SESolid EarthSESolid Earth1869-9529Copernicus PublicationsGöttingen, Germany10.5194/se-7-11-2016The Imbert Formation of northern Hispaniola: a tectono-sedimentary record of
arc–continent collision and ophiolite emplacement in the northern Caribbean
subduction–accretionary prismEscuder-VirueteJ.j.escuder@igme.esSuárez-RodríguezÁ.GabitesJ.Pérez-EstaúnA.Instituto Geológico y Minero de España, La Calera 1,
28760 Tres Cantos, Madrid, SpainInstituto Geológico y Minero de España, Av. Real 1,
24006 León, SpainPacific Centre for Isotopic and Geochemical Research,
University of British Columbia, 6339 Stores Road Vancouver, BC V6T-1Z4,
CanadaInstituto Ciencias Tierra Jaume Almera-CSIC, Lluís
Solé Sabarís s/n, 08028 Barcelona, SpaindeceasedJ. Escuder-Viruete (j.escuder@igme.es)15January201671113611May201526June201522September20158December2015This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://se.copernicus.org/articles/7/11/2016/se-7-11-2016.htmlThe full text article is available as a PDF file from https://se.copernicus.org/articles/7/11/2016/se-7-11-2016.pdf
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.
Introduction
Intra-oceanic arc systems develop as a result of subduction initiation
within oceanic lithosphere and subsequent plate convergence. In this
tectonic context, forearc basins form on the upper plate between the arc
volcanic front and the outer-forearc high (Dickinson, 1995). They differ
from the outboard trench and trench-slope basins, which form along the
boundary between the two convergent plates in response to flexure of the
subducting slab and extension of the upper plate (Draut and Clift, 2012).
The distribution and nature of sedimentary sequences in a forearc basin is
controlled by uplift or subsidence and by the composition of the rocks
eroded from the neighbouring volcanic arc, subduction complex and
continental margin (von Huene and Scholl, 1991; Dickinson, 1995; Yen and Lundberg, 2006).
Chaotic rock assemblages, often referred in a descriptive non-genetic sense
as a mélange (Cowan, 1985), are commonly found in forearc and trench
environments and are attributed either to tectonic, sedimentary or diapiric
processes, as well as their mutual interplay and superposition (Harris et
al., 2009; Festa et al., 2010; Pini et al., 2012). They are often directly
linked to the subduction zone processes. However, the genesis of any chaotic
rock assemblage must be deduced from both detailed analyses of its
lithological content, the source of its components, and the kinematic
interpretation of its fabrics, as well as independent evidence concerning its
palaeotectonic setting. A particular chaotic rock assemblage is the
olistostrome, which is a sedimentary body derived from diverse types of
gravity mass movements, such as block slides, debris avalanches, debris
flows, and hyper-concentrated turbiditic currents (Lucente and Pini, 2003).
These “sedimentary mélanges” are compatible with the classic
principles of stratigraphic superposition, whereas other mélange
occurrences in nature do not follow these principles because they are bounded
by tectonic contacts. The serpentinite-matrix mélanges typical of
subduction channel complexes are examples of this last type (Krebs et al.,
2008, 2011). Useful criteria to discriminate between chaotic units of
sedimentary and tectonic origin are the presence or absence of soft sediment
deformation, the source of the rock fragments, the nature of the fine-grained
matrix, and the tectono-stratigraphic position within the accretionary prism
(e.g. Festa et al., 2010). The internal structure and the sedimentary record
preserved in mélanges can provide a better understanding of the
tectono-stratigraphic evolution of the orogen in which they occur (e.g.
Alonso et al., 2006, 2015).
The Greater Antilles orogenic belt (Fig. 1) results from the Late
Cretaceous-Paleogene convergence and collision between the Caribbean
island arc and the North America continental margin, which led to the closure
of the intermediate proto-Caribbean oceanic domain (Escuder-Viruete et al.,
2011c, 2013b; García-Casco et al., 2008; Laó Dávila et al.,
2012; Mann et al., 1991; Pindell and Kennan, 2009; Stanek et al., 2009). As a
result, several ophiolitic massifs were emplaced in the collisional zone,
which are particularly well exposed in Cuba (Lewis et al., 2006; Marchesi et
al., 2006). In northern Hispaniola, the Puerto Plata complex forms part of
the subduction–accretionary prism of the Greater Antilles orogenic belt,
which is constituted here by a series of accreted ophiolites,
ophiolitic mélanges, intra-oceanic volcanic arcs and fragments of the
southern margin of the North America continent (Escuder-Viruete et al.,
2011a, b, 2013a, 2014).
(a) Map of the northeastern Caribbean plate margin. Box
shows location of the northern Hispaniola area. DR; Dominican Republic, H;
Haiti. (b) Geological map of Septentrional Cordillera and Samaná
Peninsula modified from Draper and Lewis (1991), Draper and Nagle (1991) and
Escuder-Viruete (2009).
In the Cordillera Septentrional (Fig. 1), remnants of a Cenozoic pre- to
syn-collision forearc sedimentary basin developed over the orogenic prism are
constituted by the Imbert Formation (Fm) and the > 5 km thick
overlying turbiditic sequence of the El Mamey Group (de Zoeten and Mann,
1991). Unlike the well-studied El Mamey Group (de Zoeten and Mann, 1991,
1999), there are various interpretations of the origin and meaning of the
Imbert Fm, as well as of its spatial and temporal relationships with other
sedimentary units. The Imbert Fm has been interpreted as a Paleocene–lower
Eocene, deep-marine sedimentary unit deposited in the outer forearc-trench
setting, presumably over the underlying Puerto Plata complex (Nagle, 1979;
Pindell and Draper, 1991), an orogenic mélange originally deposited as
trench-fill sediments (Pindell, 1985), an accretionary (subduction) complex
formed above a SW-dipping subduction zone (Bowin and Nagle, 1982; Bourgois et
al., 1982), and a sedimentary record of the cessation of subduction-related
magmatism as result of the early oblique collision of the Caribbean plate
with the Bahama Platform in the middle Eocene (Draper et al., 1994; de Zoeten
and Mann, 1999; Hernáiz-Huerta et al., 2012).
In this contribution, we present detailed maps, stratigraphic columns,
whole-rock geochemical data of volcanic rocks, and data of syn-sedimentary
deformation structures of the Imbert Fm, as well as Ar–Ar cooling ages of its
basement. Our main objective is to document the stratigraphy and structure of
the Imbert Fm, as well as its relationships with igneous and metamorphic
basement units belonging to the northern Caribbean subduction-accretionary
prism. We show that the Imbert Fm is not a subduction mélange but
represents a coarsening-upward sedimentary sequence with an olistostromal
upper part, which unconformably overlies the supra-subduction zone (SSZ)
ophiolite of the Puerto Plata complex and the suture zone of the Río San
Juan complex. Our observations and data suggest that the rocks of the Imbert
Fm (1) contain the latest volcanic activity of the Caribbean island arc; (2)
record a change in the morphology of the forearc that was induced by uplift
during the arc–continent collision and ophiolite emplacement; (3) include
serpentinite-rich, chaotic rock assemblages deposited in a basin transported
on top of the ophiolite; and (4) were followed by a syn-orogenic turbiditic
sedimentation in a subsequent phase of regional subsidence (i.e. the El
Mamey Group).
Geological framework
Located on the northern margin of the Caribbean plate, the island of
Hispaniola (Fig. 1) is a tectonic collage produced by the oblique convergence
to final collision of the Caribbean island-arc/back-arc system with the North
American plate, which began in the Lower Cretaceous (Mann et al., 1991;
Draper et al., 1994). The presence of high-P ophiolitic mélanges in
northern Hispaniola indicates that an intermediate proto-Caribbean oceanic
basin was consumed by SW-directed subduction (Draper and Nagle, 1991; Saumur
et al., 2010; Escuder-Viruete et al., 2011a, c). The magmatic arc-related
rocks of the Caribbean upper plate have ages that span the Aptian–lower
Eocene interval and are regionally overlain by Eocene to Holocene sedimentary
rocks (Draper et al., 1994; Escuder-Viruete et al., 2006, 2008). This
sedimentary cover post-dates the volcanic activity in the arc and records the
oblique arc–continent collision in the northern area of the island, as well
as the intra-arc and retroarc deformation in the central and southern areas.
In northern Hispaniola (Fig. 1), the pre-Eocene igneous and metamorphic
substratum outcrops in several inliers, termed El Cacheal, Palma Picada,
Pedro García, Puerto Plata, Río San Juan y Samaná complexes
(Draper and Nagle, 1991). These six complexes form the Caribbean
subduction-accretionary prism in Hispaniola (Escuder-Viruete et al., 2013a,
b), and include, from E to W: metasediments of the subducted continental
margin of North America; ophiolitic fragments of the proto-Caribbean
lithosphere; serpentinitic-matrix mélanges with high-P blocks; and
igneous rocks related to the Caribbean island arc and forearc. In the prism,
the constituent tectonic units were incorporated and deformed progressively
younger to the E/NE, indicating a general migration of deformation in this
direction from the Late Cretaceous to the Miocene (Escuder-Viruete et al.,
2011a, b, 2013a).
