A Review. II: Isotopic Evidences Elements
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Open Geosciences 2020; 12: 678–702 Review Article Sergio Speziale*, Francesca Castorina, Paolo Censi, Celso de Barros Gomes, Leila Soares Marques, and Piero Comin-Chiaramonti Carbonatites from the southern Brazilian Platform: A review. II: Isotopic evidences https://doi.org/10.1515/geo-2020-0032 elements. These fluids are expected to have promoted received March 13, 2019; accepted September 25, 2019 crystallization of K-rich phases in the mantle, which Abstract: Early and Late Cretaceous alkaline and alkaline– produced a veined network variously enriched in LILE ( ) carbonatitic complexes from southern Brazil are located and LREE. The newly formed veins enriched component ( ) along the main tectonic lineaments of the South America and peridotite matrix depleted component underwent a ff fl Platform. Calcium-,magnesium-, and ferrocarbonatites di erent isotopic evolution with time as re ected by the are well represented and frequently associated even in carbonatites. These conclusions may be extended to the – - the same complex. Primary carbonates present significant whole Paraná Etendeka system, where isotopically dis variations in C–O isotopic compositions, which are tinct parent magmas were generated following two main mainly due to isotope exchange with H O–CO -rich enrichment events of the subcontinental lithospheric 2 2 – – hydrothermal fluids, whereas fractional crystallization or mantle at 2.0 1.4 and 1.0 0.5 Ga, respectively, as also – liquid immiscibility probably affects the δ18Oandδ13C supported by Re Os systematics. The mantle sources values by no more than 2δ‰. Our isotope exchange preserved the isotopic heterogeneities over a long time, model implies that the most significant isotopic variations suggesting a nonconvective lithospheric mantle beneath ff took place in a hydrothermal environment, e.g., in the di erent cratons or intercratonicregions.Overall,the data indicate that the alkaline–carbonatitic magmatism range 400–80°C, involving fluids with the CO2/H2Oratio ranging from 0.8 to 1. Sr–Nd–Pb isotope systematics originated from a locally heterogeneous subcontinental highlight heterogeneous mixtures between HIMU and EMI mantle. mantle components, similar to the associated alkaline Keywords: carbonatites: southern Brazil, C–O isotopes, rocks and the flood tholeiites from southern Brazil. In Sr–Nd–Pb–Re–Os systematic spite of the strong variation shown by C–O isotopes, Sr–Nd–Pb–Os isotopic systematics could be related to an isotopically enriched source where the chemical hetero- geneities reflect a depleted mantle “metasomatized” by 1 Introduction small-volume melts and fluids rich in incompatible Southern Brazil is part of the Paraná–Etendeka Province (PAEP)[1] characterized by the emplacement of Early fl * Corresponding author: Sergio Speziale, Helmholz-Zentrum Cretaceous tholeiitic ood basalts and dyke swarms, Potsdam Deutsches, GFZ, Section 3.6, Chemistry and Physics 129–133 Ma aged [1–6], and alkaline and alkaline–carbo- of Earth Materials, 14473, Potsdam, Germany, natite complexes of Early Cretaceous to Paleogene age e-mail: [email protected] [8–12]. The alkaline and alkaline–carbonatitic complexes Francesca Castorina: Geosciences Department, Rome University, formed mainly along tectonic structures (Figure 1) active “La Sapienza”, 00185, Rome, Italy at least since Early Mesozoic, and up to the present day, as Paolo Censi: Earth and Sea Science Department, Palermo University, 90123, Palermo, Italy indicated also by the distribution of the earthquakes in Celso de Barros Gomes: Geosciences Institute, Department of southern Brazil [13]. Mineralogy and Geotectonics, University of São Paulo, Cidade Almost all the carbonatites from southern Brazil are Universitária, São Paulo, SP, 05508-900, Brasil restricted to continental areas. The criteria by which a Leila Soares Marques: Instituto de Astronomia, Geofísica e Ciências carbonate-rich rock is considered to be a true carbonatite Atmosféricas, Department of Geophysics, Universidade de São ffi fi Paulo, Cidade Universitária, São Paulo, SP, 05508-900, Brasil are di cult to apply with con dence. Although not Piero Comin-Chiaramonti: Department of Mathematics and conclusive, the following characteristics are the strongest Geosciences, Trieste University, 34127, Trieste, Italy clues, especially when they are observed together [14]: (1) Open Access. © 2020 Sergio Speziale et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 Public License. Carbonatites from the southern Brazilian Platform: a review. II: isotopic evidences 679 mainstream model based on the involvement of a deep 50°W 40°W 20°W mantle plume in magma genesis processes in the region. 