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Geology, Petrography and Petrology ofthe Rapakivi Granites; The Rapakivi Granites of Finland

Year 2004, Volume: 28 Issue: 2, 39 - 51, 01.11.2004

Abstract

The granites showing textures of plagioclase-mantled alkali feldspar megacryst are known as "Rapakivi Granites". Rapakivi granites are generally Proterozoic 1.8 to 1.0 Ga in age, and Southern Finland is the type area ofthe rapakivi granites although they are preseni in Ukraine the Baltic countries, South Greenland, mid-continental and western USA, Venezuela, Brazil, Botswana and several other Precambrian shield areas. Rapakivi granites are shallow level, multi-phctsc batholiths and stocks, having less than 10 km thick horizontal sheet-like bodies. The magmatic association of rapakivi granites is bimodal. The mafic members are represented by diabase dykes, gabbroids and anorthosites and thefelsic members by A-type granites, syenites and ryholites. The oldest rapakivi granites are generally hornblende-biotite granites whereas the youngest ones are topaz-bearing alkali feldspar granites. in these rocks, plagioclase andesine or oligoclase , orthoclase, microcline, quartz, hornblende and biotite are present as well as accessory fluorite, anatase, zircon andilmenite. The rapakivi granites are generally metaluminous or marginally peraluminous rocks, and have high Fe/ Fe+Mg . They show chemical characteristics of within-plate granites and A-type granites, and have high K andNa contents. Furthermore, they have higher Si, K, FRb, Ga, Zr, Hf, Th. U, Zn and REE contents andK/Na, Ga/Al, Fe/Mg ratios, andlower Ca, Mg, Al, P and Sr abundances than granitte rocks in general. Theformation of rapakivi granites of Finland can best be interpreted by the mafic under-plate model. Mantle-derived mafic magmas intruded at the mantle-crust boundary and into lower crust, and caused extensive partial melting ofthe deep crust, thus forming the rapakivi granites. The tectonic settings, bimodal magmatic association, geochemistry and isotope geology of the rapakivi granites can best be explained by mafic underplating, but the reasonfor the mantle melting remains largely open.

References

  • M İ, M„ Andersson, U.B., Landqvist, T. ve Sundblad, K. (Eds.), 1997. Rapakivi granites and related rocks in central Sweden. Sverige s Geologisk a Undersökning series Ca 87,99p.
  • Ahi, M., Sundblad, K. ve Schöberg, H., 1999. Geology, geochemistry, age and geotectonic evolution of the Dala granitoids, central Sweden. Precambrian Research, 95,147-166.
  • Amelin, Y., Beljaev, A., Larin, A., Neymark, L. ve Stepanov, K. 1991. Salmi batholith and Pitkaranta ore field in Soviet Karelia. 1GCP 315 Symposium rapakivi granites and related rocks, Excursion Guide. Geological Survey of Filland Guide 33, 1-57.
  • Anderson, J.L., 1983. Proterozoic anorogenic granite plutonism of North America, in: Medaris, L.G., Jr, Byres, C.W., Mickelson, D.M., Shanks, W.C. (Eds.), Proterozoic Geology: Selected papers from an International Proterozoic Symposium. Geol. Soc. Am. Mem., 161, 133-154.
  • Bettencourt, J.S., Tosdal, R.W., Leite Jr., W.B. ve Payolla, B.L., 1999. Mesoproterozoic rapakivi granites of the Rondonia Tin Province, southwestern border of the Amazonia n craton , Brasil : 1. Reconnaissance U-Pb geochronology and regional implications. Precambrian Research, 95,41-67.
  • Bonin, B., 1996, A-type granite ring complexes: mantle origin throughcrustal filters and the anorthosite-rapakivi magmatism connection. in: Demaiffe, D., (Ed.), Petrology and Geochemistry of Magmatic Suites of Rocks in the Continental and Oceanic Crusts. A volume dedicatedto Professor Jean Michot, Üniversite Libre de BnmcllesRoyal Museum for Central Africa (Tervuren), 201-218.
  • Bowden, P., 1985. The geochemistry and mineralization of alkaline ring complexes in Africa (a review). Journal of African Earth Science, 3,17-39.
  • Bridgwater, D., Sutton, J. ve Watterson, J., 1974. Crustal down-folding associated with igneous aetivity. Tectonophysics, 21,57-77.
  • Brown, P.E., Dempster, T.J., Harrison, T.N. ve Hutton, D.H.W., 1992. The rapakivi granites of S. Greeland-crustal melting in response to extensional teetonics and magmatic underplating. Trans. R. Soc. Edinburgh Earth Sci., 83,173-178.
  • Calzia, J.P., Ramo, O.T., 1997. The granite of Kingston Peak: petrogenesis of a middle Miocene post-subduction granite in the southern Death Valley region, California. TerraNova 9, EUG9 Abstract, 458
  • Eklund, O., ve Shebanov, A.D., 1999. Origin of the rapakivi texture by sub-isothermal decompression. Precambrian Research, 95,129-146.
  • Eklund, O., Fröjdö, S. ve Lindberg, B., 1994. Magma nvbeing, the petrogenetic link between anorthositic suites and rapakivi granites, Aland, SW Finland . Mineralogy and Petrology, 50,3-19.
  • Emslie, R.F., 1978. Anorthosites, rapakivi granites, and Late Proterozoic rifting of North America. Precambrian Research, 7,61-69.
  • Frost, C.D. ve Frost, B.R., 1997. Reduced rapakivi-type granites: the tholeiite

