Cadomian and Early Paleozoic Magmatic Events: Insights from Zircon Morphology and Geochemical Signatures of I- and S-Type, Granitoids (Saxo-Thuringia/Bohemian Massif/ Central Europe)

摘要

This paper presents studies of zircon morphologies and geochemical signatures of Neoprotero-zoic and Early Paleozoic metagranitoids and metarhyolites of the Saxo-Thuringian Zone (Central Europe). The Saxo-Thuringian Zone was derived from the northern periphery of Gondwana and became part of the Variscan belt of Central Europe during Paleozoic orogenic processes. Five tectonomagmatic events are preserved in the Saxo-Thuringian Neoproterozoic and Early Paleozoic igneous rocks. These different geotectonic scenarios are each characterized by distinctive geochemical signatures and zircon morphologies. Samples of felsic lithologies with age ranges of -580-560 Ma. approx 500 Ma, and approx 380-360 Ma show whole-rock compositions of dry J-type with a tendency to A-type granites and zircon crystals with strong dominance of {100} prisms and {101} pyramids. The approx 580-560 Ma and approx 500 Ma periods of predominantly juvenile magmatism both were followed by tectonothermal events producing S-type granitoids at approx 550-530 Ma and 495-480 Ma. Associated zircon populations are dominated by {110} prisms and {211} pyramids. Inasmuch as the errors of individual geochronological analyses may overlap two different geotectonic episodes, the relationship between geochemical features and zircon morphologies of the Saxo-Thuringian Neoproterozoic and Early Paleozoic igneous rocks can aid in assigning the dated sample to the proper stage of formation.