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Contribution to the Geology of the Central and Western Cordillera of Colombia in the Sector Between Ibagué and Cali

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Contribution to the Geology of the Central and Western Cordillera of Colombia in the Sector Between Ibagué and Cali Contribution to the Geology of the Central and Western Cordillera of Colombia in the sector between Ibagué and Cali BY H.W. Nelson Contents Page INTRODUCTION 5 1. Outline of the Physiography of Colombia 5 7 2. Ceological setting of the investigated areas 3. Previous studies 9 PART A: STRATIGRAPHY OP THE CENTRAL CORDILLERA I. THE CRYSTALLINE BASEMENT ROCKS 14 1, The Cajamarca Group 14 15 a. (ireensehists (prasinites) of 16 b. Amphibolites near the batholith Ibague schists 17 e. Graphite d. Quartzphyllites 17 19 e. Gneissic quartzschists f. Metamorphic Diabases 19 g. Interbedded crystalline limestones 20 h. The quartzites and amphibolites of the Bugalagrande section 22 i. The facies of the Cajamarca Group 22 2. The batholith of Ibague 25 II. THE MESOZOIC AND LOWER TERTIARY OP THE EASTERN BORDER 28 1. Rhyodacite extrusions 28 2. The Payande formations '29 30 a. The pre-Payande formation b. The Payande formation 30 33 c. The post-Payande formation 3. Jurassic intrusions 34 4. Cretaceous 35 5. Lower 40 Tertiary . III. CRETACEOUS AND TERTIARY OF THE WESTERN BORDER 41 1. Diabase Group 41 2. Nogales formation (Paleocer.c) 43 2 Pago 3. Tonalite intrusions 44 4. Upper Cauca formation 45 5. La Paila formation 45 6. Zarzal formation 47 7. Rhyolitic and dacitic stocks 47 FORMATIONS 48 IV. NEOTERTIARY AND QUATERNARY ... 1. Neovolcanic deposits 48 2. The fans of Ibague and Armenia 49 PART B: STRATIGRAPHY OF THE WESTERN CORDILLERA V. THE MESOZOIC BASEMENT 50 1. Dagua Group 50 a. The Lower Part 50 b. The Middle Part 52 53 c. The Upper Part 54 2. The Diabase Group a. Sedimentary fossiliferous intercalations 54 b. Petrographical characteristics 56 58 c. Alteration to red clayey soils VI. TONALITB INTRUSIONS 59 VII. CENOZOIC FORMATIONS 60 60 1. Lower Tertiary (Cauca formation) 62 2. Naya formation 3. Popayan formation 63 PART C: STRUCTURE AND GEOLOGIC HISTORY VI IT. STRUCTURAL GEOLOGY 64 1. Central Cordillera 64 2. Western Cordillera 66 IX. GEOLOGIC HISTORY 68 Samenvatting 72 Summary 73 References 74 Geological maps and sections (in cover). PREFACE The is the result series field and studies present paper of a of laboratoiy carried in the of the 1952—1956 in Colombia out course years (South America), during which time the author was employed as a petrologist with the Instituto Geologico Nacional de Colombia at Bogota. Concluding this publication I want to express my sincere gratitude to the Instituto Nacional who in my former colleagues of Geologico cooperated in the solution of the In the first many respects geological problems. place want to the intimate collaboration of friend and I acknowledge my colleague Mr Jan Keizer. The maps bordering either side of the Cauca valley are the result of a joint field and laboratory research. Without his experienced photo- geological interpretation the surveyed area would be of a much smaller extent. I much indebted to friend Dr T. Further, am very my V. i>. Hammen, palyno- logist of the Instituto Geologico Nacional, for the determinations carried out by him and for the interesting discussions I had with him regarding the correlation of Cretaceous and Tertiary formations. Dr H. Burgl determined the collected fossils. Dr H. C. Raasveldt furnished a general photo-geological served map of Tolima which as a basis for the mapped area of Payande. The great knowledge of the Colombian territory of Dr E. Hubach, Director of the Instituto (Jeologico Nacional, oriented in problems arising in adjacent areas. Mr Humberto Villbgas was an efficient assistant in the field as well as in the laboratory. The compilation of the various individual studies was done after my return to Holland in Institute of I want to the Geological Leyden. express my sincere gratitude to Prof. Dr L. U. ke Sitter and Prof. Dr W. P. de and valuable Roever for the interest they have shown in my work for their advice. fellow-student Dr H. J. Zwart in My former was a great help pre- paring the manuscript and he discussed several problems with me. made in and for The drawings were partly Bogota partly prepared Hooukndoorn took publication by Miss Cor Robot in Leyden. Mr J. care of the photographs. in The and the The maps were prepared by Mouton* Hague, text was printed by E. IJix), Leyden. INTRODUCTION The different character of the three main Cordilleras of Colombia has drawn the attention for a long time. Within the framework of the systematical regional survey of the Geological Institute of Bogota, three areas distributed over the Western and Central Cordilleras and with a total area 2 of 9000 km have been mapped, in close collaboration with the Department of Photogeology of the same Institute. Special attention was paid to the metamorphic basement rocks, in order to