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Precambrian tholeiitic-dacitic rock-suites and Cambrian ultramafic rocks in the Pennine nappe system of the Alps: Evidence from Sm-Nd isotopes and rare earth elements

Contributions to Mineralogy and Petrology

By:
and
DOI: 10.1007/BF00379452

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Abstract

Major element, trace element and Sm-Nd isotope analyses were made of polymetamorphic hornblendefelses, plagioclase amphibolites and banded amphibolites from the Berisal complex in the Simplon area (Italy, Switzerland) to determine their age, origin and genetic relationships. In light of major and rare earth element data, the hornblendefelses are inferred to have originally been pyroxene-rich cumulates, the plagioclase amphibolites and the dark layers of the banded amphibolites to have been tholeiitic basalts and the light layers dacites. The Sm-Nd isotope data yield isochron ages of 475??81 Ma for the hornblendefelses, 1,018??59 Ma for the plagioclase amphibolites and 1,071??43 Ma for the banded amphibolites. The 1 Ga magmatic event is the oldest one ever found in the crystalline basement of the Pennine nappes. The Sm -Nd isotope data support the consanguinity of the tholeiitic dark layers and the dacitic light layers of the banded amphibolites with the tholeiitic plagioclase amphibolites and the ultramafic hornblendefelses. The initial e{open}Nd values indicate that all three rock types originated from sources depleted in light rare earth elements. We suggest that plagioclase and banded amphibolites were a Proterozoic tholeiite-dacite sequence that was strongly deformed and flattened during subsequent folding. The hornblendefelses are thought to be Cambrian intrusions of pyroxene-rich material. ?? 1985 Springer-Verlag.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Precambrian tholeiitic-dacitic rock-suites and Cambrian ultramafic rocks in the Pennine nappe system of the Alps: Evidence from Sm-Nd isotopes and rare earth elements
Series title:
Contributions to Mineralogy and Petrology
DOI:
10.1007/BF00379452
Volume
89
Issue:
2-3
Year Published:
1985
Language:
English
Publisher location:
Springer-Verlag
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Contributions to Mineralogy and Petrology
First page:
184
Last page:
192
Number of Pages:
9