Igneous charnockites and related rocks from the Bjerkreim-Sogndal layered intrusion (Southwest Norway): a jotunite (hypersthene monzodiorite)-derived A-type granitoid suite

The upper part of the Bjerkreim-Sokndal layered intrusion (BKSK) comprises a suite of charnockitic granitoids (mangerite, quartz mangerite and charnockite) with some jotunites. The petrology and geochemistry (major and trace elements) of 8 main rock types (88 samples) are considered. The rocks form a suite of K2O-rich alkali-calcic granitoids of A-type, deriving from jotunitic magma. Two trends of inferred liquids are distinguished: the main liquid line of descent which passes from jotunites through 2-pyroxene quartz mangerites to amphibole charnockites, the second one which encompasses olivine-bearing quartz mangerites and charnockites and is rooted into mangeritic liquids. Comparison with the Tellnes rock series reveals that contamination by leucogranitic material has taken place simultaneously with fractional crystallization in both BKSK trends. Zr, Rb, Cs, and Th are particularly sensitive to assimilation and the higher water content in BKSK. Zircon and apatite have saturated at the liquidus of quartz mangerite around 900°C, close to the FMQ buffer. The two-pyroxene quartz mangerites cannot have been equilibrated with the mangerite cumulates on which they rest. A major influx of magma took place when mangeritic cumulates were being deposited. It mingled and partly mixed with the resident contaminated magma.