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Syntectonic Lower Or do vi cian migmatite and post-tec tonic Up per Viséan syenite in the west ern limb of the Orlica-Œnie ¿ nik Dome , West Sudetes : UPb SHRIMP data from zir cons
| Content Provider | Semantic Scholar |
|---|---|
| Author | Ÿniewicz, Andrzej ̄ Ela Nowak, I. Larionov, Al ex An Der Presnyakov, Sergey |
| Copyright Year | 2007 |
| Abstract | Ab stract In the Orlica-Œnie¿nik Dome, the West Sudetes, metagranites of 515–480 Ma age oc cur as coarse-grained augen gneiss es (~ Œnie¿nik type) in the mid dle of the dome, whereas fine-grained, of ten migmatitic gneiss es (~ Giera3tów type) are lo cated more ex ter nally. Both the or i gin and ge netic re la tion ships of the gneiss es have been dis puted for many years. In a quarry near Zdobnice, in the west ern part of the dome, migmatitic gneiss es and a post-tec tonic dyke of unfoliated bi o tite-hornblende high-K syenite oc cur. The migmatititc gneiss has mesosome with relic min er als, no ta bly Ca-Fe gar net and pseudo morphs af ter Al2SiO5 polymorph (?), in dic a tive of an early granulitic meta mor phism at con sid er ably high pres sure and tem per a ture. Ret ro gres sion at still high tem per a ture of ~720–750°C un der the up per am phi bo lite fa cies con di tions was ac com pa nied by migmatization which among oth ers pro duced cross-cut ting neosome veins of graphic gran ite. Zir cons from the melt de rived neosome and from the syenite dyke were ana lysed with SHRIMP II. The for mer yielded a con cordia age of 485±12 Ma which is taken to con strain the wan ing stage of the Late Cam brian–Early Or do vi cian migmatization. Migmatitic gneiss es may have rep re sented a metasedimentary-metaigneous Neoproterozoic crust that un der went mul ti stage meta mor phism, granulite fa cies in clu sive, and then yielded to ex ten sive par tial melt ing be tween 515 Ma and 480 Ma. Our new data shows that the migmatization in the Orlica-Œnie¿nik Dome was con cur rent with the in tru sion of a gra nitic pre cur sor of the augen gneiss es and does not sup port the views that the migmatitic gneiss es can be a de riv a tive of the ~500 Ma gran ite. In the Late Cam brian–Early Or do vi cian, the por phy ritic gran ite in truded in migmatitic coun try rocks which man tled the gra nitic core. Both lithologies were later ductilely sheared and de formed un der lower con di tions of the am phi bo lite and greenschist fa cies dur ing the Variscan orog eny. Four zir con grains from the post-tec tonic syenite dyke yielded a con cordia age of 326±3 Ma, which is in ter preted as the time of its in tru sion. This con strains the duc tile Variscan events in the stud ied re gion. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://geojournals.pgi.gov.pl/gs/article/download/13756/12194 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
