• Alaskan-type complex
• Cr-spinel
• Dominican Republic
• geochemistry
• Hispaniola
• intra-oceanic island arc
• petrography

The Alaskan-type mafic-ultramafic complexes are recognised as a distinct class of intrusions regarding their lithologic assemblage, mineral chemistry, and genesis. Those types of intrusion are increasingly gaining more scientific interest from an economic standpoint since they can represent one of the sources of PGE (Platinum-Group Elements) accumulation in placer deposits.
This study describes petrography, whole-rock major oxide and trace element composition and mineral chemistry of accessory and rock-forming minerals from the Arroyo Limón complex (Cordillera Central - Dominican Republic), in order to characterise the nature of this igneous body and highlighting strikingly similarities with the Alaskan-type mafic-ultramafic complexes.
The investigated samples consist of peridotite, gabbro, amphibolite and orthogneiss, collected in the central Cordillera of the Dominican Republic, along the axial portion of a Cretaceous island-arc system.
For the ultramafic rocks, high Fo contents in olivine (Fo82-87) and high Cr# [Cr/(Cr+Al)] in spinel (>78) suggest a MgO-rich and Al2O3-poor ultramafic parental magma. During the early stages the magma crystallised mostly olivine and chromite, joined afterwards by post-cumulus clinopyroxene, primary pargasitic amphibole and magnetites, forming cumulates of wehrlite. The gabbroic sample retains cumulus texture and mineralogy similar to the peridotites, with olivine (Fo77), chromian spinel (Cr# = 67-77), augite-diopside, pargasite and plagioclase (An 83-85), confirming the high Mg - low Al nature of the magma and its hydrous nature. Petrography and geochemical trends for the mafic-ultramafic suites suggest genetic relationship between the two groups of rocks.
Metamorphic rocks sampled in the Arroyo Limón complex area are classified as (Qz-)amphibolite and orthogneiss from petrographic observation. The amphibolites are variably deformed. Some samples show augen texture and directional stress features, whilst the un-foliated ones display mineral agglomeration of green amphibole and plagioclase in a microcrystalline matrix of the same phases + magnetite. Amphibolites are geochemically equivalent and are considered a product of regional metamorphism of basaltic protolith, variably overprinted by local-induced directional stress.
Petrography and mineral geochemistry results of the whole dataset suggest emplacement in an island-arc environment, with hydrous parental magma of sub-alkaline affinity, although the trace element signature lacks the typical negative Nb-anomaly associated with subduction-related magmas. The REE pattern shows enrichment with respect to chondritic values, with L-REE enrichment for amphibolites and peridotites, and M-REE enrichments for gabbro and orthogneiss.
PGE analysis for two peridotites, one gabbro and one amphibolite were carried out, showing low values and no fractionation when normalized to the primordial mantle; a positive Au anomaly is shown by two ultramafic specimens. Overall, the Pt-Pd ratios of the investigated samples are comparable with those of the Alaskan-type igneous body.
Correlations among the different rock suites sampled for the Arroyo Limón complex are discussed. Similarities and differences of the investigated specimens with respect to the Alaskan-type complexes described in literature are highlighted.
The occurrence of this type of intrusion in the central Dominican Republic may give important insight from paleotectonic and economic geology standpoints.
Further investigations are necessary in order to better understand the genetic origin of the Arroyo Limón rocks and the role of this intrusion in the tectonic and metallogenic evolution of the island of Hispaniola.