Petrogenesis of the drift magmatism in the Cabo Frio High, Campos Basin, Brazil: Evidence from Sr–Nd–Pb–Hf isotopes

Abstract

Situated between the Campos and Santos basins, the Cabo Frio High emerges as a focal point of heightened magmatic activity during the Santonian–Campanian and the Eocene period following the breakup of these basins. The geodynamic framework associated with these events took place during their passive margin stage, wherein magmatic occurrences could potentially be attributed to the reactivation of significant geological structures or thermal enhancement facilitated by proximal hotspots, within a context of lithospheric thinning (i.e., Trindade Plume). This investigation unveils novel Sr–Nd–Pb–Hf isotope data derived from alkaline magmatic rocks extracted from three boreholes strategically positioned within the Cabo Frio High area. The evolutionary trajectory of these rocks reflects the intricate processes of assimilation and fractional crystallization. The results of the analysis and binary mixing modeling point out to an involvement of both depleted (characterized by Depleted Mantle [DM]/Mid-Ocean Ridge Basalt [MORB] or HIMU compositions) and enriched (manifesting as the Enriched Mantle I [EMI] and the Enriched Mantle II [EMII]) sources in the genesis of these magmas. Moreover, the discerned incorporation of a fertile Ocean Island Basalt (OIB-like) reservoir hints at a plausible association with the Trindade Plume, amplifying the complexity of the magmatic genesis within the studied region.

KEYWORDS:
alkaline magmatism; Campos Basin; isotope geochemistry

1 INTRODUCTION

During the Late Cretaceous and Paleogene, southeastern Brazil experienced a significant surge in the magmatic activity, particularly notable within the Campos and Santos basins. This period saw the emergence of post-breakup magmatism, characterized by both extrusive and intrusive phenomena, predominantly exhibiting alkaline compositions. Coincidingtemporally and spatially with other noteworthy magmatic events, these occurrences are observable in the onshore Poços de Caldas-Cabo Frio Alignment and the offshore Vitória-Trindade Ridge (Alves, 2006; Bongiolo etal., 2015; Chang etal., 1992; Thomaz Filho & Rodrigues, 1999).

Studies on magmatic rocks in the Cabo Frio High area have predominantly relied on geophysical data, either independently or in tandem with petrological and lithogeochemical analyses to characterize these events (Gordon etal., 2023a; Moreira etal., 2006; Oreiro etal., 2003; Stanton & Schmitt, 2015). Despite the considerable attention devoted to this subject, there remains a notable dearth of lithogeochemical and geochronological data pertaining to post-breakup magmatism in this region. The understanding of mantle sources and the associated evolutionary processes remains incomplete, with the precise contribution of geodynamic elements to magma generation yet to be fully elucidated.

This study endeavors to address these knowledge gaps by presenting novel isotopic data derived from volcanic and volcaniclastic rocks associated with the drift phase in the Cabo Frio High area, situated within the Campos Basin along Brazil’s southeastern margin (Fig. 1). Through the analysis of samples obtained from three wellbores, our primary objective is to shed light on the potential evolutionary processes and mantle sources contributing to the genesis of these magmatic formations. Central to our investigation is the exploration of the geodynamic context surrounding these magmatic episodes, aiming to ascertain whether a mantle plume, such as the Trindade plume, played a role in magma formation, in conjunction with tectonic reactivation and uplift processes.

FIGURE 1
The delineated study area is demarcated within the red square. The figure also encompasses adjacent geological features, including sedimentary basins, the Cabo Frio High, the Poços de Caldas – Cabo Frio Alignment, and the Vitória – Trindade Ridge.

Magmatic events play a crucial role in sedimentary basins and petroliferous systems, profoundly shaping their geological and thermal trajectories. The thermal effects stemming from magmatic intrusions and extrusions permeate the surrounding lithosphere, inducing a notable increase in temperature. Thisthermal energy imparts a transformative impact on organic matter, dictating its maturation processes and consequently influencing the genesis, migration, and entrapment of hydrocarbons. Structuralperturbations induced by magmatic intrusions further augment this intricate geological narrative, precipitating deformations characterized by faulting, fracturing, and uplifting. These structural alterations serve as architects of hydrocarbon reservoirs, sculpting intricate traps and seals pivotal for the containment and preservation of petroleum deposits. Bystudying the interactions between magmatic phenomena and sedimentary contexts, it is possible to unlock invaluable insights into the genesis and distribution of hydrocarbon resources. Such insights hold particular significance in regions like the Brazilian southeastern margin, where the convergence of magmatic and sedimentary processes underscores the tangle dynamics shaping the hydrocarbon systems landscape (Thomaz Filho etal., 2008).

By strategically integrating isotopic data with geological context and tectonic processes, our study seeks to unravel the complex dynamics underlying the magmatic evolution of the Cabo Frio High region. In doing so, we aim to provide valuable insights into the subsurface processes of the Earth within this captivating geological setting.

Due to a confidentiality clause involved in the project associated with this study, the precise location and coordinates of the wells and samples studied in this scientific paper are not given. In addition, the identifier codes of these samples have also been changed. Nevertheless, the non-inclusion of such data does not interfere with the accuracy of the analysis and discussions carried out throughout this paper.

