As discussed elsewhere in this issue, many of the largest accumula-tions of rare earth elements (REEs) are associated with rift-related nepheline syenite and alkali granite plutons. The most extreme evolved magmas produced by our planet form the agpaitic suite, named after the headland of Agpat on T...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.677.4422 http://www.elementsmagazine.org/archives/e8_5/e8_5_dep_partingshots.pdf |
| Summary: | As discussed elsewhere in this issue, many of the largest accumula-tions of rare earth elements (REEs) are associated with rift-related nepheline syenite and alkali granite plutons. The most extreme evolved magmas produced by our planet form the agpaitic suite, named after the headland of Agpat on Tunugdliarfi k, a fjord that cuts through the extraordinary Ilímaussaq intrusion in the Mesoproterozoic Gardar rift province in South Greenland (FIG. 1). Agpaite, by defi nition, has a molar (Na + K) Al greater than 1.2; in other words, it contains much more Na and K than can be accommodated in feldspars and feldspathoids, and it also contains Na–Ti–Zr silicates. The modern view is that the Gardar alkaline rocks are the products of extreme fractionation of an alkali basaltic parent magma origi-nating from asthenospheric mantle modifi ed by alkaline, rare-element-enriched metasomatic fl uids. The magmas ponded and fractionated, perhaps at multiple levels, on their ascent, and also during their fi nal |
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