较大的颗粒的比例更大，与接触的距离增加。一个定性的模型，根据纹理和地球化学数据，属性这些变化的粒度变化的反应亲和力沿着动力学分散的渗透前沿。这项研究强调了需要调用变质矿物生长的不平衡过程，并扩大使用CSD的矿物形成系统驱动的流体渗透。
Crystal size distributions (CSD) of periclase in contact metamorphic dolomite marbles are presented for two profiles near the Cima Uzza summit in the southern Adamello Massif (Italy). The database was combined with geochemical and petrological information to deduce the controls on the periclase-forming reaction. The contact metamorphic dolomite marbles are exposed at the contact of mafic intrusive rocks and are partially surrounded by them. Brucite is retrograde and pseudomorphs spherical periclase crystals. Prograde periclase growth is the consequence of limited infiltration of waterrich fluid at T near 6058C. Stable isotope data show depletion in 13 C and 18 O over a narrow region (� 40 cm) near the magmatic contact, whereas the periclase-forming reaction front extends up to 4 m from the contact. CSD analyses along the two profiles show that the median grain size of the periclase crystals does not change, but that there is a progressively greater distribution of grain sizes, including a greater proportion of larger grains, with increasing distance from the contact. A qualitative model, based on the textural and geochemical data, attributes these variations in grain size to changing reaction affinities along a kinetically dispersed infiltration front. This study highlights the need to invoke disequilibrium processes for metamorphic mineral growth and expands the use of CSDs to systems of mineral formation driven by fluid infiltration.