The Puerto Plata complex
The Puerto Plata complex (PPC; Fig. 2) occupies a key position in the
Caribbean subduction-accretionary prism, because it is the westernmost and
structurally highest unit. It is composed of a pre-Eocene basement overlain
by a sedimentary cover (Nagle, 1979; de Zoeten and Mann, 1991; Pindell and
Draper, 1991; Hernáiz-Huerta, 2010; Monthel, 2010; Saumur et al., 2010).
The basement consists of serpentinized peridotite, layered (cumulate)
ultramafic and mafic rocks, massive gabbroic rocks, and volcanics of basic to
intermediate composition, locally pillowed with rare inter-pillow cherts and
limestones. These lithologies occur as tens of metres to hundreds of metres
spaced fault-bounded sections of rock in a structurally disrupted or
dismembered manner. On the basis of new mineral chemistry and bulk-rock
geochemical data, the mafic and ultramafic rocks of the PPC has been recently
interpreted as tectonically disrupted crust and mantle sections of Caribbean
oceanic lithosphere, which records a Cretaceous complex history of extreme
crustal thinning and related SSZ magmatism (Escuder-Viruete et al., 2014).
(a) Simplified geological map of Puerto Plata ophiolitic
complex modified from Draper and Nagle (1991), Hernáiz-Huerta (2010), Escuder-Viruete et al. (2014)
and Suárez-Rodríguez et al. (2015), showing locations of the El
Puerto (A–A′), Rancho Brugal (B–B′), Río Obispo (C–C′) and Loma
Seboruco (D–D′) sections, the location of the samples dated by
40Ar /39Ar method, and representative bedding orientations of
rocks. (b) Simplified geological map of northernmost Río San
Juan complex modified from Escuder-Viruete et al. (2013), showing locations
of the Gaspar Hernández (E–E′), Magante (F–F′), Caño Claro
(G–G′) and Hicotea (H–H′) sections, as well as representative bedding
orientations of rocks. Sample location (Lat/Long): 10JE54;
-70,74356/19,82547, JM9112; -70,74436/19,82614, HH9124;
-70,80958/19,81107.
The ophiolitic basement is overlain by the Paleocene–lower Eocene
> 500 m thick section of the Imbert Fm (Nagle, 1979), which is
composed of fine-grained turbidites interbedded with white and turquoise,
very fine-grained tuffs, pelagic sediments, rare radiolarian cherts and
basaltic sills. Pindell (1985) extends the unit including turbiditic beds, or
debris flows, of sandstone and conglomerate that contain angular to
sub-rounded lithic fragments up to 10 cm of serpentinites, as well as
metamorphic, volcanic and green siliceous rocks. Pindell and Draper (1991)
describe in detail the Imbert Fm and propose that it is coeval or slightly
older than an informal unit composed of serpentinitic-rich breccias, and the
lower-to-middle Eocene shallow-water limestones of the La Isla Fm, which
typically contains clasts of similar serpentinites. The serpentinitic
breccias are recently included at the base, and interbedded with, the lower
stratigraphic section of the San Marcos Fm (Hernáiz-Huerta et al., 2012),
which is a mud-matrix mélange. However, this interpretation disagrees
with the presence of middle Eocene to middle Miocene faunas in sedimentary
blocks included in the San Marcos Fm (Bourgeois et al., 1982;
Hernáiz-Huerta, 2010; Monthel, 2010), as well as the Miocene age of the
mudstone matrix (Monthel, 2010; Suárez-Rodríguez et al., 2013,
2015).
For Pindell and Draper (1991) and Hernáiz-Huerta et al. (2012), the
Imbert Fm records the early collision of the Caribbean island arc with the
Bahamas Platform. This is consistent with the middle to upper Eocene folding
and uplift tectonic event described in the Septentrional Cordillera by Mann
et al. (1991) and de Zoeten and Mann (1999), as well as in Puerto Rico
(Láo Dávila et al., 2012), Haiti and southwestern Cuba (Calais et
al., 1992). This tectonic event records the termination of Caribbean
arc-related activity and the formed structures are older than the
unconformably sedimentary base of the El Mamey Group. This group is composed
by the upper Eocene to lower Miocene Altamira, La Toca and Luperón Fms,
which comprise 1500 m of calcareous mudstones and siltstones, sandstones and
conglomerates (Nagle, 1979; de Zoeten and Mann, 1999). The sequence
culminates with the subhorizontal, middle Miocene to Pleistocene rocks of the
Jaiba and Villa Trina Fms.
The Río San Juan complex
The Río San Juan complex (RSJC; Fig. 2) consists of three elements
(Draper and Nagle, 1991; Krens et al., 2008, 2011; Abbott and Draper, 2013;
Escuder-Viruete et al., 2013a, b): (1) a core of Mesozoic igneous and
metamorphic rocks; (2) a group of Paleocene–lower Eocene to middle Miocene
olistostromic, turbiditic and siliciclastic rocks (Imbert, La Toca and La
Piragua Fms) that unconformably overlie the core at its periphery; and (3) a
subhorizontal cover of upper Miocene to Pleistocene limestones (Villa Trina
Fm). Recent work by Escuder-Viruete et al. (20113a) indicates that the
large-scale internal structure of the complex consists of an imbricate stack
of metamorphic rocks derived from both the Caribbean island arc and the
proto-Caribbean lithosphere. In structural ascending order, the major
tectonic nappes/units are the Gaspar Hernández peridotite, the Jagua
Clara serpentinite-matrix mélange, and the Cuaba and Morrito units.
The Gaspar Hernández unit is composed of typical abyssal serpentinized
peridotites (Saumur et al., 2010) and minor mafic sills with N-MORB
geochemical signatures, suggesting that it is a fragment of the
proto-Caribbean oceanic lithosphere (Escuder-Viruete et al., 2011c). The
Jagua Clara mélange consists mainly of schistose and sheared, antigorite
serpentinite. Blocks-in-matrix eclogites and blueschists originated from
N-MORB and IAT type magmas. The retrograde exhumation of the mafic blocks and
their re-equilibration to blueschist and greenschist-facies took place by
Campanian-Maastrichtian time (Escuder-Viruete et al., 2013b). The Cuaba unit
is mainly composed of mafic lithologies metamorphosed to amphibolite and
eclogite-facies conditions. They originated from IAT and calc-alkaline type
protoliths (Draper and Nagle, 1991; Escuder-Viruete, 2010). The Morrito unit is a nappe of metavolcanic rocks
(Draper and Nagle, 1991), which have boninite and IAT type compositions.
These protoliths are compositionally similar to the Lower Cretaceous
Caribbean island-arc rocks (Escuder-Viruete et al., 2011c). The basal thrust
zone juxtaposes the Morrito unit northward onto the Jagua Clara mélange.
This juxtaposition took place in the latest Maastrichtian to Paleocene, at
the onset of the arc–continent collision (Escuder-Viruete et al., 2013b). The
Morrito basal thrust has been interpreted as the suture zone between the
upper Caribbean island-arc terranes and the lower palaeomargin of North
America (Escuder-Viruete et al., 2011c).
The unconformably overlying olistostromic rocks of the Imbert Fm are mainly
composed of poorly sorted angular breccias and large blocks, with
subordinated sandstones, mudstones and rare white and turquoise tuffs
(Draper and Nagle, 1991; Escuder-Viruete, 2009). The clasts of the breccias
are mainly of serpentinite from the underlying Gaspar Hernández
peridotites, but also contain clasts of Jagua Clara and Morrito metamorphic
rocks. The source area for the breccias and olistostromes was probably a
fault-controlled escarpment, which indicates the exhumation of the
subduction-accretionary complex to submarine exposure before the
Paleocene–lower Eocene (Escuder-Viruete, 2009). The basal olistostrome is
overlain by the middle Eocene to Oligocene La Toca Fm, which is > 1 km thick and contains mid- to thin-bedded sandstones, siltstones and
marls, with rare intercalations of pebbly conglomerates and calcarenites.
The sediments of the La Toca Fm are thought to have accumulated in the
middle/distal area of a syn-orogenic turbiditic basin. Turbiditic
sedimentation is succeeded by alluvial-fan conglomerates of the lower/middle
Miocene Piragua Fm, and the upper Miocene-Pliocene marls and reefal
limestones of the Villa Trina Fm.
Tectonic history of the Cordillera Septentrional
De Zoeten and Mann (1999) distinguished three sedimentary intervals in the
evolution of the Cordillera Septentrional, separated by distinctive
regional-scale tectonic events. The first interval includes the Paleocene to
lower Eocene deposition of hemipelagic, fine-grained turbidites (Los Hidalgos
and Imbert Fm). Sedimentation was terminated by a folding and uplift event,
which is thought to be related to early attempted subduction of the Bahama
Platform beneath the Caribbean island arc. The second interval contains the
upper Eocene to lower Miocene deposition of deep-marine, siliciclastic
turbidites (Altamira, Las Lavas, and La Toca Fm). Siliciclastic sedimentation
was terminated by a folding and uplift event, which is thought to be
associated with transpressional strike-slip faulting related to North
America-Caribbean plate motion. The third interval includes the upper Miocene
to lower Pliocene deposition of shallow-marine limestones (Villa Trina Fm).
Carbonate sedimentation was terminated by a folding and uplift event related
to the current pattern of restraining bend tectonics (Mann et al., 2002).
