Geological history of the Cretaceous ophiolitic complexes of northwestern South America (Colombian Andes)

Tectonophysics,

143 (1987) 307- 327

Elsevier Science Publishers

307

B.V., Amsterdam

- Printed

in The Netherlands

Geological history of the Cretaceous ophiolitic complexes of Northwestern South America (Colombian Andes) JACQUES BOURGOIS ‘, JEAN-FRANCOIS TOUSSAINT 2, HUMBERTO GONZALEZ 3, JACQUES AZEMA ‘, BERNARD0 CALLE 3, ALAIN DESMET 4, LUIS A. MURCIA ‘. ALVARO P. ACEVEDO 5, EDUARDO PARRA 3 and JEAN TOURNON 6 ’ Departement

de Geotectonique,

VA 215, Vniversite Pierre et Marie Curie, Tour 26-00, itage

I, 4 place Jussieu,

75252 Paris Cedex 05 (France) ’ Uniuersid~

Naciona~ sede Medellin, A.A. 3840, Medeliin ~~o~ombia) 3 Ingeominas, A.A. 4653, Medellin (Colombia) 4 Ingeominas, A.A. 695, Popayan (Colombia)

5 Laboratoire de Petrologic, 6 Laboratoire de P~trographje,

WniversitP de Nancy 1, R.P. 239, 54506 Vandoeuvre-l&Nancy

Chdex (France}

Vn~versit~ Pierre et Marie Curie, Tour 26-00, &age 3, 4 place Jussieu, 75252 Paris Cidex 05 (France) (Received

May 23,1986;

revised version accepted

January

20,1987)

Abstract Bourgois,

J., Toussaint,

E. and Toumon, (Colombian

Andes).

The Western Cretaceous Paleozoic

and

Antioquia

batholith

of Colombia

Precambrian (60-80

during

The nappes

travelled

of the volcanoclastic

During

Cretaceous

times

originated

America

material

C., Desmet, ophiolitic

by intense

Ma B.P.) intrudes

both abducted

Cordillera.

alpine-type

of the Western

micaschists

A., Murcia,

complexes

L.A., Acevedo,

of northwestern

A.P., Parra,

South America

Therefore,

and gneiss

nappe

nappe-forming

Cordilleran

nappes

of the Central

Cretaceous

oceanic

emplacement

folding

and thrusting.

has been

abducted

Cordillera.

material

and abduction

Near

The

onto

the

Yarumal,

the

and the polymetamorphic onto

the Central

Cordillera

to Early Paleocene.

from northwest

source,

analysis probably

was formed

polymetamorphic

Late Senonian

most northwestern

J., Bernardo,

of the Cretaceous

143: 307-327.

Ma B.P.) tholeiitic

rock of the Central

occurred

H., A&ma, history

Tectonophysics,

Cordillera

(80-120

basement

J.-F., Gonzalez,

J., 1987. Geological

whereas

to southeast

so that the highest

the lowest units originated

and sandy the opening

by detachment

turbidite

material

of this marginal of a block

from

unit, the Rio Calima

from a more southeastward from each unit suggests

sea, from the South

a marginal

now on called

American

nappe

direction.

related

has the

Sedimentological

marine

the “Colombia

continent

therefore

environment.

marginal

basin”,

to the Farallon-South

plate convergence.

In the Popayan methodism.

area (southern

related

to an undated

thrust

over

Colombiano”

Colombia),

This high pressure both

metaophiohtic

the blueschist

suffered

the Central

low temperature complex.

belt

and

at least two phases

The ophiolitic

of ophiolitic

abduction

Since 1973 (Aubouin, 1973; Aubouin et al., 1973; Butte&n, 1973; Gansser, 1973; Zeil, 1979), it has been known that the Andes can be divided 0 1987 Elsevier

Science Publishers

B.V.

basement

exhibits

is of Early Cretaceous material

the metaophiolitic

Introduction

0040-1951/87/$03.50

Cordilleran

metamo~~sm

originating

complex.

These

during

Mesozoic

from data

glaucophane

schist

facies

(125 Ma B.P.) age and is the Western

suggest

that

Cordilleran the

is

“Occidente

time.

into three parts; the northern, central and southem Andes which are separated on the basis of the absence or presence of ophiolitic rocks. The presence of mafic and ultramafic rocks with tholeiitic affinities characterizes the northern section of the

308

Ridge; Fig. 1. Structural setting of the northern ophiolitic Andes. Present-day Caribbean plate boundaries. C.R.-Carnegie H-Huancabamba traverse. (Sources of data: Case and Holcombe, 1980; Warren et ai., 1982; Case et al., 1984; Burke et al., 1984; Boinet et ai., 1985a; Bourgois et al., 1985b).

Ecuadorian and Colombian Andes (Fig. 1) (Hubach and Alvarado, 1934; Grosse, 1935; Nelson, 1959; Irving, 1971; Julivert, 1973; Aubouin, 1972, 1973; Gansser. 1973; Aubouin et al., 1977; Butterfin, 1977; Goossens et al., 1977; Lonsdale, 1978; Bourgois et al., 1982a). Further, the general trend of the Andes changes at the Huancabamba traverse (Fig, 1) Iocated in northern Peru (Gerth, 1955; Ham and Herrera, 1963; De Loczy, 1968, 1970; Gansser, 1973). This major change also corresponds to the position of the Carnegie Ridge

(Fig. 1) which is one of the main structures of the Nazca Plate (Hey, 1977). In Colombia, the Andes are divided into three main cordilleras (Fig, 2), separated by deep interAndean valleys. From east to west there are the Eastern Cordillera, the Rio Magdalena Valley, the Central Cordillera, the Rio Cauca Valley and the Western Cordillera. Farther to the west and towards northern Colombia, there is the Serrania de Baudo on the Pacific coast. The Serrania de Baudo is separated from the Western Cordillera by the

UPrecambrian

w7

0

Fig. 2. The Andean cordilleras

and the geological setting of the “Occidente

Colombia, Arango et al., 1976). A,, A,,

Colombiano”

A,, B, Cl, C,, D, E, F, G,, $-location

Tertiary basin of the Rio Atrato and Rio San Juan, Mesozoic ophiolitic rocks are found only in the Western Cordillera, the Rio Cauca Valley and the western edge of the Central Cordillera. These ophiolitic rocks are usually named “Occidente

60

,

100

,

150

200km

.

