Colombian Andes-Campbell

COLOMBIAN ANDES

COLIN JOHN CAMPBELL Hawksgrove. Hawkswood Lane. Gerrards Cross, Buckinghamshire

CONTENTS

A. General data on the segment 705

B. Subdivision of the segment 714

C. Data on individual structural zones 715 1. Western Cordillera 715 2. Cauca Basin 716 3. Central Cordillera 717 4. Middle Magdalena subzone 718 5. Upper Magdalena subzone 719 6. Eastern Cordillera subzone 720 7. Garz6n-Quetame Massifsubzone 722 8. Santander Massif subzone 722

D. References 723

A. GENERAL DATA ON THE SEGMENT

1. THE SEGMENT STUDIED

This article describes the northernmost segment of the Andes marginal to the Pacific, a belt which here gives evidence of orogenic activity throughout most of Phanerozoic time. To the north the three cordillera of Colombia bifurcate, linking both with Central America via the Panama isthmus and with the Venezuelan Andes. Traced southwards into Ecuador the ranges narrow and partly merge.

Segment: the segment described here has a north-south length of 1000 kin. The margins of the orogenic belt against non-orogenic areas are both narrowly gradational ( to 3 km). The eastern margin is defined by thrusts in most places, but northward splays make it a broader zone in regional terms. Little detailed information is available on the north- west margin, which is taken at the thrust belt, although mild to moderate deformation extends beyond. The width of the orogenic belt thus defined increases from 150 km in the south to 500 km in the north and averages 400 km.

Zones: the Colombian Andes are described here in terms of eight zones and subzones. The Western Andes (zone 1) are built of metamorphic rocks (?Jurassic) overlain by thick, eugeosynclinal Cretaceous sediments and volcanics. In the Cauca Basin (zone 2) similar rocks are covered by thick, Tertiary continental strata. The Central Andes (zone 3) includes Pre-Cambrian igneous rocks, metamorphosed L. Palaeozoic to Mesozoic rocks, Jurassic-Cretaceous strata and Neogene andesitic volcanics. The M. and U. Magdalena Basins (subzones 4 and 5) contain very thick Jurassic and Triassic to Pliocene sequences; major batholiths were intruded in subzone 5 in early Triassic times. The Eastern Andes include the Eastern Cordillera (subzone 6), the Garz6n-Ouetame Massif (subzone 7) and the Santander Massif (subzone 8). The Eastern Cordillera is built of U. Palaeozoic strata, thick miogeosynclinal late Jurassic to Cretaceous strata and continental Tertiary. Subzones 7 and 8 are built dominantly of ?Pre-Cambrian plutonic basement rocks and L. Palaeozoic metamorphic rocks cut by major intrusions; late Palaeozoic and Mesozoic strata occur locally. History: Two or more post Pre-Cambrian orogenies are recognized. Intermittent movements occurred throughout the Phanerozoic and reached climaxes in mid-Palaeozoic, early Triassic, pre-Tithonian, pre-Campanian, pre-U. Eocene, pre-U. Miocene and pre-Pliocene times. The general evolution of the belt involved the progressive westerly migration of sedimentary provinces and tectonic events.

2. SHAPE OF THE OROGEN IN PLAN

in The belt continues along strike beyond the selected segment. The Central and Western Andes continue without significant change into Ecuador but the Eastern Andes die out at Moc6a. Northwards the

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706 COLOMBIAN ANDES

ranges bifurcate and change in direction. 24 General trend: although in gross terms partly arcuate, in fact the Andes consist of relatively straight and structurally uniform segments of up to 1000 km in length separated from one another by complex oroclines. Such oroclines (e.g. at Maracaibo and at Huancabamba--northern Peril) appear related to palaeogeographical gaps in earlier orogenic belts and are in places associated with (?) major wrench faults. Major wrench faults are believed (?) to exert a control on some of the major structural units (e.g. subzone 8).

I t I I I 79" 77 75 73" ~ ~ 71"

200km I, I

SANTA

Loma de

-va

c)

o

....j

g

Figure 1. Geological Provinces of Colombia showing the Segment of the Andes under consideration and the structural zones. Structural depressions are stippled.

3. SURFACE SHAPE OF THE SEGMENT IN ELEVATION

30 Highest 5% of the ground: 2500 m Average height of: 31 north-west margin of the belt, 100 m; 32 south-east margin, 500 m. 33 Geomorpho- logical surfaces are recognized by summit heights on relict peneplains, but a4 information on lower surfaces--other than in the references listed---is not available. Summit peneplains: little detailed work, see Biirgl (1961, p. 187) and Duran (1964). Reconnaissance surveys indicate an erosion surface based on summit heights at 3000 m near Bogoul and a tilted surface, dipping east at about 8 on the eastern margin of the Central Cordillera, which may be of early Tertiary age since an apparent continuation marks the base of the Tertiary in the adjacent zone 5.

4. GEOPHYSICAL DATA

a8-9 Gravity data: Bouguer anomaly map with 20 milligal interval Mapa gravimetrico (1959). See also Case et al. (1969). 41 The segment is in approximate isostatic equilibrium and 42-3 the general gravity field is parallel to the main tectonic and topographic trends.

45 Regional magnetic data are available and the anomalies are (?) con- cordant with the main tectonic and topographic trends.

5. PRESENT-DAY ACT IV ITY

68 The region is currently seismically active (see Ramlrez 1969). Map of epicentres: Ramlrez & DurUm (1957).

6. T IME RELATIONS

Pre-Cambrian gneisses are overlain by L. and U. Palaeozoic strata; a late Silurian--early Devonian orogeny can be recognized. Early Triassic movements, which are classified as a separate orogeny ('Hercynian'), are here listed with the long sequence of late Mesozoic- Tertiary movements. See Table 1.

85 The oldest undeformed rocks belong to the Pliocene Mesa Fro. (Morales et al. 1958; Houten & Travis 1968; Wellman 1970). s3 The youngest deformed rocks are the U. Miocene Real and Honda Fins (references as 85).

87-9 The initiation of mobility associated with the Mesozoic-Tertiary orogeny: probably at no time during the Phanerozoic has the segment been orogenically dormant. It is difficult to distinguish the last phases of the preceding orogeny, which reached a climax in the L.-M. Triassic, from the first phase (considered to be number 3 in the above list) of the orogeny under consideration here.

81 The oldest rocks deformed for the first time during the Mesozoic- Tertiary orogeny are: E. Andes-Payand6 Fm (Carn-Nor) (Trumpy 1943).


COLOMBIAN ANDES 707

Table 1

MESOZOIC-CENOZOIC PHASES OF MOBIL ITY

~1 Phase IV. Andes

9~ Nature of mobility

(2. Andes E. Andes

~ge

98 Maximum 94 Minimum g5 Evidence for ages

15 Uplift

14 Post- Andean movements

13 Andean

12 Proto- Andean

11 Pre- Tortonian

I0 Pre-U. Aquitanian

9 Ere- Miocene 8

Laramide

7 Proto- Laramide

Uplift of Andes

?Movement on Santa Marta fault

Tilting, broad Vulcanism folding, minor faulting

?Pleist

Moderate Onset of folding, fault- vulcanism hag & ?igneous activity

Post- late Mioc

Mild deformation involving faulting (L. Magdalena & Sinu-Athintico)

Local vulcanism

Tight folding Post- Pre-Plioc & thrusting U. Mioc

Uplift & erosion

Mild folding associated with faulting

Strong, local deformation; ?initiation or accentuation of major wrench faults

Tilting, broad folding, minor faulting & regional subsidence (especially in the L. Magdalena area)

Not recognized, ?represented by conglomerates in La Cira Fm

Post- ?Pre- Torton U. Mioc

Post- Pre- Burdigal Torton (locally post- Helvet)

Post-L. Pre-U. Aquit Aquit

Post-Olig Pre-Mioc

Igneous activity Mild deforma- Post-M. Pre-U. & ?metamor- tion associated Eoc (locally Eoc phism (also in with faulting within eastern M. Eoc) W. Andes)

(Sinu area) ?Metamor- Uplift of source folding & phism, not dis- areas faulting finguishable

from phase 8

Post- Pre-Eoc & Maestr ?Pre-U.

