Geochemistry of mafic dykes in the Corrovarre Nappe, Troms, North Norway
Abstract
Tholeiitic metadolerite dyke rocks in the Corrovarre Nappe of the Kalak Nappe Complex in North Troms show chemical traits which indicate T-MORB affinities, with fairly flat, chondrite-normalised REE patterns in a (La\/Nb)N just over 1. The low initial 87Sr\/86Sr ratio, 0.7030, and lack of Th enrichment suggest that the magma was not contaminated to any extent during upward passage from a secondarily slightly LIL element-enriched but primarily depleted mantle source. Element abundamces and ratios and the low initial Sr ratio are compar- able to those from Tertiary T-MORB dykes and lavas from the Vøring Plateau. It is suggested that the Corrovarre dykes, Sm\/Nd-dated to c. 580 Ma, penetrated a continental crust which had thinned appreciably since the time of initial rifting. The dykes probably intruded just prior to the actual inception of sea- floor spreading along this segment of the Baltoscandian margin.