Larissa Colombo Carniel, Rommulo Vieira Conceição, Carlos Augusto S. Provenzano, Andrea Sander, Felipe Padilha Leitzke, Andrea Brum da Silva, Jasper Berndt, Stephan Klemme
{"title":"巴西南部alfeu - 1煌斑岩的矿物化学特征及其对冈瓦纳破裂时期南美板块地幔非均质性的贡献","authors":"Larissa Colombo Carniel, Rommulo Vieira Conceição, Carlos Augusto S. Provenzano, Andrea Sander, Felipe Padilha Leitzke, Andrea Brum da Silva, Jasper Berndt, Stephan Klemme","doi":"10.1590/2317-4889202320220092","DOIUrl":null,"url":null,"abstract":"The Alfeu-I lamproite is one of the few alkaline rock occurrences in the South of Brazil that represents the alkaline event related to the South Atlantic opening and the enormous magmatic activity that formed the Paraná basalts. Alfeu-I lamproite is a diatreme facies and exhibits an inequigranular texture with macrocrysts of mica, spinel, garnet, and ilmenite and microcrysts of mica, pyroxene, and rare olivine, all immersed in a groundmass of pyroxene, spinel, perovskite, rutile, ilmenite, and, more rarely, olivine. Major element compositions of Alfeu-I pyroxene, garnet, ilmenite, mica, and olivine were determined by electron microprobe analyses, and trace element concentrations of clinopyroxene, garnet, ilmenite, and mica were measured using laser-ablation inductively coupled plasma mass spectrometry techniques. Temperature, pressure, and oxygen fugacity (fO2) conditions during the crystallization of Alfeu-I lamproite were calculated with the geothermobarometers and olivine, spinel, garnet, and orthopyroxene. The resulting mean equilibrium temperature ranges from 1375°C at 4 GPa to 1395°C at 5 GPa, whereas the fO2 points to ΔFMQ = +2.4 (at 4 GPa) and ΔFMQ = +2.2 (at 5 GPa). Rb-Sr and Sm-Nd isotopic data together with the trace element concentrations of minerals suggest that melting of a mantle source enriched in incompatible elements and volatiles due to previous subduction events occurred during the Gondwana breakup around 125 Ma ago. Fluids that may have originated from subducting slabs in the old subduction zone are probably the cause of the high fO2 conditions in Alfeu-I lamproite.","PeriodicalId":9221,"journal":{"name":"Brazilian Journal of Geology","volume":"40 1","pages":"0"},"PeriodicalIF":1.3000,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Mineral chemistry from the Alfeu-I lamproite (Southern Brazil) and its contribution to understand the mantle heterogeneity under South American Plate during the Gondwana breakup\",\"authors\":\"Larissa Colombo Carniel, Rommulo Vieira Conceição, Carlos Augusto S. Provenzano, Andrea Sander, Felipe Padilha Leitzke, Andrea Brum da Silva, Jasper Berndt, Stephan Klemme\",\"doi\":\"10.1590/2317-4889202320220092\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"The Alfeu-I lamproite is one of the few alkaline rock occurrences in the South of Brazil that represents the alkaline event related to the South Atlantic opening and the enormous magmatic activity that formed the Paraná basalts. Alfeu-I lamproite is a diatreme facies and exhibits an inequigranular texture with macrocrysts of mica, spinel, garnet, and ilmenite and microcrysts of mica, pyroxene, and rare olivine, all immersed in a groundmass of pyroxene, spinel, perovskite, rutile, ilmenite, and, more rarely, olivine. Major element compositions of Alfeu-I pyroxene, garnet, ilmenite, mica, and olivine were determined by electron microprobe analyses, and trace element concentrations of clinopyroxene, garnet, ilmenite, and mica were measured using laser-ablation inductively coupled plasma mass spectrometry techniques. Temperature, pressure, and oxygen fugacity (fO2) conditions during the crystallization of Alfeu-I lamproite were calculated with the geothermobarometers and olivine, spinel, garnet, and orthopyroxene. The resulting mean equilibrium temperature ranges from 1375°C at 4 GPa to 1395°C at 5 GPa, whereas the fO2 points to ΔFMQ = +2.4 (at 4 GPa) and ΔFMQ = +2.2 (at 5 GPa). Rb-Sr and Sm-Nd isotopic data together with the trace element concentrations of minerals suggest that melting of a mantle source enriched in incompatible elements and volatiles due to previous subduction events occurred during the Gondwana breakup around 125 Ma ago. 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Mineral chemistry from the Alfeu-I lamproite (Southern Brazil) and its contribution to understand the mantle heterogeneity under South American Plate during the Gondwana breakup
The Alfeu-I lamproite is one of the few alkaline rock occurrences in the South of Brazil that represents the alkaline event related to the South Atlantic opening and the enormous magmatic activity that formed the Paraná basalts. Alfeu-I lamproite is a diatreme facies and exhibits an inequigranular texture with macrocrysts of mica, spinel, garnet, and ilmenite and microcrysts of mica, pyroxene, and rare olivine, all immersed in a groundmass of pyroxene, spinel, perovskite, rutile, ilmenite, and, more rarely, olivine. Major element compositions of Alfeu-I pyroxene, garnet, ilmenite, mica, and olivine were determined by electron microprobe analyses, and trace element concentrations of clinopyroxene, garnet, ilmenite, and mica were measured using laser-ablation inductively coupled plasma mass spectrometry techniques. Temperature, pressure, and oxygen fugacity (fO2) conditions during the crystallization of Alfeu-I lamproite were calculated with the geothermobarometers and olivine, spinel, garnet, and orthopyroxene. The resulting mean equilibrium temperature ranges from 1375°C at 4 GPa to 1395°C at 5 GPa, whereas the fO2 points to ΔFMQ = +2.4 (at 4 GPa) and ΔFMQ = +2.2 (at 5 GPa). Rb-Sr and Sm-Nd isotopic data together with the trace element concentrations of minerals suggest that melting of a mantle source enriched in incompatible elements and volatiles due to previous subduction events occurred during the Gondwana breakup around 125 Ma ago. Fluids that may have originated from subducting slabs in the old subduction zone are probably the cause of the high fO2 conditions in Alfeu-I lamproite.
期刊介绍:
The Brazilian Journal of Geology (BJG) is a quarterly journal published by the Brazilian Geological Society with an electronic open access version that provides an in-ternacional medium for the publication of original scientific work of broad interest concerned with all aspects of the earth sciences in Brazil, South America, and Antarctica, in-cluding oceanic regions adjacent to these regions. The BJG publishes papers with a regional appeal and more than local significance in the fields of mineralogy, petrology, geochemistry, paleontology, sedimentology, stratigraphy, structural geology, tectonics, neotectonics, geophysics applied to geology, volcanology, metallogeny and mineral deposits, marine geology, glaciology, paleoclimatology, geochronology, biostratigraphy, engineering geology, hydrogeology, geological hazards and remote sensing, providing a niche for interdisciplinary work on regional geology and Earth history.
The BJG publishes articles (including review articles), rapid communications, articles with accelerated review processes, editorials, and discussions (brief, objective and concise comments on recent papers published in BJG with replies by authors).
Manuscripts must be written in English. Companion papers will not be accepted.