(boundaries from the Geologic map of

of the cross sections in

Fig.

3.

Colombiano” (Restrepo and Toussaint, Toussaint, 1978; Bourgois et al, 1982a, b).

1973;

In the central and southern part of the Western Cordillera, two stratigraphic units have been recognized

(Nelson,

1959):

the Diabasico

Group

310

311

Ma

PLUTONIC

Age

BODY

FLEISTOCENE

5

PLIOCENE c/v-

VOLCANISM

VOLCANIC

ASH

CONT. SED.

MIOCENE LATE EOCENE

MARINE

SED.

EOCENE

LIMESTONE

W

ASSOCIATED EARLY

60

FALEOCENE IAASTRICHTIAI

RIO

CALIMA

NAPPE

LOGOGUERRERO

60

WINDOW

9

DABElBA-

UNIT URAMITA

SANDY TURBIDITE

10 11 * 6.

UNIT

RIO DCGUA

A A . .

-------------VOLCANIC AGGLOMERATE

PILLOW

THINLY BEDDED TURBIDITE

:bms;CHIST 52

BASALT

BARKEMIAN

120

7

CENTRAL

CORDILLERP

metasedmwnt

t

ALBIAN

COVER 24

JURAS. basement

amph!bahte

Jambala blue schist 125 Ma

m/Q2

28 7% Thrust fault alder than 125 Ma _ 1st abduction

31

t

30 /(93

Thrust fault of Late Senanian to Early Paleocene 2 nd abductlan

normal series

32

Fig. 3. (continued).

$9

Past- Eocene thrust fauli

overturned

series

312

equivalent

to the Faldequera

and Alvarado material,

and the Dagua

Espinal

Formation

Hubach

(1957)

terranes.

Although

the groups

Group

equivalent

comprise

to the

Formation

of

the sedimentary

the ages suggested

group,

of Hubach the volcanic

and the Dagua

which

are variable

for the Dagua

Series

(1934) which includes

(Paleozoic

Late Jurassic

ceous-Paleocene

for the Diabasico

authors

(Hubach

and Alvarado,

Grosse,

1935; Nelson,

for each of

to Cretaceous to Late CretaGroup)

most

1932, 1934, 1945;

1959; Biirgl, 1961;;

Irving,

1971; Julivert, 1973; Barrero, 1979) acknowledge that the Diabasico Group is more recent than the Dagua Group. The lithostratigraphic and tectonic of the Buga-Buenaventura traverse study (Bourgois Group,

et al., 1982a) has shown that the Dagua

at least in part, is the sedimentary

the Diabasico

Group

cover of

(Fig. 3).

In the northern part of the Western Cordillera the terminology (Toussaint, 1978; Restrepo et al., 1979) changes. The mafic volcanic rock, tuff and diabase are termed the Barroso Formation while the sediments are included in the Penderisco Formation. The Penderisco Formation and Barroso Formation constitute the Canasgordas Group. The Penderisco Formation is divided into two members: the Urrao Member and Nutibara Member. The correlations between formations and groups used in the north and the center of Western Cordillera are not clear. However the Diabasico Group has been compared to the Canasgordas Group (Irving, 1971). The Cretaceous age of some of the various units just mentioned above is well documented by fossils and microfossils of Barremian (?)--Aptian to Coniacian ages (Olsson, 1956; Alvarez and Eckard, 1970; Feininger et al., 1972; Toussaint and Restrepo, 1974; Bourgois et al., 1982b). Eastwards, in the Western Cordillera, there are mafic and ultramafic rocks associated with marine sediments that outcrop in the Cauca Valley as well as on the Western side of the Central Cordillera. These rocks have various names: Porfiritica Formation (Grosse, 1926) Quebrada Grande Formation (Botero, 1963) or Pena Morada Formation (Paris and Marin, 1979). It is simplest to group these rocks in the Cauca ophiolitic complex as did Restrepo and Toussaint (1973).

The metamorphic complex

has

Ayura-Montebello Valdivia marca

Paleozoic

been

Group

Group Group

part of the Cauca

generally (Hall

(Nelson,

ophiolitic

included

with

(Botero,

1963)

et al., 1972) or the Caja-

1943; Irving,

to

Valdivia

groups is well documented

son, 1930; Triimpy,

the

1959). The Precambrian

age of the Ayura-Montebello,

and Cajamarca

the

(Harri-

1971; Tschanz

et

al., 1974; Barrero and Vega, 1976; Restrepo and Toussaint, 1977a, 1978; Toussaint, 1978; Toussaint et al., 1978; Boinet et al., 1985b). However,

it

must be pointed out that there is high pressure-low temperature metamorphic rock in the above groups (Orrego et al., 1980; Feininger, 1982). In the Popayan area, the glaucophane schist of Rambalo has a K/Ar age of 125 Ma B.P. (Paris and Marin, 1979) and

occurs

and metabasalt.

with

amphibolite,

The age suggest

metagabbro

the existence

of

ophiolitic rocks ranging from Upper Paleozoic to Lower Cretaceous age. Other K/Ar radiometric ages (Restrepo and Toussaint, 1977a) on the Pueblito gabbro (131 + 9 Ma B.P.) and on the Amaga stock (163 _+ 10 Ma B.P.) are consistent with such an age range. The first significant study of the Central and Western Cordillera east of Buenaventura (Fig. 3) is that of Barrero (1979) who clearly identified the tholeiitic affinities of the basalts and Three tectonic units were identified

dolerites. on the

Buga-Buenaventura traverse (Bourgois et al., 1982a). From west to east, and in order, from the lowest

to the highest, there are the Rio Dagua the Loboguerrero window unit, the unit, Dabeiba-Uramita unit and the Rio Calima nappe. All units are comprised of marine sediment and balast flows overlying a basement of mafic and ultramafic rocks. All rocks range in age from 80 to 120 Ma B.P. The Rio Dagua unit records two tectonic episodes. The two episodes produced folding and development of schistosity. During the first tectonic episode, isoclinal folds developed as the rocks were metamorphosed. The Loboguerrero window unit exhibits a large recumbent fold towards the southeast. An incipient cleavage is parallel to the axial fold plane. Deformation is weaker in the Rio Calima nappe, and appears to have formed under conditions in a higher struc-

313

tural level than

in the two other

units.

