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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 >The origin of abyssal peridotites: a reinterpretation of constraints based on primary bulk compositions
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The origin of abyssal peridotites: a reinterpretation of constraints based on primary bulk compositions

机译：深渊橄榄岩的起源：基于主要散装成分的约束条件的重新解释

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We calculated primary bulk compositions for a global suite of abyssal peridotites using primary mineral modes and either analyzed or calculated phase compositions. The latter were obtained through correlations between reported mineral compositions and modal olivine contents. Both the model data and the mineral compositions were averaged by dredge site, drill hole, or fracture zone (FZ) depending on the amount of available data. Our calculated abyssal peridotite compositions yield major-element oxide-MgO trends that are generally in good agreement with those based on compilations of ultramafic nodules and peridotite massifs. In particular, we find no statistically significant correlation between FeO~* (total Fe as FeO) and MgO and, therefore, no evidence for significant olivine accumulation. Previous reports of a positive correlation reflect an artifact of the regressions used to calculate missing phase compositions and result in a relationship between the Mg# of olivine and model olivine abundance that is inconsistent with observed variations in abyssal peridotites. There is a slight positive correlation between bulk FeO~* and MgO if individual thin sections are used to derive the mineral composition versus modal olivine regressions, but the large grain sizes and heterogeneous distributions of phases within abyssal peridotites make it unlikely that individual thin section modes accurately reflect phase proportions in meter-sized dredge-haul samples. The variability of Na and Ti contents in pyroxenes from plagioclase-free abyssal peridotites suggests to us, as it has to other workers, that a majority of these samples interacted to varying degrees with small amounts of melt. On the other hand, lower bounds on Na and Ti contents in the pyroxenes at a given dredge site as a function of modal olivine content are broadly consistent with calculated partial melting residues. Thus, abyssal peridotites may retain information both on the original partial melting process and on concurrent or later interactions with partial melts from other sources.
机译：我们使用主要矿物模式并分析或计算了相组成，计算了全球深渊橄榄岩套件的主要散装成分。后者是通过报告的矿物成分与模态橄榄石含量之间的相关性获得的。根据可用数据量，通过挖泥现场，钻孔或断裂带（FZ）对模型数据和矿物成分进行平均。我们计算出的深渊橄榄石成分产生的主要元素氧化物MgO趋势通常与基于超镁铁结核和橄榄岩块的汇编所得出的趋势一致。特别是，我们发现FeO〜*（以Fe计总Fe为FeO）和MgO之间没有统计学上的显着相关性，因此，没有证据表明橄榄石有明显的堆积。以前的正相关报告反映了用于计算缺失相组成的回归假象，并导致橄榄石的Mg＃与模型橄榄石丰度之间的关系与深海橄榄岩中观察到的变化不一致。如果使用单个薄片来推导矿物成分与模态橄榄石回归，则在主体FeO〜*和MgO之间存在轻微的正相关，但是深部橄榄岩中的大晶粒尺寸和相的非均质分布使得单个薄片模式不可能在米大小的挖泥船样本中准确反映相位比例。不含斜长石的深渊橄榄石中辉石中Na和Ti含量的变化向我们表明，与其他工作者一样，这些样品中的大多数在少量熔体之间发生了不同程度的相互作用。另一方面，在给定挖泥位处，辉石中Na和Ti含量的下限作为模态橄榄石含量的函数与所计算的部分熔融残余物大致一致。因此，深海橄榄岩可以保留有关原始部分熔融过程以及与其他来源的部分熔融同时或以后相互作用的信息。

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