Results of a microstructural study of spinel peridotite samples obtained from the Kraka massif in the Southern Urals, involving findings of Cr-spinel neomineralisations within intensive ductile deformed silicates (olivine and orthopyroxene), are presented. The new-formed Cr-spinel grains show different stages of syn-deformation growth as evidenced by investigations combining petrography, decorated dislocation structure analysis, scanning electron microscopy and electron backscatter diffraction (EBSD). Initial precipitations appearing as rods or lamellae are observed to form around structural defects of host silicate grains (olivine and orthopyroxene) by means of impurity segregation or heterogeneous nucleation in the most distorted lattice regions (i.e., in the predominant recrystallisation zones). Syn-deformational crystal growth leads to a complication and coarsening of the grain morphology by coalescence due to a reduction in grain boundary (interfacial) energy. While in the process of growing, the Cr-spinel grains capture fragments of silicate matrix in the solid-state process. The final stage of Cr-spinel growth involves a change in morphology resulting in their characteristic crystallographic forms (spheroidisation). The presence of euhedral Cr-spinel grains, typical for ophiolitic dunite bodies, is a result of interfacial energy reduction in areas of grain boundaries of the hardest phase. The general trend of the observed stages relates closely with the localisation of deformation zones in the upwelling upper mantle (diapir), which are composed by the weakest phase of olivine (dunites). The concentration of the weakest olivine phase in the mobile zones, which is energetically beneficial, explains why dunite bodies having euhedral chromite grains comprise the dynamic equilibrium rocks in the plastic flow localisation zones in upper mantle diapirs. Conversely, assemblages having pyroxene phases, which are stronger and larger in size compared to olivine, are not stable in these zones.

提出了从南部乌拉尔山脉的克拉卡断层中获得的尖晶石橄榄石样品的微观结构研究结果，涉及在强烈的延展性变形硅酸盐（橄榄石和邻二甲苯）中Cr-尖晶石新矿化的发现。结合岩石学，装饰位错结构分析，扫描电子显微镜和电子背散射衍射（EBSD）的研究证明，新形成的Cr-尖晶石晶粒显示出不同的同相变形生长阶段。观察到以棒状或片状形式出现的初始沉淀是在最扭曲的晶格区域（即在主要的重结晶区）中通过杂质偏析或非均相成核在基质硅酸盐晶粒（橄榄石和邻苯二茂合物）的结构缺陷周围形成的。由于晶界（界面）能的减少，同构变形晶体的生长导致由于聚结而导致的晶粒形态的复杂化和粗化。在生长过程中，Cr-尖晶石晶粒在固态过程中捕获了硅酸盐基质的碎片。Cr-尖晶石生长的最后阶段涉及形态变化，从而导致其特征性的晶体学形式（球化）。存在于硬脂石榴辉岩体中的正表面Cr-尖晶石晶粒，是最坚硬相的晶界区域界面能降低的结果。观测阶段的总体趋势与上升流上地幔（diapir）中变形带的位置密切相关，后者由橄榄石的最弱相（dunites）组成。流动带中最弱的橄榄石相的浓度在能量上是有好处的，这解释了为什么具有正铬铁矿晶粒的榴辉岩体在上地幔底辟的塑性流动局部化带中构成了动平衡岩。相反，具有辉石相的组合物在这些区域中不稳定，与橄榄石相比，辉石相的尺寸更大且更大。