No CrossRef data available.
Article contents
III.—The Contact-Zone of the Alps and the Apennines in Western Liguria
Published online by Cambridge University Press: 01 May 2009
Extract
In a paper on the Permian formation in the Maritime Alps, etc. (Geol.Mag., 1916, pp. 7–17), I mentioned incidentally that it extends from those Alps, viz. from the Montgioie range east into Liguria as far as the Savona Hills. As in the former so also in the latter region, that formation is composed of essentially gneissic schists known as apenninites or besimaudites belonging to the Lower Permian or Permo-Carboniferous, and of sericitic schists, quartzites, and clastic rocks or ‘anagenites’ which constitute the Upper Permian or Verrucano proper, forming a transition to the Lower Trias. The geological limit of the Permian in the Savona Hills coincides more or less with the geographical line of division of the Alps and Apennines at the Colle or saddle—also called Bocchetta—d'Altare; but another geological line of division exists still further east, at the junction of the Triassic and Eocene formations in the Chiaravagna Valley near Sestri Ponente, immediately west of Genoa. In reality the geological division is marked, not by either of those lines but by a contact-zone between them. This contact-zone occupies the whole of Western Liguria and comprises two distinct and dissimilar parts: one, the Triassic calc-schists and pietre verdi area or Voltri group, which extends for about 25 kilometres along the Riviera littoral west of Genoa from Sestri Ponente to Voltri, Varazze, and Celle Ligure, and the other or Savona group, which skirts the littoral for about 15 kilometres from Celle to Savona and Zinola, and is composed for the greater part of a crystalline massif of granitic, gneissic, and amphibolic rocks.
- Type
- Original Articles
- Information
- Copyright
- Copyright © Cambridge University Press 1916
References
page 400 note 2 This division has its exact equivalents in the Apuan Alps or Carrara Mountains as the lowest formation underlying the marmiferous Trias, and in the Verrucano—a name derived from Monte Verruca—of the Pisan Hills.
page 404 note 1 This outcrop was pointed out by G. Rovereto in a memoir to be quoted later. The small dolomitic cap is obviously in connexion with the larger deposits further north-east.
page 405 note 1 The Permo-Carboniferous gneiss is largely developed in the Quiliano and Roviasca Valleys, in the Bormida Valley west of Altare, and further north-west down to Ferrania di Mare in the same valley; also along the Lavanestra Valley in the Savona and Santuario island.
page 406 note 1 Rovereto assigns these varicoloured schisti rasati to the Middle Trias, but they are, as Termier and Boussac also point out, really Upper Permian.
page 406 note 2 Zaccagna, D., “Costituzioni Alpi Marittime”: Boll. R. Com. geol., 1884, p. 167Google Scholar et seq.; “Geologia Alpi Occid.”: ibid., 1887, p. 346 et seq.
page 406 note 3 A. Issel, L. Mazzuoli, & D. Zaccagna, Carta geol. Riviere Ligure, 1887 and 1890.
page 406 note 4 Stefani, C. De, “L'Apennino fra Colle d'Altare e la Polcevera”: Boll. R. Com. geol., 1887, fasc. 3Google Scholar; “Zona Serpentinosa della Liguria Occid.”: Atti R. Accad. Lincei, Roma, 1913, pp. 547, 661.Google Scholar
page 406 note 5 Franchi, S., “Nota preliminare formazione gneissica e sulle roccie granitiche del Massiccio Ligure”: Boll. R. Com. geol., 1893, p. 43 et seq. In this memoir Franchi also describes the principal rocks microscopically and gives a list of the literature 1841 to 1893.Google Scholar
page 407 note 1 Rovereto, G., “Zona dei Ricoprimenti del Savonese”: Boll. Soc. geol. It., 1909, p. 389 et seq. This memoir was preceded by two preliminary notes on the same subject in 1895.Google Scholar
page 407 note 2 This fan-structure, shown in general section Fig. 2, rests on the assumption that the adjoining Permo-Carboniferous island on the right is an anticline, not a syncline.
page 407 note 3 Besides this solution Rovereto adumbrates three others, which, however, he considers less tangible: the first assumes the whole massif to be a rooted, the second a transported area, and the third assumes not only the Savona area but the whole of the Apennines to be a series of transported cover-sheets.
page 407 note 4 Franchi (op. cit., p. 64) refers to the granite as being on the eastern border intrusive also in the calc-schists and pietre verdi; these being Mesozoic, the granite would be much younger than Upper Palæozoic.
page 408 note 1 Termier, P. & Boussac, I., “Le Massif Crystallin Ligure”: Bull. Soc. géol. France, 1912, p. 272 et seq., with map and 2 sections, preceded by two preliminary notes of 1911.Google Scholar
page 408 note 2 Rovereto's distribution of granite, gneiss, and amphibolites may be estimated from his map as 3/10, 6/10, and 1/10 respectively, his granite area being less than half that of Termier & Boussac.
page 408 note 3 Termier, P., “Tectonique de l'Ile d'Elbe”: Bull. Soc. géol. France, 1910, p. 314 et seqGoogle Scholar. The conclusions of this memoir were contested by Lotti, B., “L'ipotesi del Termier sulla tettonica Isola d'Elba,” Boll. R. Com. geol., 1910, p. 284 et seq.Google Scholar; and by V. Novarese, “Il presunto piano mylonitico dell'Isola d'Elba,” ibid., 1910, p. 292 et seq.
page 409 note 1 The theory of the Dinarides being the rooted origin of the three granitic areas is founded on G. Steinmann's often-quoted memoir, “Alpen und Apennin,” Monatsber. Deutsche Geol. Ges., 1907, p. 177 et seq.; his “dinaric cover-sheets”, however, are assumed to have been transported, not direct from east to west, but circuitously along the curve-line of the Alps.
page 410 note 1 L. Mazzuoli, in an interesting memoir on the “Formazione dei Conglomerati Miocenici nell'Apennino Ligure”, Boll. R. Com. geol., 1888, p. 9 et seq., mentions the noteworthy fact that soundings carried out by the Italian Marine Department along the Riviera littoral of Genoa and Savona have proved the existence of submarine river valleys at depths up to 900 metres at 4 nautical miles from the shore. The ratio of fall below sea-level is thus about the same as that from the Apennine crest-line to the coast.
page 410 note 2 The gneissic rocks of Valdana, in the south-eastern part of Elba, are by common consent of granitic origin, though older than the microgranites in the west of Elba (B. Lotti, op. cit., p. 285).
page 410 note 3 By this interpretation Termier and Boussac's exotic granite mass, section Fig. 3, whose submarine part is of course purely hypothetical, becomes simply an ordinary intrusive tongue formed in situ.
page 411 note 1 The Permo-Carboniferous ‘window’ would in that case be a syncline, and the adjacent crystalline mass west would be, not fan-shaped, but isoclinal.
page 411 note 2 Termier and Boussac themselves assume the younger formations to have moved as cover-sheets from west to east, viz. in the opposite direction of the crystalline massif.
page 411 note 3 Novarese, V., “Il Profilo della Grivola, Alpi Graje”: Bull. R. Com. geol., 1909, p. 497 et seq.Google Scholar