No abstract

Mesozoic and Cenozoic strata of the San Jacinto Fold Belt (Colombian Caribbean) provide insights about sedimentary environments and paleogeographic evolution in the transition between the northern Andes and the South Caribbean deformed belt. We report new provenance (conventional sandstone petrography, heavy mineral analysis, and detrital zircon U-Pb geochronology and typology) and micropaleontologic data (palynology, calcareous nannofossils, and foraminifera) in samples collected from the lower Eocene (San Cayetano Formation) and upper Eocene–Oligocene (Toluviejo and Ciénaga de Oro Formations) rocks in boreholes drilled by the Colombian Agencia Nacional de Hidrocarburos as well as from recently exposed Oligocene outcrops from the Ciénaga de Oro Formation. Sandstone petrography shows modal variations, with high feldspar content in the lower Eocene rocks and high quartz content in the Oligocene deposits. This shift in compositional maturity may be due to climatic variations, tectonic activity, and/or changes in source areas. Heavy mineral analyses indicate variations that suggest sources primarily related to felsic igneous and/or low-grade metamorphic and mafic and ultramafic rocks. Zircon U-Pb geochronology displays age populations mainly in the Late Cretaceous, Late Jurassic, Permian–Triassic, and Precambrian (ca. 900–1500 Ma). In addition, zircon typology analyses indicate that the igneous zircons came primarily from monzogranites and granodiorites. Finally, the micropaleontologic and sedimentary data sets indicate that the sediments were deposited in tropical coastal and shallow marine environments. The sediments were transported by short rivers from the crystalline massifs of the Lower Magdalena Valley and the northern Central Cordillera basements, while distal transport of sediments may have occurred along longer rivers, which brought sediments from southern regions located between the Central and Western Cordilleras.

FIGURE 1. A) Location of the Ladrilleros-Juanchaco Sedimentary Sequence (LJSS) on the Colombian and South American context on the Paci c coast. B) Local geological framework of the LJSS (modi ed from Montoya, 2003). C) General aspect of outcrops for the LJSS in the studied section, NW-SE.

RESUMENEn el departamento del Tolima, al noroccidente del municipio de Mariquita, se encuentra aflorando la Granodiorita de Mariquita, con edad reportada de 113 ± 4 Ma por K-Ar en biotita. El contacto es intrusivo con los esquistos verdes, grises y negros del Complejo Cajamarca, desarrollando una clara aureola de contacto, la cual alcanza aproximadamente 520 m de extensión en el sector de las Cataratas de Medina (vía Mariquita -La Victoria), y se extiende hasta la quebrada Chiminá, en donde su extensión es menor y alcanza 240 m aproximadamente. Las cornubianas cuarzo-actinolíticas y cuarzo-biotíticas se desarrollaron en un evento sobreimpuesto a un metamorfismo regional y a un metamorfismo dúctil previo. La facies de la cornubiana de albita-epidota está determinada por la paragénesis actinolita-epídota-clorita.Palabras clave: aureola de contacto, Mariquita, Colombia. PETROGRAPHY AND CARTOGRAPHY OF CONTACT AUREOLE OF THE MARIQUITA GRANODIORITE (TOLIMA DEPARTMENT, COLOMBIANCENTRAL CORDILLERA) ABSTRACTIn the Department of Tolima, northwest of the town of Mariquita, crops out the Mariquita Granodiorite, which known age is 113 ± 4 Ma K-Ar in biotite. The intrusive contact with the green, gray and black schists of the Cajamarca Complex developed a clear contact aureole with a maximum width of approximately 520 m in the area of Medina Falls (Mariquita-La Victoria road), which extends to the Chiminá creek, where its extent is reduced to approximately 240 m. Quartz-biotite and quartz-actinolite hornfels were developed as a superimposed event to a previous regional and ductile metamorphism. The albite-epidote hornfels facies is determined by the actinolite-epidote-chlorite association.