The Imbert Formation of northern Hispaniola: a tectono-sedimentary record of arc–continent collision and ophiolite emplacement in the northern Caribbean subduction–accretionary prism

Abstract

Abstract. In northern Hispaniola, the Imbert Formation (Fm) has been interpreted as an orogenic “mélange” originally deposited as trench-fill sediments, an accretionary (subduction) complex formed above a SW-dipping subduction zone, or the sedimentary result of the early oblique collision of the Caribbean plate with the Bahama Platform in the middle Eocene. However, new stratigraphical, structural, geochemical and geochronological data from northern Hispaniola indicate that the Imbert Fm constitutes a coarsening-upward stratigraphic sequence that records the transition of the sedimentation from a pre-collisional forearc to a syn-collisional basin. This basin was transported on top of the Puerto Plata ophiolitic complex slab and structurally underlying accreted units of the Rio San Juan complex, as it was emplaced onto the North America continental margin units.The Imbert Fm unconformably overlies different structural levels of the Caribbean subduction-accretionary prism, including a supra-subduction zone ophiolite, and consists of three laterally discontinuous units that record the exhumation of the underlying basement. The distal turbiditic lower unit includes the latest volcanic activity of the Caribbean island arc; the more proximal turbiditic intermediate unit is moderately affected by syn-sedimentary faulting; and the upper unit is a (chaotic) olistostromic unit, composed of serpentinite-rich polymictic breccias, conglomerates and sandstones, strongly deformed by syn-sedimentary faulting, slumping and sliding processes. The Imbert Fm is followed by subsidence and turbiditic deposition of the overlying El Mamey Group.The 40Ar ∕ 39Ar plagioclase plateau ages obtained in gabbroic rocks from the Puerto Plata ophiolitic complex indicate its exhumation at ∼ 45–40 Ma (lower-to-middle Eocene), contemporaneously to the sedimentation of the overlying Imbert Fm. These cooling ages imply the uplift to the surface and submarine erosion of the complex to be the source of the ophiolitic fragments in the Imbert Fm, during or shortly after the emplacement of the intra-oceanic Caribbean island arc onto the continental margin.

The San Marcos mélange, Cordillera Septentrional of the Dominican Republic. Nature, origin and age

“…En los complejos de Puerto Plata y Río San Juan, los primeros depósitos que registran el proceso colisional son los olistostromas ricos en clastos serpentiníticos de la Fm. Imbert de edad Paleoceno/Eoceno inferior (Draper et al, 1994), los cuales se depositan discordantes sobre diversas unidades del prisma de subducción-acreción y contienen elementos clásticos derivados tanto de la ofiolita infrayacente como del arco volcánico Cretácico (Escuder-Viruete et al, 2016).…”

“…1 y 2) de megabrechas polimícticas , brechas y conglomerados ricos en serpentinitas (e.g. Mélange de Barrabás; Escuder-Viruete et al, 2016). Estos materiales son contemporáneos o ligeramente más antiguos que las calizas someras con algas de la Fm.…”

“…Recientemente (Escuder-Viruete et al, 2016), la Fm. Imbert ha sido interpretada como una megasecuencia estratigráfica grano-creciente que registra la transi- .…”

“…Imbert infrayacente (Escuder-Viruete et al, 2016), y con los de la orientación del margen convergente Mann, 1991, 1999). La tectónica extensional sinsedimentaria resulta de la inestabilidad de la cuenca.…”

“…Recientemente, Escuder-Viruete et al (2014, 2016 han establecido que la Fm. Imbert (Paleoceno-Eoceno inferior) está estratigráficamente superpuesta por el Grupo El Mamey (Eoceno medio-superior a Mioceno inferior) en los complejos de Puerto Plata y Río San Juan, y representa la base de una cuenca de piggyback sin-colisional desarrollada en un contexto de antearco durante el inicio de la colisión arco-continente.…”