Poly-Orogenic Melting of Metasedimentary Crust From a Granite Geochemistry and Inherited Zircon Perspective (Southern Calabria-Peloritani Orogen, Italy)

Patrizia Fiannacca,Rosolino Cirrincione,Ian S Williams,Antonino Pezzino

doi:10.3389/feart.2019.00119

Patrizia Fiannacca, Rosolino Cirrincione + Show 2 more

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https://doi.org/10.3389/feart.2019.00119

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Abstract

Inherited zircon ages and geochemical features of late Cadomian and late Variscan granitoids from the north-eastern Peloritani Mountains (NE Sicily) and the western Aspromonte Massif (SW Calabria) shed new light on the sources and processes involved in poly-orogenic granitoid magmatism. The two groups of strongly peraluminous granitoids have similarities in trace element abundance patterns and Sr and Nd isotopic compositions consistent with both being derived from crustal sources, possibly with a minor contribution from mantle-related components. Comparison of the granite compositions with those of experimental melts derived from various metaigneous and metasedimentary sources indicates that both groups of granitoids originated exclusively from different degrees of melting of similar greywacke-dominated turbidite. Abundant inherited zircon cores from representative samples of metamorphosed late Cadomian (545 ± 5 Ma) granite and late Variscan (300 ± 4 Ma) leucogranodiorite have the same range of U-Pb ages, from Early Paleoproterozoic to latest Neoproterozoic, with main age clusters at ~ 0.55 and ~ 0.63 Ga, and minor age clusters at ~ 0.95 and ~ 2.5 Ga. The pattern of detrital zircon ages from a paragneiss, host rock to the late Cadomian granite, is the same, indicating, in conjunction with the geochemistry, that both granites originated by partial melting of deeper crustal equivalents of those paragneisses. The same crustal sequence melted during successive orogenies under different thermal regimes and in different post-collisional tectonic settings, giving rise to granitoid associations with different ages and geochemical features largely reflecting the melting conditions. On the other hand, the zircon inheritance patterns and specific chemical features of S-type granitoids reflect the nature of their crustal magma sources, independently from the effects of the thermal regime or tectonic setting at the time of magmatism.

Highlights

Following several decades during which zircon geochronology has been used to reconstruct the history of our planet and the timescales of geological processes since the formation of the first solid crust (e.g., Froude et al, 1983; Bowring and Williams, 1999; Wilde et al, 2001), increasing attention is being paid to combining zircon age information with the mineral’s chemistry and microstructures (e.g., Vance et al, 2003; Engi et al, 2017), opening the way to the use of zircon as a powerful petrogenetic tool in the study of magmatic, metamorphic, and sedimentary systems
The medium to high-grade basement exposed in the Peloritani Mountains and the adjacent Aspromonte Massif is characterized by the widespread occurrence of S-type granitoids emplaced during the postcollisional stages of both the Cadomian and Variscan orogenies
Comparison and discussion of existing and new results from both late Cadomian and late Variscan granitoids shows that poly-orogenic melting gave rise to granitoid associations with diagnostic zircon inheritance patterns and geochemical features, reflecting the nature of their crustal magma sources independently from the effects of the thermal regime or tectonic setting at the time of magmatism

Summary

Introduction

Following several decades during which zircon geochronology has been used to reconstruct the history of our planet and the timescales of geological processes since the formation of the first solid crust (e.g., Froude et al, 1983; Bowring and Williams, 1999; Wilde et al, 2001), increasing attention is being paid to combining zircon age information with the mineral’s chemistry and microstructures (e.g., Vance et al, 2003; Engi et al, 2017), opening the way to the use of zircon as a powerful petrogenetic tool in the study of magmatic, metamorphic, and sedimentary systems. The late Variscan (∼314–300 Ma) granitoids (Graessner et al, 2000; Fiannacca et al, 2008) intruded into the amphibolite facies basement – mostly paragneisses derived from metamorphism of flysch-like greywacke sequences, large augen gneiss bodies, and minor amounts of mica schist, amphibolite, and marble Both the late Cadomian and late Variscan granitoids are characterized by large amounts of inherited zircon, indicating the presence of a substantial component of metasedimentary crust in the source of the granite magmas (Fiannacca et al, 2008, 2013). We propose that combined studies of whole rock geochemistry and zircon inheritance patterns in crustal rocks can represent a potent method for linking S-type granites to their specific magma sources

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