Eclogite xenoliths from Orapa: Ocean crust recycling, mantle metasomatism and carbon cycling at the western Zimbabwe craton margin
Eclogite xenoliths from Orapa: Ocean crust recycling, mantle metasomatism and carbon cycling at the western Zimbabwe craton margin
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奥拉帕的榴辉岩捕虏体：津巴布韦西部克拉通边缘的洋壳循环、地幔交代作用和碳循环
DOI：
10.1016/j.gca.2017.06.038
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发表时间：
2017
影响因子：
5
通讯作者：
Viljoen KS
中科院分区：
文献类型：
--
作者：
Aulbach S;Jacob DE;Cartigny P;Stern RA;Simonetti SS;Viljoen KS
摘要研究了津巴布韦克拉通（博茨瓦纳中部）西缘奥拉帕榴辉岩和辉石岩包体中石榴石和斜辉石的主微量元素组成以及斜辉石中的87sr /86Sr和石榴石中的δ18O，探讨了它们在地幔岩石圈中的起源和演化。87sr /86Sr榴辉岩分为两组：一组为中等比值（0.7026 ~ 0.7046），另一组为87sr /86Sr比值（0.7048 ~ 0.7091）。前一组重δ18O与海底低温蚀变有关，87sr /86Sr与低压火成岩作用指标（Eu/Eu∗、Mg#、Sr/Y）有关。这表明，尽管克拉通边缘环境暴露，但变质作用后，87sr在近火成岩Rb/Sr中相对不受干扰地长期向内生长。高87sr /86Sr组以幔状δ18O为主，与富辉云母变质体形成的小体积熔体相互作用。在~ 3.2 ~ 4.9 GPa的压力区间内，含金刚石和含石墨榴辉岩和辉石岩的重叠被解释为反映了由于地热变化和/或减压，奥拉帕地下的地幔包裹已经移出了金刚石稳定性场。含金刚石榴辉岩的中值87sr /86Sr（0.7039）低于含石墨样品（0.7064）和无碳样品（0.7051），表明与可能氧化的转体熔体的相互作用导致了一些榴辉岩中的碳去除，而在其他榴辉岩中则催化了钻石向石墨的转化。这突出了小体积熔体在调节岩石圈碳循环中的作用。与非金刚石榴辉岩相比，金刚石榴辉岩包裹体中FeO含量高，SiO2、CaO和Na2O含量低，平衡温度较高，石榴石多呈地幔样O同位素组成。我们认为，这一特征是由岩石圈下的熔融作用所赋予的，这种熔融作用可能与约2.0 Ga的Bushveld事件有关。
Major- and trace-element compositions of garnet and clinopyroxene, as well as87Sr/86Sr in clinopyroxene and δ18O in garnet in eclogite and pyroxenite xenoliths from Orapa, at the western margin of the Zimbabwe craton (central Botswana), were investigated in order to trace their origin and evolution in the mantle lithosphere. Two groups of eclogites are distinguished with respect to87Sr/86Sr: One with moderate ratios (0.7026–0.7046) and another with87Sr/86Sr >0.7048 to 0.7091. In the former group, heavy δ18O attests to low-temperature alteration on the ocean floor, while87Sr/86Sr correlates with indices of low-pressure igneous processes (Eu/Eu∗, Mg#, Sr/Y). This suggests relatively undisturbed long-term ingrowth of87Sr at near-igneous Rb/Sr after metamorphism, despite the exposed craton margin setting. The high-87Sr/86Sr group has mainly mantle-like δ18O and is suggested to have interacted with a small-volume melt derived from an aged phlogopite-rich metasome.The overlap of diamondiferous and graphite-bearing eclogites and pyroxenites over a pressure interval of ∼3.2 to 4.9 GPa is interpreted as reflecting a mantle parcel beneath Orapa that has moved out of the diamond stability field, due to a change in geotherm and/or decompression. Diamondiferous eclogites record lower median87Sr/86Sr (0.7039) than graphite-bearing samples (0.7064) and carbon-free samples (0.7051), suggesting that interaction with the – possibly oxidising – metasome-derived melt caused carbon removal in some eclogites, while catalysing the conversion of diamond to graphite in others. This highlights the role of small-volume melts in modulating the lithospheric carbon cycle. Compared to diamondiferous eclogites, eclogitic inclusions in diamonds are restricted to high FeO and low SiO2, CaO and Na2O contents, they record higher equilibrium temperatures and garnets have mostly mantle-like O isotopic composition. We suggest that this signature was imparted by a sublithospheric melt with contributions from a clinopyroxene-rich source, possibly related to the ca. 2.0 Ga Bushveld event.
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影响因子：
5
作者：
D. Milidragovic;D. Francis
通讯作者：
D. Milidragovic;D. Francis
影响因子：
5
作者：
P. Deines;J. Harris;J. Gurney
通讯作者：
P. Deines;J. Harris;J. Gurney
影响因子：
64.8
作者：
Stagno, Vincenzo;Ojwang, Dickson O.;Frost, Daniel J.
通讯作者：
Frost, Daniel J.
对两个密切相关的金伯利岩（博茨瓦纳的 Letlhakane 和 Orapa）地幔中贫 13C 碳的出现有了新的认识
DOI：
--
发表时间：
2004
期刊：
影响因子：
--
作者：
P. Deines;J. Harris
通讯作者：
J. Harris
影响因子：
3.9
作者：
M. Benoit;M. Polvé;G. Ceuleneer
通讯作者：
M. Benoit;M. Polvé;G. Ceuleneer