Caledonian Magmatism in Norway: The Long-Lived Bindal Batholith through Time

The Bindal Batholith is the largest Caledonian (s.l.) batholith in the Scandinavian Caledonides. Its plutons intruded the Helgeland Nappe Complex (HNC) from 478 to 424 Ma. Magmatism began in a peri-Laurentian setting and continued through Scandian-aged (430–390 Ma) accretion of the HNC to Laurentia. Magmatism from 482 to 470 Ma overlaps with regional migmatization, and these early peraluminous to strongly peraluminous plutons have wide-ranging initial ⁸⁷Sr/ ⁸⁶Sr and εNd from -5 to -9. Source rocks included Lower Ordovician clastic deposits that and heat was provided by primitive, MORB-like basaltic magmas. From 466–465 Ma two plutons were emplaced. Both had basaltic parentage and both interacted intensely with local crustal rocks. From 450–442 Ma, magmatism was predominantly calc-alkalic to alkali-calcic, with basaltic to andesitic parental magmas. The εNd values for the mafic rocks during this time ranged from ca. 1 to -1, which suggests significant deep-crustal contamination. This was followed by mid-crustal differentiation which included assimilation of host rocks. Magmatism from 439–424 Ma was broadly similar to 450–442 Ma activity. However, higher concentrations of Sr (to 1500 ppm) and lower heavy REE contents in some plutons of this age suggest residual garnet in the source, in turn suggesting thickening and maturation of the HNC crustal section. Compared to Taconian arc magmatism, the oldest magmatic activity of the Bindal Batholith is distinctive in its strongly peraluminous characteristics and paucity of evidence for an arc source of mafic magma. Younger Bindal magmas were arc-like and by ca. 435 Ma, granitic magmatism had spread into the subjacent Rödingsfjället Nappe Complex and the Caledonian section in East Greenland.