In the Ordovician limestone of the Thorsberg quarry (South Sweden), about 130 meteorites have been found. Among the extraterrestrial material, several terrestrial Cr-spinels and zircons have been found too. In particular, in the interval 416-447 cm above the Arkeologen bed, terrestrial Cr-spinels, compositionally different from previous studied Cr-spinels of the same sequence, are present. Previous studies on zircon provided deposi-tional ages that range from 464.22 ±0.37 Ma to 465.01 ±0.26 Ma. The trace element content of zircons suggests different possible source rocks. In fact, zircons from the oldest ash lay-er resemble those from dolerite, while those in the youngest layers are similar to zircons commonly found in granitoids with more than 65% wt. SiO2. The chemistry of Cr-spinels suggests a strong alteration so that it is difficult to assign them to a specific area, however they recall the chemistry of altered spinels from ophiolitic occurrences (among other pos-sibilities). The geological setting of the Laurentia and Baltica areas, including the descrip-tion of basalts to rhyolite association and the presence of ophiolitic slices, makes us confi-dent about the derivation of these zircons and Cr-spinels from those areas.

The Österplana fossil meteorites and…what else? Terrestrial Cr-spinels and zircons in the Ordovician limestones of the Thorsberg quarry (Sweden)

Davide Lenaz
;
Matteo Velicogna;
2022-01-01

Abstract

In the Ordovician limestone of the Thorsberg quarry (South Sweden), about 130 meteorites have been found. Among the extraterrestrial material, several terrestrial Cr-spinels and zircons have been found too. In particular, in the interval 416-447 cm above the Arkeologen bed, terrestrial Cr-spinels, compositionally different from previous studied Cr-spinels of the same sequence, are present. Previous studies on zircon provided deposi-tional ages that range from 464.22 ±0.37 Ma to 465.01 ±0.26 Ma. The trace element content of zircons suggests different possible source rocks. In fact, zircons from the oldest ash lay-er resemble those from dolerite, while those in the youngest layers are similar to zircons commonly found in granitoids with more than 65% wt. SiO2. The chemistry of Cr-spinels suggests a strong alteration so that it is difficult to assign them to a specific area, however they recall the chemistry of altered spinels from ophiolitic occurrences (among other pos-sibilities). The geological setting of the Laurentia and Baltica areas, including the descrip-tion of basalts to rhyolite association and the presence of ophiolitic slices, makes us confi-dent about the derivation of these zircons and Cr-spinels from those areas.
2022
24-gen-2022
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11368/3005781
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