Cretaceous extensional and compressional tectonics

Gondwana Research 66 (2019) 207–226

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Cretaceous extensional and compressional tectonics in the Northwestern Andes, prior to the collision with the Caribbean oceanic plateau S. Zapata a,b,c,⁎, A. Cardona d, J.S. Jaramillo a, A. Patiño a, V. Valencia e, S. León a, D. Mejía a, A. Pardo-Trujillo f, J.P. Castañeda a a

Facultad de Minas, Universidad Nacional de Colombia, Cr. 80 # 65-223, Medellín, Colombia Corporación Geológica ARES, Calle 44A N. 53-96, Bogotá D.C., Colombia Institute of Earth and Environmental Sciences, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany d Departamento de Procesos y Energía, Universidad Nacional de Colombia, Cr. 80 # 65-223, Medellín, Colombia e School of Earth and Environment, Washington State University, Pullman, United States f Instituto de Investigaciones en Estratigrafía-IIES, Universidad de Caldas, Calle 65 N° 26-10, Manizales, Colombia b c

a r t i c l e

i n f o

Article history: Received 29 December 2017 Received in revised form 8 October 2018 Accepted 10 October 2018 Available online 22 November 2018 Handling Editor: R.D. Nance Keywords: Northern Andes Paleogeography Cretaceous Extension Convergent margins Provenance

a b s t r a c t The Cretaceous units exposed in the northwestern segment of the Colombian Andes preserve the record of extensional and compressional tectonics prior to the collision with Caribbean oceanic terranes. We integrated field, stratigraphic, sedimentary provenance, whole rock geochemistry, Nd isotopes and U-Pb zircon data to understand the Cretaceous tectonostratigraphic and magmatic record of the Colombian Andes. The results suggest that several sedimentary successions including the Abejorral Fm. were deposited on top of the continental basement in an Early Cretaceous backarc basin (150–100 Ma). Between 120 and 100 Ma, the appearance of basaltic and andesitic magmatism (~115–100 Ma), basin deepening, and seafloor spreading were the result of advanced stages of backarc extension. A change to compressional tectonics took place during the Late Cretaceous (100–80 Ma). During this compressional phase, the extended blocks were reincorporated into the margin, closing the former Early Cretaceous backarc basin. Subsequently, a Late Cretaceous volcanic arc was built on the continental margin; as a result, the volcanic rocks of the Quebradagrande Complex were unconformably deposited on top of the faulted and folded rocks of the Abejorral Fm. Between the Late Cretaceous and the Paleocene (80–60 Ma), an arc-continent collision between the Caribbean oceanic plateau and the South-American continental margin deformed the rocks of the Quebradagrande Complex and shut-down the active volcanic arc. Our results suggest an Early Cretaceous extensional event followed by compressional tectonics prior to the collision with the Caribbean oceanic plateau. © 2018 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

1. Introduction Accretionary orogens are characterized by continuous long-lived subduction systems and the alternation between extensional and compressional tectonics (Cawood et al., 2009; Royden, 1993; Uyeda and Kanamori, 1979). The accretion of oceanic and continental terranes results in a complex superposition of multiple sedimentary, magmatic, and deformational events (Cawood et al., 2009). The tectonic evolution of the Northern Andes is considered a typical accretionary orogeny related to different phases of extension and compression, in a subduction system active since the Jurassic (Ramos, 1999; Restrepo and Toussaint, 1991; Spikings et al., 2015). The change between contrasting geological configurations have been related to the ⁎ Corresponding author at: University of Potsdam, Institute of Earth and Environmental Sciences, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany. E-mail address: [email protected] (S. Zapata).

accretion of exotic terranes, changes in the relative plate-convergence rates, and variations in the slab subduction angle (Cochrane et al., 2014b; Kerr et al., 1996; Nivia et al., 2006; Restrepo and Toussaint, 1988; Spikings et al., 2015; Villagómez and Spikings, 2013; Zuluaga et al., 2015). However, the tectonic mechanisms and the precise temporal constraints of these extensional and compressional phases remain controversial (e.g. Nivia et al., 2006; Restrepo et al., 2009; Spikings et al., 2015). The Cretaceous tectonic reconstructions proposed for the Northern Andes can be divided into two opposite models summarized in Fig. 2. The first model proposes continuous compression related to the Early Cretaceous accretion of at least one oceanic terrane. This accretionary event was followed by the growth of a Late Cretaceous volcanic arc along the continental edge of the NW South American margin (Spikings et al., 2015; Toussaint and Restrepo, 1996; Villagómez et al., 2011; Villagómez and Spikings, 2013). The second model proposes the existence of an Early

https://doi.org/10.1016/j.gr.2018.10.008 1342-937X/© 2018 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

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S. Zapata et al. / Gondwana Research 66 (2019) 207–226

In this contribution, we present new field observations, sedimentary provenance, geochemical, U-Pb data from the Early Cretaceous volcanosedimentary record and from the Permo-Triassic continental basement exposed between 5°53′N and 5°30′N, in the western flank of the Central Cordillera, in the Colombian Andes. These results together with published data are used to reconstruct the Cretaceous tectonic evolution

Cretaceous extensional continental arc coeval with the formation of a backarc basin (141–115 Ma) (Kennan and Pindell, 2009; Nivia et al., 2006; Spikings et al., 2015; Villagómez et al., 2011). Both models suggest the collision of one or more oceanic terranes with the continental margin between the Late Cretaceous and the Paleocene (80–60 Ma).

GP

Atlantic Ocean

SNM

SMF

SP

GF

RFS

OPF

SM

CPB

CC

MV EC

CV

Fig. 2

WC

RFS

200 km Paleogene plutonic rocks Romeral fault zone (Quebradagrande C. and Arquía C.) Late Cretaceous plutonic rocks

CR

Abejorral Fm and other siliciclastic Cretaceous rocks Eastern Cordillera basin Allochthonous oceanic basement Jurassic igneous rocks Continental basement

Fig. 1. Geological provinces of the Northern Andes. The black square shows the location of the geological map presented in Fig. 2. WC: Western Cordillera; CC: Central Cordillera; EC: Eastern Cordillera; CR: Cordillera Real; CV: Cauca Valley; MV: Magdalena Valley; GP: Guajira Peninsula; SNM: Sierra Nevada de Santa Marta; SP: Serrania de Perija; SM: Santander Massif; CPB: Choco-Panama Block; GP: Garrapatas Fault; RFS: Romeral Fault System; OPF: Otu-Pericos Fault; SMF: Santa Marta Fault.


of the Colombian Andes. Our model suggests an extensional tectonic regime during the Early Cretaceous and constraints the time of the transition into a Late Cretaceous compressional regime coeval with arc magmatism. This transition to compressional tectonics was responsible for the onset of the North Andean compressional tectonic settings, prior to the collision with the Caribbean plateau. 2. Geological framework The Cretaceous tectono-stratigraphic record of the Colombian Andes is exposed along the three main Cordilleras and the intervening river valleys (Cauca and Magdalena Valleys) (Fig. 1). To the east, the Magdalena Valley and the Eastern Cordillera include up to 2 km of Berrasian to Aptian marine siliciclastic rocks deposited in extensional basins (Sarmiento-Rojas et al., 2006) with limited magmatic activity (Vasquez and Altenberger, 2005). These marine siliciclastic sequences are overlain by fine-grained siliciclastic rocks and carbonates deposited in a shallow platform environment. These fine-grained rocks were deposited during a tectonically-quiescent stage after the Albian (Villamil and Pindell, 1999). Subsequently, the stratigraphic record suggests a change to transitional-deltaic and fluvial depositional environments. This change from marine to deltaic and fluvial deposition has been linked to a Late Cretaceous collisional event, between the Great Arc of the Caribbean and the NW of the South American margin (Erlich et al., 2003; Escalona and Mann, 2011; Gomez et al., 2003). The sedimentary record in the Central Cordillera includes discontinuous exposures of Lower Cretaceous siliciclastic rocks deposited on top of a pre-Cretaceous metamorphic and igneous basement (Martens et al.,

A) Spikings et al. 2015 and Villagómez et al. 2013

209

2012; Maya and Gonzalez, 1995; Vinasco et al., 2006) (Fig. 1). The Central Cordillera siliciclastic successions are characterized by coarsegrained rocks deposited in fluvial-deltaic environments overlain by finer grain lithologies deposited in marine conditions. These sedimentary units were deposited between the Berrasian and the Aptian, as the fossil record suggests (Gomez et al., 1995; Gomez et al., 2002; González, 2001; Quiroz, 2005) (Fig. 1). These sedimentary rocks are grouped in several units including the Abejorral Fm., Valle Alto Fm., Aranzazu-Manizales Complex; and the San Luis, Berlín, la Soledad and Segovia sediments (Gomez et al., 1995; González, 2001; Quiroz, 2005). These units have been related to different tectonic settings including a passive continental margin (Gomez et al., 2002; Pardo-Trujillo et al., 2002; Toussaint and Restrepo, 1996), a backarc basin (Nivia et al., 2006) (Fig. 2B), and a foreland basin (Spikings et al., 2015; Villagómez et al., 2011) (Fig. 2A). The Central Cordillera metamorphic basement is composed of low to medium grade meta-sedimentary rocks intruded by Permo-Triassic granitoids and amphibolites; these metamorphic rocks are grouped in the Cajamarca Complex (Gómez et al., 2015; Maya and Gonzalez, 1995). The Cretaceous sedimentary rocks and the metamorphic basement of the Central Cordillera are intruded by several intermediatefelsic plutonic bodies (Fig. 1), including the Antioquia Batholith and the Altavista Stock. These intrusives have yield U-Pb crystallization ages between 90 and 63 Ma (Correa et al., 2006; Ibañez-Mejia et al., 2007; Leal-Mejia, 2011; Villagómez et al., 2011). Different deformed Permo-Triassic to Cretaceous metamorphic and volcano-sedimentary rocks are exposed at the western segment of the Central Cordillera and along the Cauca Valley. These units are limited