Rapakivi Granitlerinin Jeolojisi, Petrografisi ve Petrolojisi; Finlandiya Rapakivi Granitleri

Year 2004, Volume: 28 Issue: 2, 39 - 51, 01.11.2004

Abstract

İri alkali feldispatm plajiyoklas tarafından çevrelenmesiyle oluşan dokuyu gösteren granitler "Rapakivi Granitleri" olarak adlandırılmaktadır. Çoğunlukla Proterozoyik 1.8-1.0 milyar yıl yaşlı olan rapakivi granitleri, Ukrayna, Baltık ülkeleri, güney Grönland, orta-kıtasal ve batı ABD, Venezüella, Brezilya, Bostwana ve diğer birçok Prekambriyen kalkanında bulunmakla birlikte Güney Finlandiya tip bölge olarak kabul edilmektedir. Rapakivi granitleri sığ seviye, çok fazlı batolitleri ve stokları şeklinde olup, 10 km'den daha az kalınlıkta yatay levhasal kütleler şeklindedir. Rapakivi granitlerinin magmatik birlikteliği bimodal olup mafık üyeler; diyabaz daykları, gabroyidler ve anortozitler; felsik üyeler ise A-tipi granitler, siyenitler ve riyolitlerdir. En yaşlı rapakivi granitleri genelde hornblend-biyotit granitlerden, daha genç olanlar ise topazlı alkali feldispat granitlerden oluşmaktadır. Plajiyoklas andezin veya oligoklas , ortoklas, mikroklin, kuvars, hornblend ve biyotit gibi ana minerallerin yanında flüorit, anataz, zirkon ve ilmenit aksesuar mineral olarak bulunur. Rapakivi granitler, genellikle metalümin veya kenar zonlarmda az derecede peralümin kayaçlar olup, yüksek Fe/ Fe+Mg oranına sahiptirler. Levha içi granitleri ve A-tipi granitlerinin kimyasal özelliklerini gösteren rapakivi granitleri yüksek K ve Na içermektedir. Ayrıca Si, K, F, Rb, Ga, Zr, Hf, Th, U, Zn ve NTE içerikleri ile K/Na, Ga/Al, Fe/Mg oranları granitik kayaçlardan daha yüksek, Ca, Mg, Al, P ve Sr içerikleri ise daha düşüktür. Finlandiya'daki rapakivi granitlerinin oluşumu mafık magmanın kıta kabuğu altına yerleşmesi underplating modeliyle açıklanmaktadır. Buna göre, mantodan türeyen mafık magmalar manto-kabuk sınırında alt kabuğa yerleşerek kabuğun yoğun bir şekilde kısmi ergimesine neden olarak rapakivi granitlerini oluşmaktadır. Rapakivi granitlerinin tektonik ortamları, bimodal magmatik birliktelikleri, jeokimya ve izotop bileşimleri mafık magmanın kıta kabuğu altına yerleşmesi modeli ile çok iyi açıklanabilmesine rağmen mantonun kısmi ergimesinin nedeni büyük ölçüde tartışmalıdır.

