Smith Joseph P, Smith Frank C, Ottaway Joshua, Krull-Davatzes Alexandra E, Simonson Bruce M, Glass Billy P, Booksh Karl S
1 Department of Chemistry & Biochemistry, University of Delaware, USA.
2 Department of Geological Sciences, University of Delaware, USA.
Appl Spectrosc. 2017 Aug;71(8):1816-1833. doi: 10.1177/0003702816687573. Epub 2017 Mar 7.
The high-pressure, α-PbO-structured polymorph of titanium dioxide (TiO-II) was recently identified in micrometer-sized grains recovered from four Neoarchean spherule layers deposited between ∼2.65 and ∼2.54 billion years ago. Several lines of evidence support the interpretation that these layers represent distal impact ejecta layers. The presence of shock-induced TiO-II provides physical evidence to further support an impact origin for these spherule layers. Detailed characterization of the distribution of TiO-II in these grains may be useful for correlating the layers, estimating the paleodistances of the layers from their source craters, and providing insight into the formation of the TiO-II. Here we report the investigation of TiO-II-bearing grains from these four spherule layers using multivariate curve resolution-alternating least squares (MCR-ALS) applied to Raman microspectroscopic mapping. Raman spectra provide evidence of grains consisting primarily of rutile (TiO) and TiO-II, as shown by Raman bands at 174 cm (TiO-II), 426 cm (TiO-II), 443 cm (rutile), and 610 cm (rutile). Principal component analysis (PCA) yielded a predominantly three-phase system comprised of rutile, TiO-II, and substrate-adhesive epoxy. Scanning electron microscopy (SEM) suggests heterogeneous grains containing polydispersed micrometer- and submicrometer-sized particles. Multivariate curve resolution-alternating least squares applied to the Raman microspectroscopic mapping yielded up to five distinct chemical components: three phases of TiO (rutile, TiO-II, and anatase), quartz (SiO), and substrate-adhesive epoxy. Spectral profiles and spatially resolved chemical maps of the pure chemical components were generated using MCR-ALS applied to the Raman microspectroscopic maps. The spatial resolution of the Raman microspectroscopic maps was enhanced in comparable, cost-effective analysis times by limiting spectral resolution and optimizing spectral acquisition parameters. Using the resolved spectra of TiO-II generated from MCR-ALS analysis, a Raman spectrum for pure TiO-II was estimated to further facilitate its identification.
最近，在从约26.5亿至25.4亿年前沉积的四个新太古代球粒层中回收的微米级颗粒中，发现了高压α-PbO结构的二氧化钛多晶型物（TiO-II）。多条证据支持这些层代表远端撞击喷出层的解释。冲击诱导的TiO-II的存在提供了物理证据，进一步支持了这些球粒层的撞击起源。详细表征这些颗粒中TiO-II的分布，可能有助于关联这些层、估计这些层与源陨石坑的古距离，并深入了解TiO-II的形成。在这里，我们报告了对来自这四个球粒层的含TiO-II颗粒的研究，该研究使用了应用于拉曼显微光谱映射的多元曲线分辨率交替最小二乘法（MCR-ALS）。拉曼光谱提供了主要由金红石（TiO）和TiO-II组成的颗粒的证据，如在174 cm（TiO-II）、426 cm（TiO-II）、443 cm（金红石）和610 cm（金红石）处的拉曼谱带所示。主成分分析（PCA）产生了一个主要由金红石、TiO-II和底物粘附环氧树脂组成的三相系统。扫描电子显微镜（SEM）表明，颗粒不均匀，含有多分散的微米级和亚微米级颗粒。应用于拉曼显微光谱映射的多元曲线分辨率交替最小二乘法产生了多达五个不同的化学成分：TiO的三个相（金红石、TiO-II和锐钛矿）、石英（SiO）和底物粘附环氧树脂。使用应用于拉曼显微光谱图的MCR-ALS生成了纯化学成分的光谱轮廓和空间分辨化学图。通过限制光谱分辨率和优化光谱采集参数，在可比的、具有成本效益的分析时间内提高了拉曼显微光谱图的空间分辨率。使用MCR-ALS分析生成的TiO-II分辨光谱，估计了纯TiO-II的拉曼光谱，以进一步促进其识别。
