The age, petrography, geochemistry and tectonic setting of the late Caledonian Gåsøy Intrusion, west Norway

1989 
The GasOy In trusion of ga b b ron ori te a n d di ori te i s si tua ted i n the westernmost Norwegi a n Ca ledon i des. A Sm-Nd mi n era l i sochron on a di ori te ha s gi ven an a ge of 380 ± 26 Ma . In the ea sternmost pa rt of the pluton a gradua l cha n ge ca n b e demon strated i n the mi n era l a n d whole-rock geochemi stry from a ma ssi ve a n d la yered ga b b ron ori te to a hi ghly-differen ti a ted di ori te a s well as gra n i ti c rocks at i ts ma rgi n . Geochemi ca lly the i n trusion i s sub a lka li n e a n d i ts trace-elemen t pattern i s typi ca l of a sub ducti on -related en vi ron ment. Ma ss-b a la n ce ca lcula ti on s b a sed on ob served mi n era l da ta suggest tha t the di ori tes were derived b y fracti on a l crystalli za ti on from a b a sa lti c pa ren t. In i ti a lly, pla gi oclase a n d orthopyroxen e wi th lesser a moun ts of oli vi n e a n d cli n opyroxen e were fracti on a ted. In the producti on of the quartz-b ea ri n g di ori tes, fra cti on a ti on of pla gi oclase a n d cli n opyroxen e wi th less oli vi n e a n d mi n or i lmen i te wa s opera ti ve. Evi den ce of crusta l con ta mi n a ti on a n d ma gma mi xi n g i s gi ven b y Sr-i sotopes a n d zon ed pla gi oclase.
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