U‐PB Detrital Zircon Geochronology of the Lower Danube and Its Tributaries: Implications for the Geology of the Carpathians

Abstract

We performed a detrital zircon (DZ) U‐Pb geochronologic survey of the lower parts of the Danube River approaching its Danube delta, Black Sea sink, and a few large tributaries (Tisza, Jiu, Olt, and Siret) originating in the nearby Carpathian Mountains. Samples are modern sediments. DZ age spectra reflect the geology and specifically the crustal age formation of the source area, which in this case is primarily the Romanian Carpathians and their foreland with contributions from the Balkan Mountains to the south of Danube and the East European Craton. The zircon cargo of these rivers suggests a source area that formed during the latest Proterozoic and mostly into the Cambrian and Ordovician as island arcs and back‐arc basins in a Peri‐Gondwanan subduction setting (~600–440 Ma). The Inner Carpathian units are dominated by a U‐Pb DZ peak in the Ordovician (460–470 Ma) and little inheritance from the nearby continental masses, whereas the Outer Carpathian units and the foreland have two main peaks, one Ediacaran (570–610 Ma) and one in the earliest Permian (290–300 Ma), corresponding to granitic rocks known regionally. A prominent igneous Variscan peak (320–350 Ma) in the Danube's and tributaries DZ zircon record is difficult to explain and points out to either an extra Carpathian source or major unknown gaps in our understanding of Carpathian geology. Younger peaks corresponding to arc magmatism during the Alpine period make up as much as about 10% of the DZ archive, consistent with the magnitude and surface exposure of Mesozoic and Cenozoic arcs.

Lower Cretaceous Provenance and Sedimentary Deposition in the Eastern Carpathians: Inferences for the Evolution of the Subducted Oceanic Domain and its European Passive Continental Margin

“…A major Ordovician peak at 458 -472 Ma represents the culmination of a high-flux magmatic event (Stoica et al, 2016) that is distinctive for the Dacia mega-unit. Other significant zircon peaks are found at 520, 540, 580, and 600 Ma trailing toward slightly older ages (Figures 3a and 3b) but not beyond 750 Ma (Ducea et al, 2018). They may represent the ages of a nearby continental fragment or possibly the age of a thinned continental crust in which these arcs were emplaced.…”

“…Older inherited zircons make up a small Grenvillian peak, and few ages older than 2.0 Ga are interpreted to have been derived from a landmass close to the island arcs. A less pronounced peak at 325 -340 Ma indicates a Variscan event and is believed to record a period of regional metamorphism (Ducea et al, 2018). The Albian sedimentary cover of the Getic unit shows similar features (Figure 3c), having the most dominant peaks at 460 and 600 Ma, which shows a South Carpathians basement provenance (Stoica et al, 2016).…”

“…Despite large gaps in quantitatively understanding the geochronology of basement rocks in the Carpathians and surrounding areas, a fairly comprehensive database of zircon provenance exists to date (see Ducea et al, 2018). This database demonstrates that the two basement units bordering both sides of the Ceahlău-Severin Ocean at the time of Early Cretaceous oceanic subduction show distinct features regarding provenance zircon radiometric ages.…”

“…A Permian to Lower Cretaceous sedimentary cover overlies these units. The details regarding pre-Mesosoic island arc formation and assembly remain poorly resolved petrologically and structurally, but sufficient zircon chronology data are available (Balintoni et al, 2010b(Balintoni et al, , 2014Balintoni & Balica, 2013;Ducea et al, 2016, for a review) to fingerprint potential derivation from the Dacia mega-unit using zircon Kernel Density Estimate plots (Ducea et al, 2018) of sedimentary rocks deposited in the former Ceahlău-Severin oceanic basin. A major Ordovician peak at 458 -472 Ma represents the culmination of a high-flux magmatic event (Stoica et al, 2016) that is distinctive for the Dacia mega-unit.…”

Detrital zircon U-Pb geochronology of modern Andean rivers in Ecuador: Fingerprinting tectonic provinces and assessing downstream propagation of provenance signals

“…Detrital zircon U-Pb geochronology has become a fundamental provenance tool providing critical records of mountain building, large-scale drainage evolution related to tectonic and climatic drivers, and source-to-sink evolution of depositional systems and sedimentary basins (e.g., Dickinson andGehrels, 2003, 2008;Weislogel et al, 2006;Cawood et al, 2012;Laskowski et al, 2013;Blum and Pecha, 2014;Sharman et al, 2015;Horton, 2018;Ducea et al, 2018;Wang et al, 2018). Discrimination of competing sedimentary source regions and terranes is essential to detrital zircon provenance studies (e.g., DeCelles et al, 2000;Horton et al, 2010aHorton et al, , 2010bHorton et al, , 2015Gehrels, 2014;Saylor and Sundell, 2016;Sickmann et al, 2018).…”