Geology, geochemistry and geochronology of the Songwe Hill carbonatite, Malawi
Geology, geochemistry and geochronology of the Songwe Hill carbonatite, Malawi
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DOI：
10.1016/j.jafrearsci.2017.05.020
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发表时间：
2017-10-01
影响因子：
2.3
通讯作者：
Gunn, Gus
中科院分区：
文献类型：
--
作者：
Broom-Fendley, Sam;Brady, Aoife E.;Gunn, Gus
马拉维的Songwe山是研究最少的碳酸盐岩之一，但现在变得特别重要，因为它拥有相对较大的稀土矿藏。新的填图、岩石学、地球化学和年代学结果表明，直径0.8公里的松威山与其他赤瓦碱性省碳酸盐岩的不同之处在于，它侵入了较大(4×6公里)和稍老(134.6 Ma/-4.4 Ma)的毛泽霞石正长岩的一侧，然后演化为三种不同的碳酸盐成分(C1-C3)。早C1期碳酸盐岩稀少，由含锆石的中粗粒方解石碳酸盐岩组成，U-Pb年龄为132.9+/-6.7 Ma。它与奇尔瓦岛和奇尔瓦碱性省的屯杜鲁等世界其他碳酸盐岩杂岩中的岩浆碳酸盐岩相似。松吾山以细粒方解石碳酸盐岩(C2)最为丰富，其次为富稀土、富锶铁方解石碳酸盐岩(C3)。C2阶段和C3阶段都显示出广泛的(碳)-热液叠加作用的证据，该叠加作用产生了富含重稀土的磷灰石(
Songwe Hill, Malawi, is one of the least studied carbonatites but has now become particularly important as it hosts a relatively large rare earth deposit. The results of new mapping, petrography, geochemistry and geochronology indicate that the 0.8 km diameter Songwe Hill is distinct from the other Chilwa Alkaline Province carbonatites in that it intruded the side of the much larger (4 x 6 km) and slightly older (134.6 +/- 4.4 Ma) Mauze nepheline syenite and then evolved through three different carbonatite compositions (C1-C3). Early C1 carbonatite is scarce and is composed of medium coarse-grained calcite carbonatite containing zircons with a U-Pb age of 132.9 +/- 6.7 Ma. It is similar to magmatic carbonatite in other carbonatite complexes at Chilwa Island and Tundulu in the Chilwa Alkaline Province and others worldwide. The fine-grained calcite carbonatite (C2) is the most abundant stage at Songwe Hill, followed by a more REE- and Sr-rich ferroan calcite carbonatite (C3). Both stages C2 and C3 display evidence of extensive (carbo)-hydrothermal overprinting that has produced apatite enriched in HREE (