The synrift phase of the early Domeyko Basin (Triassic, northern Chile): Sedimentary, volcanic, and tectonic interplay in the evolution of an ancient subduction‐related rift basin

Abstract

The geodynamic setting along the SW Gondwana margin during its early breakup (Triassic) remains poorly understood. Recent models calling for an uninterrupted subduction since Late Palaeozoic only slightly consider the geotectonic significance of coeval basins. The Domeyko Basin initiated as a rift basin during the Triassic being filled by sedimentary and volcanic deposits. Stratigraphic, sedimentological, and geochronological analyses are presented in order to determine the tectonostratigraphic evolution of this basin and to propose a tectonic model suitable for other SW Gondwana‐margin rift basins. The Domeyko Basin recorded two synrift stages. The Synrift I (~240–225 Ma) initiated the Sierra Exploradora sub‐basin, whereas the Synrift II (~217–200 Ma) reactivated this sub‐basin and originated small depocentres grouped in the Sierra de Varas sub‐basin. During the rift evolution, the sedimentary systems developed were largely controlled by the interplay between tectonics and volcanism through the accommodation/sediment supply ratio (A/S). High‐volcaniclastic depocentres record a net dominance of the syn‐eruptive period lacking rift‐climax sequences, whereas low‐volcaniclastic depocentres of the Sierra de Varas sub‐basin developed a complete rift cycle during the Synrift II stage. The architecture of the Domeyko Basin suggests a transtensional kinematic where N‐S master faults interacted with ~NW‐SE basement structures producing highly asymmetric releasing bends. We suggest that the early Domeyko Basin was a continental subduction‐related rift basin likely developed under an oblique convergence in a back‐arc setting. Subduction would have acted as a primary driving mechanism for the extension along the Gondwanan margin, unlike inland rift basins. Slab‐induced dynamic can strongly influence the tectonostratigraphic evolution of subduction‐related rift basins through controls in the localization and style of magmatism and faulting, settling the interplay between tectonics, volcanism, and sedimentation during the rifting.

Stratigraphic and provenance analysis of Triassic rock units between 28-29° S, northern Chile: implications on the tectonic and paleogeographic evolution of the southwestern margin of Gondwana

“…9), and to changes on the accommodation structures and environmental conditions in the Precordillera (Cuyo basin) recorded in the Marachemill unit (Barredo et al, 2012). Recently, this unconformity has been well constrained in norther Chile at the base of the Domeyko basin (Espinoza et al, 2018).…”

Complex Basement‐Involved Contractional Structures in the Pre‐Andean Basins of Northern Chile: A Review From Seismic Data

“…The Jurassic marine and sedimentary rocks are mainly fossiliferous mudstones, limestones, shales, and calcareous sandstones toward the upper sections, whereas the Lower Cretaceous rocks are almost entirely sandstones, conglomerates, and shales. Both field and seismic data show that the Mesozoic rocks fill half‐graben structures forming stratigraphic wedges that thicken toward the master faults bounding the half‐grabens (Amilibia et al., 2008; Espinoza et al., 2018; López et al., 2019; Martínez et al., 2018). Other stratigraphic and structural characteristics such as extensional growth strata and intraformational normal faults are also found in these deposits (López et al., 2019), which indicate that they were accumulated during important extensional tectonic stages.…”

Effects of pre‐orogenic tectonic structures on the Cenozoic evolution of Andean deformed belts: Evidence from the Salar de Punta Negra Basin in the Central Andes of Northern Chile

“…Triassic and Jurassic deposits are mainly exposed along the western and easternmost parts of the basin, in the Cordillera de Domeyko (Figure 2). These mostly consist of Upper‐Triassic (220–210 Ma; González et al, 2015; Espinoza et al, 2018) continental volcanic and sedimentary successions that are composed of approximately 1,200 m of stratified laves, tuffs, breccias, conglomerates and sandstones assigned to the Sierra de Varas and Pular formations. These were recently interpreted as the syn‐rift deposits of the ancient and isolated continental rift‐related Sierra de Varas sub‐basin (Espinoza et al, 2018), which forms part of the major Tarapacá back‐arc extensional basin (Mpodozis et al, 2005; Mpodozis & Ramos, 2008).…”

“…The deposits are partially covered by a thick (approximately 2000 m) marine Upper Triassic–Lower Jurassic succession consisting of calcareous and siliciclastic rocks. They are composed of intercalated fossiliferous sandstones, mudstones, conglomerates, shales and some gypsum beds assigned to the Profeta Formation (Ardill, Flint, Chong, & Wilke, 1998; Chong, 1973; González et al, 2015, among others), which has been interpreted as a syn‐ and post‐rift transitional stratigraphic sequence within the Sierra de Varas back‐arc extensional Sub‐Basin (Espinoza et al, 2018).…”