Field Forum 2025:
The Geology of Cuba: Key for the Tectonic Evolution of the Caribbean–North American Plates

Cuba | 12–18 April 2025

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Fourth day: Tuesday 15.04.2025. Stops 14-16. Santa Clara and surroundings: Ophiolitic mélange. Time of departure: 8.00 am.

Below: Geological sketch-map and cross-section (black line) of central Cuba (based on Iturralde-Vinent, 1998) with indication of stops.

Below: Geological map of Cuba (1:250000) with indication of stops. Click here for a high-resolution version. Click here for legend.

Stop 14. Santa Clara-Placetas road. Outcrop in the railway close to the road. 22°19'49.99"N, 79°42'55.71"W. Banded gabbros of the oceanic lower crust, underlying serpentinized peridotites and late intrusive diabases.

See on 1:250K geologic map. See on geologic sketch map. See on Google Maps.

The banded plutonics include gabbronorite, olivine gabbro, troctolite, quartz diorite, tonalite, plagiogranite-diorite. In this outcrop, a common lithology is (leuco)gabbronorite made of coarse grained un zoned plagioclase and clinopyroxene with typical cumulate texture. The rocks are amphibolitized, with tremolitic amphibole, chlorite, serpentine, magnetite, prehnite, pumpellyite, and calcite as typical alteration products. Some ultramafic rocks are strongly overprinted by serpentine, calcite, and opaque minerals. Diabase – microgabbro dykes and bodies crosscut the banded structure. In these rocks magmatic plagioclase and clinopyroxene are overprinted by brown-green hormblende (brown hornblende probably late magmatic), chlorite, prehnite, pumpellyite, clinozoisite, opaque minerals, and calcite.

The chondrite-normalized REE patterns of the gabbro-gabbronorites are characterized by LREE-depleted and relatively flat HREE segments, and positive Eu anomalies. These patterns indicate that these rocks are cumulates from variably fractionated MORB- or FAB-like melts. The intrusive diabase-micrograbbro rocks significantly differ from those of layered cumulate rocks and other diabase rocks that intrude the mantle ultramafics. They display REE patterns characterized by LREE-enriched and HREE-depleted segments, typical of arc lavas. A slight negative Eu anomaly as a result of plagioclase fractionation is present, representative of evolved lavas with high REE contents. The REE patterns are similar to island arc tholeiites (IAT).

Banded gabbros:

Petrography of fresh and altered samples:

Leucocratic layer

Composition of banded gabbros (Butjosa et al., 2024).

Diabase intrusion

Composition of diabases, IAT (Butjosa et al., 2024).

Serpentinites (towards viewer) of forearc signature below banded gabbros (away viewer):

Stop 15. Santa Clara-Placetas road. Pelo Malo Quarry. 22°23'25.89"N, 79°52'9.04"W. Ophiolite mélange. Megablock of HP foliated (±dolomite) antigoritite sorrounded by "normal" (regional) serpentinte. The rock represents serpentinites of the oceanic lithosphere that were transformed into antigoritite during subduction. Fluid-rock interaction is denoted by veins made of coarse grained tremolite.

See on 1:250K geologic map. See on geologic sketch map. See on Google Maps.

Surrounding "normal" serpentinites.

Composition of Pelo Malo antigoritites (and tremolite veins compared) to other ultramatic rocks (Butjosa et al., 2023)

P-T conditions of tremolite-vein formation (Butjosa et al., 2023)

Panoramic view from Pelo Malo hill

Stop 16. Santa Clara-Encrucijada road road. Las Delicias. 22°32'21.98"N, 79°54'18.89"W. Ophiolitic mélange. Eclogite blocks within serpentinite.

See on 1:250K geologic map. See on geologic sketch map. See on Google Maps.

The eclogites are made of garnet, omphacite, sodic-calcic amphibole (barroisite), epidote, rutile and (locally abundant) phengite. The sodic-calcic amphibole retains prograde growth zoning, with cores of actinolite-magnesiohornblende. Garnet displays prograde and oscillatory zoning. The retrogressed areas contain relicts of the eclogitic assemblages (but typically little or no omphacite) overprinted by sodic-calcic and calcic amphibole, albite, epidote, chlorite, and titanite.

The composition of eclogite and retrogressed eclogite indicates MOR basaltic composition, likely of the oceanic lithosphere of the proto-Caribbean (Garcia-Casco et al., 2008), and P-T paths indicate prograde burial in a warm subduction zone reaching up to 20 kbar (Garcia-Casco et al., 2002; Garcia-Casco et al., 2006) or up to ca. 30 kbar (Rui et al. 2024) followed by strong decompression with minor cooling during amphibolitization. Age determinations in this and other eclogite blocks indicate protolith formation during the Hauterivian (U-Pb zircon: 126.3 ± 0.7 Ma; Rui et al. 2024) and Aptian subduction-related peak metamorphism and Albian exhumation and mélange formation (Ar/Ar in amphibole: 103.4 ± 1.4 Ma; Ar/Ar in phengite: 115.0 ± 1.1 Ma, Rb/Sr Ms-Omp-WR: 118.2 ± 0.6 Ma; U-Pb zircon: 118.6 ± 1.6; Garcia-Casco et al., 2002; Rui et al. 2024).

Oscillatory garnet zoning (Garcia-Casco et al., 2002; Garcia-Casco et al., 2006):

Bulk-rock composition (unpublished data):

Arriving at Hotel La Granjita and casas particulares in Santa Clara at ca. 6.30 PM   Dinner at 7.30 PM. 8.30 PM, after dinner meeting to discuss the geology of the day.