Eberhard Lisa, Mazzucchelli Mattia Luca, Schmalholz Stefan Markus, Stünitz Holger, Addad Ahmed, Cordier Patrick, Plümper Oliver
Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.
Institute of Earth Sciences, University of Lausanne, Lausanne, Switzerland.
Contrib Mineral Petrol. 2025;180(9):64. doi: 10.1007/s00410-025-02255-z. Epub 2025 Aug 23.
The dehydration of antigorite is an important reaction in subduction zones with implications on both geochemical and geophysical processes. In this experimental study we focus on the onset of antigorite dehydration and investigate various chemical and physical parameters as possible drivers for the fluid release. We performed hydrostatic and co-axial Griggs experiments on antigorite serpentinites with variable chemical composition and microstructures at high-pressure and high-temperature conditions across the antigorite dehydration (1.5 GPa, 620-670 °C). For these conditions, our thermodynamic models predict the formation of olivine from magnetite decomposition and partial dehydration of antigorite. Detailed analyses of the run products reveal limited magnetite decomposition. Antigorite dehydration is restricted to samples that have been deformed. Nano-sized olivine and orthopyroxene formed locally in oblique dehydration bands and exhibit neither a clear crystallographic preferred orientation nor a topotactic relation with precursor antigorite. We argue that limited local dehydration in our experiments is related to strain and variations in reaction kinetics. Systematic investigation excludes mineralogical and chemical heterogeneities, and temperature gradients as reaction driving potentials. The structural relation of the dehydration bands suggests deformation-related dehydration, which is supported by numerical simulations that couple reaction kinetics with mechanical work rate and self-consistently predict dehydration bands. In this scenario, strain concentration due to applied axial stress locally increases the internal energy of antigorite to reach the activation energy of the dehydration reaction, enabling dehydration. This study highlights the importance of coupled mechanical and chemical processes and provides a mechanistic framework for deformation-induced dehydration of antigorite.
The online version contains supplementary material available at 10.1007/s00410-025-02255-z.
叶蛇纹石脱水是俯冲带中的一个重要反应，对地球化学和地球物理过程都有影响。在这项实验研究中，我们聚焦于叶蛇纹石脱水的起始，并研究各种化学和物理参数作为流体释放的可能驱动因素。我们在高压和高温条件下（1.5吉帕，620 - 670°C），对具有可变化学成分和微观结构的叶蛇纹石蛇纹岩进行了静水和共轴格里格斯实验，跨越叶蛇纹石脱水阶段。对于这些条件，我们的热力学模型预测磁铁矿分解和叶蛇纹石部分脱水会形成橄榄石。对实验产物的详细分析显示磁铁矿分解有限。叶蛇纹石脱水仅限于已变形的样品。纳米级橄榄石和斜方辉石在倾斜脱水带中局部形成，既没有明显的晶体择优取向，也与前驱叶蛇纹石不存在拓扑关系。我们认为，我们实验中有限的局部脱水与应变和反应动力学的变化有关。系统研究排除了矿物学和化学不均匀性以及温度梯度作为反应驱动势。脱水带的结构关系表明与变形相关的脱水，这得到了将反应动力学与机械功率耦合并自洽预测脱水带的数值模拟的支持。在这种情况下，由于施加的轴向应力导致的应变集中会局部增加叶蛇纹石的内能，以达到脱水反应的活化能，从而实现脱水。本研究强调了机械和化学过程耦合的重要性，并为叶蛇纹石变形诱导脱水提供了一个机理框架。
在线版本包含可在10.1007/s00410 - 025 - 02255 - z获取的补充材料。
