Abstract
U-Pb spot ages have been determined on detrital zircons from two samples of volcaniclastic arenites belonging to the Tufiti di Tusa Formation (TTF) outcropping in the Lucanian Apennines (Southern Italy). Many petrographic and geochemical studies have been performed on these sandstones with the aim of defining their detritus source. A new and precise evaluation of the mineralogical composition of metamorphic lithic fragments, together with U-Pb detrital zircon ages, helps to clarify the deposition age of these syn-sedimentary volcaniclastic sandstones and constrains their source areas. Volcaniclastic arenites consist of andesitic fragments and single minerals of plagioclases, clinopyroxenes, and hornblendes, while the metamorphic lithics are mainly fragments of blue amphibole-bearing micaschists, serpentinites, ophicalcites, phyllites, and medium-grade micaschists. Phaneritic plutonic fragments consist of quartz, feldspar, and micas. Carbonate components include biomicritic and biosparitic fragments. Eighty age data collected from 56 zircons reveal a wide age spectrum, ranging from Neoarchean to Rupelian (from 2712 ± 25 to 30 ± 1 Millions of years (Ma)). The age data show that in volcaniclastic sandstones there is evidence of ancient crystalline basements involved in Cadomian and Variscan orogenesis (ages from 2712 ± 25 Ma to ≈260 Ma), whereas the measured ages of 157 Ma testify the events of Pangea fragmentation and the ages between 78 and 67 Ma are related to subduction metamorphism connected to the Alpine orogenesis. Fifty percent of the estimated detrital zircon ages show a mean concordant age of 33 ± 1 Ma, they have been measured on idiomorphic crystals with undisturbed magmatic oscillatory zoning. These data reveal the true sedimentation age of Tufiti di Tusa sandstones at least at the sampled levels, coeval with that recorded in other Rupelian volcaniclastic successions outcropping in the Northern Apennines and in the Western Alps (e.g., Val d’Aveto-Petrignacola Formation, Ranzano Formation and Taveyannaz Sandstone). These data represent preliminary suggestions of the sedimentation age of the Tufiti di Tusa Formation and Rupelian paleogeography in the Western Mediterranean area. During Priabonian-Rupelian times, the volcanic calc-alkaline detritus linked to a widespread syn-sedimentary igneous activity on the hinterland terranes of the foredeep basins in the Apennine-Maghrebian orogen extended from north to south in the Western-Central Mediterranean area.
Highlights
In the Western Mediterranean area, the Alpine belt was marked by intense deformation and high pressure-low temperature metamorphism in ophiolite sequences and their sedimentary covers, Minerals 2020, 10, 786; doi:10.3390/min10090786 www.mdpi.com/journal/mineralsMinerals 2020, 10, 786 followed by retrograde tectonic phases associated with decompression and exhumation together with continental crust sectors during the Paleocene-Eocene period [1]
Priabonian-Rupelian times, the volcanic calc-alkaline detritus linked to a widespread syn-sedimentary igneous activity on the hinterland terranes of the foredeep basins in the Apennine-Maghrebian orogen extended from north to south in the Western-Central Mediterranean area
The blue amphibole is mainly crossite and subordinately glaucophane, and it coexists with albite, quartz, phengite, epidote, garnet and titanite, indicating that high-pressure metamorphic rocks were present among the source rocks [37]
Summary
In the Western Mediterranean area, the Alpine belt was marked by intense deformation and high pressure-low temperature metamorphism in ophiolite sequences and their sedimentary covers, Minerals 2020, 10, 786; doi:10.3390/min10090786 www.mdpi.com/journal/mineralsMinerals 2020, 10, 786 followed by retrograde tectonic phases associated with decompression and exhumation together with continental crust sectors during the Paleocene-Eocene period [1]. Syn-orogenic volcaniclastic turbidite deposits began to accumulate in the internal and external areas of the Apennine-Maghrebian foredeep basin system [2,3]. The presence of syn-sedimentary volcaniclastic deposits in the Oligocene-Miocene foredeep sedimentary units of the Apennine-Maghrebian chain (Oceanic Flysch Basin) [4,5] provides important constraints for the reconstruction of the paleogeography and tectonic evolution of the Western Mediterranean area. The volcaniclastic deposits are scattered discontinuously along the Apennine-Maghrebian Chain and in the external sector of the Western Alps (Figure 1a). The upper part of the arenaceous succession contain abundant volcaniclastic detritus as single minerals or porphyritic andesite lithics, peculiar metamorphic lithics such as serpentinites, blue amphibole-bearing micaschists, garnet-bearing micaschists, epidote-bearing micaschists, orthogneisses and single heavy minerals as staurolite, glaucophane, epidote, and garnet. The chemistry of whole rocks allowed to classify the volcanic material as andesitic, consistent with the nature of the volcanic lithics and single crystals [37]
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