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首页> 外文期刊>Contributions to Mineralogy and Petrology >Ultra-depleted, shallow cratonic mantle beneath West Greenland: dunitic xenoliths from Ubekendt Ejland
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Ultra-depleted, shallow cratonic mantle beneath West Greenland: dunitic xenoliths from Ubekendt Ejland

机译：西格陵兰岛下方超枯竭的浅克拉通地幔：Ubekendt Ejland的二元异岩

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摘要

Dunitic xenoliths from late Palaeogene, alkaline basalt flows on Ubekendt Ejland, West Greenland contain olivine with 100 × Mg/(Mg + Fe), or Mg#, between 92.0 and 93.7. Orthopyroxene has very low Al2O3 and CaO contents (0.024–1.639 and 0.062–0.275 wt%, respectively). Spinel has 100 × Cr/(Cr + Al), or Cr#, between 46.98 and 95.67. Clinopyroxene is absent. The osmium isotopic composition of olivine and spinel mineral separates shows a considerable span of 187Os/188Os values. The most unradiogenic 187Os/188Os value of 0.1046 corresponds to a Re-depletion age of ca. 3.3 Gy, while the most radiogenic value of 0.1336 is higher than present-day chondrite. The Os isotopic composition of the xenoliths is consistent with their origin as restites from a melt extraction event in the Archaean, followed by one or more subsequent metasomatic event(s). The high Cr# in spinel and low modal pyroxene of the Ubekendt Ejland xenoliths are similar to values of some highly depleted mantle peridotites from arc settings. However, highly depleted, arc-related peridotites have higher Cr# in spinel for a given proportion of modal olivine, compared to cratonic xenolith suites from Greenland, which instead form coherent trends with abyssal peridotites, dredged from modern mid-ocean ridges. This suggests that depleted cratonic harzburgites and dunites from shallow lithospheric mantle represent the residue from dry melting in the Archaean.
机译：来自晚古近纪的二元异种石，碱性格陵兰岩流在西格陵兰的乌贝肯特埃格兰（Ubekendt Ejland）上含橄榄石，其橄榄石含量为100×Mg /（Mg + Fe）或Mg＃，介于92.0和93.7之间。邻二甲苯具有非常低的Al2 O3 和CaO含量（分别为0.024–1.639和0.062–0.275 wt％）。尖晶石的100×Cr /（Cr + Al）或Cr＃在46.98和95.67之间。缺少次氯环戊烯。橄榄石和尖晶石矿物分离物中的iso同位素组成显示了相当大的187 Os / 188 Os值。非辐射源性最强的187Os / 188Os值为0.1046，对应的重新耗尽年龄约为。 3.3 Gy，而最放射源的值为0.1336，高于当今的球粒陨石。异种石的Os同位素组成与它们的起源一致，这些起源是来自古生菌的熔体提取事件的镁橄榄石，随后是一个或多个随后的交代事件。 Ubekendt Ejland异岩的尖晶石中的Cr＃高和低模态辉石与电弧环境中某些高度耗尽的地幔橄榄岩的值相似。然而，与格陵兰岛克拉通的异岩体套件相比，高度贫化，与弧有关的橄榄岩在尖晶石中具有一定比例的莫来石橄榄岩中的Cr＃更高，而后者与深海橄榄岩形成了连贯的趋势，而深渊橄榄石则是从现代中洋海岭挖出的。这表明，浅层岩石圈地幔中的克拉通哈兹伯格岩和矮人岩代表了古生菌干熔过程中的残留物。

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