Timing of Palaeozoic magmatism in the Maggia and Sambuco nappes and paleogeographic implications (Central Lepontine Alps)

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State: Public
Version: Final published version
Serval ID
serval:BIB_1592742469CF
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
Timing of Palaeozoic magmatism in the Maggia and Sambuco nappes and paleogeographic implications (Central Lepontine Alps)
Journal
Swiss Journal of Geosciences
Author(s)
Bussien D., Bussy F., Magna T., Masson H.
ISSN
1661-8726
ISSN-L
1661-8726
Publication state
Published
Issued date
2011
Peer-reviewed
Oui
Volume
104
Number
1
Pages
1-29
Language
english
Abstract
Magmatic rocks from the pre-Mesozoic basements of the Sambuco and Maggia
nappes have been dated by U-Pb zircon ages with the LA-ICPMS technique.
Several magmatic events have been identified in the Sambuco nappe. The
mafic banded calc-alkaline suite of Scheggia is dated at 540 Ma, an age
comparable to that of mafic rocks in the Austroalpine Silvretta nappe.
The Sasso Nero peraluminous augengneiss has an age of 480-470 Ma, like
many other ``older orthogneisses'' in Alpine basement units. It hosts
a large proportion of inherited zircons, which were dated around 630 Ma,
a Panafrican age indicating the Gondwanan affiliation of the Sambuco
basement. The calc-alkaline Matorello pluton yielded ages around 300 Ma,
similar to numerous Late Carboniferous intrusions in other basement
units of the Lower Penninic (Monte Leone, Antigorio, Verampio) and
Helvetic domains (Gotthard and other External Crystalline Massifs).
Associated lamprophyric dykes are slightly younger (300-290 Ma), like
similar dykes sampled in gneiss blocks included in the sedimentary cover
of the underlying Antigorio nappe (290-285 Ma). The Cocco granodiorite
and Ruscada leucogranite, both intruding the basement of the
neighbouring Maggia nappe, yielded ages of ca. 300-310 Ma, identical
within errors to the age of the Matorello pluton. They are significantly
older than former age determinations. This age coincidence, coupled with
remarkable petrologic similarities between the Cocco and Matorello
granodiorites, strongly suggests paleogeographic proximity of the
Sambuco and Maggia nappes in Late Carboniferous times. In recent
publications these two nappes have been interpreted as belonging to
distinct Mesozoic paleogeographic domains: ``European'' for Sambuco
and ``Brian double dagger onnais'' for Maggia, separated by the
``Valais'' oceanic basin. In this case, the similarity of the
Matorello and Cocco intrusions would demonstrate the absence of any
significant transcurrent movement between these two continental domains.
Alternatively, according to a more traditional view, Sambuco and Maggia
might belong to a single large Alpine tectonic unit.
Create date
01/10/2012 19:07
Last modification date
20/08/2019 12:44
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