Cenozoic contractional reactivation of Mesozoic ... · Cenozoic contractional reactivation of Mesozoic extensional structures in the Eastern Cordillera of Colombia Andre´s Mora,1

Cenozoic contractional reactivation of Mesozoic extensional

structures in the Eastern Cordillera of Colombia

Andres Mora,1 Mauricio Parra,1 Manfred R. Strecker,1 Andreas Kammer,2

Cristina Dimate,3 and Fernando Rodrıguez4

Received 23 May 2005; revised 8 November 2005; accepted 23 January 2006; published 22 April 2006.

[1] The Eastern Cordillera of Colombia is key tounderstanding the role of inherited basementanisotropies in the evolution of active noncollisionalmountain belts. In particular, the Rio Blanco–Guatiquıa region of the Eastern Cordillera isexemplary in displaying a variety of phenomena thatdocument the importance of the orientation, geometry,and segmentation of preorogenic anisotropies. Wedocument the first unambiguous evidence thatextensional basement structures played an importantrole in determining the locus of deformation duringcontractional reactivation in the Eastern Cordillera.Detailed structural field mapping and analysis ofindustry seismic reflection profiles have helped toidentify the inherited San Juanito, Naranjal, andServita normal faults and associated transfer faults asimportant structures that were inverted during theCenozoic Andean orogeny. Apparently, the moreinternal faults in the former rift basin werenot properly oriented for an efficient reactivation incontraction. However, these faults have a fundamentalrole as strain risers, as folding is concentrated west ofthem. In contrast, reactivated normal faults such as themore external Servita fault are responsible for upliftingthe eastern flank of the Eastern Cordillera. In addition,these structures are adjacent and intimately linked tothe development of thin-skinned faults farther east. Inpart, the superimposed compression in this prestrainedextensional region is compensated by lateral escape.The dominant presence of basement involved bucklingand thrusting, and the restricted development of thin-skinned thrusting in this inversion orogen makes theEastern Cordillera a close analog to the intraplate AtlasMountains of Morocco and other inverted sectors ofthe Andean orogen farther south. Citation: Mora, A.,

M. Parra, M. R. Strecker, A. Kammer, C. Dimate, and F. Rodrıguez

(2006), Cenozoic contractional reactivation of Mesozoic

extensional structures in the Eastern Cordillera of Colombia,

Tectonics, 25, TC2010, doi:10.1029/2005TC001854.

1. Introduction

[2] Contractional reactivation of preexisting extensionalanisotropies in the crust is a common feature observed inmany orogens and their forelands [e.g., Coward et al., 1989;Grier et al., 1991; Lowell, 1995; Teixell et al., 2003]. Faultgeometry, thickness of sedimentary basin fills and the widthof the former zone of extension may thus influence the styleand extent of deformation and the overall configuration ofan orogen [Huyghe and Mugnier, 1995; Kley et al., 1999].In fact, in many regions the recognition of reactivatedextensional structures during shortening helped to revealthe salient structural features of mountain belts. Impressiveexamples include the western Alps [Gillcrist et al., 1987;Graciansky et al., 1989; Coward et al., 1991], the SantaBarbara structural province of NW Argentina [Grier et al.,1991; Mon and Salfity, 1995; Kley and Monaldi, 2002] orthe Atlas Mountains of Morocco [Teixell et al., 2003]. For abetter understanding of the spatial and temporal evolution oforogens it is therefore important to consider their structuralframework in the context of preexisting anisotropies andzones of weakness in the crust.[3] With a length of more than 7000 km the Andes

comprise distinct volcanic and morphostructural segmentsthat appear to be correlated with changes in subductiongeometry through time [Jordan et al., 1983; Kay et al.,1999; Ramos et al., 2002]. The importance of preexistingcrustal architecture with respect to Cenozoic tectonics isparticularly impressive in the Santa Barbara [Kley andMonaldi, 2002] and Neuquen Basin structural provincesof Argentina [Manceda and Figueroa, 1995]. In the north-ern Andes, the Eastern Cordillera fold and thrust belt ofColombia (Figures 1 and 2) is an extension of the Andeanorogen located about 500 kilometers away from the plateboundary. Being an integral part of the Andean orogen itcan be expected that plate boundary forces are transmittedto this province far from the trench similar to the case of theSanta Barbara [Kley and Monaldi, 2002] or the AtlasMountains [Teixell et al., 2003]. Therefore a fundamentalproblem is determining, as to what factors exert the primarycontrol on localizing intracontinental deformation and basininversion. In the case of the Santa Barbara province and theAtlas Mountains, for example, the presence of ancient rift

TECTONICS, VOL. 25, TC2010, doi:10.1029/2005TC001854, 2006

1Institut fur Geowissenschaften, Universitat Potsdam, Potsdam,Germany.

2Departamento de Geociencias, Universidad Nacional de Colombia,Bogota Colombia.

3Ingeominas, Bogota, Colombia.4Department of Geology and Geophysics, Texas A&M University,

College Station, Texas, USA.

Copyright 2006 by the American Geophysical Union.0278-7407/06/2005TC001854$12.00

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basins has been suggested to be an essential control deter-mining orogenic processes.[4] The Eastern Cordillera of Colombia spatially coincides

with an extensional Neocomian depocenter that subsequentlyevolved into a contractional orogen, beginning in the lateMesozoic and experiencing sustained tectonic activity intothe present [Colleta et al., 1990; Casero et al., 1997].Previous studies proposed that tectonic inheritance has greatimportance in this mountain belt [Colleta et al., 1990;Caseroet al., 1997; Sarmiento, 2001]. However, these studies werebased on regional compilations that lack evidence of theMesozoic extensional styles and modes of contractionalreactivation of the ancient rift structures in this region.Therefore the precise location of Neocomian extensionalstructures and their role in generating varying deformationstyles, different degrees of shortening, formation of hydro-carbon traps, and neotectonic activity remain speculative.[5] The Rıo Blanco–Guatiquıa region along the eastern

border of the Eastern Cordillera of Colombia is an integralpart of this inverted structural province (Figure 2) andprovides a wealth of exposures of various structural levels,ranging from metamorphic basement and Mesozoic-Paleo-gene cover sediments to poorly lithified Neogene-Quater-nary molasse units (Figures 2 and 3). This region is an idealsetting to evaluate the role of preexisting structure onCenozoic mountain building. Here we document that theinherited anisotropies in the Eastern Cordillera have acritical influence on the location of Cenozoic deformationfronts and the generation of different structural styles. Thisstudy is the result of an extensive field mapping programcarried out between 2002 and 2005 and analysis of selectedsubsurface information made available by petroleum indus-try. The combination of these data sets unambiguously

demonstrates for the first time detailed evidence of thecharacter of basin inversion in this Andean province.

