A summary of the petrography and geochemistry of the Bindal Batholith

Abstract

The Bindal Batholith is a composite intrusive complex which was emplaced into mediumgrade supracrustal rocks of the Helgeland Nappe Complex. The plutonism postdated the internal amalgamation of the Helgeland Nappe Complex, which probably took place during a Middle Ordovician tectonothermal event, and pre- dated the Silurian to Early Devonian, Scandian, collisional orogenic phase. The Batholith contains a wide spectrum of rock types with a general range in composition from mafic olivine gabbro to leucogranite. Equigranular and por- phyritic granites and granodiorites are the most common rock types. The major- ity of the rocks are high-K calkalkaline and metaluminous, but mafic to inter- mediate, calcic to alkali-calcic varieties and evolved, peraluminous granites are also present. The composition of the rocks suggest that they were derived by partial melting of multiple sources such as depleted mantle and mafic lower crust, Th-enriched lower crust and various upper crustal rocks in a general setting of converging plates. Magmatic processes associated with subduction zones, and strike-slip movements and thrusting along deapseated fault systems probabaly controlled the petrogenesis, ascent and emplacement of the granitoid magmas.