Palaeoc

The wrench fault (if correctly interpreted) shifts the Andean thrust belt & so is late Mioc (i.e. very latest Mioc or Plioc)

Unconformity beneath unfossiliferous, flat-lying beds (?Plioc) ; note that this phase, in particular, masks the effects of earlier phases

Unconformity beneath beds considered U. Mioc, although evidence not con- elusive; U. Mioc sediments usually rich in volcanic detritus from ?zone 3

Minor unconformity beneath fossiliferous Torton, which in many areas rests directly on Burdig (absence of Bulimena carmenensis biozone)

Unconformity below fossiliferous U. Aquit (C. stainforthi zone in L. Magdalena) in Western Andes

Absence of Olig in many areas, yet presence of reworked Olig foraminifera in lowest Mioc (Bfirgl 1965)

W. Andes (Sinu-Atl~mtico) : unconformity below U. Eoc fossiliferous strata; Eastern W. Andes & C. Andes: intrusions dated as 51, 49 & 47 m.y. (U.S.G.S.); also probable age of metamorphism of Cretaceous rocks in zone 3, Santa Marta Massif & Guajira; E. Andes: unconformity becoming smaller to east beneath Mirador & La Paz Fins which are palynologically dated as U. Eoc

Mild unconformity beneath, or the appearance of elastics in Palaeoc (fossils, including spores)


708 COLOMBIAN ANDES

Table 1 (continued)

91 P~Gse W. Andes

92 Nature of mobility Age

(7. Andes E. Andes 93 Maximum 94 Minimum 9s Evidence for ages

6 Subher- cynian

5 Mid- Cretaceous movements

4 Early Cretaceous movements

3 Nevadan

2 Late Triassic (post- 'Her- cynian')

1 L.-M. Triassic (Her- cynian')

Batholith Tilting, broad emplacement folding, minor

faulting

Local meta- Mild folding morphism & & faulting batholith emplacement

Tilting, broad folding, minor faulting

Intense deformation, meta- Deformation, morphism, batholith emplace- uplift, ment (radiometric date of erosion 142 m.y., U.S.G.S.)

E. Andes & eastern C. Andes: uplift & erosion probably accompanied by faulting. Intru- sive & extrusive igneous activity. Emplacement of batholiths in C. Andes

Intense folding, metamorphism, emplacement of batholiths & related volcanic activity

Block faulting, emplacement of batholiths & associated extrusive activity

E. Andes: E. Andes : post-Santon pre-

Campan C. Andes : C. Andes : Cenoman Cenoman

Post-U. E. Andes: Apt & pre-L. Alb locally C. Andes: post- pre- L. Alb U. Alb

Mainly post-L. Valang; locally post-U. Valang

E. Andes : post-Toarc C .&W. Andes: ?

Post-Nor

Post-L. Perm

Pre-Haut

Pre -

'Tith'

Pre-Sinem

Pre-Carn

E. Andes: minor unconformity beneath Campan fossiliferous strata generally leading to the absence of Santon, in such cases the youngest fossiliferous beds beneath are Coniac; C. Andes: radiometric date 79 m.y. (Botero Arango 1963)

E. Andes: unconformity between fossiliferotrs strata as indicated; C. Andes: U. Alb fossiliferous strata rest unconformably on low-grade metamorphic rocks containing Apt fossils (Bfirgl & Radelli 1962). Radiometric date of 110 m.y. on batholith (Pinson et al. 1962)

Unconformity between fossiliferous strata as indicated

E. Andes: fossiliferous 'Tith' strata rest unconformably on the Gir6n Gp in which the youngest marine intercalations contain Toarc fossils; W. Andes: Cretaceous rocks, believed to range down to Toarc (as in Guajira) rest on undated metamorphic rocks

Local fossiliferous layers in Gir6n Gp contain Sinem fossils; Gir6n Gp rests unconformably on rocks, youngest of which contain Nor fossils (Trumpy 1943); Radiometric dates of 195 (MacDonald 1964), 174, 172, 167 & 162 m.y. (U.S.G.S. show igneous activity persisted through much of the Jurassic in the C. Andes

Palaeontological dates as indicated. Radiometric date of 210 m.y. (Mencher 1963)


COLOMBIAN ANDES 709

7s-SBasement rocks: Within the orogenic segment basement rocks range from Pre-Cambrian to L. Palaeozoic in age. In the Eastern Andes ?Pre-Cambrian gneiss at Floresta underlies ?L. Palaeozoic phyllite, which is in turn below M. Devonian fossiliferous strata. In the Central Andes rocks occur of a lithology similar to those in the Sta. Marta Massif for which there are dates of 940 + 47, 1300 and 750 m.y. Basement rocks within 100 km of the south-east margin of the belt are Pre-Cambrian (1205 60 m.y., Pinson et al. 1962). No basement rocks are known within 100 km of the north-west margin of the orogenic belt.

* 77 B 73" 71 200km

I " t2 l '

I ."."~:.::.,::.. :~, .~:.: ' , ........ i:::.!~,: . . : . / :. :: : . . . , i . I ::,.:. :.-::.::: :i.i:i~: . "

. .: ::...::

/ . ~

...... : : : ::.::: : :/::::':::i!. ;::::!: ' ~

.,.....i i' :z 7} : :.,

Figure 2. Principal Fault Systems in the Segment (1 to 6). Continuous lines--thrusts; dashed lines--possible transcurrent faults.

7. SEDIMENTARY RELAT IONS

The data here apply to the Eastern Andes; different conditions occur in the Western Andes. In Table 2, pre-orogenic refers to the period between the 'Hercynian' and Nevadan movements.

Table 2

SUMMARY OF STRATAL DATA

Syn- and Post-orogenic sedimentation within 50 km outside the margins of the orogenic part

In the orogenic belt in the segment of the segment

Outside west Outside east Pre-orogenic Syn-orogenic Post-orogenic margin margin

97 Age span Jrom to

Cam 'Tith' Plioc 'Tith' 'Tith' Kimm U. Mioc Present Present Present

9s Maximum thickness

4000m 21,000m 300m 10,000m

99 Estimated volume per 100 km length of segment And probable error in this estimate

26,000 km 3 200,000 km 3 4000 km 8

20% 25% 20% 20%

l oo Dominant facies Continental Continental Fluviatile with Tertiary, evaporites miogeo-

synclinal Cretaceous

Percentage of the total volume occupied by-- and the error

ioa Dominant facies 95 + 5% 95 + 5% 75 + 20%

102 Volcanic rocks 2_+2% 0+0% 30+ 10%

103 Sedimentary 0+2% 15+ 10% 0+0% rocks with over 90% carbonate

x04 Sedimentary 50+ 10% 25_+ 5% 10_+ 5% rocks with over 95% quartz

lo5 Source area of sediments

1000 km 3

Continental with marine intercalations in west

100_+0%

Guayana Shield in late Tertiary for E. Andes


710 COLOMBIAN ANDES

,0~ Structural repetitions but not deformation have been taken into account in assessing the above stratal thicknesses, x0v Sedimentation was generally continuous in the pre- and syn-orogenic periods, but z0s major pre-Tithonian, pre-Hauterivian, pre-Albian, pre-U. Eocene and pre-U. Miocene erosion surfaces are present, z0~ Palaeogeographical maps for Triassic to Upper Aquitanian times are given in Campbell (1968).

8. STRUCTURAL RELATIONS

m-z~ Major faults. Fault 1, Eastern Andes marginal thrusts (east): these SE-directed overthrusts have several kilometres of displacements and probably moved in late Miocene times. Fault 2, Eastern Andes marginal thrusts (west): as for faults 1, but movements directed north-west. 3 Santa Marta fault: a sinistral wrench fault which has a displacement of 110 km, as shown by the offset of structural zones (see ~) ; movements probably commenced in latest Miocene to Pliocene times and are probably still active; mylonite occurs along the fault. 4 Dolores fault: movements are probably of ?dextral wrench type and commenced in the ?U. Cretaceous to U. Eocene interval, probably mainly in U. Eocene times; movements are probably still active; mylonite occurs along the fault. 5 'Medellln' fault: this fault separates zones 2 and 3 near Medellln and is a ?sinistral wrench fault, along which movements probably commenced in late Miocene times. 6 Western Andes marginal thrusts: these NW-directed overthrusts have several kilometres of displacement and probably moved in late Tertiary times. ng-~Megatectonics: there is no evidence of relative displacement of opposite sides of the whole belt. Evidence of relative lateral displacement of opposite sides of the Eastern Andes is provided by the Santa Marta

wrench fault and the fact that thrusts on the e ~st splay southwards, whereas those on the west splay northwards.

