Fenitisation associated with alkaline-silicate complexes. Implications for HFSE mobility in late-stage fluids, Gardar Rift, SW Greenland

Alkali metasomatism associated with carbonatitic-alkaline magmatism (or fenitisation) is of interest for our understanding of chemical behaviour of economically important high-field-strength (HFSE) and rare-earth (REE) elements during late-stage magmatic-hydrothermal activity. In this project, we ex...

Full description

Bibliographic Details
Main Authors: Sokół, Krzysztof, Finch, Adrian Anthony, Hutchison, William, Cloutier, Jonathan, Humphreys, Madeleine C. S.
Format: Conference Object
Language:English
Published: 2019
Subjects:
Online Access:https://risweb.st-andrews.ac.uk/portal/en/researchoutput/fenitisation-associated-with-alkalinesilicate-complexes-implications-for-hfse-mobility-in-latestage-fluids-gardar-rift-sw-greenland(bb31bca1-cbbb-4515-8546-378fc61c7b68).html
https://www.dropbox.com/s/h4ytqkelp0tu7om/eVolume%204.pdf?dl=0
Description
Summary:Alkali metasomatism associated with carbonatitic-alkaline magmatism (or fenitisation) is of interest for our understanding of chemical behaviour of economically important high-field-strength (HFSE) and rare-earth (REE) elements during late-stage magmatic-hydrothermal activity. In this project, we explore the expression of alteration and the physico-chemical factors controlling fenitisation across the Proterozoic Gardar Province of Southern Greenland. We present our findings of bulk-rock (XRF/ICP-AES) and microbeam (BSE-SEM-EDAX/EPMA) analyses. Our main case study, the Illerfissalik centre, comprises a series of nested syenitic intrusions. Fenites are exposed at its western margin, where a feldspar-poor Eriksfjord Formation quartz arenite protolith experienced intense metasomatism and deformation. Detailed petrography demonstrates interstitial K-feldspar (commonly perthitic), mafic minerals including pyroxene or Na-amphibole, and titanite (often LREE-bearing) in the proximal high-grade fenite zone. The absence of feldspar in unaltered arenite (<5% mode further than 1.5 km distance from the contact zone) suggests that K-feldspar was introduced by early-stage fenitisation, along with the relatively Na-poor pyroxene. The presence of HFSE-rich phases i.e. Sr-chevkinite also attests to variable mobility of numerous alkali, alkali-earth metals and HFSE in fenitising fluids. Bulk-rock geochemical trends away from the contact are also presented. Further work including isotope systematics will constrain the geochemistry of fenitising fluids.