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(Reference retrieved automatically from SciELO through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

The Lages diatremes: mineral composition and petrological implications

Full text
Author(s):
Giancarlo Barabino [1] ; Celso B. Gomes [2] ; Gianbosco Traversa
Total Authors: 3
Affiliation:
[1] Università di Roma La Sapienza. Dipartimento di Scienze della Terra - Itália
[2] Universidade de São Paulo. Instituto de Geociências - Brasil
Total Affiliations: 3
Document type: Journal article
Source: Anais da Academia Brasileira de Ciências; v. 79, n. 3, p. 473-501, 2007-09-00.
Abstract

Chemical data of heavy minerals from Lages diatremes in southern Brazil have been studied with the aim of characterizing the sample source(s). Three groups of minerals are recognized: I) aluminian-chromian pyroxene, pyrope garnet and 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 from an alkaline-like evolving magma; III) low-Cr aluminian diopside of crustal origin. Evidence of carbonatitic cryptic metasomatic enrichment is shown by clinopyroxenes of Groups I and II. The data do not support a kimberlitic affinity as it has been suggested for the diatremes. Rather, they are interpreted as vents related to the alkaline magmatism affecting the area in Late Cretaceous. The alkaline parental magma of the pyroxene megacrysts was generated from a metasomatized mantle at garnet facies that incorporated fragments of the surrounding still fertile mantle. Presumably at spinel-facies level the magma began to fractionate the megacrysts, whose crystallization proceeded over a large range of falling pressure and temperature. The chemical similarities between Group III clinopyroxenes and those from the 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 be discarded. (AU)

FAPESP's process: 01/10714-3 - The alkaline magmatism evolution in the South American Platform: petrogenetic and geodynamical implications
Grantee:Celso de Barros Gomes
Support Opportunities: Research Projects - Thematic Grants