Stratigraphy of the Imbert Fm
The stratigraphic relationships between the Imbert Fm and its igneous and
metamorphic basement are exposed in the PPC and RSJC, which are illustrated
with eight stratigraphic sections (Figs. 3 and 4). Three informal
stratigraphic units characterize the Imbert Fm: a fine-grained
sandstone–mudstone lower IM1 unit, interbedded with fine-grained volcanic
rocks (tuffs) and intruded by mafic sills; a coarse-grained
sandstone–mudstone intermediate IM2 unit; and an olistostromic and
heterogeneous clastic upper IM3 unit, composed of polymictic breccias,
conglomerates and sandstones. In the PPC, these units are unconformable
overlain by a chaotic pebbly mudstone–mudslate unit, the San Marcos Fm,
characterized by a block-in-matrix fabric and containing clasts of rocks
similar to, and presumably derived from, all Imbert Fm units, as well as the
underlying ophiolitic basement. In the RSJC, the IM1 and IM2 units are
absent, and IM3 unit directly overlies the metamorphic basement. The rocks of
the IM3 unit are overlain by the turbiditic sequence of the La Toca Fm, which
contain in the lowermost part calcarenites with foraminifera of
middle-to-upper Eocene age (Escuder-Viruete, 2009). During the fieldwork,
distinctive sedimentary facies associations have been used, all of which are
detailed described in the Suplement A.
El Puerto section
This section corresponds to the type section of the lower IM1unit and
illustrates the gradual change to the intermediate IM2 unit. The section lies
along the northern flank of El Puerto syncline (A–A′; Fig. 2), where the
bedding trends N110–130∘ E and
dips 14–36∘ toward the south. The substratum of the section does not
outcrop. Three facies assemblages characterize the IM1 unit: thin-bedded,
medium-to-fine-grained sandstone (Sm); thin-bedded alternance of fine-grained
sandstone, siltstone and laminated mudstone (Sf); and fine-grained tuff with
alternating fine-grained tuffaceous sandstone and mudstone (Tv; Fig. 5h). The
lower part of the section is ∼ 500 m thick (from 0 to 480 m in
Fig. 3) and lacks coarse-grained rocks. It is characterized by interbedded
light brown thin-bedded sandstone, dark mudstone and green parallel-laminated
siltstone, in beds up to 1 m thick (Sf). In these hemipelagic facies
Monthel (2010) found planktonic foraminifera of the lower Eocene. White,
cream and turquoise coloured, fine-grained tuffs with laminated internal
structure are sporadically intercalated as very thin beds (1–3 cm thick) in
the sequence (Tv). The upper part of the section attains ∼ 400 m de
thickness (from 500 to 900 m in Fig. 3) and is also constituted by
fine-grained deposits. However, this upper part is characterized by a
progressive higher occurrence of interbedded 5–50 cm thick beds of
medium-to-coarse grained sandstone (Sm), which are characterized by size
grading and planar laminations, and result a typical turbidite sequence of
alternating sandstone and mudstone. The first lenticular breccias with erosive
base typical of the intermediate IM2 unit occurs at ∼ 880 m and
contains 5–20 cm-sized subangular serpentinite clasts in a sandy matrix
composed of serpentinite, altered pyroxene, red iron oxide, chlorite and
red/green mudstone. The El Puerto section is not deformed by syn-sedimentary
faulting.
Stratigraphic sections of the Imbert Fm as exposed in the Puerto
Plata ophiolitic complex. See text and Supplementary Material A for details
and Fig. 2 for location. Sedimentary facies assemblages: Gp, clast-supported,
sandy (polymictic) breccia and conglomerate; Gm, massive breccia and
matrix-supported, muddy-sandy (polymictic) conglomerate; Sc, medium-to-thick
bedded coarse-grained sandstone and microconglomerates; Sm, thin-bedded,
medium-to-fine-grained sandstone; Sf, fine-grained sandstone, siltstone and
laminated mudstone; Tv, fine-grained tuff with alternating fine-grained
tuffaceous sandstone and mudstone.
(a) Stratigraphic sections of the Imbert Fm in the Río
San Juan complex. Facies assemblages as in Fig. 3, except Os which is
composed by lensoidal serpentinite blocks in a heterogeneous and mostly
deformed matrix composed of shale, mudstone and sandstone. See text and
Supplementary Material A for details and Fig. 2 for location. Trend and dip
data of syn-sedimentary joints and small faults affecting (b) the
Imbert Fm in the Puerto Plata complex, (c) its ophiolitic basement,
and (d) the Imbert Fm in the Río san Juan complex.
Rancho Brugal section
This section is 320 m thick, has a 60 m gap in outcrop halfway up, and
corresponds to the lower IM1 unit (B–B′; Fig. 2). The lower part of the
section exposes ∼ 180 m of alternating fine-to-medium grained
sandstone (Sf and Sm), fine-grained tuffaceous sandstone and laminated
mudstone (Tv). Bed thickness ranges from very thin-to-medium (< 30
cm thick). White and cream coloured, fine-grained tuffs also occur
intercalated as very thin beds. At several stratigraphic levels the section
contains massive flows and sills of basalt and andesite, as well as
intercalated fine-grained, mafic pyroclastic rocks. The upper part of the
section is composed by a poorly exposed sequence of alternating fine-grained
sandstone, siltstone and laminated mudstone (Sf) that attain ∼ 130 m
of thickness. Sandstone beds have a thin-to-medium thickness. This upper part
of the section is in lateral continuity with the lower part of the El Puerto
section.
Río Obispo section
This section is 580 m thick and corresponds to the type section of the
intermediate IM2 and upper IM3 units. It is located ∼ 1 km east of the
Imbert town and crops out over ∼ 500 m along the incised river valley
(C–C′; Fig. 2). The bedding trends N140–160∘ E and dips 50–85∘ toward the southwest. The
sedimentary sequence is overlain by the San Marcos Fm to the east and
southeast, and is truncated at a low-angle by the Camú Fault to the
south. Four facies associations characterize the section: massive breccia and
matrix-supported, muddy-sandy (polymictic) conglomerate (Gm);
clast-supported, sandy (polymictic) conglomerate (Gp); medium-to-thick bedded
coarse-grained sandstone and micro-conglomerate (Sc); and thin-bedded,
medium-to-fine-grained sandstone (Sm).
The lower part of the section exposes ∼ 340 m of 5–70 cm thick
beds of brown sandstone alternating with grey mudstone, with sporadic
intercalations of polymictic breccias and conglomerates. Sandstone beds are
commonly size-graded with channel bases and parallel-laminated tops that
grade into laminated mudstone. Grain size in sandstone beds grades from
fine-grained to very coarse (Sm and Sc), with rare argillite pebbles at the
base. Sandstones are rich in volcanic lithic, volcanic plagioclase, detrital
serpentinite and ferruginized grains (Fig. 6d). This assemblage of
parallel-stratified sandstones and mudstones of the IM2 unit constitutes a
typical turbiditic sequence, which sporadically intercalates < 1.5
m thick lenticular beds of clast-supported breccia and angular-to-sub-rounded
conglomerates (Gp). Some parts of the section are disrupted and deformed by
syn-sedimentary extensional faults (Fig. 5f, g). The upper part of the
section is about 240 m thick (i.e. from 340 to 580 m in Fig. 3) and
consists of thick and very thick beds of breccia and conglomerate (Gm and
Gp), which characterize the IM3 unit (Fig. 5e). Breccias are often composed
of amalgamated lenticular beds with erosive base, where individual beds are
characterized by centimetre to metre sized fragments in a fine-grained matrix
of sandstone and mudstone. Fragments include, in decreasing order of
abundance, serpentinite, peridotite, red/green volcanic rocks, laminated
sandstone, leucogabbro, (rare) white limestone, and red/green mudstone. Large
fragments (up to 1 m) of mudstone are found locally within the breccia and
are interpreted as rip-up clasts. The breccias are overlain by, and
interbedded with, sequences of 0.1–0.5 m thick beds of alternating
coarse-grained sandstone and mudstone (Sc). This upper part is strongly
deformed by syn-sedimentary extensional faults.
Loma Seboruco section
This section is located in the eastern Bahía de Maimón (D–D';
Fig. 2) and is constituted by the upper IM3 unit. Although the lower
stratigraphic contact does not outcrop, the section presumably overlies the
Puerto Plata complex. The bedding trends 18–32∘ E and dips
20–36∘ toward the east. The section can be subdivided into two
parts, in which facies show a coarsening-upward evolution. The lower part
exposes ∼ 30 m of poorly sorted, coarse-grained sandstones (Sc and
Sm), in beds of 0.1–0.6 m thick. Sandstones are rich in volcanic lithic
grains and detrital serpentinite grains (Fig. 6b, c). These rocks are
deformed by syn-sedimentary faulting. The upper part attains ∼ 100 m
(from 30 to 130 m in Fig. 3) and is characterized by massive, matrix- and
clast-supported polymictic breccias and conglomerates (Gm and Gp). They are
often chaotic or form a heterogeneous assemblage of clasts in a
serpentinite-rich, muddy matrix. The beds have a thick to very-thick
thickness and a massive internal structure. Clasts are angular to
sub-rounded, of sand to coble grain-size, and are of ophiolitic and
sedimentary nature (Fig. 5b, d). Ophiolitic clasts are mainly composed of
variably serpentinized peridotite, with subordinate layered gabbro,
leucogabbro, dolerite, basalt, and tonalite; sedimentary clasts correspond to
typical lithologies of IM1 and IM2 underlying units, as graded sandstone,
fine-grained tuff, tuffaceous siltstone and mudstone, as well as rare white
limestone. The matrix of the breccia is a serpentinite-rich,
medium-to-coarse-grained sandstone. These breccias are unconformably overlain
by the sheared pebbly mudstones of the San Marcos Fm.
