The Petrology of Grospydite Xenoliths from the Zagadochnaya Kimberlite Pipe in Yakutia
The xenoliths of garnet–clinopyroxene–disthene rocks (grospydites and associated kyanite eclogites) from the Zagadochnaya kimberlite pipe in Yakutia have been studied in detail. Contrary to previous data, the presence of a continuous range in the pyrope-grossular series of garnets is shown on the ba...
| Published in: | Journal of Petrology |
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| Main Authors: | , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1968
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| Subjects: | |
| Online Access: | http://petrology.oxfordjournals.org/cgi/content/short/9/2/253 https://doi.org/10.1093/petrology/9.2.253 |
| Summary: | The xenoliths of garnet–clinopyroxene–disthene rocks (grospydites and associated kyanite eclogites) from the Zagadochnaya kimberlite pipe in Yakutia have been studied in detail. Contrary to previous data, the presence of a continuous range in the pyrope-grossular series of garnets is shown on the basis of numerous X-ray data and 17 chemical analyses of garnets. This conclusion is confirmed by the study of separate grains with kyanite intergrowths from the kimberlite heavy fraction, which are present in the kimberlite as the result of destruction of grospydite xenoliths, and possible, of garnet-kyanite rocks also. A close connection of the calcium content in the garnet with the sodium content in the coexisting clinopyroxes is also shown. An increase in the chemical potential of sodium results in the stability of the pryoxene-kyanite assemblage instead of a garnet of intermediate composition (50 percent of grossular). The interval of the miscibility gap between calcium-rich and calcium-poor garnets is increased in this way. The data of chemical analyses of 14 pyroxenes from the xenoliths indicate that they differ in the high aluminium and sodium content from other pyroxenes of eclogite-facies rocks. Chromium-rich bands with a high chromium content in coexisting garnet, pyroxene, and kyantic have been occasionally found in the xenoliths. A study has been made of the chrome-kyanite with 12.86 per Cr202. The presence of chromium-rich minerals in the grospydite xenoliths confrms their connection with ultrabasic rocks. |
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