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Fifth day: Wednesday 16.04.2025. Stops
17-20. Breakfast 7.30 AM. Cretaceous Volcanic Arc (all outcrops are on the same road south of Santa Clara with distance intervals between 30 minutes to 1½ hours). Time of departure 8 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.
Below: Stratigraphy of the Cretaceous volcanic arc in Central
Cuba and its relation to the underlying Mabujina Amphibolite
complex (Hu
et al., 2024, slightly modified from
Iturralde-Vinent, 2021).
Stop 17. Hilario Formation (1
hour). 22°19'13.05"N, 79°57'57.72"W.
See
on 1:250K geologic map. See
on geologic sketch map.
See on Google Maps.
See
on stratigraphic chart.
Junction of the Manicaragua road with the national highway.
The section exposes a volcano-sedimentary sequence consisting of tuffaceous sandstones, tuffs, volcanic breccias with tuffogenic matrix, polymictic sandstones and limestone. The tuffs are light green (zeolitized) to greenish grey (fresh) and cream beige to brown (weathered) in color. They form strata 2-3 cm to 1-5 m in thickness. Paleontological studies constrained the age of the Formation to the Campanian. Additionally, U-Pb dating of apatite from an andesitic lava sample east of central Cuba yielded an age of 76 Ma, confirming its Campanian age (Hu et al., in prep.). The dated andesitic flow is interbedded within a sequence of pyroclastic and terrigenous rocks (Hu et al., in prep).
The Hilario Fm. lies unconformably on top of the La Bruja Fm. (next stop). Transfer to the next stop (30 min).
Below:
Well bedded tuffaceous sandstones with intercalation of limestones of Hilario Fm.
Microfossil in this section yield Campanian age.
Below: Poorly welded lapilli-tuff. Volcano-sedimentary sequence of
porphyritic andesite, tuff, conglomerate, tuffaceous shale and sandstone. Microphotograph of tuffaceous limestone with sub-angular crystals and lithic fragments.
Below. Chemical composition and apatite U-Pb concordia plot from Hilario Fm
sample 23LV41. This sample consists of an andesitic lava flow within a volcano-sedimentary sequence of tuff, conglomerate, tuffaceous shale and sandstone. The sample consist of a grey porphyritic andesite with plagioclase and amphibole phenocrysts.
Stop 18. Brujas Formation (1 ½ hour). 22°17'33.83"N 79°59'6.04"W.
See
on 1:250K geologic map. See
on geologic sketch map.
See on Google Maps.
See
on stratigraphic chart.
North of Seibabo village, secondary road towards the el Brillante Village. Volcano-sedimentary packages of stratified tuffs and agglomerates, flows of andesitic lavas with spheroidal weathering and coarse-grained tuffs with “onion skin” weathering. The age has been determined by its stratigraphic position as Upper Cretaceous, Coniacian-Santonian. However, new U-Pb data on apatite gives older ages of ca. 95 Ma (Hu et al., in prep).
A studied sample from this location was identified as a peperite. The sample is dominated by a mixture of elongated clasts of quartz and clay minerals, interpreted to represent fluidization and vesiculation of the host sediments as hot magma is violently injected. The sedimentary matrix is composed of quartz, clay minerals and carbonate. Crystal fragments of plagioclase and clinopyroxene are~ 20% of the rock. Fragments of plagioclase phenocrysts may show oscillatory zoning and coarse sieved texture. Augite fragments rarely present zoning and are free of alteration. Subangular to fluidal shaped glass represents basaltic melt of 300 to 800 microns in size.
Transfer to the next stop.
Below. Rare clinopyroxene phenocryst (dark mineral in the volcanic clast) show an overgrowth rim similar to plagioclase phenocrysts.
Below. Volcanic clast (porphyritic olivine basalt) embedded in a carbonate rich sediment. The studied sample contains a hypocrystalline matrix consisting of plagioclase and clinopyroxene laths and glass. Large plagioclase phenocrysts show a consistent texture with a coarse zoned core with glassy melt inclusions and an outer overgrowth. Olivine phenocrysts
are completely replaced by pervasive secondary saponite.
Below: Spheroidal weathering of coarse-grained tuff.
Below: Altered volcanic bomb within coarse-grained tuff.
Below: Clast rich blocky peperite
Below. Chemical composition of La Bruja volcanics.
Below: Apatite U-Pb concordia plot from
La Bruja Fm. sample 23LV10A, a highly altered seriate glomerophyric volcanic rock
consisting mainly of feldspars. The medium-grained tabular to elongated plagioclase feldspar (albite) and orthoclase of the matrix are randomly oriented and show intersertal texture, filled with fine grained quartz and glass (mostly altered in greenish brown color). A few large glomecrysts composed entirely of medium to coarse grained tabular orthoclase show perthitic texture. Apatite appears as inclusions in the feldspar phenocrysts.
Below: Apatite U-Pb concordia plot from La Bruja Fm. sample 23LV10B,
an altered massive coarse-grained seriate glomerophyric
porphyritic andesite with plagioclase phenocrysts. The matrix consists of fine to medium grained intersertal elongated plagioclase laths and tabular orthoclase filled with fine-grained quartz. The plagioclase matrix shows shallow tails and skeletal texture, indicating fast cooling. Large glomerocrysts are composed entirely of medium to coarse grained orthoclase with perthitic texture. Apatite appears as inclusions in the feldspar phenocrysts.
