Cenozoic Stages of Forearc Evolution Following the Accretion of a Sliver From the Late Cretaceous‐Caribbean Large Igneous Province: SW Ecuador‐NW Peru

Abstract

The SW Ecuador‐NW Peru forearc region is the southernmost location, where the Caribbean large igneous province (CLIP) interacted with the South American margin since the Late Cretaceous. The accretion of the CLIP to the margin led to the entrapment of the North Andean crustal Sliver, conforming the underlying basement of the forearc region in Ecuador, whereas in NW Peru, forearc depocenters involve rocks of continental affinity. Many existing tectonic reconstructions have treated these two areas independently, largely based on their crustal affinities. In contrast, this study integrates previous studies into an analysis of unpublished seismic profiles, potential field data, outcrop stratigraphy, and recent studies dealing with the dynamics of allochthonous terrane accretion along continental margins. Our integrated approach shows that SW Ecuador was dominated by a Late Cretaceous deforming outer wedge, which may have constituted a remnant of a northeast or northwest dipping obliquely obducted oceanic block at the edge of the CLIP. This tectonic phase was governed by plate instability, affecting NW Peru and SW Ecuador, followed by reestablishment of the margin by early Eocene. The resulting margin configuration and the spatial distribution of the different tectonic elements seem to have played a key role into the further Cenozoic development of the forearc region. The model presented in this study proposes that the accretion of buoyant oceanic terranes may have had a profound impact on the early margin configuration of SW Ecuador and NW Peru and led to the development of localized but genetically related forearc depocenters.

Forearc Crustal Structure of Ecuador Revealed by Gravity and Aeromagnetic Anomalies and Their Geodynamic Implications

“…Zircon ages along the metamorphic belt show a very similar pattern of Neoproterozoic age clusters and a younger group around 320 Ma and suggest a common metasedimentary origin of the entire massif [37]. Furthermore, these age clusters are similar with those in the western parts of the Eastern Cordillera and the northern section of the Occidental Cordillera of Peru suggesting a wide, 4 Lithosphere polyphase Andean metamorphic belt [37] thus excluding previous theories about the allochthonous origin for the Amotape-Tahuin Massif [33,38,39]. Moreover, its autochthonous origin was previously evidenced by the pervasive presence of Triassic (230-220 Ma) granitoids along the Amotape Massif and the Cordillera Real of Ecuador [35,40,41].…”

“…Paleomagnetic studies at the Amotape-Tahuin Massif report clockwise rotations in the order of 35°during the Late Cretaceous-Early Paleocene, related to the collision and accretion of the CLIP [33]. Fault mapping and displacement data show deformation that might be associated with a post-Paleocene reactivation, with block rotations in the order of 25° [42], of the inherited structures formed during the initial accretionary phase [4].…”

“…South of the Chongón-Colonche Hills, in the Santa Elena block (Figure 2), the stratigraphy is dominated by deformed Late Cretaceous rocks from the Santa Elena Formation, unconformably overlain by folded rocks from the Paleocene Azúcar Formation. These deformed sequences are interpreted as an accretionary wedge, which led to the development of an outer forearc high during the Oligocene, and the development of the restricted Neogene Progreso basin (Figure 2(b)) [4,29]. It is assumed that volcaniclastic sequences from the Cayo Formation and possibly mafic rocks from the Piñón Formation form the underlying basement of the Santa Elena block.…”

“…The Estancia magnetic high (70 nT) suggests that it may be underlain by mafic rocks, presumably from the Piñón formation. Farther south into the Santa Elena High and towards the Puná island, the magnetic intensity has a different anomaly pattern (Figure 4), possibly suggesting the transition into the Santa Elena accretionary complex [4].…”

“…Major continental growth took place along the NW corner of South America during the Late Cretaceous, following the collision and accretion of a sliver from the Caribbean Large Igneous Province (CLIP) [1][2][3]. Records of the interaction between the CLIP and the South America continental margin are preserved along its suture zone in the Western Cordillera and in SW coastal Ecuador (e.g., [4][5][6][7][8]) ( Figure 1). Several lines of evidence suggest that prior to the collision with South America, the CLIP was affected by the emplacement of the tholeiitic San Lorenzo/Naranjal and Rio Cala island arcs, while the western limit of the South American Plate (SAP) was most likely a passive margin [6,8].…”