10°S rch Notably, noble gases isotopic data suggest that the source s A BRAZIL ede Araguaia çâm 10°S (s) are similar to other mantle-derived magmas (e.g., -Paranaíba- Mo CaboFrio ) Po HIMU and MORB and that the carbon of carbonatites is nta Gro unlikely to be subduction-related carbon, and supports a ssa ANGOLA Arc 0°S h – - 2 t picture of C O fractionation starting from mantle derived R Bel io Piq Rio G is ra uiri’ rande alv a sources, in ametasomatized subcontinental lithospheric T R W e am orr ise idg D 20 es S R °S ( ) – – ync mantle SCLM based on Sr Nd Pb isotope systematic line R NAMIBIA [20,23–25]. io G r otion an Relative M d w lines The structure of this article will follow the same eA as from flo 0°S rch 3 structure as the first part (Speziale et al., this issue) in that MAR motion the different carbonatitic occurrences are grouped on the Africa South America Absolute motion [ ] Absolute motion basis of petrographic associations 26 as magmatic carbonatites [27,28], hydrothermal carbonatites, and Figure 1: Main tectonic structures in the Paraná–Angola–Namibia occurrences with unusual geometric relationship. (PAN) system (South American and African plates, Western (1) Magmatic carbonatites Gondwana at about 110 Ma; modified after [20]) and corresponding (A) Occurrences associated with rock types of the - to the main alignments of the alkaline and alkaline carbonatitic urtite-ijolite-melteigite series, without the presence complexes. Inset: Qualitative vector diagram showing the rela- of extrusive nephelinites (Brazil, Vale do Ribeira: tionships between absolute plate motions, relative motions, and the development of the mid-Atlantic ridge (MAR) as depicted in the Anitápolis, Ipanema, Itapirapuã, Jacupiranga, figure [21]. Mato Preto, and Juquiá; Goiás: Caiapó and Morro do Engenho; Paraguay: Cerro Sarambí and Sapucai). field evidences, e.g., subcircular or suboval or ring (B) Occurrences only with olivinites and pyroxe- structures of alkaline complexes with carbonatite body nites as ultramafitites (±syenites) as Salitre I occupying the inner part; (2) association with melilite- or and Serra Negra, and with glimmerites as nepheline-bearing rocks; (3) calcite with >1wt%SrO; (4) Araxá, Catalão I, Catalão II, and Salitre II. presence of perovskite, pyrochlore, F-REE-carbonates, and (C) Occurrences with intrusive rocks containing apatite with high silica content (e.g., >2wt%); (5) enrich- melilite, as Tapira and Lages. ment in Sr, Ba, Nb, U, Th, and rareearth elements (with (2) Hydrothermal carbonatites: those produced at tem- high LREE vs HREE fractionation) and depletion of other peratures ≤375°C (e.g., Barra do Itapirapuã, Cerro incompatible elements (e.g. K, Rb, Zr, Hf, and Ti) relative to Chiriguelo, Cerro Manomó). mantle and continental crust [15]; (6) 87Sr/86Sr initial ratios (3) Occurrences with unusual geometric relationships: a similar to those of the associated silicate alkaline rocks [16]; small number of occurrences in the form of small (7) stable isotopes (O–C) in the “primary carbonatitic box” dykes or ocelli in alkaline silicate rocks (e.g., Valle- [17,18] or following well-distinct isotopic fractionation mí, Cerro Canãda, Cerro E Santa Elena, Itanhaém; cf. trends [19]. Speziale et al., this volume). Taking into account the above criteria, this article summarizes field and geological evidences and geo- chemical characteristics in terms of C–O and Sr– Nd–Pb–Re–Os isotopic data of alkaline–carbonatitic complexes and occurrences in and around the Paraná 2C–O isotopes Basin in southern Brazil, in particular, and in the Paraná–Angola–Namibia (PAN) system in general [20]. A compilation of the C–O isotopic data for calcite and In the context of the long-standing controversy about the dolomite-ankerite (δ18O‰ vs V-SMOW and δ13C‰ vs exact mechanism that produced the South Atlantic PDB-1) is given in Table 1.TheC–Oisotopecompositions igneous province [22], our results give new important of the studied carbonatites appear to be in general information that allows one to interpret the geodynamic agreement with a magmatic origin from supercrytical framework of the whole Mesozoic magmatism of the fluids with CO2/H2O ≈ 0.2–0.6 molar ratios and tempera- southern Brazilian Platform, in alternative to the tures ranging from ∼800°C to 400°C (i.e., from 680 Sergio Speziale et al. Table 1: Representative C–O isotopic ratios in δ‰ notation for calcite and dolomite/ankerite (sometimes coexisting) in carbonatites from the Brazilian Platform. Analytical methods and uncertainties on the values reported in this table can be found in [29]. The locations of the sampling areas [30,31] are reported in detail following the references relative to the single localities: PARAGUAY: Cerro Sarambí, [32,33]; Cerro Cañada, [20,34,35]; Cerro E Santa Elena, [20,34,35]; Sapucai, [34,36]; Cerro Chiriguelo, [29,36]; Valle-mí,