9. REVIEW OF OROGENIC DEVELOPMENT

132 GEOPHYSICAL EVIDENCE OF OROGENIC STRUCTURE

Case et al. (1969) have recently furnished important gravity and magnetic data on a portion of the Western Andes, that in general lends support to the geotectonic conclusions given here. Typical Bouguer anomalies of the various provinces are as follows:

Pacific Coast Range Pacific Coast Basin Western Cordillera (zone 1)

Cauca Basin (zone 2) Central Cordillera (zone 3) Middle Magdalena Basin (zone 4)

+75 to +135 mgal up to - 74 mgal - ve north of Lat. 5 +ve south of Lat. 5 - 25 to - 75 regal -60 to - 100 mgal -75 to -150 mgal

Taking into account the elevations of the mountain ranges and the thick sections of low density rock in the sedimentary basins, the authors conclude that little or no granitic crust is present to the west of the Central Cordillera. Steep gradients along the western margin of that range probably mark the junction between Pre-Cambrian granitic crust to the east and Mesozoic and younger oceanic crust to the west. This junction also corresponds with the Dolores fault system (see a~a). A crustal model proposed by Case et al. is reproduced below. Con- sidering the uncertainties, discussed by Case et al. concerning the true thickness and density of the units, the model corresponds reasonably closely with that prepared independently in section z~n below (Fig. 3).

200-

I00-

0-

-I00-

.200- regal

X ~.x '~" Bouguer anomaly x

Computed anomaly

"x

PACIFIC COAST @,,,o r,. 7,~0, RANGE ~...o WESTERN CORDILLERA @o CENTKAL CORD/LLERA 1'4AGDALENA VALLEY

o T F . . . , . : . . -~ . - . . . . ; . . . . . . ; . - : . . ,~ : : : : : : :~ ,~. . .~; : ,~ . . .~ . : : . - - . ~;~.,, NE~mTr~lrll~ ~L 4~QUARTZIl~_%--;'c.'~I;/>~a;# ~' - - ~ : : : : : : : : :MESOZOIC AND TERTIAR.YI~.=2..5 .. i i i: i:

Tt!:: i

O I0 20km

0 100km I I

Figure 3. Crustal Model, Cabo Corrientes--Magdalena Valley (after Case et al., 1969). The assumptions used are: (i) Oceanic crust in the west is 16 km thick with a mean density of 2"9 g per cm 3. (ii) Tertiary sedimentary rocks in the Pacific Coast Basin are 10 km thick with a mean density of 2"4 g per cm 8. (iii) Mesozoic eugeosynclinal rocks have a mean density of 2.85 g per cm 8. (iv) Mesozoic and Tertiary sedimentary rocks in the Middle Magdalena Basin are 8 km thick and have a mean density of 2.5 gcm 8.


COLOMBIAN ANDES 711

133 EFFECTS OF TRANSCURRENT OR STRIKE-SLIP FAULTING

Structural interpretations involving transcurrent faulting are generally controversial, for the evidence is usually capable of more than one interpretation. This is certainly the case in Colombia: some geologists, including the writer, believe that transcurrent faulting has been of fundamental importance whereas others are equally firm in holding views to the contrary. The two major fault systems with possible transcurrent movement are described below (see also 111-18):

(1) Santa Marta Fault: This has been recognized by de Cizancourt (1933), Raasveldt (1956) and Campbell (1968). It runs S. 15 E. from the Caribbean coast near Santa Marta for a distance of 550 km to the Eastern Cordillera where it dies out in a series of thrusts. A maximum sinistral movement of about 110 km is suggested by the displacement of the following elements, believed to have been contiguous prior to the faulting: (i) Central Cordillera-Santa Marta Massif, (ii) Middle Magdalena Basin-Cdsar Basin, (iii) belt of Jurassic dykes and extrusions found along the east flank of the Central Cordillera and on the south- east flank of the Santa Marta Massif, (iv) thrust belt on west margins of Eastern Cordillera and Perij~ Range. It is also suggested by stratigraphical differences across the fault between the Cdsar Basin and the now adjacent Lower Magdalena Basin: in the former the succession consists of Palaeozoic, Jurassic, Cretaceous, Palaeocene, Eocene and Miocene sediments, whereas in the latter Miocene rocks rest unconformably on granite. Vertical separation near the Caribbean coast amounts to as much as 10,000 m, measured from the base of the Tertiary in the Lower Magdalena Basin to its inferred position above the Santa Marta Massif, which rises to 5400 m above sea level. The absence of coarse elastic sediments in the adjacent basin is also significant, implying that the massif was not in its present position during the Tertiary.

The last movement on the Santa Marta fault appears to post-date the development of the thrust belt bordering the Eastern Cordillera, which affects U. Miocene beds (Real Fro). It is therefore believed to be of latest Miocene or Pliocene age and the last major event in the Mesozoic- Tertiary orogeny. Definite evidence of earlier movements has not been found.

The alignment of the Santander Massif at an oblique angle to the

Eastern Cordillera and Mdrida Andes is believed to be related to the Santa Marta fault. The Santander Massif would then be a lineagenic element in the sense of Hills (1963, p. 315).

(2) Oca-Dolores-Guayaquil Fault System: The Oca fault (Rod 1956; Feo-Codecido 1970) runs from the mouth of Lake Maracaibo westwards along the northern boundary of the Santa Marta Massif. Parallel faults in the Guajira (Cuiza fault, MacDonald op. cit.) exhibit a dextral displacement of as much as 15 kin. Estimates of the amount of lateral displacement of the Oca fault vary; 45 km is accepted by some geologists, whilst others doubt if any transcurrent movement has occurred. The fault has probably had a long history of movement, having been especially active during the Laramide phase. The evidence for early lateral displacement is partly masked by effects of the Andean phase, when transcurrent movement may not have been dominant.

Campbell (1968) suggested that an extension of the Oca fault, displaced by the Santa Marta fault and buried below the Miocene sediments of the Lower Magdalena Basin, follows the lower reaches of the Rio Cauca. Confirmation is required, although faulting parallel with that postulated is known at outcrop in the Central Cordillera. This presumed fault is in turn displaced by the sinistral faults-- mentioned earl ier--at the northern end of the Cauca Basin. It continues southwards as the Dolores fault, forming the western boundary of the Central Cordillera, and extends into Ecuador where it connects with the Guayaquil fault, considered a dextral transcurrent fault by Marchant (1961). Positive evidence of lateral movements has, however, not been found in Colombia and the interpretation is largely conjectural.

134 THE OVERALL EVOLUTION OF THE BELT

Although confirmation must await the results of further study of the age of certain critical developments of metamorphic rocks, present evidence suggests that the evolution of the Colombian Andes was largely accomplished by the progressive westerly migration of sedimentary provinces and tectonic events through Phanerozoic time. The following brief outline of the evolution of the chain summarizes the evidence for this hypothesis.

Geosynclinal subsidence occurred in the East Andean region during

PACIFIC MIDDLE COAST PACIFIC COAST BASIN WESTERN CORDILLERA CAUCA CENTRAL CORDILLERA MAGDALENA EASTERN CORDILLERA LLANOS BASIN RANG ~ / BASIN BASIN ...I ....... I . . . . . I ........... ! .................................................................................................................. . .... [ 0

~i! i l i ! i i !~! i i !~e~ ~ ~ ~ / ~:~:~:~:~:>~:~:~

712 COLOMBIAN ANDES

the early Palaeozoic and was brought to a close by the late Silurian to early Devonian ('Caledonian') orogenic movements. The geosynclinal rocks were isoclinally folded and faulted by compressive E-W forces, mildly metamorphosed, uplifted and eroded.