2 GEOLOGICAL SETTING

2.1 Drift Magmatism in the Cabo Frio High Area, Campos Basin

The sedimentary basins along the Brazilian southeastern margin, specifically Campos and Santos, originated as rift systems resulting from the breakup between South America and Africa during the Upper Jurassic/Lower Cretaceous. Crustalextension movements subsequently led to the development of the present passive margin basins (Cainelli & Mohriak, 1999; Chang etal., 1992; Mohriak, 2003).

The Cabo Frio High is situated between Campos and Santos basins, prominent oil provinces in the southeastern margin of Brazil (Mohriak etal., 1995; Moreira etal., 2007; Winter etal., 2007). This region exhibits intense intrusive and extrusive magmatic events that date from the Santonian to the Eocene and that contributed to the geophysical and tectonostratigraphic characteristics of these basins (Mohriak etal., 1995; Oreiro, 2006). Geophysical investigations reveal the presence of various magmatic features, including dikes, sills, floods, volcanic cones, and thick volcaniclastic sequences associated with distinct episodes (Fig. 2) (Gordon etal., 2023a; Moreira etal., 2006; Oreiro, 2006; Oreiro etal., 2008). Theserock compositions consist predominantly of tuffs, hyaloclastites, breccias, and basalts, with an overall alkaline character (Frank & Valente, 2023; Moreira etal., 2006; Oreiro, 2006; Rangel, 2006). Possible fertile deep mantle sources are identified as potential elements in the origin of Santos Basin drift magmas, with a minor contribution of Enriched Mantle I (EMI) and Enriched Mantle II (EMII) components (Gordon etal., 2023b).

FIGURE 2
Volcano-sedimentary model proposed for the Cabo Frio High area. Processes include the intercalation of submarine floods with sediments deposited during volcanic quiescence periods, as well as the occurrence of slumps in beside volcanic cones burying and deforming irregularly the sequences originated by previous processes. Shallow intrusions are also observed adjacent to the cones (these are frequently eroded).

Tectonic implications of the magmatism observed in the studied area are strongly related to the extension movements during the South Atlantic Ocean opening and posterior tectonic, upwelling and thermal events that took place in the region (Almeida etal., 2021; Gibson etal., 1997; Thomaz Filho etal., 2000; Thomaz Filho etal., 2008). Further elaboration of these aspects and hypotheses will be provided in subsequent discussions.

Detailed petrographic and lithogeochemical data from the rocks studied in this paper are available in De Barros etal. (2023). The classification of these magmatic rocks is summarized in Table 1. The analysis of major and trace elements suggests that the origin of these magmas can be traced back to shallow mantle depths ranging from 35 to 80 km. Theyare associated with mixing processes involving a depleted source (Normal-Mid-Ocean Ridge Basalt [N-MORB]-like) and the local subcontinental lithospheric mantle (SCLM) (Cabo Frio High area lamprophyres) (De Barros etal., 2023). However,the present study addresses and deliberates on the potential contribution of other enriched sources as the origin of these rocks. Moreover, additional constraints are imposed on possible evolutive processes that may have influenced the development of these magmas.

Table 1.
Petrographic and lithogeochemical classification of the studied rocks. Modified from De Barros etal. (2023). Lithogeochemical classification based on Nb/Y versus Zr/Ti diagram (Pearce & Norry, 1979).

Well	Sample	Petrography	Lithogeochemistry
EG1	SPL 37	Ash tuff	Tephriphonolite
EG1	SPL 39	Alkaline diabase	Alkali basalt
EG2	SPL 40	Lapilli tuff	Alkali basalt
EG2	SPL 44	Basalt	Basalt
EG3	SPL 45	Lapilli tuff	Alkali basalt
EG3	SPL 47	Lapilli tuff	Foidite
EG3	SPL 48	Lapilli tuff	Foidite

2.2 Cretaceous alkaline magmatism in the Southeastern Region of Brazil

The alkaline magmatism in the Cabo Frio High area contemporaneously coincides with numerous magmatic events observed in the southeastern region of Brazil. Manifestations of the Trindade Plume are evident in alkaline provinces throughout southeastern Brazil, spanning the Upper Cretaceous to Paleogene, including areas such as Poxoréu, Alto do Paranaíba, Itaporá, and Serra do Mar (Gibson etal., 1995; Gibson etal., 1997; Siebel etal., 2000; Thomaz Filho & Rodrigues, 1999; Thompson etal., 1998).

The Vitória-Trindade Ridge comprises a group of seamounts oriented in an E-W, extending from the Brazilian margin to the Trindade Island and Martin Vaz Archipelago. In sequence from west to west, these seamounts are Vitória, Montague, Jaseur, Columbia, and Palma, including the Davis, Dogaressa, Asmus, and Columbia banks (Maia etal., 2021). Ranging in age from 40 Ma to the present, these seamounts, banks, and hills consist predominantly of subaerial volcanoes composed of highly alkaline silica unsaturated rocks (Fodor & Hanan, 2000; Pires etal., 2016; Siebel etal., 2000). Contributions of HIMU, EMI, and N-type MORB mantle sources are suggested to have participated in the origin of these magmas (Quaresma etal., 2023; Siebel etal., 2000).