2. Regional Tectonic Setting

[6] The regional tectonic framework of northwesternSouth America is controlled by the complex interaction

Figure 1. Main Cenozoic structures in northwestern SouthAmerica. Modified after Taboada et al. [2000]. See text fordescription.

Figure 2. Generalized geological map of the EasternCordillera. Modified after Cediel and Caceres [1988],Kammer and Mora [1999], and our own observations.Boxes denote the study area and the region where detailedmapping was carried out (Figure 4a). Abbreviations arefrom south to north: UMV, Upper Magdalena Valley; GM,Garzon Massif; QM, Quetame Massif; AOF, Apiay OilField; CD, Chingaza Dome; MS, Medina Syncline; BS,Bogota Savanna; GT, Guaicaramo Thrust; ST, ServitaThrust; EF, Esmeralda Fault; VA, Villeta Anticlinorium;YT, Yopal Thrust; FM, Floresta Massif; BSF, Bucaramanga-Santa Marta Fault; SM, Santander Massif. The CentralSegment of the Eastern Cordillera is the region with majorCretaceous exposures south of the Santander Massif andnorth of the Garzon Massif.

TC2010 MORA ET AL.: IN THE EASTERN CORDILLERA OF COLOMBIA

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between the Caribbean, Nazca and South American plates,as well as the influence of the Baudo-Panama block. Thelatter is the westernmost and last terrain to the northernAndes, and it is composed of oceanic rocks [Duque-Caro,1990] (see Figure 1). The eastward indentation of theBaudo-Panama block during the Late Miocene is consideredto be the driving force responsible for the inversion ofMezosoic rift basins in the present Eastern Cordillera[Taboada et al., 2000]. Inversion of focal mechanismsolutions [Taboada et al., 2000; Corredor, 2003; Dimateet al., 2003] and borehole breakout data [Colmenares andZoback, 2003] suggest that the recent tectonic stress field ischaracterized by a 20�SE oriented SHmax in the EasternCordillera. In contrast, GPS data show more W-E orienteddeformation [Trenkamp et al., 2002]. Cortes et al. [2005]propose a change in the northern Andes stress field fromENE-WSW orientation of SHmax until the Paleocene, to a

NW-SE to WNW-ESE position that has prevailed to thepresent-day.[7] North of 2�N the Colombian Cordillera comprises

three structural branches (Figure 1). An accretionary com-plex of Mesozoic oceanic crust, accreted to South Americaduring Cretaceous-Paleocene time, forms the Western Cor-dillera. Uplifted Precambrian and younger metamorphicrocks, locally covered by Mesozoic sedimentary units,constitute the Central Cordillera. The Eastern Cordilleracomprises the external zone of the Colombian Andes and isseparated from the Central Cordillera by the MagdalenaValley. This intramontane basin is bounded by east vergentthrust faults emerging from the Central Cordillera, and bywest vergent thrusts from the Eastern Cordillera [Butler andSchamel, 1988; Namson et al., 1994; Gomez et al., 2003].[8] The tectonically active Eastern Cordillera (Figure 2)

is bivergent and has an up to 10-km-thick Cretaceous to

Figure 3. Meso-Cenozoic stratigraphy of the eastern flank of the Eastern Cordillera and the RioBlanco–Guatiquıa region.


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Tertiary sedimentary cover in the center, and two regionalbasement exposures at its northern and southern ends,respectively (Figure 2). Structurally, it comprises three seg-ments [Kammer and Mora, 1999]. The southernmostsegment is the Precambrian Garzon basement massif(Figure 2), which is a deformed part of the Guayana Shield[Kroonenberg, 1982]. This sector of the range is fan-shapedin cross section and uplifted by dextrally oblique thrustfaults that are inferred to form a regional-scale positiveflower structure [Chorowicz et al., 1996; Velandia et al.,2005]. The central segment, north of about 4�N, is an axialdepression characterized by a thick Cretaceous and Tertiarycover [Cooper et al., 1995, Figure 2], overlying either upperPaleozoic sedimentary rocks or low-grade pre-Devonianphyllites. The pattern of deformation consists of an inter-nally folded belt without major imbrications and thrusting[Colleta et al., 1990; Kammer and Mora, 1999]. Theexposure of pre-Cretaceous rocks in this sector is restrictedto the Floresta and Quetame basement uplifts. The crystal-line Santander Massif defines the northern segment(Figure 2). On the east it is bounded by the Santa Marta–Bucaramanga Fault (Figure 2), a regional strike-slipfault with paleogeographic significance during the earlyCretaceous synrift phase, when it formed the westernboundary of a depocenter [Toro, 1990].

3. Stratigraphic Framework

[9] Phyllites and quartzites (Quetame Group) constitutethe Quetame Massif and the basement sectors of thesouthern portion of the central segment [Campbell andBurgl, 1965]. These units are unconformably overlain bythe Puente La Balsa Formation [Cortes and de la Espriella,1992], shales and sandstones of Devonian (?) age, about700 m thick. The Puente La Balsa Formation is overlainby Devonian marine to continental sandstones (Areniscasde Gutierrez Formation) of highly variable thickness, reach-ing approximately 2500 m. These units are superseded byCarboniferous red beds (Capas del Valle del GuatiquıaFormation), at least 2000 m thick. Both formations consti-tute the Farallones Group.[10] Paleogeographic and sedimentologic studies in the

