A New Look at Evidence for a Wadati-Benioff Zone and Active Convergence at the North Panama Deformed Belt

The deep structure of the south‐central Costa Rican subduction zone has not been studied in great detail so far because large parts of the area are virtually inaccessible. We present a receiver function study along a transect of broadband seismometers through the northern flank of the Cordillera de Talamanca (south Costa Rica). Below Moho depths, the receiver functions image a dipping positive conversion signal. This is interpreted as the subducting Cocos Plate slab, compatible with the conversions in the individual receiver functions. In finite difference modeling, a dipping signal such as the one imaged can only be reproduced by a steeply (80°) dipping structure present at least until a depth of about 70–100 km; below this depth, the length of the slab cannot be determined because of possible scattering effects. The proposed position of the slab agrees with previous results from local seismicity, local earthquake tomography, and active seismic studies, while extending the slab location to greater depths and steeper dip angle. Along the trench, no marked change is observed in the receiver functions, suggesting that the steeply dipping slab continues until the northern flank of the Cordillera de Talamanca, in the transition region between the incoming seamount segment and Cocos Ridge. Considering the time predicted for the establishment of shallow angle underthrusting after the onset of ridge collision, the southern Costa Rican subduction zone may at present be undergoing a reconfiguration of subduction style, where the transition to shallow underthrusting may be underway but still incomplete.

Section: Tectonic Frameworkmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The steeply subducting edge of the Cocos Ridge: Evidence from receiver functions beneath the northern Talamanca Range, south‐central Costa Rica

Dzierma

Rabbel

Thorwart

et al. 2011

“…The Cordillera de Talamanca, a ∼3800 m high extinct volcanic arc, coincides with the width of the Cocos Ridge (Figure ), which has been implicated with back‐arc migration of the volcanic arc in central Costa Rica at <2 Ma [ Marshall et al ., ]. Crustal shortening is also indicated by back‐arc thrusting and M w > 7 earthquakes along the North Panama Deformed Belt (NPDB), a seismically active fold and thrust belt [ Adamek et al ., ; Silver et al ., ; Camacho et al ., ] and incipient subduction zone [ Camacho et al ., ], running from central Costa Rica to the Maracaibo subduction zone, Colombia (Figure ).…”

Section: Introductionmentioning

confidence: 99%

Kinematics of the western Caribbean: Collision of the Cocos Ridge and upper plate deformation

Kobayashi

LaFemina

Geirsson

et al. 2014

Subduction of the Cocos plate and collision of the Cocos Ridge have profound effects on the kinematics of the western Caribbean, including crustal shortening, segmentation of the overriding plate, and tectonic escape of the Central American fore arc (CAFA). Tectonic models of the Panama Region (PR) have ranged from a rigid block to a deforming plate boundary zone. Recent expansion of GPS networks in Panama, Costa Rica, and Colombia makes it possible to constrain the kinematics of the PR. We present an improved kinematic block model for the western Caribbean, using this improved GPS network to test a suite of tectonic models describing the kinematics of this region.

“…This section of crust was first described by Kellogg and Vega [1995] as the Panama block and is moving northward relative to the Caribbean plate and eastward relative to the South American plate. The northern boundary of the Panama Block is the North Panama Deformed Belt (NPDB) characterized by the southward subduction of the Caribbean Plate [ Camacho et al , 2010]. The NPDB crosses Costa Rica on a westward trend to meet the Middle America Trench in a Caribbean Plate–Cocos Plate–Panama Block triple junction [ Mann and Kolarsky , 1995; Bird , 2003].…”

Section: Study Area and Tectonic Settingmentioning

confidence: 99%

Crystal fractionation processes at Baru volcano from the deep to shallow crust

Hidalgo

Rooney

2010

[1] Linking shallow and deep crustal processes at volcanic arcs is an important component in evaluating the growth and evolution of the continental crust. Commonly, deep crustal processes and the nature of subarc lithosphere are studied long after the volcanism has ceased in obducted arc terranes. In active arcs, studies of deep crustal processes focus on cumulates derived from middle-lower crustal levels. Although uncommon in the erupted magmas, these cumulates are required by crustal differentiation models of arc magmatism. Quaternary magmas at Baru volcano in Panama contain ubiquitous amphibole-bearing cumulates that provide an opportunity to probe the magma plumbing system of an active arc volcano. We have determined that these cumulates are related to their host magmas by crystal fractionation processes. Pressure and temperature estimates for amphiboles within these cumulates and the host rock are consistent with sampling of mush/magma zones from throughout the arc crust. These mush zones would be localized in deep hot crustal zones where magmatic differentiation of water-saturated arc magmas takes place by crystallization of amphibole-rich cumulates. The identification of middle-lower crustal cumulates is not exclusive to Baru volcano; similar cumulates are common throughout the Panamanian arc and are consistent with a widespread amphibole-rich layer present within the arc crust of Panama. Our results highlight the importance of amphibole fractionation in the differentiation sequence of island arcs effectively driving the residual magma to the average andesitic composition of the continental crust.