B) Spikings et al. 2015, Villagómez et al. 2013 and Nivia et al. 2006

160- 145 Ma

190 - 145 Ma Jurassic arc 145 - 130 Ma

145- 130 Ma Abejorral rift

130 - 115 Ma Quebradagrande arc 125- 100 Ma Quebradagrande rift 115 - 100 Ma Quebradagrande collision

Silvia Pijao San Jerónimo Fault Fault

100 - 80 ma Basin closure

100 - 90 Ma

Spikings et al. 2015 and Villagómez et al. 2013

90 - 80 Ma

75 - 70 Ma, Western Cordillera collision Cauca Almaguer Fault

Late Cretaceous plutonic rocks Quebradagrande Complex Abejorral Fm. Western Cordillera Allochthonous oceanic basement Arquía Complex Jurassic igneous rocks Continental basementt

Fig. 2. Tectonic models proposed for the Cretaceous evolution of the Northern Andes. (A), Compressional tectonic scenario, modified from Spikings et al. (2015), Restrepo and Toussaint (1988), and Villagómez et al. (2011). (B), Extensional tectonic scenario, modified from Villagómez et al. (2011), Spikings et al. (2015) and Nivia et al. (2006).

210


by the faults of the Cauca-Romeral Fault System (RFS) (Figs. 1 and 3) (González, 2001; Maya and Gonzalez, 1995; Restrepo and Toussaint, 1988; Vinasco Vallejo and Cordani, 2012). The San Jerónimo fault (SJF) separates the pre-Cretaceous metamorphic basement of the Central Cordillera from the Cauca Ophiolitic Complex and the Quebradagrande Complex (Alvarez, 1983; Borrero et al., 2012; Maya and Gonzalez, 1995; Pardo-Trujillo et al., 2011; Villagómez et al., 2011) (Figs. 1 and 3). The Cauca Ophiolitic complex is composed of several discontinuous fault-bounded bodies compose of gabbroic plutons, basaltic pillow lavas, and ultramafic rocks; which have been considered as fragments of a dismembered ophiolitic complex. The age of this ophiolite has been assumed as Cretaceous due to its close relation with the Quebradagrande Complex (Alvarez, 1983; González, 1980; Maya and Gonzalez, 1995).

The Quebradagrande Complex includes a series of discontinuous N-S trending deformed basaltic to dacitic lavas and pyroclastic rocks interbedded with mudstones, chert, conglomerates and lithic sandstones (Gomez-Cruz et al., 1995; Gomez et al., 2002; Restrepo-Moreno et al., 2009). The age of the Quebradagrande complex has been constrained between 97 and 120 Ma based on fossil occurrences and two U-Pb zircon ages from a tuff and a dioritic intrusive (Cochrane et al., 2014b; Villagómez et al., 2011). However, younger Campanian-Maastrichtian fossil ages have also been reported in several localities suggesting a more complicated accumulation history (Gomez et al., 2002; González, 1980) (Fig. 3). Tonalitic and gabbroic plutonic bodies intruding the volcanic rocks of the Quebradagrande have U-Pb crystallization ages between 78 and 90 Ma (Jaramillo et al., 2017; Villagómez et al., 2011). Previous tectonic models have related the Quebradagrande

B Jaramillo et al. 2017

A

SJF

Fig 2B

CAF

Fig 4

CAF Cambumbia Stock

SPF

Pacora Stock

SJF

Late Cretaceous plutonic rocks Cauca Ophiolithic Complex Abejorral Fm. and other siliciclastic Cretaceous rocks Arquia Complex Western Cordillera allochthonous oceanic basement Pre-Cretaceous continental basement U-Pb geochronology Geochemestry

Stratigraphic sections in Fig. 5

SJ

F

Quebradagrande Complex

SPF

Miocene and Quaternary units Paleogene plutonic rocks

Upper Cretaceous fossils Lower Cretaceous fossils

Fig. 3. (A). Simplified geological map of the Cauca Valley, the map includes published Cretaceous fossil locations (Gomez et al., 2002; González, 2001; González et al., 1988). Black boxes indicate the location of the study area and the location of the data presented in Jaramillo et al. (2017); (B) geological map from the study area modified from Modified from Gómez et al. (2015) and González (1980); stars represent the collected samples, and the numbered boxes represent the location of the stratigraphic sections presented in Fig. 5. The black box indicates the location of the mapping area presented in Fig. 4. SJF: San Jerónimo Fault; SPF: Silvia Pijao Fault; and CAF: Cauca-Almaguer Fault.


Complex and the Cauca Ophiolitic Complex to the formation of a backarc basin or to an accreted oceanic arc (Cochrane et al., 2014b; Nivia et al., 2006; Toussaint and Restrepo, 1996; Villagómez et al., 2011) (Fig. 2). The Silvia Pijao Fault (SPF) separates the Quebradagrande complex on the east from different Triassic granitic rocks, including the Pacora and the Cambumbia Stocks. Also west of the SPF have been documented Early Cretaceous high to middle-pressure metamorphic rocks grouped in the Arquía Complex (Bustamante et al., 2011b, 2011a; Cochrane et al., 2014a; Maya and Gonzalez, 1995; Ruiz-Jimenez et al., 2012; Vinasco Vallejo and Cordani, 2012). The Triassic granites have been considered as remnants of the continental margin separated during the opening of a back-arc basin (Nivia et al., 2006) (Fig. 2B). The Early Cretaceous metamorphic rocks of the Arquia Complex have been considered as a part of a subduction/accretion complex formed during the growth of the Quebradagrande oceanic arc (Cochrane et al., 2014a; Spikings et al., 2015) (Fig. 2A). Finally, the Cauca Almaguer Fault (CAF) separates the units embedded within the Romeral Fault System from the Cretaceous rocks from the Western Cordillera (Aspden et al., 1987; Barrero, 1979; Kerr et al., 1997) (Figs. 1 and 3). The Western Cordillera basement includes mafic rocks interbedded with deep-marine sedimentary rocks deposited during the formation of an Early Cretaceous oceanic plateau, in a position southwest of the present day position. The volcano-sedimentary basement of the Western Cordillera was intruded by oceanic arc plutons during the Late Cretaceous (Escalona and Mann, 2011; Rodriguez and Zapata, 2013; Villagómez et al., 2011; Weber et al., 2015; Zapata, 2009). This oceanic plateau collided with the northwestern margin of South America between the Late Cretaceous and the Paleocene (Bayona et al., 2011; Escalona and Mann, 2011; Hincapié-Gómez et al., 2018; Pindell et al., 1998; Spikings et al., 2015) (Fig. 2). 3. Methods Geological mapping was carried out in an area of ~60 km (Fig. 4). Representative samples from the Quebradagrande Complex, Abejorral Fm., Cauca Ophiolitic Complex, and the Cajamarca Complex were collected for petrography, U-Pb zircon geochronology, whole rock geochemistry, and Nd isotopes. Complementary cartographic observations and sampling were also conducted up to 50 km south of this area (Fig. 3B). 3.1. Conglomerate clast counting and sandstone petrography Conglomerate clast counting was performed following the ribbon counting method (Howard, 1993). Clasts b 2 cm in size were excluded from the analysis results are presented in Table 1. 300 points were counted in sandstone samples following both the Gazzi-Dickinson and the Indiana methods (Dickinson, 1985). Additional high-resolution petrographic discrimination of quartz was performed according to the methodology proposed by Basu et al. (1975). Petrographic results are presented in Table 2. 3.2. U-Pb geochronology U-Pb geochronology samples include Granitoids from the Cajamarca Complex and volcanic and siliciclastic rocks from the Quebradagrande Complex and the Abejorral Fm. After cathodoluminescence imaging, the Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb analyses were conducted at Washington State University. The analyses were conducted at Washington State University using a New Wave Nd:YAG UV 213-nm laser coupled to a Thermo Finnigan Element 2 single collector, double-focusing, magnetic sector ICP-MS at WSU. Operating procedures and parameters were similar to those of Chang et al. (2006). Laser spot sizes and repetition rates were

