Amphibolit der Strona-Ceneri-Zone

Rappresentazione e statuto

Rango

unità litostratigrafia

Uso

Unità non usata

Status

termine locale (informale)

Nomenclatura

Deutsch

Amphibolit der Strona-Ceneri-Zone

Français

amphibolite de la Zone de Strona-Ceneri

Italiano

anfibolite della Zona di Strona-Ceneri

English

amphibolite of the Strona-Ceneri Zone

Varianti storiche

Amphibolites (Boriani et al. 1990)

Paleogeografia e tettonica

Termini generici

• Strona-Ceneri

Tipo di origine

• sedimentaria

Metamorfismo

non metamorfo

Referenze

Definizione

Boriani A., Giobbi Origoni E., Borghi A., Caironi V. (1990) : The evolution of the "Serie dei Laghi" (Strona-Ceneri and Scisti dei Laghi): the upper component of the Ivrea-Verbano crustal section; Southern Alps, North Italy and Ticino, Switzerland. Tectonophysics 182, 103-118

The amphibolites are the first unit of the Strona Ceneri sequence and are generally strongly banded rocks with alternate levels of different composition and grain size. Despite their metamorphic condition, sedimentary features are stili recognizable and indicate. that most of the amphibolites were rather coarse-grained basaltic tuffites.
Massive garnet-bearing amphibolites. serpentinites and metagabbros also occur along the main horizon (e.g. northern slope of M. Bar, Tessin). This association is reminiscent of an oceanic sequenee redeposited as clastic debris with some remnants of the originai series. Small mafic and ultramafic rock lenses, apparently unrelated to the maÌn horizon, also occur within the Strona-Ceneri Zone.
In the region between Lago d'Orta and the eastern shore of Lago Maggiore, the amphibolites of the main horizon are sometimes very rich in K-feldspar porphyroclasts and metapegmatite lenses. These rocks, formerly interpreted as the result of metasomatic feldspathìzation (Boriani and Gìobbi Mancini, 1972), are now regarded as tuffites granitized by the magmatic residuum of the Ordovician granites (Giobbi Origoni et aL, 1982/1983), with which they are strictly associated.
Away from the main horizon (M. Gambarogno and M. Cerano zones), peculiar varieties of amphibolites occur as intercalations and xenoliths within the orthogneisses; these rocks preserve re!ics of high-pressure parageneses (eclogitic amphibolites). At M. Gambarogno. they contaìn garnet-poikiloblasts. showìng a planar internaI tectonic foliatìon dìscordant with the external regional foliation and defined by the alignment of quartz, greenish-blue amphibole, rutile and opaque grains. The high-pressure, low-temperature paragenesis appears to be older than the intrusion of the Ordovìcian granites. The structural position of these amphibolites is questionable. since they occur in the very complicated pattern of the "Schlingen" zone. Both at M. Cerano and at M. Gambarogno they represent the last metabasite occurrences in the Serie dei Laghi before the Ivrea-Verbano Zone is encountered.