Palaeomagnetic field intensity measurements from the 2.6 Ga Yandinilling dyke swarm (Western Australia)
Palaeomagnetic field intensity measurements from the 2.6 Ga Yandinilling dyke swarm (Western Australia)
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2.6 Ga Yandinilling 堤坝群（西澳大利亚）的古磁场强度测量
DOI：
10.1093/gji/ggad423
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发表时间：
2024
影响因子：
2.8
通讯作者：
Hawkins L
中科院分区：
文献类型：
--
作者：
Hawkins L
前寒武纪古强度测量为地球深部的演化提供了基本的制约因素。岩心演化模型预测了数十亿年时间尺度上偶极矩的趋势，这可以通过古地磁记录进行测试。在这里，我们报告了最近发现的西澳大利亚伊尔冈克拉通的∼2.62 Ga Yandinill岩墙群的新的古强度结果，并与已发表的跨越太古代晚期至早元古代500 -Myr的测量结果进行了比较。岩石磁学和扫描电子显微镜分析证实，磁性矿物学为细粒磁铁矿，主要以出溶片层形式存在于钛铁矿中。有六个地点通过热和微波Izzi方案实验以及双重加热技术Shaw实验得出了可接受的古强度估计。这些9-26微米T的位置平均值转化为11-44 ZAM2的虚拟偶极矩，大大低于今天∼80 ZAM2的偶极矩以及一些热演化模型对该时间段的预测值。然而，它们的平均值(中位数=2.41ZAM2)与2300-2800 Ma(中位数=2.44ZAM2；N=0.103)和10-500 Ma(中位数41ZAM2；N=0.997)期间的长期平均值相似。虽然几乎没有证据表明晚太古宙和显生宙之间的平均偶极矩有实质性的净变化，但有初步证据表明，在这两个时期之间，平均偶极矩的方差有所增加。20多亿年前的这种较低的变化支持了这样的观点，即即使地球发电机没有产生更强的磁场，但在太古代-元古代的过渡时期，地球发电机的平均稳定性比现在更高。
Precambrian palaeointensity measurements provide fundamental constraints on the evolution of the deep Earth. Core evolution models predict trends in dipole moment on billion-year timescales that can be tested by palaeomagnetic records. Here, we report new palaeointensity results from the recently identified ∼2.62 Ga Yandinilling dyke swarm of the Yilgarn Craton, Western Australia, and consider them alongside published measurements spanning 500 Myr across the late Archaean to earliest Proterozoic. Rock magnetic and scanning electron microscopy analysis confirm that the magnetic mineralogy is fine-grained magnetite, appearing mostly as exsolved lamellae with ilmenite. Six sites produced acceptable palaeointensity estimates from thermal and microwave IZZI protocol Thellier experiments and from double-heating technique Shaw experiments. These site mean values of 9–26 µT translate to virtual dipole moments of 11–44 ZAm2that are considerably lower than today's dipole moment of ∼80 ZAm2and the value predicted for this time period by some thermal evolution models. Their average (median = 41 ZAm2) is, however, similar to the long-term average during both of the intervals 2300–2800 Ma (median = 44 ZAm2;N= 103) and 10–500 Ma (median 41 ZAm2;N= 997). While there is little evidence for a substantial net change in average dipole moment between the late Archaean and Phanerozoic, there is preliminary evidence that its variance has increased between the two intervals. This lower variance more than two billion years ago supports the idea that the geodynamo, even while not producing a stronger magnetic field, was more stable on average at the Archaean–Proterozoic transition than it is today.