Recent studies combining geophysical data (gravity modeling) and isotopic signatures support the participation of the SCLM and fragments of the Eastern Brazilian and African conjugate margins to explain the volcanic processes associated with the Vitória-Trindade Ridge. The presence of these lithospheric fragments incorporated into the mantle would have influenced the magmatic activity beneath the ridge, what is corroborated by the isotopic data showing the presence of components such as HIMU and EMII in volcanic rocks (Das Flores etal., 2024).

The Abrolhos Archipelago, dated between 40 and 60 Ma, is situated northward of the Vitória-Trindade Ridge and constitutes an igneous province of mildly alkaline basalts with geochemical signatures typical of ocean island basalts (OIBs). The archipelago is part of the large volcanic province resulted from the complex interaction between the Trindade mantle plume, tectonic movements, and spreading centers observed in the South Atlantic region (Geraldes etal., 2013; Maia etal., 2021; Marques etal., 1999; Siebel etal., 2000).

The Poços de Caldas-Cabo Frio Alkaline Alignment represents a prominent magmatic lineament stretching approximately 1,150 km in length and 60 km in width, extending from Poços de Caldas to Cabo Frio (Almeida, 1991). This geological province, developed in extensive shear zones, exhibits a WNW-ESE trend, as depicted in Fig. 3. The alignment is associated with a complex geological history involving at least two distinct magmatic and reactivation episodes during the Upper Cretaceous-Paleocene and Eocene (Riccomini etal., 2004). Manifestations of both extrusive (floods and pyroclastic flows) and intrusive (dikes, stocks, and plugs) magmatic activities are observed along the entire alignment (Thomaz Filho & Rodrigues, 1999).

FIGURE 3
Distribution of the Meso-Cenozoic Poços de Caldas-Cabo Frio magmatic occurrences: Poços de Caldas (1), Bom Repouso (2), Caxambú (3), Passa Quatro (4), Itatiaia (5), Morro Redondo (6), Serra dos Tomazes (7), Tinguá (8), Mendanha-Mapicuru (9), Itaúna (10), Tanguá (11), Soarinho (12), Rio Bonito (13), Morro de São João (14), and Cabo Frio (15). Yellow area: Cenozoic sediments; green area: Cenozoic rifts; red areas: Meso-Cenozoic alkaline massifs; pink area: Moho hight; orange area: Paraná Basin; dark grey area: Post-orogenic granitoids; light grey area: Sin- to late-orogenic granitoids; dashed green lines: Cenozoic faults; dashed red lines: Atlantic Rift transfer zone; grey lines: limits of Brasiliano domains.

The principal complexes aligned along the Poços de Caldas-Cabo Frio Alignment, arranged from west to east, encompass Poços de Caldas, Passa Quatro, Itatiaia, Morro Redondo, Serra dos Tomazes, Tinguá, Marapicu-Gericinó-Mendanha, Tanguá, Soarinho, Rio Bonito, Morro de São João, and Cabo Frio (Riccomini etal., 2005).

These complexes are predominantly felsic, characterized by a limited occurrence of mafic expressions, such as dikes, sills, and lavas. The prevailing lithologies consist of nepheline syenite, often associated with trachyte, phonolite, and breccia (Brotzu etal., 1992; Brotzu etal., 2007; Motoki etal., 2010; Rosa & Ruberti, 2018). Additionally, ankaramitic lavas have been identified in the Itaboraí and Volta Redonda basins (Thompson etal., 1998).

The origin and potential continuity of the Poços de Caldas-Cabo Frio Alignment and offshore alkaline magmatism with the Vitória-Trindade Ridge have been predominantly explored through plume-related hypotheses. Thompson etal. (1998) proposed a connection between the Poços de Caldas alkaline magmatism and the Trindade mantle plume, suggesting that between 80 and 55 Ma, the plume’s upwelling was deflected by the thick São Francisco craton lithosphere. Thisdeflection could have induced decompression melting processes along the craton’s southern margin, giving rise to the alkaline complexes observed in the Poços de Caldas-Cabo Frio Alignment.

Alternatively, a theory posits the displacement of the South American plate over a hot spot, with manifestations of this structure observed from Poços de Caldas to Cabo Frio alkaline magmatism. During the Eocene, as implicated in this model, a clockwise plate rotation would have led to intense magmatism and tectonic manifestations in the surrounding areas, such as the Cabo Frio Platform and the Abrolhos Archipelago, ultimately contributing to the formation of the Vitória-Trindade Ridge formation (Thomaz Filho & Rodrigues, 1999; Thomaz Filho etal., 2008).

In contrast, a non-plume-related hypothesis attributes the magmatic episodes to the reactivation of major Proterozoic crustal discontinuities during the extensional processes that affected the South American Platform. Almeida (1983) and Riccomini etal. (2005) proposed that, through these reactivated structural weaknesses and potential mantle upwelling, the alkaline magmatism was generated and emplaced. Thisintense tectonic control is then suggested to be connected, serving as a conduit, to the alkaline drift magmatism observed in the offshore Santos Basin (Gordon etal., 2023a) and the onshore portions of both the Campos and Santos basins (Oliveira etal., 2023).

3 MATERIALS AND METHODS

The present study utilized seven sidewall core samples (SPL 37, SPL 39, SPL 40, SPL 44, SPL 45, SPL 47, and SPL 48) comprising volcanic and volcaniclastics rocks obtained from three wells drilled in the Cabo Frio High area, situated between the Campos and Santos basins. As elucidated before, well coordinates are not revealed due to confidentiality clause. Well profiles were employed to characterize and estimate the emplacement time of these magmas and the associated stratigraphic formations. Both the samples and well profiles were acquired through the Brazilian National Agency for Petroleum, Natural Gas and Biofuels (ANP).