Nappe

emplacement occurred during the first phase and from northwest to southeast. quently,

the upper Rio Calima

a site that was farther during Cretaceous Lithostrati~rap~c new traverses

tectonic Conse-

nappe originated

at

away from South America

times than the Rio Dagua unit. and tectonic analyses of three

are presented.

ture of the Western

They show the struc-

Cordillera

(cross sections

A,,

(1) Amygdaloidal

basalt

flows that are green or purple coloured

basalts

alternate

and

massive

in colour.

in flows of 0.70 m to 50

m thick. Both the green and purple

basalts

the same petrologic composition (Parra, (2) A 400-500 m thick sedimentary overlies

the basalts.

well exposed section

basalt

Different

This sedimentary

in the Quebrada

A 3, Fig. 3). From

have

1978). sequence sequence

Las Havas

base to top it includes:

A,, A,, C,, C,, D,, G,, G,, Figs. 2 and 3); and of

grey, white and black cherts in beds from 0.340

the Central

cm thick. Next in the section

Cordillera

Figs. 2 and 3) between

{cross

sections

3, E, F,

1 O and 7 o N.

Rio Calima nuppe One of the best sections of the Rio Calima nappe is exposed in the Dabeiba area (Fig. 3, cross section A,) and in the Giraldo area east of Canasgordas (Fig. 3, cross sections A, and A,). The lithofogy is shown in Fig. 4, column A and is described below.

4

RIO CALlMA

is

(cross

there follows

thinly

bedded greywacke with grain size from 0.1-l cm. Volcanogenic detritus is abundant in this sequence; however, it does include non-volcanic sandy material. Upsection in the greywacke sequence, white and black limestones 20-40 cm thick gradually appear. The limestone contains volcanic fragments. Locally in the sequence there are thin abundant.

sandy beds and lamellibranchiata are A Middle Albian ammo&e has been

found by Etayo Sema et al. (1980). Greywacke and limestone are overlain by thinly bedded sandy

NAPPE OLISTOSTROME CONGLOMERATE COARSE

GRAIN

PILLOW

BASALT

tkm

Fig. 4. Lithostratigraphic of El Siete (cross section text.

columns of the upper Rio Calima nappe, A. East of Canasgorda (cross sections A, and A,, Fig. 3). B. West C’,, Fig. 3). C. In the Loboguerrero area (cross section D, Fig. 3). For explanation of numbers 1-6, see the

314

turbidite

that

includes

ments.

Upsection,

locally

includes

become

chert

and

the sandy chert

and

diabase

turbidite limestone

more and more frequent

the three upper

frag-

Fig. 4). This

sequence beds

(1) The volcanic

that

upward.

(3) The volcanic sequence consists mainly of pillow basalt interbedded with massive basalt flows.

This

volcanic

sequence

is 1~0-15~

m

thick. The more frequent petrologic type is a plagioclase and clinopyroxene rich basalt. A lowgrade metamo~~sm pumpellyite

and

is characterized chlorite.

The

by prehnite,

inter-pillow

sedi-

ments are quite scarce, indicating intense volcanic activity with flows separated by short intervals of inactivity. Microgabbros are frequently found towards the base of massive basalt flows. (4) This sequence is mainly composed of volcanic breccias (agglomerates) and tuffs 600-7~ m thick. stratified.

Beds are frequently thick and poorly The fragments are subangular, seldom

reach a size of 10 cm, and are exposed in very thin beds. Chert, tuff, fine sediment or green aphanitic rocks are also found as fragments, The matrix is generally a fine grained lava or tuff. Other beds occur in thin sequences, and these are thin pyroelastic layers, chert, radiolarite and silicified limestone, Gasteropods were found in the silicified limestone. (5) The lithostrati~ap~c succession of column A of the Rio Calima Unit is overlain by 3000-4000 m thick Giraldo

turbidites.

The

best

area (Fig.

3, cross

section

section

is in

AX) where

sequences

section

it

was studied by Zuluaga (1978). He named this formation “‘miembro arenoso-arcilloso”. It is mainly thickly bedded turbidites which comprise megasequences up to 8-10 m thick. The detrital material is mainly quartz sandstone. Chert, volcanic rock and micaschist fragments are also present. The material is generally poorly rounded indicating a proximal source. The grain size is generally 1 mm. Upsection, the coarsening sandy beds could represent part of a mid-fan environment. Another well exposed section (Fig. 4, column B) of the Rio Calima nappe is located between El Siete and the Quebrada Girardet on the Quibdo traverse (Fig. 3, cross section C,). This cross section does not exhibit the five sequences of the previously described succession; but instead only

breccia

3, 4 and 5 on

some peculiarities:

of sequence

4 is thicker

and the fragments coarser than in the Dabeiba area. (2) There are siliceous limestone and shale between sequences 4 and 5. They outcrop at the Rio El Toro. The siliceous limestone has provided Coniacian near

microfaunas

at the Quebrada

El Siete. (3) Upsection,

La Calera

the coarse

grained

turbidites of sequence 5 exhibit glomerates. In the Quebrada

well rounded La Favorita

rounded

upsection

conglomerates

grade

conthe

to olis-

tostromes which include blocks up to 1 m in size. The matrix of the olistostromes is black shale and the

reworked

blocks

are

gneiss,

quartz,

schist,

black limestone, conglomerate and volcanic rock. Basalt flows are associated with the olistostromes. This section of the Rio Calima nappe exhibits coarser material than the previous cross section of Dabeiba where the fragments of the volcanic breccia sequence 4 and the grain size of turbidite sequence 5 are smaller. Thus the sources for material in El Siete-Quebrada Girardet region more proximal. This is the general situation in Western Cordillera: the volcanic breccia and

the are the the

turbidite coarsen westward. The upper part of the Rio Calima nappe is not exposed in the Loboguerrero region (Fig. 31 cross section

the

(labeled

exhibits

D). There

and its sedimentary

is only

the basaltic

basement

cover of chert (Fig. 4, column

C). Basalt flows exhibit

sparse associated

volcano-

genie sediment. Locally, the sediment provides fossils that are Turonian and Coniacian in age Nelson, 1959; Biirgl, 1961; Barrero, 1979). The basalt flows are overlain by 200-300 m of black cherts. Thus, in the Buga-Buenaventura region the volcanic breccias and the coarse grained turbidite sequences are not known because they have been eroded.

