ZIRCONIUM IN ALKALINE DYKES FROM THE TUGTUTÖQ REGION, SOUTH GREENLAND

• Main Authors: Raymond Macdonald, A. Parker
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Greenland
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.545.7351; http://2dgf.dk/xpdf/bull20-01-59-63.pdf

Zr values are reported for 30 alkaline dykes from the Tugtutoq area, South Greenland. Concentrations increase in the fractionation series trachydolerite'-» • aegirine microgranite to a maximum of 7175 p.p.m., hut it is not yet clear how Zr is distributed between the various mine-rals in the silicic dykes. The rocks occur as swarms of dykes of Gardar age intruded into basement granites some 1150 m years ago (Bridgwater, 1965). The geological setting and details of the igneous activity have been given by Upton (1962, 1964a), while Macdonald (1969) has described the petrology of the dykes, giving 33 rock-analyses. Macdonald & Edge (1970) have presented data for F, Cl, Rb, Sr, Ba, Sc, Y, La, Ce, Nb, Cr, Cu, Ga and Pb in the analysed speci-mens. The dykes form a series from trachydolerites through hastingsite- and riebeckite-microsyenites to devitrified microgranites and rhyolites. Though the dykes are thought to represent the products of the extreme fractionation of alkali basalt magma, the compositions of the acid types have been modified by devitrification, resulting in a loss of Na (and to a lesser extent