Polymetamorphic sapphirine rocks of the Irumide age in lower Luangwa Valley, Zambia

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doi: 10.1127/0077-7757/2008/0101
Authors:Vrána, Stanislav; Sulovsky, Petr
Volume Title:Neues Jahrbuch für Mineralogie. Abhandlungen
Source:Neues Jahrbuch für Mineralogie. Abhandlungen, 184(3), p.315-328. Publisher: E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany. ISSN: 0077-7757
Publication Date:2008
Note:In English. 44 refs.
Summary:Mg-Al-rich rocks of the Southern Irumide Belt in Zambia contain several assemblages of sapphirine-enstatite with minor spinel and later retrogressive anthophyllite-chlorite. The whole-rock compositions have Mg numbers of 0.88 and 0.89, indicating a sedimentary or volcanosedimentary protolith. The monazite-dominated pattern of normalized REE abundances is steep with high LaN/YbN values of 96.1 and 67.4 and a negative Eu anomaly. This occurrence is an example of sapphirine formed near the low-temperature limit of its stability field. Sapphirine-enstatite geothermometry indicates equilibration T of 680-780°C. This estimate is in agreement with the relatively low Al2O3 contents in enstatite (∼ 4.4 wt %). Chemical dating of monazite gave an Irumide age of metamorphic crystallization of 1044 ± 16 Ma. A minor fraction of monazite shows a superimposed partial recrystallization at ∼ 520 Ma, during the Pan-African event, and may correlate with partial retrogression of enstatite and sapphirine to anthophyllite and chlorite. EPMA results are reported for sapphirine, orthopyroxene, spinel, ilmenite, apatite, anthophyllite and chlorite. [R.A.H.]
Sections:Age determination
Subsections:Metamorphism: regional, dynamic
Subjects:Absolute age; Aenigmatite group; Amphibole group; Anthophyllite; Apatite; Chain silicates; Chlorite; Chlorite group; Electron probe; Geochemistry; Geologic thermometry; Ilmenite; Lanthanum; Major elements; Mesoproterozoic; Metals; Metamorphic belts; Metamorphism; Mineral localities; Monazite; Niobium; Orthoamphibole; Orthopyroxene; Oxides; Paragenesis; Phosphates; Polymetamorphism; Precambrian; Proterozoic; Pyroxene group; Rare earths; Sapphirine; Sheet silicates; Silicates; Spinel; Upper Precambrian; Africa; East Africa; Southern Africa; Zambia; Irumide Belt; Luangwa Valley; Muva Supergroup; Rufunsa Formation
Abstract Numbers:08M/1536
Record ID:2011023047
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom, Reference includes data from Geoline, Bundesanstalt fur Geowissenschaften und Rohstoffe
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