Staff directory
Jean-Paul Liégeois
Earth Sciences
Geodynamics and mineral resources
Geodynamics and mineral resources
Publication details
Bogaerts, M, Scaillet, B, Liégeois, J.P. & Vander Auwera, J. 2003. ‘Petrology and geochemistry of the Lyngdal granodiorite (Southern Norway) and the role of fractional crystallization in the genesis of Proterozoic ferro-potassic A-type granites’. Precambrian Research 124: 149-184. Amsterdam : Elsevier. (PR).
Article in a scientific Journal / Article in a Journal
Abstract
In Southwestern Norway, the Sveconorwegian orogenic thickening (1024-970 Ma) is followed by an important post-collisional magmatism (950-930 Ma), divided . in two suites (Vander Auwera et al., this issue): the AMC suite (Anorthosite-Mangerite-Charnockite) and the HBG suite (Hornblende/Biotite Granitoids). The HBG suite displays a continuous trend from gabbronorites to granites.
This paper presents the petrography and geochemistry (major and trace elements, Sr-Nd isotopes) of the Lyngdal granodiorite and associated massifs (Tranevåg and Red Granite massifs), which belong to the HBG suite, although being very close to the anorthosite massifs. Mafic microgranular enclaves (MME), resulting from magma mingling, can be abundant and will be demonstrated to correspond to the parent magma of the studied plutons. The latter plutons are subalkaline, metaluminous A-type granitoids with high FeOt/(FeOt+MgO) ratio and K2O content, forming a ferro-potassic A-type continuous trend from quartz monzodiorite to granite (~ 56 to 72 wt% SiO2). In Harker diagrams, the Lyngdal-Tranevåg plutons share the Proterozoic rapakivi granites trend that they extend to lower SiO2 content.. Major and trace element modelling, as well as Sr-Nd isotopes, show that fractional crystallization - without assimilation - is the differentiation process for Lyngdal-Tranevåg. Fractionating minerals are clinopyroxene, hornblende, plagioclase, oxides, biotite, apatite, zircon and allanite. The Red Granite (71-75 wt% SiO2) does not belong to this trend, probably due to a different initial magma composition.
This study shows that ferro-potassic A-type granitoidscan be derived by fractional crystallization from mafic magmas.
Keywords : Norway, Sveconorwegian, post-collisional, A-type, granitoids, liquid line of descent