Interpretation of High-Resolution Remote Sensing Data for Plio-Pleistocene Tectonic Structures Studies in the Trindade Island Volcanic Building, South Atlantic Ocean, Brazil

Abstract

Trindade Island (20°31′0’ S and 29°19′0 W) is a large alkaline volcanic edifice and is the only emerging part of the Vitória-Trindade ridge, 1140 km from the Brazilian offshore, whose summit is around 600 meters high. The lineament orientation pattern of Plio-Pleistocene dykes and fracture swarms identified by high-resolution remote sensing allowed identifying the paleo-stresses that acted on Trindade Island. Our research suggests that Trindade Island suffered two distinct tectonic events between 3.6 Ma and 0.25 Ma: the first event is related to the island formation and shows a NW-SE (compressional) and NE-SW (extensional) stress orientation, while the second event shows different stress, namely ENE-WSW (compressional) and NNW-SSE (extensional). These events may also be associated with the opening of the South Atlantic Ocean, during movement and torsion of the South American Plate in the NE-SW direction, evidencing compression toward ENE or due to the influence of the Trindade mantle plume on the South American Plate which generated intraplate stress.

1. Introduction

The theoretical concept of plate tectonics, in which the lithosphere is divided into a mosaic of plates, which move and sink into the weaker ductile asthenosphere, is that tectonic plates are rigid and deformations only occur at convergent, divergent, and transform boundaries and that the driving force of plate drift is due to their subduction on convergent boundaries [1, 2, 3, 4, 5, 6], but in recent years, has discovered the existence of intraplate deformation in Atlantic oceanic crust, associated to regional efforts due to mantle plume influence [7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17].

The South American Plate occupies a large area between the Caribbean Sea, the Peru-Chile Trench, Nazca Plate, Cocos Plate, and the Caribbean, and Atlantic Plates. It represents one of the regions with strong tectonic deformation in the Southern Hemisphere and has a peculiar tectonic feature (e.g., Andes Cordillera). This tectonic plate shows activities such as earthquakes and volcanic eruptions, which are due to the eastward drift of the Nazca Plate and westward expansion of the mid-Atlantic ridge that imposes intra- and inter-plate deformation and different drifts between them. This is a consequence of the long duration of Mid-Atlantic Ridge expansion, provoked not only by mantle plumes but also by whole-mantle convection, with ridge up-welling acting as a counterweight to crustal subduction [9, 18].

This jigsaw puzzle is responsible for several morphological features observed onshore and offshore worldwide: for example, Himalayas, Saint Andreas Fault, Mesoceanic Ridges, Alps, Mariana’s Trench, and so on. On the Atlantic Ocean side, after Gondwana breakup, several transform faults structured its basement and supported the almost orthogonal opening of its counterparts ([19]). In southeast Brazil, during Atlantic Ocean overture, several fracture zones were formed and extended continental inland forming preferential zones for magma ascending [20]. These structures supported magma ascending and generation and are associated with a complex involvement with an orogenic process starting in the Pangea fragmentation, going through the Brasiliano Orogeny and Gondwana breakup [21]. These authors also claimed for a shallow mantle plume in a convective system responsible for ascending hybrid metasomatized melt homogenized prior to eruption from a multivariate mantle reservoir, with elemental chemical imprint from ancient subducted oceanic slabs, and delaminated SLCM [22]. In this context, the Vitória-Trindade Ridge (Figure 1) has a controversial evolutionary history dividing authors between plate tectonics generation and its fracture zones [20, 24, 25] and a combined shallow mantle plume genesis [19].

Figure 1.

