The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW China: Insights from volatile compositions and C-Hf-Sr-Nd isotopes
The origin of the Zhubu mafic-ultramafic intrusion of the Emeishan large igneous province, SW China: Insights from volatile compositions and C-Hf-Sr-Nd isotopes
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中国西南峨眉山大型火成岩省竹布镁铁质-超镁铁质侵入体的起源：来自挥发性成分和 C-Hf-Sr-Nd 同位素的见解
DOI：
10.1016/j.chemgeo.2017.02.009
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发表时间：
2017
期刊：
影响因子：
3.9
通讯作者：
Li Zhongping
中科院分区：
文献类型：
--
作者：
Tang Qingyan;Zhang Mingjie;Wang Yuekun;Yao Yunsheng;Du Li;Chen Liemeng;Li Zhongping
峨眉山大火成岩省（LIP）朱埠镁铁质-超镁铁质岩体中赋存有岩浆型镍、铜、铂族元素（PGE）存款。它由一个层状层序组成，其中近水平的模态分层被近垂直的边缘带包裹。新的锆石U-Pb同位素测年结果表明，该层状层序的平均年龄为263.2 ± 5.6Ma。从朱埠岩体矿物分离物中提取的挥发分主要由H2O（11，769.84 mm 3·STP/g，STP-标准温度和压力）和少量H2和CO2组成。与边缘带相比，层状层序H_2O含量低，H_2、CO_2、H_2S和SO_2含量高。在400-900 °C和900-1200 °C提取的CO2和CH 4的轻δ 13 CCO 2变化在− 17.45‰至− 7.10‰之间，δ 13 CCH 4变化在− 41.35‰至− 22.88‰之间。辉石分离物的（87 Sr/86 Sr）i值（0.705882 ~ 0.708912）明显低于全岩，εNd（t = 263 Ma）值（− 2.8 ~ 0.7）略高于全岩。锆石晶体的εHf（t = 263 Ma）值在− 3.05到+1.90之间变化。朱埠岩体挥发分的化学成分表明，其母岩浆处于轻微还原状态，为富H_2O的岩浆。朱埠岩体的C-Hf-Sr-Nd同位素与~ 15wt%的上地壳被幔源岩浆同化一致。碳同位素结果表明，混染岩浆中存在来自沉积有机质的生热组分。挥发分含量与PGE含量以及C-Hf-Sr-Nd同位素之间的弱正相关性表明，朱埠岩浆中硫化物饱和是由地壳混染（包括挥发分的加入）触发的。
The Zhubu mafic-ultramafic intrusion of the Permian Emeishan large igneous province (LIP), SW China hosts a magmatic Ni, Cu and platinum-group element (PGE) deposit. It consists of a layered sequence with sub-horizontal modal layering wrapped by a sub-vertical marginal zone. Our new zircon U-Pb isotopic dating gives a mean age of 263.2 ± 5.6 Ma for the layered sequence. The volatiles extracted from the mineral separates of the Zhubu intrusion are composed of predominant H2O (11,769.84 mm3·STP/g, STP-standard temperature and pressure) and minor H2and CO2. The layered sequence has lower H2O but higher H2, CO2, H2S and SO2contents than the marginal zone. The CO2and CH4extracted at 400–900 °C and 900–1200 °C have light δ13CCO2varying from − 17.45‰ to − 7.10‰ and δ13CCH4varying from − 41.35‰ to − 22.88‰. The pyroxene separates have significantly lower (87Sr/86Sr)ivalues (0.705882 to 0.708912) and slightly higher εNd(t = 263 Ma) values (− 2.8 to 0.7) than the whole rocks. The εHf(t = 263 Ma) values of zircon crystals vary from − 3.05 to + 1.90. The chemical compositions of volatiles from the Zhubu intrusion indicate a slightly reduced condition and a H2O-rich parental magma. The C-Hf-Sr-Nd isotopes for the Zhubu intrusion are consistent with ~ 15 wt% assimilation of the upper crust by a mantle-derived magma. The carbon isotopes indicate that a thermogenic component from sedimentary organic materials was present in the contaminated magma. A weak positive correlation between volatile and PGE contents, together with the C-Hf-Sr-Nd isotopes, indicates that sulfide saturation in the Zhubu magma was triggered by crustal contamination including the addition of volatiles.