Mineral chemical evidence for extremely magnesian subalkaline melts from the Antarctic extension of the Karoo large igneous province
Mineral chemical evidence for extremely magnesian subalkaline melts from the Antarctic extension of the Karoo large igneous province
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卡鲁大型火成岩省南极延伸部分存在极镁亚碱性熔体的矿物化学证据
DOI：
10.1007/s00710-010-0115-9
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发表时间：
2010
影响因子：
1.8
通讯作者：
A. Luttinen
中科院分区：
文献类型：
--
作者：
J. Heinonen;A. Luttinen
我们提供了一个完整的矿物化学数据集(∼400分析)，这些数据来自德隆宁毛德西部韦斯特菲拉的卡鲁大火成岩省(LIP)的南极延伸部分的亚碱性脉岩(镁 = 74-80)和铁苦铁岩脉(镁 = 67-69)。一些早先被认为是来自苦铁矿岩浆的堆积体，其特征是镁橄榄石(核心成分高达Fo92)与主岩处于或接近Fe-Mg平衡。橄榄石为亚面体到正面体，含有富钛(火山)尖晶石包裹体，CaO含量高(≥0.19wt.%)，因此不太可能代表地幔橄榄岩的捕虏晶。在橄榄石赋存的结晶熔体包裹体中发现了火成岩角闪石，表明母岩浆的H2O含量为1-2wt.%。橄榄石数据表明，在卡鲁岩浆作用期间，产生了极富镁(高达25%)的熔体。根据我们的岩石成因模拟，这种熔体很可能起源于石榴石橄榄岩在高压(5-6 Gpa)和地幔潜在温度(>；1600℃)下的部分熔融，这与地幔热柱参与Karoo唇部的生成是相容的。通过对来自西伯利亚圈闭的Vestfjella meimechite与来自西伯利亚圈闭的meimechite的地球化学对比，以及假定的霍林拜苦橄岩(Paraná-Etendeka Lip)的科马提质母熔体，揭示了关键的相似之处，表明所有这些岩套都来自广泛相似的来源和/或来自异常高温的次大陆地幔的相似的熔融过程。
We present a comprehensive mineral chemical dataset (∼400 analyses) on subalkaline meimechitic (Mg-number = 74–80) and ferropicritic (Mg-number = 67–69) dike samples from the Antarctic extension of the Karoo large igneous province (LIP) in Vestfjella, western Dronning Maud Land. Some of the meimechites, previously considered to be cumulates from ferropicritic magmas, are characterized by forsteritic olivine (with core composition up to Fo92) that is in, or close to Fe-Mg equilibrium with the host rock. The olivines are subhedral to euhedral, contain Ti-rich (volcanic) spinel inclusions, have a high CaO content (≥0.19 wt. %), and are thus unlikely to represent xenocrysts from mantle peridotite. Igneous amphibole is found in olivine-hosted, crystallized melt inclusions, indicating that the parental magmas had a H2O content of 1–2 wt. %. The olivine data suggests generation of extremely MgO-rich (up to 25 wt. %) melts during the Karoo magmatism. Based on our petrogenetic modeling, such melts are likely to have originated from the partial melting of garnet peridotite at high pressures (5–6 GPa) and mantle potential temperatures (>1,600°C) that are compatible with the involvement of a mantle plume in the generation of the Karoo LIP. A geochemical comparison of the Vestfjella meimechites with meimechites from the Siberian Traps LIP and the assumed komatiitic parental melts of the Horingbai picrites (Paraná-Etendeka LIP) reveals key similarities, suggesting that all these suites were generated from broadly similar sources and/or by similar melting processes in anomalously hot subcontinental mantle.