Structural development of a high-pressure collisional accretionary wedge: The Samaná complex, Northern Hispaniola
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Article history:Received 25 August 2010Received in revised form16 February 2011Accepted 21 February 2011
this underplating process include faults that were for a period oftime subduction thrusts. Depending on their depth of accretion, therocks preserve a record of deformation and metamorphism during
accretionary wedges may result in their uplift and exhumation.These exhumed rocks form usually nappes thrust towards thepaleo-trech, of hectometric to kilometric thickness, with lowermetamorphic units structurally overlain by higher metamorphicunits (Kimura et al., 1996; Agard et al., 2001, 2009; Lister andForster, 1996; Stanek et al., 2006). These nappes started todevelop under high-pressure (P)/low-temperature (T) conditions,generally under blueschist facies conditions, suggesting that theearly exhumation is accommodated by thrusting.
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Journal of Structural Geology 33 (2011) 928e950Rodrguez).1. Introduction
Accretionary wedges (or prisms) comprise materials that havebeen transferred from the lower plate to the upper plate in intra-oceanic or continental subduction zones. At all but the shallowestlevels of the forearc, near the front of the wedge, these materialshave been underthrust with the lower plate and accreted to theupper plate. This accretion process involves a downward migrationof the subduction thrust. Thus, accretionary prisms constructed by
the burial in the lower plate, the accretion process at maximumdepth, and exhumation in the upper plate. In addition to the faultsactive during the initial emplacement of their rocks, accretionaryprisms can be cut by later reverse faults, or out-of-sequence thrusts,high-angle and detachment normal faults, and strike-slip faultsystems (Ring and Brandon, 1994; Ring et al., 1999; Ring and Layer,2003; Mann, 2007), which alter substantially their originalarchitecture.
Progressive addition or underplating of material at the base ofAvailable online 2 March 2011
Keywords:Accretionary wedgeDuctile thrustingHigh-pressure metamorphism40Ar/39Ar geochronologyCaribbean plate0191-8141/$ e see front matter 2011 Elsevier Ltd.doi:10.1016/j.jsg.2011.02.006The Saman metamorphic complex exposes a segment of a high-pressure collisional accretionarywedge, built during Caribbean island arc-North America continental margin convergence. Combineddetailed mapping, structural and metamorphic analysis, and 40Ar/39Ar geochronology show that thedeformation can be divided into ve main events. Early subduction-related D1 deformation and high-P/low-T M1 metamorphism under lawsonite blueschist (325e425 C/12e18 kbar; Rincon Marbles andSanta Brbara Schists lower structural nappes) and eclogite facies conditions (425e450 C/18e20 kbar;Punta Balandra upper structural nappe), was followed by M2 decompression and cooling in theblueschist facies conditions during D2 folding, thrusting and nappe stacking. 40Ar/39Ar plateau ages andT-t/P-t estimations revealed Late Eocene to earliest Miocene retrograde M2 metamorphism in thedifferent nappes for a consistent D2 top-to-the-ENE tectonic transport, which suggests a generalnortheastward progradation of deformation. The D3 event substantially modied the nappe stack andproduced open to tight folds with amplitudes up to kilometer-scale and the D4 ductile to brittle normalshear zones and faults, and related subhorizontal folding, record a late extensional deformation, whichalso affects the whole nappe pile. Non-penetrative D3 and D4 fabrics indicate M3 cooling in and underthe M3 greenschist-facies conditions. From the Miocene to the Present, the nappe pile was cut andlaterally displaced by a D5 sinistral strike-slip and reverse fault system associated with the Septentrionalfault zone.
