THE EARLY CAMBRIAN BASIN REORGANIZATION AND RELEVANT TECTONICS IN CENTRAL BALTICA: DETRITAL ZIRCON CHRONOLOGY OF THE EDIACARAN-CAMBRIAN SANDSTONES IN ESTONIA

In order to clarify tectono-sedimentary history of Ediacaran-Paleozoic Baltica, age spectra of detrital zircon grains in the Ediacaran and Lower Cambrian sandstones in western Estonia (in central Baltica) were analyzed by LA-ICPMS. The abundant occurrence of the Archean to Mesoproterozoic (2800-1000 Ma) zircon grains was confirmed in both samples. The new data provided the following new information on the provenance of the siliciclastics and sedimentary regime change in Cambrian Baltica. 1) The Ediacaran-Lower Cambrian mid-Baltic basin received abundant terrigenous clastics from the core of Baltica underlain by the Archean-Mesoproterozoic crystalline crust. 2) The surface-exposure of the Rapakivi granites was more extensive during the Ediacaran-Early Cambrian than in the present. 3) The rapid uplift in eastern Baltica (+ Sarmatia) in the middle Early Cambrian (ca. 530-515 Ma) totally changed the basin geometry and provenance, in contrast to no significant reactions to the Caledonican orogeny and/or Avalonian collision in the Early Paleozoic. 4) Possible sources of the Neoproterozoic zircon grains since the Early Cambrian include the peripheral mobile belts around Baltica with the pan-African signatures; e.g., the Timanian belt along the northern Ural and the so-called Gondwanan fragments (Avalonian-Cadonian blocks) along the Tornquist margin.