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Abstract:

Over the past decade several restorations of the hypothetical Mesoproterozoic to Neoproterozoic supercontinent have been suggested. In this paper, we summarize the most recent data on Mesoproterozoic to Neoproterozoic geology of the Siberian craton to test different restorations.

U-Pb zircon ages of the Siberian craton basement are typically older than 2300 Ma or have Paleoproterozoic ages between 2050 Ma and 1700 Ma, whereas Sm-Nd model ages (TDM) are typically older than 2100 Ma. A similar radiometric age profile has been reported from basement of crystalline massifs exposed to the east of the Siberian craton. An important feature for paleocontinental correlation is a widespread anorogenic magmatic belt (ca. 1740-1700 Ma) that links the Aldan shield, the Okhotsk massif, and the Prikolyma terrane.

Mesoproterozoic magmatic events are represented by mafic dike swarms with chemistry typical of continental flood basalts. Most of the dated examples come from the Anabar shield and yield ages of ca. 1500 Ma, 1410-1380 Ma, and 1320 Ma. In contrast, two Neoproterozoic magmatic events (1000-930 Ma and 760-720 Ma) are typical of the eastern and southern margin of the craton. These areas contain significant portion of MORB-like basalts, implying extensive rift events.

The most complete Mesoproterozoic to Neoproterozoic type section is located in the Sette-Daban Range of southeast Siberia and contains several hiatuses. The largest is between the Vendian Yudoma Group (younger than 620 Ma) and the Uy Group (older than ca. 930 Ma). Sedimentary successions on the western and southern margins of the craton contain rock units younger than ca. 720 Ma (Baikalian Complex) that are absent in the type section. On the margins of the Anabar shield below the Yudoma group, only rock units older than ca. 1380 Ma have been reported. The Mesoproterozoic to Neoproterozoic sedimentary cover of the Okhotsk and Omolon massifs correlates well with successions on the eastern margin of the Siberian craton. The Yudoma Group typically unconformably overlies underlying sedimentary rock units and locally rests on the crystalline basement.

The data show inconsistency between Mesoproterozoic to Neoproterozoic sedimentary and magmatic evolution with paleocontinental restorations that plot Siberia as a single continent within the World Ocean without connection to other continental masses. Reconstructions that juxtapose southern Siberia to northern Laurentia (cf. Rainbird et al., 1998) or eastern Siberia to western Laurentia (cf. Sears and Price, 2003) show better fit with geological data, but more isotopic studies are necessary for a final assessment.

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