Eastern Cordillera [Fabre, 1985; Hebrard, 1985; Colleta etal., 1990; Dengo and Covey, 1993; Cooper et al., 1995;Sarmiento, 2001] suggest a Late Jurassic–Early Cretaceousregional rifting event associated with a megasequence ofterrestrial and marine synrift deposits that overlie basementor Paleozoic units. The southern boundary of this riftdomain is approximately at 4�N, marked by the limit ofdeposition of Berriasian to Barremian age sediments onlap-ping against a paleohigh at the southern end of the studyarea (Figure 4).[11] The basal synrift sequence begins with coarse clastic

units with pronounced facies and thickness changes (Bue-navista Formation, Figure 3 [Dorado, 1992; Mora andKammer, 1999]). These deposits are covered by a succes-sion of marine shales and sandstones of highly variablethickness due to differential tectonic subsidence [Fabre,1985] (Figure 3). In the Rıo Blanco–Guatiquıa region the

maximum thickness of these strata reaches 4000 m. Albianto Cenomanian shallow marine sandstones (Une Forma-tion), about 1000 m thick, cover the inferred rift troughs andadjacent regions and document the onset of postrift thermalsubsidence [Fabre, 1985; Sarmiento, 2001]. The Une for-mation is in turn overlain by Upper Cretaceous marine blackshales (Chipaque Formation) and quartz-sandstones (Gua-dalupe Group), about 2000 m thick. The Guadalupe Groupis superseded by Cretaceous to Paleogene paralic to fluvialinterbedded sandstone and shales ranging between 500 and1500 m in thickness in the western and eastern sectors of thestudy area, respectively.[12] Neogene units, restricted to the synclinal inliers

within the orogen, but much more extensive in the foreland(Figures 2 and 3), comprise coarsening upward continentalstrata, locally 3000 m thick, inferred to be related to lateMiocene uplift and unroofing of the Eastern Cordillera[Cooper et al., 1995].

4. Structural Setting

[13] The thrust faults located along the eastern andwestern mountain fronts (Figure 2) are typically associatedwith hanging wall synclines, which acted as Neogenedepocenters [Cooper et al., 1995]. These basins preservethick Tertiary sequences recording the growth history of theadjacent structures [Gomez et al., 2003], similar to wedge-top basins reported from the Bolivian Andes [e.g., Horton,1998]. At both mountain fronts the wedge-top basins as wellas the thrust faults are arranged in an en echelon pattern.Two basement highs, the Villeta Anticlinorium on the west,and the Quetame Massif (Figure 2) on the east, respectively,separate the frontal thrusts and associated synclines from acentral, topographically elevated structural depression[Julivert, 1970]. This central structure is known as theBogota Savanna (Figure 2), where the majority ofCretaceous to Tertiary strata is preserved. The deformationstyle in the Bogota Savanna, with locally periodic patternsof symmetrical box folds, partially resembles a detachmentfold system [Kammer, 1997; Kammer and Mora, 1999].However, decreasing fold amplitude with depth and anapparent homogenous flattening in the lower part of thecover (as shown by axial plane cleavage) precludes inter-preting them as conventional detachment folds. Kammerand Mora [1999, Figure 4] proposed a geometric model,intermediate between detachment folding and homogenousshortening, to accommodate shortening at depth. In thisgeometric model the amplitudes of the folds observed at thesurface are linearly reduced proportional to the distancefrom the surface outcrop, toward an unfolded basement-cover interface; except in those cases where field datashows that the basement is involved in folding. In our crosssections we adopt the model of Kammer and Mora [1999]to accommodate shortening at depth in the folds of theBogota Savanna.[14] At the eastern mountain front (Figures 2 and 4) the

subdued topographic and structural relief of marginal syn-clinal thrust pairs contrasts with the up to 3000-m-highinternal basement uplifts of the Quetame Massif. This


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relationship is evident where the Servita thrust fault sepa-rates the topographically elevated basement exposures fromthe Medina Syncline (Figure 2), which is bounded by theGuaicaramo thrust to the east. These two faults and theYopal Fault form an en echelon relay pattern (Figure 2).[15] In the Rıo Blanco–Guatiquia region the Servita

Fault (Figure 2) has the longest surface trace and isassociated with the Farallones Anticline, located in itshanging wall (Figures 2 and 4). The northeastward decreasein displacement of the Servita Fault is directly proportionalto the reduction of structural relief of the Farallones Anti-cline in the same direction. The general trend of the jaggedSan Juanito Fault (Figure 4) is parallel to the rectilinearServita Fault. Finally, the Naranjal Fault is located south ofthe San Juanito Fault (Figure 4).

5. Reactivation of Extensional Structures

[16] In the following sections we first demonstrate thesalient characteristics of the most important Mesozoicextensional structures. Secondly, we document that theinversion styles are rather different in each case. Finally,

we discuss possible factors conditioning the different con-tractional response of these structures and present a view ofthe inversion type localities in the context of the regionalevolution of the Eastern Cordillera.

5.1. San Juanito Fault, a Former East DippingNormal Fault

[17] Footwall uplift, before the onset of local depositionof Cretaceous strata, and controlled by the San JuanitoFault, can be interpreted from the presence of differentunits underlying the basal Cretaceous Buenavista Formationon either side of the San Juanito Fault (Figures 4a and 5). Inthe western block the units underlying the basal Cretaceousrocks become progressively younger to the west (Figure 5).The lowest Cretaceous units rest on the Devonian (?) PuenteLa Balsa Formation, about 5 km west of the fault, whereasimmediately next to the fault trace in the western block theyoverlie pre-Devonian phyllites (Figure 5). However, theCarboniferous strata are always below the lowermost Cre-taceous rocks east of the San Juanito Fault (Figure 5).[18] The timing of the San Juanito Fault as a lower

Cretaceous structure can be evaluated by the geometry

Figure 4. (a) Geological map of the Rıo Blanco–Guatiquıa region depicting the cross sections shown in other figures.(b) Sketch with the Lower Cretaceous extensional structural grain in the Rıo Blanco Guatiquıa Region.

Figure 5. Cross section A-A00 (location and legend in Figure 4a). The cross section shows the foldedbelt west of the San Juanito Fault and the relationships illustrating the role of this fault as LowerCretaceous extensional fault, namely, footwall uplift indicated by the eroded upper Paleozoic sequencewest of the fault. The stratigraphic logs above show facies and thickness changes in the basal Cretaceoussequence. See discussion in the text.


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and the character of lower Cretaceous sediments. In theeastern block of the San Juanito Fault, the marine basalshale and carbonate sequence is more than 2.5 km thick;locally, it contains megabreccias sourced from the basementrocks in the western block, whereas a thinner basal terrig-enous sandstone sequence in the former footwall blockonlaps the basement and pinches out (Figures 5 and 6).

