Petrology of potassic alkaline ultramafic and carbonatitic rocks from Planalto da Serra (Mato Grosso State), Brazil

Abstract

Abstract:The Planalto da Serra igneous rocks form plugs, necks and dykes of carbonate-rich ultramafic lamprophyres (aillikites and glimmerites with kamafugitic affinity) and carbonatites (alvikites and beforsites). Phlogopite and/or tetraphlogopite, diopside and melanitic garnet are restricted to aillikitic rock-types, whereas pyroclore occurs only in carbonatites. Aillikites and carbonatites are altered to hydrotermalites, having chlorite and serpentine as dominant minerals. Planalto da Serra igneous rock association has kamafugitic affinity (i.e. effusive, ultrapotassic. High LREE/HREE fractionation, incompatible elements data and Sr-Nd isotopes, suggest that the K-ultramafic alkaline and carbonatite rocks originated from a variably metasomatized mantle source enriched in radiogenic Sr. Crustal contamination is negligible or absent. Age values of 600 Ma rule out the geochronological relationship between the investigated intrusions and the Mesozoic alkaline bodies from the Azimuth 125 • lineament. The TDM model ages allow to conclude that Planalto da Serra magma is derived from the partial melting of a mantle source metasomatised by K-rich carbonatated melt during the Early to Late Neoproterozoic. On the basis of alkaline magmatism repetitions at 600 Ma and 90-80 Ma we question the subsistence of a stationary mantle plume for so long time. Keywords

Mafic-ultramafic rocks and alkaline-carbonatitic magmatism and associated hydrothermal mineralization: A special issue (Part-I) dedicated to Piero Comin-Chiaramonti

“…Hydrous fluids from less alkaline mafic-ultramafic complexes seem different and are more specific for tellurium and PGE concentration as suggested by the papers of Dora et al [5], who studied the mineralisation of Gondpipri, Central India, and the paper by Devaraju et al [6], which describes the Channagiri complex, India. Even small volcanic or subvolcanic outcrops may have undergone the intense action of magmatic fluids as observed in the small melilitolitic sub-volcanics in Central Italy described by Stoppa and Schiazza [7], or the regional swarm of ultramafic dykes described by Comin-Chiaramoti et al [8] from Planalto da Serra, Brazil, which show several generations of latestage minerals. These two localities have a kamafugitic affinity and are related by the authors to a metasomatised mantle source enriched in K and radiogenic Sr.…”

Controle litoestrutural e caracterização geofísica do Complexo Alcalino Planalto da Serra, Mato Grosso

“…Contudo, novos estudos indicam que são rochas com idades mais antigas, de aproximadamente 600 Ma, e atribuem a intrusão do CAPS a períodos extensionais relacionados à separação entre o Laurentia e o Cráton Amazônico (De Min et al, 2013). Apesar de existirem trabalhos de mapeamento geológico sistemático na escala de 1:100.000 desenvolvidos pela Companhia de Pesquisa de Recursos Minerais do Serviço Geológico do Brasil (CPRM-SGB) (Lacerda Filho et al, 2004), trabalhos de graduação e pósgraduação (Ormond, 2006;Stropper, 2014) e estudos geocronológicos (Comin-Chiaramonti et al, 2014;De Min et al, 2013), a gênese do CAPS, assim como o modelo evolutivo e o controle estrutural, ainda permanece incompreendida.…”

Identification of mineralized zones in the Zardu area, Kushk SEDEX deposit (Central Iran), based on geological and multifractal modeling

“…To aid in this purpose, detailed studies of the lithology and mineralogy of mineral deposits are important, and a number of conventional models have been proposed based on petrological and mineralogical studies including the determination of rock types, alteration zones, and minerals using thin/polished sections [1][2][3][4][5][6][7][8]. Based on this geological dataset, geological 3D models are then generated, plotting rock types, ore minerals, alteration zones, and stratigraphy [9,10].…”