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  Interaction between basaltic melts and their wallrock in dykes and sills in Åland, southwestern Finland
Titel: Interaction between basaltic melts and their wallrock in dykes and sills in Åland, southwestern Finland
Auteur: Eklund, Olav
Lindberg, Bo
Verschenen in: GFF
Paginering: Jaargang 114 (1992) nr. 1 pagina's 93-102
Jaar: 1992-03-10
Inhoud: Middle Proterozoic dykes and sills of mostly continental tholeiitic composition occur along the contact between the Middle Proterozoic Åland rapakivi batholith and the Early Proterozoic Svecofennian country rock of southwestern Finland. These dykes and sills have interacted with their granitic wallrocks in different ways. The dykes in two studied localities formed breccias in which the xenoliths are partly disaggregated due to melting along the grain contacts. The xenoliths are also depleted in feldspars and relatively enriched in quartz as compared with the wallrock, and are mantled by thin amphibole rims. In contrast, a basaltic sill melted the wallrock and mixing occurred between the basaltic magma and the palingenic granitic melts. This resulted in the formation of porphyry-like hybrid rocks and mafic enclaves. The difference between the dykes and the sill as regards interaction with their wallrocks shows that the heat flow from the sill was high enough to produce local palingenic melts, whereas only small portions of such melts were produced as xenoliths disaggregated in the mafic dykes. Mantled rock fragments, mafic and hybrid enclaves, labradorite megacrysts and inclusions of quartz-feldspar rocks are abundant components in the heterogeneous 'mafic melt—crustal rock' hybrids. These features occur also in the Middle Proterozoic quartz-feldspar porphyries of the Åland Rapakivi batholith, which outcrop in the vicinity of the study area. The quartz-feldspar porphyries are therefore suggested to have the same origin as the hybrid rocks in the study area: palingenic granitic magmas were generated by frequent intrusions of mafic melts into the crust, with subsequent magma mixing between the palingenic magmas and the basaltic melts.
Uitgever: Taylor & Francis
Bronbestand: Elektronische Wetenschappelijke Tijdschriften

                             Details van artikel 10 van 23 gevonden artikelen
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