5.2. Cenozoic Reactivation of the San Juanito Fault

[19] The present-day structural style of the San JuanitoFault involves an anticline in the footwall (Chingaza

Dome) which terminates as a periclinal structure to thenorth and south (Figures 6, 7, and 8); its hanging wallforms a west dipping monoclinal panel in the unitslocated east of the San Juanito Fault (Figure 8). Foldingaffecting the Cretaceous and older rocks in the ChingazaDome is mostly related to Cenozoic contraction, assuggested by axial planar cleavage associated with thefolds. Folding thus occurred at sufficiently deep levels togenerate a pressure solution planar anisotropy that notonly affected the pelites but also the quartz-sandstonelevels. Interestingly, the southern periclinal termination of

Figure 6. (a) Geological map of the Chingaza Dome showing different facies at each side of the SanJuanito Fault. (b) Detailed cross section (see projected location in Figure 5) showing onlap relationshipsand facial changes in the Lower Cretaceous basal units toward the structural culmination of the ancestralfootwall of the San Juanito normal fault. The sandy facies unit to the east of the Guajaro Fault probablypostdates the fault.


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the Chingaza Dome occurs where the San Juanito Faultends (Figure 8). This shows that the vertical offset of thefault is much more important than the horizontal compo-nent of movement, and that Cenozoic reactivation isminor and only due to folding in the western blocks

(Figure 8). In addition, Lower Cretaceous depositionaland erosional patterns (Figures 5 and 6b) reveal that thepresently uplifted western block was also an area ofpositive relief during lower Cretaceous extension. Crosssections A-A00 (Figure 5), B-B00 (Figure 7) and I-I00

Figure 7. Serial cross sections perpendicular to the San Juanito and Naranjal faults. Notice that the faultrelated paleohigh is in the eastern block for the Naranjal Fault and in the western block for the SanJuanito Fault. Nonetheless, higher amplitude folding is concentrated west of both structures. See locationin Figure 4a and text for discussion.


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demonstrate shorter wavelength folding restricted to thewest of the San Juanito Fault, and a general westwardvergence of the anticlines.

6. Naranjal Fault

6.1. Evidence of Mesozoic Activity

[20] The bends and zigzag map patterns of the NaranjalFault (Figure 4b) are reminiscent of segmented normalfaults in extensional terrains [e.g., Morley, 1995]. Theactivity of the Naranjal Fault before the onset of localdeposition of Cretaceous strata can be assessed by thedifferent pre-Cretaceous rocks underlying the Lower Creta-ceous unconformity at each side of the fault (Figure 4).Lowermost Cretaceous rocks are on top of the Devonianwest of the Naranjal Fault, whereas they overlie Pre-Devonian rocks to the east. Thus the pattern of footwalluplift and erosion before the onset of local deposition ofCretaceous strata is opposite between the San Juanito andNaranjal faults (Figures 4 and 7). The map pattern issuggestive of a conjugate accommodation zone in thetransition between both structures (Figure 4b).

[21] A rapid east-west lateral change from a boulderconglomerate to shaly units in the basal Cretaceous strataof the western block of the Naranjal Fault indicates sedi-ment transport from a structural high in the same direction.[22] The lower Cretaceous Puente Quetame synthetic

normal fault west of the Naranjal Fault has been deducedby extrapolating of the basal Cretaceous unconformity onboth sides of the inferred structure. On the basis of thesurface data it is not possible for the unconformity to reachthe same elevation on both sides. Therefore a normal faultthat delimits an adjacent half graben depocenter and con-trols the maximum thickness of lower Cretaceous sedimentsin the investigated area is proposed (Figure 7, cross sectionD-D00).

6.2. Cenozoic Reactivation of the Naranjal Fault

[23] The fold patterns west of the Naranjal Fault(Figure 9) clearly show fault control. The Puente La BalsaAnticline to the west has a curved axial trace that mimicsthe shape of the Naranjal Fault (Figure 9). The fold traceswest of the Puente La Balsa Anticline are funnel shapedin plan view and converge next to the Naranjal Fault

Figure 8. Structure contour map of the Chingaza Dome, Puente La Balsa Anticline, and FarallonesAnticline. Contours to the basal Cretaceous unconformity. The elevation of the basal Cretaceousunconformity in those areas where it has been eroded away, especially the culmination of the FarallonesAnticline, is determined from down plunge projection of the elevation in areas to the south and northwhere the contact is exposed. The projection was made assuming no major variations in the plunge of thestructures.


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(Figure 9). The dominant eastward fold vergence west of theNaranjal Fault suggests tectonic transport against the base-ment high in the footwall of the main fault (Figure 7). Crosssection D-D00 (Figure 7) shows that most of the shorteningby folding is concentrated west of the Puente Quetamenormal fault. As this fault loses displacement toward thesouth and eventually disappears, the maximum amplitudefold is shifted to the Naranjal Fault in the same way as thelower Cretaceous normal fault displacement is transferred toit (section E-E00). A steadily increasing fold amplitudetoward the basement highs (profile E-E00, Figure 7) westof the Naranjal Fault contrasts with the broad Une Synclinein the westernmost sector of the study area (Figures 4 and7). Interestingly, the down plunge-projected elevation of thelower Cretaceous unconformity in the Puente La BalsaAnticline is still lower than in the adjacent basement higheast of the fault (cross section E-E00 Figure 7). This indicatesthat the structural relief produced by Lower Cretaceousnormal faulting along the Naranjal Fault was not inverted

in contraction. Fold wavelengths are shorter to the west ofthe Naranjal Fault than to the east (Figures 4 and 7). Inaddition, lower Cretaceous extensional folds (Figures 7and 10) were differentially amplified in contraction oneither side of the lower Cretaceous Rıo Blanco Fault, afault located west of the Naranjal Fault, which is virtuallyparallel to the shortening direction. This initially extensionalstructure therefore acted in contraction as a transverse zoneseparating different fold geometries (Figure 10).

