Geology and U-Pb geochronology of rocks of the Eokuk Uplift: a pre-2.8 Ga basement inlier in the northwestern Slave Province, Nunavut, Canada
Rocks of the Eokuk Uplift have been mapped in detail along the coast of Coronation Gulf and 10 key units have been dated by U-Pb analysis of zircon, monazite, and titanite. The combined data indicate that this inlier of the Slave Province has a >3.2 Ga crustal component, evidence of a granuli...
Published in: | Canadian Journal of Earth Sciences |
---|---|
Main Authors: | , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Canadian Science Publishing
1999
|
Subjects: | |
Online Access: | http://dx.doi.org/10.1139/e98-094 http://www.nrcresearchpress.com/doi/pdf/10.1139/e98-094 |
Summary: | Rocks of the Eokuk Uplift have been mapped in detail along the coast of Coronation Gulf and 10 key units have been dated by U-Pb analysis of zircon, monazite, and titanite. The combined data indicate that this inlier of the Slave Province has a >3.2 Ga crustal component, evidence of a granulite-grade orogenic event predating 2.8 Ga and a lack of evidence for any significant orogenic activity corresponding to the 2.7-2.6 Ga events common in the rest of the Slave Province. The oldest rocks in the study area are a succession of granitoid and supracrustal gneisses that have been metamorphosed to amphibolite to granulite facies. From field relationships, the oldest rock is a granodiorite to tonalite orthogneiss, with a zircon crystallization age of 3254 +13 -6 Ma. A granite gneiss, which may be a small felsic intrusion or an anatectic melt of the tonalite gneiss, yields a zircon age of 3216 +14 -13 Ma. A K-feldspar megacrystic monzogranite gneiss contains old, discordant, possibly inherited zircons with 207 Pb/ 206 Pb ages ranging from 3103 to 3039 Ma, together with coexisting 2879 ± 3 Ma zircon and monazite. These high-grade gneisses are intruded by two megacrystic granite plutons, dated at 2887 ± 2 and 2881 +4 -3 Ma. The absence of extensive recrystallization and complex structures in these plutons indicates that this igneous event postdated the high-grade metamorphism. An amphibolite-grade synplutonic metamorphic event is dated at ~2880 Ma by new monazite in the older gneiss units. A series of variably deformed mafic to felsic dykes and pegmatites intrude both the granites and gneisses and constrain the end of penetrative deformation in the area. Of these, a boudinaged diorite dyke, with a strong internal foliation parallel to the regional fabric, is dated at 2877 ± 3 Ma. A younger granodiorite dyke that crosscuts the regional fabric at a high angle and has only a weak internal foliation yields an age of 2864 +3 -9 Ma. An undeformed syenogranite pegmatite, which represents a suite that intrudes all other ... |
---|