We studied mantle xenoliths sampled from two late Miocene volcanic centers located immediately north of the North Anatolian Fault Zone (NAFZ) in western Turkey. The spinel lherzolite and harzburgite xenoliths equilibrated at temperatures ranging from 757 to 1019 °C, estimated from two-pyroxene geothermometry. Pressures estimated from the Cr-in-clinopyroxene geobarometer and pseudosection modelling range from 1.0 to 2.1 GPa, which correspond to depths of 38–75 km. We used X-ray computed tomography to quantify the three-dimensional shape preferred orientation of spinel grains. Spinel displays dominantly oblate fabric ellipsoids, consistent with flattening strain. Olivine crystallographic preferred orientation (CPO), determined by electron backscatter diffraction, exhibits chiefly axial-[010] and A-type patterns. The axial-[010] CPO pattern is consistent with the spinel fabric that shows flattening strain, and is primarily developed in xenoliths from the volcanic center nearer to the NAFZ. Obliquity of olivine CPO to the spinel lineation decreases with proximity to the NAFZ, suggesting an increase in shear strain. Our results favor an interpretation of transpressional deformation in the upper mantle below the NAFZ. We attribute this pattern to a restraining bend in the mantle section of the NAFZ.

我们研究了从位于土耳其西部北安纳托利亚断层带 (NAFZ) 以北的两个晚中新世火山中心采集的地幔包体。尖晶石二辉石和菱镁矿捕虏体在 757 至 1019 °C 的温度范围内平衡，根据双辉石地球测温法估计。根据 Cr-in-clinopyroxene 地质气压计和假剖面模型估计的压力范围为 1.0 至 2.1 GPa，对应于 38-75 公里的深度。我们使用 X 射线计算机断层扫描来量化尖晶石晶粒的三维形状优选取向。尖晶石显示主要是扁圆的织物椭球体，与压扁应变一致。橄榄石晶体择优取向 (CPO)，由电子背散射衍射确定，主要表现出轴向 [010] 和 A 型图案。轴向-[010] CPO 图案与尖晶石织物一致，显示出扁平应变，并且主要在来自更靠近 NAFZ 的火山中心的捕虏体中发育。随着接近 NAFZ，橄榄石 CPO 与尖晶石线的倾斜度降低，表明剪切应变增加。我们的结果有利于对 NAFZ 下方上地幔的挤压变形进行解释。我们将这种模式归因于 NAFZ 地幔部分的抑制弯曲。我们的结果有利于对 NAFZ 下方上地幔的挤压变形进行解释。我们将这种模式归因于 NAFZ 地幔部分的抑制弯曲。我们的结果有利于对 NAFZ 下方上地幔的挤压变形的解释。我们将这种模式归因于 NAFZ 地幔部分的抑制弯曲。