Controls on the PGE distribution of Permian Emeishan alkaline and peralkaline volcanic rocks in Longzhoushan, Sichuan Province, SW China
Controls on the PGE distribution of Permian Emeishan alkaline and peralkaline volcanic rocks in Longzhoushan, Sichuan Province, SW China
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四川龙州山二叠系峨眉山碱性和过碱性火山岩中PGE分布的控制
DOI：
10.1016/j.lithos.2008.07.012
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发表时间：
2008-12
期刊：
影响因子：
3.5
通讯作者：
中科院分区：
文献类型：
--
作者：
中国西南和越南北方的峨眉山大火成岩省（约260 Ma）主要发育低钛拉斑玄武岩、高钛碱性玄武岩和少量过碱性火山岩。四川龙州山溢流玄武岩由四个单元组成，每个单元底部都有火山角砾岩。从底部向上，1号和2号单元的岩石为高钛玄武岩，具有相对较高的MgO（7.6- 11.0wt%），二氧化钛（1.7-4.5重量%）和Ti/Y比（420-790）。单元3由具有较低MgO（0.87- 6.2wt.%）的硫铁矿组成，二氧化钛（0.96-2.14重量%）和Ti/Y比（190-530），而单元4由具有中等MgO（3.5-4.8重量%）的玄武安山岩组成，二氧化钛（2.2-3.1重量%）和Ti/Y比（383-606）。高钛玄武岩可能来源于OIB型地幔源区，玄武安山岩可能是高钛玄武岩浆经地壳混染和分异作用形成的。火山灰显示出高的Nb/Y（1.2 ~ 2.7）和Th/Y（0.31 ~ 0.55）比值，可变的Zr/Hf比值（40 ~ 49）和相对较低的εNd（t）（−0.7 ~+0.28）值，表明软流圈地幔的贡献被富碳酸盐流体改变。高钛玄武岩含有相对较高的和可变的PGE和它们的Cu/Pd比是相对恒定的（相比于陨石），从8,500到86000不等。我们属性这样的相对恒定的Cu/Pd比的存在下，残留的硫化物在源的高钛岩石和随后的结晶从S-不饱和熔体。玄武安山岩的Cu/Pd比值相对较高且恒定（130，000 - 370，492），PGE含量最低（平均Pd为0.12 ppb，Pt为0.20 ppb），表明硫化物在侵位前因地壳污染而较早被去除。火山灰富含铂族元素（Pt为0.057 ~ 1.89 ppb，Pd为0.11 ~ 2.10 ppb），但Cu/Pd比值比玄武安山岩高（33，300 - 429，000）的岩石比玄武安山岩的岩石更易变，表明在岩浆侵位过程中，火山岩可能经历了硫饱和分馏作用，并从源岩浆中微弱地去除了硫化物。铬铁矿的早期分馏以及从母岩浆中去除的月桂石和/或Os-Ir-Ru合金可能是造成闪长岩、高Ti玄武岩和玄武安山岩的负Ru异常的原因。
The ~260-Ma Emeishan large igneous province in SW China and northern Vietnam contains low-Ti tholeiitic basalts, high-Ti alkaline basalts and minor peralkaline volcanic rocks. The flood basalts in Longzhoushan, Sichuan Province, SW China, comprise four units, each of which has volcanic breccia at the base. From the base upward, rocks of Units 1 and 2 are high-Ti basalts with relatively high MgO (7.6–11.0 wt.%), TiO2(1.7–4.5 wt.%) and Ti/Y ratios (420–790). Unit 3 is composed of tephrites with lower MgO (0.87–6.2 wt.%), TiO2(0.96–2.14 wt.%) and Ti/Y ratios (190–530), whereas Unit 4 consists of basaltic andesites with moderate MgO (3.5–4.8 wt.%), TiO2(2.2–3.1 wt.%) and Ti/Y ratios (383–606). The high-Ti basalts may have been derived from an OIB-like mantle source and the basaltic andesites were probably generated by crustal contamination and fractionation of high-Ti basaltic magmas. The tephrites show high Nb/Y (1.2 to 2.7) and Th/Y (0.31 to 0.55) ratios, variable Zr/Hf ratios (40 to 49) and relatively low εNd(t) (−0.7 to +0.28) values, suggesting an asthenospheric mantle contribution modified by carbonate-rich fluids. The high-Ti basalts contain relatively high and variable PGE and their Cu/Pd ratios are relatively constant (compared to the tephrites) and vary from 8,500 to 86,000. We attribute such relative constancy of the Cu/Pd ratios to the presence of residual sulphide in the source of the high-Ti rocks and subsequent crystallization from S-undersaturated melts. The basaltic andesites have relatively high and constant Cu/Pd ratios (130,000–370,492) and the lowest PGE contents (average 0.12 ppb for Pd, 0.20 ppb for Pt), suggesting an earlier removal of sulfide due to crustal contamination before emplacement. The tephrites have PGE abundances (0.057 to 1.89 ppb for Pt and 0.11 to 2.10 ppb for Pd) higher than those for basaltic andesites, however, the Cu/Pd ratios (33,300 to 429,000) of the rocks are more variable than those for the basaltic andesites, suggesting that the tephrites may have undergone both S-saturated fractionation during emplacement of the magmas and weak removal of sulfides from the source magmas. Early fractionation of chromite together with removal of laurite and/or Os–Ir–Ru alloys from the parental magmas may be responsible for the negative Ru anomalies of the tephrites, high-Ti basalts and basaltic andesites.
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影响因子：
3.5
作者：
Xie‐Yan Song;Mei‐Fu Zhou;R. Keays;Z. Cao;M. Sun;L. Qi
通讯作者：
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影响因子：
0.8
作者：
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Hong‐fu Zhang;M. Sun;F. Lu;Xin-hua Zhou;Mei‐Fu Zhou;Yongshun Liu;Guohui Zhang
影响因子：
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作者：
S. Aulbach;W. Griffin;N. Pearson;S. O’Reilly;K. Kivi;B. Doyle
通讯作者：
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影响因子：
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作者：
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通讯作者：
K. Righter;A. Campbell;M. Humayun;R. Hervig
影响因子：
5.8
作者：
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通讯作者：
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