Lithospheric Structure of Northwestern Venezuela From Wide‐Angle Seismic Data: Implications for the Understanding of Continental Margin Evolution

Abstract

Northwestern Venezuela is located in the complex deformation zone between the Caribbean and South American plates. Several models regarding the lithospheric structure of the Mérida Andes have been proposed. Nevertheless, they lack relevant structural information in order to support the interpretation of deeper structures. Therefore, a 560‐km‐long refraction profile across the northern part of Mérida Andes, oriented in a NNW direction, covering areas from the Proterozoic basement in the south, to both Paleozoic and Meso‐Cenozoic terranes of northwestern Venezuela to the north, is analyzed in this contribution. Thirteen land shots were recorded by 545 short‐deployment seismometers, constraining P wave velocity models from first‐arrival seismic tomography and layer‐based inversion covering the whole crust in detail, with some hints to upper mantle structures. The most prominent features imaged are absence of a crustal root associated to the Mérida Andes, as the Northern Andes profile is located marginal to the Andean crustal domain, and low‐angle subduction of the Caribbean oceanic slab (~10–20°) beneath northwestern South America. Further crustal structures identified in the profile are (a) crustal thinning beneath the Falcón Basin along the western extension of the Oca‐Ancón fault system interpreted as a back‐arc basin; (b) suture zones between both the Proterozoic and Paleozoic provinces (Ouachita‐Marathon‐related suture?), and Paleozoic and Meso‐Cenozoic terranes (peri‐Caribbean suture) interpreted from lateral changes in seismic velocity; and (c) evidence of a deep Paleozoic(?) extensional basin, underlying thick Mesozoic and Cenozoic sequences (beneath the Guárico area).

Kinematics and Convergent Tectonics of the Northwestern South American Plate During the Cenozoic

“…Seismicity and tomographic imaging to the west of the high seismicity zone indicate that the Caribbean plate is shallowly subducting in this area (Figure 4). Mazuera et al (2019) interpret that the Caribbean plate continues shallowly subducting as a single slab beneath northwestern Venezuela. However, in the model of Mazuera et al (2019), the tomographic model is restricted to the upper 60 km.…”

“…Mazuera et al. (2019) interpret that the Caribbean plate continues shallowly subducting as a single slab beneath northwestern Venezuela. However, in the model of Mazuera et al.…”

“…However, in the model of Mazuera et al. (2019), the tomographic model is restricted to the upper 60 km. Nevertheless, the high seismicity zone (WBZ) with events between 90 and 160 km at about 73.5°W (Figure 4b) indicates that the subducting Caribbean slab is sinking beneath the Eastern Cordillera in eastward direction (Vargas & Mann, 2013), which is not consistent with flat‐slab subduction east of the WBZ.…”

“…Oceanic rocks accreted to SA indicate that initial collision of the PCA was located at 3°N (Duque‐Caro, 1990) and then the accretion migrated northward, currently reaching as far as 8°N (Figure 3). Based on seismological and tomography interpretations, several authors have proposed that the current geometry of the Caribbean slab is characterized by shallow subduction beneath northern Colombia and western Venezuela (e.g., Cornthwaite et al., 2021; Mazuera et al., 2019; Syracuse et al., 2016; Taboada et al., 2000). Nevertheless, some previous studies suggest that flat‐slab subduction may not be present in western Venezuela (Bezada et al., 2010; Sun et al., 2022).…”

Regional Geophysics of the Caribbean and Northern South America: Implications for Tectonics

“…In order to fill these data gaps, we added velocity models obtained from seismic refraction/wide‐angle reflection surveys (“seismic refraction data”) carried out along the Galapagos spreading center (Canales et al., 2002) and the Carnegie ridge (Sallarès et al., 2005). We also added crustal measurements from receiver function studies over NW South America (Poveda et al., 2015), Venezuela (Mazuera et al., 2019), Peru (Condori et al., 2017), and Brazil (Albuquerque et al., 2017). Although the seismic refraction and receiver function methods differ, both methods are reliable in defining the depth to the Moho discontinuity, assuming good quality data.…”