Reconstructing the crustal section of the intra-oceanic Caribbean island
arc: contraints from the cumulate layered gabbronorites and pyroxenites
of the Rio Boba plutonic sequence, northern Dominican Republic
J. Escuder-Viruete 1, M. Castillo-Carrión1, F. Pérez Valera 2, P.
Valverde-Vaquero 1, Á. Rubio Ordónez3, F.J. Fernández 3
1Instituto Geológico y Minero de España, C. La Calera
1, 28760 Tres Cantos, Madrid. Spain
2Departamento de Ciencias de la Tierra y del Medio
Ambiente, Universidad de Alicante. 03080 Sant Vicent de Raspeig,
Alicante. Spain
3Departamento de Geología, Universidad de Oviedo. C.
Jesús Arias de Velasco, 33005 Oviedo. Spain
Corresponding author: Javier Escuder-Viruete (j.escuder@igme.es)
Key Points:
- The Rio Boba mafic-ultramafic plutonic sequence is a lower crust
section of the Caribbean island arc
- It is made up by gabbroic rocks and subordinate lenses of pyroxenite
- Their magmatic evolution record subduction initiation and subsequent
arc building
Abstract
Located in northern Dominican Republic, the Early Cretaceous Rio Boba
mafic-ultramafic plutonic sequence constitutes a lower crust section of
the Caribbean island arc, made up by gabbroic rocks and subordinate
lenses of pyroxenite. Modal compositions, mineral chemistry, whole-rock
compositions and thermobarometric calculations indicate that pyroxenites
and gabbronorites represent a cumulate sequence formed by fractionation
of tholeiitic magmas with initially very low H2O content
in the lower crust of the arc (0.6-0.8 GPa). Melts evolved along a
simplified crystallization sequence of olivine → pyroxenes → plagioclase
→ Fe-Ti oxides. The magmatic evolution of the Rio Boba sequence and
associated supra-crustal Puerca Gorda metavolcanic rocks is multi-stage
and involves the generation of magmas from melting of different sources
in a supra-subduction zone setting. The first stage included the
formation of a highly depleted substrate as result of decompressional
melting of a refractory mantle source, represented by a cumulate
sequence of LREE-depleted IAT and boninitic gabbronorites and
pyroxenites. Sub-horizontal ductile stretching, deformation fabrics and
recrystallization microstructures show that this substrate was variably
deformed at upper amphibolite to mid-P granulite facies conditions. The
second stage involved volumetrically subordinate troctolites and
gabbros, which preserve cumulate textures and are not penetratively
deformed. The mantle source was refractory and enriched by a LILE-rich
hydrous fluid derived from a subducting slab and/or overlying sediments,
and possibly by a LREE-rich melt. The third stage is recorded in the
upper crust of the arc by the Puerca Gorda ‘normal’ IAT protoliths,
which are derived from an N-MORB mantle source enriched with a strong
subduction component. This magmatic evolution has implications for
unravelling the processes responsible for subduction initiation and
subsequent building of the intra-oceanic Caribbean island arc.