Refined insight into 40Ar/39Ar progressive crushing technique from K-Cl-Ar correlations in fluid inclusions
Refined insight into 40Ar/39Ar progressive crushing technique from K-Cl-Ar correlations in fluid inclusions
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从流体包裹体中的 K-Cl-Ar 相关性深入了解 40Ar/39Ar 渐进式破碎技术
DOI：
10.1016/j.chemgeo.2019.03.037
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发表时间：
2019-06-20
期刊：
影响因子：
3.9
通讯作者：
Qiu, Hua-Ning
中科院分区：
文献类型：
--
作者：
Bai, Xiu-Juan;Hu, Rong-Guo;Qiu, Hua-Ning
由于高精度质谱技术的最新进展，与地质过程相关的热液流体活动现在可以通过矿物的40 Ar/39 Ar渐进破碎来确定年代。然而，这些高分辨率测量的数据分析和解释方法仍需改进。在这项研究中，我们报告了进一步的见解，使用K-Cl-Ar图作为工具来解释年龄的次生和原生流体从40 Ar/39 Ar逐步破碎实验。采用激光增量加热和单矿物分级破碎的40 Ar/39 Ar技术，研究了华南某钨存款中白云母和黑钨矿的3对共生矿物。白云母的增量加热分析产生了平坦的年龄谱，确定高原年龄为156-153 Ma。黑钨岩的逐步破碎实验由于过量的40 Ar而获得了异常古老的表观年龄。然而，表观年龄在初始阶段后迅速下降，并稳定形成156-153 Ma的年龄平台，没有过量的40 Ar。高原年龄的步骤解释为来自原生流体包裹体（PFIs）的气体的年龄，产生定义明确的等时线，年龄范围从157至153 Ma和初始的40 Ar/39 Ar值是无法区分的现代大气值。数字化生成的K-Cl-Ar相关性的2D和3D图可以很容易地揭示破碎步骤的分布趋势和相关平面。这些图解的解释进一步揭示了次生流体包裹体（SFIs）（87 - 83 Ma）和原生流体包裹体（PFIs）（159 - 150 Ma）的年龄。来自在初始破碎步骤期间脱气的SFI的原始数据在逆等时线图上形成散点。而二维和三维K-Cl-Ar图解给出的SFI年龄与切割钨矿体的钾长石脉的40 Ar/39 Ar年龄一致。
Hydrothermal fluid activity associated with geological processes can now be dated by 40Ar/39Ar progressive crushing of minerals thanks to recent advances in high precision mass spectrometry. However, methods of data analysis and interpretation for these high-resolution measurements still need to be refined. In this study, we report further insights into using K-Cl-Ar diagrams as tools for interpreting ages of secondary and primary fluids from 40Ar/39Ar stepwise crushing experiments. Three paragenetic mineral pairs of muscovite and wolframites from a southern China tungsten deposit were investigated using the 40Ar/39Ar technique through laser incremental heating and progressive crushing of single minerals. Incremental heating analyses of muscovites yielded flat age spectra defining plateau ages of 156-153 Ma. Progressive crushing experiments of wolframites yielded anomalously old apparent ages due to excess 40Ar. However, the apparent ages decline quickly after the initial steps and stabilize to form age plateaus of 156-153 Ma without excess 40Ar. The plateau age steps interpreted as ages of gases derived from primary fluid inclusions (PFIs), yield well-defined isochrons with ages ranging from 157 to 153 Ma and initial 40Ar/39Ar values that are indistinguishable from the modern atmospheric value. Digitally created 2D- and 3D-diagrams of K-Cl-Ar correlations can easily reveal distribution trends and correlation planes from the crushing steps. Interpretations of these diagrams further reveal the ages of secondary fluid inclusions (SFIs) (87 to 83 Ma) and primary fluid inclusions (PFIs) (159 to 150 Ma). Raw data from SFIs degassed during the initial crushing steps form scatters on inverse isochron plots. However, 2D and 3D K-Cl-Ar diagrams yield SFI ages that agree with 40Ar/39Ar ages of K-feldspar veins cutting the tungsten ore bodies.