Structure, tectonics and metamorphic development of the Sancti Spiritus Dome (eastern Escambray massif, Central Cuba)

The Sancti Spiritus Dome of the eastern Escambray (Cuba) represents a metamorphic fold and thrust structure which was part of the Cretaceous subduction-accretion complex of the Greater Antillean Arc. On the basis of structural data and pressure-temperature-time evolution the metamorphic complex can be subdivided into four units interpretable as nappes: a high-grade greenschist-facies unit (Pitajones unit), a high-pressure tectonic mélange (Gavilanes unit), high-pressure amphibolites (Yayabo unit) and - tectonically overlying - low-pressure metagabbros of the Greater Antillean Arc (Mabujina unit). The oldest rock fabrics are preserved in eclogite- and blueschist-facies rocks of the Gavilanes unit, indicating arc-parallel extension. Maximum metamorphic conditions are recorded in eclogites (16-20 kbar, 580-630 °C) and garnet-mica schists (16-23 kbar, 530-610 °C) of the Gavilanes unit. Field observations and fabric studies show that greenschist-facies dynamic indicators are dominated by top-to-NE tectonic transport in the lowermost nappes. The greenschist-facies shear zone between the Yayabo unit and the Mabujina unit is viewed as the main detachment zone between the subduction complex and the overlying arc complex. Active subduction ceased at about 70 Ma, followed by rapid uplift, exhumation and thrusting to the north

Foundations of Gulf of Mexico and Caribbean evolution : eight controversies resolved

Eight points of recurring controversy regarding the primary foundations of models of Gulf of Mexico and Caribbean tectonic evolution are identified and examined. The eight points are controversial mainly because of the disconnect between different scales of thinking by different workers, a common but unfortunate problem in the geological profession. Large-scale thinkers often are unaware of local geological detail, and local-scale workers fail to appreciate the level of evolutionary precision and constraint provided by regional tectonics and plate kinematics. The eight controversies are: (1) the degree of freedom in the Gulf-Caribbean kinematic framework that is allowed by Atlantic opening parameters; (2) the existence of a South Bahamas-Guyana Transform, and the role of this structure in Cuban, Bahamian, Trinidadian, and Guyanese evolution; (3) the anticlockwise rotation of the Yucatán Block during the opening of the Gulf of Mexico; (4) the Pacific origin of the Caribbean oceanic crust; (5) the Aptian age and plate boundary geometry of the onset of west-dipping subduction of Proto-Caribbean beneath Caribbean lithospheres; (6) the origin and causal mechanism of the Caribbean Large Igneous Province…not Galapagos!; (7) the number and origin of magmatic arcs in the northern Caribbean; and (8) the origin of Paleogene "flysch" deposits along northern South America: the Proto-Caribbean subduction zone. Here we show that there are viable marriages between the larger and finer scale data sets that define working and testable elements of the region's evolution. In our opinion, these marriages are geologically accurate and suggest that they should form discrete elements that can and be integrated into regional models of Gulf and Caribbean evolution. We also call upon different facets of the geological community to collaborate and integrate diverse data sets more openly, in the hopes of improving general understanding and limiting the publication of unnecessary papers which only serve to spread geological uncertainty

Semi-empirical Gibbs free energy formulations for minerals and fluids for use in thermodynamic databases of petrological interest

ISSN:0342-1791ISSN:1432-202

Structure, tectonics and metamorphic development of the Sancti Spiritus Dome (eastern Escambray massif, Central Cuba)

The Sancti Spiritus Dome of the eastern Escambray (Cuba) represents a metamorphic fold and thrust structure which was part of the Cretaceous subduction-accretion complex of the Greater Antillean Arc. On the basis of structural data and pressure-temperature-time evolution the metamorphic complex can be subdivided into four units interpretable as nappes: a high-grade greenschist-facies unit (Pitajones unit), a high-pressure tectonic mélange (Gavilanes unit), high-pressure amphibolites (Yayabo unit) and - tectonically overlying - low-pressure metagabbros of the Greater Antillean Arc (Mabujina unit). The oldest rock fabrics are preserved in eclogite- and blueschist-facies rocks of the Gavilanes unit, indicating arc-parallel extension. Maximum metamorphic conditions are recorded in eclogites (16-20 kbar, 580-630 °C) and garnet-mica schists (16-23 kbar, 530-610 °C) of the Gavilanes unit. Field observations and fabric studies show that greenschist-facies dynamic indicators are dominated by top-to-NE tectonic transport in the lowermost nappes. The greenschist-facies shear zone between the Yayabo unit and the Mabujina unit is viewed as the main detachment zone between the subduction complex and the overlying arc complex. Active subduction ceased at about 70 Ma, followed by rapid uplift, exhumation and thrusting to the north

Significado de las paragénesis de anfíboles en metagrabos relacionados con secuencias de margen continental en el NW de Cuba