7. Servita Fault

7.1. Inherited Pre-Cretaceous and Lower CretaceousStructures

[24] Stratigraphic relations suggest that the hanging wallof the Servita Fault constituted a downdropped fault blockbefore the onset of local deposition of Cretaceous strata; itpreserves up to of 5 km Upper Paleozoic sediments whilethis sequence is absent in the footwall to the east(Figures 4, 11, and 12). The westward thinning of UpperPaleozoic strata is interpreted to be an erosional truncationrelated to activity of the Servita Fault before the onset oflocal deposition of Cretaceous strata (Figure 11, profile K).In addition, the Lower Cretaceous Buenavista Formation ofthe Buenavista Anticline consists of coarse terrigenousconglomerates [Dorado, 1992] that are absent in the out-crops of the lowest Cretaceous rocks in the hanging wall ofthe Servita Fault (Figure 11 cross section K and Figure 12).In addition, the thickness of the Lower Cretaceous rocks, inthe area between the San Juanito and Servita faults, exceeds2000 m and is thus much greater than to the east (Figure 12),where a condensed Berriasian to Barremian interval has athickness of 1000 m. The region between the San Juanitoand Servita faults, also coincides with an area where thePaleozoic sequence is preserved, thus contrasting to struc-tural highs to the east and to the west, where it was originallydeposited but subsequently eroded (Figure 12). These obser-vations indicate differential subsidence associated with theSan Juanito and Servita faults (Figure 12) before the onset ofLower Cretacecous deposition and also during the deposi-tion of most of the synrift sequence, in an area that we termthe Guatiquıa Graben.

7.2. Inversion of the Servita Fault and the GuatiquıaGraben: Farallones Anticline and Mirador FrontalShortcut Thrust

[25] The Farallones Anticline appears to be controlled bythe ancestral Guatiquıa Graben and particularly by theinversion of the Servita Fault. The orientation of the foldaxis of the Farallones Anticline is parallel to the rectilinearServita Fault but also to the internal San Juanito Fault(Figures 2, 4, and 9). Thus its origin might be eithercompletely related to inversion or an extensional rolloverlater amplified in contraction. It evolves from a symmetricanticline to the north coinciding with the area where it issuperposed over the Guatiquıa Graben (Figure 11a), to ahighly asymmetric structure with a steeply dipping fore-limb, coinciding with a southern half graben region

Figure 9. Structural grain and fold patterns in the RıoBlanco–Guatiquıa region. Notice that the general trend ofthe folds is N-S and therefore oblique to the orientation ofthe San Juanito and Servita faults. Near the trace of theServita Fault, structures like the Monfort Anticline under-score the obliquity of most of the folding structures withrespect to the Servita Fault.


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(Figure 11b). Consequently, the degree of symmetry inthe extensional Lower Cretaceous structure fundamentallyconditions the geometry of the inversion structure.[26] Farther east, the Mirador thrust can be inferred from

an exploratory well (Anaconda-1) located in the hangingwall block and documenting a basement wedge overlyingTertiary units. Its geometry is further corroborated byseismic reflection profiles [Narr and Perez, 1993].[27] The presence of coarse conglomerates in the Buena-

vista Formation in the hanging wall of the Mirador Fault hasbeen interpreted by Dorado [1992] to mark high reliefconditions to the east during the Berriasian. However, inthe Apiay oil field, 25 km to the east, there is a much thinner

Cretaceous sequence (Figure 2). This suggests that yetanother Lower Cretaceous normal fault may exist betweenboth places. However, we do not infer a potential low anglepaleo-Mirador normal fault as the boundary fault for thishigh relief which is responsible for the Cretaceous facialchanges; instead this structure is more likely a shortcutgenerated by the Farallones Anticline that pushed from therear during Cenozoic inversion. We therefore suggest that aformer extensional border fault is located east of theMirador Fault, as indicated in cross sections I, K and J(Figures 11 and 12).[28] When comparing the dip of the outcropping units

at each side of the Servita Fault with the rectilinear trace

Figure 10. (a) Detail of the southern part of Figure 4b. The Lower Cretaceous normal fault (Rıo BlancoFault) acts as a transverse zone in contraction as the direction of shortening is almost parallel to the fault.The map and cross sections F, G, H (see Figure 7) show a pre-Buenavista Formation syncline in thesouthern block contrasting with a pre-Buenavista Formation anticline in the northern block. Note thedifferent styles of Cenozoic contractional folding at each side of the fault. (b) Longitudinal cross sectionP-P00 showing that the pre-Cretaceous erosion level at each side of the fault defines a normal fault with thedownthrown block to the south. The fault in contraction separated blocks where extensional folds weredifferentially amplified, but the steeply dipping panel of Devonian rocks in the longitudinal cross sectionshows that in some specific contexts, there is also folding perpendicular to the main structures.


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of the fault itself, it is evident that the fault is dippingsteeper than the units, resulting in a ramp over rampgeometry (Figures 4 and 8). Nonetheless, a steeplydipping fault plane of the Servita Fault is not favorablefor a forward breaking relationship with the Miradorshortcut and a shallower, more frontal horizontal detach-ment on top of the Cretaceous sequence (cross section I,Figure 11). We therefore assume that the fault flattens outat depth.[29] In addition, a gently dipping western panel of the

Farallones Anticline, only disrupted by the San JuanitoFault, can be explained in terms of a long backlimbproduced by displacement along the listric fault plane atdepth of the Servita Fault (cross section I, Figure 11). Theseobservations and the presence of an inferred lower Creta-ceous rift related roll-over anticline (Figure 12) west of theServita Fault are best explained by a deep listric segment of

the Servita Fault that reactivates a former extensionaldetachment (Figures 11 and 12).

8. Along-Strike Inversion Examples

[30] The Guaicaramo thrust fault, a relay of the ServitaFault, has evolved as a more eastern frontal thrust between4� and 4�500N (Figure 2). It can be interpreted as an invertedwest dipping normal fault as it has Lower Cretaceous rocksin its hanging wall that are absent in the footwall forelandblock, where only post-Albian rocks occur (Figures 13–15).There are remarkably different styles of deformation andfolding in the hanging wall of the Guiacaramo Fault. Asouthern segment comprises open folds with gentle limbs,but north of about 4�450 the style changes to tight folds withupright limbs (Figures 13b, 14, and 15). This segmentationcoincides with the segmentation of the basement highs

Figure 11. Regional cross sections through the study area. (a) Section I-I0. Note the marked westwardvergence of the folds west of the San Juanito Fault. The amplitudes of the folds observed at the surfacewest of the San Juanito Fault were linearly reduced proportional to the distance from the surface outcropin section I-I0 toward an unfolded basement-cover interface based on published observations [Kammerand Mora, 1999]. (b) Section K-K0. Note the presence of reactivated normal faults defining half grabenswith the hanging wall block to the NW, contrasting with section I-I0. The easternmost structures in bothcross sections were constrained with a combination of surface geology and seismic reflection profiles.See text for further discussion. See Figure 4a for location.


