An ultramafic primary magma for a low Si, high Ti-Fe gabbro in the Panxi region of the Emeishan large igneous province, SW China

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• 作者：J. Gregory Shellnutt ; Kuo-Lung Wang
• 关键词：Ti-rich gabbro ; Ultramafic ; Permian ; Emeishan large igneous province
• 刊名：Journal of Asian Earth Sciences
• 出版年：5 January, 2014
• 年：2014
• 卷：79
• 期：part_PA
• 页码：329-344
• 全文大小：3397 K

文摘

The Kelang gabbro (256 卤 3 Ma) is in contact with the peralkaline syenite of the Late Permian (鈭?60 Ma) Fe-Ti oxide-bearing Baima igneous complex and contains high contents of TiO₂ (鈭?.0 wt.%) and Fe₂O₃t (鈭?0 wt.%) and low SiO₂ (鈭?2 wt.%) and Al₂O₃ (鈭?1 wt.%) content. The gabbros are primarily composed of plagioclase, clinopyroxene, olivine (Mg# 鈭?0), ilmenite, magnetite, orthopyroxene (Mg# 鈭?0), biotite and apatite. The Sr-Nd whole rock isotope data (I_Sr = 0.7046, 蔚Nd_(T) = +2.5) and positive primitive mantle normalized anomalies of Ba, Sr and Ti and high Eu/Eu^* (鈭?.1) of the Kelang gabbro suggest a possible connection to the Baima cumulate gabbro (I_Sr = 0.7047-0.7052, 蔚Nd_(T) = +1.6 to +4.2, Eu/Eu^* = 1.5-3.6) but the bulk Cr content (鈭? ppm) and mineralogy are very different. Mass-balance, least-squares modeling suggests that the low Cr content of the Kelang gabbro is likely a result of fractionation of Cr-spinel from a picritic primary magma. After early fractionation of Mg-rich mafic silicates and Cr-spinel, the residual liquid will be enriched in Ti and Fe, depleted in Cr, have low Si and Al and resemble the bulk composition of the Kelang gabbro. Consequently, the Kelang gabbro may be the uppermost portion of a large mafic-ultramafic intrusion unrelated to the Baima igneous complex.