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Third day: Monday
14.04.2025. Stops 11-13. Breakfast at 6.30 AM. Leaving Pinar del Rio to Santa Clara (central Cuba).
Time of departure 7.30 AM, arriving at ca. 2.00 PM.
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 11. Santa Clara airport-Minerva road.
22°29'54.95"N, 79°53'14.13"W. Sediments of the Bahamian
borderland. Placetas belt (relative autochtonous of the ophiolitic mélange). Veloz Fm.: Thin to medium
well stratified beds of slightly argillaceous micritic limestones with
variable dolomitization degree and intercalated shales. Ammonites (Haploceras aff. H. gallardoi)
and microfossils (Calpionella alpina, C. elliptica, Tintinopsella sp., Calpionellopsis sp., Nannoconus spp.)
allow determining a Tithonian-Berriasian age. This formation documents platform sedimentation during the Jurassic-Early Cretaceous prior to
the deepening of the Placetas basin during the Upper Cretaceous.
See
on 1:250K geologic map. See
on geologic sketch map.
See on Google Maps.
Stop 12. Santa Clara airport-Minerva road.
22°28'58.23"N, 79°50'42.10"W. Looking from the bus, serpentinite
mélange with blocks of veined amphibolitized eclogite.
See
on 1:250K geologic map. See
on geologic sketch map.
See on Google Maps.
The eclogitic mineral assemblage consists of garnet, scarce omphacite, barroisite, epidote, paragonite, phengite and rutile overprinted by magnesiohornblende, albite, K-feldspar, epidote, chlorite and titanite.
Garnet porhoyroblasts are relatively well preserved with nice
prograde growth zoning. Relict omphacite is essentially located within garnet porphyroblasts. Late epidote is coarse grained and is concentrated in thin veins that crosscut earlier structures and indicate infiltration of fluids. The phase relations suggest decompression and cooling during fluid infiltration.
The chemical composition of the rocks indicates MOR basaltic composition. Fluid infiltration and associated amphibolitization and vein formation did not affect significantly the concentration of REE and
other immobile trace elements.
Veined amphibolite (regrogressed eclogite)
Relict garnet porphiroblasts in an amphibole-epidote-sodic
plagioclase matrix.
BSE and XR Al-Ka images of retrogressed eclogite (omphacite is preserved within garnet porphyroblast) with abundant albite and amphibole and epidote forming the matrix, and REE / chondrite patterns of MOR basaltic retrogressed eclogites. The XR Al-Ka image shows the distribution of Al in amphibole on top of the BSE image.
Stop 13. Santa Clara airport-Minerva road.
22°28'4.55"N, 79°49'26.84"W. Serpentinite mélange
with tectonized low-P mafic intrusives (amphibolite).
See
on 1:250K geologic map. See
on geologic sketch map.
See on Google Maps.
Below, map of central Cuba mélange (from
Butjosa
et al., 2024, compiled after Kantshev et al., 1978, 1480
pages; unpublished;
part 1,
part 2,
part 3,
Álvarez et al., 1991;
unpublished and García Delgado et al., 1998, Mapa geológico de Cuba central (provincias Cienfuegos, Villa Clara y Sancti Spiritus)
escala 1:100000, Instituto de Geología y Paleontología, La Habana).
Ultramafics: Abyssal (blue squares) and forearc (red
squares) ultramafics, mixed in the mélange and distinguished
only by chemical composition (Butjosa
et al., 2024).
Diabase: Forearc basalts-like (FAB, red circles) and
island arc tholeiitic basalt-like (IAT, green circle)
distinguished by chemical composition and intrusive relations
(FAB dominates as intrusions in ultramafics -this outcrop-, or
as massive bodies associated with micrograbbros and locally
heavily altered basalts, while IAT intrudes the plutonic
section of the ophiolite in stop 14) (Butjosa
et al., 2024)
When occurring as massive outcrops
of (meta)basalt-(meta)diabase/micrograbbro is defined as the Zurrapandilla
Fm. The rocks are essentially made of (altered) igneous plagioclase, brown-green amphibole of probable metamorphic origin and opaque minerals. Relicts of magmatic clinopyroxene replaced by amphibole are common. Plagioclase is replaced by epidote and albite. Chlorite, prehnite, and pumpellyite are late minerals, the latter typically located in voids and fractures. No foliation is apparent, in spite of the existence of foliation in the enclosing serpentinite. P-T paths are only retrograde (i.e., do not have prograde
sections). Phase relations indicate low-P metamorphism in an
oceanic context (Caribbean forearc).
The composition of these
rocks are similar to fore-arc basalts (FAB-like;
Butjosa
et al., 2024) or back-arc basalts (Niu
et al., 2022), and their intrusion age has been dated at 135
Ma (Niu
et al., 2022), similar to other FAB-like low-P metadiabase
blocks within serpentinite in eastern Cuba (Lázaro
et al., 2016) that date subduction initiation in the region.
Microscopic views of (meta)diabase (Butjosa
et al., 2024).
Composition of (meta)diabase from central
Cuba (Butjosa
et al., 2024).
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.
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