U. Mass Lowell |
Prof. Nelson Eby | Department of Environmental, Earth, & Atmospheric Sciences |
| Mid-Proterozoic Rapakivi Granite Association of the Fennoscandian Shield, Finland (2007) |
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A two day field trip led by Tapani Rämö to outcrops of Mid-Proterozoic rapakivi granite and associated lithologies in the Finnish portion of the Wiborg batholith. Most of these outcrops were visited during the first day of the EUROGRANITES 2005 field trip. Detailed descriptions of the various stops and the general geology of the region can be found in Rämö et al. (2005) EUROGRANITES 2005-Proterozoic and Archean Granites and Related Rocks of the Finnish Precambrian. Eurogranites 2005 Field Conference, September 11-17, 2005. Publication of the Department of Geology A1, 130 p. Stop 1 - Topaz-bearing alkali feldspar granite and associated marginal pegmatite. Stop 2 - Wiborgite at Summa, Vehkalahti, south-central part of the Wiborg batholith Stop 3 - Pyterlite at Virolahti, south-central part of the Wiborg batholith Stop 4 - Anorthositic raft in wiborgite at Ylijärvi, Ylämaa, east-central part of the Wiborg batholith |
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Top - Geology and major structural units of the Fennoscandian shield. Right - Petrological map of the Finnish part of the Wiborg rapakivi area. Field trip stops are shown on the map. Figures are from Rämö et al. (2005). |
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| Porphyritic central granite, Kymi stock (Stop 1). | Porphyritic central granite, Kymi stock (Stop 1). | Equigranular marginal granite (bottom) and porphyritic central granite. The central porphyritic granite seems to be slightly older than the marginal granite (stop 1). | Camp at pegmatite mine. Antero Karjalainen, Brent Elliot, Kari Parviainen, Tampani Rämö, and Paula Kosunen. |
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| Sausages on the fire. | Cooking sausages the "Finnish way". | Pegmatite between the Kymi stock and the surrounding wiborgite and pyterlite. Dendritic biotite, K-feldspar, quartz, and topaz (Stop 1). | Close-up of pegmatite. Quartz and topaz (Stop 1). |
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| Wiborgite (rapakivi granite proper). The rock is loaded with 1 to 10 cm rounded alkali feldspar megacrysts, most with an oligoclase rim (Stop 2). | Close-up of Wiborgite showing mantle alkali feldspar megacrysts (Stop 2). | Wiborgite (Stop 2). | Spectrolite (Stop 4). |
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| Close-up of spectrolite (Stop 4). |
Megacrystic anorthosite xenoliths in a 1633-Ma leucogabbronorite
raft, east-central Wiborg batholith.
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Glacial grooves and striations in bedrock (Stop 4). | Granite pegmatite dike cutting coarse-grained leucogabbronorite (Stop 4). |
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| Mixed rock. Labradorite megacrysts in granitic matrix. | Close-up view of labradorite megacrysts in granitic matrix. | Dimension stone quarry (Haikanvuori pyterlite: from a nearby quarry). In the 19th century stone from this quarry was shipped to St. Petersburg. Carmen Red is the commercial name for pyterlite (Stop 3). | Pyterlite. Texturally similar to wiborgite except only some of the alkali feldspar are mantled by oligoclase (Stop 3). |
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| Close-up view of pyterlite. Note that only a few of the feldspar megacrysts are rimmed by oligoclase (Stop 3). | Close-up view of pyterlite (Stop 3). | ||
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