Linking temperature estimates and microstructures in deformed polymineralic mantle rocks
Linking temperature estimates and microstructures in deformed polymineralic mantle rocks
复制标题
将变形多矿物地幔岩石的温度估计和微观结构联系起来
DOI：
10.1029/2011gc003536
复制
发表时间：
2011
期刊：
影响因子：
3.7
通讯作者：
O. Müntener
中科院分区：
文献类型：
--
作者：
J. Linckens;M. Herwegh;O. Müntener
为了限制地幔剪切带的变形温度，我们研究了走滑剪切带（Hilti 地块、Semail 蛇绿岩、阿曼），并重点关注微观结构机制与化学平衡过程之间的相互作用。将斜方辉石地温测量相结合，对不同变形强度的方辉橄榄岩（斑屑构造岩、糜棱岩和超糜棱岩）进行定量微结构分析。所有相的平均晶粒尺寸随着剪切区厚度的减小而减小。碎卟啉的动态重结晶与溶解沉淀和成核相结合，产生小尺寸、化学平衡的辉石。斜方辉石的成分用于计算变形温度。对于碎斑岩构造岩，斜方辉石的化学成分已通过扩散重置，产生的温度估计为 880–900°C。糜棱岩因橄榄石的位错蠕变而变形，并显示出较宽的计算温度范围，这是晶粒尺寸减小和早期高温事件和扩散所继承的平衡成分共同作用的结果。在糜棱岩中，扩散剖面结合地温测量和粒度分析表明糜棱岩变形温度为 800–900°C，可能随后发生扩散。在超糜棱岩中，最小的晶粒（<30 μm）在延性变形的最后阶段在〜700°C的温度下显示出平衡，这主要是橄榄石的扩散蠕变。我们的结果提供了温度与地幔剪切带中从位错蠕变到扩散蠕变的微结构演化之间的关键联系。
To constrain deformation temperatures of mantle shear zones, we studied a strike‐slip shear zone (Hilti massif, Semail ophiolite, Oman) and focused on the interaction between microstructural mechanisms and chemical equilibration processes. Quantitative microfabric analysis on harzburgites with different deformation intensity (porphyroclastic tectonite, mylonite, and ultramylonite) was combined with orthopyroxene geothermometry. The average grain size of all phases decreases with decreasing shear zone thickness. Dynamic recrystallization of porphyroclasts in combination with dissolution‐precipitation and nucleation result in small‐sized, chemically equilibrated pyroxenes. The composition of orthopyroxene was used to calculate deformation temperatures. In the case of the porphyroclastic tectonites, the chemical composition of orthopyroxene has been reset by diffusion yielding temperature estimates of 880–900°C. The mylonites were deformed by dislocation creep of olivine and show a broad range of calculated temperatures, which result from a combination of grain size reduction and inheritance of equilibrium compositions from earlier high‐temperature events and diffusion. In mylonites, diffusion profiles combined with geothermometry and grain size analysis indicate a mylonitic deformation temperature of 800–900°C possibly followed by diffusion. In ultramylonites, the smallest grains (<30 μm) reveal equilibration at temperatures of ∼700°C during the last stages of ductile deformation, which was dominated by diffusion creep of olivine. Our results provide a crucial link between temperature and evolution of microstructures from dislocation creep to diffusion creep in mantle shear zones.