Vestige of an Early Cambrian incipient oceanic crust incorporated in the Variscan orogen: Letovice Complex, Bohemian Massif
Abstract
The Letovice Complex, composed of E-MORB metabasalts with trondhjemite sheets, gabbroic and ultrabasic bodies, is exposed within an important Variscan suture separating the Moldanubian Domain (W) from the Brunovistulicum (E). Its polyphase tectonic evolution was connected with underthrusting and subsequent exhumation of the former oceanic realm, which resulted into three deformation phases (D1-D3).
New U-Pb LA ICP-MS dating of magmatic Zrn from amphibolite and trondhjemite yielded statistically identical concordia ages of 530 +- 6 Ma and 529 +- 7 Ma, respectively. These are interpreted as dating intrusions of the Early Cambrian protoliths of the studied rocks.
Based on this age as well as whole-rock geochemical and Nd isotopic data, the Letovice Complex is interpreted as a vestige of an incipient oceanic basin developing on attenuated crust. The most likely geotectonic setting was a post-Cadomian extensional regime at the northern margin of Gondwana that marked the onset of its breakup.