During the late Palaeozoic a new geosyncline is thought to have developed in the Central Andes, represented by pre-Triassic schists and phyllites. Shelf and continental conditions prevailed in the Eastern Andes, where geosynclinal conditions existed previously. This cycle was brought to a close by early Triassic so-called ('Hercynian') movements that were responsible for the metamorphism of the geosynclinal prism and for the emplacement of batholiths in both the Central and Eastern Andes. Widespread volcanic activity, especially along the eastern margin of the Central Andes, characterized the later phases of the orogeny possibly as a result of tensional faulting.

During the early (pre-Tithonian) Mesozoic, geosynclinal conditions prevailed in the western Central Andes, the Cauca Basin and the Western Andes and are represented by the Dagua Group (pre- Cretaceous). Mainly continental conditions prevailed in the Eastern Andes although temporary marine incursions entered from the west and may have been responsible for the deposition of evaporites. The cycle was brought to a close by Nevadan orogenic movements that metamorphosed the geosyncline. They were less intense in the Eastern Andes where they were nevertheless responsible for a major unconformity below the Tithonian.

During the late (post-Tithonian) Mesozoic, miogeosynclinal conditions set in to the east of the Central Andes, while eugeosynclinal conditions, characterized by the extrusion of submarine lavas, persisted to the west, from the western Central Andes through the Western Andes to the Pacific. The Central Andes formed a partly submerged welt between the two geosynclines and was characterized by the

emplacement of late Cretaceous batholiths, locally accompanied by metamorphism. Although the sea withdrew from the miogeosynclinal province in the Maestrichtian and paralic conditions set in during the Palaeocene and early Eocene, and although diastrophism occurred during the Palaeocene in the eugeosynclinal province to the west, essentially the late Mesozoic tectonic cycle persisted until the outbreak of Laramide orogenic disturbances in the late M. Eocene. These movements were most intense in the West Andean region where they were accompanied by igneous activity and possibly even metamorphism along the western flank of the Central Andes. Deformation was apparently caused partly by major wrench faulting (see 133).

After the Laramide phase continental conditions continued in the East Andean region, which now received the greater part of its sediment by erosion of the Central Andes which had been uplifted during the preceding movements. Marine conditions persisted in the West Andean province. The latter was affected by several phases of intra-Tertiary diastrophism that was responsible for thrusting in the Montafias de Maria. The majority of these movements were also felt less intensely in the western part of the East Andean region, especially in the Magdalena basins, where they caused faulting and important changes in the sedimentary history. The last phase of this cycle of tectonism was the pre-U. Miocene 'proto-Andean' movement during which volcanic activity broke out in the Central Andes.

The main Andean orogenic phase of late Miocene to Pliocene age is responsible for the greater part of the present structure. In contrast to earlier orogenic movements, the Andean phase was more intense in the east than the west. The Eastern Andes were moderately folded and cut by marginal thrusts. The chain is bilaterally symmetrical suggesting that deformation was due mainly to vertical movements of the crust, possibly caused by isostatic adjustment after the long period of sub-

0

10-

20-

30-

40-

50km-

J w PACIFIC COAST CAUCA RANGE PACIFIC COAST BASIN WESTERN CORDILLERA BASIN CENTRAL _

_~ "I':,,. T 7W~ - - ' T ' , . . . . . . '--, .., - , , , - .K-~,.. ~,_ - ; . ~-_, . . . . ~ . . - , . . . . . . ~_ ,'- ",:, ,'.--,'-, . . . . ...:~:::..~.. ~..~.~.~.~.~:.~.~.~F`~:.:~::~::~:~`:::~?~:~::~::~:~:

K '~* ~- " -'- ]-

T Tertiary D-P Devonian to Permian

K Cretaceous & Tithonian -S Cambrian to Silurian

J Jurassic & Triassic P- C Pre- Cambrian

~ Non - marine Sediments (T and J)

[ IMarine (T) Jmiogeosynclinal (K) shallow marine & non marine (D.- P) .and shelf deposits (E- S)

Figure 5. Profile across


COLOMBIAN ANDES 713

sidence to which the belt had been subjected. Indirect evidence from mineralization suggests that igneous rocks were intruded along the margins of the chain but they are not exposed. The last major effect of the phase was the development of a major wrench fault (see ~aa).

In the Central Andes volcanic activity intensified during the Andean phase, and the Western Andes were also subjected to moderate to mild diastrophism.

The westerly migration of tectonic elements may result from the easterly underthrusting of oceanic crust below the continent. It appears that initially the leading edge of the continent is dragged down by sub- crustal currents to form a geosyncline. At a critical point when subsidence has reached a depth of about 15,000 m stress can no longer be released in this manner, and instead the geosyncline is deformed and metamorphosed, with the concurrent formation of igneous rocks by fusion of sediments and the addition of material from the mantle. In this way the geosynclines become welded to the shield. After stabiliza- tion the process begins again to the west of the previous geosyncline that now acts as the leading edge of the continent.

This hypothesis may explain the observation that intrusions become progressively younger and more basic in composition from east to west across the Andes. The Central Andes may mark the western limit of Pre-Cambrian sialic rocks, and the Western Andes may rest on a basement composed of oceanic crust, possibly in part represented by the immense quantities of spilitic lava extruded in this region during the Cretaceous.

~a5 (i) CYCLICAL SEDIMENTATION IN RELATION TO TECTONISM In the Colombian Andes Cretaceous and Tertiary sedimentation was

largly controlled by tectonic activity. The phenomenon is particularly well demonstrated in the East Andean Cretaceous miogeosyncline.

Biirgl (1960) and Stainforth (1968) have given details of the age and character of, respectively the Cretaceous and Tertiary cycles. A typical Cretaceous cycle opens with the deposition of shallow marine to epicontinental sands, which commonly rest on an eroded surface of older rocks. Deeper water limestones and shales, passing upwards into shales alone, follow and are in certain cases succeeded by a return to shallow water sandstone deposition at the close of the cycle. Such a cycle is characteristic of the eastern margin of the geosyncline, but may be also recognized in the central parts--beyond the limit of sandstone deposition--by alternating shallow and deep water faunas. These cycles range through several stages and are distinct from the short-term cyclical sedimentation characteristic of, for example, coal measure deposition.

The cycles are essentially synchronous and recognizable over great distances: the cycle which opened in the Albian may, for example, be traced from Venezuela through Colombia and Ecuador to Peril. They apparently reflect fundamental events in the structural evolution of the region that cause uplift of the source areas, concomitant subsidence of the geosyncline and in many cases mild deformation of the geosynclinal margin.

Superimposed on the regional cycles are the effects of purely local tectonic events giving rise to minor stratigraphic variation and perhaps delaying or advancing the development of the relevant phase of the regional cycle. These local events may lead to diachroneity which is, however, measured in sub-stages and not the several stages of the regional cycle and is not, therefore, considered evidence against the synchroneity of the regional cycles.

EIN 47" W S 47" E l

MIDDLE MAGDALENA

CORDILLERA BASIN EASTERN CORDILLERA LLANOS BASIN ~ / . / - - - ~ . .~T- - . - -~ . , , .~ . . _ ! . . , . . . . . ,~ ]

K . . . . . . . . . . . . .

g,.-;,:,.{ .:rj + + l ~ ' t n ' / ' d c ' ~ ~ , , " ~ . - ' v / ~ ,~g...c.,.~,,~ l ~ - 4 ~ ~ / + ,-, -o-+ + +

4- 4- 4- 4

Eugeosynclinal rocks Metamorphosed geosynclinal rocks

Igneous rocks ~ Pre- Cambrian igneous & metamorphic rocks forming continental crust ~ Igneous rocks generated by

the fusion of buried sediments and by additions from the mantle (diachronous- old in east, young in west)

0 IOOkm

the Colombian Andes.