211

30–20 μm and 10 Hz, respectively. U and Th concentration were monitored by comparing to NIST 610 trace element glass. In the case of the zircons recovered from magmatic rocks, the analyses were conducted after reviewing cathodoluminescence (CL) analysis, and zircon rims and well-defined cores were used to constrain the zircon crystallization history (Valencia et al., 2005). In detrital samples, only the cores of the grains were analyzed to avoid complex zircon histories (Gehrels et al., 2006). For all samples, probability density plots and weight-average ages were obtained with ISOPLOT 3.62 (Ludwig, 2007). For the detrital samples, only the grains with discordance b 20% and errors b 5% were considered. The volcanic ages were obtained using the grains with the lower errors and avoiding inherited ages. The maximum depositional ages were calculated using a weighted average age from the three youngest zircons that overlap at 2 sigma (Dickinson and Gehrels, 2009). Analytical results are presented in Table A1. 3.3. Whole-rock geochemistry Whole rock chemical analyses were conducted in volcanic and plutonic rocks from the Abejorral Fm. and the Cauca Ophiolitic Complex. Samples were analyzed with an inductively coupled plasma mass spectrometry (ICPMS) at Acme Analytical Laboratories Ltd. in Vancouver, Canada. A 0.2 g aliquot was weighed into a graphite crucible and mixed with 1.5 g of LiBO2 flux. The crucibles are placed in an oven and heated to 1050 °C for 15 min. The molten sample was dissolved in 5% HNO 3. Calibration standards and reagent blanks were added to the sample sequence. Sample solutions were aspirated into an ICP emission spectrograph (Jarrel Ash Atom Comb 975) for determining major oxides and certain trace elements (Ba, Nb, Ni, Sr, Sc, Y and Zr), while the sample solutions are aspirated into an ICP-MS (Perkins–Elmer Elan 6000) for determination of the trace elements, including rare earth elements. The Results are presented in the Table A2. Standard SO-8 were measured (Table A3) with standard deviations of 0.01 for TiO 2 , 0.753 for Nb and 0.739 for Y. 3.4. Nd isotopes The analyses were done on a Thermo-Finnigan Neptune multicollector system at Washington State University in Pullman, and the results are presented in Table 3. The procedures for sample preparation and Nd dilution can be found in Gaschnig et al. (2011). The Sm and Nd isotope analyses followed procedures described in Vervoort and Blichert-Toft (1999). Sm concentrations were corrected using 147 Sm/152Sm: 0.56081, and Nd was corrected for mass fractionation using 146Nd/144Nd: 0.7219 and normalized using the Ames Nd standard (±0.000020 2σ average reproducibility). The εNd values were calculated using present-day values of 143Nd/144Nd: 0.512630 and 147 Sm/144Nd: 0.160 for CHUR (Bouvier et al., 2008). 4. Field observations and petrography Most of the units within the study area record various stages of ductile and brittle deformation, which resulted in highly deformed rocks. The main characteristics of four major units are described from the east to the west as follows (Fig. 4). 4.1. Gneisses, granitoids, and schists Gneisses and schistose rocks with an NW-SE foliation were mapped within the study area (Fig. 4). The gneissic rocks include two different foliated metagranitoids locally known as the Pantanillo and Abejorral gneisses. These gneisses are composed of quartz (4–56%), plagioclase (6–10%), K-feldspar (10–15%), and different amounts of muscovite and biotite with minor sillimanite (24–12%) defining the main foliation.

212


Fig. 4. Geological map and cross-section of the mapping area. White and black stars denote the sample location. SJF: San Jeronimo Fault.

The Abejorral and the Pantanillo gneisses have yield Permo-Triassic UPb zircon crystallization ages (Vinasco et al., 2006). The schists include centimetric to decametric intercalations of chlorite + amphibole

+ feldspar schist with muscovite + quartz + feldspar schists. Both units are included in the Cajamarca Complex (Maya and Gonzalez, 1995), which is the oldest basement of the Central Cordillera.

Table 1 Results of conglomerate clast counting analysis. Unit Lower Abejorral Member Upper Abejorral Member Quebradagrande Complex

Quartz (%)

Sandstones (%)

Mudstones (%)

Chert (%)

Metamorphic (%)

Plutonic (%)

Volcanic (%)

85 32 6

0 16 45

14 16 5

0 0 26

0 25 1

0 2 0

0 9 17


213

Table 2 Sandstone framework analysis. Qm: monocrystalline quartz; Qsed: polycrystalline sedimentary quartz; Qpd: polycrystalline diffuse quartz; Qpf: polycrystalline foliated quartz; Qct: chert; Pl: plagioclase; Fk: orthoclase; Lsl: sedimentary lithic siltstone; Lsl: sedimentary lithic mudstone; Lmm: muscovite metamorphic lithic; Lmb: biotite metamorphic lithic; Lmc: chlorite metamorphic lithic; Lma: amphibolitic metamorphic lithic; Lmn: gneissic metamorphic lithic; Lh: hypabyssal lithic; Lvf: felsic volcanic lithic; Lvv: vitreous volcanic lithic; Msc: muscovite; Cl: chlorite; Px: pyroxene; Bt: biotite; Hm: heavy minerals; opaques; Qp2–3: polycrystalline quartz 2–3 grains; Qp + 3: polycrystalline quartz N3 grains; Qn: non-undulatory quartz; and Qund: undulatory extension quartz. West Abejorral

Lower Abejorral Member

SL-046 Qm (%) Qsed (%) Qpd (%) Qpf (%) Qpoli (%) QCt (%) Pl (%) F (%) Lss (%) Lsl (%) Lmm (%) Lmg (%) Lmb (%) Lmc (%) Lma (%) Lmn (%) Lp (%) Lvf (%) Lvv (%) Lvi (%) Msc (%) Cl (%) PX (%) Bt (%) Hm (%) Op (%)

Upper Abejorral Member


SZ-009F

SZ-009a

AP-005

SZ-009e

SZ-009h

AP-034

AP-036

SZ-022

SZ-027

JPC 002

JPC012

54 1 0 0 9

39 0 2 0 24

40 0 1 0 25

59 0 5 1 11

70 0 3 1 18

42 1 4 0 17

27 1 15 3 11

23 1 15 7 9

58 1 1 0 1

49 0 7 0 21

68 9 0 0 0

58 6 0 0 0

0 0 0 7 8 3 0 0 0 0 0 0 0 0 0 6 10 0 0 0 3

26 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 2 0 2

15 0 3 0 0 0 0 0 0 0 0 0 0 0 0 16 0 0 0 1 0

2 0 3 1 0 5 0 0 0 0 0 0 0 0 0 11 0 0 0 1 0

3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5 0 0 0 0 0

11 0 0 0 0 0 0 0 0 0 0 0 0 0 0 12 0 0 10 1 2

16 1 0 6 6 0 0 3 3 0 0 4 0 0 2 1 0 0 1 0 0

6 2 0 11 1 6 1 0 4 7 1 1 1 0 4 0 3 0 0 0 0

0 0 0 0 0 2 1 0 0 0 0 0 0 2 0 25 0 2 7 1 0

2 0 0 1 0 1 0 0 0 0 2 1 0 2 1 6 0 1 6 0 0

0 5 0 0 0 0 0 0 0 0 0 0 0 0 0 12 0 0 0 0 6

0 19 0 6 0 5 0 0 0 0 0 0 0 0 0 3 0 0 0 0 4

High resolution quartz analysis (Basu et al., 1975) West Abejorral


SL-046

SZ-009F

SZ-009a

AP-005

SZ-009e

SZ-009h

AP-034

AP-036

SZ-022

SZ-027

JPC 002

JPC012

18 38 31 13

17 32 23 27

7 17 27 49

9 18 29 44

20 23 34 23

1 61 16 22

6 58 11 25

1 4 82 13

15 24 40 21

4 3 23 71

4 6 75 16

Qp2–3 (%) Qp + 3 (%) Qn (%) Qund (%)

6 7 6 81


4.2. Abejorral Formation Due to the discontinuous nature of the field exposures and the overimposed deformation (i.e. folding and faulting), we were not able to measure a continuous stratigraphic section within the study area. However, the more representative lithologies of this formation were mapped, sampled, described, and correlated with more continuous published stratigraphic sections, in equivalent structural positions outside of the study area (Figs. 3B and 5). Siliciclastic rocks of the Abejorral Formation can be divided into two informal members. (1) The Lower Abejorral Member includes thick to very thick (0.5–3 m) tabular beds of structureless matrixsupported and poorly-sorted conglomerates, with pebble-sized rounded clasts and a medium-grained sandy matrix, with quartz


as the most abundant component. This member rests on top of the Abejorral gneiss on the east and is overthrusting the schists of the Cajamarca Complex in the west (Fig. 4). (2) The Upper Abejorral Member is mainly composed of thin tabular beds of black mudstones with planar lamination, interbedded with thin levels of medium to fine-grained muddy sandstones and metric levels (1–5 m) of tabular beds of black chert and siliceous mudstones. A series of andesitic lava flows and pyroclastic beds are interbedded with the sedimentary rocks of the Upper Abejorral Member. Additionally, several metric-scale sub-volcanic rocks were observed intruding mudstones of the Upper Abejorral Member. These volcanic rocks exhibit porphyritic and glomeroporphydic textures. Plagioclase is euhedral and is replaced by carbonates. The pyroxenes are replaced by chlorite.

