Tectono‐stratigraphic response of the Sandino Forearc Basin (N‐Costa Rica and W‐Nicaragua) to episodes of rough crust and oblique subduction

Abstract

The southern Central American active margin is a world-class site where past and present subduction processes have been extensively studied. Tectonic erosion/accretion and oblique/orthogonal subduction are thought to alternate in space and time along the Middle American Trench. These processes may cause various responses in the upper plate, such as uplift/subsidence, deformation, and volcanic arc migration/shut-off. We present an updated stratigraphic framework of the Late Cretaceous-Cenozoic Sandino Forearc Basin (SFB) which provides evidence of sedimentary response to tectonic events. Since its inception, the basin was predominantly filled with deep-water volcaniclastic deposits. In contrast, shallow-water deposits appeared episodically in the basin record and are considered as tectonic event markers. The SFB stretches for about 300 km and varies in thickness from 5 km (southern part) to about 16 km (northern part). The drastic, along-basin, thickness variation appears to be the result of (1) differential tectonic evolutions and (2) differential rates of sediment supply. (1) The northern SFB did not experience major tectonic events. In contrast, the reduced thickness of the southern SFB (5 km) is the result of at least four uplift phases related to the collision/accretion of bathymetric reliefs on the incoming plate: (i) the accretion of a buoyant oceanic plateau (Nicoya Complex) during the middle Campanian; (ii) the collision of an oceanic plateau (?) during the late Danian-Selandian; (iii) the collision/accretion of seamounts during the late Eocene-early Oligocene; (iv) the collision of seamounts and ridges during the Pliocene-Holocene. (2) The northwestward thickening of the SFB may have been enhanced by high sediment supply in the Fonseca Gulf area which reflects sourcing from wide, high relief drainage basins. In contrast, sedimentary input has possibly been lower along the southern SFB, due to the proximity of the narrow, lowland isthmus of southern Central America. Moreover, two phases of strongly oblique subduction affected the margin, producing strike-slip faulting in the forearc basin: (1) prior to the Farallon Plate breakup, an Oligocene transpressional phase caused deformation and uplift of the basin depocenter, triggering shallowing-upward of the Nicaraguan Isthmus in the central and northern SFB; (2) a Pleistocene--

Comment on “The Chongón/Colonche orocline transrotational bending and the coeval opening of the Progreso basin in southwestern Ecuador” by Alemán et al

“…An interpretation that led Aizprua et al, [2020] to outline the presence of an outer forearc high, which is defined as well by seismic profiles. Similar potential field anomalies along forearc regions, associated with the development of an outer forearc high, are for instance described in Alaska [the Border Range Fault system, Mankhemthong et al, 2013]; California [Great Valley Forearc basin, Godfrey et al, 1997]; and Central America [Sandino Basin, Andjić et al, 2018]. Alemán et al, [2021] associate the timing of subduction initiation with the emplacement of the Macuchi volcanic arc during the Middle Eocene, based on a whole-rock K/Ar radiometric age of 41.6 ± 2.1 Ma for a basaltic andesite sample [Egüez, 1986], later confirmed by a more reliable 40 Ar/ 39 Ar age of 42.62 ± 1.3 Ma from a plagioclase of an andesite lava flow [Vallejo et al, 2009].…”

Rapid vertical motions and formation of volcanic arc gaps: Plateau collision recorded in the forearc geological evolution (Costa Rica margin)

“…also covered areas previously dominated by shallow-shelf deposits (Baumgartner et al, 1984;Di Marco, 1994;Seyfried et al, 1991). in NW Costa Rica Jaccard et al, 2001) and the Sapo a limestones (Andji c, Baumgartner-Mora, Baumgartner, & Petrizzo, 2018;Weyl, 1980) in SW Nicaragua ( Figure 3). ; Astorga, 1987).…”

“…Forearc basins may record a decrease or interruption in the supply of arcderived material when they are located inboard of volcanic arc gaps (Ballance et al, 1989). Whether they become accreted or subducted, colliding features may leave a distinct uplift pattern in the evolution of forearc basins, with a total surface uplift generally comprised between 1 and 3 km (Meffre & Crawford, 2001;Andji c et al, 2016Andji c et al, , 2018 as solid evidence of past episodes of rough crust subduction associated with volcanic activity cessation. Besides the Costa Rican type examples discussed above and in the literature (Table 1), two other sites may represent archetypal examples of collision recorded in the forearc sedimentary record.…”

“…to shallow-water environments, allowing the deposition of the Barra Honda Fm. in NW Costa Rica Jaccard et al, 2001) and the Sapo a limestones (Andji c, Baumgartner-Mora, Baumgartner, & Petrizzo, 2018;Weyl, 1980) in SW Nicaragua (Figure 3). These conditions did not persist for long after the Palaeocene-Eocene boundary, since the shallow-water limestones were rapidly replaced by deep-water turbidites (Cur u and Descartes fms.…”

“…was unconformably deposited on palaeosols that rested on deeply eroded, deep-water lithologies Jaccard et al, 2001). Similarly, in the Sandino Forearc Basin of SW Nicaragua, the latest Danianearly Selandian Sapo a limestones were unconformably deposited on an andesitic flow that rested on deeply eroded hemipelagics (Andji c et al, 2018). Penecontemporaneous deposition of pelagic limestones in the basin depocentres (Buenavista Fm.…”