-0

- I0

-20

-30

40

-50kin


714 COLOMBIAN ANDES

135 (ii) CORRELATION OF THE COLOMBIAN ANDES WITH THE ADJACENT OROGENIC BELTS

The Central and Western Andes merge south of Pasto and continue as a single chain through Ecuador, although the Cuenca Basin and the graben near Quito form an extension of the intermontane depression that separates the ranges in Colombia. The Eastern Andes impinge upon the Central Andes near Moco~ and do not extend as such into Ecuador, although the Napo and Cutucu uplifts are to a certain extent analogous structures.

In northern Colombia the Eastern and Western Andes bifurcate, while the Central Andes swing abruptly eastwards along the northern margin of the continent. The bifurcation of the Western Andes occurs at a point of 100 km south-east of the Gulf of Urubd. One branch, represented by a belt of igneous intrusions forming in part the Loma de Cuchillo, crosses the lower Atrato valley into Panam~ and forms a connection between the Andes and the Central American fold-belts. A parallel and possibly related element is the Pacific Coast Range that follows the coast from Cabo Corrientes into Panama. The other branch of the Western Andes swings north-eastwards to form the Montafias de Maria that pass offshore near Barranquilla.

The Eastern Andes bifurcate at a point 70 km east of Bucaramanga. One branch continues across Venezuela as the M6rida Andes to impinge on the Coast Range near Barquisimeto. The other swings northwards as the Santander Massif, in turn passing into the Perij~ Range that is ultimately truncated by the Oca Fault. The orientation of this branch is thought to be largely controlled by the Santa Marta fault (see 133).

The Central Andes extend from the Ecuadorian border to a point near E1 Banco where they partly plunge below the Miocene sediments of the Lower Magdalena Basin and are partly truncated by the Santa Marta fault. The Santa Marta Massif and the Guajira are believed to represent parts of an extension of the Central Andes that swings eastwards below the Gulf of Venezuela and the younger and differently oriented structures of Falc6n to connect with the Coast Range of Venezuela. The recognition of this orocline, which is partly offshore, is made difficult by the effects of major wrench faulting (see 133) and the superimposition of younger structures in Falc6n. A correlation between the Central Andes of Colombia and the Coast Range of Venezuela is, however, suggested by similarities in the evolution of the two chains, especially the existence of Mesozoic batholiths and late Cretaceous to Eocene phases of metamorphism.

B. SUBDIV IS ION OF THE SEGMENT

Table 3

~IZONES AND ELEMENTS IN THE SEGMENT

Elements

1 2 3 4 5 6 Middle Upper Eastern

Western Cauca Central Magdalena Magdalena Cordillera Cordillera Basin Cordillera subzone subzone subzone

a Volcanic cap (?U. Mioc) Plioc-Rec

b Sedimentary cover (Devonian- U. Mioc)

c Metamorphic rocks of uncertain ages (L. Devonian + L.-M. Trias + pre-'Tith' + ?Cretaceous)

d L. Palaeozoic strata metamorphosed at end of L. Palaeozoic

e Pre-Cambrian basement

X X X X

X X X X X X

x x x Inferred Inferred

x Inferred Inferred Inferred

[? if? ]:x Oceanic Oceanic Lcrust _! Lcrust _1

Inferred Inferred Inferred

7 8 Gar zdn- Quetame Santander subzone subzone

X X

X X

?x ?x


COLOMBIAN ANDES 715

C. DATA ON INDIV IDUAL STRUCTURAL ZONES

ZONE 1. WESTERN CORDILLERA

~o~ Zone margins are narrowly gradational ( to 3 kin). ~0s-:z Areas o f the zone occupied by the outcrop o f rock types: volcanic 40%; plutonic 5%; sedimentary 10% ; metamorphic 45%.

~z~-:: Elements: the strata of the Sedimentary cover (element b) are faulted and isoclinally folded. The schists and phyllites of the 1V[etamorphic complex (element c) are ?isoclinally folded. Deformation has probably produced E-W shortening of elements b and c, although vertical movements are mainly responsible for the structure. Element b rests unconformably on element c. Any basement rock unit (?oceanic crust) beneath element c is unexposed.

Table 4 STRATIGRAPHY IN ZONE 1

~ Element ~o Age and in which

evidence for ~ Thickness the rocks ~:~ Unit age 3~: Lithology m occur

Diabase Cret (?& 'Tith') ; Black shale, siliceous ?10,000 b Gp oldest fossils argillite, chert,

Barrem, youngest spilitic pillow lava & Senon andesitic tuff & lava

Dagua ?Jur; metamorphic Phyllite & schist, with ?10,000 c Gp rocks underlying graphitic, tuffaceous,

?'Tith' & Cret calcareous & siliceous members

~:~-:~ Outcrop areas o f the elements: b and c both outcrop over the whole zone (length 800 kin; width 50-100 kin, average (60 kin). 3~6-3~ Igneous activity: Episode 1--metamorphosed intermediate and basic tufts of?Jurassic age occur in element c (Nelson 1962). Episode 2 --Cretaceous and 'Tithonian' vulcanism is indicated by the intermediate and basic lavas and tufts of element b; submarine activity, probably in deep water, is indicated by pillow structures; the pro- portion of volcanic components decreases from about 90% in zone 2 to about 10% on the Pacific Coast, and is perhaps 75% in zone 1, thus suggesting derivation from the western margin of the Central Cordillera (zone 3). Volume (for zones 1 and 2 combined)--?250,000 km 3. Episode 3--acid and intermediate major intrusions cut elements b and c and are probably of Tertiary age; they cut Cretaceous strata and ?pre-date the U. Eocene and/or the U. Miocene phases of mobility; also, there is evidence of Laramide and proto-Andean igneous activity in adjoining basins. Volume--?20,000 km 3. ~5-4~ Metamorphism: low-grade regional metamorphism affected element c in pre-Barremian times, probably in the late Kimmeridgian (i.e. Nevadan): the metamorphism pre-dates the fossiliferous Cretaceous strata of element b. Basic rocks contain chlorite, actinolite, albite, clinozoisite, epidote, titanite, leucoxene, calcite and quartz. Pelitic rocks contain quartz, albite, biotite, calcite and graphite.

Unconfirmed reports indicate that Tertiary rocks are metamorphosed locally and these should therefore be removed from the Dagua Gp. Differentiation is not possible, however, on present information. 34~-s Deformation: (Phase 1 Nevadan)--intense folding and faulting, leading to regional metamorphism, affected element c in pre-Barremian times, probably in the late Kimmeridgian: the movements pre-date the fossiliferous Cretaceous strata of element b. Later phases--direct

L _1 NW I~ ZONE I

~" ~ l SE ~,,o

-- ~" - (.f,x

8ii _ .

0 10kin I I I ~ Tertiary strata Kd Diabase Gp ~ Calcareous ~ Members Jn ~he

Tertiary granitic rocks Dg Dagua Gp ~ Volcanic j> Dagua Gp

Figure 6. Profile across the Western Cordillera (zone I).

IOkm


716 COLOMBIAN ANDES

evidence of the occurrence of later phases in zone 1, other than the deformed nature of the Cretaceous, is lacking; the adjacent basins were affected by Palaeocene, Laramide (late M. Eocene), proto-Andean (late M. Miocene) and Andean (late U. Miocene) phases, however.

85o-5 Fold structures: details of the folds produced by phase 1 are not known and on present information it is not possible to distinguish the effects of later, individual phases. The axial surfaces of the phase 1 and later folds are mainly steeply dipping and lineation and foliation structures are present in element c as a result of phase 1 (Nelson 1957, 1962).

