METHOD FOR DETERMINING THE AGE OF IGNEOUS ROCKS USING THE ACCESSORY MINERALS

METHOD FOR DETERMINING THE AGE OF IGNEOUS ROCKS USING THE ACCESSORY MINERALS
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使用副矿物测定火成岩年龄的方法

DOI：
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发表时间：
1952
期刊：
影响因子：
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通讯作者：
H. C. Harrison
H. C. Harrison
中科院分区：
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文献类型：
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作者：
E. S. Larsen;N. Keevil;H. C. Harrison

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火成岩的年龄是根据所含的副矿物来确定的。在普通火成岩中，铅大部分集中在钾矿物中，放射性大部分集中在锆石等副矿物中。钾矿物中的铅被认为主要是原生铅;锆石中的铅可能主要是放射成因铅。通过分离新鲜火成岩中的锆石，用摄谱仪测定铅量，用α计数器测定放射性，可以测定古生代和前寒武纪岩石的年龄，准确度约为90%。锆石是最令人满意的矿物。磷灰石和铼的结果很高，因此一定含有原生铅。Sphene给出了不稳定的结果。
The age of igneous rocks is determinable by a method based on the included accessory minerals. In the common igneous rocks, most of the lead is concentrated in the potassium minerals, and most of the radioactivity is in the zircon and other accessory minerals. The lead in the potassium minerals is believed to be mostly primary lead; that in zircon is probably chiefly radiogenic lead. By separating the zircon of fresh igneous rocks, determining the amount of lead with the spectrograph and the radioactivity by alpha counters, the age of Paleozoic and Precambrian rocks can be determined with an accuracy of approximately 90 per cent. Basalts and gabbros may contain too few accessory minerals for satisfactory age determination by this method. Zircon is the most satisfactory mineral for this kind of determination. Apatite and sphene give high results and therefore must contain primary lead. Sphene gives erratic results.