(A) Trindade Island location, South Atlantic Ocean, Brazil (regional bathymetric map of the Brazilian southeastern continental margin, modified from the ridge multibeam synthesis (GeoMapApp (www.geomapapp.org) [23], (B) 3D color TDM view over Vitória-Trindade ridge (predicted bathymetry based on the TOPEX/Poseidon ver. 15.1, modified from [23]. 1– Abrolhos volcanic complex, 2– Vitória seamount, 3– Besnard Bank, 4– Champlain seamount, 5– Congress seamount, 3 nt, 6 – Montague, 7– Jaseur seamount, 8– Columbia seamount, 9– Davis Bank, 10– Asmus Bank, 11– Dogaressa Bank, 12– Gilberto Amado Hill, 13– Motoki Hill, 14– Columbia bank, 15– Palma seamount, 16– Trindade Island, 17– Martin Vaz archipelago. Black beachball: Nodal-plane solution from 6.5 earthquake of march/1955: 19.9°S; 36.7°W (based 87).

The Atlantic Ocean is one of the least studied ones on the planet, with several volcanic edifices lacking geological and scientific studies. The Brazilian conjugated Margin has been studied since the past century, mostly in the platform area due to the oil & gas industry. As it advances ocean ward, indirect scientific studies (potential methods; seismic and other geophysics methods) have been conducted in the last 70 years. Concerning the geological studies of islands and seamounts, the first study was conducted by Almeida in the 1950s, and not before the 1970s, the third research has been conducted in the islands. Most of the knowledge we do have now related to the Meso-Cenozoic Brazilian offshore volcanics comes from the past 10 years of our research team, publishing over 15 papers. Most of them concerning the genesis and evolution of the biggest volcanic ridge in the Brazilian offshore area: the Vitória-Trindade Ridge (VTR), composed of more than 30 seamounts, banks, guyots and one island and one archipelago Trindade Island and Martin Vaz Archipelago (Figure 1).

In line with this research field, the objective of this chapter is to discuss the tectonic forces that control the magmatism on the Trindade Island, apparently associated with the Trindade Plume influence [7, 17], from the Interpretation of high-resolution remote sensing data for Plio-Pleistocene tectonic structures, like dykes and fault orientations. Dykes and faults orientation are indicators of tectonics, since they are positioned at 90° from the least stress tensor - σ₃ [26, 27, 28, 29]. There is an agreement between σ₁ and σ₂, “calculated through both the orientation of dykes and faults” movement, at the same efforts field [30]. This relationship is also valid for volcanic areas and for intrusive bodies, and not only for purely extensive structures but also for transtensive ones [31].

2. Geological context

After the first work made by Almeida [32] in the Trindade Island, publishing the first geological map for Trindade Island (Figure 2), isolated publications about the Vitória-Trindade Ridge (VTR) raised a possible relationship between a mantle plume and oceanic lithosphere interaction in the South American Plate [37, 38, 39, 40, 41]. The VTR is an alignment composed of guyots, banks, seamounts, and islands, where Trindade Island and Martin Vaz Archipelago are inserted in the easternmost part of it. Several alkaline massifs inland Brazil territory are linked to the offshore extension, roughly parallel to the ca. 20°S, through a seamount ridge toward the islands 1200 km away from the Brazilian coast (Figure 1).

Figure 2.

Simplified geological map from the Trindade Island, Atlantic Ocean, Brazil. Based on [33, 34, 35, 36].

The seamounts and islands are linked to the Trindade Plume and they are from west to east (Figure 1): Abrolhos Magmatic Province (1), Besnard Seamount (2), Vitória Seamount (3), Hotspur Seamount, Congress Bank (4), Montague Seamount (5), Jaseur Seamount (6), Colúmbia Bank (7), Davis Bank (8), Asmus Bank (8A), Dogaressa Bank (9), Colúmbia Seamount (10), Palma Seamount (11), and Trindade-Martin Vaz Archipelago. Motoki Hill (12) is at south Colúmbia Seamount (10), which includes Asmus Bank, Palma Seamount, and Motoki Hill [19, 42, 43, 44, 45, 46, 47, 48]. There are controversies about this magmatism, some authors related this magmatism to the Atlantic Ocean break-up in the Lower Jurassic [33, 37, 39, 49], while other researchers (e.g., [19, 20, 21, 25, 43, 44, 50, 51, 52, 53, 54, 55, 56]) concluded that the alkaline rocks are associated with the Trindade mantle plume. Some of these latter authors proposed that the original composition of Trindade plume magmas was enriched by oceanic lithospheric mantle fragments and detached subcontinental lithospheric blocks, left at shallow levels during the Gondwana breakup, and which underwent thermal remobilization by the Trindade plume.

