ABSTRACT Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb detrital zircon isotope data from Mesoproterozoic to Lower Cambrian strata of the St Petersburg region are used to characterize the paleogeographic and tectonic evolution of the Baltica continent. We dated fifteen samples and divided them into three groups based on their distribution of detrital zircons. The first group (comprising Lower Mesoproterozoic rocks) is dominated by Early Mesoproterozoic and Late Paleoproterozoic zircons, mostly derived from weathering of proximal source region including rapakivi granites exposed across the neighboring Baltic Shield. The second group includes Upper Ediacaran samples (Redkino and Kotlin Regional Stages), with major zircon populations ranging in age between 1970–1850 and 1600–1550 Ma, respectively, correlating with magmatic and metamorphic events within the Svecofennian Orogeny and rapakivi granite igneous activity in the interior of Fennoscandia. The third group of samples, collected from both the uppermost Ediacaran and lowermost Cambrian deposits (Kotlin, Lontova and Dominopol Regional Stages), contains older Paleo-Mesoproterozoic zircons as well as Late Neoproterozoic-earliest Cambrian zircons, indicating a Timanian source area and exhibiting a age spectra similar to spectra for coeval rocks of the Scandinavian Caledonides. Therefore, we conclude that reworking and transport of continental detritus from the Timanian Orogen began during Late Ediacaran, earlier than previously supposed, with transport of Timanian detritus not only to the marginal part of Baltica (known from the Scandinavian Caledonides), but also to the distal interior of Baltica.

中文翻译：

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俄罗斯西北部中元古代至下寒武统序列的碎屑锆石记录：对波罗的海内陆古地理的影响

摘要 激光烧蚀电感耦合等离子体质谱 (LA-ICP-MS) U-Pb 碎屑锆石同位素数据从圣彼得堡地区的中元古代到下寒武统地层用于表征波罗的海大陆的古地理和构造演化。我们对 15 个样品进行了测年，并根据碎屑锆石的分布将它们分为三组。第一组（包括下中元古代岩石）以早中元古代和晚古元古代锆石为主，主要来源于近源区的风化作用，包括暴露在邻近波罗的海地盾上的 rapakivi 花岗岩。第二组包括上埃迪卡拉纪样本（Redkino 和 Kotlin 区域阶段），主要锆石种群年龄分别在 1970-1850 和 1600-1550 Ma 之间，与 Svecofennian 造山运动中的岩浆和变质事件以及 Fennoscandia 内部的 rapakivi 花岗岩火成岩活动相关。第三组样品采集自埃迪卡拉纪最上层和寒武纪最下层（Kotlin、Lontova 和 Dominopol 区域阶段），包含较旧的古-中元古代锆石以及晚新元古代-最早的寒武纪锆石，表明是提曼纪源区并显示出年龄光谱类似于斯堪的纳维亚 Caledonides 同期岩石的光谱。因此，我们得出结论，来自提曼尼亚造山带的大陆碎屑的再加工和运输开始于埃迪卡拉纪晚期，比以前假设的要早，而且提马尼亚碎屑不仅运输到波罗的海的边缘部分（从斯堪的纳维亚的 Caledonides 中得知），