Gaspar Hernández section
This section is ∼ 240 m thick and lies along several quarries located
in the northwestern end of the Río San Juan complex (E–E′; Fig. 2).
The bedding trends N100–126∘ E
and dips 10 to 36∘ toward the southwest. The sedimentary sequence
corresponds to the upper IM3 unit and overlies a basement made up of the
Gaspar Hernández serpentinites. Sedimentary facies show an evolution
(Fig. 4, base to top) from matrix-supported polymictic breccia and
conglomerate (Gm), to lensoidal serpentinite blocks in a heterogeneous matrix
(Os and Ms), and clast-supported polymictic breccia and conglomerate (Gp and
Gm). In the lower part of the stratigraphic section (from 30 to 100 m), the
matrix-supported breccia contains (∼ 60 %) 5–20 cm-sized
angular to subrounded clasts in a serpentinite-rich, muddy–sandy matrix (Gm;
Figs. 5c, 6a). Clasts are mainly composed of serpentinite and serpentinized
harzburgite, with subordinated red/green volcanic rocks, laminated sandstone,
ferruginized microbreccia, porphyritic lavas, isotropic gabbro and dolerite.
The breccia beds are internally massive and often have an amalgamated
lenticular geometry with erosive bases. These rocks show evidence of
syn-sedimentary extensional deformation. The breccias are overlain by an
olistostromic intermediate subsection of lensoidal serpentinite blocks in a
heterogeneous and mostly deformed matrix, composed of serpentinite-rich
sandstone, pebbly mudstone and shale (Os; Fig. 5a). Block range in size from
a few centimetres to several metres (up to 20 m). Blocks and clasts are
angular and of a similar nature than in lower breccias. Breccias are
intercalated in 0.1–2 m thick beds of massive varicoloured (red, green
and grey) mudstone–mudslate (Ms), which also contain serpentinitic clasts and
blocks. This chaotic and strongly faulted intermediate section is at least
50 m thick. The upper part of the section is characterized by massive,
clast-supported polymictic breccia and conglomerate (Gp, Gm). The sequence
attains ∼ 30 m (from 160 to 190 m in Fig. 4). The beds often have a
lenticular geometry, a massive or normally graded internal structure, and a
clast-supported fabric. Clasts are angular and of sand to pebble grain-size.
These rocks show syn-sedimentary deformation structures.
Field photographs of Imbert Fm. (a) Os facies assemblage
composed of lensoidal serpentinite blocks in a heterogeneous and faulted
matrix composed of breccia, sandstone, and mudstone. Note serpentinized
peridotite blocks (p) randomly distributed in a polymictic brecciated
matrix (b) and the structureless layers of silts and muds. Angular
block attains several metres in size. IM3 unit, Gaspar Hernández section.
(b) Gm facies assemblage composed by serpentinite-rich, massive
breccia and matrix-supported, muddy–sandy (polymictic) conglomerate. Note the
serpentinized peridotite (p) nature of the clast in the breccia. IM3 unit,
Loma Seboruco section. (c) Gp facies assemblage composed of
clast-supported, sandy (polymictic) breccia and conglomerate. Note inverse-to-normally graded internal structure, dominant clast-supported
fabric. Massive internal structure also occurs. Breccia beds are often
lenticular with erosive base and interbedded with pebbly conglomerate and
coarse-grained sandstone. IM3 unit, Gaspar Hernández section.
(d) Detail of matrix-supported breccias of IM3 unit (Gm facies
assemblage). Clast shown a random orientation and compositionally are of
(mainly) serpentinite, red/green volcanic rocks, laminated sandstone and
(rare) white limestone. IM3 unit, Gaspar Hernández section. (e)
Gm facies assemblage typical of IM3 unit composed by massive breccia and
matrix-supported, muddy–sandy (polymictic) breccia and conglomerate. Note in
the breccia body the disorganized internal structure, pebble to cobble size,
often erosive base, and random clast orientation of (mainly) serpentinite.
(f) Strata disruption by layer-parallel extension in lithified
medium thick sandstones controlled by conjugate extensional fractures and
pinch-and-swell structures. Note as disrupted layers are fossilized by
younger breccia strata. IM2 unit, Río Obispo section. (g)
Conjugate sets of normal fault zones deforming the bedding (S0) surfaces of a
thick bedded coarse-grained sandstone-laminated mudstone alternating
sequence. Note as small faults are fossilized by younger sandstone strata.
IM2 unit, Río Obispo section. (h) Tv facies assemblage typical
of IM1 unit composed of fine-grained tuff with alternating fine-grained
tuffaceous sandstone and mudstone. Río Obispo section.
(a–d) Microphotographs (PPL) of the Imbert Fm sandstones
and matrix of the breccias consisting of microlitic volcanic rock (v),
plagioclase (pl), serpentinized peridotite (sp), serpentinite rock fragments
(s), and rare microfossils (f). Volcanic sources of the grains
range in composition from basaltic to andesitic. Note the absence of quartz
grains. Sandstone grains composition suggest provenance from erosion of
volcanic arc and ophiolitic complexes. (e) Basaltic sill intruding
an alternance of fine-grained sandstone, siltstone and laminated mudstone of
the IM1 unit, Rancho Brugal section. (f) Basalt with
microporphyritic textures defined by clinopyroxene (cpx), plagioclase (pl)
and orthopyroxene (opx) micro-phenocrysts (XPL).
Magante section
This section is ∼ 10 km east of the Gaspar Hernández section
(F–F′; Fig. 2), and also correspond to the IM3 unit, although the basement
here consists of the Jagua Clara serpentinite-matrix mélange. The
bedding trends N90–110∘ E and dips 60–75∘ toward the
south. The section can be subdivided into two subsections, where facies show
a crudely finning-upward evolution. The lower part exposes ∼ 24 m
(from 30 to 54 m in Fig. 4) of massive and matrix-supported, muddy-sandy
polymictic breccia and conglomerate, with cm-sized clasts of ophiolitic,
metamorphic and sedimentary rocks (Gm). Ophiolitic clasts are composed of
serpentinite, peridotite, and various types of gabbro, dolerite and volcanic
rocks. Metamorphic clasts consist of eclogite, blueschist, metagabbro and
felsic orthogneiss. Sedimentary clasts are typical lithologies of IM1 unit,
as brown, graded sandstone, white fine-grained tuff and tuffaceous siltstone,
limestone and mudstone. The matrix of the breccia is medium-to-coarse-grained
sandstone, rich in serpentinite grains. In the upper part of the section,
breccias have a clast-supported fabric (Gp) and are overlain by ∼ 16 m
of well-bedded and normally graded coarse- to fine-grained sandstones. The
contacts between these sandstone beds are commonly scoured. Sandstones
contain reworked foraminifera of middle to upper Paleocene age
(Escuder-Viruete, 2009), so they are younger in age.
Caño Claro and Hicotea sections
The Caño Claro and Hicotea sections are ∼ 1 km apart, and about
and 3.5 km south and 9 km east of the Magante section (G–G′
and H–H′; Fig. 2). In both sections the
unconformable contact between the serpentinite-matrix mélange and the
overlying IM3 unit is exposed. In the Caño Claro section, the metamorphic
substrate is directly overlain by ∼ 18 m of matrix- and
clast-supported polymictic breccia and conglomerate (Gm and Gp),
characterized by centimetre-to-decimetre-sized fragments in a
serpentinite-rich sandy matrix. Clasts are of similar nature that in the
Magante section. Breccia and conglomerate beds (up to 2.5 m thick) have a
crudely finning upward grading, with basal erosive surfaces and
coarse-to-medium-grained sandstone tops. In the Hicotea section, the
mélange is directly overlain by only 8–10 m of matrix- and
clast-supported, muddy-sandy polymictic breccia (Gp). The matrix contains
pebble-to-coble size clasts of metamorphic rocks, such as metagabbro,
eclogite and mafic blueschist. As in the Jagua Clara section, the breccias
are immediately overlain by a turbiditic sequence of interbedded sandstone
and mudstone of the La Toca Fm, with basal calcarenites containing middle and
upper Eocene foraminifera.
Volcanic rocks of the Imbert Fm and coeval unitsField relations and petrography
The volcanic rocks present in the Imbert Fm form up to 10 m thick coherent
bodies and well-stratified, fine-grained volcaniclastic rocks, which are
interbedded with the fine-grained sandstones and mudstones of the IM1 lower
unit (Fig. 3; Escuder-Viruete, 2010). The coherent bodies are composed of
brown-to-dark green mafic rocks, forming lava flows, autoclastic breccias, and
massive intrusive sills (Fig. 6e). Autoclastic breccias are generally
composed of monogenetic clasts. These rocks were erupted in a submarine
environment and were intruded by rare syn-volcanic, feeder dykes of
microgabbro and dolerite. Fine- to very fine-grained volcaniclastic deposits
are white to turquoise in colour (Fig. 5h) and are overlain, or interbedded
by, ribbon cherts. Under the microscope, the coherent rocks are ortho and
clinopyroxene-bearing porphyritic basalts (Fig. 6f), plagioclase-phyric
basalts and basaltic andesites, hornblende-phyric andesites with minor
olivine, and clinopyroxene-bearing basalts. The textures are porphyritic,
glomeroporphyritic, fluidal, amygdaloidal, and aphyric.