Moreover, mantle metasomatism has been invoked to explain trace element enrichment and the highly alkaline nature of the volcanic rocks (e.g., [57, 58, 59, 60, 61, 62]). Niu et al. [63] described the pre-metasomatic material source being the primitive mantle or a depleted reservoir left behind after extraction of the Atlantic Ocean crust. Ocean Island Basalt (OIB) is usually enriched in incompatible trace elements and this signature involves the need of a previous or simultaneous volatile-rich event melt infiltration in the mantle (F-; Br-; Cl-; H₂O; CO₂), enriching the melts in incompatible trace elements [64].

Trindade Island (TI) is situated in the South Atlantic Ocean at coordinates 20°31′0”S and 29°19′0”W, approximately 1140 km away from the Brazilian coast (see Figures 1 and 2). This island represents the exposed portion of a large alkaline volcanic structure, with its base submerged at a depth circa 5000 m. The island spans an area of 10.2 km² and rises approximately 625 m above the current sea level, featuring three distinct peaks. It is closely associated with the aseismic Vitória-Trindade Ridge, a significant geographic feature in the South Atlantic Ocean, which exhibits an east-west direction (see Figure 1).

The Vitória-Trindade Ridge (VTR) was formed from the passage of the South American Plate over the Trindade Plume (TP) in the Cenozoic [19, 24, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75]. To Brazil, the Island’s geology is an important preserved record of an undersaturated alkaline Plio-Pleistocenic volcanism. These geological features include volcanic relief such as phonolitic necks and dykes (e.g., nephelinite; sannaite; phonolite) and sub-horizontal layers of pyroclastic rocks and lava. These rocks were classified into five lithostratigraphic units [32]. These units represent the five distinct volcanic episodes associated with the island’s formation and evolution.

The first volcanic event gave rise to the Trindade Formation (TF) composed of pyroclastic and subvolcanic rocks of diverse composition (e.g., basanites, lamprophyre, and phonolite). The four subsequent Formations (Desejado – DF; Morro Vermelho MVF; Valado – VF; and Paredão Volcano Formation – PVF) correspond to diversified pyroclastic and volcanic lithology (e.g., nephelinite and phonolite) (Figure 2) [25, 33, 34, 35, 36].

⁴⁰Ar/³⁹Ar, ⁴⁰K/⁴⁰Ar, and ¹⁴7Sm/¹⁴³Nd dating [25, 67, 68] indicate aerial volcanism starting at 3.6 Ma and continuing up to 0.25 Ma, thus being one of the youngest volcanic episodes in the Brazilian geological record together with Martin Vaz Archipelago [52, 53, 69].

The VTR, as depicted in Figure 1, is believed to be linked to the reactivation of the Vitória-Trindade Fracture Zone (VTFZ) in conjunction with the TP [52, 53, 54, 55, 69]. This ridge serves as a volcanic trail created by the TP on the South American plate. The VTFZ played a role as a conduit for the transportation of magma derived from the enriched mantle during this process [7, 17, 24, 41, 45, 50, 52, 53, 54, 63, 66, 69, 70, 71, 72]. The VTR shows a general direction of E-W between 20° and 21°S, showing a geomorphological structure described by the alignment of banks and seamounts [52]. This ridge extends for about 1100 km, from the Besnard Bank and the Vitória Seamount south of Abrolhos Volcanic Complex (Figure 1). These submarine banks, seamounts, and guyots, with some of them presenting flat-topped shape, for example, Davis Bank located less than −100 m from actual sea level, rising from - 5000 m from the continental slope and foot ridge [7, 17, 21, 50, 70, 71]. The ridge is wider toward the west, due to the combination of the banks and seamounts by the algae and bryozoan carbonate reefs development [11, 73, 74].