References

  • M İ, M„ Andersson, U.B., Landqvist, T. ve Sundblad, K. (Eds.), 1997. Rapakivi granites and related rocks in central Sweden. Sverige s Geologisk a Undersökning series Ca 87,99p.
  • Ahi, M., Sundblad, K. ve Schöberg, H., 1999. Geology, geochemistry, age and geotectonic evolution of the Dala granitoids, central Sweden. Precambrian Research, 95,147-166.
  • Amelin, Y., Beljaev, A., Larin, A., Neymark, L. ve Stepanov, K. 1991. Salmi batholith and Pitkaranta ore field in Soviet Karelia. 1GCP 315 Symposium rapakivi granites and related rocks, Excursion Guide. Geological Survey of Filland Guide 33, 1-57.
  • Anderson, J.L., 1983. Proterozoic anorogenic granite plutonism of North America, in: Medaris, L.G., Jr, Byres, C.W., Mickelson, D.M., Shanks, W.C. (Eds.), Proterozoic Geology: Selected papers from an International Proterozoic Symposium. Geol. Soc. Am. Mem., 161, 133-154.
  • Bettencourt, J.S., Tosdal, R.W., Leite Jr., W.B. ve Payolla, B.L., 1999. Mesoproterozoic rapakivi granites of the Rondonia Tin Province, southwestern border of the Amazonia n craton , Brasil : 1. Reconnaissance U-Pb geochronology and regional implications. Precambrian Research, 95,41-67.
  • Bonin, B., 1996, A-type granite ring complexes: mantle origin throughcrustal filters and the anorthosite-rapakivi magmatism connection. in: Demaiffe, D., (Ed.), Petrology and Geochemistry of Magmatic Suites of Rocks in the Continental and Oceanic Crusts. A volume dedicatedto Professor Jean Michot, Üniversite Libre de BnmcllesRoyal Museum for Central Africa (Tervuren), 201-218.
  • Bowden, P., 1985. The geochemistry and mineralization of alkaline ring complexes in Africa (a review). Journal of African Earth Science, 3,17-39.
  • Bridgwater, D., Sutton, J. ve Watterson, J., 1974. Crustal down-folding associated with igneous aetivity. Tectonophysics, 21,57-77.
  • Brown, P.E., Dempster, T.J., Harrison, T.N. ve Hutton, D.H.W., 1992. The rapakivi granites of S. Greeland-crustal melting in response to extensional teetonics and magmatic underplating. Trans. R. Soc. Edinburgh Earth Sci., 83,173-178.
  • Calzia, J.P., Ramo, O.T., 1997. The granite of Kingston Peak: petrogenesis of a middle Miocene post-subduction granite in the southern Death Valley region, California. TerraNova 9, EUG9 Abstract, 458
  • Eklund, O., ve Shebanov, A.D., 1999. Origin of the rapakivi texture by sub-isothermal decompression. Precambrian Research, 95,129-146.
  • Eklund, O., Fröjdö, S. ve Lindberg, B., 1994. Magma nvbeing, the petrogenetic link between anorthositic suites and rapakivi granites, Aland, SW Finland . Mineralogy and Petrology, 50,3-19.
  • Emslie, R.F., 1978. Anorthosites, rapakivi granites, and Late Proterozoic rifting of North America. Precambrian Research, 7,61-69.
  • Frost, C.D. ve Frost, B.R., 1997. Reduced rapakivi-type granites: the tholeiite
There are 14 citations in total.

Details

Primary Language Turkish
Journal Section Research Article
Authors

Mehmet Arslan This is me

Zafer Aslan This is me

Publication Date November 1, 2004
Published in Issue Year 2004 Volume: 28 Issue: 2

Cite

APA Arslan, M., & Aslan, Z. (2004). Rapakivi Granitlerinin Jeolojisi, Petrografisi ve Petrolojisi; Finlandiya Rapakivi Granitleri. Jeoloji Mühendisliği Dergisi, 28(2), 39-51.