2011 Elsevier Ltd. All rights reserved.a r t i c l e i n f o a b s t r a c tStructural development of a high-pressuSaman complex, Northern Hispaniola
Javier Escuder-Viruete a,*, Andrs Prez-Estan b, Jaa Instituto Geolgico y Minero de Espaa, C. La Calera 1, 28760 Tres Cantos, Madrid, Spb Instituto Ciencias Tierra Jaume Almera-CSIC, Llus Sol Sabars s/n, 08028 Barcelona, Sc Pacic Centre for Isotopic and Geochemical Research, University of British Columbia, 6d Instituto Geolgico y Minero de Espaa, Av. Real 1, 24006 Len, SpainAll rights reserved.e collisional accretionary wedge: The
t Gabites c, ngela Surez-Rodrguez d
Stores Road, Vancouver, BC V6T-1Z4, Canada
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elsevier .com/locate/ jsg
StruHowever, recent petrological and geophysical data indicate thatduring intra-oceanic subduction the oceanic crust and the over-lying sediments, part of which can be accreted to form theaccretionary wedge, are also dragged at depth along the subduc-tion plane into the so-called subduction channel (Cloos andShreve, 1988). Therefore, exhumation of subducted rocks meta-morphosed under high-P/low-T conditions may then take place inthe wedge and/or in the channel (Platt, 1993; Ring et al., 1999;Jolivet et al., 2003; Agard et al., 2009; Guillot et al., 2009).Underthrusting, detachment faulting and erosion, which are thedriving exhumation mechanisms for the sediments in the upperlevels of the subduction channel, often preserve the continuity ofthe PeT conditions within the accreted sedimentary material(Agard et al., 2001; Yamato et al., 2007). In contrast, blueschist andeclogite mac bodies are systematically associated with serpen-tinites and/or a mechanically weak matrix, and eclogites wrappedby a serpentinitic-matrix mlange mostly crop out in an internalposition in the orogen (Wakabayashi, 1990; Guillot et al., 2004;Tsujimori et al., 2006). The exhumation of mac oceanic rocksfrom the lower levels of the subduction channel was facilitated bytheir association with serpentinites, which would counterbalancetheir negative buoyancy and enhance mechanical decoupling(Hermann et al., 2000; Guillot et al., 2001; Garca-Casco et al.,2006; Agard et al., 2009). Finally, when a large continental piece(i.e., a passive margin or an isolated block) enters the subductionzone it may also be dragged by continental subduction, butgenerally only during a restricted period of time (c. 10 Ma; Ernst,2005; Chopin, 2003), after which collision develops. The intro-duction of the low-density continental material is generallythought to be responsible for the choking of subduction, whichthen stops or jumps outboard of the continental block (e.g. Stern,2004).
In this tectonic context, the igneous and metamorphic inliersoutcropping in the Septentrional Cordillera and Saman Peninsulaof the northern Dominican Republic include part of an accre-tionary wedge, built during Mesozoic to Cenozoic convergenceand collision between the Caribbean island-arc and the NorthAmerica southern continental margin. In the part of the collisionalacretionary wedge outcropping as a nappe pile on SamanPeninsula, the aim of this work is: (1) to analyze the structuralevolution of each nappe and its relationship to the metamorphicPeT paths; (2) to evaluate the obtained 40Ar/39Ar age data in thecontext of the tectonometamorphic history of the complex; and(3) to discuss possible exhumation mechanisms and structuralsettings for the high-P rocks, particularly for the mac eclogiteblocks, and its bearing within the framework of the northernCaribbean tectonics.
2. Regional setting
Located on the northern margin of the Caribbean plate, thetectonic collage of Hispaniola results from the oblique convergenceof the Caribbean island-arc system with the North American plate,which began in the Cretaceous. The arc-related rocks are regionallyoverlain by Paleocene/Lower Eocene to Holocene siliciclastic andcarbonate sedimentary rocks that post-date volcanic activity, andrecord the oblique arc-continent collision in the north, as well asthe active subduction along the southern Hispaniola margin (Mann,1999). Today, the oblique convergence between Caribbean andNorth America in Hispaniola is partitioned between plate boundaryparallel motion on the Septentrional and Enriquillo strike-slipfaults in the overriding plate, and plate boundary normal motion atthe plate interface on the offshore low-angle subduction thrusts ofthe Northern Hispaniola fault and Los Muertos trench (Fig. 1; Mann
J. Escuder-Viruete et al. / Journal ofet al., 2002; Manaker et al., 2008).In the northern Dominican Republic, the SeptentrionalCordillera-Saman Peninsula geological domain is a compositeof arc and oceanic derived units which were built during arc-continent convergence an accretionary wedge (Draper andLewis, 1991). Accreted units outcrop in several inliers, termedEl Cacheal, Palma Picada, Pedro Graca, Puerto Plata, Ro SanJuan and Saman complexes, which constitute the pre-Eoceneigneous and metamorphic basement complexes of the Septen-trional Cordillera (Fig. 1). These six complexes include meta-sedimentary rocks of the subducted continental margin ofNorth America, serpentinitic-matrix mlanges containing blocksof blueschists and eclogites, ophiolitic fragments of the proto-Caribbean lithosphere, plutonic and volcanic rocks related withthe Cretaceous Caribbean island-arc, and non-metamorphicrocks deposited in pre-collisional forearc sedimentary basins(Escuder-Viruete, 2008b). In Puerto Plata and Ro San Juancomplexes, the rst foreland deposits associated to the colli-sional processes are the Paleocene?/Lower Eocene olistostromesof the lower Imbert Fm (Draper et al., 1994), which containclastic elements derived from the Cretaceous volcanic arc,the metamorphosed ophiolites and, in minor amounts, thehigh-P metasediments derived from the subducted continentalmargin.
