Large‐scale tectonic cycles in Europe revealed by distinct Pb isotope provinces

Abstract

Significance statements We have compiled and mapped out ~6800 Pb isotope measurements of lead ores and Kfeldspars across Europe and the circum-Mediterranean  Lead model ages define spatially distinct age provinces consistent with major tectonic events ranging from the Paleozoic to the Archean  Time-integrated U/Pb and Th/Pb ratios are decoupled from the age provinces and suggest foundering of the lower crust in southern Europe Abstract Lead isotopic systematics of U-poor minerals, such as sulfides and feldspars, can provide unique insights into the origin and evolution of continents because these minerals 'freeze in' the Pb isotopic composition of the crust during major tectonothermal events, allowing the history of a continent to be told through Pb isotopes. Lead model ages constrain the timing of crust formation while time-integrated U/Pb, Th/Pb, and Th/U ratios shed light onto key geochemical processes associated with continent formation. Using ~6800 Pb isotope measurements of primarily lead ores and minor K-feldspar, we mapped out the Pb isotope systematics across Europe and the Mediterranean. Lead model ages define spatially distinct age provinces, consistent with major tectonic events ranging from the Paleozoic to the Proterozoic and latest Archean. However, the regions defined by time-integrated U/Pb and Th/Pb ratios cut across the boundaries of age provinces, with high U/Pb systematics characterizing most of southern Europe. Magmatic influx, followed by segregation of densesulfide-rich mafic cumulates, resulted in foundering of U-and Th-poor lower crust, thereby changing the bulk composition of the continental crust and leading to distinct time-integrated U-Th/Pb provinces. We show that the tectonic assembly of small crustal fragments leaves the crust largely undifferentiated, whereas the formation of supercontinents results in fundamental changes in the composition of the crust, identifiable in time and space by means of Pb isotope systematics. Observations based on Pb isotopes open up a new perspective on possible relationships between crustal thickness and geodynamic processes, in particular the role of crustal foundering into the mantle and the mechanisms responsible for the existence of cratons.

Economic resilience of Carthage during the Punic Wars: Insights from sediments of the Medjerda delta around Utica (Tunisia)

“…This natural Pb isotopic composition is also easily readable using the geochemically informed parameters T mod [Pb model ages in million years (Ma)] and κ (the 232 Th/ 238 U ratio), which are derived from the time-integrated Pb isotopic compositions using the equations given by Albarède et al (27). The advantages of this representation over that based on raw Pb isotopic ratios have been demonstrated in a number of geological (28), archaeological (27), and geoarchaeological contexts (11 i) The 69 Pb-polluted sediments differ from the unpolluted samples in both their Pb content and Pb isotopic composition. Lead concentrations and EF Pb range between 10 and 210 ppm (mean = 59.1 ppm) and 2.13 and 20.9 (mean = 6.9), respectively ( Fig.…”

ROME'S Rise to Power. Geochemical Analysis of Silver Coinage from the Western Mediterranean (Fourth to Second Centuries BCE)

“…Variations in U‐Th‐Pb characteristics derived from Pb isotope data extend over spatially distinct model age provinces across Europe (Blichert‐Toft et al . ) and reflect the regional geodynamic and metallogenic evolution (e.g. Tosdal et al .…”

Medieval Silver Production Around Sijilmâsa, Morocco

“…This is consistent with the calculated high 232 Th/ 238 U ratio ( K ≥ 4.00, for average 50% of ores), which characterizes a lower crustal rocks contribution (Blichert‐Toft et al . ), such as the Neoproterozoic crystalline basement. A Pb isotopic average effect of slags from Sijilmâsa and ores from Bou Madine could persist, as is well illustrated by the 208 Pb/ 204 Pb versus 206 Pb/ 204 Pb ratios (Fig.…”