Caracterización geoquímica del complejo plutónico de Taliga-Barcarrota (Badajoz, España)

[Resumen] En el Complejo Plutónico de Táliga-Barcarrota se distinguen dos tendencias geoquimicas: la primera de ellas corresponde a una "asociación peralumínica" representada por los granitos biotíticos de Táliga, la segunda de caracter "cafémico-subalcalino" está constituida por rocas de tipo básico e intermedio del macizo de Barcarrota[Abstract] In the Plutonic Táliga-Barcarrota Complex two geochemical tendences can be differenciated: the first one corresponds to "peraluminical assoeiation" represented by biotite granites of Táliga, the second one with a "cafemic-subalkaline"character is constituted by basic and intermediate type of the massif of Bacarrot

Rasgos generales de los skarns y mineralizaciones asociadas del Sistema Central español

[Resumen] La existencia en el Sistema Central Español de gran variedad de mineralizaciones ligadas a skarns permite discriminarlas en base al protalito, profundidad de emplazamiento y composición del granito asociado.Estas variables definen las condiciones fisicoqu!micas de la alteración metasomitica y por lo tanto, la paragJnesis de la ganga Y mineralización.[Abstract] The ecurrence in the Spanish Central 5ystem of a great variety of ore shewings related te skarns allew te discriminate them in basis to the original rack petrology, deepness and composition of related granite. Those parameters characterize the physicochemical conditions of metasomatic alteration, gangue minerelogu and ore campositio

The significance of «S-C» structures found in the Berzosa-Honrubia region (Spanish Central System)

[Resumen] En el extremo oriental del Sistema Central Español, existen evidencias de un episodio tect6nico fini -hercínico, que se manifiesta en el desarrollo de una banda de 1 a 2 Km de anchura, de dirección submeridiana y buzamiento al este en la que son frecuentes estructuras de tipo «S-C» dúctiles. Esta banda probablemente extensional, se superpone a la estructura singular de segunda fase hercínica (D2), conocida como Zona de Cizalla de Berzosa (Z.C.B., CAPOTE, R. et alters, 1981; GONZALEZ CASADO,]. M., 1986), tradicionalmente interpretada como un cabalgamiento dúctil hacia el noroeste retrovergido por la fase de pliegues longitudinales D3. La zona descrita coincide además espacialmente con una banda donde existen procesos hidrotermales tardíos, los cuales podrían relacionarse genéticamente con la estructura citada. El probable episodio extensional descrito, puede relacionarse con la etapa de extensión regional generalizada que se desarrolla durante el final del ciclo hercínico en toda la cadena. Período este bien reflejado en muchos puntos del Sistema Central Español, en forma de importantes accidentes tectónicos extensionales, principalmente de dirección este-oeste y buzamiento norte o sur.[Abstract] In the east end of the Spanish Central System there are sorne evidence of a latehercynian tectonic event. Field evidences includes the presence of «S» and «C» planes (composite planar fabrics), in a band of 1 or 2 Km of wide, with an eastwest direction and dipping to the east. This area has probable an extensional origin and has been superimposed to a structure related to the herc.ynian second phase (D2) know as the Berzosa Shear Zone (B.S.Z., CAPOTE, R., et alters, 1981; GONZALEZ CASADO, J. M., 1986). The B.S.Z. has ben interpreted as a ductil thrust towards the nort-oest, backfolded by a phase of longitudinal folds 03. The investigated region shows a spatial correlation with a band where there are sorne late hidrotermal process, what could be genetic related with the studied structure. Microstructural evidence are internally consistent with field observations. It appears that data are compatible with N-S oriented extensional detachment, dipping to the east, with and east-under-west sense of movement. This event could be correlated with a period of regional extension found elsewhere in the Spanish Central System. Developped for aH the belt during the end of the hercynian cicle. This last even is weH developped in several points of the Spanish Central System and can be seen as severa! E-W oriented detachment systems, dipping to the N and S (extensional tectonics)

Hydrothermal alteration and accessory minerals in a fault zone of the La Cabrera granite (Spanish Central System)

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasFALSEEspaña. Ministerio de Educación y Cienciapu

Metamorphic inversion in the famatinian orogen, Sierra de San Luis, Argentina

P-T conditions of Famatinian metamorphism (c. 465 Ma) were determined along a cross section in the central southern part of the Sierras de San Luis, Eastern Sierras Pampeanas. A continuity from low to high grade metamorphism is recorded here with an inverted disposition of metamorphic zones, i.e., higher grade rocks structurally overlying lower grade rocks. Foliation dip decreases accordingly downward in a fan-like arrangement. Shear zones are boundaries to the main metamorphic zones. The cross section is located on the eastern side of a large scale transpressional double vergence positive flower structure which involves most of the Sierra de San Luis. Calculated peak P-T values are: 790º and 800ºC and 7.2 to 8.9 kbar for the gneiss zone, 600º to 650ºC and 5.9 to 6.4 kbar for schist zone, and 550 ºC and 4.7 kbar for the transition schist – phyllite zone. Highest grade rocks show a clockwise P-T path with a nearly isothermal decompression to P values which are similar within error to those of the lower grade rocks. The latter suggests that metamorphic inversion was largely synmetamorphic and that it was driven by movement along shear zones and ductile flow within domains. Reactivation of shear zones is invoked however to explain some mistmach of P values particularly among the lower grade zone

Episodic palaeo-hydrothermal activity in the Sierra de Guadarrama (Spanish Central System): new K-Ar ages and tectonic correlation with the Iberian chain

