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Volume 1 Proterozoic
Jorge GÓMEZ and Daniela MATEUS–ZABALA
Table of Contents
Only the abstracts and keywords of the manuscripts accepted up to now have been included.
By Victor A. RAMOS
By Jorge GÓMEZ, Alberto NÚÑEZ TELLO, Daniela MATEUS ZABALA , Fernando Alirio ALCÁRCEL GUTIÉRREZ and Ana Oliva PINILLA PACHON
Physiographic and Geological Context of the Colombian Territory
By Jorge GÓMEZ TAPIAS and Alberto NÚÑEZ TELLO
Contribution of New Airborne Geophysical Information to the Geological Knowledge of Eastern Colombia
By Ismael Enrique MOYANO NIETO, Renato CORDANI, Lorena Paola CARDENAS ESPINOSA, Norma Marcela LARA MARTÍNEZ, Oscar Eduardo ROJAS SARMIENTO, Manuel Fernando PUENTES TORRES, Diana Lorena OSPINA MONTES, Andrés Felipe SALAMANCA SAAVEDRA and Gloria PRIETO RINCÓN
Manuscript accepted October 29, 2018
Airborne geophysics is an easy way to increase and complement the geological knowledge of large areas, especially very remote areas like the Colombian Amazonia. For this objective and to identify areas of interest for mineral resources, the Colombian government has made extensive efforts to fly the Andean and eastern parts of the country, collecting more than 400 000 linear km of magnetic and gamma spectrometric information over the Colombian Amazonia. This document focuses on describing the potential of these data to increase the geological knowledge of the Amazonian region. It presents a methodology for interpretation of geophysical data and its application over a specific area in the eastern Guainía Department, where the Paleoproterozoic to Mesoproterozoic igneous and metamorphic rocks of the Guiana Shield (Mitú Complex, Parguaza Granite) and several lineaments and structural trends that have not been previously reported were identified. These crystalline basement rocks are partially covered by Miocene sedimentary rocks, recent alluvial deposits and dense rainforest coverage, which make geological mapping very difficult. The results increase the relevance of this type of geophysical interpretation to the geoscientific knowledge about Colombia. This paper also highlights the training of Colombian geoscientists in modern geophysical interpretation techniques.
Tectonostratigraphic Terranes in Colombia: An Update
First Part: Continental Terranes
By Jorge Julián RESTREPO and Jean–François TOUSSAINT
Manuscript accepted March 6, 2019
The quite abundant geological information that has been produced in recent years in Colombia, especially in geochronological and geological mapping, necessitates updating the mosaic of geological terranes that comprise the Colombian territory. Several modifications to these characteristics and boundaries are proposed for terranes such as Chibcha, Tahamí, and Calima. Some small terranes that have been defined recently, including Anacona, Ebéjico (Quebradagrande), and Pozo (Arquía), are placed within the context of the larger terranes. In addition, some new terranes, including Yalcón, Bocaná, Aburrá, Kogi, and Tairona, are defined and their characteristics are described. With these new geochronological data, we propose that the Cajamarca Metamorphic Complex be replaced by two new lithodemical units: the Antioquia Complex, which covers mostly rocks that formed during Permian and Triassic metamorphism, and the Coello Complex, which comprises metamorphic rocks that formed during Jurassic metamorphism. Future lines of investigation are proposed to solve remaining problems, especially the boundaries of some of the newly defined terranes.
Keywords: continental terranes, accretions, displaced terranes, Colombia, Andes.
Zircon U–Pb Geochronology and Hf–Nd–O Isotope Geochemistry of the Paleoproterozoic to Mesoproterozoic Basement in the Westernmost Guyana Shield
By Mauricio IBANEZ–MEJIA and Umberto G. CORDANI
Precambrian Records of the Llanos Orientales Basin, Colombia
By Hernando DUEÑAS–JIMÉNEZ and Jorge MONTALVO–JÓNSSON
Manuscript accepted May 15, 2019
In the Llanos Orientales Basin of Colombia, below thick Tertiary and Cretaceous strata, Paleozoic sedimentary sequences are present, which yield good, diverse and well–preserved assemblages of palynomorphs. In the northeastern part of the basin in the Arauca Graben, after crossing the unconformity at the base of the Cretaceous sequence, oil wells face the presence of Cambrian and Precambrian (Ediacaran – Cryogenian) sediments deposited in low latitudes under shallow marine settings that yield abundant, diverse, poorly preserved and dark–colored sphaeromorph acritarch assemblages.
