Study of Iron Cosmic Spherules from 1.8Ga and 1.6Ga Proterozoic Strata of the Ming Tombs District, Beijing
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摘要: 北京十三陵中元古代常州沟组底部的粗砂岩（1.8 Ga）和大红峪组硅化碳酸盐岩（1.6 Ga）中都发现了众多铁质宇宙球粒。大多数未喷膜的二次电子像宇宙球粒是圆形的，少数呈长条状，由于在大气层中熔融作用，多数球粒表面具有金相饰纹和“排气”孔洞。使用电子探针分析对30个颗粒中44个测点的检测结果（%）：FeO 80～95，Cr2 O30.78～6.56，NiO 0.06～0.41，CoO 0.02～0.46。相对比较Cr2O3 在常州沟组中较多一些，而FeO在大红峪组中稍多一些。宇宙球粒的氦同位素分析值却截然不同；3He/4He×10-8分别为：57.50±2.16（常州沟组）和1.23±0.43（大红峪组）；4He×10-8 cm3STP/g分别为：55.54（常州沟组）和809.6（大红峪组）；然而宇宙球粒的氦同位测定值都比各自的母岩高出许多;氦同位素的异常为所发现的宇宙球粒的地外来源更加确定。Abstract: Numerous iron spherules have been found from coarse sandstone in the bottom of the Changzhougou Formation (1.8Ga) and silicified carbonate rock of the Dahongyu Formation (1.6Ga) of Proterozoic strata of the Ming Tombs District, Beijing. Most of them are round shaped as rod. Surface of iron cosmic spherules are observed by secondary back scanned image without carbon coating showing matallogenic graphs and “gas escape” holes so common during intro\|atmosphere melted and crystallized again. 44 testing points of 30 iron cosmic spherules have been measured by means of electron probe analysis average data as follows(%): FeO 8095; Cr2O3 0.786.56; NiO 0.060.41. Relatively, Cr2O3 is higher in spherules of the Changzhougou Formation but FeO higher in the Dahongyu Formation. However, the helium isotope analysis data are quite different between them. The abnormal of helium isotope made sure of extraterrestrial origin of iron cosmic spherules.
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Key words:
- Proterozoic era /
- cosmic spherules /
- Beijing Ming Tombs
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