The Sm-Nd isotope characteristics of c. 1.9 and c. 1.8 Ga granitoids occurr
ing close to the edge of the Archaean craton in northern Sweden have been s
tudied. Strongly negative epsilon(Nd(t)) values occur farther southwest in
the potassic 1.8 Ga granitoids than in the calc-alkaline 1.9 Ga granitoids.
Intrusions of the younger granitoids with distinctly negative epsilon(Nd(t
)) values are surrounded by granitoids of the older group with positive val
ues. Northeast of the 1.8 Ga granitoids discussed here, the c. 1.9 Ga calc-
alkaline intrusions formed within the Archaean continent have the same Sm-N
d isotope characteristics as the 1.8 Ga granitoids to the southwest. Our in
terpretation is that a juvenile volcanic-arc terrane to the south collided
with and was thrust onto the Archaean continent after the formation of the
1.9 Ga granitoids. The outcome was that these juvenile rock masses were obd
ucted onto the reworked Archaean continent. The 1.8 Ga granitoids were form
ed by remobilisation of continental crust. Partial melting at 1.8 Ga result
ed in the intrusion of granitoids carrying the Sm-Nd isotopic signature of
the Archaean continent into juvenile rocks. It is probable that the collisi
on discussed here was part of a major accretion and amalgamation to the Arc
haean craton after the formation of the calc-alkaline 1.9 Ga granitoids, bu
t before the formation of the 1.8 Ga granitoids. (C) 1999 Elsevier Science
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