Mineral chemical evidence for extremely magnesian subalkaline melts from the Antarctic extension of the Karoo large igneous province

作者：Heinonen Jussi S^*; Luttinen Arto V

来源：Mineralogy and Petrology, 2010, 99(3-4): 201-217.

DOI：10.1007/s00710-010-0115-9

We present a comprehensive mineral chemical dataset (similar to 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 Fo(92)) 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 (a parts per thousand yen0.19 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 H(2)O 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 (> 1,600A degrees 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 (Parana-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.

• 出版日期2010-7