The selection of sidewall core samples was based on criteria, such as minor loss on ignition (LOI), petrographic and lithogeochemical data, and spatial distribution. Subsequently,the samples underwent a thorough washing process under running water and a soft brush to enhance the removal of impurities. Post-cleaning, the samples were dried, crushed, and powdered, preparing them for subsequent isotopic analysis.

Sr–Nd–Pb–Hf isotopic data were acquired at the New Mexico State University Johnson Mass Spectrometer Laboratory in the United States. The analyses were conducted using the Thermo Scientific Neptune Plus Multicollector-Inductively Coupled Plasma-Mass Spectrometer (MC-ICP-MS). Standardreference material, NBS 987, yielded the following results: ⁸⁷Sr/⁸⁶Sr = 0.710284 ± 0.000011; ¹⁴³Nd/¹⁴⁴Nd = 0.512099 ± 0.000008; ²⁰⁶Pb/²⁰⁴Pb = 18.898 ± 0.001; ²⁰⁷Pb/²⁰⁴Pb = 15.485 ± 0.001; ²⁰⁸Pb/²⁰⁴Pb = 38.678 ± 0.002; ¹⁷⁶Hf/¹⁷⁷Hf = 0.282161 ± 0.000007.

A compilation effort was undertaken to gather isotopic data and end members pertaining to the following mantle reservoirs: Depleted Mantle (DM)/MORB, HIMU, EMI, and EMII, and data for Poços de Caldas-Cabo Frio and Vitória-Trindade magmas. These data were employed in the formulation of petrological models, contributing to the advancement of geodynamic discussions regarding the Santonian–Campanian magmatism in the studied area. The compiled information was sourced from the GEOROC (https://georoc.eu/georoc/new-start.asp) and EarthRef (https://earthref.org/) databases. The compiled spreadsheets containing this information can be accessed in the Complementary Material associated with this study.

4 RESULTS

Volcanic and volcaniclastic rocks analyzed in this study were collected in three wells, namely EG1, EG2, and EG3, located within the Cabo Frio High area situated between the Campos and Santos basins. These rocks occur interbedded to Cretaceous sedimentary deposits (Ubatuba and Carapebus formations), which encompass sandstones, shales, siltstones, and marls (Fig. 4), associated with the drift phase.

FIGURE 4
Schematic sections of EG1, EG2, and EG3 wells. The studied sidewall core samples are indicated.

4.1 Magma evolution processes

As depicted by De Barros etal. (2023), lithogeochemical data from alkaline volcanic and volcaniclastic rocks in the Cabo Frio High area have their evolution associated with fractional crystallization processes. According to the authors, more complex disequilibrium processes, such as liquid immiscibility, are also possibly be associated with these magmas and can be observed in the crossover pattern of most and less evolved EG1, EG2, and EG3 samples.

Despite that, simple fractional crystallization processes may not be sufficient to explain certain concentrations observed in trace and rare earth elements (REEs) in the studied magmas. Peaks observed in Ba, Rb, Sr, Th, and K are thought to be associated with alteration processes, most commonly observed in these rocks as depicted by their LOI and petrographic data (De Barros etal., 2023). Nevertheless, crystallization processes and the associated assimilation of different magmas can be explained by the high concentrations observed in such mobile trace elements. Notorious variations in Sr and Nd isotopic ratios (Table 2) are also strong evidence that these magmas went through assimilation–fractional crystallization (AFC) or even more complex processes.

Table 2.
Isotopic ratios from the studied samples and their respective wells. MgO (wt.%), LOI (wt.%), La (ppm), Yb (ppm), and Nb (ppm) contents from De Barros etal. (2023). Initial (i) content refers to measured data (m) recalculated to 82 Ma (based on Moreira etal. [2006] and geological setting bibliographic research). Normalization factors (N) are from McDonough and Sun (1995).

Well	EG1	EG1	EG2	EG2	EG3	EG3	EG3
Sample	SPL 37	SPL 39	SPL 40	SPL 44	SPL 45	SPL 47	SPL 48
SiO 2	55.02	44.31	32.41	39.12	33.83	45.88	38.71
MgO	2.49	4.56	4.01	2.57	4.73	0.7	4.74
LOI	7.52	7.57	19.95	14.02	17.52	11.21	14.68
La/Yb (N)	43.562	5.036	21.663	2.714	23.567	29.218	20.905
La/Nb (N)	0.9851	0.8814	1.0264	0.5927	1.0058	0.9644	0.9669
87 Sr/ 86 Sr (m)	0.705942	0.704979	0.716609	0.708871	0.705719	0.704951	0.705604
87 Sr/ 86 Sr (i)	0.705180	0.704578	0.716055	0.708016	0.704970	0.704426	0.705323
143 Nd/ 144 Nd (m)	0.512333	0.512806	0.512396	0.512893	0.512605	0.512584	0.512647
143 Nd/ 144 Nd (i)	0.512294	0.512726	0.512339	0.512805	0.512551	0.512533	0.512591
176 Hf/ 177 Hf (m)	0.282576	0.283074	0.282856	0.283136	0.282843	0.282811	0.282860
176 Hf/ 177 Hf (i)	0.282575	0.283072	0.282855	0.283134	0.2828418	0.282810	0.282859
206 Pb/ 204 Pb	17.929	18.804	18.581	19.058	18.704	19.166	18.973
207 Pb/ 204 Pb	15.529	15.574	15.553	15.589	15.521	15.569	15.536
208 Pb/ 204 Pb	39.437	38.984	38.767	39.124	38.861	39.590	39.011

