CORRELATIONS BETWEEN U, TH CONTENT AND METAMORPHIC GRADE IN THE WESTERN NAMAQUALAND BELT, SOUTH AFRICA, WITH IMPLICATIONS FOR RADIOACTIVE HEATING OF THE CRUST
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dc.contributor.author | Andreoli M.A.G. | |
dc.contributor.author | Hart R.J. | |
dc.contributor.author | Ashwal L.D. | |
dc.contributor.author | Coetzee H. | |
dc.date.accessioned | 2024-08-03T06:10:48Z | |
dc.date.available | 2024-08-03T06:10:48Z | |
dc.date.issued | 2006 | |
dc.identifier | https://elibrary.ru/item.asp?id=10499474 | |
dc.identifier.citation | Journal of Petrology, 2006, 47, 6, 1095 | |
dc.identifier.issn | 0022-3530 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/44588 | |
dc.description.abstract | The digital image of airborne radiometric data across South Africa reveals that the largest anomaly, ?100?nGy/h, is caused by the granulite-facies rocks of the Namaquan metamorphic complex, whereas most of the country is <60?nGy/h. This observation is consistent with geochemical data that show that the ?1900 ± 100?Ma greenschist-facies Richtersveld Terrane near Namibia (max. U = 3·4?ppm; Th = 20·1?ppm) and the adjacent, 1100 ± 100?Ma, amphibolite-facies Aggeneys/Steinkopf Terranes (max. U ≈ 10?ppm; Th ≈ 52?ppm) are the least enriched in U, Th and K. In contrast, the lower-T granulite-facies Okiep Terrane near Springbok hosts more enriched granites (max. U ≈ 17?ppm; Th ≈ 66?ppm) and noritic intrusions (max. U = 14?ppm; Th = 83?ppm). The most enriched rocks are found in the 1030?Ma higher-T granulite-facies core of the Namaquan belt and include quartzo-feldspathic gneisses (max. U = 46?ppm; Th = 90?ppm) and charnockites (max. U = 52?ppm; Th = 400?ppm). Our findings contradict the notion that granulite-facies terrains are characteristically depleted in U and Th. In this study we modeled the heat production in the core of the Namaquan complex, where the granulites have had a very unusual metamorphic history, and show that ultra-high-T (?1000°C, P ? 10?kbar) metamorphic conditions could have been achieved by radiogenic heating without invoking external heat sources. However, monazite-rich veins of charnockite and patches of granulites mark the passage of CO2-dominated melts and fluids derived from fractionated noritic intrusions. | |
dc.subject | charnockite | |
dc.subject | granulite | |
dc.subject | Namaqualand | |
dc.subject | thorium | |
dc.subject | uranium | |
dc.subject | radioactive heating | |
dc.subject | metamorphism | |
dc.title | CORRELATIONS BETWEEN U, TH CONTENT AND METAMORPHIC GRADE IN THE WESTERN NAMAQUALAND BELT, SOUTH AFRICA, WITH IMPLICATIONS FOR RADIOACTIVE HEATING OF THE CRUST | |
dc.type | Статья |
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