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inferred from gravimetry (Figure 13). This view is alsosupported by neotectonic structures [Dimate et al., 2003]and seismicity (see Figure 13b).[31] As already pointed out by Rowan and Linares [2000]

based on evidence from seismic information [see Rowanand Linares, 2000, Figures 15 and 16], we suggest that theGuaicaramo Fault south of about 4�450N appears to be adetachment shortcut fault, conditioned by an underlyingundisturbed pre-Cretaceous normal fault (Figure 14), whose

presence is supported by a gravity anomaly below theGuavio Anticline (Figure 13). In contrast, north of 4�450Nthe Guaicaramo Fault appears to have a steeply dippingfault plane as shown by earthquake aftershocks [Dimate etal., 2003, Figure 15]. The hanging wall of this faultapparently overlies an area where the basement is structur-ally in a lower position as suggested by gravity and densitymodeling [Velasquez, 2002]. The tight short wavelengthfolding restricted to the hanging wall at the northern

Figure 12. Regional cross section (location in Figure 4a), showing a Lower Cretaceous graben (theGuatiquıa Graben) defined by normal faults dipping in opposite senses. The Lower Cretaceous timing ofthe different faults is defined by the facies and thickness changes in each faulted block (see thestratigraphic profiles above). The graben is transported by the only reactivated fault, the Servita Fault,which generates a compressional shortcut to the east (Mirador shortcut thrust). The Servita Fault at depthis interpreted based on the presence of a zone of seismicity and the depth inferred when restoring theoriginal position of the Lower Cretaceous unconformity before its movement over the hanging wall of theServita and Mirador faults.


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Figure

13


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segment, reveals that here the fault may have primarilyacted as a buttress like the Naranjal and San Juanito faults(Figures 13 and compare Figure 15 with cross section E inFigure 7), although with a lesser degree of reactivationwhen compared to the Servita Fault/Mirador shortcut.Therefore the Guaicaramo Fault appears to reflect thereactivation of different segments of a former basin bound-ing normal fault array; each segment probably havingdifferent Lower Cretaceous stratigraphic sequences(Figures 14 and 15). The boundary between both segmentsis inferred to be a transverse NNW-SSE striking blindancestral fault, an interpretation supported by the presenceof aligned periclinal terminations along the inferred trace ofthis zone (Figure 13). In addition the aftershocks of the1997 Mw = 6.5 Tauramena earthquake [Dimate et al., 2003]were concentrated along the NW prolongation of thistransverse discontinuity (Figure 13).[32] When viewed in cross section (Figures 14 and 15),

the northern segment appears to accommodate less short-ening than the southern ramp anticline segment. As aconsequence the low angle decollement ramp thin-skinnedstyle of deformation appears to be transferred from the

southern segment of the Guaicaramo Fault to the morefrontal Cusiana and Yopal faults (see Figure 13 and Cazieret al. [1995] and Cooper et al. [1995]).[33] About 36 kmwest of the Guaicaramo Fault, the normal

Esmeralda Fault strikes parallel to the San Juanito Fault(Figures 2 and 14), and probably depicts a change in polaritywith respect to it. It has also been interpreted as a lowerCretaceous normal fault [Rowan and Linares, 2000; Branquetet al., 2002] but evidence collected during our field work andinvestigations by others [Branquet et al., 2002; Rowan andLinares, 2000] do not point toward a significant reactivation,but rather suggest that the fault acted as a buttress. The latterpoint is suggested by the fact that analogous to the Naranjaland San Juanito faults the Esmeralda Fault separates a shorterwavelength folding domain from the wide basement culmina-tion of the Farallones Anticline (Figure 14).

9. Discussion

[34] We have presented evidence that structures generatedduring lower Cretaceous rifting were important in config-uring and conditioning contractional structures and their

Figure 13. (a) Compilation of main structural features and gravimetry showing the segmentation of the Eastern Mountainfront and the location of the inferred inherited anisotropies. The map depicts variations in Bouguer anomaly in mGal [afterVelasquez, 2002]. Gravimetrical lows are in green colors; orange and red colors show gravimetrical highs. (b) Structurecontour map to the top of the Cretaceous and aftershocks of the Tauramena earthquake (the star shows the location of themain shock) showing the different structural styles in two different segments of the Guaicaramo thrust. Note the tightfolding and periclinal terminations in the northern segment and the presence of seismicity just north of these periclinalterminations (see text for further discussion).

Figure 14. Cross section through the Esmeralda Fault, Guavio Anticline, and southern GuaicaramoThrust. The Guavio Anticline is interpreted as a fault bend fold above a Lower Cretaceous normal fault,similar to the interpretation by Rowan and Linares [2000]. For location, see Figures 2 and 13.


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protracted tectonic activity into the present. Reactivation ofpreexisting structures is dependent on several factors thatwill be further assessed below.

9.1. Orientation of Preexisting Structure and Long-Term Cenozoic Strain Patterns

[35] The mechanics of contractional fault reactivation hasbeen analyzed in various studies, based on the Navier-Coulomb criteria for brittle failure [Sibson, 1985; Gillcristet al., 1987; Sibson, 1995; Turner and Williams, 2004].From these investigations it can be concluded that the mainfactor conditioning reactivation is the interaction betweenthe superimposed compressional stresses and the geometryand dip of any preexisting anisotropy.[36] The most important structural relief in the central

segment of the Eastern Cordillera is associated with theinversion of the Servita normal fault, whereas the lesspronounced Naranjal and San Juanito faults are passivelyuplifted in the hanging wall of the Servita Fault, preservingan inherited pattern of extensional structural relief(Figures 11 and 12). Apparently, these faults have actedas buttresses separating a western structural domain where

