Early Archean spherule layers from the Barberton Greenstone Belt, South Africa: Mineralogy and geochemistry of the spherule beds in the CT3 drill core
Early Archean spherule layers from the Barberton Greenstone Belt, South Africa: Mineralogy and geochemistry of the spherule beds in the CT3 drill core
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南非巴伯顿绿岩带的早期太古代小球层：CT3 钻芯中小球床的矿物学和地球化学
DOI：
10.1111/maps.12998
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发表时间：
2017
影响因子：
2.2
通讯作者：
Schmitt
中科院分区：
文献类型：
--
作者：
Oezdemir;Schulz;Koeberl;Reimold;Mohr-Westheide;Hoehnel;Schmitt
人们对Hadean和太古宙在地球上的撞击记录知之甚少。在Barberton绿岩带北部无花果树群的CT3钻芯中，出现了17个球层交叉点，这为深入了解陨石对早期地球的轰击提供了一个绝佳的新机会。作为主要特征的CT3球体，大多表现出与其他巴伯顿球体层相似的结构模式，但局部观察到矿物学和化学成分的差异，这可能是不同程度蚀变的结果。观察到的球状层的矿物学是二次成因的，包括钾长石、层状硅酸盐、碳酸盐、硫化物和氧化物，但次生镍铬尖晶石除外。我们的岩石学研究表明，蚀变作用主要表现为钾交代、绢云母化、硅化和碳酸盐化。大块样品中亲铁元素含量明显富含Ni(高达2wt%)和Ir(高达3ppm)，与前人研究的太古宙球层相似。这些数值表明存在陨石成分。另一方面，亲石元素和亲硫元素的丰度表明热液叠加在CT3样品上；这也可能影响了陨石成分的重新分布(S)。最后，我们根据CT3球层的岩石学和地球化学特征，将其分为三个时段(A、B和C)进行分组，这表明在影响原始矿床的构造叠加之前，至少发生了三次不同的撞击事件。
Little is known about the Hadean and the Archean impact record on Earth. In the CT3 drill core from the Fig Tree Group of the northern Barberton Greenstone Belt, 17 spherule layer intersections occur, which, provide an outstanding new opportunity to gain insights into meteorite bombardment of the early Earth. CT3 spherules, as primary features, mostly exhibit textural patterns similar to those of the other Barberton spherule layers, but locally mineralogical and chemical compositional differences are observed, likely as a result of various degrees of alteration. The observed mineralogy of the spherule layers is of secondary origin and comprises K‐feldspar, phyllosilicates, carbonates, sulfides, and oxides, with the exception of secondary Ni‐Cr spinel that is of primary origin. Our petrographic investigations suggest alteration by K‐metasomatism, sericitization, silicification, and carbonatization. Siderophile element contents of bulk samples show significant enrichments in Ni (up to 2 wt%) and Ir (up to ~3 ppm), similar to previously studied Archean spherule layers. These values are indicative of the presence of a meteoritic component. On the other hand, lithophile and chalcophile element abundances indicate hydrothermal overprint on the CT3 samples; this may also have influenced the redistribution of the meteoritic component(s). Last, we group the CT3 spherule layers, which occur in three intervals (A, B, and C), according to their petrographic and geochemical features, which indicate evidence for at least three distinct impact events before tectonic overprint that affected the original deposits.
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DOI：
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DOI：
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期刊：
影响因子：
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