Origin and regional significance of late Precambrian and early Palaeozoic granitoids in the Pan-African belt of Somalia
作者： J. -L. Lenoir , J. -P. Li�geois , D. K�ster , A. Utke , G. Matheis
DOI: 10.1007/BF01083233
关键词:
摘要: Granitoids within the Precambrian basement of north-eastern and southern Somalia are subdivided on basis geology, geochronology petrology into three different assemblages. The post-kinematic assem- blage in (~ 630 Ma) comprises granodiorites granites which belong to a medium-K calc-alkaline suite. Average initial Sr, Nd Pb isotopic ratios (Sri = 0.7048, end --1.8, 2°6pb/2°4pb(i) 17.704 2°Tpb/2°4pb(i)= 15.611) indicate that these melts were derived from mantle or juvenile crustal source with only slight involvement pre-existing crust as contaminant. Two assemblages found Somalia. older assemblage is composed anatectic, synkinematic, parautochthonous grani- tes 600 related amphibolite facies retrogres- sion an intensively reworked pre-Pan-African (Sr i 0.7100, ~Na --8.4, 15.403 2°7pb/2°4Pb(i) 15.259). Thesemonzo-andsyenograni- moderately potassic peraluminous. younger 470 consists post-kine- matic monzonites syenogranites A-type affinities. Initial data for this metaluminous 0.7114, --13.1, 16.913 2°TPb/2°4pb(i) 15.512) signifi- cant lower component but, however, also signature. late Proterozoic early Palaeozoic toids thus express contrasting regimes, charac- terized by strong input north, close Arabian- Nubian Shield, whereas intense rewor- king little addition material prevailed south. was definitively not cratonic area
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