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首页> 外文期刊>The American mineralogist >Ferruginous seawater facilitates the transformation of glauconite to chamosite: An example from the Mesoproterozoic Xiamaling Formation of North China
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Ferruginous seawater facilitates the transformation of glauconite to chamosite: An example from the Mesoproterozoic Xiamaling Formation of North China

机译：铁海水促进了甘油酮转化为倒角：来自中国华北夏代夏代形成的一个例子

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Berthierine and chamosite are iron-rich clay minerals that share similar chemical compositions. Berthierine forms at low temperature (25-45 degrees C) during early diagenesis and may transfer to chamosite at temperatures of >= 70 degrees C. Because the formation of berthierine and chamosite requires significant amount of Fe2+ supply, their presence in marine sediments is often used as a mineral proxy for ferruginous conditions in porewater. Recent studies reveal that the Precambrian oceans were characterized by pervasive ferruginous water-column conditions that may favor the formation of iron-rich clay minerals like berthierine and chamosite. To evaluate if ferruginous water-column conditions in the Precambrian ocean played a role on iron-rich clay mineral formation, we conducted an integrated petrographic, mineralogical, and geochemical study on the chamosite- and glauconite-bearing strata of the Mesoproterozoic Xiamaling Formation (similar to 1.40-1.35 Ga) in North China. Petrographic, XRD, SEM, and EDS analyses show that the chamosites of the Xiamaling Formation was transferred from glauconite, with berthierine as an intermediate mineral phase during early diagenesis. Geochemical analyses indicate that a complete transformation from glauconite-dominated to chamosite-dominated end-members (samples) requires an addition of a large amount of Fe (16.9 wt%), Mg (2.4 wt%), and a small amount of Al (1.4 wt%), but a simultaneous release of Si (11.8 wt%) and K (6.0 wt%). Considering that the glauconite-and chamosite-bearing strata are devoid of iron-rich detrital minerals (e.g., biotite and iron oxides) and lack evidence of hydrothermal alteration, the required Fe2+ for glauconite-berthierine-chamosite transformation was most likely from Fe2+-rich (ferruginous) seawater, which may have promoted glauconite-berthierine transformation at the very early diagenetic stage when Fe2+ exchange between porewater and seawater was still available. This interpretation is consistent wi
机译：白榴石和黄榴石是化学成分相似的富铁粘土矿物。贝氏铁矾在早期成岩作用期间的低温（25-45摄氏度）下形成，并可能在>=70摄氏度的温度下转移到黄钾铁矾。由于贝氏铁矾和黄钾铁矾的形成需要大量的Fe2+供应，它们在海洋沉积物中的存在通常被用作孔隙水中含铁条件的矿物替代物。最近的研究表明，前寒武纪海洋的特点是普遍存在的铁质水柱条件，这可能有利于形成富铁粘土矿物，如白铁石和黄铁矾。为了评估前寒武纪海洋中的铁质水柱条件是否对富铁粘土矿物的形成起到作用，我们对中国北方中元古代下马岭组（类似于1.40-1.35 Ga）的含镁铁矾石和海绿石的地层进行了综合岩相学、矿物学和地球化学研究。岩相、XRD、SEM和EDS分析表明，下马岭组的角质岩是从海绿石中转移而来的，在早期成岩作用中，贝锡林是中间矿物相。地球化学分析表明，从海绿石为主的端部构件（样品）完全转变为蓝辉石为主的端部构件（样品）需要添加大量铁（16.9 wt%）、镁（2.4 wt%）和少量铝（1.4 wt%），但同时释放硅（11.8 wt%）和钾（6.0 wt%）。考虑到含海绿石和黄钾铁矾的地层不含富铁碎屑矿物（如黑云母和氧化铁），且缺乏热液蚀变证据，海绿石-贝氏黄钾铁矾转化所需的Fe2+很可能来自富Fe2+（含铁）的海水，这可能促进了海绿石-贝氏体在成岩早期的转化，当时孔隙水和海水之间仍然存在Fe2+交换。这一解释是一致的

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