Deformation history of Pinatubo peridotite xenolith: constraint from microstructural observation and determination of olivine slip system
Deformation history of Pinatubo peridotite xenolith: constraint from microstructural observation and determination of olivine slip system
复制标题
皮纳图博橄榄岩捕虏体的变形历史：微观结构观察和橄榄石滑移体系确定的约束
DOI：
10.1007/s00269-016-0853-2
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发表时间：
2017
影响因子：
1.4
通讯作者：
T.
中科院分区：
文献类型：
--
作者：
Yamamoto;T.;Ando;J.;Tomioka;N.;and Kobayashi;T.
通过对皮纳图博橄榄岩包体的微观构造观察和橄榄石滑移体系的测定，估计了皮纳图博橄榄岩包体的变形历史。后者是通过三种方法进行的：晶格优选取向（LPO），亚晶界的晶体学分析和位错的直接表征。Pinatubo橄榄岩由含有大量流体包裹体的粗橄榄石颗粒和一些正辉石和角闪孔颗粒的细聚集体组成，表明流体-岩石相互作用强烈。粗橄榄石晶粒内沿愈合裂纹发育自面体细再结晶橄榄石晶粒，表明静恢复过程中无应变晶粒形核长大。LPO模式和亚晶界分析表明[100]{0kl}滑移系统在高温、低压和干变形条件下发育。虽然位错主要表现为[100]{0kl}滑移体系，但也发育了其他滑移体系，这些滑移体系可能是在中高含水量和低温条件下变形形成的。位错表征结果与其他两种方法的差异可能是由于满足von Mises准则或套印位错微观结构所致。无论哪种方式，皮纳图博橄榄岩的可能变形历史都可以用以下情景来解释。在地幔楔块的角流作用下，橄榄岩塑性地从弧后向弧前邻区移动，在弧前邻区富含co2的含盐流体被圈闭。然后，它们在上涌岩浆的夹闭过程中被退火和交代。
The deformation history of the Pinatubo peridotite xenoliths was estimated on the basis of the microstructural observations and the determination of olivine slip systems. The latter was performed by using three methods: lattice-preferred orientation (LPO), crystallographic analysis of subgrain boundaries, and direct characterization of dislocations. The Pinatubo peridotites are composed of coarse olivine grains containing numerous fluid inclusions and some fine aggregates of orthopyroxene and amphibole grains, which implies intense fluid–rock interaction. The development of euhedral fine recrystallized olivine grains along the healed cracks within the coarse olivine grains suggests that the strain-free grains were nucleated and grew during static recovery. The LPO patterns and the analyses of subgrain boundaries indicate the activation of a [100]{0kl} slip system that developed under high temperature, low pressure, and dry deformation conditions. Although dislocations showing the [100]{0kl} slip system are dominantly observed, the other slip systems which could be formed by the deformation under moderate–high water content and lower-temperature conditions are also developed. The discrepancy between the results of dislocation characterization and the other two methods might have been caused by fulfilling the von Mises criterion or overprinting dislocation microstructures. Either way, the possible deformation history of the Pinatubo peridotites can be explained by the following scenario. The peridotites plastically moved from the back-arc to the fore-arc adjacent region, where CO2-rich saline fluid was trapped, by the corner flow of a mantle wedge. They were then annealed and metasomatized during entrapment of the upwelling magma.