Single Spot Rb‐Sr Isochron Dating of Biotite by LA‐MC‐ICP‐MS / MS
Single Spot Rb‐Sr Isochron Dating of Biotite by LA‐MC‐ICP‐MS / MS
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LA-MC-ICP-MS / MS 对黑云母进行单点 Rb-Sr 等时线测年
DOI：
10.1111/ggr.12518
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发表时间：
2023
影响因子：
3.8
通讯作者：
Bouman, Claudia
中科院分区：
文献类型：
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作者：
Cruz‐Uribe, Alicia M.;Craig, Grant;Garber, Joshua M.;Paul, Bence;Arkula, Cemil;Bouman, Claudia
激光烧蚀串联质谱法是原位Rb-Sr年代学的一个新兴领域。在这里，我们使用ESL™ imageGEO™193准分子激光烧蚀系统与Thermo Scientific™ Neoma™ MC-ICP-MS/MS耦合，同时测定了缅因州西部变质黑云母中87 Sr/86 Sr和87 Rb/86 Sr的同位素比。在法拉第杯上进行测量，Rb+质量为87; Sr同位素与SF6气体反应，测量为SrF+质量为103-107。从一个黑云母样品中的22个激光点得到的“传统”Rb-Sr等时线年龄为289 ± 6 Ma。时间分辨信号在单点分析中揭示了87 Sr/86 Sr和87 Rb/86 Sr的显著分带，这些分带用于构建单点等时线。单个激光点包含多个等时线亚群;一些点包含多达三个不同的Rb-Sr等时线，这些等时线与Rb/Sr的变化无关。使用这种“子点”方法确定了35个等时线日期，其中87 Sr/86 Sr截距随Rb-Sr日期系统地变化;基于这些可变截距计算了单个积分的两点等时线（n= 780）。这两种方法产生的年龄峰值在303，270和240 Ma。这些数据表明，Rb-Sr系统有可能在单个黑云母晶体的小区域内记录多个加热，冷却或流体蚀变事件，跨度约为100 My。
Laser ablation tandem mass spectrometry is a burgeoning field forin situRb‐Sr geochronology. Here, we determined simultaneous isotope ratios of87Sr/86Sr and87Rb/86Sr in metamorphic biotite from western Maine, using an ESL™ imageGEO™193 excimer laser ablation system coupled to a Thermo Scientific™ Neoma™ MC‐ICP‐MS/MS. Measurements were made on Faraday cups with Rb+at mass 87; Sr isotopes were reacted with SF6gas and measured as SrF+at masses 103–107. Twenty‐two laser spots in biotite from a single sample yield a "traditional" Rb‐Sr isochron date of 289 ± 6 Ma. Time‐resolved signals reveal significant zoning in87Sr/86Sr and87Rb/86Sr within single spot analyses, which were used to construct single spot isochrons. Individual laser spots contain multiple isochronous subpopulations; some spots contain up to three distinct Rb‐Sr isochrons that are decoupled from variations in Rb/Sr. Thirty‐five isochron dates were determined using this "sub‐spot" approach, with87Sr/86Sr intercepts that systematically vary with Rb‐Sr date; two‐point isochrons were calculated for individual integrations (n= 780) based on these variable intercepts. Both methods yield age peaks at 303, 270 and 240 Ma. These data suggest that the Rb‐Sr system has the potential to record multiple heating, cooling or fluid‐alteration events spanning ~ 100 My within small domains in single biotite crystals.