Melange del Pizzo Castello

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Darstellung und Status

Farbe CMYK
Farbe RGB
R: 245 G: 245 B: 195
lithostratigraphische Formation
Element ist in Gebrauch
informeller Begriff


Mélange du Pizzo Castello
Melange del Pizzo Castello
Pizzo Castello Melange
Herkunft des Namens

Pizzo Castello (TI)

Historische Varianten

Mulde des Pizzo Castello = Zone des Pizzo Castello (Bosshard 1925), randliche Basis des Maggia-Lappens = Alkalifeldspatgneise des Pzo. Castello (Günthert 1958), Pizzo Castello wildflysch (Matasci et al. 2011 p.267)

Hierarchie und Abfolge


Chevauché par le lobe de Sambuco (nappe de la Maggia)


Contact érosif sur le Groupe d'Antabia


Geographische Verbreitung
Lepontin: Pizzo Castello.
Point of interest


Matasci Battista, Epard Jean-Luc, Masson Henri (2011) : The Teggiolo zone: a key to the Helvetic–Penninic connection (stratigraphy and tectonics in the Val Bavona, Ticino, Central Alps). Swiss J. Geosci. 104, 257–283

p.267: 3.5.4 The Pizzo Castello wildflysch

This complex forms spectacular outcrops in the cliffs of the Pizzo Castello (Fig. 7). It consists entirely in a thick accumulation of blocks of all sizes imbedded in the calcschists. The base of the pile lies directly on the Antabia group and its top is overlain by the Sambuco thrust. Like in the other Robièi wildflysches the blocks show a conspicuous size gradient, but in this case it is stronger laterally than vertically. Coming from the W, the blocks appear suddenly at Corte di Là (1 km W P. Castello) as elongated lenses of metric to decametric size (Fig. 8). However, very rapidly in the P. Castello they become gigantic and reach a hectometric or even kilometric length (Fig. 7). The marble quarry at Ghiéiba in Val Peccia is in such a giant block of marble. The excellent outcrops make it obvious that these blocks are not connected: one can observe at many places that they are separated one from the other and completely surrounded by the calcschist matrix. For the very large blocks whose size exceeds that of the outcrop this is more difficult to prove, but the gradual transition from the smaller to the larger ones looks convincing. Three rock types can form these blocks: (1) A light grey, rather homogeneous gneiss, different from the Antigorio, the Lebendun, and the gneiss blocks of the Tamier–Zött wildflysch; (2) a coarse-grained calcareous sandstone, similar to the Sevinèra sandstone; (3) a white or yellowish to slightly brownish-reddish marble, similar to the Sevinèra marble. These three rock types are often associated in the same block. In this case the sandstone is always sandwiched between the gneiss and the marble (Fig. 9). Thus these composite blocks present an internal stratigraphic sequence identical to that of the Antigorio nappe itself below the wildflysch, but for the fact that the gneiss is different from the usual Antigorio gneiss. However, the thickness of the sandstone intermediate layer is variable: in some blocks it reaches several m, in others it is much thinner and can even completely disappear (e.g. in the largest block of Fig. 7 where the contact marble/gneiss is repeated several times by folding). In this last case microscopic examination of thin sections through the contact reveals no hint of abnormal tectonization. This supports the interpretation of a stratigraphic contact: at these places the marble transgresses directly on the gneiss. The consequences of this fact will be developed farther (cf. Sect. 5.3). In the classical literature (e.g. Günthert 1954, 1958; Burckhardt and Günthert 1957) the marble blocks are ascribed to the Triassic, the large blocks of the P. Castello being considered as tectonic slices (‘‘Verschuppung’’) at the base of the Sambuco (formerly Maggia) nappe. However, a Triassic age is impossible for the same reasons as presented above (cf. Sect 3.3.6). The metasediments in the blocks are so similar to the Sevinèra marble and sandstone that their age must be the same. Moreover, there is no connection with the Sambuco nappe. More recently, Grujic and Mancktelow (1996) represented the structures of the P. Castello cliff as an example of superimposed folding. Folds of several generations are indeed numerous and spectacular border: just on the contrary the axial surfaces of these folds are cut by the limit of the block. In other words such folds precede the formation of the block. They might be the earliest Alpine folds presently known in the Lepontine Alps. One example in a large block is pointed on Fig. 7. This point will be developed below (cf. Sects. 4.4 and 5.6).

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