The petrogenesis of the Kangerdlugssuaq alkaline intrusion, east Greenland

Compositional variation in the pyroxenes and amphiboles of the Kangerdlugssuaq intrusion, East Greenland: further evidence for the crustal contamination of syenite magma

“…resembling a pile of saucers (Kempe et al, 1970), within which the distribution of rock types appears to be concordant. Silica contents are found to decrease inwards and upwards, the rock types varying from quartz nordmarkite at the margins through nordmarkite and pulaskite to foyaite at the centre of the intrusion.…”

“…In view of the important bearing of the Kangerdlugssuaq intrusion on the petrogenesis of alkaline rocks, we are undertaking more detailed mineralogical and chemical studies, and present here an electron microprobe investigation of the pyroxenes and amphiboles of the intrusion. The work supplements by microprobe methods the study of Kempe and Deer (1970), who reported wet-chemical analyses on mineral separates of seven pyroxenes and five amphiboles. For the sake of consistency, the rock names employed by Kempe et aL (1970) and Kempe and Deer (1970) have been retained in subsequent work and are retained by us.…”

“…There is no field evidence for more than one phase of injection, and the intrusion is a prominent example of the class of alkaline complexes in which a homogeneous syenite magma appears to have differentiated from an initially over-saturated composition to an undersaturated residual liquid, in apparent violation of phase relations in the system NaA1SiO4 KAISiO4-SiO2 (see Tilley, 1957). Kempe and Deer (1976), treating the intrusion as a closed system, discussed several mechanisms by which the magma composition might have crossed the thermal barrier in this system, but reached no conclusion as to which, if any, had operated. On the basis of isotopic evidence, however, Pankhurst et al (1976) demonstrated that the outer parts of the intrusion had undergone considerable chemical interaction with the surrounding gneisses, and the notion of simple differentiation of an isolated magma in situ could no longer be regarded as an acceptable explanation of the development of the intrusion.…”

The petrology, chemistry and crystallization history of the Velasco alkaline province, eastern Bolivia

“…3) together with some accumulation of nepheline, this is expected as Heier (1966) has demonstrated that K/Rb in alkali feldspar is higher than in the coexisting melt. Complementary to this is the probability that K/Rb in nepheline is lower than in alkali feldspar as indicated by data from the Kangerdlugssuaq intrusion (Kempe & Deer 1970) and Stjern6y syenites (Heier 1966). K/Rb ratios for the trachytes overlap those of the pulaskites, whereas K/Rb ratios of the normal and RE melasyenites overlap with, or are lower than, those of the foyaitic rocks.…”

“…Electron microprobe data indicate values from 600 to 1200 ppm. Gomes et al (1970) and Kempe & Deer (1970) combined with the ease with which some elements form complexes in hydrous fluids. It is probable that most of these elements are contained within britholite and apatite.…”