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Aquí reportamos por primera vez la ocurrencia de un "exoskarn cálcico de reacción", el cual corresponde a tales rocas metacarbonatadas, tomando en cuenta que un skarn puede desarrollarse como consecuencia del metamorfismo regional y por diferentes procesos metasomáticos, adyacente a cuerpos intrusivos, a lo largo de fallas y zonas de12:52 p.m. Ellas usualmente ocurren como esazas intercalaciones a escala milimétrica a métrica, dentro de las rocas pelíticas de alto grado, en la parte inferior de la sección metamórfica, aunque la proporción de rocas metacarbonatadas puede se mas alta y diferentes niveles de mármol son explotados en esta región. Estas rocas son interpretadas como derivadas de una secuencia sedimentaria (incluyendo calizas y dolomías, lodositas con presencia de carbonato, areniscas, sedimentos tobáceos y evaporíticos y margas) afectada por metamorfismo regional casi isoquímico. Las rocas metacarbonatadas (mármoles puros o impuros, rocas carbonatosilicatadas, rocas calcosilicatadas y rocas silicatadas con presencia de carbonato) forman un grupo muy complejo dentro de la secuencia metamórfica de la Formación Silgará en la región central del Macizo de Santander. Key words: Metacarbonate Silgará Formation exoskarn diopside garnet. Several reaction-zones occur in the contact between impure calcite marble and garnet-bearing metapelite and the sequence of mineral assemblages in these reaction zones is: biotite + plagioclase ± K-feldspar ± garnet (Zone I), biotite + plagioclase ± K-feldspar ± garnet ± staurolite ± epidote (Zone II), plagioclase + amphibole ± garnet ± epidote (Zone III), amphibole + diopside + garnet + plagioclase (Zone IV), plagioclase + diopside ± scapolite (Zone V), epidote ± calcite (Zone VI), and calcite ± dolomite (Zone VII).
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Therefore, this paper focus attention to the occurrence of metacarbonate and related rocks, which occurs as small scale reactions zones that show a gradational contact from garnet-bearing pelitic rocks to marbles or carbonate-silicate rocks, giving particular interest to the calc-silicate rocks, which are characterized by the presence of elongated grains of banded clinopyroxene (diopside) and scapolite and massive or scattered garnet. We report for the first time the occurrence of a "reaction calcic exoskarn", which corresponds to such metacarbonate rocks, taking into account that a skarn can be developed during regional metamorphism and by different metasomatic processes, adjacent to intrusive bodies, along faults and shear zones, and what defines these rocks as a skarn is its mineralogy, which includes a variety of calc-silicate and associated minerals, usually dominated by garnet and pyroxene. They usually appear as scarce intercalations from millimeter up to meter scale, within the high-grade pelitic rocks, in the lower part of the metamorphic section, although the proportion of metacarbonate rocks can be higher and different marble layers are exploited. These rocks are interpreted as derived from a sedimentary sequence (including limestones and dolostones, carbonate-bearing mudstones, sandstones, tuffaceous and evaporitic sediments and marlstones) overprinted by near-isochemical regional metamorphism. Metacarbonate rocks (pure and impure marbles, carbonate-silicate rocks, calc-silicate rocks and carbonate- bearing silicate rocks) form a very complex group within the metamorphic sequence of the Silgará Formation at the central Santander Massif (CSM). 2ġ Escuela de Geología, Universidad Industrial de Santander, Bucaramanga, ColombiaĢ Programa de Geología, Universidad de Pamplona, Colombia. PETROGENESIS OF THE METACARBONATE AND RELATED ROCKS OF THE SILGARÁ FORMATION, CENTRAL SANTANDER MASSIF, COLOMBIAN ANDES: AN OVERVIEW OF A "REACTION CALCIC EXOSCARN"