This unit outcrops on the Buga-Buenaventura traverse (Fig. 3, cross section D) around the village of Loboguerrero. The lithology is shown in Fig. 5, and is described below. (1) A 10 m thick white chert resting upon

315

LOBOGUERRERO

WINDOW

U.

DABEIBA-URAMITA

U.

h t

h

EI DOLERITE AN0 BASALT

RIO DAGUA

U.

lkm

Fig. 5. Li~ostrati~ap~c

columns of the lower units. The Loboguerrero window unit (Fig. 3, cross section D), the Dabeiba-Ura~ta

unit (Fig. 3, cross section A, and A*), the Rio Dagua unit (Fig. 3, cross section D). For explanation of numbers i-4,

massive basalt flows, dolerite and gabbro that are interpreted as remnants of oceanic crust as in the other units. (2) Overlying the ophiolitic basement there is a thick segmental sequence (6~-8~ m) mainly composed of tuff and greywacke. Black chert up to 50 m thick is interlayered in this sequence. (3) The tuff and greywacke sequence grades upsection through volcanogenic turbidite and shale to the Espinal Formation, reflecting a gradual introduction of sandy detritus in this area. In this intermediate sequence there are two thick (SO m) basalt flows. (4) The Espinal Formation ranges in age from Coniacian to Santonian (Nelson 1959; Aluja et al., 1975; Bourgois et al., 1982a). Generally this formation begins as a shale-rich section with thinly bedded turbidites, overlain by more sand-rich se-

see the text.

quences of more thickly bedded turbidites. They correspond to a lower fan facies association representing distal turbidites. The overlying thickly bedded turbidites are generally 30-80 cm thick. They commonly exhibit cross laminations and sole marks. Slumps often appear. Thin beds of black cherts appear, sometimes marking the top of a sequence. The thickly bedded turbidite series represents a very fine elastic detritus that consists of reworked volcanic (50%) and sandy material. The upper Espinal Formation probably represents a lower fan en~ronment. The most complete section of the Espinal Formation is 1500-2000 m thick. Lkbeiba- ~ra~i~a unit

The Dabeiba-Uramita unit is well exposed on the Dabeiba traverse (Fig. 3, cross sections A, and

316

AZ).

The

described

lithology

is shown

(1) A basement mainly

in Fig.

5, and

is

below. composed

are few pillow

of volcanic of massive

basalts

rocks

basalt

westward

area, and there is relatively

which

is

in the Dabeiba

abundant

and

above the volcanic

siliceous

Uramita Cenomanian

limestone

area.

The

interlayered

to Turonian

basement,

are well exposed

siliceous

which is commonly

named

limestones

chert

thickness

of

of the turbidite

Dabeibaformation Urrao”.

contact

where

a shear

of the mafic basement

strong

zone.

the mafic

basement The cherts

bedded

black

quence

is about basement

cover of

consists

of white

or black

grade

upsection

to inter-

and grey siliceous

shales.

This se-

100 m thick.

(3) In several localities, mafic

The

is not known.

(2) The basal part of the sedimentary

in the are

age based on the occur-

“miembro

indicates

stretching

metacherts.

rence of Rotalipora appenninica, R. cushmani, Praeglobotruncana coronata and Globotruncana angusticarinata. The Turonian age was first mentioned in this area by Olsson (1956). It is difficult to appraise the thickness of the chert and limestone because of folding. We assume they reach several hundreds of meters. In the upper part of this sequence there are interbedded basalt flows up to 10 m thick. (3) The upper sequence Uramita unit is a fine grained

cover

mineral flows. There

tuff. (2) Resting

rock-sedimentary

cherts which overlie the

are concordantly

overlain

by the

Dagua schist (Fig. 5). It consists of interbedded siliceous phyllites, rare limestones and red and green unit. very thinly clase. main ual

schists which are specific to the Rio Dagua The siliceous phyllite commonly exhibits a fine lamination. It is very fine grained and bedded, with reworked quartz and plagioThe phyllite, quartz and plagioclase are the components of the detrital material. Individbeds

are

subtly

graded.

The

Dagua

schist

probably corresponds to basin plain or lower fan facies associations. A microfauna of Aptian age was found

by Aluja (1975) in the Dagua

schist.

The

most complete section suggests a total thickness of 2000-3000 m. The age of the fine grained turbidite formation is not known. It generally begins with a shale-rich section as in the Espinal Formation. The Dabeiba-Uramita unit grades upward to a section with more interbedded turbidites which reflects gradual introduction of elastic and volcanic detritus. They correspond to lower fan facies associations. The fine-grained turbidite facies is extensive and extends from north to south in the Western Cordillera. The Espinal Formation and the Dagua schist are proposed equivalents to the fine grained turbidite in the Buenaventura region. Rio Dagua unit This unit outcrops along the LoboguerreroBuenaventura road (Fig. 3, cross section D). It is a rock assemblage of low temperature greenschist facies. The lithology is shown in Fig. 5, and is described below. (1) A mafic basement composed mainly of dolerite and massive basalt flows. The mafic material is slightly deformed. Tectonic deformation is generally concentrated at the mafic

Internal tectonic deformation Cordillera tectonic units

of

the

Western

Besides its lithostratigraphy each tectonic unit of the Western Cordillera of Colombia has its own tectonic deformational style. Rio Calima nappe Analysis of tectonic deformation in the Rio nappe is possible where the sedimentary

Calima

polarity can be determined. This is frequently possible in the pillow basalt flows and in the coarse grained turbidites. The Dabeiba (Fig. 3, cross sections A,, A, and As) and Buga-BuenaVentura (Fig. 3, cross section D) sections exhibit large parts of a series that is in normal or in overturned positions. This suggests large recumbent folds. The hinges of such folds were observed in the coarse grained turbidites, on the Quibdo traverse (Fig. 3, cross section C,). To the East of El Siete, axial planes of the recumbent folds plunge towards N320 O. The emplacement of these folds was probably from northwest to southeast.

