Enriched, HIMU-type peridotite and depleted recycled pyroxenite in the Canary plume: A mixed-up mantle
Enriched, HIMU-type peridotite and depleted recycled pyroxenite in the Canary plume: A mixed-up mantle
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DOI：
10.1016/j.epsl.2008.11.013
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发表时间：
2009-01
影响因子：
5.3
通讯作者：
A. Gurenko;A. Sobolev;K. Hoernle;F. Hauff;H. Schmincke
中科院分区：
文献类型：
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作者：
A. Gurenko;A. Sobolev;K. Hoernle;F. Hauff;H. Schmincke
地球的地幔在化学和同位素上是不均匀的，通常怀疑对流地幔中有再循环洋壳的成分[Hofmann和白色，1982年。来自古老洋壳的地幔柱。地球星球。Sci. Lett. 57，421-436]。实际上，HIMU组分（高μ= 238 U/204 Pb）是地幔中四种同位素不同的端元之一，通常归因于相对较老（≥1-2 Ga）的榴辉岩/辉石岩形式的再循环洋壳，例如[Zindler和哈特，1986年。化学地球动力学《地球星球报》。Sci. 14，493-571]。虽然元素和同位素数据普遍支持回收组分的存在，但对其在地幔深处的物理状态知之甚少。在这里，我们表明，来自Canarian盾阶段熔岩的橄榄石中的Ni、Mn和Ca的浓度可用于评估源材料的物理性质（橄榄岩与不含橄榄石的辉石岩）[Sobolev等人，2007.地幔源熔融物中再循环地壳的数量。Science 316，412-417]，与块体岩石Sr、Nd和Pb同位素比值密切相关。从我们的数据得出的最重要的结果是，富集的，HIMU型（具有较高的206 Pb/204 Pb比一般发现在其他地幔端元）签名的加那利热点岩浆不是由羽辉岩/榴辉岩成分，但似乎已主要由橄榄岩托管。这意味着古老的洋壳（年龄大于1Ga），其放射性同位素组成演化程度更高，与地幔发生了搅拌/反应，因此没有留下明显的榴辉岩，而较年轻的再循环洋壳，其亏损的MORB同位素特征（<1Ga）可以作为榴辉岩保存下来，当熔融时可以生成反应辉石岩。
The Earth's mantle is chemically and isotopically heterogeneous, and a component of recycled oceanic crust is generally suspected in the convecting mantle [Hofmann and White, 1982. Mantle plumes from ancient oceanic crust. Earth Planet. Sci. Lett. 57, 421–436]. Indeed, the HIMU component (high µ=238U/204Pb), one of four isotopically distinct end-members in the Earth's mantle, is generally attributed to relatively old (≥1–2 Ga) recycled oceanic crust in the form of eclogite/pyroxenite, e.g. [Zindler and Hart, 1986. Chemical geodynamics. Ann. Rev. Earth Planet. Sci. 14, 493–571]. Although the presence of the recycled component is generally supported by element and isotopic data, little is known about its physical state at mantle depths. Here we show that the concentrations of Ni, Mn and Ca in olivine from the Canarian shield stage lavas, which can be used to assess the physical nature of the source material (peridotite versus olivine-free pyroxenite) [Sobolev et al., 2007. The amount of recycled crust in sources of mantle-derived melts. Science 316, 412–417], correlate strongly with bulk rock Sr, Nd and Pb isotopic ratios. The most important result following from our data is that the enriched, HIMU-type (having higher206Pb/204Pb than generally found in the other mantle end-members) signature of the Canarian hotspot magmas was not caused by a pyroxenite/eclogite constituent of the plume but appears to have been primarily hosted by peridotite. This implies that the old (older than ~1 Ga) ocean crust, which has more evolved radiogenic isotope compositions, was stirred into/reacted with the mantle so that there is not significant eclogite left, whereas younger recycled oceanic crust with depleted MORB isotopic signature (<1 Ga) can be preserved as eclogite, which when melted can generate reaction pyroxenite.