Mineralogia e petrologia de xenólitos mantélicos das regiões de Ubatuba (SP) e Monte Carmelo (MG): evidências de fusão parcial e metassomatismo no manto superior do sudeste do Brasil

Abstract

Mineralogical and petrological studies were conducted in mantle xenoliths included in a kaersutite lamprophyre dyke from Ubatuba (SP) (Serra do Mar Igneous Province), and in the Limeira 1 Kimberlite (Monte Carmelo, MG; Alto Paranaíba Alkalic Province), using petrography and major and trace element geochemistry in minerals by electron microprobe and LA-ICPMS. The Ubatuba spinel lherzolites, with equilibrium temperatures ranging from 750 to 950°C, represent a fertlie mantle affected by variable but moderate depletion. Evidence of two types of mantle metasomatis were detected in different samples. Clinopyroxene crystals of the samples with evidence of stronger previous depletion (olivine and pyroxenes with higher Mg#, pyroxenes with lower Al and Na, few proportion of spinel) show enrichment with high LILE/HFSE, attributed to fluids/melts derived from subduction zone. On the other hand, a spinelpoor wehrlite shows a clinopyroxene with both LILE and HFSE enrichment, suggestive of interaction with alkaline fluids/melts. The Limeira 1 mantle xenoliths correspond to lherzolites and dunites showing more textural and mineralogical variety and equilibrium temperatures ranging from 760 to 820°C. Modal metasomatism was identified by the presence of abundant pockets with concentration of LILE and HFSE-rich secondary minerals, including in some cases, exotic phases typical of upper mantle metasomatism. The chemical signature of the metasomatic minerals is similar to those found in MARID and in veined metasomatic peridotites from South Africa kimberlite xenoliths. Petrographic and chemical evidences of decompression (suggesting the former presence of garnet) were observed in a sample affected by enrichment with high LILE/HFSE. The different evidences of depletion and enrichment processes observed in the two groups of xenoliths (Ubatuba and Monte Carmelo) indicate a lateral variability of the spinelfacies upper mantle in southeast Brazil, which may reflect the distinct tectonic and magmatic processes that affected these two regions.

Mineralogia e Petrologia de xenólitos mantélicos da Província Kimberlitica de Juína, MT

“…: Camargo & Leite, 1968;Sial, 1977;Leonardos et al, 1993;Carvalho, 1997;Rivalenti et al, 2000;Da Costa, 2008;Almeida, 2009;Nannini, 2011).…”

Oxygen fugacity of Alto Paranaíba kimberlites and diamond instability: Três Ranchos IV and Limeira I intrusions

“…By applying several geothermobarometers from TR-IV xenoliths, Costa (2008) presented a temperature range of 974 to 1,139°C, a pressure range of 36 to 51 Kbar, and geotherms of about 38 and 63 mW/ m 2 . For LM-I kimberlite xenoliths, Almeida (2009) introduced temperatures ranging from 622 to 921°C that were obtained from orthopyroxene, clinopyroxene, olivine, and spinel geothermometers. A compilation of geochemical data from several publications on the APAP allowed Cabral Neto et al (2017) to determine, from the clinopyroxene geothermobarometer of Nimis and Taylor (2000), a geotherm ranging from 40 to 50 mW/m 2 for the lithosphere related to the LM-I kimberlite and 35 to 40 mW/m 2 for TR-IV.…”

Os distintos tipos petrográficos da intrusão Kimberlítica Pântano, Província Alcalina Alto Paranaíba (MG): evidências de um sistema magmático aberto

“…Para o kimberlito Limeira I, foram descritos xenólitos do manto de até 15 cm com composição de dunito, harzburgito e espinélio lherzolito (Svisero & Ulbrich, 1992;Almeida, 2009), em parte portadores de flogopita (Meyer et al, 1991 Howarth and Taylor, 2016), lamproítos (Jaques & Foley, 2018;Shaik et al, 2018) e lamprófiros ultramáficos (Nosova et al, 2018;Tappe et al, 2006;Veter et al, 2017).…”