Antigorite Pressure and temperature dependence of polysomatism and water content
Antigorite Pressure and temperature dependence of polysomatism and water content
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DOI：
10.1127/0935-1221/2001/0013-0485
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发表时间：
2001-05
影响因子：
2.1
通讯作者：
B. Wunder;R. Wirth;M. Gottschalk
中科院分区：
文献类型：
--
作者：
B. Wunder;R. Wirth;M. Gottschalk
本文研究了MgO-SiO_2-H_2 O（MSH）体系中叶蛇纹石多体反应的压力和温度依赖性。TEM研究表明，MSH-叶蛇纹石形成的升高的温度和降低的压力与较短的a-晶胞周期性相关，即较小的m-值（m =沿波长a沿着的单链中四面体的数目）。对于所研究的P、T条件，叶蛇纹石的组成m范围相当窄（14-18），对应于Mg2.79Si2O5（OH）3.57 - Mg2.83Si2O5（OH）3.67。叶蛇纹石晶体结构的变化与逐渐的部分脱水过程和MgO的损失相结合。对于包括叶蛇纹石的反应的公式化，必须考虑叶蛇纹石的化学组成的P、T依赖性。然而，我们的研究结果支持了Mellini等人（1987）的结论，即调制相关的地质温压计的适用性有限，因为叶蛇纹石调制的平衡状态在自然界中很少观察到，在我们的实验中也没有达到。在含蛇纹岩的大洋岩石圈俯冲过程中叶蛇纹石的连续部分脱水可能影响其流变学性质。
The pressure and temperature dependence of antigorite polysomatism was investigated in the P,T-range of 350-710°C, 0.2-5.0 GPa within the system MgO-SiO2-H2O (MSH). TEM-study indicated that increasing temperature and decreasing pressure of MSH-antigorite formation are correlated with a shorter a-cell periodicity, i.e. smaller m- value (m = number of tetrahedra in a single chain along the wavelength a). For the P,T-conditions investigated, the compositional m-range of antigorite is rather narrow (14-18) corresponding to Mg2.79Si2O5(OH)3.57 - Mg2.83Si2O5(OH)3.67. The change in the crystal structure of antigorite is combined with a gradual partial dehydration process and loss of MgO. For the formulation of reactions that include antigorite, the P,T-dependence of the chemical composition of antig- orite has to be considered. However, our results support the conclusion of Mellini et al. (1987) of the limited appli- cability of a modulation-dependent geothermobarometer, because equilibrium states of antigorite modulation are rarely observed in natural occurrences and have not been reached in our experiments. The successive partial dehydration of antigorite during ongoing subduction of serpentine-bearing oceanic litho- sphere probably influences its rheological properties.