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The Orivesi granite batholith, Southern Central Finland - characteristics and emplacement
oleh: O. Selonen, C. Ehlers
| Format: | Article |
|---|---|
| Diterbitkan: | Geological Society of Finland 1996-06-01 |
Deskripsi
The Orivesi granite batholith is situated in an E-W trending belt of granite intrusions along the southern margin of the Central Finland Granitoid Complex (CFGC). It consists of the dominant Orivesi granite and of two minor components: a coarse-grained quartz-rich porphyritic granite (the Särkijärvi granite) and an aplite granite. No associated mafic components are found. The Orivesi granite is light red to red, coarse-grained and porphyritic with a magmatic foliation. The porphyritic texture is formed by potassium feldspar phenocrysts, which are in general euhedral, but oval (and mantled) megacrysts occur. The granite is extracted as dimensional stone ("Cardinal Red"/"Crystal Rose") from the southwestern part of the batholith. Additional potential sites for dimension stone are identified in same part of the batholith. The Orivesi granite batholith has intruded along regional shear zones in the southern part of the CFGC. The intrusion was diapiric at least during the final emplacement, and produced the magmatic structures in the batholith. Regional deformation has affected the batholith only as semi-brittle movements along aplites and narrow shear bands. The magmatic foliation is concentric in relation to the margins of the batholith. The ductile structures in the host rocks are parallel to the long axis of the batholith and do not continue into its marginal parts. The Orivesi granite is intrusive against both the surrounding granodiorites and the mica schists and can be regarded as post-tectonic in relation to the ductile deformation in the host rocks. A NNW-SSE trending fault zone cuts the Orivesi granite batholith into two halves. The western half has been uplifted in relation to the eastern half producing different structural features in the batholith halves at the present level of erosion. A section representing a lower crustal level, the western half, consists of sparsely fractured Orivesi granite with well developed, steep, penetrative and concentric foliation. The upper parts of the batholith in the eastern half, on the contrary, are characterized by intrusions of late magmatic melts in the Orivesi granite: the Särkijärvi granite and the aplite sheets and dykes. The foliation in the Orivesi granite is poorly developed in the eastern half and the late fracturing on outcrop scale is dense. In consequence the quarries and potential sites of dimension stone are in the western half, where the Orivesi granite is as dimension stone material more homogeneous and sound.