Boletín de Geología ISSN: 0120-0283 [email protected] Universidad Industrial de Santander Colombia García, C. A.; Ríos, C. A.; Castellanos, O. M. MEDIUM-PRESSURE METAMORPHISM IN THE CENTRAL SANTANDER MASSIF, EASTERN CORDILLERA, COLOMBIAN ANDES Boletín de Geología, vol. 27, núm. 2, julio-diciembre, 2005, pp. 43-68 Universidad Industrial de Santander Bucaramanga, Colombia Available in: http://www.redalyc.org/articulo.oa?id=349631990004 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative Boletín de Geología Vol. 27, No. 2, julio-diciembre de 2005 MEDIUM-PRESSURE METAMORPHISM IN THE CENTRAL SANTANDER MASSIF, EASTERN CORDILLERA, COLOMBIAN ANDES García, C. A.1; Ríos, C. A.1; and Castellanos, O. M.2 ABSTRACT The Central Santander Massif exposes its metamorphic basement, which mainly consists of medium- to high-grade pelitic schists, paragneisses, migmatites and orthogneisses. For delineating its metamorphic evolution, we have examinated mineral assemblages, metamorphic reactions and P-T conditions of metamorphic rocks of this region. Metamorphism has occurred under conditions of high-temperature and medium-pressure (Barrovian type metamorphism), and three metamorphic zones were developed: staurolite-kyanite, sillimanite and migmatite zones. Pressure and temperature o conditions, estimated by TWQ program, are in the range of 5.0-9.5 kbar and 630-727 C. The P-T path of the metamorphic units is clockwise suggesting a collision model for this region of the Colombian Andes. Keywords: Metamorphism; Santander Massif; Barrovian type; P-T path; collision METAMORFISMO DE PRESION INTERMEDIA EN LA REGION CENTRAL DEL MACIZO DE SANTANDER, CORDILLERA ORIENTAL, ANDES COLOMBIANOS RESUMEN La región central del Macizo de Santander expone su basamento metamórfico, el cual consiste de esquistos pelíticos, paraneises, migmatitas y ortoneises de medio a alto grado. Para delinear su evolución metamórfica, hemos examinado las paragénesis minerales, reacciones metamórficas y condiciones de P-T de las rocas metamórficas de esta región. El metamorfismo ocurrió bajo condiciones de alta temperatura y presión intermedia (metamorfismo tipo Barroviano), con el desarrollo de tres zonas metamórficas: estaurolita-cianita, silimanita y migmatita. Las condiciones de presión y o temperatura, estimadas mediante el programa TWQ, están en el rango de 5.0-9.5 kbar y 630-727 C. La trayectoria de P- T de las unidades metamórficas es en sentido horario sugiriendo un modelo de colisión para esta región de los Andes Colombianos. Palabras claves: Metamorfismo; Macizo de Santander; tipo Barroviano; trayectoria de P-T; colisión. 1 Escuela de Geología, Universidad Industrial de Santander, A. A. 678, Bucaramanga, Colombia. 2 Universidad de Pamplona, Pamplona, Colombia. Medium-pressure metamorphism in the Central Santander Massif, Eastern Cordillera, Colombian Andes INTRODUCTION The purpose of this paper, which is concerned with the description of a high-T and medium-P facies series of the The Santander Massif is located into the northern part of central Santander Massif, is to determine the P-T path Eastern Cordillera of the Colombian Andes. The basement followed by the metamorphic basement. The of this massif is composed by igneous and metamorphic reconstruction of the tectono-metamorphic evolution of rocks, which reflect a complex geological history. During these metamorphic rocks is based on the detailed the last years, the Santander Massif metamorphic rocks petrographical study, reaction history, chemistry of the have been studied to know their mineral compositions, constituent minerals, and geothermobarometry, and the textural and microstructural features, mineral chemistry results of this are very important to understand the and thermobarometric estimates. Some of these studies evolution of orogenic processes of the Andes. have been focused to determine the tectono-metamorphic evolution of the southwestern Santander Massif region, GEOLOGICAL SETTING which has constitued a valuable contribution for interpretation of geologic and tectonic evolution of the The Santander Massif is situated in the northeastern part northwestern continental margin of South America. of Colombia (FIGURE 1). The basement complex of the 0 0 Y=1´132.00 Y=1´147.00 Lower Sillimanite Zone M K s f s + + Q S t i z l Staurolite- Upper Kyanite Zone Sillimanite PCM-666 G G G G S S S Zone S 45 t t t t r r r r + + + PCM-351 + t t t t + + + + M M M M S S S S s s s s i i i i + + + + l l l l + + + + Q Q Q Q B B B B X=1´305.000 t t t t t t t t z z z z CALIFORNIA PCM-1670 35 PCM-19 SANTANDER 35 PCM-1144 PCM-20 MASSIF PCM-21 PCM-156 PCM-618 50 65 MUTISCUA VETAS 50 PCM-636 50 LEGEND PCM-855 PCM-29 PCM-907 Mesozoic-Cenozoic sediment ary rocks 35 PCM-766 35 PCM-737 Triassic-Jurassic intrusive rocks PCM-985 PCM-905 Orthogneiss Formation 35 PCM-965 PCM-972 Silgar á Fo rm at ion 40 65 50 PCM-974 Bucaramanga Gneiss Format ion X=1´290.000 Migmatites Isograd Lithological contact 5km Fault 35 Metamorphic foliation FIGURE 1. Generalized geological map of the Santander Massif (left side), showing the distribution of the metamorphic (grey colour), igneous (black colour) and sedimentary (white colour) rocks modified after Goldsmith et al. (1971), as well as the study area, and geological map of the central Santander Massif (right side) modified after Ward et al. (1973). 