3. Methodology

Remote sensing and digital image processing were used on the World View-2 satellite, which shows a multispectral resolution of 1.86 m and a Panchromatic resolution of 0.46 m, featuring 9 bands ranging from 400 to 1040 nm (Table 1). Those images are processed using the software ArcGIS and QGIS. The structural and volcanic features were established based on [77].

RGB 8–6–5	Near Infrared 2 (366–1040 nm)	Red Edge (705–745 nm)	Red (630–690 nm)
Pyroclastic rock (Trindade Formation)	Low	Low	Low
Volcanic rock (Trindade Formation)	Moderate	High	Moderate
Subvolcanic rock (Trindade Formation)	High	High	High
Pyroclastic rock (Desejado Formation)	Low	Moderate	Low
Pyroclastic rock (Morro Vermelho Formation)	Low	Moderate	Moderate
Pyroclastic rock (Paredão Volcano Formation)	Low	Moderate	Moderate
Pyroclastic and Olivine-Nephelinite Tuff (Valado Formation)	Moderate	Moderate	Moderate
Beaches related to weathering	Low	High	High
Dune Beaches	Very High	Very High	Very High
Vegetation	High	High	High

Table 1.

Spectral characteristics of the main lithologies of Trindade Island in the RGB 8–6–5 composition, based on [76].

The scene dates from 2015/05/08 and was submitted to atmospheric correction and Pansharpen through ERDAS Imagine and ER Mapper software. The RGB 8–6–5 + PAN composition was demonstrated to be the best false color composition without the use of mathematical devices between bands. This composition enhances the dyke contacts in relation to their wall rocks and between the rocks (Figure 3; Table 2).

Figure 3.

Satellite imagery: False color RGB 8–6–5 + PAN hybrid composition from Trindade Island, South Atlantic Ocean.

	Dyke	Faults
Length (m)	5–665	4–283°
Geometric Mean	59	34
Standard Deviation	40.14	27.28
n	980	1188

Table 2.

Summary of dykes and faults identified by remote sensing imagery.

The 3D bathymetry model of the ocean floor was used in the Satellite data from the TOPEX/Poseidon database by the Institute of Oceanography of the University of California (UCSD–SIO), with “Global Topography 1 minute resolution v. 19.1” and processed by software ERDAS IMAGINE, with the tool Rapid Atmospheric Correction. This data comes from the analysis of the artificial satellite orbits, which provides local gravity variations from each area scanned, this makes it possible to acquire data on a global scale with the exception of the northernmost part of the planet, where the satellite does not orbit. After correcting the data, the first free-air anomaly points are created and then a global map is generated. The combination of the free-air anomaly and known reference data (benchmarks) that were acquired through conventional ship bathymetry, allows the creation of a bathymetric map on a world scale or the predicted bathymetry map, with an apparent resolution of 900 m. Although these techniques do not have a detailed resolution, they make it possible to cover a large area and explore all kinds of features and morphologies around the globe. In the study, the data obtained from the TOPEX/Poseidon database were tied through a regular kriging mesh to interpolate the local data using the software ArcGIS (Spatial analyst tools: kriging).

After processing all the data, we utilized ArcGIS and QGIS software to analyze the images, delineating the structural framework and identifying the main volcanic features observed on Trindade Island.

4. Results and discussion

Based on the hybrid composition RGB 8–6–5 + PAN, it was possible to distinguish the main lithology that comprises the Island (Figure 3; Table 1), subdivided into five Formations [32, 36].

It should be noted that there are areas with high reflectance in all bands (Figures 3 and 4), which is due to the weathering of mafic minerals, which generates soils and sand riches in silica. Due to their bright color compared to the different geological structures around them, they can present a reflectance of up to 90% [76, 77, 78].

Figure 4.