Table 3 Sm-Nd isotopic composition of the Cretaceous igneous rocks from the Central Cordillera. Sample SL-0013 JS-050 DM-017 JS-023 SZ-012

Sm (ppm)

Nd (ppm)

3.02 0.82 1.65 1.41 1.9

8.95 1.7 3.89 3.69 6.95

147

Sm/144Nd

Error abs

0.20430 0.29200 0.25760 0.23090 0.16531

0.000007 0.000024 0.000004 0.000004

143

Nd/144Nd

Error abs

ε(0)

0.513149 0.513215 0.513164 0.513133 0.513046

0.000008 0.000007 0.000008 0.000007

10.12 11.41 10.41 9.812 8.115

T1 (Ma) 100 100 100 100 112

ε(T1) 10.027 10.318 9.679 9.420 8.563


Cobb

Pebb

mS

vcS Gran

vfS

cS

fS

Clay

Grain size Silt

Lithology

Cobb

Pebb

mS

vcS Gran

vfS

E) Section 5

Quebrada Arenosa stratigraphic section Gomez et al.1995

Grain size Clay

Thickness (m)

Cobb

Pebb

mS

vfS

Grain size vcS Gran

Thickness (m)

Cobb

Pebb

vfS fS mS cS vcS Gran

~30 km

D) Section 4

Monteverde stratigraphic section

Thickness (m)

Guayaquil stratigraphic section

Grain size Clay Silt

Lithology

Thickness (m)

Cobb

Pebb

mS

vcS Gran

vfS

cS

Clay

fS

Silt

Lithology

Thickness (m)

Grain si ze

~5 km

C) Section 3

Lithology

~3 km

B) Section 2

Clay Silt

~50 km

A) Section 1

Quebrada Honda stratigraphic section Rio Pozito stratigraphic section

Lithology

214

200

2000

250 200

200

100

Marine shelf

150

100

150

Proximal alluvial

100

50

Shoreface

500

50 0

50

Proximal turbiditic fans

1000

Albian

Proximal alluvial

Marine shelf

200

Marine shelf

Marine shelf

1500

50

Berrasian 10

0

0 0 0

Upper Abejorral Member (110 - 100 Ma). Chert and siliceous mudrock Ammonites

Medium-Fine sandstone

Bivalves

Plant remains

Lower Abejorral Member (130 - 110 Ma).

Mudstone

Coarse sandstone

Cross stratification

Trough stratification

Conglomerate

Planar lamination

Fig. 5. Stratigraphic sections of the Abejorral Fm. and correlatable sedimentary formations north and south of the studied region. The locations of the stratigraphic section are presented in Fig. 3B. The stratigraphic columns are arranged from north to south. The distances between the sections are indicated on the top of the figure.

Deformational structures within the two members include asymmetric folds with rounded hinges accompanied by several NW inverse fault planes dipping to the northeast (Fig. 4). This informal subdivision between Lower and the Upper members can also be applied to the published stratigraphic sections, north and south of the study area (Gomez et al., 1995; Gomez et al., 2002; González, 1980; Quiroz, 2005) (Figs. 3B and 5). Within these stratigraphic sections, the Lower Member is composed of oligomictic quartz-conglomerates interlayered with sandstones and is unconformably accumulated on top of metamorphic rocks of the Cajamarca Complex; abundant plant remains have been described within this member. The Upper Member is composed of fine mudstones and minor siltstones, which include Aptian-Albian gastropods and ammonites (Gomez et al., 2002; González, 1980) (Fig. 5). 4.3. Cauca Ophiolitic Complex This unit is composed of discontinuously exposed gabbroic serpentized peridotites and basaltic rocks in fault-contact with volcano-sedimentary rocks from the Quebradagrande Complex (Fig. 4). This faulted contact is characterized by local mylonitic

fabrics. The gabbros are massive and texturally heterogeneous, varying from fine-grained to pegmatitic. They are composed of plagioclase (28–59%) and augite pyroxene (9–33%), which ophitic and subophitic textures and opaques (1–5%). The pyroxene is replaced by amphibole (hornblende or actinolite). Plagioclase composition is labradorite (An50-An60) but is commonly replaced by pumpellyite and epidote. Intrusive relations with the basaltic rocks and the micaceous schist of the Cajamarca Complex are marked by the presence of small dikes, silicification, and crystal size variations near the contacts. The volcanic rocks are composed of clinopyroxene (35%) with variolitic and ophitic textures commonly replaced by amphibole, saussuritized plagioclase (39%) with labradorite composition (An55) embedded within an aphanitic matrix (6%). The clinopyroxenes exhibit ophitic textures, whereas olivine (3%) is highly altered to serpentine, calcite and chlorite. 4.4. Quebradagrande Complex The volcanic and sedimentary rocks from the Quebradagrande Complex crop out in the western segment of the study area in the Campanas


215

a succession of black shales, chert, very fine grain sandstones, and lava flows. Aptian-Albian fossils have been recognized in the shale levels of this succession (González, 1980) (Fig. 4). Towards the west, this succession has fault contacts with the Triassic plutonic rocks of the Pacora and Cambumbia stocks (Fig. 3B). Farther south similar successions of mudstones, sandstones and basaltic rocks with Albian-Aptian fossils have been described (Alvarez, 1983) (Fig. 3B). These rocks have been included as part of the Quebradagrande Complex (González, 1980; Maya and Gonzalez, 1995). However, the described angular discordance with the Quebradagrande Complex and the temporal constraints suggest that this unit is correlatable with the Abejorral Fm.

creek (Fig. 4). Based on the dominant lithology a volcanic and a sedimentary member can be discriminated. The volcanic member is mainly composed of andesitic and basaltic lava flows locally autobrecciated, with interbedded agglomerates (Fig. 6D). These volcanic beds exhibit porphyritic and glomeroporphiric textures, with plagioclase and pyroxene as phenocrysts in a crystalline or vitreous matrix. Black to gray laminated beds of mudstones are intercalated with these volcanic rocks. Locally these units are found as proto-mylonites and mylonites, with neoformed chlorite and white mica surrounding feldspar porphyroclasts. The sedimentary member is composed of thick beds of sedimentary breccias, coarse-grained to fine-grained conglomeratic sandstones, interbedded with thinner beds of laminated black and gray mudstones.

5. Conglomerate clast counts 4.5. West Abejorral Fm. Clast counts were performed in conglomeratic beds of the Lower and the Upper Abejorral Members and in the Quebradagrande Complex (Fig. 6A, Table 1). The Lower Abejorral Member includes pebble-sized

In the west of the studied area in the Campanas creek, the volcanic rocks of the Quebradagrande Complex are unconformably overlaying

A) Clast Counts

Quartz

Sandstones and conglomerates

Chert

Metamorphic rocks

Mudstones

Volcanic rocks

Quebradagrande Upper Abejorral Lower Abejorral

0%

1:3

L

E

F

hic orp tam me

ic

igh

hic orp tam

Polycrystalline quartz (>3 crystal units per grain)

L Lower Abejorral Member

m-h

me

F


West Abejorral

ton

Volcanic Rifted Margin

Low

ose c Ark Lithi

ose Ark

ite

1:1

aren

Litharenite

3:1

Lith

Feldspathic

F

diu

Sublitharenite

75

Plu

Subarkose

D)

Q

100%

Undulatory quartz

Tra Co nsiti Ba sem nti on ne al en nta tU l Cr pli ft Int aton eri or

Quartz arenite

Me

C)

Q 95

Non-undulatory quartz

B)

Polycrystalline quartz (2-3 crystal units per grain)


LV

Qm Px LM 500 um

500 um

Fig. 6. (A), Clast counts from the Abejorral Fm. and the Quebradagrande Complex; (B), sandstone classification after Folk (1980); (C), rifted margin provenances after Garzanti et al. (2006); (D), quartz classification after Basu et al. (1975); (E), polarized thin section from the Upper Abejorral Fm., sample Ap-009e. Lm: metamorphic lithic and Qm: monocrystalline quartz; (F), polarized thin section from the Upper Abejorral M., sample SZ-027. Lv: volcanic lithic and Px: pyroxene.

216


rounded clasts composed of mudstone (15%) and milky colored quartz (85%). The Upper Abejorral Member is characterized by a more diverse clast composition including milky quartz (32%), sandstones (16%), schistose and gneissic rocks (25%), andesites (9%), and plutonic lithics (2%). The massive angular breccias of the Quebradagrande Complex include sandstone (45%), chert (26%), and volcanic fragments (17%), as well as low contents of milky quartz (6%), mudstones (5%) and micaceous schists (5%).

6. Sandstone petrography Sandstones from the Lower Abejorral Member are poorly to very poorly-sorted, medium to coarse-grained, with angular to subangular grains in a clay matrix (5–15%). Compositionally, the sandstones are classified as quartz-arenites (Fig. 6B and E). They include abundant phyllosilicates such as muscovite, biotite, and chlorite (7–23%) and high contents of mono and polycrystalline quartz (N80%) (Fig. 6B and C). The high-resolution discrimination of quartz after Basu et al. (1975) shows the presence of monocrystalline quartz with undulatory extinction and polycrystalline quartz clasts with more than two grains (Fig. 6D). Sandstones of the Upper Abejorral Member are fine to mediumgrained, with rounded to subrounded grains in a clay matrix (≤15%) and are classified as sub-lithoarenites and lithoarenites (Fig. 6B). Compositionally, the samples include sedimentary lithic (quartz-arenites and mudstones up to (15%), metamorphic lithics (micaceous schists, 8–30%), and lower quartz contents (50–80%) compared to the Lower Member (80–100%). In the quartz type discrimination diagram after Basu et al. (1975), the Abejorral Upper Member shows affinity with both metamorphic and plutonic sources (Fig. 6D, Table 2). A sandstone sample from the West Abejorral Fm. is characterized by poor to moderately sorted material with rounded to subrounded grains and 10–12% of 7 matrix. Compositionally, the sample is classified as a sub-litharenite (Fig. 6B), with mono and polycrystalline quartz characteristic of low to high-grade metamorphic rocks (Basu et al., 1975; Bouvier et al., 2008) (Fig. 6C). We analyzed two sandstone samples of the Quebradagrande Complex. They are fine-grained sandstones, with angular to highly angular spherical grains, moderately sorted and matrix content between 5 and 8%. Compositionally, they are classified as subarkose and lithic arkose (Fig. 6B) and are characterized by the presence of plagioclase (5–19%), sedimentary quartz (6–9%). In the quartz type discrimination diagram after Basu et al. (1975), the Quebradagrande Complex shows affinity with both metamorphic and plutonic sources (Fig. 6D, Table 2).