44 García, C. A.; Ríos, C. A. ; Castellanos, O. M. Santander Massif comprises metamorphic rocks of pre- trending antithetic faults, counterclockwise rotation of rigid Devonian age, which are cut by intrusive bodies of Triassic internal blocks and inversion of Mesozoic NS trending to Cretaceous ages (e.g. Goldsmith, 1971; Boinet et al. extensional structures. 1985), although age of several igneous bodies is still under debate, due to scarce isotopic data. The metamorphic The first study on the metamorphism of the Santander rocks of this basement have been divided into three units Massif was done by Ward et al (1973). Studies based on from bottom to top Bucaramanga Gneiss (BG), Silgará a collecting of information about the distribution of facies Formation (SF), and Orthogneiss (O). The basement of of metamorphism in Colombia are presented by Maya, the Santander Massif is unconformably overlain by 1997. More recent works (e.g., Restrepo-Pace, 1995; unmetamorphosed rocks of the Floresta Formation. Schafer et al. 1998; García y Ríos, 1997; García y Carboniferous and Permian clastic to calcareous sediments Castellanos, 1998; Ríos, 1999; Ríos and Takasu, 1999; unconformably overlain this unit. However, due to pre- García y Ríos, 1999; García y Campos, 2000; Castellanos, Cretaceous erosional events, the occurrence of these 2001; Ordoñez; 2003; Ríos et al. 2003; Cardona, 2003) sequences is restricted. Triassic sedimentary rocks of the have placed considerable reliance in the results of Tiburón Formation overlay these sequences. Post- mineralogical, petrographical, geochemical, Paleozoic sediments, which overlay the Upper Paleozoic thermobarometric, and geochronological studies of the marine sediments, include the Bocas and Jordán metamorphic rocks in different regions of the Santander formations. The latter consists of fine-grained red beds Massif. with interlayered volcanic rocks and intrusive clasts, which is discordantly overlain by the red bed sequence of the The metamorphic sequence exposed in the study area, Girón Formation of Jurassic age. Cretaceous sedimentary which is extended from California to Mutiscua, rocks occur around the Santander Massif and are corresponds to the CSM. A generalized geological map of preserved as erosional relicts. the study area is shown in FIGURE 1. The oldest lithologic unit in the CSM corresponds to the BG that crops out The first study on the geology of the Santander Massif between California and Vetas towns and is a sequence was done by Julivert (1958, 1959, 1961a, 1961b, and consisting of pelitic and mafic gneisses, with subordinate 1963, 1970), and later described in detail by Ward et al. amounts of amphibolites, migmatites which was (1973). Most of the previous studies have used mainly metamorphosed to high grade. The SF, a younger and geological, structural, paleontological or isotopic data to overlying unit, is a middle- to high-grade metamorphic decipher the evolution of the Santander Massif. Structural sequence, which consists of metapelitic rocks with studies in the Santander Massif have been generally related intercalations of metamafic, quartzfeldspar and to stratigraphic work. Julivert (1970) discusses mainly metacarbonate rocks. It partially envelops the BG and O the relationships between basement and sedimentary cover, units and crops out from southern part of Berlin towards since these determine the main structural features of the the north, as well as to the west of the Mutiscua Fault. Its Eastern Cordillera. lithology changes in composition to the west, from top to bottom, from marble through different varieties of mica The Santander Massif is a structurally uplifted block, limited schist to quartzite. The O unit occurs to the southwest, to the west by the Bucaramanga - Santa Marta Fault and north and northeast of Berlín, and is highly distributed in to the east by the fault system Pamplona - Cubogón - the middle- and high-grade metamorphic rocks. It consists Mercedes. According to Ward et al. (1973), in the on quartz-feldspar and biotite gneiss and generally shows Santander Massif the foliation and fold orientations are concordant foliation and lineation with those of neighboring approximately similar in the BG, SF and O metamorphic of the BG and SF metamorphic rocks. The contact rocks. Regionally, these orientations are N-S, and tend to between the Silgará Formation and the Orthogneiss is be parallel to the axis of the orogenic belt (Eastern intrusive, which evidence the emplacement of orthogneiss Cordillera), showing local variations and discontinuity masses.