Investigation of the Fe-Ti-HFSE enrichment in the Raftsund intrusion, Årsteinen, Lofoten-Vesterålen archipelago, Northern Norway

• Main Author: Maute, Donald
• Other Authors: Barnes, Calvin G., Coint, Nolwenn, Hetherington, Callum J.
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: Iron; Titanium; Oxides; High field strength elements; HFSE; Raftsund intrusion; Årsteinen; Zircon; Apatite; Clinopyroxene; Olivine; Magnetite; Ilmenite; Norway; Lofoten; Vesterålen; Mineral accumulation; Liquid immiscibility; Hydrothermal enrichment; Residual liquids; LA-ICPMS; EPMA; XRF; Northern Norway
• Online Access: https://hdl.handle.net/2346/85033

Iron+Ti±P±HFSE enriched rocks are found in a variety of localities worldwide, including some that are temporally and spatially related to Proterozoic AMCG (Anorthosite-Mangerite-Charnokite-Granite) suites. The origin of these enriched rocks has been widely debated and petrogenetic models such as liquid-liquid immiscibility, fractional crystallization and mineral accumulation, hydrothermal fluid enrichment, and residual liquids concentrated by filter pressing have all been proposed to explain occurrences of these rocks associated with AMCG suites. This locality is particularly distinct for two reasons, 1) abundant and large (>2.5mm) zircon, which contrasts with many Fe+Ti±P±HFSE enriched rocks where apatite is the main REE carrier 2) the mineralized zones are located as thin veins (up to 3 cm wide) located at the contact between two rock-types – an equigranular olivine-clinopyroxene-monzonite and a porphyritic orthopyroxene-clinopyroxene monzonite. Field relationships down to the microscale suggest the mineralization is related to the equigranular monzonite - the mineralized zones show planar contacts with the porphyritic monzonite, while it protrudes in between mesoperthitic feldspar grains of the equigranular monzonite. The mineralized zones likely developed from the equigranular monzonite, while the porphyritic monzonite served as a boundary where the mineralization was concentrated. Mg# and Fo% in clinopyroxene and olivine, respectively, are highest in phases of the mineralization (35.0 and 6.17) compared to the equigranular monzonite (22.2 and 2.50) and are can be suggested to be early-forming. Magnetite in the mineralization also has relatively elevated V and Al, which are known to behave as fractionation indices, and indicates earlier forming magnetite compared to magnetite in the equigranular monzonite. Strontium content and Eu/Eu* of apatite in the mineralization indicate a contradicting relationship – having more evolved signature compared to apatite of both the equigranular monzonite indicating ...