tight folding is dominant from an eastern area with openfolds and basement thrusts (Figures 7 and 11). Theseobservations underscore that the Mesozoic basement highshave served as rigid backstops where Cenozoic shorteningwas absorbed, similar to structures described in the Appa-lachian Blue Ridge province [e.g., Bailey et al., 2002] or inthe Devonian basins of northern Scotland [cf. Coward et al.,1989, Figure 11]. In these case studies the conventional useof basement buttressing assumes a rheologic contrast be-tween a rigid basement and layered rocks. However, in thearea investigated by us ‘‘basement’’ units appear to beinvolved in buckling in the hanging wall of the inheritednormal faults against the structural highs. We note that thelow degree of metamorphism and the preserved sedimentarytexture of the exposed basement allow it to fold togetherwith the overlying cover. Conversely, adjacent footwalluplifts are cored by crystalline basement units, thereforefavoring the presence of a rheologic contrast. Increasingbedding dip toward the west in the eastern block of the SanJuanito Fault together with concentrated penetrative defor-mation in the steeper dip domain is a remarkable westvergent contractional feature possibly related to back fold-ing and buttressing of the San Juanito Fault, analogous to

Figure 15. Cross section through the folded belt to the west of the northern segment of the GuaicaramoFault. The Guaicaramo Fault angle was inferred with the aftershocks of the Tauramena earthquake[Dimate et al., 2003]. The star shows the main shock. Those aftershocks, defining a roughly eastwarddipping pattern, are inferred to be the prolongation of the transverse zone separating the two foldingdomains. For location, see Figures 2 and 13.


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the Bourg-d’Oisans half graben as described by Gillcrist etal. [1987] and Graciansky et al. [1989].[37] A primary controlling factor for this differential

behavior of extensional structures appears to be faultgeometry. The Servita Fault is rectilinear and has a listricprofile, compared to the more segmented and verticalNaranjal and San Juanito faults (Figures 9 and 11). Thismay have resulted in a reactivation and the formation of ashortcut in the former and locking of the latter.[38] The second important aspect in reactivation is the

long-term Andean strain pattern superimposed on LowerCretaceous structures. There are no published paleostressstudies for the study area. However, the variable struc-tural trends in the Eastern Cordillera (Figure 2) posemajor questions. Can the Cenozoic paleostress orienta-tions obtained in other locations in the orogen [e.g.,Cortes et al., 2005] be inferred to influence this region?Or are the variable structural trends a response to localvariations in the tectonic stress field? An additionalcomplication in answering these questions is that thetiming of the major contractional structures in the studyarea remains unknown due to the lack of datable growthstrata. Given these limitations, we assume for our pur-poses a local shortening direction, perpendicular to themajor fold axes. We furthermore assume that this direc-tion is roughly parallel to the dominant compressionalstresses that acted on this part of the orogen at the timeof contractional deformation. The major fold orientationswest of the Naranjal and San Juanito faults and to thesouth of the study area are N-S (Figure 9). This characterprevails westward in the synclines of the axial zone ofthe Eastern Cordillera between 3.5� and 4.5�N (Figure 2).In contrast, the orientation of the Farallones Anticline,preconditioned by the Guatiquia Graben, is NNE-SSW(Figure 9). This suggests a deviation of the orientation ofthe lower Cretaceous structures and the shortening direc-tion (see also the fold traces terminating obliquely againstthe Servita Fault in its hanging and footwall blocks,Figure 9). We therefore suggest that such an obliquepattern would favor a transpressional reactivation of theServita Fault. Conversely, the Naranjal Fault strikesapproximately parallel to the N-S folds to the west. TheSan Juanito Fault is also oblique at a smaller scale,exemplified by the orientation of the folds immediately tothe west compared to the orientation of the fault itself(Figures 8 and 9). In this case, however, an east dippingfault plane would not be favorably oriented as the dominantvergence of the Cenozoic contractional folds and faults istoward the east (Figure 11). These two factors could havegenerated the final contractional pattern of minor uplift bybuckling in the western blocks of the internal half grabens;in this case the half grabens would have been mainlypassively uplifted by the external Servita Fault. Thusunderthrusting in contraction along a listric Servita Faultwould be the main mechanism that had uplifted the entireeastern mountain front and the internal preexistent halfgrabens. This behavior is reminiscent of the ‘‘interior rampsupported uplifts’’ described by Schmitt and Steidtmann[1990] in northwestern Wyoming.

[39] The angular pattern between Cenozoic fold orien-tations and lower Cretaceous extensional structures is notevident along the eastern mountain front, north of about4�400N (Figure 2). Instead, the principal orientation of theCenozoic folds in the axial zone of the Eastern Cordilleraturns parallel to distal thrusts generally striking NNE-SSW. This structural pattern is compatible with a recentESE-WNW orientation of Shmax inferred from boreholebreakouts, earthquake focal mechanisms, and fault kine-matic data [Colmenares and Zoback, 2003; Corredor,2003; Dimate et al., 2003]. Thus the inherited anisotro-pies along the eastern section of the fold belt north of4�400N are in principle not suitable for a reactivation incontraction. For instance, the northern segment of theGuaicaramo Fault (Figures 2 and 13) is parallel to theAndean fold orientations and perpendicular to the com-pressional patterns. Dimate et al. [2003] argue that areactivation in such a case might be caused by either highfluid pressure or low friction conditions [e.g., Sibson,1995]. Assuming a similar dip angle in comparison toother faults, like the Esmeralda and Naranjal faults, it islikely that this particular case of reactivation might beaided by fluid overpressure [Sibson, 1995].

9.2. Periclinal Terminations and Lateral Escape inContraction

[40] An important aspect of the reactivation of struc-tures in the Cordillera Oriental is the close association ofpericlinal terminations of Cenozoic anticlines and thesegmentation of inherited normal faults. For example,the southern periclinal termination of the Chingaza Domeis located at the termination of the San Juanito Fault,while the northern termination coincides with a significantreduction in displacement of this fault (Figure 8). Inaddition, the northern periclinal termination of the PuenteLa Balsa Anticline coincides with the termination of theNaranjal Fault (Figure 8). In this context the overturnedsouthern termination of the Farallones Anticline against asegment of the Naranjal Fault is remarkable (see Figure 4),suggesting that all of these cases are related to some degreeof nonplain strain deformation. Also folding parallel to theRıo Blanco Fault (see cross section in Figure 10) is expli-cable with lateral escape of material. The backstop effect ofthe Naranjal Fault prompts a N-S extrusion that encounters anew obstacle in the Rıo Blanco Fault, analogous to obser-vations reported from the Alps (Figures 4b and 10) [e.g.,Coward et al., 1991].[41] In the case of the Guaicaramo Fault, the boundary

between the segments north and south of 4�450N is depictedby the change in the style of folding, where the tight folds ofthe northern segment end as periclinals (compare Figures 8and 13b). These periclinal terminations may also be inter-preted as the result of lateral escape, similar to the locationof periclinal terminations controlled by ancestral faultsdiscussed above. In this case, the inferred transverse blindfault separating the southern and northern segments of theGuaicaramo Fault may have acted as a lateral buttress incontraction (Figure 13).