The volcanic rocks of the Palma Picada volcanic complex and the igneous rocks
of the Curtiembre plutons are coeval with those of the Imbert Fm
(Escuder-Viruete, 2010). Part of the Palma Picada volcanic complex crops out
south of the Camú fault zone, about 1–2 km southeast of Imbert town
(Fig. 1; de Zoeten and Mann, 1991, 1999). It is mainly composed of basalts,
basaltic andesites and andesites, with subordinate mono and polymictic
breccias and volcaniclastic rocks. The andesites have provided
40Ar /39Ar hornblende plateau ages between 51 and 46 Ma
(lower Eocene; Escuder-Viruete, 2010). These volcanic rocks are also in part
coeval with the limestones the fine-grained volcaniclastic rocks of the Los
Hidalgos Fm, which contains upper Maastrichtian to lower Eocene-age fossils.
Both units are regionally unconformable overlain by the upper Eocene to
Oligocene turbiditic sequence of the Altamira and La Toca Fms. Located in the
Eastern Cordillera, the hornblende (Hbl)-bearing diorites of the Curtiembre
plutons are geochemically similar to the volcanic rocks of the Palma Picada
complex. They have yielded 40Ar /39Ar hornblende plateau ages
between 68 and 63 Ma (upper Maastrichtian to lower Paleocene;
Escuder-Viruete, 2010). These plutons could be close to the Palma Picada
complex in the Eocene and were after separated by the Septentrional fault
strike-slip movement.
Bulk-rock major and trace elements compositions
Bulk-rock compositions of major and trace elements were obtained by
inductively coupled plasma–mass spectrometry (ICP–MS) analysis with
LiBO2 fusion. The results for selected samples are reported in
Supplementary Material B, as well as details of analytical accuracy and
reproducibility. Mafic rocks of the Imbert Fm have a narrow SiO2
content, ranging from 52.9 to 55.2 wt. % (major oxides recalculated to
an anhydrous basis), for relatively low TiO2 contents between 0.7 and
1.3 wt. % (Fig. 7). Their low Mg# values (40–35) indicate that the
magmas were extensively fractionated, with exception of one un-fractionated
sill in which Mg# = 60 (sample 13JE27). These basalts and basaltic
andesites have generally low contents in CaO (6.7–9.0 wt. %), for
moderately high Al2O3 (16.1–16.8 wt. %) and Fe2O3T
(9.6–12.2 wt. %) contents, which increase progressively for decreasing
MgO. These trends are tholeiitic and related to the fractionation of olivine
plus Cr-spinel, pyroxene, plagioclase and Fe-Ti oxides.
Variation diagrams for rocks from the Imbert Fm, Palma Picada
complex and Curtiembre plutons. MgO vs. TiO2(a), SiO2(b), Zr (c), and Nb (d). NVTZ, CG, and SR fields
are respectively for the northern volcano–tectonic zone, the Central Graben and
spreading ridge fields of the Mariana Arc–Trough system, which are shown for
comparison. MORB glasses are from a Pacific compilation. The different
geochemical groups of Lower Cretaceous igneous rocks in Hispaniola are the following: IAT,
normal island-arc tholeiites; low-Ti IAT, low-Ti, and LREE-depleted island-arc
tholeiites; Bon, boninites; and felsic volcanic rocks and tonalites. Ti
vs. Nb / Th (e), (La / Yb)N(f), and
Zr,/ Hf (g), and (La / Nd)N vs. Nb*(h) diagrams are for rocks from the same lithological units. See
text for explanation.
In the MgO vs. TiO2 diagram of the Fig. 7, volcanic rocks of the
Imbert Fm are compared with the volcanic rocks of the Palma Picada complex
and the Hbl-diorites of the Curtiembre plutons. They are also compared to the
volcanic rocks of the Lower Cretaceous primitive Caribbean island arc of
central and eastern Hispaniola, which record a progressive increase in
TiO2 contents from the boninites and depleted low-Ti island-arc
tholeiites (IAT) to normal IAT and back-arc basin basalts (BABB;
Escuder-Viruete et al., 2008, 2010),
as well as representative Pacific IAT and mid-oceanic ridge basalts (MORB)
groups. In terms of MgO contents, the studied samples of the Palma Picada
complex and the Curtiembre plutons range from moderately to highly
fractionated, including relatively low- and mid-Ti compositions. Samples of
the Imbert Fm and Curtiembre plutons have similar TiO2 contents than the
BABB of the Rio Verde complex and the mid-Ti tholeiitic suite of the Mariana
Arc–Trough system (Gribble et al., 1998), but lower than the compilation of
Pacific MORB (PetDB, 2007). TiO2 contents of the mafic volcanic rocks of
the Imbert Fm are higher to those of the IAT, low-Ti IAT, and boninites of the
Los Ranchos Fm. However, these rocks are highly fractionated and some samples
contain abundant phenocrysts, so they do not provide good estimates of liquid
compositions. TiO2 contents in samples of the Palma Picada complex are
similar to the IAT and low-Ti IAT groups.
In the Nb / Y vs. Zr / TiO2 immobile trace elements plot of
the Fig. 8a, all mafic igneous rocks of the Imbert Fm and Palma Picada
complex are subalkalic basalt/andesites and andesites, respectively, and plot
within the field of the Caribbean island arc. For these rocks, Ti / V
ratios range between 10 and 20, plotting in the subduction-related field
(Fig. 8b). Samples of the Palma Picada complex plot in the IAT and low-Ti IAT
fields of the Los Ranchos Fm. However, samples of the Imbert Fm and
Curtiembre plutons generally plot at higher Ti and V values, which can be
related to the accumulation of Fe–Ti phases in these highly fractionated
magmas. In a MORB-normalized multi-element plot (Fig. 8; data normalization from Sun and McDonough, 1989), the volcanic rocks
of the Imbert Fm have light rare earth elements (LREE) enriched ([La / Nd]N=1.4–1.8) and
slight heavy rare earth elements (HREE) depleted ([Sm / Yb]N=0.8–1.8) patterns, with low
Nb contents (1.7–2.5 ppm). They exhibit positive Ba, U, K, and Pb spikes,
and negative Nb–Ta (and Ti) anomalies, typical of subduction-related rocks
(Pearce and Peate, 1995). These patterns and the values of the trace element
ratios Ti / V ≤ 20, Zr / Nb < 5 and
Zr / Nb > 10, are characteristic of IAT magmas (e.g. Pearce
and Peate, 2005). In this sense, their patterns are very similar to the IAT
of the Los Ranchos Fm (Escuder-Viruete et al., 2006, 2010). The low TiO2 content
and (Sm / Yb)N ratios suggest that the mantle source of these
mafic magmas was depleted and did not contain garnet.
(a) Nb / Y vs. Zr / TiO2 diagram and
(b) Ti–V diagram for rocks from the Imbert Fm, Palma Picada
complex, and Curtiembre plutons. MORB-normalized extended trace-element plots for
volcanic rocks of the (c) Imbert Fm, (d, e, g) Palma Picada
complex, and (h) Curtiembre plutons. The diverse geochemical groups
of Lower Cretaceous igneous rocks in Hispaniola shown in (f) are (Escuder-Viruete et al., 2006, 2010):
IAT, normal island-arc tholeiites; low-Ti IAT, LREE-depleted island-arc
tholeiites; and Bon, boninites. See text for explanation.
In the Palma Picada complex, three compositional groups have been defined
(Escuder-Viruete, 2010): normal IAT, low-LREE IAT and calc-alkaline basalts
to andesites. These all display a variably LREE enrichment and a flat HREE
pattern, with minor Zr–Hf but marked negative Nb–Ta anomalies (Fig. 8), which
also are features typical of subduction-related magmas. The LREE enrichment,
monitorized by the [La / Nd]N ratio, increase from the low-LREE
IAT (1.1–1.7), to the IAT (1.5–2.0) and calc-alkaline (2.4–3.1) groups.
Respect to the IAT group, the low-LREE group of the Palma Picada complex
contains lower absolute abundances of HREE and a more prominent negative
Zr–Hf anomaly. The LREE depletion, low-TiO2 contents and lower Ti / V
values, as well as the lower HREE levels, suggest that the mantle source for
this group was more depleted than for the IAT group of the Imbert Fm. The
calc-alkaline group of the Palma Picada complex is characterized by a higher
LILE and LREE enrichment, as well as higher (La / Yb)N ratios,
suggesting a more “slab” component added to the depleted source (Pearce and
Peate, 1995). Samples of the Curtiembre plutons also display a
subduction-related trace element pattern and are compositionally similar to
the Imbert Fm and the calc-alkaline group of the Palma Picada complex
(Fig. 8). The calc-alkaline character of these Hbl-diorites is reinforced by
their relatively high (La / Yb)N values (Fig. 7f). A
calc-alkaline character of the mafic magmas has been related to a more mature
evolutionary stage of the Late Cretaceous volcanic arc (i.e. Lewis et al.,
2006).
