Detrital zircon record of the Mesoproterozoic to Lower Cambrian sequences of NW Russia: implications for the paleogeography of the Baltic interior

Abstract

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb detrital zircon isotope
\ndata from Mesoproterozoic to Lower Cambrian strata of the St Petersburg region are used to characterize
\nthe paleogeographic and tectonic evolution of the Baltica continent. We dated fifteen samples
\nand divided them into three groups based on their distribution of detrital zircons. The first group
\n(comprising Lower Mesoproterozoic rocks) is dominated by Early Mesoproterozoic and Late
\nPaleoproterozoic zircons, mostly derived from weathering of proximal source region including rapakivi
\ngranites exposed across the neighboring Baltic Shield. The second group includes Upper Ediacaran
\nsamples (Redkino and Kotlin Regional Stages), with major zircon populations ranging in age between
\n1970–1850 and 1600–1550 Ma, respectively, correlating with magmatic and metamorphic events within
\nthe Svecofennian Orogeny and rapakivi granite igneous activity in the interior of Fennoscandia. The
\nthird group of samples, collected from both the uppermost Ediacaran and lowermost Cambrian
\ndeposits (Kotlin, Lontova and Dominopol Regional Stages), contains older Paleo-Mesoproterozoic
\nzircons as well as Late Neoproterozoic-earliest Cambrian zircons, indicating a Timanian source area
\nand exhibiting a age spectra similar to spectra for coeval rocks of the Scandinavian Caledonides.
\nTherefore, we conclude that reworking and transport of continental detritus from the Timanian
\nOrogen began during Late Ediacaran, earlier than previously supposed, with transport of Timanian
\ndetritus not only to the marginal part of Baltica (known from the Scandinavian Caledonides), but also to
\nthe distal interior of Baltica.