In magmas derived from a common source, discernible distinctions in the fourth decimal place for ⁸⁷Sr/⁸⁶Sr and the fifth decimal place for ¹⁴³Nd/¹⁴⁴Nd ratios serve as robust indicators, suggesting that the exclusive influence of crystallization processes is insufficient to account for such dissimilarity (Valente, 1997; Rollinson & Pease, 2021). Notably, samples SPL 37 and SPL 39 from well EG1 representing the least and most evolved states, respectively, exhibit significant fluctuations in both ⁸⁷Sr/⁸⁶Sr (0.705180–0.704578) and ¹⁴³Nd/¹⁴⁴Nd (0.512294–0.512726) ratios, commencing at the third decimal place. These data imply that crystallization processes may have been intricately associated with assimilation processes (AFC) in the genesis of the studied rocks (Valente, 1997; Rollinson & Pease, 2021). A similar pattern can be observed in EG2 and EG3 samples. Nonetheless, the observed isotopic variation cannot be explained solely by single crystallization processes.

It is crucial to consider that these samples show significant alterations and high LOI contents (De Barros etal., 2023), potentially affecting Nd and mainly Sr isotopic ratios. Despitethat, the data provided by Sr and Nd isotopic analyses are critical in refining the petrogenetic model for the studied magmas especially in the Cabo Frio High area where alteration and contamination are significant factors in the origin and evolution of magmatic events. It is worth noting, however, that the number of samples studied and the amount of isotopic data are quite limited. A more robust discussion in a petrological scenario involving more complex evolutionary processes requires more evidence.

In EG3, two samples, SPL 45 (MgO = 4.73 wt.%) and SPL 48 (MgO = 4.74 wt.%) despite sharing a similar level of evolution, display unexpected differences in ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios. Unlike expectations for cogenetic magmas, the Sr isotopic ratio is higher for the less evolved sample, diverging from the trend observed in EG2 samples. However,the Nd isotopic ratio aligns with ordinary assimilation processes, with the more evolved sample showing a lower content of ¹⁴³Nd/¹⁴⁴Nd. This supports the notion that alteration processes may have influenced these samples, particularly Sr isotopic data mobility.

In a broader context, AFC emerges as the predominant process shaping the origin of these magmas, given the notable variation in ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd contents that cannot be exclusively attributed to fractional crystallization. It is essential to note challenges such as high LOI values, especially in EG2 and EG3 samples, and their petrographic characterization as highly altered rocks, susceptible to Sr remobilization. Thelimited sample number constrains a more in-depth discussion regarding the evolution of these magmas. The existence of magmas with the same MgO composition but remarkably different Sr and Nd composition is a strong indicator that different sources are related to the origin of these rocks, as depicted by De Barros etal. (2023), and the subsequent results regarding possible mantle sources involved in the studied magmatic events.

4.2 Mantle sources

Both N-MORB and fertile asthenospheric mantle sources (SCLM in onshore Cabo Frio) are suggested to be the origin of magmas from EG1, EG2, and EG3 (De Barros etal., 2023). La/Yb_(N) (> 1) and La/Nb_(N) (< 1) ratios from SPL 37, SPL 47, and SPL 48 (Table 2) are very likely to represent the enriched mantle source. Despite that, values that are close to unit might also account for more enriched or fertile mantle sources. La/Nb_(N) (> 1) ratio in the studied rocks SPL 40 and SPL 45 indicates that they are supposed to have the contribution of a more fertile mantle source, such as an OIB plume-like, during their formation.

Based on lithogeochemical data results from De Barros etal. (2023) and on the major geodynamic context in which Cabo Frio High post-breakup magmas were emplaced, it is possible to ascertain that mantle sources involved to give origin to these magmas are not completely clear. Among a diverse possibility of mantle sources, discrimination diagrams using ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, ¹⁷⁶Hf/¹⁷⁷Hf, and ²⁰⁶Pb/²⁰⁴Pb (Figs. 5 and 6) were then used to help elucidate such contributions. Data from coeval and adjoining alkaline magmatism from the Poços de Caldas-Cabo Frio alignment and Vitória-Trindade Ridge were also compared to the studied samples.