Syn-sedimentary deformation in the Imbert Fm
The structural evolution of the Imbert Fm can be broken down into three
broad stages: (1) pre-collisional, syn-sedimentary deformation; (2)
syn-collisional deformation, which represent the main regional phase in the
middle-to-upper Eocene, forming inverse faults, thrusts and folds; and (3)
post-collisional deformation, which include two generations of faults and
folds that show significant contrast in geometry, timing and structural
style. This part of the paper focuses on the syn-sedimentary deformation
structures, which are well preserved in areas less deformed by the
syn-collisional tectonic processes.
The bedded successions of the Imbert Fm present evidence for initial
disruption occurring prior to and during lithification, as gravitational
debris flow, sliding and fragmentation, as well as a continuous process of
syn-sedimentary extensional faulting (see below). The resulting chaotic rock
assemblages are characterized by clasts and blocks dispersed in a detrital
matrix produced by disaggregation and new deposition. Therefore, formation of
a clastic fabric indicates that the mixing processes are of sedimentary
nature. In the Loma Seboruco section of the PPC, the breccia deposits include
angular and sub-rounded blocks of ophiolitic lithologies, up to 0.5 m long,
floating with a random distribution in the polymictic micro-conglomerate to
sandstone-size matrix (Fig. 5d). In the Gaspar Hernández section of the
RSJC, large blocks of serpentinized peridotites represent slipped blocks (up
to 30 m in size; Fig. 5a). The matrix is devoid of sedimentary structures,
except for locally developed fining-upward grading. The breccia alternate
locally with laminated to massive sandstone and mudstone, indicating
turbiditic deposition in a deep-marine sedimentary environment.
Syn-sedimentary faulting produces discontinuous structures in the Imbert Fm
that are spatially limited and generally not accompanied by an extensive
strata disruption or a block-in-matrix style of deformation. They consist of
conjugate sets of extensional shear fractures and small faults,
“en-échelon” vein systems, cataclastic fault rocks, local symmetric and
asymmetric pinch-and-swell and boudinage structures, as well as very rare
folds. Syn-sedimentary folds have metric amplitudes and are disharmonic,
close to isoclinal, and asymmetric with vergence toward the NE and SW.
Locally NW–SE hinge lines are present. Folds can occur associated with small
normal detachments that display a coherent NE and SE-directed sense of normal
movement. All these structures are not pervasively developed and characterize
the IM2 and, particularly, the IM3 units.
The stress regime prevailing in the depositional setting can be deduced from
the syn-sedimentary deformation structures. In the PPC, the debris flow and
turbiditic deposits of the Imbert Fm are affected by WNW–ESE to NW–SE and
WSW–ENE to W–E trending joints and small faults (Fig. 4b), which generally
present a high angle of dip (> 70∘). In the RSJC, the
debris flows are deformed by W–E to WNW–ESE and NNW–SSE to NNE–SSW trending
small faults (Fig. 4d), that have a mid- to high angle of dip
(> 30∘). According to the geometry of the fracture
system, they can be classified as hybrid (combined tensional and shear) with
two joint sets forming an angle < 60∘, or shear, organized
by two joint or small fault sets with an angle about 60∘. As new
turbiditic strata seal the hybrid joints and the half-graben structures
developed by the movement of the faults, these structures are temporally
syn-sedimentary (Fig. 5g). However, to know the original geometry of these
structures and to deduce the syn-sedimentary stress regime, they must be
restored to the horizontal. Unfolding of the bedding at each station made
this correction and results are shown in Fig. 9.
(a, b) Stereoplots of bedding planes (S0) of the Imbert Fm
in the Puerto Plata and Río San Juan complexes. (c, o)
Stereoplots of fault, joints and calcite veins affecting Imbert Fm deposits
from several measurement stations at Puerto Plata and Río San Juan
areas. The upper number indicates the station. (p) Stereoplot of
stress-axes in all stations. Stereoplots also include the stress-axes
obtained from the palaeostress analysis. The white arrows indicate the trend
of subhorizontal extension. Equal angle, lower hemisphere projection.
In each station, the corrected orientations of shear and hybrid joints are
distributed in two conjugate sets, which generally have high angles of dip
(> 60∘). The more frequent trends are WNW–ESE to NW–SE,
W–E to WSW–ENE, and SW–NE. The associated small faults are organized in two
similar conjugate sets in each station, which present opposite normal sense
of movement. The joints and small faults developed in the gabbros and
peridotites of the PPC also record these main trends. The restored normal
sense of fault movement generally has a minor oblique slip component,
developing graben and semi-graben structures up to several metres wide. The
maximum vertical slip range from several centimetres to few metres. In
occasions, the fault planes are gently striated, showing slickensides that
enable kinematic interpretation. In several stations, the restored geometry
of the brittle structures that affect the sedimentary rocks indicates a
general subvertical compression and a NNE–SSW to NE–SW trend of subhorizontal
extension (Fig. 9). In the PPC, a NW–SE trend of subhorizontal extension is
also locally recorded.
More precise information about the syn-sedimentary stress can be obtained
from the palaeostress analysis of the small brittle structures. The
palaeostress analysis allows to establish the main stress axis direction and
the axial ratio (shape) R=(σ2-σ3)/ (σ1-σ3) of the stress ellipsoid. For this analysis the FaultKin software (Marrett and Almendinger, 1990) was used in nine outcrops
of the Imbert Fm (Suplement C). The results were interpreted in combination
with other types of data with kinematic significance, such as conjugate shear
fractures, tension fractures, and calcite-filled tension gashes.
Ar–Ar geochronological data
The main objective of Ar–Ar geochronology was to obtain age constraints for
the exhumation of the ophiolitic basement of the PPC, source of the rock
fragments found in the Imbert Fm. For this goal, three samples were taken:
two gabbros from the ophiolitic substrate and other gabbroic clast from the
breccias of the overlying IM3 unit. Sample locations are shown in Fig. 2.
Analytical procedures and results are reported in the Suplement D. All ages
are quoted at the 2σ level of uncertainty. Geologic time scale is
from Gradstein et al. (2012).
Sample 10JE54 is a coarse-grained leucogabbro from the PPC, collected in a
quarry on the road Puerto Plata, Imbert. Under the microscope, it displays a
layered adcumulate igneous texture, defined by variations in modal contents
of plagioclase and clinopyroxene, with minor orthopyroxene, olivine and
spinel. The obtained plagioclase plateau age is 44.0 ± 3.1 Ma
(MSWD = 1.2) for seven steps (1–7) and 100.0 % of the 39Ar
released (Fig. 10a). The inverse isochron age on these seven points is
42.8 ± 5.3 Ma (MSWD = 1.5), with an initial 40Ar–36Ar
intercept at 350 ± 20. The inverse isochron has high initial
40Ar–36Ar argon ratios, indicating the presence of trapped argon
with a composition differing from that of atmospheric argon. The isochron age
is considered as the best age of the sample, which is similar to the plateau
age within error. Sample JM9112 is a coarse-grained leucogabbronorite from
the PPC, collected at the same quarry that sample 10JE54. It contains
plagioclase, clinopyroxene and orthopyroxene, with minor olivine and spinel.
The obtained plagioclase plateau age is 35.1 ± 8.1 Ma (MSWD = 4.6)
for eight steps (3–10) and 96.0 % of the 39Ar released (Fig. 10b).
The inverse isochron age is 34 ± 13 Ma (MSWD = 3.8), with an
initial 40Ar–36Ar intercept at 300 ± 18. As the inverse
isochron 40Ar /36Ar intercepts equivalent to the atmosphere
(295.5), the plateau age is the best estimated age for the sample in spite of
its high uncertainty. Sample HH9124 is a block of coarse-grained troctolite
from the IM3 unit of the Imbert Fm, collected in the Arroyo Seco outcrop at
the Cerro de Gran Diablo. It contains igneous plagioclase and olivine, with
minor ortho and clinopyroxene, and secondary hornblende. The obtained
hornblende plateau age is 55.0 ± 8.1 Ma (MSWD = 0.1) for six steps
(2–7) and 69.9 % of the 39Ar released (Fig. 10c). The inverse
isochron age is 55.5 ± 9.6 Ma (MSWD = 0.1), with an initial
40Ar–36Ar intercept at 294.1 ± 9.2. The sample yielded
release spectra with plateau and inverse isochron 40Ar /36Ar intercepts equivalent to the atmosphere (295.5), and therefore the plateau
age is the best estimated age for the sample in spite of its high
uncertainty.
(a, b, c)40Ar /39Ar spectrum and isochron
diagrams of plagioclase from leucogabbros of the Puerto Plata ophiolitic
complex and of hornblende from a troctolite block in the Imbert Fm.
