Partial melting and reaction along deformation features in plagioclase
Partial melting and reaction along deformation features in plagioclase
复制标题
DOI：
10.1111/jmg.12702
复制
发表时间：
2022-11
影响因子：
3.4
通讯作者：
Sarah Incel;M. Baïsset;L. Labrousse;A. Schubnel
中科院分区：
文献类型：
--
作者：
Sarah Incel;M. Baïsset;L. Labrousse;A. Schubnel
涉及变形和/或反应的地质过程受到岩石粒度的高度影响，特别是如果发生扩散控制过程，如变质反应和扩散蠕变。虽然许多过程，诱导晶粒尺寸减小，记录和理解在相对高的应力和低温（例如，碎裂）以及在较低应力和较高温度条件下（例如，膨胀和亚晶粒旋转），变形孪晶，一种在较低温度下在各种矿物中活跃的塑性变形机制，被忽略为熔融和反应的成核位点，因此到目前为止是晶粒尺寸减小的原因。我们在2.5至3 GPa的围压和700°C至950°C的温度下，使用两种不同的变形装置，变形多砧装置（DDIA）和Griggs压力机，以及活塞缸装置，对天然斜长石骨料进行了实验。无论仪器类型如何，我们都观察到斜长石分解为榴辉岩相共生体，这与榴辉岩相高温域的部分熔融有关。部分熔化主要发生在沿着晶界和相间边界。然而，几个熔融斑块或斜长石分解产物与斜长石中变形孪晶和晶粒尺度微裂纹的发生同时发生，表明除了沿着晶粒和相间边界的熔融和反应之外，还存在晶内熔融和反应。在本研究中，我们展示了脆性微裂纹和塑性变形孪晶之间的相互作用如何导致晶内熔融和/或反应，这有可能降低富含斜长石的岩石的有效晶粒尺寸，从而影响它们的反应性和变形行为。
Geological processes involving deformation and/or reactions are highly influenced by the rock grain size, especially if diffusion‐controlled processes take place such as metamorphic reactions and diffusion creep. Although many processes, inducing grain‐size reduction, are documented and understood at relatively high stresses and low temperatures (e.g., cataclasis) as well as at lower stress and higher temperature conditions (e.g., bulging and subgrain rotation), deformation twinning, a plastic deformation mechanism active in various minerals at lower temperatures, has been neglected as nucleation site for melting and reaction and thus as a cause for grain‐size reduction so far. We conducted experiments on natural plagioclase‐bearing aggregates at 2.5 to 3 GPa confining pressure and temperatures of 700°C to 950°C using two different deformation apparatus, a deformation multianvil apparatus (DDIA) and a Griggs press, as well as a piston‐cylinder apparatus. Regardless of the apparatus type, we observe the breakdown of plagioclase into an eclogite‐facies paragenesis, which is associated with partial melting in the high temperature domain of the eclogite facies. Partial melting mostly takes place along the grain and interphase boundaries. However, several melt patches or plagioclase decomposition products coincide with the occurrence of deformation twins and grain‐scale microcracking in plagioclase indicating intracrystalline melting and reaction in addition to melting and reaction along grain and interphase boundaries. In the present study, we demonstrate how the interplay between brittle microcracking and plastic deformation twinning can cause intracrystalline melting and/or reaction, which has the potential to lower the effective grain size of plagioclase‐rich rocks and thus impacts their reactivity and deformation behaviour.