FIGURE 5
Mantle source discrimination diagrams for the studied samples: (A) εNd x ⁸⁷Sr/⁸⁶Sr; (B) ⁸⁷Sr/⁸⁶Sr x ²⁰⁶Pb/²⁰⁴Pb; (C) ²⁰⁸Pb/²⁰⁴Pb x ²⁰⁶Pb/²⁰⁴Pb; (D) ¹⁴³Nd/¹⁴⁴Nd x ²⁰⁶Pb/²⁰⁴Pb; (E) ²⁰⁷Pb/²⁰⁴Pb x ²⁰⁶Pb/²⁰⁴Pb. EG1 (SPL 47 and SPL 39), EG2 (SPL 40 and SPL 44), and EG3 (SPL 45, SPL 47, and SPL 48) rocks. ⁸⁷Sr/⁸⁶Sr, ¹⁴³Nd/¹⁴⁴Nd, and ¹⁷⁶Hf/¹⁷⁷Hf ratios were recalculated to estimated initial age 82 Ma (based on Moreira etal. [2006] and geological setting bibliographic research). Data from Vitória-Trindade Ridge are from Bongiolo etal. (2015), Quaresma etal. (2023); Fodor and Hanan (2000); Marques etal. (1999); Peyve and Skolotnev (2014); and Siebel etal. (2000). Data from Poços de Caldas-Cabo Frio Alkaline Alignment are from Valente (1997); Guarino etal. (2021); Rosa (2017); and Thompson etal. (1998). DM/MORB stands for general depleted mantle sources. DM/MORB, HIMU, EMI, and EMII data can be found in complementary material and were obtained from GEOROC (https://georoc.eu/georoc/new-start.asp) and EarthRef (https://earthref.org/) databases.

FIGURE 6
Mantle source discrimination diagrams for the studied samples: (A, B, C) EG1 (SPL 47 and SPL 39), EG2 (SPL 40 and SPL 44), and EG3 (SPL 45, SPL 47, and SPL 48) rocks. 87Sr/86Sr, 143Nd/144Nd, and 176Hf/177Hf ratios were recalculated to estimated initial age 82 Ma (based on Moreira etal. (2006) and geological setting bibliographic research). DM/MORB stands for general depleted mantle sources. DM/MORB, HIMU, EMI, and EMII data can be found in complementary material and were obtained from GEOROC (https://georoc.eu/georoc/newstart.asp ) and EarthRef (https://earthref.org/) databases.

In general, diagrams in Figs. 5 and 6 support the hypothesis of an enriched mantle (EM) source along with N-MORB (here represented by DM+mantle sources) to have given origin to the magmatism in the offshore Cabo Frio High area during the Santonian–Campanian period.

The isotopic data of EG1 samples (SPL 37 and SPL 39) suggest that these rocks originated from an enriched mantle source, either EMI type (Figs. 5A-5E, and Figs. 6A-6C) or EMII type (Figs. 5A-5E). The possible contribution of a depleted source (such as MORB) is evidenced in Figs. 5C and 5E, and Fig. 6C. As for EG2 samples (SPL 40 and SPL 44), they exhibit a similar pattern, being associated with EMII mantle sources (Figs. 5A-5E, and Fig. 6B). The contribution of DM/MORB sources is indicated in Figs. 5C-5E and Fig. 6C, as well as possible involvement of HIMU (Figs. 5A, 5D, and 5E). Itis important to emphasize that particularly high ⁸⁷Sr/⁸⁶Sr isotopic ratios in EG2 samples are possibly be associated with Sr remobilization, given the stage of alteration these rocks exhibit.

Samples SPL 45, SPL 47, and SPL 48 from EG3 possess similar isotopic ratios. They can be associated with the EMI-enriched mantle source (Figs. 5A, 5B, and 5D, and Figs. 6A and 6B). Some diagrams also suggest the contribution of EMII (Figs. 5B, 5C, and 5D, and Fig. 6C). Data from the SCLM are supposed to be similar to the ones found in EMI.

The genetic association of the Cabo Frio High alkaline post-breakup magmatism with either Vitória-Trindade Ridge or the Poços de Caldas-Cabo Frio Alignment is still in discussion, and the thermal or geochemical contribution of these features is not a consensus among studies in the area (Almeida, 1983, 1991; Gordon etal., 2023a; Gordon etal., 2023b; Thomaz Filho & Rodrigues, 1999; Thompson etal., 1998). Some samples from the studied wells exhibit isotopic signatures similar to the ones observed in both the adjacent magmatic provinces (Fig. 5) and are in correspondence with enriched and fertile La/Yb_(N) and La/Nb_(N) indicators (Table 2). Despite that, considering the predominancy of results and the discrimination diagrams, these associations can only be suggested, not determined. Furtherstudies involving petrogenesis, geophysics, and geodynamic data are needed to clarify such associations.

Precise mantle sources remain unclear even while considering discrimination diagrams. Despite that, it is possible to ascertain the contribution of both enriched and DM sources. Additionally, a fertile OIB-like source is to be considered given the discrimination diagrams and La/Yb_(N) and La/Nb_(N) ratios. Binary mixing models can then be elaborated to help determine EMI, EMII, DM/MORB, HIMU, and OIB-like mantle sources as possible input to the formation of the studied magmas and their rate of contribution.

5 DISCUSSION

The indication that more than one mantle source originated from the studied magmatism made it necessary to elaborate binary mixing modeling to determine which sources are involved in this mixture and their specific percentage of contribution. These models were elaborated based on the equations and modeling from Faure (1986). Once the mixture curve is created, each point represents a percentual of mixing between two different end members (mantle sources). Previous studies indicate the contribution of EMI and EMII, mainly fertile mantle sources, for drift magmatism in Campos and Santos basins (Gordon etal., 2023b), as well as the SCLM and N-MORB (De Barros etal., 2023).