ZONE 2. CAUCA BASIN

808 Zone margins are narrowly gradational ( to 3 km). 808-11 Areas of the zone occupied by the outcrops of rock types: volcanic 30%; plutonic 3%; sedimentary 65% ; metamorphic 2%. 813-14 Elements: the oldest rocks of the Volcanic cap (element a) are


~22 Thickness 323 Element

~2o Age and m in which evidence for the rocks

~19 Unit age 321 Lithology Average occur

Gale6n Fm ?Plioc, strati- Volcanic con- 450 a graphical position glomerate, tuff,

sandstone

Patia & ?U. Mioc, Continental 1500 Buga Fms stratigraphical conglomerate,

position sandstone

Marafi6n & ?L.-M. M ioc , Continental 2500 Morales stratigraphical massive sandstones (> 1300, Fms position

COLOMBIAN ANDES 717

0

I

2

3

4

5kin

L_. I-- W'NW

ZONE 2

.A~o( c ~ " ~" 3~, ~ ~)0\0~2 Serp ESE I

0 5k in [ I I I I I

Figure 7. Profile across Cauca Basin (zone 2). (Kd--Diabase Gp; Tc--Cauca Gp; Tm--Marafion Fm; Tp--Patia Fm; Ta--Arboleda Fm; Tg--Gale6n Fm; Q--Quaternary terrace). The majority of the faults are thought to have transcurrent displacements: the Mercaderes Shear-Fold is interpreted

as a flexure genetically associated with transcurrent faulting.

separated by wide synclines. They do not exhibit recognizable stratigraphical separation, which together with their al ignment parallel with the Dolores fault may mean that the movements (possibly not great, ?dextral) have been mainly lateral. The youngest beds affected are U. Miocene but faulting may have commenced in the U. Eocene or earlier.

ZONE 3. CENTRAL CORDILLERA

303 Zone margins are narrowly gradational ( to 3 km). 30s-zi Areas o f the zone occupied by the outcrop o f rock types: volcanic 17%; plutonic 30%; sedimentary 3% ; metamorphic 50%.

~z~-z4 Elements: rocks of the Volcanic cap (element a) are flat lying and rest unconformably on older rocks. Sedimentary cover rocks (element b) occur in minor grabens filled with Cretaceous strata; they rest unconformably on the isoclinally folded schists and phyllites of the Metamorphic complex (elements c and d) ; these two groups of elements (b, c-d) have probably been affected by E -W shortening due to deformation. Unconformably beneath elements c-d lie the gneisses and plutonic rocks of the Pre-Cambrian basement (element e).

815-16 Outcrop areas of the elements: a outcrops as dissected terraces mainly surrounding volcanic centres; b occurs over 230 x 5-15 km; c and d outcrop over the whole zone (length 1000 kin; width 30-150 km, average 80 kin).

Table 6 STRAT IGRAPHY IN ZONE 3

330 Age and evidence for

8z~ Unit age 831 Lithology

822 Thickness m

Maxi- Mini- Aver- mum mum age

823 E lement

in which the rocks occur

Volcanic Plioc (& ?U. Andesite lava rocks Mioc) to Present; & tuff

undeformed, therefore post- Andean phase

Creta- Alb, fossils Limestone, ceous basal con-

glomerate

Jurassic &U. Triassic

*Caja- marca Gp Pre- Cam-

brian

Locally present in fault blocks on the east of the zone but essentially part of zones 4 and 5

Ordovic--late Schist, phyllite, 20,000 10,000 Cret slate

Radiometric ages determined by the U.S.G.S.

Igneou~ rocks

?200 a

?200 b

c, d

* Cajamarca Gp is a blanket term which covers metamorphic rocks from several distinct sequences that may have been affected by more than one phase of metamorphism.


718 COLOMBIAN ANDES

326--32 Igneous activity: Episode 1--Pre-Cambrian radiometric ages have been determined for acid, major intrusives by the U.S.G.S. Episode 2- - intermediate lavas and tufts and alkaline major intrusions formed in early Triassic times; they underlie fossiliferous U. Triassic strata. Episode 3--intermediate lavas and tufts and intermediate and basic dykes and sills of Jurassic age occur interbedded in the Giron Gp along the east margin of the zone (see zone 4). Episode 4--acid major intrusions in elements c and d have given radiometric age of 79 m.y. and 110 m.y. (Cretaceous). Episode 5--Pliocene (?and U. Miocene) to Recent vulcanism has produced intermediate lavas and tufts; the age of these rocks is indicated by their unfolded nature and the existence of volcanoes with minor current activity; an U. Miocene tuff in zone 4 has probably been derived from the same sources; the volcanoes occur in a straight line, parallel with and possibly related to the Dolores fault on the west margin of the zone. Volume--?4500 km 3.

335-~2 Metamorphism: the metamorphic history of this zone has not been worked out in detail but evidence from isolated localities points to the following phases (Nelson 1957). Phase 1--high grade metamorphism of Pre-Cambrian age is inferred by analogy with the Santa Marta Massif. Phase 2--low-grade regional metamorphism affected elements c and d in mid-Palaeozoic times, probably in the early Devonian: the metamorphosed rocks locally contain Ordovician graptolites (Harrison 1930). Phase 3--low-grade regional metamorphism affected elements c and d in the early Mesozoic, probably in L.-NI. Triassic times: the metamorphosed rocks underlie fossiliferous Carnian strata (Trumpy I943). Phase 4 low-grade regional metamorphism affected elements c and d in the late Aptian to pre-U. Albian interval : the metamorphosed rocks locally contain Aptian fossils and underlie fossiliferous U. Albian strata (Bfirgl & Radelli 1962). Phase 5--low-grade regional (and ?partly thermal) metamorphism affected elements c and d in the post-

Albian to pre-U. Eocene interval, probably during the Subhercynian or Laramide phases: Cretaceous fossils occur locally (Senonian forams) in the metamorphosed rocks (Bfirgl, personal communication).

344-8 Deformation: zone 3 has a long history of deformation, the details of which are not known (see Feininger 1970). The above phases of metamorphism correspond to the main movements. In addition, the zone was uplifted and faulted during the Tertiary, especially during the Laramide, proto-Andean and Andean phases. 366-72 Faulting: Tertiary faults, probably originating in the Laramide phase but since rejuvenated, affect all elements except a. Details are not known, but many of the faults parallel the Dolores fault and may belong to the same system.

SUB-ZONE 4. MIDDLE MAGDALENA BASIN

3o3 Zone margins are narrowly gradational ( to 3 km). 310 Sedimentary rocks outcrop over the whole zone. 312-14 Elements: the strata of the Volcanic cap (element a) are undeformed and rest unconformably on older rocks. Rocks of the Sedi- mentary cover (element b) are moderately folded and faulted; deformation has produced some E-W shortening, although vertical movements are dominant. The rocks of elements c-d (1V[etamorphic complex) and e (Pre-Cambrian basement) are unexposed. 315-16 Outcrop areas of the elements: a and b outcrop over the whole zone width (90-20 kin, average 55 km); b outcrops along the whole length of the zone (350 km).

L WNW I" ZONE 3 ~ ESE

o I '

t- QUATERNARY & ~ Alluvial fan 0 10km I I UPPER TERTIARY ~ I Extrusive rocks ~Grandior i tes ~Gne iss ic quartzschists CAJAMARCA

L. TERTIARY ~] Shales & Sandstones ~-~Undifferentiated ~ Quartzphyllites GROUP metamorphic rocks

M- U. CRETACEOUS ~] Diabase flows ~-~Greenschists i"~JiDiabase flows " ' & amphibolites

PERMIAN ~ Rhyodacitic flows ~Graph i te schists [~-'~CrystaHine limestone

Figure 8. Profile across Central Cordillera (zone 3) (After Nelson, 1957).


COLOMBIAN ANDES 719

Table 7 STRAT IGRAPHY IN ZONE 4

319 Unit

320 Age and evidence for age 321 Lithology

322 Thickness m

Maxi- Mini- Aver- mum mum age

Mesa Fm

Real Fm

Plioc, Tuffaceous sand, stratigraphic gravel position

U. Mioc, Continental stratigraphic sandstone, shale, position conglomerate

323 Element

in which the rocks OCCUr

600 0 300 a

Chuspas Olig-Mioc, Continental Gp fossils clay, sandstone,

siltstone

3600 400 2000

Chorro Gp U. Eoc, fossils Continental including sandstone, clay pollen

3200 575 1000

Lisama Fm Palaeoc, Continental pollen siltstone, minor

sandstone

2300 1225 1500

Umir Fm Campan- Paralic, Maestr, pollen carbonaceous

siltstone, coal

La Luna Turon-Santon, Argillaceous 675 Fm ammonites limestone, chert

Tablazo, Alb-Cenoman, Limestone, 1095 Simiti & ammonites shale Salto Fms

1225 950 1000

1000

280 500 I b

a9 Unit

322 Th ickness m

3~o Age and evidence Maxi- Mini- Aver-

for age 391 Lithogy mum mum age

Rosa Haut-Barrem, Limestone Blanca ammonites Limestone

425 150 300

Tamb6r Haut, Sandstone 650 0 500 Fm ammonites

333 Element

in which the rocks oc~lgr

450 750

Gir6n Gp Jurassic, Red beds, 4000 1000 2000 palaeobotany sandstone, clay, & local conglomerate ammonites

3~6-32 Igneous activity: intermediate lavas and tufts, with associated dykes, occur interbedded in the Gir6n Gp of Jurassic age; they are exposed only along the west marg in of the zone and adjacent to zone 3.