317

Loboguerrero window unit (Fig. 3, cross section D)

The

first

phase

greenschist The analysis

of the tectonic

deformation

Loboguerrero

window

clear polarity

based on a general

succession

and

in the

unit was easier because

graded

bedding

of a

the

and

nappe

recumbent

window

the character

of Loboguer-

with

of the

window

Rio Calima

unit.

unit, like the Rio Dagua

Each phase

associated

with

has a specific

style,

of which can be identified

throughout

zero (Fig. 3), the mafic basement occurs with its sedimentary cover of cherts. The sequence is in an

the Western Cordillera, from north to south. D, is characterized by isoclinal folds related

upright

a good

position

and exhibits

a 50”

to 70 o west-

to poorly

developed

schistosity

pending

by a thrust fault where the overlying Rio Calima unit is thrust over the Loboguerrero window unit.

exampie S, is well developed in the fine grained turbidites and pelitic facies whereas it is seldom

Eastward Loboguerrero,

observed

basement

also dips

westward.

Dips

range

from

20° to 70*. However, the sedimentary structures indicate a general overturning of the series. The series also exhibits a very flat cleavage which dips gently westward. This fracture cleavage is parallel to drag fold axial planes that are well developed l-l.5 km westward of Loboguerrero. The mafic basement of the Loboguerrero unit outcrops between the two previously described sites. The basement is concordantly overlain by the sedimentary cover. Thus the internal structure of the Loboguerrero window unit is a vast recumbent fold toward the east, the inverted limb being de-

in the cherts

of the original

to

(S, ) de-

ward dip. The upper part of this cover is truncated

in the tectonic window, near the sedimentary cover of the mafic

on the facies

a

of the Rio Dagua

two phases of folding

two sehistosities. in the tectonic

folding

and Loboguerrero

unit exhibits

Espinal

Formation. Westward

contemporaneous

The Dabeiba-Uramita

lithostratigraphic in

unit

was

facies metamorphism

rock.

For

or in the mafic basement.

Isoclinal folds are ten to several hundred metres in size and are frequently observed in fine grained turbidite

and chert. Isoclinal

the thickened similar folds.

folds in chert exhibit

hinges and stretched limbs of other S, is seen to correspond to a bed-

ding-schistosity surface where sedimentary structures are commonly preserved in the fine grain turbidite. Thus the main reference surface in the sedimentary rocks of the. Dabeiba-Uramita and Rio Dagua units is not a simple bedding. The bedding

(S,) is isoclinally

accordion. The mafic folded

basement

during

D,. Folds

folded

to look like an

of basalt

flows was also

are on a regional

scale.

veloped much better than the normal limb. The schistosity of the Loboguerrero window unit generally dips westward; however, it exhibits some

They correspond

variation

to observe the recumbent fold roots. Only the inverted fold hinges are preserved. Thus, the mafic

in dip, indicating

that the schistosity

is

deformed by folding. The recumbent fold structure described above, is regional. It extends 30 km northward of Loboguerrero. This makes it possible to estimate a N40 0 E general trend of the fold axis, consistent with a N130”E emplacement and in good agreement with the previously discussed results about the Upper Rio &lima unit.

Dabeiba-Uramita

and Rio Dagua units

The main tectonic deformation of the Rio Dagua unit occurred in two tectonic phases (the D, and D, tectonic deformations) of folding

accompanied

by the development of a schistosity.

to vast recumbent

folds. In the

Rio Dagua unit (Fig. 3, cross section D) younger phase deformation and erosion make it impossible

basement appears in large inverted masses so that it lies above the sediments (Fig. 3, cross sections A, and D). The inverted fold hinges are the only sites where the original basalt-sedimentary contact is preserved. The limbs of the recumbent folds exhibit shear zones at the sedimentary-mafic basement boundary. The shear zones folded during the second phase of deformation, are related to D,. D, is marked mainly by a crenuiation cleavage (S,) which gives rise to a tectonic layering. This layering is from lo-100 cm thick depending on the facies. It is well developed in the sediment and it does not appear in the mafic basement. In

318

various places (Fig. 3, cross sections A,, C, and D) S, parallels the axial plane of asymmetric folds which are commonly hundreds of meters across. Apparent movement is from west to east. On the other hand, S, also parallels the axial planes of minor folds trending N20 * E-N50 o E. Minor structures such as fold and kink bands also have an eastward vergence. The dip of S, is general of a low angle and it rarely exceeds an average of 30 at however, it occasionally reaches 50 O. A younger folding may explain these variations in the dip. ~eg~~c~res

of the Western Cordillera.

Nappes have been recognized on the BugaBuenaventura traverse (Bourgois et al., 1982a, b). The vergence of these nappes was southeastward. Evidence for such nappes are the large thrust faults separating tectonic sheets that expose different ~thostratigrap~es, tectonic styles and metamorphism. On the other hand, each nappe includes rocks of same age, between 80 Ma and 120 Ma P.B. One of the best examples of low angle thrust faults is associated with the Rio &lima nappe (Figs. 3 and 6, cross section D). It overlies the Loboguerrero tectonic window where the Lobo-

Western

w

Rio &lima

guerrero window unit outcrops under the Rio CaIima nappe. The Quibdo traverse (Figs. 3 and 6, cross section C) exhibits the thrust fault that separates the Rio Calima nappe from the underlying Dabeiba-Ura~ta unit. Three kilometers east of the village of El Siete (Fig. 3, cross section C, ), the coarse grained turbidites of the Rio Calima nappe rest above the fine grained turbidite of the Dabeiba-Ura~ta unit. The fine grain turbidite exhibits two well developed schistosities that are absent in the coarse grain turbidite. Furthermore, 2 km west of the village of El Siete (Fig. 3, cross section C,), a very complete section of the upper Rio Calima nappe is exposed which includes its mafic basement. A similar tectonic relations~p between the Rio Calima nappe and the Dabeiba-Uramita unit has been observed in the Giraldo region (Fig. 3, cross sections A, and A,) where the inverted coarse grained turbidites lie above the fine grained turbidite with its two schistosities. In that region (Fig. 3, cross sections A,, A,, A,) both the Rio &lima nappe and the Dabeiba-Ura~ta unit exhibit complete sections that include their volcanoclastic and mafic basement. Thus several sites on the Dabeiba and Quibdo traverses show that the Rio Calima nappe was

Cordillera

E

Nappe

ioboguerrero Window Unit

Dabeiba_Uramita

O,.,

Fig. 6. Simplified

Unit

5km

cross sections

of the Western

Cordiilera.

