The Tugtutoq Younger Giant Dyke Complex, South Greenland: fractional crystallization of transitional olivine basalt magma

• Main Authors: B. G. J. Upton, J. E. Thomas
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1980
• Subjects: Greenland; Narssaq
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1027.5979; http://petrology.oxfordjournals.org/content/21/1/167.full.pdf

The Younger Giant Dyke Complex consists of a set of massive coalescing dykes of Proterozoic age (c. 1170 Ma), resulting from intrusion of a suite of transitional olivine basaltic/hawaiitic magmas in a continental rift setting. The suite, compositionally related by low pressure (< 10 kb) olivine-plagioclase fractionation, is believed to have had a deeper level evolution dominated by pyroxene and possibly garnet fractionation. Slow cooling in situ of the interior parts of the dyke complex produced cumulitic suites. Those exposed range from gabbroic to syenitic; residual bodies of riebeckite granite and, very subordinate, feldspathoidal syenite were also generated. The basic magmas had notably low/O2 values, leading to delayed magnetite and clinopyroxene precipitation, relatively iron-rich differentiates and some residual liquids of pantelleritic composition. The basic magmas had high F/Cl values and are inferred to have had low H2O contents. They were also characterized by relatively high K/Rb and low 87Sr/**Sr values; these characteristics imply a mantle source with high F/Cl but depleted in Rb relative to K and Sr. Basaltic magmas responsible for (a) the preceding Older Giant Dyke Complex and (b) a suite of anorthositic xenoUths within the Younger Giant Dyke Complex, are inferred to have been derived from separate primary magma batches independent of those that yielded the Younger Giant Dyke Complex. The giant dykes are the highest-level representatives of a larger basic complex responsible for the extensive linear gravity 'high ' in the Tugtutoq-Narssaq area.