Upper-plate deformation in response to flat slab subduction inboard of the aseismic Cocos Ridge, Osa Peninsula, Costa Rica

Abstract

Along the Middle America Trench in southern Costa Rica, fl at slab subduction of the aseismic Cocos Ridge has uplifted and exposed the outer forearc, shortened the Térraba forearc basin sequence in the inner forearc (i.e., the Fila Costeña thrust belt), and uplifted the magmatic arc. The Osa Peninsula, an outer forearc high ~20 km inboard of the Middle America Trench and ~3 km to ~10 km above the plate interface at its trenchward edge, is deforming in response to variations in the bathymetry of the subducting aseismic Cocos Ridge where relief locally exceeds 1 km. Modern topography of the Osa Peninsula, elevation of the basement rocks (Early to Middle Tertiary Osa mélange), elevations of Quaternary marine deposits (Marenco formation), and distribution of late Quaternary uplift rates directly mirror the bathymetry on the Cocos Ridge outboard of the Middle America Trench. Rates of late Quaternary uplift are calculated from eight new radiocarbon ages, fi ve new optically stimulated luminescence ages, and 10 previously published radiocarbon ages. Rates of uplift range from 1.7 m/k.y. to 8.5 m/k.y. The Osa Peninsula is fragmented into small (~5 km), independently deforming blocks bounded by trench-parallel and trench-perpendicular, subvertical, normal and reverse faults that extend down to the plate interface, allowing for greatly different deformation histories over short distances. Quaternary deformation on the Osa Peninsula is modeled as a thin, outer-margin wedge that deforms in response to subduction of short-wavelength, high-relief asperities on the downgoing plate. Permanent deformation is largely accomplished by simple shear on a complex array of subvertical faults that allow the upper plate to adjust to variations in the slope of incoming ridges and seamounts. Currently, permanent deformation of the outer forearc does not appear to involve signifi cant subhorizontal shortening of the margin wedge, although the global positioning system velocity fi eld records elastic shortening related to locking of the plate interface. Permanent uplift and uplift rates in the outer forearc in southern Costa Rica are driven, to the fi rst order, by the bathymetry associated with the subducting Cocos Ridge and not by the basal shear stress on the plate interface.

Kinematic 3-D Retro-Modeling of an Orogenic Bend in the South Limón Fold-and-Thrust Belt, Eastern Costa Rica: Prediction of the Incremental Internal Strain Distribution

“…ABRATIS and WÖ RNER (2001) assume that the Cocos Ridge has been subducting since 8 Ma, whereas other studies propose a much younger history, depending on the method used: 3.6 Ma (COLLINS et al 1995) and 3-2 Ma (MACMILLAN et al 2004). The studies of MORELL et al (2012),GARDNER et al (2013), andLONSDALE andKLITGORD (1978) support the assumption that the front edge of the ridge arrived at the trench later than 3 Ma. In the most recent modeling study, ZEU-MANN and HAMPEL (2015) derive an onset of Cocos Ridge subduction at *2 Ma.…”

“…The Costa Rican part of the island arc can be subdivided into a northern and a southern arc segment (SEYFRIED et al 1991). The southern Costa Rican arc segment is influenced by flat subduction of the Cocos Ridge (CORRIGAN et al 1990;GARDNER et al 2013), which results in deformation and uplift on the upper-plate forearc (MORELL et al 2008(MORELL et al , 2012 (Fig. 1).…”

“…Early work on the bivergent southern Costa Rican landbridge was carried out by GREB et al (1996). The structural evolution of the forearc fold-and-thrust belt (Fila Costeña) has been comprehensively studied during the last decade (MENDE 2001;FISHER et al 2004;SITCHLER et al 2007;MORELL et al 2008MORELL et al , 2012MORELL et al , 2013GARDNER et al 2013). The onshore and offshore back-arc fold-and-thrust belt (South Limón belt) was analyzed by MENDE (2001) and BRANDES et al (2007a, b, c;; the latter focuses on basin dynamics (burial history and temperature evolution) and the architecture of the fold-and-thrust belt.…”

Kinematic reconstruction of the Caribbean region since the Early Jurassic

“…LaFemina et al (2009 suggested that the collision of the Cocos Ridge contributes to the northwestward motion of the forearc sliver. The buoyant, thickened crust of the Cocos Ridge acts as an indenter (Gardner et al, 2013) and arc-parallel forearc motion, as well as relative (north)eastward motion of the Panama-Chocó block represents tectonic escape (Kobayashi et al, 2014). Phipps Morgan et al (2008) noticed that the Motagua fault zone at present does not crosscut the Central American forearc and does not continue towards the Central American trench.…”

Normal faulting and mass movement during ridge subduction inferred from porosity transition and zeolitization in the Costa Rica subduction zone

“…The seafloor offshore the Osa Peninsula stands $2.5 km higher than the surrounding seafloor [Barckhausen et al, 2001;Walther, 2003], due to the subduction of the aseismic Cocos Ridge, a 200 km wide and 1000 km long seamount chain formed at the Galapagos hot spot [Johnson and Lowrie, 1972;Werner et al, 2003] on the eastern edge of the Cocos Plate. The subduction of the buoyant Cocos Ridge has affected the upper plate structure, causing erosion of the outer forearc and the uplift of the Osa Peninsula and the Quepos region [Gardner et al, 1992[Gardner et al, , 2013Fisher et al, 1998;Sak et al, 2004].…”