Geochemistry and mineralogy of saprolite in Finnish Lapland |
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| Institution: | 1. Yonsei University, Republic of Korea;2. Korea Institute of Construction Technology, Republic of Korea;1. Department of Ecosystem Science and Management, College of Agriculture and Natural Resources, University of Wyoming, Laramie, WY 82071, USA;2. Department of Biological Sciences, Boise State University, Boise, ID 83725, USA;1. Utah Division of Wildlife Resources, Great Basin Research Center, Ephraim, UT 84627, USA;2. US Department of Agriculture Forest Service, Rocky Mountain Research Station, Shrub Sciences Laboratory, Provo, UT 84606, USA;3. Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84604, USA;1. Plant Ecologist, US Department of Agriculture–Agricultural Research Service, Exotic and Invasive Weeds Research Unit, Reno, NV 89512, USA;2. Senior Research Scientist, US Department of Agriculture–Agricultural Research Service, Exotic and Invasive Weeds Research Unit, Reno, NV 89512, USA;3. Graduate Student, Environmental Science and Natural Resource Management, University of Nevada, Reno, Reno, NV 89557, USA |
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| Abstract: | An ancient saprolite has developed on the Palaeoproterozoic granulite, granite gneiss and amphibolite bedrock of the Vuotso–Tankavaara area of central Finnish Lapland. The present day climatic regime in Finnish Lapland lies within the northern boreal zone and so the saprolite there can be regarded as fossil. Cores of saprolite were collected from 4 sections (42 samples) and analyzed chemically and mineralogically. In the study area, progressive weathering of the rocks has been marked by gradual enrichment in Al, Fe and Ti; and depletion of Na, K and Ca. The higher concentration of Fe(III) and water and reduced Na and Ca in weathered bedrock in the 4 sections are indicative of oxidation, hydration and leaching processes involved during weathering. The primary minerals in the saprolite are plagioclase feldspar, K-feldspar, quartz, garnet (almandine) and hornblende; the common secondary minerals are kaolinite, halloysite, and vermiculite in addition to minor amounts of sericite. Intense weathering is indicated by: (1) the presence of kaolinite and halloysite in 4 sections of different bedrock types, and (2) the comparatively lower SiO2/Al2O3 (wt.%) ratio (2.30) of weathered granulites (3 sections) as compared to fresh granulite (4.33) and that of weathered amphibolite (2.68) as compared to fresh amphibolite (3.56). In general, kaolinite and halloysite have formed through the weathering of feldspars, garnet, and biotite. Vermiculite is the most probable alteration product of biotite. The formation of kaolinite and halloysite in Finnish Lapland indicates wetter and warmer climatic conditions during the time of their formation than at present. The possible time for formation of the saprolite is early Cretaceous–early Tertiary into Middle Miocene. |
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