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The influence of mantle metasomatism on the oxidation state of the lithospheric mantle.

机译：地幔交代作用对岩石圈地幔氧化态的影响。

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摘要

The oxidation state, reflected in the oxygen fugacity (fO 2), of the lithospheric mantle is both laterally and vertically heterogeneous. Depth-fO2 profiles from kimberlite-borne peridotitic mantle xenoliths from the Bultfontein kimberlite, Kimberley, South Africa and the A154-N and A154-S kimberlites of the Diavik Mine, NWT, Canada were constructed by measuring ferric iron concentrations in garnets using the flank method. These data demonstrate that mantle metasomatic re-enrichment processes had a significant effect on fO2. In the garnet stability field, the Kaapvaal lithospheric mantle becomes progressively more reducing with increasing depth from Deltalog fO2 (FMQ) of -2 at 110 km to -4 at 210 km. The lithospheric mantle beneath Diavik is vertically layered with respect to its bulk and trace-element composition. The shallow 'ultradepleted' layer is oxidized, to the point that carbonate rather than graphite is the anticipated carbon host. The deeper layer is more fertile and has fO2 conditions extending down to Deltalog fO2 (FMQ) -3.8.;Diavik xenoliths preserve evidence for events similar to the fluid and 'common' melt metasomatism seen in the Bultfontein samples. Fluid metasomatism affected the entire depth range of xenoliths sampled from Diavik and was oxidizing. A stage of melt metasomatism affected only the deeper (>140 km) portion of the lithospheric mantle and had an overall reducing effect. The observation of sharp-edged octahedral diamonds in microxenoliths affected by the fluid metasomatic event may indicate that this was a major diamond-forming event in the mantle beneath Diavik.;Deviations from predicted depth-fO2 trends in both xenolith localities result from metasomatic re-enrichment caused by transient fluids and melts. Diamond formation in the Kaapvaal lithospheric mantle may have occurred through the infiltration of reduced fluids into relatively more oxidized mantle. Trace-element concentrations in garnets preserve evidence of two distinct melt metasomatic enrichment events. One was a craton-wide event that is commonly observed in garnet peridotite xenoliths and xenocrysts worldwide; the other was melt infiltration event, preserved as MARID xenoliths, related to the eruption of the Group 2 kimberlites in the western portion of the Kaapvaal craton. The effect of the former melt metasomatism on fO2 is unclear ambiguous whereas the MARID event was clearly oxidizing.
机译：岩石圈地幔的氧气逸度（fO 2）所反映的氧化态在横向和纵向都是不均匀的。来自金伯利的Bultfontein金伯利岩的金伯利岩传播的橄榄石幔幔异岩的深度-fO2剖面图是通过使用侧面测量石榴石中三价铁的浓度来构造的，该金伯利的金伯利岩是来自南非的金刚利。方法。这些数据表明，地幔交代复富过程对fO2有显着影响。在石榴石稳定性场中，随着从Deltalog fO2（FMQ）的110 km的-2到210 km的-4的深度增加，Kaapvaal岩石圈地幔逐渐减少。 Diavik下方的岩石圈地幔相对于其体积和微量元素组成而言是垂直分层的。浅的“超商业化”层被氧化，以至于碳酸盐而不是石墨是预期的碳主体。更深的一层更肥沃，并且具有fO2条件，一直延伸到Deltalog fO2（FMQ）-3.8。流体交代作用影响了从迪亚维克（Diavik）采样的异种石的整个深度范围，并且正在被氧化。熔融交代作用的一个阶段仅影响岩石圈地幔的较深部分（> 140 km），并具有总体降低作用。在受流体交代学事件影响的微异岩中观察到锋利的八面体钻石可能表明这是Diavik下地幔中的一个主要的金刚石形成事件。瞬态流体和熔体引起的富集。 Kaapvaal岩石圈地幔中的钻石形成可能是由于还原流体渗透到相对氧化程度更高的地幔中而发生的。石榴石中的痕量元素浓度保留了两个明显的熔体交代富集事件的证据。一个是在整个石榴石范围内发生的事件，这种现象通常在全世界的石榴石橄榄岩异种岩和异变体中观察到。另一个是熔岩浸润事件，保存为MARID异岩，与Kaapvaal克拉通西部的第2组金伯利岩的喷发有关。以前的熔融交代作用对fO2的影响尚不清楚，而MARID事件则明显被氧化。

著录项

  • 作者

    Creighton, Steven.;

  • 作者单位

    University of Alberta (Canada).;

  • 授予单位 University of Alberta (Canada).;
  • 学科 Geology.;Geochemistry.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 136 p.
  • 总页数 136
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 老年病学;
  • 关键词

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