Letters

are those of cross sections

A, C, 1), and G of Fig. 3.

319

Central

w

Cordillera

~Oph~ol~tic Obductlon

complex of the 2 Is 70 M Y.J

Ophmlltic Obductlon

complex of the 1 I- 125 M.Y.1

n

Basement and sedimentary of the Central Cord~llera

u

5km

Fig. 7. Simplified

thrust

onto

cross sections

of the Central

the Dabeiba-Uramita

unit.

Cordillera.

On

the

cover

-

Obduction

Letters are those of cross sections

structural

eastern side of the Western Cordillera, a low angle thrust that separates these two units dips eastward whereas on the western side of the Cordillera dips westward. These opposed dips of bedding

Discussion

the eastern

and western

thrusts

are consistent

bent as antiformal

our interpreta-

with

the general dip of bedding in the upper nappe and of S, in the lower unit. The eastward and westward dips define a general antiformal structure of the Western Cordillera. A line of intrusive bodies (Fig. 2) underlines the antiform axis. The intrusive rocks were formed 8-13 Ma B.P. (Toussaint, 1978) which thus dates the antiformal structure of the Western Cordillera. We assume that the western and eastern low angle thrusts are part of the same thrusting event which was subsequently Cordillera acquired its

B, E and F of Fig. 3.

map (Fig. 8) summarizes

tion of the region.

it in

1

the Western shape. The

structures illustrated in Fig. 3 are simplified in Figs. 6 and 7 to show the main tectonic units and nappes of the Western and Central Cordillera respectively. In the north and the south, the Rio Calima nappe rests on the lower units (i.e. Lobogerrero, Dabeiba-Uramita and Rio Dagua units). Thus the general structure of the Western Cordillera is a stack of nappes recently deformed to an antiformal configuration. This explains how: (1) the Rio Calima nappe outcrops on the either side of the Western Cordillera and (2), the lower units are at the core of the Cordillera. A simplified

The Central Cordillera is composed mainly of gneiss and micaschist of Paleozoic to Precambrian age (Hubach, 1957; Nelson, 1959; Irving, 1971; Gansser, 1973; Zeil, 1979). However, mafic and ultramafic rocks associated with sediments outcrop in the Medellin and Yarumal area (Fig. 3, cross section B). The mafic and ultramafic rocks arC peridotite, gabbro, massive basalt and pillow basalt. Barrero (1979), Hall et al. (1972) and Feininger et al. (1972) have considered these rocks to be of local origin with

volcanic

(1974), Toussaint have interpreted quence abducted

as intrusive

flows.

Restrepo

bodies

associated

and

Toussaint

(1978), Bourgois et al. (1985) these rocks as an ophiolitic seonto the Central Cordillera.

From base to top the Yarumal complex (Fig. 9) includes the following lithologies: (1) Serpentinite and peridotite associated with gabbros. (2) Coarse layered gabbro in beds lo-70 cm thick. The coarse grain gabbro frequently exhibits a graded structure. (3) Massive tholeiitic basalt flows and pillow basalts which are associated with cherts, tuffs and

320

andesit~cvalcanism

(Pl~o-Ruaternary)

Ter tlary volcanhz arc

l,“olsedunentary

basin

itonic rock 8to

* j-0 n 13Ma

Eastern Cordillera ~wer Cretaceous to Tertiary) posl-~iaceoe

thrust fautt

Llanos sedimentary cover (Upper Cretaeeous to Q~ate~nar~} basement (Paleozoic and PrecambrianI OPHILITIC

COMPLEX

Upper Unit

(80

to UtJMa 1

(Rio Calima

N.)

Lower Units with 2sckistosity (Qabeiba.Uramits, Loboguerrero and Uagua U.) thrust plane and abduction of Upper Senonian age plutonic

rock 150 to 1OCl Ma

OLD META OPHIOLITIC (OLDER THAN 125 Ma

COMPLEX

1

Rio San Francisco

Nappe

blue schist

)

abduction Platonic

(125 Ma of Lower

1

CrataceDus

age

rock (110 to160 Ma) (I? subduction 1

OPH1OLITIC COMPLEX (UNOIVIDED)

H

Fig,

8. Tectonic

sketch

map

of the “Occidente

Colombiano” (Western and Central Cordilkra).

321

(60 to 80 m.y.) Sedimentary (Albian) Paleozoic Precambrian

YARUMAL

OPHlOLlTlC

cover

and basement

COMPLEX

\M

Gabbro

IT-,l

I

Peridotfte

NNW

____-s

Fig. 9. Simplified geologic map of the Yarumal region (Central Cordillera). Boundaries from Hall et al. (1972). The sequence of the Yarumal ophiolitic complex is that of the Rio Calima nappe.

volcanic agglomerates. (4) Sedimentary rocks (San Pablo Formation) which include sandy turbidites and thinly bedded pelite. The sandy turbidites grade upsection to well rounded polimict conglomerate through coarse sandy turbidite. The pebbles of the conglomerate include quartzite, chert, basalt and gabbro. The matrix is sandy or volcanoclastic material. The age of the San Pablo Formation is not

known, however Hall et al., (1972) established that it is the sedimentary cover of the previously described tholeiitic basalts. Thus the sequence of the Yarumal complex displays a lithostratigraphic succession that is similar to that of the Rio Calima nappe of the Western Cordillera. The Antioquia batholith (60-80 Ma B.P.; Irving, 1971, 1975) intrudes the Yarumal ophiolitic complex (Figs. 8 and 9). A north-south trend-

