Microanalytical methods for in-situ high-resolution analysis of rock varnish at the micrometer to nanometer scale
Microanalytical methods for in-situ high-resolution analysis of rock varnish at the micrometer to nanometer scale
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DOI：
10.1016/j.chemgeo.2015.06.023
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发表时间：
2015-09
期刊：
影响因子：
3.9
通讯作者：
Dorothea S. Macholdt;K. Jochum;C. Pöhlker;B. Stoll;U. Weis;B. Weber;Maren Müller;M. Kappl;S. Buhre;A. Kilcoyne;M. Weigand;D. Scholz;A. Al-amri;M. Andreae
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作者：
Dorothea S. Macholdt;K. Jochum;C. Pöhlker;B. Stoll;U. Weis;B. Weber;Maren Müller;M. Kappl;S. Buhre;A. Kilcoyne;M. Weigand;D. Scholz;A. Al-amri;M. Andreae
广泛的分析技术被用来调查不同地点的岩石清漆（以色列内盖夫;南非克涅斯特拉克特;加州死亡谷和莫哈韦沙漠）：200 nm飞秒激光烧蚀电感耦合等离子体质谱仪（LA-ICP-MS），电子探针显微分析仪（EPMA），聚焦离子束（FIB）切片，扫描透射X射线显微镜-近边X射线吸收精细结构谱（STXM-NEXAFS）。这种组合能够对岩石清漆进行全面的高空间分辨率分析。飞秒LA-ICP-MS和EPMA用于元素浓度的定量测定。在厚切片和薄切片上进行了原位测量，分辨率分别为10-40 μm和2 μm。结果表明，一些元素，如锰，钴，铅，镍，铜，是高度富集在清漆相对于上陆壳（高达100倍）。清漆组合物不受下层岩石的组合物的影响，这是由MnO 2 vs图证明。SiO2含量。来自不同地点的清漆在某些元素比率上显示出明显的差异，特别是Mn/Fe（0.3-25.1）、Mn/Ba（4-170）、Ni/Co（0.03-1.8）和Pb/Ni（0.4-23）。稀土元素（REE）模式随LaN/YbN= 3.5-12和不同程度的Ce异常（Ce/Ce* = 1.5-5.3）而变化。为了研究清漆的内部结构，制备了100-200 nm厚的FIB切片，并在nm尺度上进行了Fe、Mn、N、CO 32-、Ca、C和Si的映射。在以色列和加利福尼亚州的样品中观察到了锰、铁和有机碳的带状内部结构，而在南非的岩石清漆样品中没有出现富铁层。此外，发现空腔部分地由富含C、Fe和Mn的材料填充。不同产地的清漆内部结构不同，可能反映了不同的成因类型。结合微观分析技术的结果提供了重要的详细的见解对解开岩石清漆的成因。
A wide range of analytical techniques were used to investigate rock varnish from different locations (Negev, Israel; Knersvlakte, South Africa; Death Valley and Mojave Desert, California): a 200 nm-femtosecond laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS), an electron probe microanalyzer (EPMA), focused ion beam (FIB) slicing, and scanning transmission X-ray microscopy–near edge X-ray absorption fine structure spectroscopy (STXM–NEXAFS). This combination enables comprehensive high-spatial-resolution analysis of rock varnish. Femtosecond LA-ICP-MS and EPMA were used for quantitative determination of element concentrations. In-situ measurements were conducted on thick and thin sections with a resolution of 10–40 μm and 2 μm, respectively. The results demonstrate that some elements, such as Mn, Co, Pb, Ni, and Cu, are highly enriched in varnish relative to the upper continental crust (up to a factor of 100). The varnish composition is not influenced by the composition of the underlying rock, which is witnessed by plots of MnO2vs. SiO2contents. Furthermore, the Mn-free end members fall in the range of average dust compositions.The varnishes from the various locations show distinct differences in some elemental ratios, in particular Mn/Fe (0.3–25.1), Mn/Ba (4–170), Ni/Co (0.03–1.8) and Pb/Ni (0.4–23). The rare earth element (REE) patterns vary with LaN/YbN= 3.5–12 and different degrees of Ce anomalies (Ce/Ce* = 1.5–5.3).To study the internal structure of the varnish, 100–200 nm thick FIB slices were prepared and mappings of Fe, Mn, N, CO32 −, Ca, C, and Si at the nm scale performed. Banded internal structures of Mn, Fe and organic C were observed in the Israeli and Californian samples, however, no Fe-rich layers are present in the South African rock varnish samples. Furthermore, cavities were found that are partly filled by C, Fe, and Mn rich material. Internal structures are different for varnish from different locations, which might reflect different types of genesis. The results of the combined microanalytical techniques give important detailed insights towards unraveling the genesis of rock varnish.