Mafic plutonic rocks in a continental-arc setting: geochemistry of 1.87–1.78 Ga rocks from south-central Sweden and models of their palaeotectonic setting
Article first published online: 30 JUL 2008
Copyright © 2008 John Wiley & Sons, Ltd.
Volume 44, Issue 3, pages 241–279, May 2009
How to Cite
Rutanen, H. and Andersson, U. B. (2009), Mafic plutonic rocks in a continental-arc setting: geochemistry of 1.87–1.78 Ga rocks from south-central Sweden and models of their palaeotectonic setting. Geol. J., 44: 241–279. doi: 10.1002/gj.1133
- Issue published online: 23 APR 2009
- Article first published online: 30 JUL 2008
- Manuscript Accepted: 3 JUN 2008
- Manuscript Received: 24 JAN 2008
- Transscandinavian Igneous Belt;
- mafic plutonic rock;
- Sr and Nd isotopes;
- mantle enrichment;
- continental arc
Mafic intrusive rocks (1.79–1.78 Ga) of the Transscandinavian Igneous Belt (TIB) and the c. 1.87 Ga Hedesunda Igneous Complex in the Fennoscandian Shield of south-central Sweden were studied using whole-rock and isotope geochemistry.
Rock types vary from gabbros/norites (and leucogabbros) to quartz diorites, with Mg# between 76 and 49, and wt% SiO2 between 43.6 and 59.7, indicating some variation in evolutionary levels and variable cumulus components. Geochemical signatures are calc-alkaline to shoshonitic, large ion lithophile elements and light rare earth elements enriched and high-field strength elements depleted of continental-arc type.
εNd(t) ranges between +1.0 and +2.7, and 87Sr/86Sr(t) between 0.7020 and 0.7038. There is no systematic correlation between chemical parameters and isotope ratios. These isotopic data overlap with other mafic plutonic TIB rocks; samples from the Dala Province (DP) tend to overlap with the c. 1.7 Ga basic Dala lavas of TIB at slightly elevated relative Sr/Nd ratios.
With two exceptions, the εNd(t) of +1 to +2 conform to an isotopically ‘mildly depleted’ source, typical for mafic TIB rocks and many Svecofennian rocks in the region. Reported values above εNd(t) +2.0 are scarce in the TIB. Mantle sources represent depleted mantle wedge material that was enriched by fluids/melts not long before (TDMc. 2.0 Ga), that is during subduction in the preceding Svecofennian (2.0–1.87 Ga) and/or during the TIB-0&1 event (1.85–1.78 Ga). The palaeotectonic settings inferred are active continental margins; N–S-directed convergence at 1.87 Ga and E–W-directed at 1.79–1.78 Ga. Copyright © 2008 John Wiley & Sons, Ltd.