Origin and evolution of calcalkaline plutons in the Northeast Kingdom batholith, Vermont

Geochemical and petrographic study of five calcalkaline Devonian plutons in the Northeast Kingdom batholith suggests that they were generated from similar sources but evolved differently. The modally homogeneous Willoughby granite (WG) and the Derby granodiorite (DG) are the most aluminous plutons and contain muscovite and biotite (+/- garnet). The West Charleston diorite (WCD) and the Nulhegan granodiorite (NG) are relatively mafic plutons containing pyroxene, hornblende, and biotite. The Echo Pond (EP) has a granodioritic core but is dioritic along its southern margin. Regular variations of major and trace elements are found in NG and in the relatively sodic DG. More erratic chemical variations are found for WG. The more mafic plutons have higher Sr and lower Rb, Nb and Ta compared to the more felsic WG and DG. Rare-earth patterns for all plutons show higher light than heavy rare-earths. However, the more mafic plutons are comparatively less enriched, have smaller Eu anomalies, and tend to have higher contents of heavy rare earths than the WG and DG. The felsic Willoughby pluton is the best candidate for an upper crustal minimum melt. A deeper origin for the more mafic plutons is likely. Significant differences in the rare earths and ferromagnesian elementsmore » indicate that the WG, DG, and EP cannot be related by a simple fractionation scheme to the more mafic plutons.« less