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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Seismic properties of an asthenospherized lithospheric mantle: constraints from lattice preferred orientations in peridotite from the Ronda massif
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Seismic properties of an asthenospherized lithospheric mantle: constraints from lattice preferred orientations in peridotite from the Ronda massif

机译：软弱的岩石圈地幔的地震特性：来自朗达地块的橄榄岩中晶格优先取向的约束

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Above a mantle plume, the lithosphere is thermally 'eroded'. It is however not clear whether heating and partial melting of the lithosphere may erase the mineral lattice preferred orientation (LPO) inherited from previous tectonic events or if, in the absence of large-scale flow, this fabric is preserved. To evaluate the effect of heating and partial melting on the seismic properties of the lithospheric mantle, we have measured the LPO and computed the seismic properties of peridotites from the Ronda massif (Spain). In this massif, a narrow (≤400 m) coarsening front separates a porphyroclastic peridotite domain, interpreted as old lithospheric mantle, from a coarse-granular peridotite domain produced by annealing and limited partial melting (<6.5%) of the porphyroclastic peridotites. The olivine LPO in the porphyroclastic peridotites is moderate. The [100] and [001] axes are distributed within the foliation with a maximum of [100] parallel to the lineation, and the [010] axes are concentrated close to the normal to the foliation. The olivine LPO does not vary drastically across the coarsening front: the LPO strength decreases slightly and symmetry of the pattern progressively turns more orthorhombic. On the other hand, the strength of the orthopyroxene LPO increases. The consistency of olivine LPO translates to similar seismic properties of peridotites in the two domains. Especially, the anisotropy of both compressional and shear waves (P- and S-waves) remains almost unchanged across the entire massif. These results support that heating and partial melting (asthenospherization) of the lithospheric mantle do not necessarily obliterate the minerals LPO inherited from previous tectonic events. The 'structural memory' of the lithosphere may therefore be preserved even in the 'asthenospherized' mantle. In a region of asthenosphere-lithosphere interaction, tomography studies would indicate a largely attenuated lithosphere from the presence of a shallow low-velocity anomaly while S-wave splitting measurement yields delays between arrivals of the fast and slow split waves requiring a larger lithosphere thickness. This apparent discrepancy may be resolved considering the existence of a 'ghost lithosphere' having lithospheric characteristics regarding anisotropy studies and asthenospheric properties regarding seismic waves velocities.
机译：在地幔柱上方，岩石圈被热“侵蚀”。然而，尚不清楚岩石圈的加热和部分融化是否会消除先前构造事件所继承的矿物晶格偏好取向（LPO），或者是否在没有大规模流动的情况下保留这种织物。为了评估加热和部分融化对岩石圈地幔地震特性的影响，我们测量了LPO并计算了来自隆达地块（西班牙）的橄榄岩的地震特性。在该地块中，狭窄的（≤400m）粗化锋面将解释为旧岩石圈地幔的卟啉-橄榄岩橄榄岩域与通过退火和有限的部分熔融（<6.5％）的卟啉-橄榄岩橄榄岩产生的粗粒状橄榄岩域分开。杂碎橄榄岩橄榄岩中的橄榄石LPO中等。 [100]和[001]轴在叶面内分布，最大[100]平行于该直线，[010]轴集中在靠近叶面法线的位置。橄榄石的LPO在整个粗化锋线上并没有显着变化：LPO强度略有下降，并且图案的对称性逐渐变为斜方晶。另一方面，邻苯二酚LPO的强度增加。橄榄石LPO的稠度转化为橄榄岩在两个区域中的相似地震特性。特别是，压缩波和剪切波（P波和S波）的各向异性在整个地块上几乎保持不变。这些结果表明，岩石圈地幔的加热和部分熔融（非球形）并不一定能消除以前构造事件所继承的LPO矿物。因此，即使在“非球面化”地幔中也可以保留岩石圈的“结构记忆”。在软流圈-岩石圈相互作用的区域，层析成像研究表明，由于浅层低速异常的存在，岩石圈已大大衰减，而S波分裂测量产生了需要较大岩石圈厚度的快波和慢波分裂到达之间的延迟。考虑到具有各向异性研究的岩石圈特征和关于地震波速度的软流圈性质的“鬼怪岩石圈”的存在，可以解决这种明显的差异。

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