Carbonatite diversity in the Central Andes: the Ayopaya alkaline province, Bolivia

The Ayopaya province in the eastern Andes of Bolivia, 100 km NW of Cochabamba, hosts a Cretaceous alkaline rock series within a Palaeozoic sedimentary sequence. The alkaline rock association comprises nepheline-syenitic/foyaitic to ijolitic intrusions, carbonatite, kimberlite, melilititic, nephelini...

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Published in:Contributions to mineralogy and petrology 2004-12, Vol.148 (4), p.391-408
Main Authors: Schultz, Frank, Lehmann, Bernd, Tawackoli, Sohrab, Rössling, Reinhard, Belyatsky, Boris, Dulski, Peter
Format: Article
Language:English
Subjects:
Carbon
Cretaceous
Fractionation
Geochemistry
Immiscibility
Mesozoic
Mineralogy
Neodymium
Paleozoic
Petrology
Rifting
Rocks
Sediments
Strontium
Volcanoes
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Summary:The Ayopaya province in the eastern Andes of Bolivia, 100 km NW of Cochabamba, hosts a Cretaceous alkaline rock series within a Palaeozoic sedimentary sequence. The alkaline rock association comprises nepheline-syenitic/foyaitic to ijolitic intrusions, carbonatite, kimberlite, melilititic, nephelinitic to basanitic dykes and diatremes, and a variety of alkaline dykes. The carbonatites display a wide petrographic and geochemical spectrum. The Cerro Sapo area hosts a small calciocarbonatite intrusion and a multitude of ferrocarbonatitic dykes and lenses in association with a nepheline-syenitic stock. The stock is crosscut by a spectacular REE-Sr-Th-rich sodalite-ankerite-baryte dyke system. The nearby Chiaracke complex represents a magnesiocarbonatite intrusion with no evidence for a relationship to igneous silicate rocks. The magnesiocarbonatite (Sgr REE up to 1.3 wt%) shows strong HREE depletion, i.e. unusually high La/Yb ratios (520-1,500). Calciocarbonatites (Sgr REE up to 0.5 wt%) have a flatter REE distribution pattern (La/Yb 95-160) and higher Nb and Zr contents. The sodalite-ankerite-baryte dyke system shows geochemical enrichment features, particularly in Na, Ba, Cl, Sr, REE, which are similar to the unusual natrocarbonatitic lavas of the recent volcano of Oldoinyo Lengai, Tanzania. The Cerro Sapo complex may be regarded as an intrusive equivalent of natrocarbonatitic volcanism, and provides an example for carbonatite genesis by late-stage crystal fractionation and liquid immiscibility. The magnesiocarbonatite intrusion of Chiaracke, on the other hand, appears to result from a primary carbonatitic mantle melt. Deep seated mantle magmatism/metasomatism is also expressed by the occurrence of a kimberlite dyke. Neodymium and strontium isotope data (epsivNd 1.4-5.4, 87Sr/86 Sr
ISSN:0010-7999
1432-0967
DOI:10.1007/s00410-004-0612-0