(A) Contact between the subvolcanic rocks of the Trindade formation (TF) and the pyroclastic rocks of the Desejado formation (DF) is shown by white dashed line; red dashed line shows silica-rich residual soils and in black line delimited the weathered areas of the subvolcanic rocks from the TF; (B) contact between yellowish-green colored extrusive rocks and bluish colored pyroclastic rocks from the TF. Red to white colored subvolcanic dykes are visible, cutting through the pyroclastic rocks; (C) phonolite plug is white colored, showing alteration products in white-red color. The white areas correspond to weathered areas enriched in silica; (D) phonolite and nephelinite flows from Desejado formation show white color that corresponds to weathered areas enriched in silica (red line) and pyroclasts rocks showing bluish-green color, similar to the rocks of the Trindade formation; (E) pyroclastic rocks from Morro Vermelho formation show textures related to pyroclastic bedding and white colored area corresponds to weathered areas enriched in silica; (F) rocks from Paredão volcano formation show moderate reflectance in red and red edge and low reflectance in near-infrared 2. Red dashed line shows soils and sand riches in silica.

The rocks of the basal Trindade Formation (TF) are predominantly composed of phonolite and nephelinite of pyroclastic nature, extrusive and subvolcanic character [32, 36]. Extrusive phonolites usually have high reflectance in the Red Edge band (705–745 nm), exhibiting green colors ([78] and Reference therein). Subvolcanic phonolites have high reflectance in all bands, exhibiting a whitish color and, when altered show a reddish color, indicating high reflectance in Near Infrared 2 (860–1040 nm, see Table 1). Finally, pyroclastic rocks have low reflectance in all bands, exhibiting a bluish color (Figure 4A). The presence of whitish to reddish subvolcanic dykes cutting through the pyroclastic is also notable. Finally, the pyroclastic rocks exhibit a darker color, indicating low reflectance in all bands (Figure 4B, C).

Desejado Formation (DF) is composed of phonolite and nephelinite flows and various pyroclastic flows. The pyroclastic rocks have a similar spectral response to the pyroclastic rocks of the Trindade Formation and exhibit high reflectance in the Red band (705–745 nm, see Table 1). The phonolite and nephelinite flows also resemble strew and subvolcanic rocks from the Trindade Formation. However, they have a higher reflectance and display intense white colors and a lower level, which correspond to alteration products of mafic minerals (Figure 4D).

Morro Vermelho Formation (MVF) is essentially composed of nephelinite and pyroclastic flows. The spectral response of both rocks is similar to the pyroclasts of the Trindade Complex and Desejado Formation (see Table 1). However, the reflectance in these rocks is lower, with a decrease in the Red band and an increase in the Red edge band response, showing textures related to the pyroclastic bedding (Figure 4E). The white colored area corresponds to weathered areas enriched in silica.

Valado Formation (VF) rocks are nephelinite tuffs and pyroclastic flows, outcrop in rare and little area of the Island (20°30′03.6″S and 29°19′15.6″W), being characterized by moderate reflectance in all bands, presenting a whitish color with red alteration products (see Table 1).

Paredão Volcano Formation (PVF) is composed of nephelinite tufts and pyroclastic, and presents a spectral response similar to the rocks from the Morro Vermelho Formation. It exhibits moderate reflectance in the Red band and moderate reflectance in the Red Edge band (see Table 1), and shows a greenish-to-bluish coloration. It is remarkable that the presence of altered areas, with moderate reflectance in the Near Infrared 2 band, exhibits a red color (Figure 4F).

The underwater portion of the Island was mapped using the RGB 3–2–1 composition, which is based on the Coastal Blue and Blue bands, presenting great penetrability in water bodies and allowing the underwater features visualization (Figure 5).

Figure 5.

Trindade Island and its underwater surroundings, viewed through the RGB 3–2–1 composition satellite imagery.

Our interpretations of satellite imagery allowed building a geological map of Trindade Island (Figure 6), with the lithology divided into five Formation. The phonolite domes and necks were distinguished from the other lithologies from Trindade Formation because these bodies are intensely fractured and show several dykes cutting them. The satellite-interpreted geological map of Figure 6 is very similar to the field-interpreted geological map from Figure 2 based on [32, 36].

Figure 6.

Simplified geological map of Trindade Island based on satellite imagery.

4.1 Tectonic structure view by remote sensing imagery

The lineaments are roughly linear surface elements directly interpreted from remote imagery and can be related to structural tectonic movements. Dykes and faults are excellent tectonic indicators because they are positioned at 90° from the extension vector σ₃ [31, 79, 80, 81, 82, 83].

