Secular variations in the composition of the subcontinental lithospheric mantle (SCLM) are intimately controlled by multiple geological processes, including diverse melting mechanisms and complex metasomatic processes. We present comprehensive analyses of whole rock and mineral chemistry, along with Re-Os isotopic system of the Eastern Pyrenean orogenic mantle massifs, supported by quantitative modeling through alphaMELTS thermodynamic software. The Eastern Pyrenean lherzolites display consistent negative correlations of TiO2/Al2O3, TiO2 versus MgO and relatively high and unfractionated heavy rare earth elements. These chemical features shed light on the diverse melting mechanisms responsible for these rocks, encompassing passive continuous melting in regions of lithospheric extension and decompression melting linked to the upwelling asthenospheric mantle. Some refractory harzburgites exhibit elevated TiO2/Al2O3, TiO2 contents and moderate light rare earth element enrichment. This suggests chromatographic metasomatism due to the reactive porous flow of evolved melts/fluids in the upper part of the lithosphere during their ascent to the surface. An isochron analogy between 187Os/188Os and Al2O3 yields an age of ∼ 1.5 Ga, constraining the timing of partial melting responsible for the formation of SCLM beneath the Eastern Pyrenean region. We then expand the scope of our study to encompass on– and off-cratonic SCLM on a global scale. This expanded analysis explores the variations in melting mechanisms across different tectonic settings and geological epochs and scrutinizes the role of diverse metasomatic processes in shaping the characteristics of the lithospheric mantle and its longevity on a broad scale. Silicate metasomatism typically produces fertile peridotites at the asthenosphere-lithosphere boundary, making them vulnerable to thermomechanical erosion, whereas cryptic metasomatism, commonly observed in refractory mantle rocks induced by evolved melts at decreasing melt-rock ratios (e.g., hydrocarbon-bearing silicate melt, carbonatite melt etc.), generally forms enrichment of highly incompatible elements but less significant influence on the mineral assemblages and major element geochemistry of the on-cratonic refractory SCLM, making them remain stable for extended periods.

中文翻译：

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破译东比利牛斯造山地幔地块中多次部分熔化、交代和再熔化过程


次大陆岩石圈地幔 （SCLM） 成分的长期变化受到多种地质过程的密切控制，包括不同的熔融机制和复杂的交代过程。我们提出了对整个岩石和矿物化学的综合分析，以及东比利牛斯造山地幔地块的 Re-Os 同位素系统，并通过 alphaMELTS 热力学软件进行定量建模。东比利牛斯山脉的锂辉石显示出 TiO2/Al2O3、TiO2 与 MgO 以及相对高且未分级的重稀土元素的一致负相关关系。这些化学特征揭示了导致这些岩石的不同熔化机制，包括岩石圈延伸区域的被动连续熔化和与上升流软流圈地幔相关的减压熔化。一些难熔哈茨堡石表现出较高的 TiO2/Al2O3、TiO2 含量和适度的轻稀土元素富集。这表明色谱交代是由于岩石圈上部的演化熔体/流体在上升到地表过程中的反应性多孔流造成的。187Os/188Os 和 Al2O3 之间的等时线类比得出的年龄约为 1.5 Ga，限制了导致东比利牛斯地区下方形成 SCLM 的部分熔化的时间。然后，我们将研究范围扩大到包括全球范围内的克拉通和非克拉通 SCLM。这项扩展分析探讨了不同构造环境和地质时期的熔融机制变化，并仔细研究了不同交代过程在塑造岩石圈地幔特征及其大范围寿命方面的作用。 硅酸盐交代作用通常在软流圈-岩石圈边界产生肥沃的橄榄岩，使其容易受到热机械侵蚀，而隐蔽的交代作用，常见于熔岩比降低的演化熔体（例如，含碳氢化合物的硅酸盐熔体、碳酸盐熔体等）诱导的难熔岩中，通常形成高度不相容的元素富集，但对矿物组合和主要元素地球化学的影响较小的克拉通耐火性 SCLM，使它们长时间保持稳定。