SL-057, Pacora Stock. 295

7. Geochronology 7.1. Pre-Cretaceous basement U-Pb zircon ages were obtained from igneous rocks located in the westernmost segment of the RFS, immediately west of the Abejorral Formation, the Cauca Ophiolitic Complex and the Quebradagrande Complex (Fig. 3B). A total of 52 individual zircon crystals from the Pácora Stock were analyzed (sample SL-057, Fig. 7). Crystal sizes varied between 30 and 160 μm, with length/width ratios between 1:1 and 1:2. Most of the zircon crystals are characterized by oscillatory and zoned cores with rim overgrowths. Whereas, a portion of the grains is characterized by single oscillatory zoning patterns. Th/U ratios are between 0.2 and 1.55, which is typical of zircons formed in igneous environments (Rubatto, 2002). Twenty-one zircon crystals yielded a weighted age of 260.5 ± 4.7 Ma (MSWD: 5.2), which we interpreted as the time of igneous crystallization of the sample (Fig. 7). Zircons with older ages of 530 Ma, 660 Ma and 1210 Ma ages are considered inherited crystals (Table A1). Sample SG-013 is a granodiorite collected from the Cambumbia Stock (Fig. 3B). Thirty-eight analyzed zircon are characterized by sizes between 50 and 170 μm and are predominantly prismatic with length/width ratios between of 3:1 and 2:1. CL images showed single oscillatory zoning patterns. Th/U ratios are between 0.2 and 0.7; these values are characteristic of igneous zircons (Rubatto, 2002). This rock yielded an age of 232.9 ± 1.2 Ma (MSWD: 1.8), which is considered to be the magmatic crystallization age (Fig. 7). Zircons cores older than 332 Ma, 355 Ma, and 983 Ma are considered inherited ages (Table A1). 7.2. Lower Abejorral Member U-Pb data was obtained from two detrital samples of quartz sandstones and a quartz-conglomerate (Fig. 4). A total of 207 single grain U-Pb ages were obtained from the sample PAN-1. The age distribution is characterized by a major Triassic population of ca. 241 Ma, with minor Jurassic (153 Ma), Paleozoic (537 Ma) and Mesoproterozoic ages (1006.5 and 1189.5 Ma). The youngest population has an age of 149.5 ± 2.7 Ma (Fig. 8). For sample SZ-008, a total of 94 single grain U-Pb ages were obtained. The age distribution is characterized by minor Mesoproterozoic-Neoproterozoic age populations (955 and 1168 Ma) and a major Permian peak (275.8 Ma), which is the youngest population (Fig. 8). 7.3. Upper Abejorral Member Three samples of medium-grained lithic sandstones were analyzed (Fig. 9). A total of 89, 140 and 104 individual U-Pb ages were obtained

SG-013, Cambumbia Stock. 244

n=52

n=38

240

285

236 275

232 265

228 255

224 245

235

220

Mean Age= 260.5 ± 4.7 Ma

100 um 216

Mean Age= 232.9 ± 1.2 Ma

Fig. 7. U-Pb zircon ages and cathodoluminescence images acquired from Pre-Cretaceous basement west of the Silvia Pijao Fault.

100 um


217

SZ-008, Lower Abejorral M.

PAN - 1, Lower Abejorral M.

Max.Dep : 236.1+/- 3.45 Ma

241.5

Max.Dep : 149.5 +/- 2.7 Ma

275.8

n=94

n=207 40

277.5

241.5

153

275

30

30

184.5 127.5

20 153

537

20

1006

10

954

10

1189

1167.6

0 0

500

1000

1500

2000

2500

3000

3500

0

0

Time (Ma)

500

1000

1500

2000

2500

3000

Time (Ma)

SL-046, West Abejorral.

JPC-002, West Abejorral.

Max.Dep : 488.1+/- 18 Ma

265

Max. Dep : 253.3+/- 4.6 Ma

n=92

n=107 556 536 160 20

40

265 1066

30

20

10

1050 10

0 0

500

1000

1500

2000

2500

3000

3500

0

4000

0

Time (Ma)

500

1000

1500

2000

2500

3000

3500

4000

Time (Ma)

Archean Mezoproterozoic (3000 - 1250Ma) a)

Neoproterozoic (1250 - 800 Ma) a)

Neoproterozoic-Paleozoic (350 - 800 Ma) a)

Lower er Creta etaceous eous (150 - 110 Ma) a)

Aptian-Albian (110 - 90 Ma) a)

Coniacian-Santonian (90 - 80 Ma) a)

Paleozoic-Triassic (350 - 200 Ma) a)

Jurassic (200 - 150 Ma) a)

Fig. 8. U-Pb detrital zircon ages acquired in samples from the Lower Abejorral Member and the West Abejorral Fm.; detrital populations are presented for each sample.

from samples AP-33, PAN-2 and SZ-023, respectively. All three samples are characterized by Early Cretaceous zircon U-Pb age populations of 123.5 Ma (sample AP-33), 103.9 Ma (sample PAN-2) and 104.3 Ma (sample SZ-023) (Fig. 9). Older zircon U-Pb ages include relatively similar populations of Premo-Triassic (271.25 Ma and 249 Ma), Paleozoic (463, 512, 520, and 535 Ma). As well as and Paleoproterozoic (1052, 1205, and 1225 Ma), and Archean (3122 Ma) detrital populations (Fig. 9). 7.4. Volcanic rocks of the Upper Abejorral Member Zircons from two andesites interlayered with sandstones and mudstones of the Upper Abejorral Member and one porphyritic intrusive layer were analyzed (Fig. 4). A total of 28 zircon crystals were analyzed from the andesite sample (SZ-012) (Fig. 10). Zircons are between 30 and 250 μm in size. Prismatic zircons have length/width ratios of 3:1. CL images showed a single oscillatory zoning pattern, characteristic of an igneous origin (Vavra et al., 1999). Th/U ratios are between 0.2 and 0.6, these values are characteristic of magmatic zircons (Rubatto, 2002). Twenty-two zircon crystals from this sample yielded a weighted mean age of 103.1 ± 1.5 Ma interpreted as the crystallization age (Fig. 10). Older ages in zircon cores are Triassic (225 Ma and 238 Ma) and Paleozoic (411 Ma) and are interpreted as inherited ages (Table A1). Sample SZ-018 is an andesitic tuff intercalated within the Upper Abejorral Member sedimentary rocks (Fig. 4). Zircon crystal sizes are between 30 and 100 μm, with a length/width ratio of 2:1 for the

prismatic crystals. The zircons showed complex zoned patterns including homogeneous and oscillatory zoning, with Th/U ratios between 0.09 and 0.85. Inherited zircon crystals have ages between 343 Ma and 2240 Ma. The youngest Cretaceous zircons (n: 27) yielded a weighted mean age of 111.5 ± 7.9 Ma interpreted as the magmatic crystallization age (Fig. 10). Sample SZ-011 is a weathered sample that preserves igneous porphyritic textures and intrudes the mudstones and fine-grained sandstones from the Upper Abejorral Member (Fig. 4). Zircon crystals sizes are between 50 and 300 μm, with length/width ratios of 3:1. CL images revealed oscillatory zoning patterns. The Th/U ratios are between 0.2 and 0.6, which is characteristic of magmatic zircons (Rubatto, 2002; Vavra et al., 1999). 16 zircons yielded a weighted mean U-Pb age of 103.5 ± 1.8 Ma interpreted as the magmatic crystallization age (Fig. 10). 7.5. West Abejorral Fm. We analyzed two sandstones and one andesitic lava from this unit, which is overlain in angular discordance by the volcanic rocks of the Quebradagrande Complex (Figs. 3 and 4). A total of 92 single grain UPb ages were obtained from a quartzose sandstone (sample SL-046), the age distribution is characterized by major Neoproterozoic age populations of ca. 556 Ma and 1050 Ma and less abundant Proterozoic to Archean ages (2000–3500 Ma) (Fig. 8). Sample JPC-002 is also a quartzose sandstone. A total of 107 individual zircon U-Pb ages are between 160 and 3339 Ma with major peaks at 160, 263, 535, and 974–1223 Ma (Fig. 8).

218


SZ-023, Upper Abejorral M.

AP-033, Upper Abejorral M. 124.8 154.7

Max.Dep : 104.3 +/- 2.2 Ma

Max.Dep : 123.5+/- 2.3 Ma n=89

124.8

10

105

n=104

105 462.8

12

271.25

255.5

271.2 519.7

8 8

6

1051.7

5

1205.1

512.2

4

1162 1846

3122

1764

4

2 0

0

0

500

1000

1500

2000

2500

3000

0

500

1000

1500

Time (Ma)

PAN-2, Upper Abejorral M.

