The Stromsbro granite complex in eastern south-central Sweden occurs a
n the north side of the Gavle graben, which is filled with Jotnian (Me
soproterozoic) sandstones. It has the form of a half oval of which the
southern part is covered by the Jotnian rocks, thus rendering the sub
-Jotnian label adequate. The granites are undeformed, red, and coarsel
y porphyritic. A few dolerite dykes are interpreted as associated with
the granite. The Stromsbro granites show considerable geochemical sim
ilarity with the rapakivi granites of the Fennoscandian Shield. They a
re metaluminous, within-plate, A-type granites. The dolerites are alka
li-rich quartz tholeiites showing marked similarities with other rapak
ivi-associated basic rocks. The U-Pb zircon age of the granite massif
is 1500+/-19 Ma (MSWD=1.7), which is similar to other sub-Jotnian comp
lexes in Sweden. The low initial epsilon(Nd) values of the Stromsbro r
ocks, and especially the dolerite, suggest the involvement of Archaean
crustal material in the magmas. The granites are interpreted as deriv
ed by melting of non-depleted, tonalitic granodioritic, early Svecofen
nian (and partly Archaean), lower crustal protoliths in response to he
at brought by mantle-derived magmas, now represented by the dolerites.