An 40Ar/39Ar geochronological and electron microprobe investigation of an Archean pyroxenite and its bearing on ancient atmospheric compositions
An 40Ar/39Ar geochronological and electron microprobe investigation of an Archean pyroxenite and its bearing on ancient atmospheric compositions
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对太古代辉石岩及其对古代大气成分的影响的 40Ar/39Ar 年代学和电子显微探针研究
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发表时间：
1985
期刊：
影响因子：
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通讯作者：
C. Hall
中科院分区：
文献类型：
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作者：
J. Hanes;D. York;C. Hall
对加拿大优势省阿比提比绿岩带太古代阿比提比绿岩带中的辉石矿物进行了详细的40Ar/39Ar阶梯加热年代学研究，获得了2703 ± 11 Ma(1σ)的精确原始年龄。这与包体长英质火山岩2 70 0~2 712 Ma的锆石U-Pb年龄和基台的Sm-ND年龄2 6 2 2 ± 60 Ma非常吻合。电子探针分析，结合Ar的演化模式，证明了这一原始年龄是由氢化角闪石造成的，而体积优势的透辉石则显示出异常年轻的年龄。同位素相关图揭示了污染Ar的两个组分，在明显不同的地点具有不同的40Ar/36Ar比值。其中一个组分是在角闪石的氢形成过程中捕获的，其40Ar/36Ar的比值(258Ar± 3)明显低于现在的大气值295.5。这可能是大气层比2.7 Ga前的一个指示。另一个比较..。
A detailed 40Ar/39Ar step-heating geochronological study of pyroxene mineral separates from the Munro–Warden ultramafic sill in the Archean Abitibi Greenstone Belt of the Canadian Superior Province yields a precise primary age of 2703 ± 11 Ma (1σ). This is in excellent agreement with previous U–Pb zircon dates of 2700–2712 Ma for the enclosing felsic volcanics and a Sm–Nd age of 2622 ± 60 Ma for the sill. Electron microprobe analyses, coupled with the argon evolution patterns, demonstrate that deuteric amphibole is responsible for this primary age, whereas the volumetrically dominant diopside shows anomalously young ages. An isotope correlation plot reveals two components of contaminating argon with differing 40Ar/36Ar ratios in distinctly different sites. One component, trapped during the deuteric formation of amphibole, has an 40Ar/36Ar ratio that is significantly less (258 ± 3) than the present-day atmospheric value of 295.5. This may be an indication of the atmospheric ratio 2.7 Ga ago. The other comp...