2500

3000

3500

4000

JPC-008, Quebradagrande C. Max.Dep : 84.0+/- 0.5 Ma

Max. Dep : 103.9 +/- 2.8 Ma

261.8

n=77

103.5

n=140

2000

Time (Ma)

249

18

103.5

261.8

276 535.5

30

239.4

249

10

81.2 20

1225.5 1062 6

10 81.2

1759.5

561.4

1016.4

0

0 0

500

1000

1500

2000

2500

3000

0

3500

500

Time (Ma)

1000

1500

2000

2500

3000

Time (Ma)

Archean Mezoproterozoic (3000 - 1250Ma) a)

Neoproterozoic (1250 - 800 Ma) a)

Neoproterozoic-Paleozoic (350 - 800 Ma) a)

er Creta etaceous eous Lower (150 - 110 Ma) a)

Aptian-Albian (110 - 90 Ma) a)

Coniacian-Santonian (90 - 80 Ma) a)

Paleozoic-Triassic (350 - 200 Ma) a)

Jurassic (200 - 150 Ma) a)

Fig. 9. U-Pb detrital zircon ages acquired in samples from the Upper Abejorral Member and the Quebradagrande Complex; detrital populations are presented for each sample.

Sample M9 is andesitic lava interlayered with the analyzed sandstones from the West Abejorral Fm. (Fig. 4). Zircon crystal sizes are between 50 and 150 μm, with length/width ratios between 2:1 and 3:1. CL images revealed a simple oscillatory zoning pattern. Th/U ratios are between 0.31 and 0.86. Ten zircons yielded a weighted mean age of 115.7 ± 7.7 Ma, which is considered to be the maximum age of crystallization (Fig. 8). Inherited zircon crystals yielded Cretaceous and Jurassic ages (130 to 184 Ma) (Table A1).

7.6. Quebradagrande complex Sample JPC-008 is a quartzose sandstone from the sedimentary member of the Quebradagrande Complex (Fig. 4). A total of 77 individual zircon U-Pb ages have ages between 81 Ma and 2700 Ma, with age peaks at 81, 239, 262 Ma and 1020 Ma (Fig. 9). The youngest detrital zircon age population had a weighted mean age of 84.0 ± 0.5 Ma, which is considered the maximum depositional age. The sample JPC-13 corresponds to an andesitic lava from the Quebradagrande Complex (Fig. 4). Zircon crystals have sizes between 50 and 170 μm, with length/width ratios between 2:1 and 3:1. CL images revealed a single oscillatory zoning pattern and Th/U ratios are between 0.3 and 2.1, which are typical of igneous zircons (Rubatto, 2002). This sample yielded a U-Pb zircon weighted mean age of 83.2 ± 0.7 Ma obtained from 63 zircon crystals, which is considered the magmatic

crystallization age. Older ages in zircon cores yielded Cretaceous and Proterozoic ages considered inherited zircon ages (Fig. 10). Sample SL-029 is a dacitic crystal-rich tuff interlayered with fine to medium-grained sediments from the Quebradagrande Complex (Fig. 3). Zircons have crystal sizes between 60 and 130 μm, with length/width ratios of 2:1. CL images revealed simple oscillatory zoning. Th/U ratios varied between 0.1 and 1.1, which are characteristic of igneous zircons. This rock yielded a U-Pb zircon age of 85.7 ± 0.4 Ma from 86 zircon crystals (Fig. 10), which is interpreted as the age of crystallization. Older ages in zircon cores with Cretaceous, Paleozoic and Proterozoic ages are considered inherited. 8. Geochemistry of volcanic and plutonic rocks Major and trace element geochemistry of the igneous rocks from of the Upper Abejorral Fm. and rocks of the Cauca Ophiolitic Complex are presented in Table A2. Lost on ignition values from the analyzed samples are around 3.6%. Therefore, we have used immobile trace elements (Pearce, 2008) to avoid the possibility of major element and trace element mobility during hydrothermal or low-grade metamorphism. 8.1. Upper Abejorral Member Samples from the Upper Abejorral Member are characterized by SiO2 values between 56.84% and 60.35% with total alkali values (Na2O


219

Fig. 10. U-Pb mean zircon ages acquired in the volcanic rocks of the Upper Abejorral Member and the Quebradagrande Complex. Cathodoluminescence images are presented for each sample.

+ K2O) between 4.18% and 4.99% and are classified as andesites. Fe2O3 values are between 4.89% to 5.07% and the magnesium number (Mg#) between 43.3 and 49.1, which are typical of rocks derived from calcalkaline magmas. Trace element diagrams from these samples also follow an intermediate–calc-alkaline trend in the immobile element ratio-based Nb/Y vs. Zr/Ti and V vs. Ti discrimination diagrams (Fig. 11A and B). Rare earth element (REE) abundances are characterized by a weak enrichment in Light Rare Earth Elements (LREE), with (La/Sm)n ratios between 1.07 and 1.37, a relatively flat trend of the Heavy Rare Earth Elements (HREE), with (Gd/Yb)n values between 1.09 and 1.19, and a negative Eu anomaly between 0.81 and 0.83 (Fig. 11C). Multielemental diagrams normalized to the primitive mantle are

characterized by enrichment in the Large Ion Lithophile Elements (LILE) and a well-defined depletion in High Field Strength Elements (HFSE), including a negative anomaly of Nb and Ti (Fig. 11E). These signatures are characteristic of mantle-derived rocks formed in convergent margins, as is also suggested by the calc-alkaline character of the analyzed samples and the tectonic setting discrimination diagrams (Fig. 11B). 8.2. Cauca Ophiolitic Complex In contrast to the intermediate composition of the volcanic rocks of the Upper Abejorral Member, the volcanic and plutonic rocks of the Cauca Ophiolitic Complex are characterized by a more basic


V(ppm)

0.050

Trachyte

Trachy andesite

r Teph

ipho

nolit

e

site Ande ndesite ltic a

1.0

10

10

1

ites

1

0.1

Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

La Ce Pr

Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

100

E

10 1 0.1

F 10 1 0.1 0.01

0.01 Sr 10.4

10

D

Sample/MORB

100

5

100

C

La Ce Pr

0

Ti(ppm)/1000

Nb/Y

Sample/REE Chondrite

0.001

Sample/REE Chondrite

Quebradagrande C. from Jaramillo et al. (2017)

0.10

0.1

Sample/MORB

Foiditic 0

0.01

Quebradagrande C. from Rodriguez et al. (2016)

100

Alkali basalt

Basalt

300

200

Basa

0.005

Zr/Ti

Rhyolite Dacite

400

Bonin

0.500

Phonolite

100

B

Alkali rhyolite

(a BA nd MO BB sla R B an b-d d ist F al AB )

500

A

IAT (& BA Sla BB b-p an rox d F ima AB l)

220

K

Rb Ba Th Ta Nb Ce P

Zr

Hf Sm Ti

Y

Yb

Sr

12

G

K

Rb Ba Th Ta Nb Ce P

H

10

DM Cauca Ophiolitic Complex

ε Nd

6

ε Nd

Hf Sm Ti

Y

Yb

Andesites Upper Abejorral member

8

9.6

Zr

4

Ophiolitic gabbros Ophiolitic gabbros Ophiolitic basalts Ophiolitic basalts Jurassic arc

2

CHUR

0 -2

9.0

-4 -6 8.4

-8 0.2

0.6

(La/Sm) n

1.0

1.4

0

100

Age (Ma) 200

300

Fig. 11. (A), Nb/Y vs. Zr/Ti rock classification diagram (Pearce, 1996); (B), Ti versus V tectonic discrimination diagram after Shervais (1982). (C), Rare Earth Element (REE) patterns normalized to Chondrite (Nakamura, 1974) from the analyzed volcanic rocks; (D), Rare Earth Element (REE) patterns normalized to Chondrite (Nakamura, 1974) from the analyzed plutonic rocks; (E), NMORB normalized multi-elemental patterns of the analyzed volcanic rocks (Pearce et al., 1984); (F), MORB normalized multi-elemental patterns of the analyzed volcanic rock (Pearce et al., 1984); (G), εNd vs. L/Sm as a monitor of crustal input; (H), εNd values from the analyzed Cretaceous volcanic and plutonic rocks (This study) compare with εNd values from the Jurassic continental arc (Cochrane et al., 2014a; Bustamante et al., 2017; Quandt et al., 2018).

composition and higher TiO2 contents (0.42–0.47% versus 0.66–3.22%) (Fig. 11A). The eight volcanic rocks presented SiO2 values between 43.87% and 52.57% with total alkalis values (Na2O + K2O) of 1.91% to 5.35%, which are both characteristic of basalts. Fe2O3 values ranged between 5.29% to 15.84% and Mg# between 25.5 and 69.6, suggesting that these rocks experienced differentiation. In the Nb/Y vs. Zr/Ti and the Zr

vs. Y diagrams, the rocks are tholeitic basalts with a single sample within the field of andesites (Fig. 11A). REE elements are characterized by negative to horizontal trends in the LREE (Fig. 11C), with (La/Sm)n ratios between 0.37 and 1.07 and a flat trend in the HREE with (Gd/Yb)n between 0.97 and 1.26. Samples also show a weak Eu anomaly (Eu/Eu*: 0.86 to 1.05), with one sample


