Latest Precambrian to Early Cambrian U–Pb zircon ages of augen gneisses from Calabria (Italy), with inference to the Alboran microplate in the evolution of the peri-Gondwana terranes

Abstract

In situ U-Pb dating of zircons from five samples of Calabrian augen gneisses shows that their protoliths are Latest Precambrian to Early Cambrian in age (562 ± 15, 547 ± 7, 540 ± 4, 539 ± 16 and 526 ± 10 Ma), and contain Archaean (3.1 Ga), Palaeoproterozoic (1.7-2.4 Ga) and Neoproterozoic (0.6-0.9 Ga) inheritance. Geochemical signature of augen gneisses is typical of high-K calc-alkaline post-collisional magmatism. Their Sr-Nd isotopic compositions [0.7093 < ( 87 Sr/ 86 Sr) i < 0.7139; -3.2 < e Nd(t) < -5.4; 1.5 < T DM < 1.7 Ga] indicate the involvement of a crustal component in significant proportions. The Calabrian augen gneisses have, therefore, to be distinguished from the orthogneisses of Sardinia and northern Algeria, and from the porphyroids of Sicily, which are Middle Ordovician. By contrast, the Calabrian augen gneisses show a close similarity to the Pan-African post-collisional granitoids of the northern edge of the West African craton (e.g. the Moroccan Anti-Atlas). This suggests a periGondwana origin and corroborates previous palaeogeodynamic reconstructions attributing the Alboran microplate to the northern margin of the West African craton.

Precambrian protoliths and Early Paleozoic magmatism in the French Massif Central: U–Pb data and the North Gondwana connection in the west European Variscan belt

“…7). Similar ages are widely known in western Europe for example in Montagne Noire and Limousin ( [Gebauer et al, 1989] and [Alexandre, 2007]), and other massifs of the North Gondwana margin, such as in Neoproterozoic and Lower Paleozoic metasedimentary and volcanosedimentary rocks of NW Spain ( [Fernández-Suárez et al, 2000], [Montero et al, 2007] and [Castiñeiras et al, 2008]), in Calabrian orthogneiss (Micheletti et al, 2007), in orthogneiss from the Ruitor massif in internal Western Alps (Guillot et al, 2002) or in metasediments and orthogneiss of the Cyclades in Greece (Keay and Lister, 2002). Moreover, Armorican metasediments of the Mid-German Crystalline Rise in Central Germany (Gerdes and Zeh, 2006) also show such zircon populations.…”

U–Pb zircon data of Variscan meta-igneous and igneous acidic rocks from an Alpine shear zone in Calabria (southern Italy)

“…The Variscan (Borsi and Dubois 1968) plutonites are clearly intrusive in the rocks of the Castagna Unit, whereas the relationships between the various types of augen gneisses are not clear. Some authors (Borsi and Dubois 1968;Faure 1980) interpreted the augen gneisses as derived from the Alpine reworking of Variscan intrusives, whereas, on the basis of U-Pb spot analyses on zircon, Micheletti et al (2007) documented an Early Cambrian age of the protoliths of the biotite-rich types, which have been related to sin-post-collisional hybrid magmatism ). At kilometer scale, the rocks of this unit show variable degrees of Alpine low grade reworking overprinting the Variscan upper greenschist-amphibolite facies effects.…”

“…The continental metamorphic and igneous rocks have been interpreted as derived from (a) the African margin (Amodio Morelli et al 1976;Grandjacquet and Mascle 1978); (b) the European continental margin (Bouillin et al 1986;Dietrich 1988); (c) the microplate located between the European and African margins (Guerrera et al 1993;Bonardi et al 1994). The pre-Triassic crustal units include meta-igneous rocks derived from Pre-Cambrian-Early Cambrian acidic and basic protoliths (Schenk and Todt 1989;Senesi 1999;Micheletti et al 2007Micheletti et al , 2008.…”

“…The data relative to granitic-granodioritic biotite augen gneisses which were not pervasively affected by Alpine tectonism come from Micheletti et al (2007); mylonitic leucogranite (GO 39) and trondhjemite (GO 95), as well as a mylonitic pegmatite (GO 82), were selected within the Alpine shear zone between the Castagna and Sila Units ( Fig. 1) for U-Pb analyses on zircon using LA-ICP-MS technique.…”

“…The present study regards the shear zone of the Sila, which includes cataclastic to mylonitic leucogranites and trondhjemites derived from former augen gneisses as well as Variscan pegmatites. Previous geochronological data assigned different ages to the protoliths of the augen gneisses: Variscan (Rb-Sr mica age; Borsi and Dubois 1968) and Early Cambrian (U-Pb on zircon; Micheletti et al 2007). LA-ICP-MS analyses on zircon from the mylonitic leucogranite and trondhjemite related to former muscovite-rich and albite-rich augen gneisses as well as from a mylonitic pegmatite have been performed to gain information about the chronological memory they preserve and their relative geological significance.…”