Seafloor abyssal peridotites are products after partial melting and melt-rock interaction, providing constraints on upper mantle processes and heterogeneity. Despite extensive studies of ophiolitic peridotites and a burgeoning dataset for dredged abyssal peridotites, limited studies have been undertaken on abyssal peridotite drill core samples. This omission means a lack of comparison between modern ocean mantle lithosphere and that of ophiolites, where field context is possible in the latter, but not the former. Ocean Drilling Program (ODP) Leg 153 near the Kane fracture zone, and ODP Leg 209, near the Fifteen-Twenty fracture zone, both on the mid-Atlantic Ridge but ∼1000 km distant from one another, recovered serpentinized mantle peridotites. We report whole-rock major-, trace- and highly siderophile-element (HSE: Re, Pd, Pt, Ru, Ir, Os) abundances and Os/Os ratios of peridotites from three cores (maximum depth of 200.8 m) from the two Legs to explore mantle heterogeneity within the Atlantic Ocean basin. Peridotites from ODP Leg 153 are relatively fertile, with AlO contents ranging from 1.1 to 2.7 wt%. They are characterized by relatively radiogenic Os/Os (0.1259 ± 0.0017; 2 S.D.) and uniform HSE abundances. The ODP Leg 209 peridotites are highly refractory, with AlO contents ranging from 0.1 to 0.8 wt%, and imply that they record an extensively depleted mantle. They have Os/Os of 0.1207 ± 0.0023 (2 S.D.) and fractionated HSE abundances, indicative of depletion occurring > 1 billion years ago. Marked heterogeneity both in the extent and timing of depletion are therefore evident along a large segment of the mid-Atlantic ridge that produces zero-age basalts. Measurement of Os isotopes in spatially associated mid-ocean ridge basalts (MORB) is challenging due to their sub ng/g Os contents. Instead, Nd isotopes of MORB are used to show that they are unlikely to have formed directly from abyssal peridotite-like sources. Abyssal peridotites therefore represent long-lived refractory residues during mantle upwelling with the sources of MORB being more enriched. Comparison between drilled abyssal peridotites and ophiolitic mantle reveals larger compositional variations in the latter. The overall higher melting extent in ophiolite mantle is likely reflective of a more complex life cycle than the modern oceanic lithosphere.

中文翻译：

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来自 Leg 153 和 209 橄榄岩的大西洋地幔中大规模、长期的高亲铁元素异质性的证据


海底深渊橄榄岩是部分熔融和熔岩相互作用后的产物，为上地幔过程和非均质性提供了限制。尽管对蛇绿橄榄岩进行了广泛的研究，并且疏浚深海橄榄岩的数据集不断涌现，但对深海橄榄岩钻芯样本的研究仍然有限。这一遗漏意味着现代海洋地幔岩石圈与蛇绿岩之间缺乏比较，后者可能存在野外环境，但前者则不然。凯恩断裂带附近的海洋钻探计划 (ODP) 第 153 段和靠近 15-20 断裂带的 ODP 209 段均位于大西洋中脊，但彼此相距约 1000 公里，回收了蛇纹石化地幔橄榄岩。我们报告了来自三个岩心（最大深度 200.8 m）的橄榄岩的全岩主要、微量和高亲铁元素（HSE：Re、Pd、Pt、Ru、Ir、Os）丰度和 Os/Os 比率。两条腿探索大西洋盆地内的地幔异质性。 ODP Leg 153 的橄榄岩相对肥沃，Al2O 含量范围为 1.1 至 2.7 wt%。它们的特点是相对放射性的 Os/Os (0.1259 ± 0.0017; 2 S.D.) 和均匀的 HSE 丰度。 ODP Leg 209 橄榄岩非常难熔，Al2O 含量范围为 0.1 至 0.8 wt%，这意味着它们记录了广泛耗尽的地幔。它们的 Os/Os 为 0.1207 ± 0.0023 (2 S.D.) 和分级的 HSE 丰度，表明消耗发生在 > 10 亿年前。因此，在产生零年龄玄武岩的大西洋中脊的一大部分地区，消耗的程度和时间都存在明显的异质性。 空间相关的洋中脊玄武岩 (MORB) 中锇同位素的测量具有挑战性，因为它们的锇含量低于纳克/克。相反，MORB 的 Nd 同位素被用来表明它们不太可能直接由深海橄榄岩类来源形成。因此，深渊橄榄岩代表了地幔上涌过程中长寿命的难熔残留物，MORB 的来源更加丰富。钻探深海橄榄岩和蛇绿岩地幔之间的比较揭示了后者更大的成分变化。蛇绿岩地幔总体较高的熔化程度可能反映了比现代海洋岩石圈更复杂的生命周期。