In general, binary mixing modeling results suggest the involvement of a depleted and an enriched mantle source for the studied samples. EG1 sample SPL 37 exhibits a high contribution of DM (99.7%–95%) in a possible mixing with EMI and EMII (Figs. 7A and 7B). In the case of mixing between EMI and HIMU, the enriched mantle source exhibits higher values (approximately 85%), as observed in sample SPL 39 (about 95% contribution from EMI) (Fig. 7C).

FIGURE 7
Binary mixing models involving mantle sources EMI, EMII, HIMU, DM/MORB, and OIB-like (Trindade Plume). The studied wells and the respective samples are indicated: EG1 (SPL 47 and SPL 39), EG2 (SPL 40 and SPL 44), and EG3 (SPL 45, SPL 47, and SPL 48). ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios were recalculated to estimated initial age 82 Ma (based on Moreira etal. (2006) and geological setting bibliographic research). (A) End members: DM (⁸⁷Sr/⁸⁶Sr = 0.701978; ¹⁴³Nd/¹⁴⁴Nd = 0.513266; ²⁰⁶Pb/²⁰⁴Pb = 18.275; ²⁰⁷Pb/²⁰⁴Pb = 15.486; ²⁰⁸Pb/²⁰⁴Pb = 37.920/Salters and Stracke [2004]; Workman and Hart [2005]) and EMI (⁸⁷Sr/⁸⁶Sr = 0.705108; ¹⁴³Nd/¹⁴⁴Nd = 0.512582; ²⁰⁶Pb/²⁰⁴Pb = 17.826; ²⁰⁷Pb/²⁰⁴Pb = 15.496; ²⁰⁸Pb/²⁰⁴Pb = 38.887/Eisele etal. [2002]; Jackson & Dagsputa [2008]); (B) End members: DM and EMII (⁸⁷Sr/⁸⁶Sr = 0.708478; ¹⁴³Nd/¹⁴⁴Nd = 0.512453; ²⁰⁶Pb/²⁰⁴Pb = 19.237; ²⁰⁷Pb/²⁰⁴Pb = 15.647; ²⁰⁸Pb/²⁰⁴Pb = 39.862/Workman etal. [2004]); (C) and (D) End members: EMI and HIMU (⁸⁷Sr/⁸⁶Sr = 0.702663; ¹⁴³Nd/¹⁴⁴Nd = 0.512865; ²⁰⁶Pb/²⁰⁴Pb = 21.199; ²⁰⁷Pb/²⁰⁴Pb = 15.767; ²⁰⁸Pb/²⁰⁴Pb = 40.382/Jackson & Dagsputa [2008]); “(E) End- members: OIB (⁸⁷Sr/⁸⁶Sr 0.704065; ¹⁴³Nd/¹⁴⁴Nd 0.512781 Bongiolo etal. [2015)]) and EMI (⁸⁷Sr/⁸⁶Sr 0.704532; ¹⁴³Nd/¹⁴⁴Nd 0.512489 Eisele etal. [2002]; Jackson & Dagsputa [2008]).

Samples from EG2 exhibit a discrepant pattern in mixing using ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios (Figs. 7A, 7D, and 7E). Such values may reflect an increment of radiogenic strontium by alteration and contamination with seawater (Hofmann & White, 1982). This alteration is also observed in LOI values and petrographic descriptions of these samples (De Barros etal., 2023). As for diagrams using radiogenic Pb data, the results were very precise and indicate the contributions of about 99% of DM for SPL 44 and 99.7% for SPL 40 in the case of a mixing with EMII (Fig. 7B), 10% of EMI for sample SPL 40, and 19% for sample SPL 44 when mixed with HIMU (Fig. 7C). Another possible mixing between HIMU and EMI could have generated SPL 45 and SPL 47, with a considerable contribution of EMI (Fig. 7D). Lastly, OIB sources from the Trindade plume were modeled with EMI, and SPL 47 could represent about 10% of OIB in this mixture (Fig. 7E).

All three EG3 samples can be associated with an equalized mixing between EM and EMI (Fig. 7A). When observed in a mixing of EMI and HIMU, they plot slightly out of the curve, but still following the same trend, indicating the possible contribution of these mantle sources, accounting for 10–20% of HIMU for SPL 45, SPL 47, and SPL 48 (Fig. 7C).

Numerous possible mantle sources and combinations can be associated with the heterogeneity and enrichment of the SCLM underneath the Campos and Santos basins during the Neoproterozoic events that originated from the Ribeira Orogen (Heilbron etal., 2008; Schmitt etal., 2008; Valeriano etal., 2004). The interaction of SCLM fragments and the underlying mantle are supposed to have contributed to the magmatic activity that is recognized in Santos Basin (Mohriak & Szameitat, 2023). Contributions of EMI and EMII end members are commonly observed in the literature, mainly regarding the drift magmatism in the studied area (Gordon etal., 2023b; Louback etal., 2021). An HIMU component could be associated to metasomatic processes in the SCLM (Stracke etal., 2005). This mantle source is also observed as an end member of the Vitória-Trindade magmatism (Quaresma etal., 2023; Maia etal., 2022; Marques etal., 1999; Santos etal., 2019).

The contribution of the Trindade Plume to the offshore magmatism in the studied area, observed specifically in SPL 47, is still debated in the literature (Thomaz Filho & Rodrigues, 1999; Thompson etal., 1998). Despite that, it is important to consider that the plume head positioning in 85 Ma was near the Alto Paranaiba Province (Gibson etal., 1997), considerably far from the studied area. Its geochemical contribution to the magmatic events in the Cabo Frio High area could then represent an indirect effect and possibly a reflection of the main events in the onshore Brazil alkaline events.

