Geochemical Constraints on the Origin of the Late Archean Skjoldungen Alkaline Igneous Province, SE Greenland
The present work reports the first broad geochemical investigation of the recently discovered late Archean (2700 Ma) Skjoldungen alkaline igneous province (SAP) in southeast Greenland. The rocks studied range in composition from ultramafic to felsic and comprise pyroxenites, hornblendites, hornblend...
| Published in: | Journal of Petrology |
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| Main Authors: | , , , |
| Format: | Text |
| Language: | English |
| Published: |
Oxford University Press
1995
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| Subjects: | |
| Online Access: | http://petrology.oxfordjournals.org/cgi/content/short/36/2/515 https://doi.org/10.1093/petrology/36.2.515 |
| Summary: | The present work reports the first broad geochemical investigation of the recently discovered late Archean (2700 Ma) Skjoldungen alkaline igneous province (SAP) in southeast Greenland. The rocks studied range in composition from ultramafic to felsic and comprise pyroxenites, hornblendites, hornblende norites and diorites, monzonites, syenites, and nephelinitic rocks and carbonatites. Various lithologic units from the host Archean gneissic basement are also investigated. The magmatic rocks show remarkably coherent major element, trace element, rare earth element (REE), and Sr and Nd isotope systematics, suggesting a petrogenetic relationship. The most important geochemical features are high normative proportions of nepheline, forsterite and albite, low TiO 2 (<1�5 wt %) and moderate FeO (total) (<12 wt %) contents, enrichments in large ion lithophile elements (LILE) and light rare earth elements both absolute and relative to high field strength elements (HFSE) that display large negative anomalies, and generally low to moderate abundances of compatible elements. Field relations and REE and compatible element systematics among Skjoldungen rocks suggest that mafic and ultramafic hornblende-rich samples may represent cumulate lithologies of the regional parental magma. On the basis of mineral data, this is deduced to have had mg -number of 0�64, shoshonitic affinities (K 2 O∼1�5 wt %), been close to silica saturation and volatile rich. Major element, trace element and REE systematics further suggest that felsic intrusions are related to the mafic regional parental magma through extensive olivine, hypersthene and hornblende fractionation. Lack of correlation between La/Yb and other critical trace and REE ratios indicates that apatite, zircon and titaniferous minerals were not important cumulus phases at advanced stages of evolution. The measured Sm–Nd whole-rock isochron age is 2716 �23 Ma (2σ error) [mean square of weighted deviates (MSWD) = 1�4], whereas linear regression of the Sr isotope data yields an age ... |
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