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- Title
Origin of megacrysts in volcanic rocks of the Cameroon volcanic chain — constraints on magma genesis and crustal contamination.
- Authors
Rankenburg, K.; Lassiter, J.C.; Brey, G.
- Abstract
Lavas of the Biu and Jos Plateaus, Northern Cameroon Volcanic Line (CVL), contain abundant genetically related megacrysts of clinopyroxene, garnet and subordinately plagioclase, ilmenite and amphibole. P, T-estimates of crystallization for the primitive group of cpx and gnt megacrysts are 1.7-2.3 GPa and ∼1,400 °C. Because crustal thickness in these areas is only ∼30 km (∼0.9 GPa), megacrysts must have formed within the lithospheric mantle. Primitive Biu and Jos lavas are isotopically heterogeneous in Sr-Nd isotope space (878r/86Sr=0.70285-0.70360 and εNd=7.5-4.6). Biu Plateau megacrysts overlap the range of Biu lavas in Sr-Nd isotope composition, indicating that crustal contamination of Biu lavas was minor. Jos Plateau lavas are isotopically more enriched than their associated megacrysts. Therefore an additional contamination of Jos lavas due to assimilation of continental crust (∼5%) or enriched shallow lithospheric mantle is indicated. Lavas of Biu and Jos Plateau do not reflect simple fractionation or equilibrium crystallization products, but instead reflect mixing between primary melts and their fractionated derivatives.
- Subjects
BIU Plateau (Nigeria); LAVA; VOLCANIC ash, tuff, etc.; VOLCANIC soils; PYROXENE; GARNET; SILICATE minerals
- Publication
Contributions to Mineralogy & Petrology, 2004, Vol 147, Issue 2, p129
- ISSN
0010-7999
- Publication type
Article
- DOI
10.1007/s00410-003-0534-2