Association of Mg-rich Olivine with Magnetite as a Result of Brucite Marble Assimilation by Basaltic Magma in the Emeishan Large Igneous Province, SW China
Association of Mg-rich Olivine with Magnetite as a Result of Brucite Marble Assimilation by Basaltic Magma in the Emeishan Large Igneous Province, SW China
复制标题
峨眉山火成岩省玄武岩浆同化水镁石大理岩导致富镁橄榄石与磁铁矿的伴生
DOI：
10.1093/petrology/egx031
复制
发表时间：
2017-04
影响因子：
3.9
通讯作者：
Xiong Feng
中科院分区：
文献类型：
--
作者：
Tang Qingyan;Li Chusi;Tao Yan;Ripley Edward M.;Xiong Feng
中国西南二叠纪峨眉山大火成岩省（LIP）与层状侵入体相关的岩浆铁钛氧化物矿床的一个不寻常的特征是成矿与橄榄石的关联，橄榄石的富镁程度明显高于其他地方。峨眉山铁钛氧化物矿床形成过程中，碳酸盐发生了明显的同化作用，这是富镁橄榄石形成的一个有效假设。本文从朱家包堡攀枝花层状岩体下盘的一个同时期的苦泥质岩脉中，提供了几条支持证据。乡村岩石以朱家宝堡苦橄岩脉为主，均为水闪石大理岩。岩脉中橄榄石斑晶的Fo含量在79% ~ 91%之间。富镁橄榄石斑晶（Fo89-91）出现在岩脉边缘，含有未溶解的方解石。边缘样品中的橄榄石斑晶在Fo含量上表现出相反的分带性，其Ni含量比附近同时期苦橄岩中相似Fo含量的橄榄石斑晶低20%左右。该样品中含有橄榄石的氧化物包裹体完全是cr -磁铁矿（计算原子Fe3+/Cr3+ > 1），而不是铬铁矿或cr -尖晶石(计算原子Fe3+/Cr3+ (Nd)值（1中心点4-2），但对比Sr同位素组成。富镁橄榄石样品（Fo89-90）初始Sr-87/Sr-86比值最高（0中心点7054），富铁橄榄石样品（Fo78-83）初始Sr-87/Sr-86比值较低（0中心点7046-0中心点7049）。混合计算的结果表明，高达25 wt %的水镁石大理岩被玄武岩岩浆同化，其成分与同期高钛玄武岩的平均值相似，可以很容易地解释岩脉内观察到的矿物学和同位素变化。岩脉结果表明，玄武岩岩浆对碳酸盐的同化作用是形成磁铁矿与异常富镁橄榄石结合的有效途径。
An unusual feature of the magmatic Fe-Ti oxide deposits associated with layered intrusions in the Permian Emeishan large igneous province (LIP) in SW China is the association of the mineralization with olivine that is significantly more Mg-rich than those that occur elsewhere. A working hypothesis for the production of Mg-rich olivine is that significant assimilation of carbonate occurred during the formation of the Fe-Ti oxide deposits in the Emeishan LIP. This study provides several lines of supporting evidence from a coeval picritic dyke in the footwall of the Panzhihua layered intrusion at Zhujiabaobao. Country rocks to the Zhujiabaobao picritic dyke are brucite marbles. Olivine phenocrysts in the dyke have Fo contents varying from 79 to 91 mol %. The most Mg-rich olivine phenocrysts (Fo89-91) are present in the margins of the dyke and contain undissolved calcite. Olivine phenocrysts in the marginal sample show reversed zoning in Fo content and contain similar to 20% lower Ni than those with similar Fo contents in the coeval picrites emplaced in the nearby area. Olivine-hosted oxide inclusions in this sample are exclusively Cr-magnetite (calculated atomic Fe3+/Cr3+ > 1) instead of chromite or Cr-spinel (calculated atomic Fe3+/Cr3+ (Nd) values (1 center dot 4-2) but contrasting Sr isotope compositions. The sample with the most Mg-rich olivine (Fo89-90) has the highest initial Sr-87/Sr-86 ratio (0 center dot 7054), whereas samples with more Fe-rich olivine (Fo78-83) have lower initial Sr-87/Sr-86 ratios (0 center dot 7046-0 center dot 7049). The results of mixing calculations indicate that up to similar to 25 wt % assimilation of brucite marble by basaltic magma with a composition similar to that of the average of the coeval high-Ti basalts can readily explain the observed mineralogical and isotopic variations within the dyke. The results from the dyke show that carbonate assimilation by basaltic magma is an efficient way to produce the association of magnetite with olivine that is anomalously rich in magnesium.
登录
查看更多内容
影响因子：
1.8
作者：
Qingyan Tang;Chusi Li;Mingjie Zhang;Yao Lin
通讯作者：
Qingyan Tang;Chusi Li;Mingjie Zhang;Yao Lin
中国西南至越南北部峨眉山溢流玄武岩省PGE随Sr-Nd同位素和亲石元素变化的意义
影响因子：
3.5
作者：
Li Chusi;Ripley Edward M.;Tao Yan;Hu Ruizhong
通讯作者：
Hu Ruizhong
影响因子：
8.9
作者：
C. Ganino;N. Arndt;C. Chauvel;Alexandre Jean;Charlotte Athurion
通讯作者：
C. Ganino;N. Arndt;C. Chauvel;Alexandre Jean;Charlotte Athurion
影响因子：
3.5
作者：
KRESS, VC;CARMICHAEL, ISE
通讯作者：
CARMICHAEL, ISE
影响因子：
3.5
作者：
G. Howarth;S. Prevec;Mei‐Fu Zhou
通讯作者：
G. Howarth;S. Prevec;Mei‐Fu Zhou