being characterized by a strong Eu anomaly. The multi-elemental diagram normalized to the primitive mantle showed that the lack of Ti or Nb anomalies with HFSE contents was similar or less abundant than N-MORB (Fig. 11E). The 13 gabbroic samples are characterized by SiO2 values between 48.17% and 50.50% and total alkalis (Na2O + K2O) between 2.23% and 4.87%, which classifies them as gabbros and gabbro-diorites (Middlemost, 1994). MgO and Fe2O3 varied between 7.03% and 10.09% and 5.51% to 11.83%, which is also characteristic of a tholeitic trend. Basic and tholeitic patterns are seen in the Nb/Y vs. Zr/Ti (Fig. 11A). The REE patterns of the gabbroic rocks are characterized by depletion in the LREE (Fig. 11D), (La/Sm)n between 0.37 and 0.94, flat trends in the HREE with (Gd/Yb)n between 0.97 and 1.19, and a negative to strongly positive Eu anomaly (Eu/Eu*: 0.92 to 2.9), which can be attributed to plagioclase fractionation. A slightly negative Nb and a flat trend in the Ti anomaly characterized most of the samples in the multielement patterns. These trends are characteristic of convergent margins with limited sediment and fluid inputs (Fig. 11F). Both the gabbroic and basaltic rocks of the Cauca Ophiolite Complex are characterized by a tholeitic character, a N-MORB REE trend, and weak Nb and Ti anomalies suggesting that these rocks may have formed in a distal position in relation to the slab (Dilek et al., 2007; Pearce, 1996; Taylor and Martinez, 2003). REE and trace element geochemical characteristics from the volcanic rocks of the Cauca Ophiolitic Complex bear strong similarities with the results of other volcanic rocks associated analyzed by Rodríguez et al. (2016), farther south, which are characterized by MORB to E-MORB signatures; and with less evolved Cretaceous samples reported by Jaramillo et al. (2017) to the north (Fig. 11B, C, and E). 8.3. Whole rock Sm-Nd isotopes The Sm-Nd isotope composition for both the volcanic and plutonic rocks from the Upper Abejorral Member and the Cauca Ophiolitic Complex are presented in Table 3. Initial Nd isotope values were calculated from a U-Pb crystallization age of 112 Ma for the Abejorral Formation (sample SZ-018). For the samples from the Cauca Ophiolitic Complex, we assumed the same 100–112 Ma age of the Abejorral Fm. (see Discussion section). The sample of the Upper Abejorral Member is characterized by an initial εNd(t) of +8.6. The volcanic rocks of the Cauca Ophiolitic Complex also presented εNd(t) values of +10.0, which are similar to the three gabbroic rocks from this unit, which yielded initial εNd (t) between +9.4 and +10.32 (Fig. 11H). These values plotted close to the depleted mantle field, which suggests that older crustal input is not significant. The plot of the La/Sm ratios vs. εNd values from the Cretaceous samples can be used to monitor differentiation or increase of the sedimentary input. The values from the Cauca Ophiolitic complex do not fit in any trend. Although, when the value of the Upper Abejorral Member is considered, a trend can be identified. Therefore, it's possible to suggest that magmatic processes associated Upper Abejorral Fm. may record the presence of some crustal input. We also included Sm-Nd isotope results from the Jurassic continental arc rocks emplaced in pre-Jurassic continental crust (Bustamante et al., 2016; Cochrane et al., 2014a; Quandt et al., 2018; Vinasco et al., 2006). The Cretaceous units exhibit a stronger mantle component compare to the Jurassic samples (Fig. 11H). 9. Discussion 9.1. Timing of sedimentation and magmatism in the western flank of the Central Cordillera The integration of field, petrographic, geochemical and geochronological constraints enables the discrimination of coherent Early

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Cretaceous tectono-stratigraphic domains in the study area, which can be used to reconstruct discrete tectonic environments that together provide major insights on the geological evolution of the Northern Andes. Zircon U-Pb detrital ages recovered from the Lower Abejorral Member suggest that this unit is younger than ~150 Ma. Moreover, the volcanic rocks and the detrital zircons of the Upper Abejorral Member and the Western Abejorral succession were deposited age between 115 and 104 Ma (Fig. 2). The composition of the siliciclastic rocks and their association with Early Cretaceous volcanic rocks suggest that the West and the Upper Abejorral units were part of the same or similar sedimentary basins. Previous Aptian-Albian temporal constraints obtained for the Quebradagrande Complex have been established based on the presence of Albian-Aptian fossils and zircon U-Pb ages between 114 and 113 Ma (Arévalo et al., 2001; Gerardo and Arango, 1975; Gomez et al., 2002; Maya and Gonzalez, 1995; Villagómez et al., 2011). U-Pb samples with Aptian-Albian ages seem to be more spatially related to the clastic rocks of the Abejorral Fm. The Lower Cretaceous volcano-sedimentary record described as part of the Quebradagrande Complex in previous publications can be equivalent to the Upper Abejorral Member described in this contribution. Unfortunately, neither our efforts or previous ones have successfully dated the Cauca Ophiolitic Complex. However, this ophiolitic complex is characterized by deformation and metamorphism restricted to local high strain zones and below the greenschist facies. In contrast, Triassic mafic units are metamorphosed and associated with to s-type micaceous granitoids which are also characterized by more negative εNd signatures (Cochrane et al., 2014b; Spikings et al., 2015). A Jurassic volcano-sedimentary protolith is also unlikely since these Jurassic volcanic rocks are also metamorphosed in the amphibolite facies (BlancoQuintero et al., 2014). More geochronological data is necessary; but nevertheless, we favor a Cretaceous origin for Cauca Ophiolitic Complex based on the close relation with the Cretaceous units discussed in this contribution and the aforementioned arguments. Late Cretaceous volcanic rocks with crystallization ages of 83–85 Ma are unconformably deposited on top of the Early Cretaceous West Abejorral Fm. This new Late Cretaceous volcanic crystallization ages in rocks mapped as the Quebradagrande Complex suggest a younger magmatic record for this unit compare to the age proposed by previous authors (Maya and Gonzalez, 1995; Nivia et al., 2006; Spikings et al., 2015; Villagómez and Spikings, 2013) (Fig. 10). These findings are consistent with Upper Cretaceous fossil occurrences (Pardo-Trujillo et al., 2002) (Fig. 3) and with U-Pb zircon ages from plutonic bodies north and south of the study area (Jaramillo et al., 2017; Villagómez et al., 2011) (Fig. 3B). 9.2. Sedimentary provenance The Lower and Upper members of the Abejorral Fm. are characterized by the presence of micaceous schist, gneissic and quartz clasts in the conglomerates and the presence of foliated polycrystalline quartz and undulatory monocrystalline quartz in the sandstones. These provenance modes suggest a metamorphic terrain as a primary source for both members. The relations between the type of monocrystalline quartz and the number of grains of polycrystalline quartz after Basu et al. (1975) in the Lower Abejorral Member suggests that low-grade rocks were a significant portion of this metamorphic source. Detrital zircon age populations in lower member include Triassic (231–246 Ma), Permian (274 Ma), Devonian to early Paleozoic and Proterozoic ages. These age populations are similar to the ages of the Permo-Triassic and the Paleozoic basement rocks exposed in the Central Cordillera and west of the SPF (Cochrane et al., 2014b; Martens et al., 2012; Spikings et al., 2015; Villagómez et al., 2011; Vinasco et al., 2006) (Fig. 3). Conglomerates and sandstones from the Upper Abejorral Member show a decrease in quartz content, an increase of siltstone fragments

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and the apparition of volcanic clasts (Fig. 6B and C). Detrital zircons also have Permo-Triassic and Proterozoic populations and younger AptianAlbian maximum depositional ages (124–100 Ma) compare to the lower member. These younger zircon populations are similar to the age of the intercalated volcanic units suggesting a coexistence of magmatism and sediment deposition. These results suggest that the Permo-Triassic and Paleozoic basement exposed towards the eastern and western limit of the Abejorral Fm. were the main metamorphic sources of both members of the Abejorral Fm. The Upper Abejorral Member was deposited in a basin with coeval volcanism and sedimentary recycling of the coarse-grained Lower Abejorral Member (Fig. 12C). The Upper Cretaceous sandstones and conglomerates of the Quebradagrande Complex show mixed provenance with sedimentary, volcanic and plutonic lithic fragments (Fig. 6B and C). Detrital zircon populations include Permo-Triassic and

A) 80 - 60 Ma

Z

Caribbean plateau collision SPF CAF

older ages similar to ages of the Central Cordillera basement (Fig. 9). The presence of a Late Cretaceous detrital zircon age population (ca. 84 Ma) similar to the magmatic ages of the associated volcanic rocks suggest basin filling coeval or posterior to the volcanic activity (Figs. 8 and 9). 9.3. Tectonic implications Field observations, geochemical data, new temporal constraints, stratigraphy and sediment provenance suggest that the Abejorral Fm. records the development of one or several Early Cretaceous backarc basins along the South American margin (Figs. 12E and 13E). The climax of this extensional event was recorded in these backarc basins during the Albian-Aptian and preserved within the RFS and in the Central Cordillera of Colombia.

Z´

Paleogene plutonic rocks

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C) 110 - 100 Ma Advanced backarc stage OPF SJF

?

?

?

D) 130 - 110 Ma Backarc opening

OPF SJF

E) 180 - 130 Ma Jurassic - Early Cretaceous volcanic arc and backarc

Fig. 12. Proposed tectonic evolution of northwestern South America in the Cretaceous (180–65 Ma). SJF: San Jerónimo Fault; SPF: Silvia Pijao Fault; CAF: Cauca-Almaguer Fault; WC: Western Cordillera; and CC: Central Cordillera. Black arrows denote basement erosion and exhumation.

S. Zapata et al. / Gondwana Research 66 (2019) 207–226 80°0'0"W

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Pre-Cretaceous basement

Fig. 13. Conceptual paleogeographic model illustrating the evolution of northwestern South America during the Cretaceous (140 Ma–65 Ma), modified from the available regional models (Burke et al., 1984; Jaramillo et al., 2017; Kennan and Pindell, 2009; Pindell et al., 2005; Spikings et al., 2015; Toussaint and Restrepo, 1996; Villamil and Pindell, 1999; Vinasco and Cordani, 2012).