335-4~ Metamorphism: see zone 5. 344-8 Deformation: see zone 5. 3ee-72 Faulting: sub-surface studies indicate periods of fault ing (probably normal and reverse block faults) pr ior to U. Miocene and U. Eocene times. I t is difficult to identify these systems of faults because they are masked by younger faults. The ant ic l inal structures are main ly fault control led. Naps showing faults--see Morales et al. (1958).

Paja Shale Barrem-Apt, Shale 625 125 400 ammonites

NW

SUB-ZONE 5. UPPER 1VIAGDALENA BASIN

3o3 Zone margins are narrowly gradat ional ( to 3 km). The northern boundary with zone 4 is gradat ional ; some authors place it further south (Houten & Travis 1968; Corr igan 1967). 30s-n Areas of the zone occupied by the outcrop of rock types: volcanic 2%; plutonic 5%; sedimentary 93%.

312-14 Elements: the strata of the Volcanic cap (element a) are un-

SE

J r5 -6 ~: ,o r , -3 T I6 - 17 T I I -15

0 _ ' - :~i;!i; ::~~ >-~:~:-~:~~'~:~: .................. ='~:~: :~: . . . . - i~ -

S -

rocks I

IOkm-

0 IOkm IL ! , $

Figure 9. Profile across Middle Magdalena Basin (zone 4) (J--Jurassic: K3-5--Hauterivian to Aptian; Ke---Albian; KT-X--Cenomanian to Santonian; K 11-12~ Campanian and Maestrichtian; T1-3--Danian to Ypresian; TS-6--Ledian and Ludian; T 7-1 --Lattorfian to L. Aquitanian; Tn-15--U. Aquitanian to Tortonian

T 16-17 Sarmatian and Pontian).


720 COLOMBIAN ANDES

deformed and rest unconformably on older rocks. Rocks of the Sedi- mentary cover (element b) are moderately folded and faulted; deformation has produced some E-W shortening, although vertical movements are dominant. The rocks of elements c-d (Metamorphic complex) and e (Pre-Cambrian basement) are unexposed (Fig. 10). 3x5-1n Outcrop areas of the elements: a occurs in isolated terraces derived from zone 3 and on the western margin of the Basin; b outcrops over the whole zone (length 500 kin; width 20-60 kin, average 35 km).

Table 8

STRAT IGRAPHY IN ZONE 5

322 Th ickness m 323 E lement

32o Age and in which evidence for Maxi- Mini- Aver- the rocks

319 Unit age 321 Lithology mum mum age occur

Mesa Fm Plioc, stratigraphic position

Honda Fm U. Mioc, vertebrates & stratigraphic position

La Cira L. Mioc (?& Fm Olig) pollen?

& vertebrates

Gualanday U. Eoc-Olig Continental 3400 Gp pollen conglomerate

& clay

Guaduas Late Cret & Clay, sandstone, 2000 Fm Palaeoc local con-

glomerate, mixed marine & non-marine

Guadalupe Maestr, Sandstone & Fm molluscs local conglom-

erate (marine)

Villeta Fm Alb-Campan, Black shale, ammonites chert, limestone

Caballos Alb (?& Apt), Sandstone & Fm ammonites limestone

Motema L.-M. Jur, Red sandstone, 1000 Fm (post- correlation volcanic rocks, Payand6 local marine Red Beds of limestone Trumpy 1943)

Payand6 Nor & Cam Fm

Tuffaceous 1200 700 I000 a sand, gravel

Conglomerate & sandstone, continental

3100 1200 2000

Continental 1500 600 1000 clay & sandstone

600 1500

700 1000

100 30 100

1000 400 1000

300 100 200

500 500

Limestone, basal red beds (Pre- Payande Fm)

300

32n-3~ Igneous activity: Episode 1--alkaline batholiths and related acid to alkaline extrusive rocks formed in L. to M. Triassic times; intrusive contacts are not exposed but the rocks must be earlier than the fossiliferous U. Triassic strata; also, on the evidence from zone 6 (position of extrusive equivalents-), they must be post-Carboniferous. Volume-- ?125,000 km 3. Episode 2--acid and intermediate lavas and tufts occur interbedded in the Gir6n/Motema Fms and are of L. Jurassic age. Volume--160 km 3. 335-~2 Metamorphism: the presence of metamorphic rocks, of mid- Palaeozoic and L.-M. Triassic age, beneath the zone is inferred from the conditions in zones 3 and 7. 344--8 Deformation: Phase 1--intense deformation and metamorphism probably affected the rocks of element d in this zone in late Silurian times, by analogy with zone 6. Phase 2--deformation affected elements b, c and d in the Permian to late M. Triassic interval, probably in L.-M. Triassic times; block faulting occurred in the east and intense deformation in the west; this phase is based on the presumed existence in this zone of metamorphic rocks beneath fossiliferous Carnian strata. Phase 3 (Nevadan)--deformation may have affected element b in the post-M. Jurassic to pre-Albian interval, probably in early 'Tithonian' times; the existence of this phase is suspected on regional grounds. Phase 4 (Laramide)--faulting and folding affected element b in the post-Palaeocene to pre-U. Eocene interval and is evidenced by an unconformity beneath U. Eocene strata. Phase 5 (Andean)--folding and faulting affected element b in the U. Miocene to Pliocene interval and is evidenced by an unconformity beneath Pliocene strata.

350-5 Fold structures: folds produced during the earlier phases are masked by the effects of the stronger Andean phase. Phase 5 folds have varying sizes, typical apical angles of 70 and east-dipping axial planes; on average, two folds larger than 1 km in size occur in a cross-section of the zone. 366--74 Faulting: details of faults developed before the Andean phase are not known. The northern part of the sub-zone is affected by block faulting (mainly normal faults downthrowing < 100 m to the east), probably initiated during the Laramide phase but periodically re- activated especially during the Andean phase. Andean thrusting affects the zone (see lXl). Map showing faults--Morales et al. (1958).

SUB-ZONE 6. EASTERN CORDILLERA

303 Zone margins are narrowly gradational ( to 3 km). 310 Sedimentary rocks outcrop over the whole of the zone. 312-14 Elements: the strata of the Sedimentary cover (element b) are moderately folded and thrusted; they have been affected by some E-W shortening, but movements were mainly vertical. The rocks of elements c-d (iVfetamorphic complex) and e (Pre-Cambrian basement) are unexposed. 315-16 Outcrop areas of the elements: b outcrops over the whole zone


COLOMBIAN ANDES 721

O-

5km

(length 140-600 km, average 400 km; width 60-200 kin, average 150 km); d probably underlies b throughout the zone.


