TY - JOUR
T1 - Petrology and isotope geochemistry of the Pan-African Negash pluton, northern Ethiopia
T2 - Mafic-felsic magma interactions during the construction of shallow-level calc-alkaline plutons
AU - Asrat, A.
AU - Barbey, P.
AU - Ludden, J. N.
AU - Reisberg, L.
AU - Gleizes, G.
AU - Ayalew, D.
N1 - Funding Information:
We are grateful to C. Spatz, S. Barda and A. Kohler for technical assistance. Our sincere gratitude goes to Mr and Mrs Vilain, T. Nardos, T. Yemane, D. Hailu and Yonas for their invaluable assistance during the field work. We are indebted to C. G. Barnes, W. J. Collins, V. Janousek and N. Petford for their thorough and constructive reviews, and to P. D. Kempton for her careful editorial handling. They helped us very much to improve this paper. This work was supported by a Ph.D. research grant to A.A. from the French Ministry of Foreign Affairs and by funding from INSU---CNRS Ethiopie 2000 Project. We would like to acknowledge the Department of Geology and Geophysics, Addis Ababa University, for logistical support during the field work. This paper is CRPG Contribution 1659.
PY - 2004/6
Y1 - 2004/6
N2 - The Negash pluton consists of monzogranites, granodiorites, hybrid quartz monzodiorites, quartz monzodiorites and pyroxene monzodiorites, emplaced at 608 ± 7 Ma (zircon U-Pb) in low-grade volcaniclastic sediments. Field relationships between mafic and felsic rocks result from mingling and hybridization at the lower interface of a mafic sheet injected into partially crystallized, phenocryst-laden, granodiorite magma (back-veining), and hybridization during simultaneous ascent of mafic and felsic magmas in the feeder zone located to the NW of the pluton. The rock suite displays low 87Sr/86Sr(608) (0·70260-0·70350) and positive εNd(608) values (+3·9 to + 5·9), along with fractionated rare earth element patterns [(La/Yb)N = 9·9-17·7], enrichment in large ion lithophile elements (Ba, U, K, Pb and Sr) and depletion in Nb and Th compared with the primitive mantle. Monzogranites, granodiorites and hybrid quartz monzodiorites define a calc-alkaline differentiation trend, whereas the quartz monzodiorites have higher Fe/Mg ratios. The pyroxene monzodiorites show anomalously high Ti/Zr, Ti/Y and Ti/V ratios, suggesting that they are cumulates. Chemical modelling suggests that pyroxene and quartz monzodiorites could derive from a common gabbrodioritic parent by fractional crystallization. Structural and chemical data suggest that (1) the pluton results from the assembly of several, low-viscosity, melt-rich batches (sheeting/dyking), differentiated in intermediate chambers prior to their emplacement; (2) in situ differentiation is limited to the coarse-grained pyroxene monzodiorites; (3) mafic-felsic magma interactions at the emplacement level were essentially limited to mingling.
AB - The Negash pluton consists of monzogranites, granodiorites, hybrid quartz monzodiorites, quartz monzodiorites and pyroxene monzodiorites, emplaced at 608 ± 7 Ma (zircon U-Pb) in low-grade volcaniclastic sediments. Field relationships between mafic and felsic rocks result from mingling and hybridization at the lower interface of a mafic sheet injected into partially crystallized, phenocryst-laden, granodiorite magma (back-veining), and hybridization during simultaneous ascent of mafic and felsic magmas in the feeder zone located to the NW of the pluton. The rock suite displays low 87Sr/86Sr(608) (0·70260-0·70350) and positive εNd(608) values (+3·9 to + 5·9), along with fractionated rare earth element patterns [(La/Yb)N = 9·9-17·7], enrichment in large ion lithophile elements (Ba, U, K, Pb and Sr) and depletion in Nb and Th compared with the primitive mantle. Monzogranites, granodiorites and hybrid quartz monzodiorites define a calc-alkaline differentiation trend, whereas the quartz monzodiorites have higher Fe/Mg ratios. The pyroxene monzodiorites show anomalously high Ti/Zr, Ti/Y and Ti/V ratios, suggesting that they are cumulates. Chemical modelling suggests that pyroxene and quartz monzodiorites could derive from a common gabbrodioritic parent by fractional crystallization. Structural and chemical data suggest that (1) the pluton results from the assembly of several, low-viscosity, melt-rich batches (sheeting/dyking), differentiated in intermediate chambers prior to their emplacement; (2) in situ differentiation is limited to the coarse-grained pyroxene monzodiorites; (3) mafic-felsic magma interactions at the emplacement level were essentially limited to mingling.
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U2 - 10.1093/petrology/egh009
DO - 10.1093/petrology/egh009
M3 - Article
AN - SCOPUS:3242766862
SN - 0022-3530
VL - 45
SP - 1147
EP - 1179
JO - Journal of Petrology
JF - Journal of Petrology
IS - 6
ER -