Pressure-temperature estimates of the lizardite/antigorite transition in high pressure serpentinites
Pressure-temperature estimates of the lizardite/antigorite transition in high pressure serpentinites
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DOI：
10.1016/j.lithos.2012.11.023
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发表时间：
2013-09
期刊：
影响因子：
3.5
通讯作者：
S. Schwartz;S. Guillot;B. Reynard;Romain Lafay;B. Debret;C. Nicollet;P. Lanari;A. Auzende
中科院分区：
文献类型：
--
作者：
S. Schwartz;S. Guillot;B. Reynard;Romain Lafay;B. Debret;C. Nicollet;P. Lanari;A. Auzende
天然样品中蛇纹石矿物以利蛇纹石和叶蛇纹石为主。尽管有许多实验室实验，这些物种的稳定领域仍然很难约束。本文介绍了阿尔卑斯山古增生楔中天然蛇纹岩的岩石学观察、拉曼光谱和X射线衍射分析。沿着沿着俯冲地热梯度，从亚绿片岩（P < 4 kbar，T ~ 200-300 °C）到榴辉岩相条件（P > 20 kbar，T > 460 °C）的一系列变质压力和温度条件下，确定了蛇纹石品种。我们使用所观察到的矿物组合在天然蛇纹岩沿着与Tmax估计的拉曼光谱的碳质物质在相关的变质沉积物约束的温度在高压下的利蛇纹石叶蛇纹石过渡。我们发现，在300 °C以下，利蛇纹石和局部温石棉是网状结构中的优势物种。在320 °C至390 °C之间，在富SiO2流体的存在下和在利蛇纹石网的核心中，利蛇纹石通过溶解-沉淀过程在晶界处逐渐被叶蛇纹石取代。在390 °C以上，在高品位蓝片岩到榴辉岩相条件下，叶蛇纹石是唯一稳定的蛇纹石矿物，直到460 °C时二次橄榄石结晶开始。
Serpentine minerals in natural samples are dominated by lizardite and antigorite. In spite of numerous laboratory experiments, the stability fields of these species remain poorly constrained. This paper presents petrological observations and the Raman spectroscopy and XRD analyses of natural serpentinites from the Alpine paleo-accretionary wedge. Serpentine varieties were identified from a range of metamorphic pressure and temperature conditions from sub-greenschist (P < 4 kbar, T ~ 200–300 °C) to eclogite facies conditions (P > 20 kbar, T > 460 °C) along a subduction geothermal gradient. We use the observed mineral assemblage in natural serpentinite along with the Tmaxestimated by Raman spectroscopy of the carbonaceous matter in associated metasediments to constrain the temperature of the lizardite to antigorite transition at high pressures. We show that below 300 °C, lizardite and locally chrysotile are the dominant species in the mesh texture. Between 320 and 390 °C, lizardite is progressively replaced by antigorite at the grain boundaries through dissolution–precipitation processes in the presence of SiO2enriched fluids and in the cores of the lizardite mesh. Above 390 °C, under high-grade blueschist to eclogite facies conditions, antigorite is the sole stable serpentine mineral until the onset of secondary olivine crystallization at 460 °C.