Stop 19. Mataguá Formation. (40 Min).
22°12'48.69"N, 79°59'29.74"W.
See
on 1:250K geologic map. See
on geologic sketch map.
See on Google Maps.
See
on stratigraphic chart.
Under the bridge of the Los Pasos River, on the Santa Clara-Manicaragua road. Volcanic sequence of amygdaloidal basalts, aphyric basalts, pyroclastic flow and volcanic breccias. In this outcrop, in the upper section the basalt shows flow banding, and lower sequence contain a pyroclastic sequence and volcanic breccias with fragment of variable size.
According to the geochemistry, the Matagua Fm. marks a transition from the tholeiitic to the calc-alkaline series, with a predominance of the latter. A Lower Cretaceous (Aptian-Albian) age is constrained by its stratigraphic position, concordant on top of the Los Pasos Fm. (next stop). A new U-Pb Apatite age from the unit give an age of ~121 Ma confirming the age of the unit.
Below: Overview of the outcrop at Los Pasos River.
Below: Sample
23LV26A. Black aphyric basalt with weakly flow banding
identified at outcrop.
Below: Sample 23LV26A is a fine- to medium-grained volcanic rock made up
of vitrophyric lithic fragments and phenocrysts fragments of plagioclase and clinopyroxene. The glass is strongly altered, replaced by chlorite and palagonite. Lithic fragments are made up mostly of fine-grained plagioclase microliths and a few clinopyroxene grains embedded in strongly altered glass matrix. Medium-grained clinopyroxene are fresh and rarely present zonation.
Below: Amygdaloidal basalt.
Below: Volcanic breccias.
Below. Chemical composition of Mataguá Fm. volcanics.
Below: Apatite U-Pb dating on sample 23LV45B. This location was marked as La Rosita Formation in the geological map of Central Cuba. Glomerophyric volcanic rocks consisting of phenocrysts, essentially of plagioclase and K-feldspar, and minor magnetite and clinopyroxene, in a spherulitic matrix. Plagioclase phenocrysts are strongly altered by saussarization and sericitization, locally zoned with inclusions now replaced by chlorite. Clinopyroxene glomerocrysts are mostly replaced by epidote and chlorite. The matrix is made up of fine-grained spherical plagioclase and minor anhedral quartz. The mafic phase in the matrix is completely replaced by chlorite and epidote. Fine-grained magnetite appears as accessory mineral in the matrix and forms needle shaped grains associated with spherical plagioclase. Euhedral apatite is present both in matrix and as inclusions in plagioclase phenocrysts. Secondary calcite replaces plagioclase.
Stop 20.
Los Pasos Formation. (40 Min). 22°10'35.21"N, 79°58'42.06"W.
See
on 1:250K geologic map. See
on geologic sketch map.
See on Google Maps.
See
on stratigraphic chart.
Quarry of massive light grey plagiorhyolites intruded by mafic dykes.
In general, the Los Pasos Fm. consists of rhyolites, plagiorhyolites, rhyodacites, dacites, basalts, basaltic andesite and tuffs of felsic and mafic composition, subordinately andesite, as well as tuffites, breccias and agglomerates, sandstones, and siltstones. This bimodal volcanic assemblage is characterized by effusive and subvolcanic facies that predominate over explosive facies. Hydrothermal alteration is widespread, including propylitic with epidote-actinolite associations and chlorite alteration with actinolite, sericite, quartz, carbonate, prehnite-pumpellyite. Replacement of primary plagioclase by albite is commonly observed, also in veins.
Los Pasos formation is considered as an island arc tholeiitic series, although subordinate samples pertain to the calc-alkaline series.
The lower contact is unknown since it is cut by a fault to the south or is intruded by the Manicaragua batholith. Its contact with the overlying Matagua Fm is covered,
though their beddings are concordant.
The age is considered Lower Cretaceous (pre-Albian) due to its stratigraphic position and U/Pb zircon dating from unfoliated granodiorite intrusions yielding ages of 125 Ma (Rojas-Agramonte et al., 2011; Hu et al, in prep).
Below:
Massive light grey plagiorhyolite. Fine- to medium-grained volcanic rock dominated by anhedral partly recrystallized medium-grained plagioclase (albite) phenocrysts, embedded in a matrix mainly composed of recrystallized fined-grained quartz. Fine-grained acicular actinolite present as mafic phase in this rock, in some parts showing radiating texture
indicating secondary origin. Fine to medium-grained magnetite and tiny apatite rods appear as accessory minerals.
Below: Plagiorhyolite with hydrothermal alteration.
Below: Chemical composition of Los Pasos Fm.
Below: Zircon U-Pb concordia diagram and petrography of
of granitoid intrusion in Los Pasos Fm (sample 23LV-24 ). This coarse-grained
granitoid (trondhjemite) consists of quartz and plagioclase with minor amphibole. Plagioclase crystals are commonly zoned and highly altered to saussurite, giving a cloudy appearance among the weakly deformed quartz. Secondary epidote and chlorite replaced primary fine-grained acicular or medium-grained anhedral amphibole crystals. Few igneous grains of epidote may be present. Magnetite and zircon make up the accessory mineralogy.
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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