6 CONCLUSIONS

The following conclusions can be made based on previously presented data and discussions:

• The studied drift-related magmatism in the Cabo Frio High area is characterized by alkaline rocks that evolved by AFC processes as depicted by ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd range of variation, which cannot be explained exclusively by single crystallization processes. Further studies are needed to determine such contribution processes. Thefact is that the amount of isotopic data available is still insufficient for more refined petrological modeling of the complex magmatic differentiation processes involved in the genesis of these rocks;

• The cogeneticity of EG1, EG2, and EG3 is still unclear, but discrepancy in ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios in samples with the same level of evolution (SPL 45 and SPL 48) indicates that different mantle sources were involved in the formation of the studied rocks. An alternative hypothesis is the involvement of different proportions of mantle components, including variation in composition and age;

• Binary mixing models suggest the contribution of EMI, EMII, DM/MORB, and HIMU as the origin for the Cabo Frio High area drift magmatism. Such mixing models can reflect the SCLM characteristics and origins, which should be related to previous mantle complex subduction events beneath the studied area (Valente etal., 2007). However,alternative models propose that enriched mantle components are not solely derived from the subducted material. Quaresma etal. (2023) and Maia etal. (2022) suggest that mantle enrichment may also result from the detachment of the metasomatized SCLM (EMI component) during the Gondwana breakup and/or from the delamination of the South American SCLM induced by edge-driven convection. Additionally, the presence of a recycled subducted oceanic crust component, related to an HIMU-type end member, has been proposed to explain the isotopic signatures observed in the region. These processes, along with the assimilation of oceanic crust slabs linked to the Brasiliano Event (Nd model ages ranging from 407 Ma to 767 Ma), suggest a complex interaction between asthenospheric and lithospheric sources in the mantle beneath the study area. A possible contribution of OIB (plume-like) mantle sources can still be taken into consideration, and in this case, the most probable scenario is an association with the Trindade Plume.

• The studied magmatism is possibly associated with the partial melt of asthenospheric mantle sources in shallow depths, corresponding to a relatively thinned lithosphere (Fig. 8). Thecontribution of SCLM in generating these magmas would be reflected in EMI end members, observed in binary mixing models for all the studied samples. Interactions between the SCLM and the Trindade Plume, as also presented by Quaresma etal. (2023), evidence the contribution of both elements in generating the studied magmatic events. Isotopic data may also suggest possible crustal contamination in the process to generate these magma. HIMU components may indicate the involvement of metasomatic processes in the mantle that gave origin to these magmas, while EMII could reflect the complex and enriched mantle affected by crustal contamination during preterits subduction processes. OIB-like, represented by the Trindade Plume, should be taken into consideration, but given the limited results (a positive association with only one of the studied samples) and the plume head positioning during the formation of these magmas, more studies should be undertaken to determine the contribution of this source. Nevertheless, trace and isotopic data indicate a strong fertile component in these magmas’ origin. Meanwhile, the presence of deep structures and crustal discontinuities during the extensional processes suffered by the studied basins would have facilitated the ascension and displacement of magmas.

FIGURE 8
Conceptual geodynamic model for the origin of magmatism in the Alto de Cabo Frio region during the Santonian–Campanianperiod.

The diversity of potential mantle sources contributing to the formation of the magmas under study indicates the heterogeneous nature of the mantle and the geodynamic setting in which they are emplaced. The origins of these magmatic events within the Campos and Santos passive margin basins during the Santonian–Campanian period remain uncertain, as do the principal geotectonic processes responsible for significant thermal input or the reactivation of deep structures necessary for generating such magmatism.

Given the relevance of the Campos and Santos basins for the hydrocarbon industry and for the understanding of Brazilian geological evolution, further studies are necessary to clarify the geodynamic context associated with the drift magmatism, its effects on tectono-sedimentary evolution of these regions, and the reflects caused in the adjacent petroliferous systems.

ACKNOWLEDGMENTS

We acknowledge the support and funding from Equinor Brazil and the support of ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. Master’s student Tatiele Marques Jatobá de Barros acknowledges CAPES scholarship, a research funding agency in Brazil. We would also like to acknowledge the reviewers for their constructive comments and insightful suggestions, which helped improve the quality of this manuscript.

ARTICLE INFORMATION

• Manuscript ID: 20240040. Received on: 15 JULY 2024. Approved on: 28 FEB. 2025.
  How to cite: Barros, T., Corval, A., Valente, S. C., & Miranda, A. W. A. (2025). Petrogenesis of the drift magmatism in the Cabo Frio High, Campos Basin, Brazil: Evidence from Sr–Nd–Pb–Hf isotopes. Brazilian Journal of Geology, 55, e20240040. https://doi.org/10.1590/2317-4889202420240040

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Edited by

• Scientific Editor:
  Carlos Henrique Grohmann https://orcid.org/0000-0001-5073-5572

• Associate Editor:
  Andres Folguera https://orcid.org/0000-0001-8965-8543

Publication Dates

• Publication in this collection
  26 May 2025
• Date of issue
  2025

History

• Received
  15 July 2024
• Accepted
  28 Feb 2025