Detrital zircon U‐Pb ages and Hf isotopic constraints on the terrigenous sediments of the Western Alps and their paleogeographic implications

Abstract

Detrital zircons from Cretaceous micaschist, late Eocene‐earliest Oligocene sandstone and early Oligocene siltstone of the Western Alps fall into three main separable age clusters at 610–540 Ma, 490–430 Ma, and 340–280 Ma that correspond to the Cadomian (Neoproterozoic), Ordovician, and Variscan (Carboniferous) events widespread in western and central Europe. Hf isotopic results indicate that these three magmatic and tectonic episodes did not give rise to significant production of juvenile crust. A distinguishable group of Triassic zircons, around 250–200 Ma which is considered to derive from the Southern Alps, has been detected in the early Oligocene “Schistes à Blocs” formation and the Briançonnais “Flysch Noir”. In contrast, this age group is absent in late Eocene to earliest Oligocene sandstones. In agreement with sedimentological studies, our results show that the main source areas of the Eocene sandstone were probably located in the European continent. The arrival of detritus from the Internal Zone occurred in early Oligocene, coeval with the tectonic rotation from northwestward to westward in the propagation of allochthonous units. Based on previous studies and our new data, we argue that the Briançonnais Zone was likely a paleorelief since the middle Eocene that accounts for the lack of detritus from the Adriatic units. Contemporary sediments were accumulated in the foredeep of the Adriatic plate. From Oligocene time onward, the blockage was cut through after a regional uplifting, and thus, the Internal Zone started to provide detritus into the western flexural basins.

Detrital zircon age patterns from turbidites of the Balagne and Piedmont nappes of Alpine Corsica (France): Evidence for an European margin source

“…Hf values for Ordovician rocks fit with the bimodal sources of the volcanism from the neighboring Sardinia where three main events were recognized according to is consistent with results obtained in the Alps (Schaltegger and Gebauer, 1999;Chu et al, 2016). All the analyses of zircon are below the curve of the depleted mantle, suggesting that the magmas from which most of zircons crystallized, formed by partial melting of pre-existing crustal rocks, rather than from a juvenile source ( Fig.…”

“…Thus, an integration of the different analytical datasets applied to detrital zircons in sedimentary basins offers the possibility to assess the tectonic evolution history of the orogen from which the sediments were derived in terms of ages, rock types and source materials (Wysoczanski et al, 1997;Carter and Moss, 1999;Bruguier et al, 1997;Cawood et al, 2012). Detrital zircon age patterns and Lu-Hf isotopic analysis were recently used to unravel the origin of terrigenous sediments and the growth of the crusts in the Western Alps in a situation close to Alpine Corsica environment (Bütler et al, 2011;Beltrán-Triviño et al, 2013;Malusà et al, 2013Malusà et al, , 2016aManzotti et al, 2015Manzotti et al, , 2016Chu et al, 2016 and references therein; Anfinson et al, 2016).…”

The birth of the Alps: Ediacaran to Paleozoic accretionary processes and crustal growth along the northern Gondwana margin

“…Figure 7b summarizes Lu-Hf data of Neoproterozoic to Paleozoic detrital zircons of the Alps (Supplementary Material 5; Chu et al 2016;Siegesmund et al 2018), which are also comparable for all Alpine basement units, similarly to the U-Pb detrital zircon age pattern (Fig. 8).…”

“…Interestingly, these Paleoproterozoic and Neoarchean compositions are aligned along an apparent crustal array with 176 Lu/ 177 Hf = 0.015, typical for a crustal reservoir (e.g., Griffin et al 2002). (Chu et al 2016…”

Detrital signatures of impending collision: The deep-water record of the Upper Cretaceous Bordighera Sandstone and its basal complex (Ligurian Alps, Italy)

“…Available datasets from recent studies on detrital zircon assemblages of Upper Penninic flysch successions (Chu et al, 2016;Lin et al, 2018) allow a comparison of the detrital suites of this study.…”