TY - JOUR
T1 - The chemistry of barium anomalies in the Berisal Complex, Simplon Region, Switzerland
AU - Hetherington, Callum J.
AU - Lundmark, Mattias
AU - Graeser, Stefan
AU - Gieré, Reto
N1 - Funding Information:
Acknowledgments Research was supported by grants 20-46906.96 and 20-46906.00 from the Swiss National Research Foundation. CJH acknowledges funding from the Freiwillige Akademische Gesellschaft in Basel and the Universities Natural History Museums, University of Oslo, in Norway. Franc¸ois Bussy and an anonymous reviewer are thanked for their reviews of the manuscript. Jürgen von Raumer and Sheila Seaman are acknowledged for constructive comments on early versions of this paper. Jeremy Inglis is thanked for several enlightening discussions about U-Pb zircon chronology.
PY - 2008/2
Y1 - 2008/2
N2 - The petrographic and geochemical features of two zoisite-celsian gneiss outcrops from the Berisal Complex, characterised by a syn-kinematic mineral assemblage that contains celsian and barium white micas and a maximum whole-rock BaO content of 8.36 wt%, are described. The outcrops are enclosed in a larger body of garnet-bearing two-mica augen-gneiss, which has intrusive contacts with the surrounding garnet-biotite-muscovite paragneiss, and also contains small outcrops of two-mica clinozoisite gneiss. The zoisite-celsian gneisses are strongly enriched in all alkaline-earth elements, are depleted in the alkali elements, and have high Zr/Hf and Nb/Ta ratios compared with the surrounding gneisses. The zoisite-celsian, two-mica clinozoisite, and garnet-bearing two-mica augen-gneisses have Al/CNK molar ratios >1, and the zoisite-celsian gneisses are also enriched in Zr, Y, and Nb. Chondrite-normalised patterns for the rare earth elements (REE) show light REE enrichment, with a negative Eu anomaly. On the basis of field and geochemical data it is argued that the barium anomalies in the Berisal complex are the result of igneous fractionation of barium into anorthosite-dominated cognate inclusions within a larger volume of calc-alkaline peraluminous melt. On the basis of U-Pb zircon ages, a conservative estimate for the age of magma crystallisation is placed at 460 ± 10 Ma, and thus was related to significant late Ordovician granitoid magmatism in Gondwana-derived microcontinents during collision between Avalonia-Cadomia and Gondwana.
AB - The petrographic and geochemical features of two zoisite-celsian gneiss outcrops from the Berisal Complex, characterised by a syn-kinematic mineral assemblage that contains celsian and barium white micas and a maximum whole-rock BaO content of 8.36 wt%, are described. The outcrops are enclosed in a larger body of garnet-bearing two-mica augen-gneiss, which has intrusive contacts with the surrounding garnet-biotite-muscovite paragneiss, and also contains small outcrops of two-mica clinozoisite gneiss. The zoisite-celsian gneisses are strongly enriched in all alkaline-earth elements, are depleted in the alkali elements, and have high Zr/Hf and Nb/Ta ratios compared with the surrounding gneisses. The zoisite-celsian, two-mica clinozoisite, and garnet-bearing two-mica augen-gneisses have Al/CNK molar ratios >1, and the zoisite-celsian gneisses are also enriched in Zr, Y, and Nb. Chondrite-normalised patterns for the rare earth elements (REE) show light REE enrichment, with a negative Eu anomaly. On the basis of field and geochemical data it is argued that the barium anomalies in the Berisal complex are the result of igneous fractionation of barium into anorthosite-dominated cognate inclusions within a larger volume of calc-alkaline peraluminous melt. On the basis of U-Pb zircon ages, a conservative estimate for the age of magma crystallisation is placed at 460 ± 10 Ma, and thus was related to significant late Ordovician granitoid magmatism in Gondwana-derived microcontinents during collision between Avalonia-Cadomia and Gondwana.
KW - Anorthosite
KW - Barium
KW - Berisal Complex
KW - European Alps
KW - Hun Superterrane
KW - Ordovician magmatism
KW - Peraluminous magma
UR - http://www.scopus.com/inward/record.url?scp=38049029146&partnerID=8YFLogxK
U2 - 10.1007/s00531-006-0154-y
DO - 10.1007/s00531-006-0154-y
M3 - Article
AN - SCOPUS:38049029146
SN - 1437-3254
VL - 97
SP - 51
EP - 69
JO - International Journal of Earth Sciences
JF - International Journal of Earth Sciences
IS - 1
ER -