Episodic hydrothermal alterations in the Sierra de Guadarrama took place between ca. 300 Ma and 10 Ma. New K-Ar ages for hydrothermal minerals have been obtained that along with previous data allow to better constrain the late- to post-Variscan history of tectono-hydrothermal activity. This activity can further be correlated with Alpine tectonic events in central Iberia recorded in Permian to Cainozoic sedimentary basins. Dating of hydrothermal events in the basement is thus a useful tool to better constrain the chronology of tectono-sedimentary events in the cove

Hydrothermal alteration in granites from La Cabrera (Spanish Central System). Study of secondary minerals (SEM) in halos of calcium bearing mineral druses

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasFALSEEspaña. Ministerio de Educación y Cienciapu

Metamorfismo de alto gradiente P/T en la Sierra de Pie de Palo (Sierras Pampeanas, Argentina): modelado de equilibrio de fases minerales e implicancias geodinámicas en el antearco famatiniano

La Sierra de Pie de Palo (SPP, Sierras Pampeanas Occidentales) presenta evidencia de dos metamorfismos: uno de edad mesoproterozoica (orogenia Grenvilliana) y otro de edad ordovícica (orogenia Famatiniana). Este último es el único registrado en las secuencias sedimentarias neoproterozoicas-cámbricas que forman la cubierta del basamento grenvilliano. Un esquisto estaurolítico procedente de la Secuencia Metasedimentaria Difunta Correa (Ediacarense) en el sector suroriental de la SPP permite deducir, mediante la construcción de pseudosecciones, una evolución prograda desde los ca. 3 kbar y 515 ºC hasta los ca. 9 kbar y 640 ºC correspondiente a un alto gradiente P/T. Junto con Loma de Las Chacras, ubicada inmediatamente al este del área de estudio, la Sierra de Pie de Palo forma parte del antearco famatiniano el cual muestra variaciones de P-T transversalmente al arco magmático famatiniano. Dichas variaciones se registran como una disminución de P (desde ca. 13 hasta 6 kbar), T (desde ca. 900 hasta 450 ºC) y gradiente geotérmico (desde ca. 85 hasta 35 ºC/kbar) desde el área adyacente al arco magmático al este (Loma de Las Chacras) en dirección hacia el margen continental activo al oeste. El sector más próximo al mismo es el Grupo Caucete en el flanco occidental de la Sierra de Pie de Palo. El metamorfismo ocurrió, aparentemente, de forma sincrónica con el magmatismo famatiniano y con un sistema de infra-corrimientos dúctiles de vergencia oeste, a los ca. 470-465 Ma como consecuencia de la inhumación del antearco por debajo del arco magmático

U-Pb SHRIMP dating of detrital zircons of Neoproterozoic para-amphibolites from the Difunta Correa sequence (Western Sierras Pampeanas, Argentina)

The Neoproterozoic Difunta Correa meta-sedimentary sequence (DCSS) of Western Sierras Pampeanas is a cover to a rejuvenated Grenvillian basement. The Western Sierras Pampeanas are allegedly part of the exotic Precordillera Terrane, which was accreted to the proto-Andean margin of Gondwana in lower Palaeozoic times. A para-amphibolite from this sedimentary sequence contains abundant zircons mostly consisting of detrital igneous cores with a metamorphic overgrowth. The latter formed at 439±34 Ma, i.e., during the Famatinian orogeny, although mantles are also found with mixed Grenvillian - Ordovician ages due to Pb-loss. Ages of igneous cores are ~ 625 Ma , 1050-1150 Ma and 1200-1500 Ma with a peak at c. 1.4 Ga. The ~ 625 Ma group zircon is of Gondwanan provenance and this age is an upper value for the age of the host amphibolite. An age between 580 Ma and 620 Ma is inferred for the DCSS. The provenance of zircons between 1.05 Ga and c. 1.2 Ga probably lies in the underlying Grenvillian basement. However zircons older than 1.2 Ga were derived from an unexposed area: palaeogeographical considerations suggest that this area could be either in Laurentia (trans-Laurentia belt) or in southern Amazonia (Rondonia- San Ignacio belt), both 1.3-1.5 Ga in ag

Review of the Cambrian Pampean orogeny of Argentina; a displaced orogen formerly attached to the Saldania Belt of South Africa?

The Pampean orogeny of northern Argentina resulted from Early Cambrian oblique collision of the Paleoproterozoic-Mesoproterozoic MARA block, formerly attached to Laurentia, with the Gondwanan Kalahari and Rio de la Plata cratons. The orogen is partially preserved because it is bounded by the younger Córdoba Fault on the east and by the Los Túneles-Guacha Corral Ordovician shear zone on the west. In this review we correlate the Pampean Belt with the Saldania orogenic belt of South Africa and argue that both formed at an active continental margin fed with sediments coming mainly from the erosion of the Brasiliano–Pan-African and East African–Antarctica orogens between ca. 570 and 537 Ma (Puncoviscana Formation) and between 557 and 552 Ma (Malmesbury Group) respectively. Magmatic arcs (I-type and S-type granitoids) formed at the margin between ca. 552 and 530 Ma. Further right-lateral oblique collision of MARA between ca. 530 and 520 Ma produced a westward verging thickened belt. This involved an upper plate with high P/T metamorphism and a lower plate with high-grade intermediate to high P/T metamorphism probably resulting from crustal delamination or root foundering. The Neoproterozoic to Early Cambrian sedimentary cover of MARA that was part of the lower plate is only recognized in the high-grade domain along with a dismembered mafic–ultramafic ophiolite probably obducted in the early stages of collision. Uplift was fast in the upper plate and slower in the lower plate. Eventually the Saldania and Pampean belts detached from each other along the right-lateral Córdoba Fault, juxtaposing the Rio de la Plata craton against the internal high-grade zone of the Pampean belt.Centro de Investigaciones Geológica