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9.3. Regional Implications and Analogs

[42] Our assessment of the reactivation of inheritedextensional structures during Cenozoic contraction contrastswith previous investigations evaluating the evolution of theEastern Cordillera. For example, Roeder and Chamberlain[1995] argue for a typical thin-skinned thrust belt deforma-tion in this region independent of Neocomian grabenstructures. In addition, they suggest that low angle thrustingalso characterizes the central structure of the Bogota Sa-vanna. Alternatively, Dengo and Covey [1993] proposedinitial Miocene age thin-skinned thrusting overprinted byPlio-Pleistocene out-of-sequence uplift and reactivation ofancestral normal faults. They suggest that the Miocene thin-skinned structural style also applies to the interior of theorogen. Finally, Colleta et al. [1990] pointed out theimportance of inversion tectonics but they did not unequiv-ocally document the presence of ancestral normal faultsbounding Jurassic to Lower Cretaceous depocenters.[43] Our compilation and structural analysis of previously

unmapped areas clearly supports a model of fault inversionfor the Eastern Cordillera of Colombia. Our data documentthe presence of different structural styles in close proximityto each other; from a central folded belt to an external thick-skinned thrust belt that has ultimately evolved into a thin-skinned style of deformation toward the foreland.Deformation in the internal sectors involves buttressingand basement involved buckling and has generated lessstructural relief; this situation differs from conventionalfolding models and is therefore different from the modelinvolving the ubiquitous presence of fault related folds aspreviously suggested [Dengo and Covey, 1993]. We docu-ment that deformation and shortening by thrusting are onlyconcentrated in the external foothill sectors, which spatiallycoincide with the location of recent seismicity [Taboada etal., 2000]. The Rıo Blanco-Guatiquıa region is a typelocality to document an exemplary variety of inversionstyles. Lower Cretaceous extensional faulting appears toguide the evolution of variable structural styles and alsoaids in understanding the nature of the along-strike segmen-tation of the orogen. In addition, the inherited structures alsoappear to be the most important factor conditioning that thisorogen did not evolve into a classic wedge-shaped fold andthrust orogenic wedge geometry. Therefore, in this particularaspect this setting is very similar to the basement coreduplifts of the northernmost Sierras Pampeanas [e.g., Hilleyet al., 2005; E. Mortimer et al., Compartmentalization of aforeland basin in response to plateau growth and diachro-nous thrusting: El Cajon—Campo Arenal basin, NWArgentina, submitted to Geological Society of AmericaBulletin, 2006] or the Santa Barbara province of northwest-ern Argentina [Grier et al., 1991; Mon and Salfity, 1995].

[44] In this context the spatial coincidence of the Neo-comian graben and contractional structures within theorogen, as well as the absence of extremely shortenedinversion structures, such as in the French Alps, makesthe Eastern Cordillera a very close analog to the AtlasMountains of Morocco [e.g., Teixell et al., 2003]. Thissimilarity is further underscored by the fact that shorteningoccurs by basement involved buckling in the internal areas.Basement involved thrusting is restricted to the foothills,which may be conditioned by westward underthrusting ofthe undeformed foreland continental crust, similar to thesituation of the Atlas.[45] Interestingly, in those places in the Eastern Cordil-

lera where Neocomian extensional structures are absent aprominent change in contractional structural style is notable.South of 4�N the Garzon and southern Quetame massifscorrespond to broad asymmetric basement arches. TheGarzon massif is an uplifted part of the Guyana Shieldcrystalline basement, which had not been affected by rifting.West of the Garzon Massif the Upper Magdalena Valleybasin has also a contractional architecture conditioned bytectonic inheritance from a Jurassic rift (M. de Freitas, oralcommunication, 2004), and the exposed prerift substrataeither consist of sedimentary rocks or very low grademetamorphic units as in the Rıo Blanco Guatiquıa region.[46] Viewing our results in light of other structural

provinces in the Andes, the main factors conditioning theextensional structural style, as well as the contractionalinversion are closely related to the nature of the basementand preexistent zones of weakness. In fact, the width ofdeformation, the degree of shortening, the spatial develop-ment of structures, and the locus of ongoing tectonicactivity are fundamentally influenced by the inheritedstructures in the basement rocks. This is a unifiying char-acteristic with respect to other Andean structural provincesthat have experienced similar complex histories of extensionand subsequent and protracted contraction. In conclusion,our study illustrates the fundamental role of inheritedbasement structures in influencing mountain-building pro-cesses and localizing and guiding deformation and uplift incontinental interiors.

[47] Acknowledgments. The authors wish to thank Manuel Julivert,Antonio Teixell, and Jonas Kley for recommendations that improved themanuscript. Fruitful discussions with Rick Allmendinger, Anke Friedrich,Helmut Echtler, Jonas Kley, Ed Sobel, and Dietrich Lange helped focusingour interpretations. Funding was provided by the German ResearchFoundation (DFG STR373/16-1) and Petrobras Colombia. A. Mora andM. Parra are grateful to the German Academic Exchange Service (DAAD)for funding their stay at the University of Potsdam. M. Strecker alsoacknowledges the A. Cox Fund of Stanford University for additionalsupport.


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A. Mora, M. Parra, and M. R. Strecker, Institut furGeowissenschaften, Universitat Potsdam, D-14415,Potsdam, Germany. ([email protected])

F. Rodrıguez, Department of Geology andGeophysics, Texas A&M University, College Station,TX 77843-3115, USA.

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Cenozoic contractional reactivation of Mesozoic ... · Cenozoic contractional reactivation of Mesozoic extensional structures in the Eastern Cordillera of Colombia Andre´s Mora,1