Calibrating Ti concentrations in quartz for SIMS determinations using NIST silicate glasses and application to the TitaniQ geothermobarometer
Calibrating Ti concentrations in quartz for SIMS determinations using NIST silicate glasses and application to the TitaniQ geothermobarometer
复制标题
DOI：
10.2138/am.2011.3702
复制
发表时间：
2011-07
影响因子：
3.1
通讯作者：
W. Behr;Jay B. Thomas;R. Hervig
中科院分区：
文献类型：
--
作者：
W. Behr;Jay B. Thomas;R. Hervig
摘要Wark和沃森（2006）和托马斯等人（2010）最近开发的石英中钛（TitaniQ）地质温压计具有广泛应用于火成岩和变质岩的潜力。对于Ti浓度>~ 10 ppm，可以使用电子微探针测量浓度，但较低浓度低于检测限，需要使用激光烧蚀电感耦合等离子体质谱法（LA-ICP-MS）或二次离子质谱法（西姆斯）等技术。西姆斯是这方面的理想选择，因为它最大限度地提高了横向和深度分辨率。我们使用西姆斯来分析通过电子探针表征的Ti浓度（18-813 ppm Ti）的合成石英晶体，并使用高质量分辨率（HMR）和常规能量过滤（CEF）技术将该校准与常用的NIST 61 X玻璃进行比较。我们使用了16 O-离子的初级束，并检测到正二次离子。在HMR会话期间，质谱仪在~2000的质量分辨能力（M/ΔM）下操作，以将分子离子与元素Ti峰分离。对于CEF分析，仪器检测到从样品溅射的具有75 ± 20 eV的过量动能的二次离子。钛石英测量揭示一般的均匀性和线性增加Ti+/Si+离子比与Ti浓度的增加。背景信号表示0-1 ppm。二氧化钛石英晶体的校准曲线的斜率是使用NIST玻璃构建的曲线的约70%，表明与硅的简单氧化物相比，来自玻璃的Ti的离子产率高得多。然而，我们证明，一个简单的校正因子允许NIST玻璃被用来定量测定石英的钛浓度（与3.8%的误差使用HMR，和8.2%的误差使用CEF），直到均匀的，良好表征的SiO2样品变得普遍可用。
Abstract The recently developed titanium-in-quartz (TitaniQ) geothermobarometer of Wark and Watson (2006) and Thomas et al. (2010) has the potential to be applied to a wide range of igneous and metamorphic rocks. For Ti concentrations > -10 ppm, the concentrations can be measured using an electron microprobe, but lower concentrations are below detection limits and require techniques such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) or secondary ion mass spectrometry (SIMS). SIMS is ideal for this purpose as it maximizes lateral and depth resolution. We used SIMS to analyze synthetic quartz crystals characterized for Ti concentration by electron probe (18-813 ppm Ti) and compare this calibration to the commonly available NIST 61X glasses using both high mass resolution (HMR) and conventional energy filtering (CEF) techniques. We used a primary beam of 16O- ions and detected positive secondary ions. During HMR sessions, the mass spectrometer was operated at a mass resolving power (M/ΔM) of ~2000 to separate molecular ions from elemental Ti peaks. For CEF analyses, the instrument detected secondary ions sputtered from the sample with excess kinetic energies of 75 ± 20 eV. Titanian quartz measurements reveal general homogeneity and a linear increase in Ti+/Si+ ion ratios with increasing Ti concentrations. Background signals represent 0-1 ppm. The slopes of the calibration curves for the titanian quartz crystals are -70% of the curves constructed using NIST glasses, indicating a much higher ion yield for Ti from the glasses compared to the simple oxide of silicon. We demonstrate, however, that a simple correction factor allows NIST glasses to be used to quantitatively determine the Ti concentrations of quartz (with 3.8% error using HMR, and 8.2% error using CEF) until homogenous, well-characterized samples of SiO2 become generally available.