Analytical procedures are described in Escuder-Viruete et al. (2014). A
summary of 40Ar–39Ar incremental heating experiments is in
Supplementary Material D. Age uncertainties are 2σ and include
uncertainty in monitor age and decay constant. (d) Temporal
relationships between the exhumation of the Jagua Clara mélange (end of
oceanic subduction), the latest Caribbean arc magmatism, the exhumation of
the SSZ ophiolite, and the sedimentation of the Imbert Fm in the central
Septentrional Cordillera, as well as the subduction and exhumation of the
Samaná nappes (continental subduction). See text for discussion.
DiscussionA Caribbean supra-subduction zone setting for the Imbert Fm
volcanism
Geochemical data show that the mafic volcanic rocks within the Imbert Fm
present typical subduction-related features (e.g. Pearce and Peate, 1995):
LILE (large-ion lithophile elements) are enriched relative to LREE, and both
element groups are enriched relative to high field strength elements (HFSE), giving the characteristic
negative Nb–Ta anomalies (Fig. 8). These rocks are interbedded with, and
intrude to, the fine-grained rocks of the IM1 lower unit, which also
intercalate distal tephra fallout deposits. Therefore, these sedimentary
rocks were deposited in a supra-subduction zone setting with ongoing
arc-volcanic activity, more probably at the deep-water area of the forearc
(e.g. Draut and Clift, 2012). Coeval related volcanic rocks are the
tholeiitic and calc-alkaline basalts to andesites of the Palma Picada complex
and the Hbl- diorites of the Curtiembre plutons, which also recorded a SSZ
magmatism, probably more closely to the volcanic front. The arc-like
geochemical similarity between the mafic volcanic rocks of the Imbert Fm and
the Palma Picada complex, support the interpretation that the lower Eocene
igneous rocks of the Septentrional Cordillera records the latest volcanic
activity of the Caribbean island arc. On the other hand, these volcanic rocks
are geochemically comparable to the upper Maastrichtian to lower Paleocene
mafic plutonic rocks of the Curtiembre, which also implies that this latest
arc-like magmatism was also recorded in the Cordillera Oriental of
Hispaniola. As it has been recently suggested, both lithotectonic domains
belong to the Caribbean plate (Escuder-Viruete et al., 2014).
Regional lithological correlations and implications
The stratigraphic columns for the Imbert Fm are synthesized in Fig. 11, which
also illustrates the inferred lithological correlations and lateral facies
variations between different sections. The figure shows that the IM1 unit is
essentially made up of thin to medium-bedded sandstones and mudstones,
interbedded with fine-grained volcanic rocks, that can form sections several
hundreds of metres thick (El Puerto section, PPC), but that can also be
entirely absent (RSJC) due to erosion or non-deposition. These rocks are
interpreted as result of dilute turbidity currents, hemipelagic
sedimentation, and volcanic particle fall in a deep-water, forearc
depositional environment. Evidence of coeval syn-sedimentary tectonics are
absent. The IM2 unit is a typical turbiditic sequence composed of alternating
coarse-grained sandstones and mudstones, which have been deformed by
syn-sedimentary extensional faulting. These deposits are interpreted as
result of high-concentrated turbidity currents in a proximal submarine fan
and/or channel-fill setting, affected by syn- to post-depositional slumping
or sliding processes. The IM3 unit is a variably thick, olistostromic
(chaotic) unit, composed of serpentinite-rich polymictic breccias,
conglomerates and sandstones. The matrix- and clast-supported breccias are
mainly interpreted as product of gravity-driven mass-transport processes
(non-cohesive debris flows, debris avalanches, slumps and block slides) in a
slope setting, or subaqueous fault scarp. The mesoscopic structures of
boudinage, pinch-and-swell and slumping are interpreted as result of
layer-parallel extension related to submarine sliding. The serpentinite-rich
debris flows, typical of the IM3 unit, are indicative of mobilization of
hydrated ultramafic rocks, as those of the underlying PPC and RSJC.
Figure 11 also shown that the IM3 unit unconformably overlies different
tectonostratigraphic units in the RSJC (serpentinites at the Gaspar
Hernández section and a metamorphic mélange with high-P blocks at
the other sections), indicating clearly that its lower contact is an
erosional surface, over an already structured subduction-accretionary prism.
In the PPC, the lower stratigraphic contact of the Imbert Fm does not
outcrop, but clasts in the breccias are of serpentinized peridotites,
gabbroic rocks and basaltic extrusives, typical of the underlying complex,
which suggest that the Imbert Fm unconformably overlies the SSZ ophiolite.
Therefore, depositional facies, bed thickness and grain size in the Imbert Fm
define a large-scale, coarsening-upward sequence, developed between two
unconformity surfaces (E1 and E2 in Fig. 11). However, an intra-formational
unconformity between IM2 and IM3 units cannot be ruled out. In the PPC
sections, distal turbidites and hemipelagic mudstones, radiolarites and
coeval arc-related volcanism, pass upwards into a more proximal turbiditic
sequence and to ophiolite-derived breccias and conglomerates. Some of the
ophiolite-derived conglomerates include sub-rounded serpentinite and basalt
clasts suggestive of a high-energy, more shallow-water setting. This
evolution indicates sediment accumulation in a progressively shallower,
marine palaeoenvironment. Also, the Imbert Fm is affected by syn-sedimentary,
small-scale, high-angle faults in the IM2 unit, and by low-angle extensional
faults and block slides in the IM3 unit. This evolution suggests an increase
of the instability upward. The shallowing and the increase instability in the
basin are interpreted as a response to uplift, erosion and/or tectonic
denudation of the underlying basement. These processes could be induced by
subduction of the North America continental margin and the isostatic rebound
of the overlying Caribbean SSZ ophiolite, as in the southern Urals (Brown et al.,
2001).
Synthetic diagram for the stratigraphy of the Imbert Fm in the
Puerto Plata ophiolitic and Río San Juan complexes. See Fig. 2 for
locations of sections and text for discussion.
This interpretation agrees with the drastic change of the thickness of the
Imbert Fm and the resulting wedge-shaped geometry in cross section for the
unit. The wedge-shaped sequence thickens to the SW in the PPC and pinches
out at the RSJC to the NE. This geometry is the result of the seafloor
morphology created by the rising of the NE edge of the basin, or outer
forearc, with exhumation and erosion of the ophiolitic basement and other
underlying units of the accretionary prism, as well as the reworking of the
turbiditic and volcanic rocks of the IM1 unit to form debris flow deposits.
The breccias were shed from subaqueous scarps created by the uplift and
faulting and filled rugged seafloor topography produced over the emplaced
ophiolitic thrust sheet. In this sense, palaeocurrent data indicate the
existence of a serpentinite source area in the NE.
Palaeostress analysis of the syn-sedimentary deformation
The result of the palaeostress analysis of small fault arrays and joint sets
that affect the rocks of the Imbert Fm in selected locations establishes an
extensional stress ellipsoid for the syn-sedimentary tectonics in all cases
(Fig. 9). These stress ellipsoids are characterized by a subvertical σ1 axis and a subhorizontal, NNE–SSW to NE–SW σ3 trending axis.
The axial ratios of these ellipsoids are generally high (0.5–0.9;
Suplement C), and indicate a pure to horizontal axially symmetric extension
(σ1∼σ2) stress tensor, which is characteristic of
pure normal to normal strike-slip deformation. Although most stress
ellipsoids show a NE–SW trending σ3 axis, in some of them (sites
11JE15, 10JE224B and 10JE53), this orientation corresponds to σ2
probably due to an axis permutation or local perturbations of the regional
stress field. The restored syn-sedimentary NW–SE trending normal faults and
the metre-scale graben structures that affect the youngest breccia and
olistostromic successions of the IM3 unit, such as the 11JE51 and 11JE252
sites, all indicate a general NE–SW extension. Therefore, a gravity-driven
extensional stress-field affects the uppermost levels of the crust during the
sedimentation of the Imbert Fm at least in the lower to middle Eocene.
The gravity related tectonics results from instability in the forearc basin.
The Imbert Fm records a progressive increase in the syn-sedimentary tectonic
activity, culminating in the upper IM3 unit, which include metre to tens of
metres-size blocks/olistoliths of variably serpentinized peridotite. These
sedimentary relations suggest gravitational collapse associated with
submarine sliding as the main disruption mechanism for the generation of the
IM3 olistostromic unit, rather that tectonic deformation. After their initial
collapse, different types of mass-wasting phenomena, starting from gravity
sliding and followed by slumping and debris flows, contributed to the final
emplacement of the blocks as downslope deposits. The NNE–SSW to NE–SW trend
of subhorizontal extension indicates that the sedimentary basin was most
probably oriented WNW–ESE to NW–SE (actual coordinates). The
sub-perpendicular trends of palaeocurrent and sliding directions (Figs. 3, 4)
are also consistent with this orientation for the basin.
Age constraints for the Imbert Fm
40Ar /39Ar ages reported for the gabbroic rocks of the PPC are
presumed to be amphibole and plagioclase-cooling ages because all of the
dates are from plutonic rocks with high crystallization temperatures.
Therefore, the 40Ar /39Ar plateau ages of 44.0 ± 3.1 Ma
and 35.1 ± 8.1 Ma obtained in plagioclase from the gabbros suggests
cooling of the PPC at ∼ 45–40 Ma (middle Eocene), due the assumed
closure temperature of plagioclase (200–235 ∘C). In spite of its
high uncertainty, the 40Ar /39Ar plateau age obtained for
hornblende in a block from the IM3 unit of the Imbert Fm also indicate a
cooling at T < 500 ± 50 ∘C (closure temperature of
amphibole) in the lower-to-middle Eocene.