The Saman complex (Fig. 2) consists of syntectonicallymetamorphosed pelitic, carbonate and mac rocks, alternating invariable relative amounts. Joyce (1991) recognized a sequence ofthree metamorphic mineral zones, ranging from lawsonite-bearing schists in the NE to eclogites and garnet-blueschistspresents as lenses in the SW. Rocks preserving relict primarystructures and recrystallized to lawsonitealbite-bearing assem-blages characterize Zone I (Santa Barbara unit; De Zoeten et al.,1991). A 1e2 km width narrow intermediate Zone II is denedby lawsonite albite glaucophane assemblages in macrocks. In the southern side of the peninsula, garnet omphacite phengite and garnet clinozoisite glaucophane-bearing assemblages in intercalated mac lenses and blockswithin micaschists and marbles, dene a Zone III (Punta Balandraunit). The metamorphic sequence represents a metamorphicprole generated during SW-dipping Cretaceous-Eocene subduc-tion (Joyce, 1991). However, the increase in grade occurs overa short distance and it can be better explained by tectonic juxta-position of units that were metamorphosed at different depths(Escuder-Viruete and Prez-Estan, 2006). Minimum PeT condi-tions achieved were about 13 2 kbar and 450 70 C in thePunta Balandra unit and 7.5 2 kbar and 320 80 C in the SantaBrbara unit (Joyce, 1991; Gonalves et al., 2000). Structural dataand the pressure gap between them permitted Gonalves et al.(2000) to deduce that the Punta Balandra unit is thrust over theSanta Brbara unit and to interpret the metamorphic nappe stackof Saman complex as a fragment of an accretionary wedge thrustonto the North American continental shelf.
The mac eclogites, blueschists and other high-P rocks of thePunta Balandra unit are usually found as boulders in the riversthat drain the unit and ow to the beach of the Saman Bay. Theyhave been object of numerous petrological and geochemicalstudies (Pert et al., 1982; Giaramita and Sorensen, 1994;Sorensen et al., 1997; Catlos and Sorensen, 2003; Zack et al.,2004; Escuder-Viruete and Prez-Estan, 2006), but withouta precise indication of its structural context. Trace and majorelement geochemistry and Nd-isotopic patterns of eclogites andblueschists indicate that the protoliths originated at a mid-oceanridge and a volcanic arc setting, and subsequently were meta-morphosed and metasomatized in a mantle wedge abovea subduction zone (Pert et al., 1982; Joyce, 1991; Sorensen et al.,
ctural Geology 33 (2011) 928e950 9291997).
Fig. 1. (a) Map of the northeastern Caribbean plate margin. Box shows location of the northern Hispaniola area. (b) Geological map of Septentrional Cordillera and Saman Peninsula greatly modied from Draper and Lewis (1991),Draper and Nagle (1991), Escuder-Viruete (2008a), and Escuder-Viruete (2009a). SFZ, Septentrional fault zone.
StruFig. 2. Simplied geological and tectonic map of Saman Peninsula modied from Joyce
J. Escuder-Viruete et al. / Journal of3. Geology of Saman Peninsula
3.1. The metamorphic complex
Our mapping at the 1:50000 scale covered the whole SamanPeninsula and complemented the work of Joyce (1991). Thegeneral geology of the Saman Peninsula is composed of threeelements (Escuder-Viruete, 2008a, b; Fig. 2): (1) a subduction-related metamorphic complex whose internal structure consistsof a imbricate stack of discrete high-P nappes; (2) a group ofMiocene coarse-grained siliciclastic rocks that are both in faultcontact and unconformably overlie the metamorphic complexalong the south coast; and (3) an unconformable cover of sub-horizontal Late Miocene to Pleistocene limestone formations.This study is only concerned with the metamorphic complex. Thewhole of the Saman Peninsula is deformed by sinistral strike-slip and reverse faults associated with the (at least) earliestMiocene to Present movement of the Septentrional fault zone.This large-scale, subvertical fault zone occurs onshore just southof the complex.
The nappe stacking of the Saman complex is essentiallycomposed of high-Pmetasedimentary rocks. In ascending order themajor tectonic nappes are: Playa Colorado Phyllite, Rincn Marbles,Santa Brbara Schists, Punta Balandra, and Majagual-Los CacaosMarbles. This nappe pile is described in Table 1. Cross-sections andorientation data (Figs. 3 and 4) show that the nappe pile dips to theS-SSW. Several additional points to have in account are describedbelow.
The Playa Colorado Phyllite outcrops in a tectonic window at theNE sector of the complex. The Rincn Marbles consists of three
and ticks on thehangingwall sides), aswell as representative structural attitudes of rocks. Thedon top of the Santa Brbara Schists nappe. The Majagual-Los cacaos basal thrust is a late-D2 stnormal D5 faults overprinted all earlier ductile contacts. Saman Conglomerate lls a NeogenePositions of cross-sections IeI0 , IIeII and IIIeIII (Fig. 3), serpentinized peridotite lenses (s) an1) and Escuder-Viruete (2008a), showingmajor rock units, thrusts and faults (with barbs
ctural Geology 33 (2011) 928e950 931lithologically distinctmetacarbonate sub-units and, in theu...