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首页> 外文期刊>Contributions to Mineralogy and Petrology >Application of thermodynamic modelling to natural mantle xenoliths: examples of density variations and pressure-temperature evolution of the lithospheric mantle
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Application of thermodynamic modelling to natural mantle xenoliths: examples of density variations and pressure-temperature evolution of the lithospheric mantle

机译：热力学模型在天然地幔异种岩中的应用：岩石圈地幔密度变化和压力-温度演化的例子

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In this paper, we show how the results of phase equilibria calculations in different mantle compositions can be reconciled with the evidence from natural mantle samples. We present data on the response of bulk rock density to pressure (P), temperature (T) and compositional changes in the lithospheric mantle and obtain constraints on the P-T evolution recorded by mantle xenoliths. To do this, we examine the mantle xenolith suite from the Quaternary alkali basalts of Pali-Aike, Patagonia, using phase equilibria calculation in six representative compositions. The calculations were done subsolidus and in volatilefree conditions. Our results show that the density change related to the spinel peridotite to garnet peridotite transition is not sharp and strongly depends on the bulk composition. In a depleted mantle composition, this transition is not reflected in the density profile, while in a fertile mantle it leads to a relative increase in density with respect to more depleted compositions. In mantle sections characterized by hot geothermal gradients (similar to 70 mW/m(2)), the spinel-garnet transition may overlap with the lithosphere-asthenosphere boundary. Phase equilibria calculations in peridotitic compositions representative of the Pali-Aike mantle were also used to constrain the origin and evolution of the mantle xenoliths. Our results indicate that the mineral modes and compositions, and the mineral zonation reported for the low-temperature peridotites (spinel and spinel + garnet harzburgites and lherzolites), are linked to a cooling event in the mantle which occurred long before the eruption of the host basalts. In addition, our phase equilibria calculations show that kelyphitic rims around garnets, as those observed in the high-temperature garnet peridotites from Pali-Aike, can be explained simply by decompression and do not require additional metasomatic fluid or melt.
机译：在本文中，我们展示了如何将不同地幔成分的相平衡计算结果与天然地幔样品的证据相吻合。我们介绍了岩石密度对岩石圈地幔中压力（P），温度（T）和成分变化的响应的数据，并获得了对由地幔异岩记录的P-T演化的约束。为此，我们使用六种代表性成分中的相平衡计算方法，研究了巴塔哥尼亚Pali-Aike的第四纪碱性玄武岩中的地幔异岩体组。计算是在固相下和无挥发条件下进行的。我们的结果表明，与尖晶石橄榄石到石榴石橄榄石转变有关的密度变化不明显，并且强烈依赖于整体组成。在贫化的地幔组合物中，这种转变没有反映在密度剖面中，而在肥沃的地幔中，相对于更贫化的组合物，它导致密度的相对增加。在以热地热梯度（类似于70 mW / m（2））为特征的地幔剖面中，尖晶石-石榴石过渡可能与岩石圈-软流圈边界重叠。代表Pali-Aike地幔的橄榄岩成分的相平衡计算也被用来限制地幔异岩的起源和演化。我们的结果表明，低温橄榄橄榄岩（尖晶石和尖晶石+石榴石harzburgite和lherzolites）的矿物模式和组成以及矿物区带与地幔冷却事件有关，该事件发生在宿主喷发之前很久玄武岩。另外，我们的相平衡计算表明，如在Pali-Aike的高温石榴石橄榄岩中观察到的那样，石榴石周围的凯夫特岩缘可以简单地通过减压来解释，不需要额外的交代流体或熔体。

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