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首页> 外文期刊>Journal of Asian earth sciences >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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An ultramafic primary magma for a low Si, high Ti-Fe gabbro in the Panxi region of the Emeishan large igneous province, SW China

机译：中国西南峨眉山火成岩省攀西地区低硅高钛铁辉长岩的超镁铁质原生岩浆

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摘要

The Kelang gabbro (256 ± 3 Ma) is in contact with the peralkaline syenite of the Late Permian (～260 Ma) Fe-Ti oxide-bearing Baima igneous complex and contains high contents of TiO_2 (～4.0 wt.%) and Fe_2O_3t (～20 wt.%) and low SiO_2 (～42 wt.%) and A1_2O_3 (～11 wt.%) content. The gabbros are primarily composed of plagioclase, clinopyroxene, olivine (Mg# ～50), ilmenite, magnetite, orthopyroxene (Mg# ～60), biotite and apatite. The Sr-Nd whole rock isotope data (I_(sr)- 0.7046, _εNd_(T) - +2.5) and positive primitive mantle normalized anomalies of Ba, Sr and Ti and high Eu/Eu' (～1.1) of the Kelang gabbro suggest a possible connection to the Baima cumulate gabbro (I_(sr) - 0.7047-0.7052, _εNd_(T) - +1.6 to +4.2, Eu/Eu - 1.5-3.6) but the bulk Cr content (～4 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.
机译：Kelang gabbro（256±3 Ma）与晚二叠世（〜260 Ma）含Fe-Ti氧化物的白马火成岩的高碱性正长岩接触，并含有高含量的TiO_2（〜4.0 wt。％）和Fe_2O_3t（约20 wt。％）和低SiO_2（约42 wt。％）和Al_2O_3（约11 wt。％）含量。辉长岩主要由斜长石，斜辉石，橄榄石（Mg＃〜50），钛铁矿，磁铁矿，原辉石（Mg＃〜60），黑云母和磷灰石组成。 Sr-Nd整个岩石同位素数据（I_（sr）-0.7046，_εNd_（T）-+2.5）和Ba，Sr和Ti的正原始地幔归一化异常以及巴生辉长岩的高Eu / Eu'（〜1.1）暗示可能与白马累积辉长岩（I_（sr）-0.7047-0.7052，_εNd_（T）-+1.6至+4.2，Eu / Eu-1.5-3.6）有关，但总Cr含量（〜4 ppm）和矿物学有很大的不同。质量平衡，最小二乘模型表明，克朗辉长岩的Cr含量较低，可能是由于来自一小块岩浆岩中Cr-尖晶石的分离所致。在富镁的镁铁质硅酸盐和Cr-尖晶石的早期分馏后，残留的液体将富含Ti和Fe，Cr贫乏，Si和Al含量低且类似于Kelang长辉石的整体组成。因此，巴生辉长岩可能是与白马火成岩无关的大型镁铁质-超镁铁质侵入体的最上部。

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