322

ing fault

network

the primary

slices up the complex,

tectonic

contact

between

ophiolitic

complex

cambrian

rocks of the Central

only northwest cross

of Yarumal.

section

ophiolite

and the Paleozoic

A)

the

complex

micaschist of Ayura-Montebello

and the Pre-

Toussaint,

Cordillera

gabbros

outcrops

of the the gneiss

Yarumal and

the

Valdivia Group and the Group (Botero, 1963; Radelli,

1967; Irving, 1971, 1975; Toussaint, 1978; Feininger, 1982; Bourgois et al., 1984). The flat contact (Fig. 9, cross sections A and B) that separates the two complexes is underlain by a shear zone and

locally

peridotite.

by a tectonic Eastward

slice of serpentinized

of Yarumal

(Fig.

3, cross

section B) the sedimentary cover of the gneiss and the micaschist of the Central Cordillera outcrops. It was described (Hall et al., 1972) as the Soledad Formation. Lower Albian fossil assemblages were documented in the deposits of the Soledad Formation which enters under the Yarumal ophiolitic complex thrust sheet (Fig. 8). The granodiorite of the Antioquia batholith (60-80 Ma B.P.) intrudes both the Soledad Formation and the Yarumal ophiolitic complex (Fig. 3, cross section B). Thus, emplacement of the Yarumal ophiolitic nappe complex occurred during Late Cretaceous or Early Paleocene time, that is to say 60-100 Ma B.P.. We also assume that the Yarumal ophiolite complex originated from the Rio Calima nappe of the Western Cordillera where Santonian microfossils were found.

Thus,

we assume

complex was abducted during Late Senonian 60-80 Ma B.P.. Upper Jurassic-Lower duction 1)

that

the ophiolitic

onto the Central Cordillera or Early Paleocene time

Cretaceous

the Cauca those

In that region (Fig. 9,

rest above the

so that

the Yarumal

abduction

(ob-

ophiolitic

concerning

These

results

lombiano”

history

of the “Occidente

Co-

as the result of only one tectonic

phase

Aptian-Albian

time

(120

Ma-110

phase is inconsistent

the tectonic

observed

evolution

area. In the Jambalo Jambalo

and

the Meso-

B.P.). A single tectonic

glaucophane

and

(Restrepo

1977b) led them to explain

zoic geodynamic during

complex.

the magmatism

area (Fig.

schist outcrops

(Orrego

Ma with

in the Popayan

3, cross section

E)

east of the village of

et al., 1980) on the western

side

of the Central Cordillera. These rocks include albite-quartz-paragonite; glaucophane, garnet, calcite assemblages and quartz, albite, paragonite, muscovite, glaucophane, epidote, chlorite assemblages that indicate a temperature of about 350”-4OO’C and a pressure of 5-7 kbar (Feininger, 1982). K/Ar whole rock analyses show that the blueschists range between 125 + 15 Ma B.P. (Orrego et al., 1980)-104 + 14 Ma B.P. (De Souza et al., 1984). The blueschist has been interpreted by Feininger (1982) as resulting from a Lower Cretaceous subduction metamorphism. The blueschist of Jambalo exhibits a foliation that dips westward. This foliation is marked by a first generation of glaucophane which does not exhibit any trend in the foliation. Thus the main foliation is associated with the high pressure-low temperature metamorphism. However, the glaucophane is not uniformly dispersed and appears in beds that have an original mafic composition (such as basalt and diabase or greywacke) as suggested by Orrego et al. (1976) who considered the Jambalo blueschist part of an ophiolitic complex. It must be noted that glaucophane-rich horizons are interbedded with chlorite-rich schist, amphibolitic schist, quartzite, marble and graphitic

South of Medellin, the Cauca Valley and the western side of the Central Cordillera exhibit outcrops of a metamorphic ophiolite complex. It was described as the Cauca ophiolitic complex by Restrep0 and Toussaint (1973). From radiometric dating (Restrepo and Toussaint, 1974) that indi-

schist, all facies that are known in the Paleozoic Cajamarca Group previously defined by Nelson (1962). That is why we assume that the blueschist of Jambalo did not originate from an ophiolitic complex, but is from the Paleozoic or even older series which forms the Central Cordillera. In the Jambalo region (Fig. 3, cross section E), the San Antonio amphibolite previously described

cated ages from 163 f 10 to 131 f 9 Ma B.P., they proposed a Jurassic to Lower Cretaceous age for

by Orrego et al. (1980), was thrust eastward onto the Jambalo blueschist. The low angle thrust dips

323

westward and is underlain by a thrust sheet of serpentinized peridotite (see cross section). The

Thus, the Paispamba cross section mainly shows a

San Antonio

basement. Unit (2) is a metaop~olite complex which is quite similar to the Rio San Antonio

amp~bo~te

is composed

of meta-

gabbro, metadiabase, metabasalt and metasediment which exhibit a strong foliation. The general

tectonic window exposing the Central Cordillera

nappe whereas unit (1) is an equivalent

to the

dip of the foliation is westward. The mineral association is amp~bolite-epidote metamorphic

Western Cordillera ophiolite nappes. The Paispamba region exhibits the two main

facies.

ophiolite complexes previously defined, both lying

A greenschist previously described as the La Mina greenschist (Orrego et al., 1976; Paris and

over the Central Cordillera basement. The lack of

Marin, 1979) also outcrops eastward of Jambalo.

tion during the second one.