obtain additional information about their composition and origin. The areal survey was extended with comple- broader mentary cross-sections through all three Cordilleras, leading to a con- cept of their structural relation and constitution. Geological investigation of the Andean mountain ranges by means of terrestrial made dif- survey as well as by means of aerial photographs is ficult by various circumstances. In the first place younger volcanism has that lie covered vast areas with its products. Especially the volcanoes on of top of the Central Cordillera have produced large amounts pyroclastic materials which filled the on both sides of the Cordillera. up steep valleys The tuffs have only partly been removed by the rivers and the remnants form conspicuous high terraces in the valleys. In the second place climato- caused rather intensive alteration. These effects logic agents a are very resulted in pronounced in the Western Cordillera and a profound lateritization of the Mesozoic volcanic rocks Apart from these natural factors terrestrial and observation is restricted to a certain degree by the activity of political isolated of the Cordilleras and criminal groups that have taken refuge in parts make penetration into this area rather hazardous. Although several important studies have been published by various authors, the systematical regional survey is still in an initial stage. Under these small scale. of circumstances it was necessary to map on a We are aware and in various the fact, that corrections completions are needed parts. They can be made by means of a series of check-ups in the field. 1. Outline of the Physiography of Colombia the discussion of first Before we start the investigated areas, we give Colombia short for those readers not familiar with the physiography of a exposure of the topographic conditions. Physically the Colombian territory is built up of two different parts: mountainous the and vast a region occupying western part a plain extending towards the East. The mountains belong to the Andean system and enter Ecuador mountain interandean from as two parallel ranges separated by an The western follows at short distance the Pacific coast. high plateau. range a Pasto and the into two Between Popayan eastern range splits up ramifications, which continue their course in a northern and a north-eastern direction. In indicated Western the Central this way three ranges originate, as the Cordillera, 6 studied. areas the of location the showing map Index 1. Fig. 7 Cordillera and the Eastern Cordillera*). The highest elevations are formed into snow-clad by volcanoes, now extinguished and changed peaks (nevados). In the Central Cordillera the most famous are the Nevados del Quindio (5.150 m), Tolima (5.620 m), Santa Isabel (5.100 m), Ruiz (5.400 m) and Huila (5.750 m). In the Eastern Cordillera the highest elevation is the Sierra Nevado del Cocuy (5.493 m). Still active volcanoes are in the departments of Cauca and Narino. these three lower mountain chain borders Apart from Cordilleras a the Pacific coast in the department of Choco. This Coastal Cordillera — according to Gankser (1950) — trends in Cabo Corrientes into the sea, but in the then off Tumaco and is reappears Gorgona Islands, probably passes observed again in the Esmeralda Province of Ecuador (see fig. 3). A conspicuous isolated mountain-stock is the Sierra Nevada de Santa Marta, whose peaks reach up to 5.800 m. Based on geological reasons, it is supposed to be the continuation of the Central Cordillera. The tropical lowlands that extend east of the Eastern Cordillera occupy more than one half of the total area of Colombia. Yet this vast area (about 600.000 km2) contains less then one-tenth of the Colombian population. The be divided into different line that follows lowlands can two parts by a more is treeless or less the Rio Guaviare. The northern part a nearly plain (llanos), whereas the southern part is covered by jungle (selva). the is oriented Although Colombia borders on two Oceans, drainage Sea the Atlantic Ocean. The mainly towards the Caribbean or continental water divide is formed by the Western Cordillera and passes in Choco by the so-called Isthmus of San Pablo to the Coastal Cordillera. The inter- drained the Rio Cauca and Rio andean depressions are by Magdalena, Rio the Atrato. The llanos belong to the Orinoco basin and the jungle area to Amazonas basin. The climate is dominated by the altitude more than by annual seasons. the torrid In rough outlines three elimatologic zones are distinguished: zone (tierra caliente), to which belong the lowlands and the large interandean the river-valleys; the temperate zone (tierra templada), to which belong about 2000 cold lower parts of the Cordilleras up to a height of m; the which the of the Cordilleras. The zone (tierra Ma) to belong higher parts the cold capital Bogota lies on a high plateau or sabana (2600 m) in zone, with of 13° C and an of a average yeartemperature atmospheric pressure the 560 mm.
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