The lineaments identified by this work were divided into two categories: dykes (show thickness) and faults (no thickness). This distinction is important for a better understanding of the tectonic process throughout the Trindade Island genesis (Figure 6).

It identified 979 dykes and 1188 faults (see Table 2) that crop out in emerged and underwater rocks of the Trindade Island (Figure 7). Figure 6 shows a simplified geological map based on satellite imagery, where can see all dykes and faults from TI and Figure 8 shows the Rose diagram with the projections of respective directions.

Figure 7.

(A) Dykes cutting the Trindade formation, with NW-SE trend; (B) dykes cutting Desejado formation, with ENE-WSW trend; (C) dykes cutting Desejado formation, with trend near NNW–SSE and presenting different spectral responses Figure 7. (A) Dykes cutting the Trindade formation, with NW-SE trend; (B) dykes cutting Desejado formation, with ENE-WSW trend; (C) dykes cutting Desejado formation, with trend near NNW–SSE and presenting different spectral responses.

Figure 8.

Rose diagram projection of dykes (A) and faults (B) direction identified by satellite imagery from Trindade Island.

Projection of the poles from lineament directions at Lower-hemisphere, equal-area stereo-plot [84], shows two general directions at N50°W and N75°E and the straight dihedral-angle method [84] defines the following compression axes σ₁ 117/90 and σ₃ 27/90 (Figures 9 and 10, Table 3). The stress ax direction related to the underwater dykes is located approximately 90° from the crop-out rocks, suggesting a compression and further stretching related to the Vitória-Trindade Fracture Zone [24].

Figure 9.

Rose diagram with the directions of the dykes from the outcrop and underwater areas of Trindade Island identified from remote sensing imagery: (A) underwater dykes; (B) Trindade formation dykes; (C) phonolite dome and necks; (D) Desejado formation dykes; (E) Bingham distribution [66] with the dyke stress axes from Trindade Island.

Figure 10.

Rose diagram with the fault direction from Trindade Island identified by remote sensing imagery: (A): Trindade formation; (B): Dome and neck of phonolite; (C): Desejado formation; (D): Morro Vermelho formation; (E) Paredão volcano formation; (F) Bingham distribution [45] of fault tension axes from Trindade Island.

	σ1	σ3
All dykes	117°	27°
Underwater dyke	33°	120°
Trindade Formation dyke	119°	29°
Desejado Formation dyke	108°	26°
Phonolite Dome and Neck	116°	17°

Table 3.

Summary of dyke directions identified by remote sensing imagery.

The faults show a predominantly NE-SW orientation, and more rarely NW-SE and NNE-SSE (Figure 10A–E; Table 4). The only earthquake recorded in the last 68 years along the Vitória-Trindade Fracture Zone is characterized by maximum compression in the ENE direction compatible with the formation of open old fractures identified on Trindade Island [20, 85]. Mendiguren & Richter [86] assert that the existence of intraplate stress in the middle South America Plate is due to thrust-faulting mechanisms for intraplate earthquakes that show a dominant horizontal deviatory compressional stress oriented in a NW-SE direction and this stress is due to forces connected with spreading center (mantle plumes) on the Mid Atlantic Ridge (Figure 1).

	σ1	σ3
All Faults	40°	130°
Trindade Formation fault	40°	130°
Desejado Formation fault	36°	126°
Morro Vermelho Formation fault	60°	130°
Paredão Volcano Formation Fault	18°	135°
Phonolite Dome and Neck	45°	108°

Table 4.

Summary of faults identified by remote sensing imagery.

According to the seismic analysis conducted by the same authors, the epicenter of an earthquake (March/1955) with a magnitude of 6.4 was located slightly north (19.9°S, 36.7°W) of the Victoria-Trindade ridge (see Figure 1). The geological setting of this specific region suggested that the source mechanism of the earthquake might be attributed to stresses of topographic origin associated with the Victoria-Trindade ridge and Trindade mantle plume [86, 87]. The direction was similar to the one related to the formation of the Trindade Island which we defined as the first event, with NW-SE (compressional) and NE-SW (extensional) direction. Another event happened later, this one is characterized by ENE-WSW (compressional) and NNW–SSE (extensional) direction, we call this the second event.