The schists include metadiabase,

metabasalt

blueschist indicates a renewal of the first obduc-

and

metagabbro some of the latter being pegmatitic layered gabbro. All rocks of the La Mina greenschist exhibit a westward dipping foliation. The difference between the La Mina and the San

Geodynamic

histoT

The “Occidente

of the “Occidente Colombiano”

Colombiano”

which forms the

Therefore, the mafic basement complex and the San Antonio quite similar, including their That is why the two complexes

Western Cordillera and part of the Central Cordillera was found to consist of two main ophiolitic complexes. The older one is the Rio San Francisco ophiolitic complex, the age of which is not exactly known. The initial process of obduction (i.e. abduction 1) originated by eastward emplacement onto the Central Cordilleran basement

are grouped into one unit named the Rio San Antonio nappe. The Rio San Antonio nappe is defined as a

during Late Jurassic or Early Cretaceous time (140-90 Ma B.P.). The younger ophiolitic complex is mainly observed in the Western Cordillera and

metaophiolite complex of unknown age. However, we assume that the high pressure-low temperature metamo~~sm of the Jambalo blueschist dates the

subsequently thrust and folded during Late Creta-

Antonio complexes lies only in the abundance of metasediments (metachert, metatuff, metagreywacke and shale). of the La Mina amphibolite are tectonic features.

abduction of the Rio San Antonio ophiolite onto the Central Cordillera. That is to say, it was sometime between 90-140 Ma. Thus, this obduction is older than the abduction (i.e. abduction 2) described in the Yarumal region. Consequently the San Antonio ophiolite complex is older than all the ophiolitic basement of the Western Cordillera nappes, including the Yarumal ophiolitic complex. South of Jambalo, the Paispamba area, (Fig. 3, cross section F) exhibits three mega-units. From base to top there are: (1) the micaschist and the gneiss of the Cajamarca group; (2) amphibolite (on the eastern side, near Paispamba) and metagabbro, metabasalt and metasediment (on the western side) and (3) non-metamorphic gabbros, massive basalt flows and pillow basalts associated with turbiditic sediments. The low-angle thrust fault that separates unit (2) from unit (3) is underlain by a serpentinized peridotite thrust sheet.

includes rocks formed 80-120

Ma B.P.. It was

ceous to Early Paleocene time 68-80 Ma B.P. During the same period, the younger ophiolitic complex was also abducted eastward onto the Central Cordillera basement as exposed in the Yarumal region. This is the second abduction (i.e. abduction 2), in the geodynamic evolution of the “Occidente Coiombiano”. Magmatic bodies intruded the Central Cordillera (Fig. 8). They are commonly interpreted as the consequence of subduction east of the Central Cordillera. Two periods of such subduction are indicated by radiometric ages (Restrepo and Toussaint, 1977a; Toussaint and Restrepo, 1982); one from 50-100 Ma B.P., the other from 110-160 Ma B.P.

Thus abduction

of ophiolitic

material

oc-

curred during the subduction process. Moreover it must be noted that subduction prevailed during a long period (50 Ma) whereas abduction seems to have occurred during a short period (lo-15 Ma). Data on the first abduction are still fragmentary, but the second abduction and related ophio-

_ _ _ ^

of the “Occidente

crust

,, _

_

- -

Island

-

,/,

=”

Upper

^

_

-

breccla

_

MARGINAL

time (75-90

Rio Callma

.

.

^

,,

,.-..

Ma). Note on sketch

N.

BASIN

_

_

^

.,

,

.

^

_

/,_

_.

to be of continental

-

M.Y.

sandy

,,

__

,.

\.

material

-

=

San

COROILLERA

75

material.

CENTRAL

=

nation

of the quartz

COADILLERA

A the coarsening

and Rio Dagua)

SEA

CENTRAL

Baudo island arc is thus inferred

UPPER UNIT

of the Cretaceous

Cretaceous

Volcanic

Nappe

COLOMBIA

SERRANIA BAUD0

Lower Units (Dabeiba_Uramita.Loboguerrero

Rio Calima

The basement

during

Obduction

Subduction

Arc

plate

source.

Colombiano”

--

_

a westward

_

crust

crust:

from east to west indicating

Fig. 10. Evolution

breccia

Obducted

Continental

Oceanic

Baudo

Farallon

W

M.Y.

formation

and of the volcanic

90

Pablo

E

325

lite sequences model

of

are known

well enough

geodynamic

evolution

Cretaceous time (Fig. 10). The Western Cordillera tense alpine-type Senonian main units

to Early

nappe

Calima

folding

was formed

north

the Rio Calima Ma) to Santonian

units.

nappe:

during

time.

The

Cordillera

Cordillera) mented

highest

(1) include

Nappe

Aptian

(120

(2) have a mafic

and uhramafic basement and (3) exhibit a sedimentary cover composed mainly of westward coarsening sandy turbidites. Nappe emplacement was from northwest to southeast (Bourgois et al., 1982a) and the highest, the Rio Calima nappe, has therefore traveled farthest. Thus during Late

time is docuUpper

activity

in the Central

emplacement

Cretaceous

including

Late Cretaceous the well known

Creta-

Cordillera

(Fig. 8), and (2) the volcaniclastic material Upper Cretaceous San Pablo Formation.

the lower

the Loboguerrero

(l),

plutonic

Western

All the units,

(80 Ma) strata;

inLate

during

from

is the Rio

to south

are the Dabeiba-Uramita,

and the Rio Dagua

during

and thrusting

Paleocene

From

a

Late

ceous

of the Western

nappe.

to propose during

Cordillera

to Paleocene

the Serrania America ombia

and

ophiolite

de Baudo

Continent marginal

abduction occurred

time. island

marked

of the of

the

during

Collision

Late

between

arc and the South the end of the Col-

sea. We assume

that

the nappe

emplacement and abduction process indicated Fig. 10 were related with that collision.

in

Acknowledgements

This research was supported by UA 21.5 of the Centre National de la Recherche Scientifique

Cretaceous time (Fig. lo), the lower units (Dabeiba-Urarnita, Loboguerrero and Rio Dagua) were east of the Rio Calima nappe. The litho-

(CNRS-INSU) as well as by the ASP GCodynamique. The U~versidad National sede Medellin

stratigraphy and sedimentology of the volcaniclastic and sandy turbidite material as well as the

and Ingeominas provided a large part of the field logistics. We very much thank Roland Von Huene

petrology and geoche~st~ (Bourgois et al., 1982a, b) of mafic basement indicates a marginal marine

whose discussions manuscripts greatly

environment. Ninety million

work.

Colombia American

years ago this marginal

marginal continental

and comments on earlier helped us to improve this

sea, the

sea, was between the South margin (i.e. basement of the

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