El Terreno Guaniguanico se extiende por todo el NW de Cuba occidental. Está compuesto por depósitos sedimentarios jurásicos-paleógenos de margen continental pasivo. En su extremo meridional se localiza la Faja Cangre, la cual a través de un plano de sobrecorrimiento ocupa la posición más alta en el corte y está integrada por intercalaciones de rocas metasiliciclásticas y metacarbonatadas (formaciones Arroyo Cangre, San Cayetano, Jagua y Guasasa). Los cuerpos estudiados de metagabros se encuentran dentro de las metasiliciclastitas de la Formación Arroyo Cangre (Jurásico Inferior - Jurásico Superior), secuencia que experimenta el mayor grado de metamorfismo dentro de esta faja. Los metagabros fueron estudiados en el microscopio de polarización y mediante microsonda electrónica; a partir de estas técnicas se pudo determinar que están integrados por la asociación mineral anfíbol-albita-cuarzoepidota- clorita-zoisita. La variabilidad composicional de los anfíboles brinda información acerca del metamorfismo, variando desde cálcicos hasta sódicos, con la existencia de actinolita, magnesiohornblenda y glaucofana. Los anfíboles no se generaron bajo las condiciones de P/T vinculadas con el transporte tectónico (Paleoceno Superior - Eoceno Inferior), que afectó las secuencias de todo el terreno, sino en una etapa anterior asociada a un metamorfismo regional. Los diferentes tipos de anfíbol en los metagabros indican varias facies (esquistos verdes; esquistos verdes-anfibolitas; esquistos glaucofánicos) en la evolución metamórfica experimentada por esas rocas. Probablemente, la Formación Arroyo Cangre y demás secuencias de la Faja Cangre son representativas del metamorfismo regional ocasionado por uno de los eventos de subducción propuestos para el Cretácico; o quizás hayan servido de "rampa frontal" al inicio de los cabalgamientos originados por la Orogenia Laramide, generándose presiones dirigidas elevadas y, como consecuencia, un metamorfismo que no afectó al resto del Terreno Guaniguanico

The crystal-structure of synthetic NaNa(2)Mg(5)Si(8)O(21)(OH)(3), a triclinic C(1)over bar amphibole with a triple-cell and excess hydrogen

Synthetic NaNa2Mg5Si8O21(OH)(3) is the first triclinic member of the amphibole group, and has a tripling of the unit cell in the b direction. The space group is C1 and the triple-b repeat gives Z = 6. The unit-cell parameters are: a = 9.883(2), b = 54.082(9), and c = 5.277(1) Angstrom, alpha = 90.045(4)degrees, beta = 103.068(3)degrees, gamma = 89.960(4)degrees, and V = 2748(1) Angstrom(3). The crystal structure has been refined to R-1 = 7.6 and wR(2) = 16.7% for the 1835 reflections with F-o > 4sigma(F) and for 4832 supercell reflections in the 2theta range 2-25degrees, respectively. The structure is pseudo-monoclinic, but both the intensity distribution and refined model indicate space group C1. Compared with the common C2/m amphibole structure, the two halves of an I-beam unit are no longer mirror-related, and the overall structure can be rationalized in terms of two different types of I-beam occurring in the unit cell. The first (with multiplicity 2) is centrosymmetric, and the second (with multiplicity 4) is non-centrosymmetric. There are also significant displacements of the cations, especially at the M4 sites, from their corresponding locations in the C2/m structure. The correlated displacements of Na atoms at the M4 sites permit incorporation of excess protons in pseudo-tetrahedral cavities between two adjacent chains of tetrahedra belonging to different I-beams. Bond-valence calculations and crystal-chemical analysis suggest that excess protons are bonded to O atoms at the O4 sites, and are hydrogen bonded to O atoms at adjacent O2 sites. The infrared spectrum of the amphibole in the principal OH-stretching region has a triplet of sharp bands at 3740, 3727, and 3711 cm(-1), which are assigned to the three independent "normal" O3-H groups in the triclinic structure. There is an additional intense and very broad absorption at 3430 cm(-1) that is resolved only when adsorbed moisture is removed. This band is assigned to the extra H in the structure. All the details provided by structure refinement and the proposed location of the excess H atoms is in accord with previous HRTEM and Si-29- and H-1 MAS NMR studies of this amphibole

Structure and phase transition of synthetic NaNa2Mg5Si8O22 (OH)(3)

Na Na2 Mg5 Si8 O22 (OH)3 is the first amphibole composition with a rigorously documented excess of protons. It is triclinic, space group C-1, and the unit-cell derives from a tripling of the b edge. This symmetry allows off-centring of the B-cations [1], as well as different conformations of the two sides of the double chains. The correlated displacements of BNa atoms permit the incorporation of excess protons in pseudo-tetrahedral cavities between two adjacent chains of tetrahedra belonging to different I-beams. Bond-valence calculations and crystal-chemical analysis suggest that the excess proton is bonded to the oxygen atom at the O4 site, and is hydrogen bonded to that at the adjacent O2 site. The observed cation arrangement is coherent with previous 29Si- and 1H MAS NMR studies of this amphibole [2]. Na Na2 Mg5 Si8 O22 (OH)3 undergoes a triclinic-tomonoclinic C-1 \uae C2/m phase transition in the T range 100-160 \ub0C [2]. The transition has now been studied by FTIR in the T range 25-250 \ub0C. In the OH region, the room-T spectrum shows a triplet of very sharp bands, at 3740, 3727 and 3711 cm-1, respectively, which can now be assigned to three distinct O-H dipoles locally interacting with a strongly ordered A-cation, and a very broad band centered around 3300 cm-1. There is a systematic peak shift and intensity decrease with T. At 180 \ub0C the three peaks merge into one single absorption at 3723 cm-1, and no significant change is observed beyond this T. Part of the broad band centered at 3300 cm-1 vanishes with increasing T, while a strongly asymmetric and well defined peak at 3430 cm-1 is resolved. The intensity of this peak remains constant at any T, even for long heating stages at T > 250 \ub0C. This absorption is assigned to the excess proton, and the measured frequency confirms that it is strongly involved in hydrogen bonding with surrounding oxygen atoms; the width of the band implies local disorder. All these changes are completely reversible during cooling. [1] C\ue1mara et al. Am. Mineral, 2004, in press. [2] Liu et al. Eur. J. Mineral., 1996, 8, 223

Petrography, mineralogy and geochemistry of jadeite-rich artefacts from the Playa Grande excavation site, northern Hispaniola: Evaluation of local provenance from the Río San Juan Complex

Archaeology of the America