The arrangement of the studied units resembles the geometry of an inverted backarc basin. This geometry is defined by continental PermoTriassic blocks in the east and west boundaries of the Cretaceous volcano-sedimentary strata (i.e. Pacora stock, Cambumbia stock, Abejorral gneiss and Pantanillo gneiss) (Cochrane et al., 2014a; Vinasco et al., 2006); several of these blocks were described and/or dated in this contribution (Fig. 3). On both sides of the basin, sedimentary rocks from the Abejorral Fm. were deposited on top of the PermoTriassic basement. In the middle of these continental basement blocks and the siliciclastic strata are the Ophiolitic remnants of the Cauca Ophiolitic Complex; these suprasubduction ophiolitic rocks may be the result of seafloor spreading during advanced stages of the backarc extension (Figs. 12C and 13C). We compiled several stratigraphic columns from the Abejorral Fm. in other localities and correlated them with the observations in the study area (Fig. 3). These sections record a transition from fluvial-

deltaic to a marine depositional environment between 125 and 100 Ma (Gomez et al., 2002; González, 1980; Quiroz, 2005). This transition is marked by an upward-fining and thinning pattern, the appearance of interlayered chert, and the contrast in the fossil record between the Lower and the Upper Abejorral members (Fig. 5). The provenance of the Upper Abejorral member is characterized by continental basement sources, reworked sedimentary sources and by the appearance volcanism coeval with the basin filling. The limited enrichment of LREE recorded and the positive εNd values of the volcanic rocks of the Upper Abejorral member (Fig. 11H) suggest that magmatic interactions with the continental crust were limited, these observations are compatible with the existence of a thinned continental crust and a structural controlled magmatic emplacement. This extended crust provided the space for fast emplacement of magmas at shallow depths, the volcanic rocks in the Upper Abejorral Formation were emplaced in an extended continental crust. The

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MORB to supra-subduction affinity of the Cauca Ophiolitic Complex may represent more advanced stages of backarc basin extension characterized by the formation of oceanic crust (Figs. 12C and 13C). The field relations, the provenance, the transition to marine conditions, the apparition of syn-sedimentary volcanism and the geochemical character of the ophiolitic remnants can be interpreted as the result of the progressive development of a backarc basin. The development of this basin was accompanied by the unroofing of continental horst blocks on both sides of the basin (Figs. 12 and 13). Continental extension and associated magmatism may have continued until the Albian (100 Ma) as suggested by the youngest magmatic ages. This tectonic settings differs from previous models, which have considered that during this time the backarc basin was closed due to the accretion of an oceanic terrane or to major changes in the subduction zone (Cediel and Shaw, 2003; Cochrane et al., 2014b; Spikings et al., 2015; Villagómez and Spikings, 2013) (Fig. 2). These previous models were based on the lack magmatism after 114 Ma and on the coeval cooling/exhumation events in the Central Cordillera basement and in the Arquía Complex. According to these models, the Abejorral Fm. was deposited in a foreland basin. The data presented here show that magmatism was active until 100 Ma; our data also suggest that basin filling is more compatible with an extensional tectonic setting (Figs. 12B and 13B). Therefore, published cooling ages may also be interpreted as extensional-controlled horst exhumation. Regional tectonic models for the western margin of South America typically show an oblique convergence between South America and the Pacific plate during the Early Cretaceous (Burke et al., 1984; Kennan and Pindell, 2009; Pindell et al., 2005; Villamil and Pindell, 1999). Paleomagnetic data of Jurassic rocks and provenance analysis on Oligocene strata indicate at least 500 km of northward displacement of the Central Cordillera; this relative displacement took place during the Meso-Cenozoic from a southern position (Bayona et al., 2010, 2006; Lamus Ochoa et al., 2013). The documented extensional phase was coeval with the northern translation of the studied tectonic blocks. Therefore, it is feasible that these backarc extensional and compressional events had a strike-slip component responsible for the latitudinal translation of these blocks and the subsequent reincorporation to the margin in a different paleogeographic position (Figs. 12B and 13B). Between 86 and 83 Ma, andesitic lava flows and coarse-grained sediments of the Quebradagrande Complex were deposited in an angular unconformity over volcanic and sedimentary rocks of the Abejorral Fm. This Late Cretaceous magmatic arc also includes intrusive facies with ages between 90 and 80 Ma exposed north and south of the study area (Jaramillo et al., 2017; Villagómez et al., 2011) (Fig. 3A). This younger Quebradagrande Complex records the erosion of the older siliciclastic rocks and post-date the closure of the former backarc basin (Figs. 12B and 13B). We proposed a transition to a compressive tectonic setting between 100 and 86 Ma. This compressive tectonic scenario was responsible for the closure of the former backarc basin and the development of a new Late Cretaceous volcanic arc. We also suggest that the large plutonic province that formed the Antioquia Batholith in the Central Cordillera and the Quebradagrande Complex were part of this Late Cretaceous volcanic arc (Figs. 12B and 13B). This transition between extensional and compressional tectonic settings resulted in the onset of the compression in the Northern Andes. Similar Early Cretaceous extensional tectonics and Late Cretaceous compressional tectonics have been extensively documented along the west South-American margin (Baby et al., 2013; e.g. Jaillard and Soler, 1996; Jaimes and de Freitas, 2006; Martini et al., 2013, 2011; Mora et al., 2009; Pindell and Erikson, 1993; Salfity and Marquillas, 1994; Sarmiento-Rojas et al., 2006; Tunik et al., 2010; Viramonte et al., 1999). After the deposition of the Quebradagrande Complex the northern continental margin of South America collided with an intra-oceanic plateau derived from the southeast Pacific as part of the Caribbean plate between the Late Cretaceous and the Paleocene (80–60 Ma) (Hastie and

Kerr, 2010; Kerr et al., 1997; Pindell and Kenan, 2009; Pindell et al., 2005; Spikings et al., 2015; Vallejo et al., 2006; Van Der Lelij et al., 2010; Villagómez et al., 2011) (Figs. 12A and 13A). Previous models have interpreted the Cretaceous evolution of the Colombian Andes as the result of local compressional tectonics due to the accretion of exotic oceanic crust (Cediel et al., 2003; Van Der Lelij et al., 2010; Pindell and Erikson, 1993; Spikings et al., 2015). In contrast, in our model the transition from extension to compression took place prior to the accretion of the exotic oceanic terranes between the Late Cretaceous and the Paleocene. Additionally, the regional extension of these extensional and compressional tectonic settings suggests that the Cretaceous tectonic evolution of the Northern Andes was controlled by plate scale Andean tectonics. 10. Conclusions Integrated field, stratigraphic, provenance, geochemical, and geochronological constraints of the Cretaceous sedimentary, volcanic and plutonic rocks from the western flank of the Central Cordillera of Colombia documents an extensional phase characterized by a transgressive basin filling, sedimentary recycling, and volcanism during the Early Cretaceous (150–100 Ma). The transition from extensional to compressional tectonic settings closed this backarc basin during the Late Cretaceous (100–90 Ma). The volcanic rocks of the Quebradagrande Complex and the Antioquia Batholith were formed in a Late Cretaceous volcanic arc built on top of the deformed backarc basin. A final accretionary event occurred between the Late Cretaceous and the Paleocene due to the accretion of the Caribbean oceanic plateau. Our model documents the onset of Cenozoic compressional tectonics in the Northern Andes prior to the accretion of the Caribbean plateau. Acknowledgments We acknowledge COLCIENCIAS for the financial support to the Corporación Geológica ARES within the program of “Fortalecimiento Institucional” that granted Sebastian Zapata Henao with a scholarship. Funding was also received from the National University of Colombia projects 25452, 25340, 29182, 18593, 24208, and the Fundación para la Promoción de la Investigación y la Tecnología del Banco de la República de Colombia, project 3451. Germán Bayona, Gaspar Monsalve, students from the EGEO research group and those from different courses of field geology in the National University of Colombia are acknowledged for their discussions and help during fieldwork. We acknowledge Paul Mann and the other anonymous reviewers for reviewing this contribution and for all their helpful comments. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.gr.2018.10.008. References Alvarez, J., 1983. Geología de la Cordillera Central y el Occidente colombiano y petroquímica de los intrusivos granitoides Mesocenozóicos. Arévalo, O.J., Mojica, J., Patarroyo, P., 2001. Sedimentitas del Aptiano tardío al sur de Pijao, Quebrada La Maizena, Flanco occidental de la Cordillera Central, Departamento del Quindío, Colombia. Geología Colombiana 26, 29–43. Aspden, J.A., McCourt, W.J., Brook, M., 1987. Geometrical control of subduction-related magmatism: the Mesozoic and Cenozoic plutonic history of Western Colombia. Journal of the Geological Society of London 144, 893–905. Baby, P., Rivadeneira, M., Barragán, R., Christophoul, F., 2013. Thick-skinned tectonics in the Oriente foreland basin of Ecuador. Geological Society of London, Special Publication 377, 59–76. Barrero, D., 1979. Geology of the Central Western Cordillera, West of Buga and Roldanillo, Colombia. vol. 4. Publicaciones Espec. del Ingeominas, pp. 1–75. Basu, A., Young, S.W., Suttner, L.J., James, W.C., Mack, G.H., 1975. Re-evaluation of the use of undulatory extinction and polycrystallinity in detrital quartz for provenance interpretation. Journal of Sedimentary Research 45.

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