The analysis of the fractures on Bingham distribution [84] shown in Figure 10F and Table 4 suggests NE–SW direction for σ₁ (compression) and NW-SE for σ₃ (distension).

All dyke directions are equivalent to those described by [20, 34, 36, 72, 85]. The NE-SW dykes from the Desejado Formation also suggest a NE-SW shortening explained by the faults. However, the rocks of the Desejado Formation are heavy vegetation cover, requiring field confirmation of our measurement interpretation.

Shortening axes (σ₁) inferred from fractures can only be used if these are open fracture, similar to dykes. The analysis of the few conjugated pairs from Trindade Island (n: 20) shows much dispersed data, with a possible E-W compression (Figure 11).

Figure 11.

Rose diagram with the conjugate faults directions from Trindade Island identified by remote sensing imagery.

The dykes present a general direction of NW-SE, secondarily to ENE-WSW. When inserted in the Trindade Formation or Desejado formation, they replicate this general orientation. In the most recent unit (Desejado Formation), the occurrence of similar amounts of ENE-WSW dykes is notable.

Field data indicate a vertical dip, suggesting a simple shear regime with a vertical dip [20, 34, 36, 72, 85]. Assuming all dykes are perpendicular to the lowest regional extension vector σ₃ [81] and the paleo-stress analysis through the Bingham distribution [84] suggests shortening (σ₁) at N28W, similar to the values from [20, 72, 85]. For ENE-WSW dykes, the maximum shortening direction (σ₁) is N81E.

The Faults from Trindade Island present a general trend of ENE-WSW. Assuming a distensile character in a simple shear regime (e.g., T-joints of the Riedel fracture system), the direction of shortening (σ₁) at ENE-WSW and extension (σ₃) at NNW-SSE is inferred.

5. Conclusion

Assuming that the dykes are lodged in extensive fractures, which the fractures denote the same character, it was inferred that the paleo-tensions acting in the Trindade Island presented two distinct events throughout its evolution. The first event is related to the island genesis and is characterized by NW-SE compression and NE–SW extension, the second event is characterized by compression at ENE-WSW direction and extension at NNW–SSE direction. These old stresses are similar to the stress from the latest earthquake of magnitude 6.4 recorded in 1955 in the Vitória-Trindade Submarine Volcanic Ridge [86]. Our data reveal, therefore, that the Trindade Island suffered two distinct tectonic events between 3.6 and 0.25 Ma. Such events can be associated with the torsion that the South American plate suffered during the opening of the Atlantic Ocean or effects of the passage of the South American plate over the Trindade mantle plume, which causes spot stress field [88].

Acknowledgments

Fieldwork in the Trindade Island was only possible due to the cooperation with the Brazilian Navy and National Council for Scientific Research (CNPq) through the PRO-TRINDADE Program, which is responsible for the supervision and maintenance of scientific research in different areas of knowledge for this region of the Brazilian territory. The present work is linked to the Ministry of Science and Technology and Innovation and National Council for Scientific Research (MCT/CNPq project n ° 442805/2015-2), under the coordination of researchers from Federal University of Rio Grande do Norte. The Brazilian Navy maintains a military base at the Trindade Island Oceanographic Post (POIT), which included a scientific station of the Trindade Island for research and lodging of the researchers (ECIT).

Conflict of interest

The authors declare no conflict of interest.

Notes/thanks/other declarations

We thank the Brazilian Navy cooperation during the field work and operation, particularly the staff at the POIT, and support through the PRO-TRINDADE Program (Scientific Research Program on Trindade Island). We are also grateful to the LEPLAC Project for providing the seismic dataset in the deep-water region of the Espírito Santo Basin. We thank Digital Globe Foundation provided the imagery from WorldView-2 Satellite and the Hexagon Geospatial provided the Erdas Imagine and ER Mapper software.