Deformation, Annealing, Melt‐Rock Interaction, and Seismic Properties of an Old Domain of the Equatorial Atlantic Lithospheric Mantle
Deformation, Annealing, Melt‐Rock Interaction, and Seismic Properties of an Old Domain of the Equatorial Atlantic Lithospheric Mantle
复制标题
赤道大西洋岩石圈地幔旧域的变形、退火、熔岩相互作用和地震特性
作者：
Shiran Liu;A. Tommasi;A. Vauchez;M. Mazzucchelli
本文分析了费尔南多-迪诺罗尼亚群岛的地幔捕虏体，探讨了变形、冷却、退火和熔融渗流在赤道大西洋地幔岩石圈演化中的作用。橄榄岩以辉橄榄岩为主，微结构粗粒状或斑岩碎屑状。平衡温度范围在850和1000°C之间。橄榄石晶体择优取向（CPO）主要为正交晶型，具有清晰的[100]和[010]点最大值或纤维-[100]倾向；这些模式暗示变形是由位错蠕变引起的，[100]（010）滑移系统起主导作用。橄榄石纤维‐[010]图案不太常见；它们可能是再结晶或熔体-岩石相互作用的结果。变形后的退火部分恢复了组织，降低了橄榄石CPO的强度。辉石型CPO与橄榄石型CPO的一致性较弱，暗示变形后再作用。化学成分系统上比大西洋中脊的深海橄榄岩更为丰富。这些成分和微观结构表明熔体-岩石相互作用的两个阶段。早期岩石圈底部由于小熔体组分的连续渗透作用而发生再成矿作用，后来，更重要的是，局部的化学变化（再成矿作用和多元石化作用）以及由反应性熔体渗透作用引起的再结晶作用可能与新生代火山作用有关。通过将计算的地震性质与现有地震资料进行比较，我们认为Fernando de Noronha地幔捕虏体显示的中等地震各向异性可能记录了在板块冷却时冻结在岩石圈地幔中的平行扩张方向的过去水平软流圈流动。
We analyzed a set of mantle xenoliths from the Fernando de Noronha archipelago to constrain the roles of deformation, cooling, annealing, and melt percolation in the evolution of the mantle lithosphere of the equatorial Atlantic. The peridotites are dominantly lherzolites with coarse granular or porphyroclastic microstructures. Equilibrium temperatures range between 850 and 1,000 °C. Olivine crystal preferred orientations (CPO) have mainly orthorhombic patterns characterized by clear [100] and [010] point maxima or a fiber‐[100] tendency; these patterns imply deformation by dislocation creep with dominant activation of the [100](010) slip system. Olivine fiber‐[010] patterns are less common; they probably result from recrystallization or melt‐rock interaction. Annealing after deformation partially recovered the microstructures and reduced the olivine CPO strength. Pyroxene CPOs often have weak consistency with olivine CPO, implying post‐deformation refertilization. Chemical compositions are systematically more fertile than those from abyssal peridotites from the Mid‐Atlantic Ridge. These compositions together with the microstructures suggest two stages of melt‐rock interaction. An early refertilization of the base of the lithosphere due to continuous percolation of small melt fractions and later, more important, but local chemical changes (both refertilization and dunitization) as well as recrystallization due to reactive melt percolation likely associated with the Cenozoic volcanism. By comparing the calculated seismic properties with existing seismological data we argue that the moderate seismic anisotropy displayed by the Fernando de Noronha mantle xenoliths likely records past horizontal asthenospheric flow parallel to the spreading direction frozen in the lithospheric mantle as the plate cooled.
影响因子：
2.9
作者：
Colli, Lorenzo;Fichtner, Andreas;Bunge, Hans-Peter
通讯作者：
Bunge, Hans-Peter
影响因子：
3.5
作者：
J. Warren
通讯作者：
J. Warren