The Transgressive granophyres are a swarm of silicic dikes and sills in the Layered Series of the Skaergaard intrusion that range in composition from ferrodiorites to granites. Although originally thought to be derived by differentiation of Skaergaard magma, accumulated evidence indicates that the origin of these granophyres is more complex and involves contributions from melted country rocks. In the present study it is shown that field relations are inconsistent with any genetic relationship between the Transgressive granophyres from the Layered Series and differentiated Skaergaard magma. Although new Sr isotope analyses confirm that these granophyres are at least partly derived by fusion of Archean country rock, field relations preclude derivation of this crustal component from partially melted gneissic xenoliths from the Skaergaard magma chamber or from melting along the contact between the gneisses and the Skaergaard pluton. Major- and trace-element compositions, together with Sr isotope ratios indicate that the Transgressive granophyres from the Layered Series represent a cogenetic suite of magmas related to each other primarily by a closed system process such as crystal fractionation, and that the parental magma that gave rise to these granophyres was formed beneath the Skaergaard intrusion by contamination of differentiated post-Skaergaard mafic magmas with partially fused Archean crust.
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I wish to thank A.R. McBirney for suggesting that the Transgressive granophyres would make an interesting topic of study and D.J. Geist for inviting me to contribute to this volume in honor of Mac's retirement. Thanks to H.R. Naslund and H. Anderson for providing logistical support in East Greenland and to R.St.J. Lambert for access to the isotope facilities at the University of Alberta. Thanks also to G. Bergantz, I.S. McCallum, and H.R. Nas-lund for helpful discussions; to A.R. Mc-Birney, A.D. Johnston, G.G. Goles, M.A. Kays and D.L Whitney for critical reviews of earlier versions of this manuscript; to D. Bostok, D. Krstic, J. MacKinnon, and C. McBirney for technical assistance; and to C.E. Lesher, and an anonymous reviewer for helpful reviews of the present version. This work was supported by NSF grant EAR-8503428 to A.R. McBirney and by a Grant-in-Aid from Sigma Xi and a GSA research grant to the author.