Integrated Geophysical Investigations of the Pre-Andean Basins in Peru and Bolivia—A Search for Depocenters Concealed beneath a Foreland Basin

The Acre Basin basement (NW Brazil) and the transition from the intracratonic to retroarc foreland basin system

“…The dominance of rocks with a density between 2.70 and 2.71 g/cm 3 , locally interrupted by lower density granitic intrusions (Data S3), is compatible with the basement characteristics previously modelled for Marañon, Ucayali and Madre de Dios basins (Stewart et al, 2018), indicating that the Sub-Andean and Acre Basins share compositionally similar basements. In this way, the paleogeographic location, the evolutionary model for the region (Boger et al, 2005;Cordani & Teixeira, 2007;Jaillard et al, 2000;Ramos, 2008), the structural geometry of lineaments (Figure 12) and the dominance of meta-sedimentary and low-grade metamorphic rocks and granites (Figures 13 and 14) allow associating the Acre Basin basement with the Sunsás event (Data S3).…”

“…The positioning and implantation of the Iquitos forebulge in the Acre Basin is another relevant topic for understanding the influence of the Andean orogeny in the Acre Basin. Possibly, the gravity high with an elongated NW-SE trend, observed in the study area (Figure 4a, numbers 2, 3, 4 and 5), is compatible with the high pointed out by Stewart et al (2018) and establishes a limit with the positions indicated in the Marañon Basin for the Iquitos Arch (Jacques, 2003;Roddaz et al, 2005;Stewart et al, 2018;Wesselingh et al, 2006). Despite the few available publications specifically focused on the arrangement of the Iquitos Arch in the Brazilian territory, our data point to a significantly different position from that established in recent decades (Milani & Zalán, 1999;Wesselingh et al, 2006;Zalán, 2004 and references therein;Milani et al, 2007) and contribute to understanding the foreland system in the Amazon region.…”

“…Even younger K-Ar ages between 849 and 935 Ma were considered isotopic rejuvenation via high-grade metamorphism or related to Ar escapes in the crystalline lattice (Cordani et al, 1984). Furthermore, the main E-W trend of the geophysical lineaments interpreted in the Acre Basin differs from the dominant NW-SE trends identified in the other Sub-Andean basins (Stewart et al, 2018) and is close to the WNW deformation proposed for the Nova Brasilândia metasedimentary mobile belt (Quadros et al, 2020(Quadros et al, , 2021Tohver et al, 2004) (Figure 1). The origin of this mobile belt in the Sunsás (Cordani et al, 2000;Tassinari & Macambira, 1999) or Sunsás-Aguapeí Province (Teixeira et al, 2010) is related to intraplate extensional tectonics, through the reactivation of the Guaporé suture zone and intraplate rifting, followed by an accretionarycollisional orogeny that developed between 1137 and 1010 Ma (Quadros et al, 2021;Rizzotto et al, 2014).…”

“…Seismic data indicate that this structure is sealed by the Cretaceous unconformity (Figure 13c) and can, therefore, be interpreted as the structure generated during the Juruá orogeny (Late Jurassic), which corroborates the thesis of de Oliveira (1994). Such arches, sealed by Cretaceous deposits and the Cenozoic foredeep, have already been described in the region (e.g., Madidi Arch in Madre de Dios Basin; see Baby et al, 2018;Stewart et al, 2018) and in the specific case of Acre Basin, divides the depocenter into the Jaquirana Trough to the north and the Central Trough to the south (de Oliveira, 1994;Wanderley Filho et al, 2010). The similar high of the Moho in the southwestern-most portion is interpreted here as the Contaya Arch edge, which corresponds to a structure with an NW-SE trend formed during the Triassic-Jurassic and later reactivated F I G U R E 1 0 Arbitrary well correlation showing smoothed gamma-ray log, density log and simplified lithologies, indicating the top of basement estimated by tilt depth and datum at the ground level.…”

“…in the Neogene, establishing the boundary between the Marañon and Ucayali basins near the western edge of the Acre Basin (Hermoza et al, 2006;McGroder et al, 2015;Stewart et al, 2018;Zelasco, 2010). The gravity low between 15 and 50 km is related to the larger depths of the basement identified in the seismic profile, which coincides with the Batã Fault, close to well L10-1.…”