322 Thickness m .q23 Element

3~0 Age and in which evidence for Maxi- Mini- Aver- the rocks

az9 Unit age 3~z Lithology mum mum age occur

Usme-Con- U. Eoc-?Mioc, centraci6n forams & Fins pollen Regadera- U. Eoc, Picacho stratigraphic Fins position Guaduas U. Maestr- Fm Palaeoc, pollen

& ammonites Guadalupe Campan- Fm Maestr, fora-

minit~ra Villeta Gp Haut-Santon,

ammonites

Clay, fine sand- 1300 500 500 "~ stone, ironstone, local coal Conglomeratic 180 90 150 sandstone

Red & grey 1000 300 500 clay, coal, sandstone Sandstone, 800 400 700 siliceous argillite Black shale, 5700 2200 4000 limestone, sandstone

C~iqueza 'Tith'-Valang, Black shale, lime- 3000 I500 2500 Gp ammonites stone, sandstone,

turbidites, basal conglomerate

Gir6n Fm L.-M. Jur, Continental red 2500 (subsurface) marine fossils beds with marine

intercalations & ?evaporites

U. Palaeo- M. Devon, Shallow marine 1200 zoic Carb & ?Perm, sandstones, shales

molluscs & limestone & continental red beds

NW

~-i~- _1, "ill--%,, xt ~1" .... r . . . . . . . . . . . . . . . . ~' "~

722 COLOMBIAN ANDES

SUB-ZONE 7. GARZ(~N-QUETAME MASSIF

3o8 Zone margins are narrowly gradational ( to 3 km). 808-10 Areas of the zone occupied by the outcrop of rock types: plutonic 45% ; sedimentary 5% ; metamorphic 50%.

~1~-14 Elements: the strata of the Sedimentary cover (element b) are moderately deformed and have been affected by some NW-SE shortening, but their structure is mainly due to vertical movements; they rest unconformably on the older rocks. The rocks of the Meta- morphic complex (element d) are strongly deformed and have been affected by NW-SE shortening. The Pre-Cambrian basement rocks (element e) consist of high-grade metamorphic and plutonic rocks which are strongly deformed.

315--16 Outcrop areas of the elements: b now outcrops only in isolated patches; d and e outcrop over the whole zone (length 600 km; width, average 50 kin, maximum 85 km).

885-4~ Metamorphism: Phase I--low-grade regional metamorphism affected element d in the Ordovician to M. Devonian interval, probably in late Silurian to early Devonian times. Phase 2 ('Hercynian')-- metamorphism, probably of contact type, produced local high-grade rocks associated with 'Hercynian' granites in the Garz6n Massif during the Carboniferous to U. Triassic interval, probably in L.-M. Triassic times.

844-SDeformation: Phase 1--intense folding and faulting affected element d in mid-Palaeozoic times, see metamorphic phase 1. Phase 2--?block faulting affected elements b and d in the post-Carboniferous to pre-Carnian interval, probably in L.-M. Triassic times. Deformation phases 4 to 8 of zone 6 have probably affected this zone also, but they cannot be specifically identified. 85-~Fold structures: deformation phase 1 produced isoclinal folds with axial planes whose dip varies from 30 to the SE in the north-west, through vertical, to 60 to the NW in the south-east of the zone. Fold structures due to later movements have not been distinguished.

Table 10

STRAT IGRAPHY IN ZONE 7

333 Element 820 Age and 833 Thickness in which

evidence for m the rocks Sl9 Unit age 331 Lithology Average occur

Red Beds L.-M. Trias?, Continental red 2000 stratigraphic beds with volcanic position rocks

U. M. Devon, Carb & Marine shale, 1100 Palaeozoic ?Perm fossils sandstone & lime-

(Campbell & stone & continental Biirgl 1965) red beds

Q.uetame L. Palaeozoic Phyllite & ?3000 Gp (mainly Ordo- quartzite locally

vician), graptolites passing into slate & & stratigraphic quartzite with position limestone

Granites ?Pre-Cambrian, (in Garz6n petrological Massif) conclusions of

Radelli (1967)

8~6-89. Igneous activity: Episode 1--alkaline major intrusions cut the Quetame Gp but underlie M. Devonian strata; they are little known (Radelli 1967, p. 135). Episode 2--alkaline major intrusions cut Carboniferous strata but underlie Jurassic rocks; together with the associated acid lavas and tufts they are probably of L.-M. Triassic age.

SUB-ZONE 8. SANTANDER MASSIF

803 Zone margins are narrowly gradational ( to 3 km). 809-n Areas of the zone occupied by the outcrop of rock types: plutonic 50% ; sedimentary 5% ; metamorphic 45%. 812-14 Elements: the strata of the Sedimentary cover (element b) are moderately deformed and rest unconformably on older rocks. The Metamorphic complex (element d) consists of strongly deformed metamorphic rocks. The Pre-Cambrian basement (element e) consists of high-grade metamorphic and plutonic rocks. 315-16 Outcrop areas of the elements: b is only preserved in isolated outliers; d and e outcrop over the whole zone (length 400 km; width, average 50 kin, maximum 70 km). 82~-3~ Igneous activity: alkaline major intrusions, lavas and tufts of various ages (U. Devonian, L. Carboniferous, early Triassic) occur but are poorly known.

835-42 Metamorphism : Phase l--low-grade regional metamorphism affected elements b and d in the Ordovician to M. Devonian interval, probably in late Silurian to early Devonian times; muscovite, biotite, chlorite and albite occur in pelitic rocks. Phase 2 ('Hercynian')--high- grade gneisses formed in elements b and d associated with granite emplacement in the M. Devonian to Jurassic interval, probably in Carboniferous to early Triassic times.

844-SDeformation: Phase 1---intense folding and faulting affected element d in mid-Palaeozoic times, see metamorphic Phase 1. Phase 2 - mild deformation affected elements b and d in the L. to M. Pennsyl- vanian interval and is evidenced by an unconformity below M. Pennsylvanian strata. Deformation phases 2 to 8 of zone 6 have


COLOMBIAN ANDES 723

10km-

[_ J F ZONE 8 -I

w E

MIDDLE MAGDALENA VALLEY ~.~ ~- SANTANDER MASSIF N, LLANOS FOOTHILLS

.~ ..~. D-C

. . . . " ' . . . . . . . . . . . . . . . ~ ~-~ .~ . . . . . - ~ ~ - - . ~ - ~ ,~ . . . . . . . v,-,~ " ~ ' - '"

0 ,Okra ~ Tertiary strata ~ Triassic granite ~Tr iass ic migmatite

Figure 11. Profile across Santander Massif (zone 8) (C-O--Cambro-Ordovician; D-C--Devonian to Carboniferous; KS-5--Hauterivian to Aptian; K~-~Alb ian to

333 Element 330 Age and in which

evidence jbr 333 Thickness the rocks 819 Unit age 331 Lithology m occur

Umir Fm

La Luna Fm

Uribante Fm

Gir6n Gp

Cenomanian; KS-12--Turonian to Maestrichtian; for legend in Middle Magdalena Basin, see Fig. 9.)

Table 11 probably affected this zone but cannot be distinguished. Wrench STRATIGRAPHY IN ZONE 8 faulting related to the Santa Marta fault is believed to be responsible

for the dominant structure of the zone. 36G-V~Faulting: groups of faults occur which are parallel with and related to the Santa Marta fault (see z33).

Campan-Maestr, Carbonaceous 1000 foraminifera shale

Turon-Santon, Black shale, chert, 200 ammonites argillaceous

limestone

Alb, *Cenom Sandstone & 500 limestone

Jur, ammonites in Continental red 1000 marine inter- beds (< 3500, calations > 100)

Bocas Fm Pennsylvanian, palaeobotany

Surat/t Fm Mississippian, marine fossils

Ouetame L. Palaeozoic Gp (in (?mainly Ordo- Floresta vician), strati- Massif only) graphic position

Continental red 300 beds

Sandstone, shale & 600 marl

Phyllite & 590 quartzite

Gneiss (in ?Pre-Cambrian, Floresta inferred from high Massif only) metamorphic grade

& stratigraphic position

* Some authors indicate that the Cretaceous succession ranges down to the Valan- ginian, a conclusion based on lithological comparisons with zone 4, but this is doubted by the writer.

ACKNOWLEDGEMENTS

This contribution derives from a study of the geology of Colombia made in 1966 for the British Petroleum Company Limited whose help in releasing information is gratefully acknowledged. The author wishes to thank Dr. J. E. Ramlrez (Director, Instituto Geoflsico de Los Andes Colombianos, Bogota) for supplying geophysical and seismic information and the United States Geological Survey for allowing unpublished radiometric dates to be included.

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-I Okra


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Colombian Andes-Campbell