Schematic sedimentary and tectonic evolution of the Imbert Fm and
the basal El Mamey Group along the northeastern edge of the pre-collisional
forearc (a, b)and the syn-collisional basin (c, d) of the
northern Caribbean subduction-accretionary prism.
This range of Ar–Ar ages indicates the following: (1) exhumation and cooling at rates of
∼ 30 ∘C Ma-1 of the ophiolitic PPC during the
lower-to-middle Eocene; (2) erosion of this complex, which is the source of
the ophiolitic fragments in the Imbert Fm; and (3) the coeval sedimentation
of the Imbert Fm (IM2 and IM3), which is also indicated by its
Paleocene/lower Eocene palaeontological age in the PPC (Pindell and Draper,
1991; Monthel, 2010;) and RSJC (Draper and Nagle, 1991; Escuder-Viruete,
2009) complexes. These relationships also imply the uplift to the surface of
the SSZ ophiolite during of shortly after the emplacement of the
intra-oceanic Caribbean island arc onto the North America continental margin.
Figure 10d includes temporal relationships between the exhumation of the
Jagua Clara mélange (end of oceanic subduction), the latest Caribbean
arc magmatism, the exhumation of the SSZ ophiolite, and onset of syn-orogenic
sedimentation in the central Septentrional Cordillera, as well as the
continental subduction and exhumation of the Samaná nappes. In the RSJC,
the final juxtaposition of the arc terrains onto the Jagua Clara mélange
along the Morrito fault zone, took place in the latest Maastrichtian to
Paleocene, at the onset of the arc–continent collision (Escuder-Viruete et
al., 2013a). As these units form the basement over which the breccias of the
upper IM3 unit of the Imbert Fm were deposited, this stratigraphic
relationship implying a lower age limit of ∼ 60 Ma (lower Paleocene)
for the Imbert Fm. Also, this juxtaposition of arc- and oceanic-derived
terrains is coeval with the onset at 60 ± 5 Ma of the prograde high-P
metamorphism in the metasedimentary nappes of the Samaná complex
(Escuder-Viruete et al., 2011b). Interestingly, a regionally consistent
top-to-the-NE/ENE tectonic transport took place in the nappes of the
Samaná complex during the Eocene to earliest Miocene (Escuder-Viruete et
al., 2011a). This kinematic data indicates that the tectonic incorporation of
continental-derived terrains to the developing Caribbean
subduction-accretionary prism in a deep crustal level produces a sub-parallel
extension at a shallow crustal level, which is a typical process in the
dynamics of an accretionary complex (Agard et al., 2009). All sections of the
Imbert Fm in the RSJC are unconformably overlain by the La Toca Fm, which
contains in the lowermost strata middle-to-upper Eocene foraminifera. In
summary, the time constraints and stratigraphic relationships establish that
the Imbert Fm is upper Paleocene to lower/middle Eocene in age.
Tectono-sedimentary evolution
The tectono-sedimentary evolution recorded in the Imbert Fm comprises three
main phases, which are schematically shown in the Fig. 12. The first phase
includes the deposition of distal turbidites of the lower IM1 unit in the
upper Paleocene to lower Eocene, which are interbedded with volcaniclastic
rocks and subduction-related mafic sills and dykes. The arc-like magmatism is
also represented by the Palma Picada complex and the Curtiembre plutons.
Volcanic rocks are also common in the coeval Los Hidalgos Fm (de Zoeten and
Mann, 1999). These relationships imply the presence of a forearc basin in the
Paleocene to lower Eocene interval, developed above an ESE–SE-dipping slab of
subducted proto-Caribbean oceanic crust, and the existence to the SW of an
active volcanic arc that constitutes the Hispaniola segment of the
intra-oceanic Caribbean island arc. The stratigraphic sections show that the
lower contact of the Imbert Fm is depositional and corresponds to an
erosional unconformity.
The second phase includes the exhumation and erosion of both ophiolitic and
metamorphic rocks of the Caribbean subduction–accretionary prism, whose
first appearance as clasts occurs in the serpentinitic breccias of the
intermediate IM2 unit. Plagioclase 40Ar /39Ar dating implies
that the cessation of arc volcanism at 48–45 Ma (lower to middle Eocene)
was coeval or slightly older than the exhumation of the ophiolite at about
45–40 Ma (middle Eocene). The regional uplift is recorded with the sediment
accumulation of the Imbert Fm in a progressively shallower marine
palaeoenvironment. Uplift follows with the deposition of the shallow-marine
limestones of La Isla Fm in the lower to middle Eocene on top of the exhumed
mantle in the PPC. The turbidites of the IM1 unit, the limestones of La Isla
Fm, the mafic to ultramafic rocks of the ophiolite and the high-P metamorphic
rocks of the subduction channel, were reworked to form the chaotic and
debris-flow deposits of the upper IM3 unit. Pebble and cobble-sized fragments
were derived from both mantle and crustal levels of the exhumed ophiolite.
The angularity of fragments means erosion of a proximal source. Chemical data
from the harzburgites and associated boninitic cumulate gabbros imply the
highly depleted nature of the PPC ophiolite
(Escuder-Viruete et al., 2014), which is a typical feature of SSZ-type
ophiolites (e.g. Marchesi et al., 2009). These relationships indicate that
breccias and olistostromes formed as culmination of regional uplift and
exhumation during the middle Eocene; i.e. during or soon after the latest
stages of ophiolite emplacement onto the margin, still in a subaqueous
setting. This regional uplift is related to an isostatic response induced by
the underplating of (low-density) continental material during the
arc–continent collision (Fig. 12). These features are consistent with
deformation and sedimentation processes that occurred at shallow crustal
levels in a basin, located at the top of an advancing accretionary wedge
(e.g. Brown et al., 2001; Schroetter et al., 2006; Lin et al., 2009). In this
tectonic context, the Imbert Fm records the evolution of a forearc basin into
a suture forearc basin in the upper Paleocene to middle Eocene, as a
consequence of arc–continent collision and SSZ ophiolite emplacement.
This interpretation agrees with the general absence of continentally derived
clasts in the Imbert Fm, such as marbles and micaschists of the Samaná
metamorphic complex, suggesting that it is being subducted and metamorphosed
beneath the accretionary prism (Escuder-Viruete et al., 2011b). The second
phase ended with the compressive deformative event in the middle to upper
Eocene that forms folds and thrust in the rocks of the Imbert Fm. This event
has been related to the oblique collision of the Caribbean island arc with
the Bahama Platform (Draper et al., 1994; de Zoeten and Mann, 1999).
The third phase includes the deposition of the El Mamey Group in the upper
Eocene to lower Miocene. The deep-marine turbidite succession of the La Toca,
Altamira and San Marcos Fms implies a period of tectonic subsidence following
uplift. These units represent the infilling of a tectonically more mature and
relatively stable, onlapping forearc basin. This indicates that uplift of the
ophiolite and underlying metamorphic units was followed shortly by
subsidence. Subsidence in the basin may have been produced by the progressive
movement toward the NE of the orogenic wedge onto the continental margin
(Fig. 12).
The Imbert Fm unconformably overlies the PPC and RSJC. This stratigraphic
position and upwards gradation to the overlying El Mamey Group, is not
compatible with a genesis for the Imbert Fm as sediments deposited in a
trench or inner trench-slope basin, and then incorporated to a subduction
complex (Bourgois et al., 1982; Pindell, 1985; Hernáiz Huerta et al.,
2012). In this sense, the relationships between the Imbert Fm and the
underlying SSZ ophiolite and overlying flysch deposits are similar to those
of the La Picota Fm of eastern Cuba, the basal Great Valley Supergroup of the
coastal California, the Saint-Daniel mélange in southern Quebec, the
Ordovician South Mayo Trough of western Ireland and the olistostromes,
mélanges and terrigenous sediments in Albania, overlying the
corresponding Caribbean, Franciscan, Taconian/Grampian and Tethyan (Mirdita)
ophiolites (Cobiella-Reguera, 2009; Dewey and Mange, 1999; Hitz and Wakabayashi, 2012;
Robertson, 2002; Robertson
et al., 2012; Ryan and Dewey, 2011; Schroetter et al., 2006). Therefore,
there have been similar upper crustal processes during arc–continent
collision in the past to the present. In the Greater Antilles orogenic belt,
the Imbert Fm represents the base of a syn-collisional basin developed in a
forearc setting during the arc–continent collision.
The Supplement related to this article is available online at doi:10.5194/se-7-11-2016-supplement.
Acknowledgements
The authors wish to thank Gren Draper (Florida International University,
Miami) for their comments on the geology of Dominican Republic and
Jacques Monthel (BRGM) and Pedro-Pablo Hernáiz (Inypsa) for their
involvement in mapping and sampling the Puerto Plata area. Gren Draper,
Paul Ryan and Joaquina Álvarez-Marrón provided careful and
constructive reviews. The Dominican Servicio Geológico Nacional is also
thanked for collaboration, particularly to Ing. Santiago Muñoz. The
research has been funded by the CGL2009-08674/BTE and CGL2012-33669/BTE
projects. Edited by: J. Alvarez-Marron
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