Browsing by Author "Tainio, Jasper"

The studied appinite intrusions are situated in Central Lapland, within the municipality of Rovaniemi. On a bedrock map the Lehmikari and Äijävaara appinite intrusions are situated in the western parts of the Central Lapland Granitoid Complex, whereas the Vanttaus appinite intrusion is located in the eastern part of the Peräpohja Schist Belt. Geochemical assay data from drill core and field samples, used in this study, were originally requested by the Geological Survey of Finland and produced by Labtium Oy. Analytical methods used in assaying major element oxides and trace elements include XRF, ICP-MS, ICP-OES and ICP-AES. Polished thin sections used in petrographic examinations were produced by the Geological Survey of Finland. Granites that are found in the study area are closely related in space and time with the postorogenic Central Lapland appinite intrusions (1.79 Ga) but do not show petrogenetic affinities with them. However, mingling and mixing relationships are common, and can be observed in the field, drill core samples and geochemistry. According to their mode, Lehmikari and Äijävaara appinitic rocks include diorite and quartz diorite, whereas the Vanttaus appinite is more heterogenous. Based on petrography and geochemistry, four subgroups are recognized within the Vanttaus intrusion: 1) appinitic rocks (by mode: diorite, quartz diorite and quartz monzodiorite) 2) acidic appinites (SiO2: 62.7–65.8 %) 3) syenites and 4) Ba-Sr-granites (Ba: 1360–3240 ppm, Sr: 399–766). Rock forming minerals in all three intrusions include Na-rich plagioclase, hornblende, biotite and quartz (appinitic rocks from Vanttaus include K-feldspar as well). Hydrothermal alteration is common in the studied appinites and so is the abundance of hydrous minerals (hornblende and biotite), although quantities vary between the intrusions. The Vanttaus, Lehmikari and Äijävaara appinites show the typical geochemical features of appinitic rocks. These include high Na2O + K2O, P2O5, Ba, Sr, Zr and LREE as well as Na2O / K2O > 1. In contrast to 'type appinites' from western and northern Scotland, tholeiitic parent magmas of the studied appinites have developed further along the 'Fenner trend', producing more Fe-, Ti- and V-rich appinites, which are depleted in MgO, Ni and Cr. Appinites from Vanttaus are richer in K2O and REE compared to appinites from Lehmikari and Äijävaara. On the basis of several different variation diagrams, AFM- and KFM-ternary diagrams and REEN-distribution, the Vanttaus Ba-Sr-granites are considered to belong to the Vanttaus appinite group.