In the Chiguiro–1, La Coral–1 and Pato–1 wells drilled in 1985, the presence of Ediacaran palynomorphs was observed for the first time in Colombia. This discovery can be considered to be the oldest sediment dated by paleontological methods reported in Colombia. Twenty–six years later, analysis of samples from the Chilacoa–1S, Coralito–1S, Torodoi–1X and Vaco–1X wells confirmed the presence of Ediacaran sediments in the Llanos Orientales Basin. All these wells are located in the Arauca Graben, which is a northeast tectonic depression that extends north, reaching Venezuelan territory.
In the Arauquita–1—Torodoi–1X seismic transect it is possible to observe the presence of a general pinch–out of Tertiary and Cretaceous stratigraphic units towards the east. Under the basal Cretaceous unconformity, all of the stratigraphic units have suffered a great tectonic activity that divides the Arauca Graben into narrow blocks. In those narrow blocks, it is possible to observe the presence of a not yet drilled stratigraphic sequence with a thickness of several thousand feet that could involve pre–Ediacaran sediments. The detailed palynological analysis of those sediments could aid in the interpretation of the evolution of life during early times.
The Putumayo Orogen of Amazonia: A Synthesis
By Mauricio IBANEZ–MEJIA
Paleontology of the Paleozoic Rocks of the Llanos Orientales Basin, Colombia
By Hernando DUEÑAS–JIMÉNEZ, Victoria Elena CORREDOR–BOHÓRQUEZ and Jorge MONTALVO–JÓNSSON
The Anacona Terrane: A Small Early Paleozoic Peri–Gondwanan Terrane in the Cauca–Romeral Fault System
By Jorge Julián RESTREPO, Uwe MARTENS and Wilmer E. GIRALDO–RAMÍREZ
Manuscript accepted October 29, 2018
The Anacona Terrane is a small terrane south of Medellín that underwent a geologic history dissimilar to that of the adjacent Tahamí Terrane to the east and the Quebradagrande (Ebéjico) Terrane to the west. The metamorphic basement of the Anacona Terrane is relatively old, comprising amphibolites and metasedimentary rocks, with probable late Neoproterozoic depositional ages, and granitic orthogneisses, with Ordovician magmatic ages. The age of the last metamorphic event to affect the Anacona Terrane is constrained to the Devonian or earliest Carboniferous, while Triassic metamorphism, which is widespread in the Tahamí Terrane, has not been documented in the Anacona Terrane, indicating that the terranes were amalgamated during or after the Triassic. Correlatives of the terrane are the Acatlán Complex in southern México and the Marañón Complex and coastal islands in Perú; we surmise that the Anacona Terrane may have originated in a southerly position and migrated northwards, similar to the motion of the Caribbean Plate relative to the South American margin.
Paleozoic of Colombian Andes: New Paleontological Data and Regional Stratigraphic Review
By Mario MORENO–SÁNCHEZ, Arley GÓMEZ–CRUZ and José BUITRAGO–HINCAPIÉ
Fragments of a Permian Arc on the Western Margin of the Neoproterozoic Basement of Colombia
By Gabriel RODRÍGUEZ–GARCÍA, Ana María CORREA–MARTÍNEZ, Juan Pablo ZAPATA–VILLADA and Gloria OBANDO–ERAZO
Manuscript accepted October 29, 2018
New petrographic, whole–rock geochemical and U–Pb–zircon geochronologic data combined with data from previous studies enabled identification of a fragmented Permian magmatic arc with ages ranging from 294 to 260 Ma in the Colombian Andes. The arc is exposed along the southeastern slope of the Central Cordillera towards the Upper Magdalena Valley (UMV), San Lucas range (SLR) and Sierra Nevada de Santa Marta (SNSM). The arc fragments consist of plutons on the western margin of the Neoproterozoic basement and show wide lithological variation in both igneous (monzodiorites, quartz monzonites, tonalites, granodiorites, monzogranites, and syenogranites) and metamorphic (migmatites, gneisses and mylonitic gneisses) rocks. The granites have a metaluminous to peraluminous character and correspond to calc–alkaline to high–potassium calc–alkaline series formed in a continental arc environment. Some bodies are associated with metamorphic rocks (the La Plata Granite and Icarco Complex), which may correspond to the roots of the arc, and others show superimposed dynamic metamorphism (the Nechí Gneiss and El Encanto Orthogneiss). The Permian plutons, unidentified in previous studies because of their lithological similarities to the large volume of magmatism that occurred during the Early to Middle Jurassic, are dispersed along with the Neoproterozoic basement. The Permian magmatism that intruded the basement of the northern Andes possibly originated in a subduction zone located on the western margin of Gondwana.