The Lages diatremes: mineral composition and petrological implications
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| Format: | Artículo científico |
| Language: | en |
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Academia Brasileira de Ciências
2007
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| author | Giancarlo Barabino |
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| contents | The Lages diatremes: mineral composition and petrological implications Giancarlo Barabino Celso de Barros Gomes Gianbosco Traversa Multidisciplinaria (Ciencias Naturales y Exactas) Brazil mantle megacryst metasomatism clinopyroxene Chemical data of heavy minerals from Lages diatremes in southern Brazil have been studied with the aim of characterizingthe sample source(s). Three groups of minerals are recognized: I) aluminian-chromian pyroxene, pyrope garnetand chromian spinel, which represent disaggregated fragments of spinel, spinel+garnet and garnet facies peridotite;II) low-Cr aluminian pyroxene that occurs as megacrysts are high pressure phases (7-12 kb) being crystallized froman alkaline-like evolving magma; III) low-Cr aluminian diopside of crustal origin. Evidence of carbonatitic crypticmetasomatic enrichment is shown by clinopyroxenes of Groups I and II. The data do not support a kimberlitic affinityas it has been suggested for the diatremes. Rather, they are interpreted as vents related to the alkaline magmatismaffecting the area in Late Cretaceous. The alkaline parental magma of the pyroxene megacrysts was generated from ametasomatized mantle at garnet facies that incorporated fragments of the surrounding still fertile mantle. Presumablyat spinel-facies level the magma began to fractionate the megacrysts, whose crystallization proceeded over a largerange of falling pressure and temperature. The chemical similarities between Group III clinopyroxenes and those fromthe differentiated lithotypes indicate that the magma carried this mineral phase on its evolution, at crustal conditions,towards a more evolved alkaline composition. Still, a non-cognate origin for the Group III clinopyroxenes cannot bediscarded. 2007 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32779310 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.3 Vol.79 |
| format | Artículo científico |
| id | redalyc_32779310 |
| institution | Redalyc |
| language | en |
| publishDate | 2007 |
| publisher | Academia Brasileira de Ciências |
| spellingShingle | The Lages diatremes: mineral composition and petrological implications Giancarlo Barabino Multidisciplinaria (Ciencias Naturales y Exactas) Brazil mantle megacryst metasomatism clinopyroxene The Lages diatremes: mineral composition and petrological implications Giancarlo Barabino Celso de Barros Gomes Gianbosco Traversa Multidisciplinaria (Ciencias Naturales y Exactas) Brazil mantle megacryst metasomatism clinopyroxene Chemical data of heavy minerals from Lages diatremes in southern Brazil have been studied with the aim of characterizingthe sample source(s). Three groups of minerals are recognized: I) aluminian-chromian pyroxene, pyrope garnetand chromian spinel, which represent disaggregated fragments of spinel, spinel+garnet and garnet facies peridotite;II) low-Cr aluminian pyroxene that occurs as megacrysts are high pressure phases (7-12 kb) being crystallized froman alkaline-like evolving magma; III) low-Cr aluminian diopside of crustal origin. Evidence of carbonatitic crypticmetasomatic enrichment is shown by clinopyroxenes of Groups I and II. The data do not support a kimberlitic affinityas it has been suggested for the diatremes. Rather, they are interpreted as vents related to the alkaline magmatismaffecting the area in Late Cretaceous. The alkaline parental magma of the pyroxene megacrysts was generated from ametasomatized mantle at garnet facies that incorporated fragments of the surrounding still fertile mantle. Presumablyat spinel-facies level the magma began to fractionate the megacrysts, whose crystallization proceeded over a largerange of falling pressure and temperature. The chemical similarities between Group III clinopyroxenes and those fromthe differentiated lithotypes indicate that the magma carried this mineral phase on its evolution, at crustal conditions,towards a more evolved alkaline composition. Still, a non-cognate origin for the Group III clinopyroxenes cannot bediscarded. 2007 artículo científico 0001-3765 https://www.redalyc.org/articulo.oa?id=32779310 en http://www.redalyc.org/revista.oa?id=327 Anais da Academia Brasileira de Ciências application/pdf Academia Brasileira de Ciências Anais da Academia Brasileira de Ciências (Brasil) Num.3 Vol.79 |
| title | The Lages diatremes: mineral composition and petrological implications |
| topic | Multidisciplinaria (Ciencias Naturales y Exactas) Brazil mantle megacryst metasomatism clinopyroxene |
| url | https://www.redalyc.org/articulo.oa?id=32779310 |