In-site mineral geochemistry and whole-rock Fe isotopes of the quartz-magnetite-pyroxene rocks in the Wuyang area, North China Craton: Constraints on the genesis of the pyroxene-rich BIF
In-site mineral geochemistry and whole-rock Fe isotopes of the quartz-magnetite-pyroxene rocks in the Wuyang area, North China Craton: Constraints on the genesis of the pyroxene-rich BIF
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华北克拉通舞阳地区石英-磁铁矿-辉石岩现场矿物地球化学及全岩Fe同位素：对富辉石BIF成因的制约
DOI：
10.1016/j.precamres.2019.105445
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发表时间：
2019-10
影响因子：
3.8
通讯作者：
Zhai Mingguo
中科院分区：
文献类型：
--
作者：
Lan Caiyun;Long Xiaoping;Zhao Taiping;Zhai Mingguo
具有高铁含量的石英-磁铁矿-辉石（QMP）岩石具有重大的经济和岩石学重要性，并且通常出现在地球上保存的最古老和最大的表壳岩石中。然而，QMP 岩石的化学成分和成因仍不清楚。为了确定原岩和成因，我们提供了华北克拉通舞阳地区 QMP 岩石的新的全岩地球化学和铁同位素数据、矿物 EPMA 和 LA-ICP-MS 分析以及 X 射线绘图。舞阳QMP岩石经历了高温变质作用，具有特殊的矿物组合，共存有磁铁矿、石英、单斜辉石和变斜方辉石。舞阳 QMP 岩石的辉石显示出与附近辉石大理石和辉石岩侵入体非常不同的主量、微量和稀土元素 (REE) 成分。这种差异排除了 QMP 岩石辉石的接触变质成因。 X射线元素图谱表明，这些辉石颗粒中贫铁碳酸盐矿物（白云石和方解石）和石英包裹体保存完好，并且它们之间没有观察到反应现象，这表明这些辉石不是先存沉积二氧化硅和富铁碳酸盐相变质脱碳反应的产物。全岩样品和辉石的页岩归一化 REE+Y 模式显示出与经典带状铁地层 (BIF) 一致的地球化学特征，显示出 REE 轻度损耗、正 LaSN、EuSN 和 YS 异常。这表明地球化学特征在成分上继承自其原始的纯化学沉积物。因此，舞阳 QMP 岩石被认为是富含辉石的 BIF。 QMP 岩石中辉石颗粒中的新辉石和新辉石包裹体可能是辉石出现之前一些早期富铁和富锰硅酸盐的变质产物。此外，舞阳 QMP 岩石富含轻铁同位素，与太古代 BIF 中其他富含铁和钙的矿物类似。因此，我们推测QMP岩石中的辉石可能是由初始沉积的含水Ca、Mg和Mn的Fe(II)硅酸盐凝胶在成岩作用和后期变质作用的重结晶过程中脱水形成的，这为富含辉石的BIF的成因提供了新的解释。
Quartz-magnetite-pyroxene (QMP) rocks with high Fe contents are of greatly economic and petrological importance and generally occur within the oldest and largest exposures of supracrustal rocks preserved on Earth. However, the chemical composition and genesis of QMP rocks remain unclear. To constrain the protolith and genesis, we present new whole-rock geochemistry and Fe isotopic data, mineral EPMA and LA-ICP-MS analysis and X-ray mapping for the QMP rocks in the Wuyang area, North China Craton. The Wuyang QMP rocks have undergone high-temperature metamorphism and have special mineral assemblages with coexisting magnetite, quartz, clinopyroxene and variable orthopyroxene. Pyroxenes of the Wuyang QMP rocks show very distinct major, trace and rare earth element (REE) compositions from those of the nearby pyroxene-marbles and pyroxenite intrusions. Such difference excludes a contact metamorphic origin for pyroxenes of the QMP rocks. X-ray elemental mapping suggests that Fe-poor carbonate minerals (dolomite and calcite) and quartz inclusions are well preserved in these pyroxene grains and no reaction phenomenon can be observed between them, indicating that these pyroxenes are not the product of metamorphic decarbonation reactions of pre-existing sedimentary silica and Fe-rich carbonate phase. Shale-normalized REE + Y patterns of the whole-rock samples and pyroxenes display geochemical features consistent with classic banded iron formations (BIFs), which show light REE depletion, positive LaSN, EuSNand YSNanomalies. This indicates that the geochemical features are compositionally inherited from their original pure chemical sediments. The Wuyang QMP rocks are therefore considered as pyroxene-rich BIF. Neotocite and hisingerite inclusions in pyroxene grains from the QMP rocks could be metamorphic products of some early Fe- and Mn-rich silicates before pyroxene. Moreover, the Wuyang QMP rocks are enriched in light iron isotopes similar to other Fe- and Ca-rich minerals in Archean BIFs. Therefore, we inferred that pyroxene from the QMP rocks could result from dehydration of initial sedimentary hydrous Ca-, Mg- and Mn-containing Fe(II)-silicate gel during diagenesis and re-crystallization in later metamorphism, providing a new interpretation for the origin of pyroxene-rich BIF.
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DOI：
10.1007/978-3-030-54851-3_1
发表时间：
2020
期刊：
Chemistry in Action: Making Molecular Movies with Ultrafast Electron Diffraction and Data Science
影响因子：
--
作者：
L. C. Liu
通讯作者：
L. C. Liu
DOI：
10.1016/b978-0-12-818264-2.00001-4
发表时间：
2019
期刊：
Well Productivity Handbook
影响因子：
--
作者：
B. Guo
通讯作者：
B. Guo
DOI：
10.1007/978-3-030-87128-4_1
发表时间：
2021
期刊：
The Economic Rise of East Asia
影响因子：
--
作者：
L. Glawe;H. Wagner
通讯作者：
L. Glawe;H. Wagner
影响因子：
5.8
作者：
C. Klein
通讯作者：
C. Klein
影响因子：
5
作者：
Alibert, Chantal
通讯作者：
Alibert, Chantal