A significant seawater sulfate reservoir at 2.0 Ga determined from multiple sulfur isotope analyses of the Paleoproterozoic Degrussa Cu-Au volcanogenic massive sulfide deposit, Western Australia
A significant seawater sulfate reservoir at 2.0 Ga determined from multiple sulfur isotope analyses of the Paleoproterozoic Degrussa Cu-Au volcanogenic massive sulfide deposit, Western Australia
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通过对西澳大利亚古元古代 Degrussa Cu-Au 火山成因块状硫化物矿床的多次硫同位素分析确定了一个重要的 2.0Ga 海水硫酸盐储层
DOI：
10.1016/j.gca.2020.12.018
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发表时间：
2021
影响因子：
5
通讯作者：
Joshua Bell
中科院分区：
文献类型：
--
作者：
C. Laflamme;G. Barré;M. Fiorentini;G. Beaudoin;S. Occhipinti;Joshua Bell
元古代岩石记录显示，在20亿年的时间里，从含铁水圈到含氧水圈的长期变化;然而，关于大气氧化的周期性、变化率和步骤的争论仍在继续，最终导致了含氧海洋。这部分是由于古元古代海洋沉积记录在大氧化事件后的数亿年中保存不好。而2.0 Ga的岩石记录只保留了罕见的化学沉积物，它包含了显着的镁铁质火成岩省，这是已知的本地主机火山成因块状硫化物（VMS）矿床。这些热液环境揭示了海底火山岩与海水之间的古老相互作用。在此背景下，2.01 Ga Degrussa VMS存款古元古代摩羯造山带，西澳大利亚州提供了一个机会，以探讨古代海洋组成。Degrussa VMS存款保存了块状硫化物矿化（黄铁矿-黄铜矿-磁黄铁矿±闪锌矿±方铅矿），该矿化位于浊积岩沉积岩中，与玄武岩流互层，并被许多辉长岩岩床切割。喷盐岩层由赤铁矿和与磁铁矿共生的碧玉组成。本研究通过综合分析方法记录了Degrussa VMS存款的多种硫同位素组成，该分析方法包括体相色谱同位素比值质谱和原位二次离子质谱。通过比较超高精度的整体测量（n= 21）与黄铁矿、黄铜矿和磁黄铁矿的可变结构颗粒的原位测量（n= 252），我们确定VMS矿化产生的δ 34 S在+2‰和+5‰之间，峰值在+2.9‰，负Δ 33 S信号范围为-0.08至0.00‰。双组分δ 34 S-Δ 33 S混合模型表明，11%的H2S来自热化学还原的海水硫酸盐与岩浆H2S的混合。最负的Δ 33 S值必须通过与近地表硫酸盐的相互作用来解释，经历复杂的溶解-再沉淀反应，需要至少1.2 mmol/L的海水硫酸盐储层，或7%的现代海水在2.01 Ga。
The Proterozoic rock record displays secular change from ferruginous to an oxic hydrosphere over the course of 2 billion years; however, debate continues on the periodicity, rate of change and steps in following atmospheric oxygenation that ultimately led to an oxygenated ocean. This is partly due to poor preservation of the Paleoproterozoic marine sedimentary record in the few hundred million years after the Great Oxidation Event. Whereas the 2.0 Ga rock record preserves only rare chemical sediments, it contains significant mafic igneous provinces, which are known to locally host volcanogenic massive sulfide (VMS) deposits. These hydrothermal environments fossilize the ancient interaction at the seafloor interface between volcanic rocks and seawater. In this context, the 2.01 Ga Degrussa VMS deposit of the Paleoproterozoic Capricorn Orogen, Western Australia offers an opportunity to probe the ancient ocean composition. The Degrussa VMS deposit preserves massive sulfide mineralisation (pyrite – chalcopyrite – pyrrhotite ± sphalerite ± galena) hosted in turbiditic sedimentary rocks interlayered with basaltic flows and cut by numerous gabbroic sills. Exhalite layers are composed of hematite and jasper associated with magnetite. This study documents the multiple sulfur isotope composition of the Degrussa VMS deposit through an integrated analytical approach, which comprises bulk fluorination gas chromatography isotope ratio mass spectrometry and in situ secondary ion mass spectrometry. By comparing the ultra-high precision bulk measurements (n= 21) with in situ measurements of variably-textured grains of pyrite, chalcopyrite and pyrrhotite (n= 252), we determine that VMS mineralisation yields δ34S between +2‰ and +5‰ with a peak at ∼+2.9‰, and negative Δ33S signal ranging from −0.08 to 0.00‰. A two component δ34S-Δ33S mixing model indicates 11% of H2S derived from thermochemically reduced seawater sulfate mixed with magmatic H2S. The most negative Δ33S values must be explained by interaction with sulfate in the near-surface, undergoing complex dissolution-reprecipitation reactions, necessitating a minimum seawater sulfate reservoir of ∼2 mmol/L, or 7% modern seawater at 2.01 Ga.
影响因子：
3.8
作者：
M. Reuschel;V. Melezhik;M. Whitehouse;A. Lepland;A. Fallick;H. Strauss
通讯作者：
M. Reuschel;V. Melezhik;M. Whitehouse;A. Lepland;A. Fallick;H. Strauss
影响因子：
5
作者：
Johnston, David T.;Poulton, Simon W.;Farquhar, James
通讯作者：
Farquhar, James
影响因子：
5.3
作者：
Martin A
通讯作者：
Martin A