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NEW U-PB GEOCHRONOLOGICAL INSIGHTS INTO THE TECTONIC EVOLUTION OF NORTHWESTERN : THE MESO- NEOPROTEROZOIC PUTUMAYO OROGEN OF AMAZONIA AND IMPLICATIONS FOR RECONSTRUCTIONS

by

Mauricio Ibanez-Mejia

A Prepublication Manuscript Submitted to the Faculty of the

DEPARTMENT OF GEOSCIENCES

In Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE

In the Graduate College THE UNIVERSITY OF ARIZONA 2010

New U-Pb geochronological insights into the Proterozoic tectonic evolution of northwestern South America: The Meso- to Neoproterozoic Putumayo Orogen of Amazonia and its implications for Rodinia reconstructions

Mauricio Ibanez-Mejia

Abstract Outcrops of Meso- Neoproterozoic crust in northwestern South America are restricted to isolated exposures of basement inliers included within the northern of . However, evidence for the existence of an autochthonous Grenville-age belt in northern Amazonia that has not suffered significant disturbance during Andean orogenesis has not been recognized so far. The present contribution reports ~1200 new single-zircon U-Pb geochronological results from Proterozoic rocks of northwestern South America collected from Andean cordilleran inliers, drilling-core samples from the basement, and outcrops of cratonic Amazonia in eastern Colombia (western ). We document the existence of a previously unrecognized Meso- to Neoproterozoic Grenville- age orogenic belt buried under the north , herein termed the Putumayo Orogen, and discuss its implications for Proterozoic tectonic reconstructions involving the northwestern South American margin. Based on the interpretations of our data, we propose a two-stage tectonometamorphic evolution for this orogenic segment characterized by -facies and melting between ca. 1.05 and 1.01 Ga by inferred arc-continent collision during amalgamation of a peri-Amazonian fringing-arc system to the continental margin, shortly followed by final continent- continent collision and –facies metamorphism at ~0.99 Ga. Geochronological and paleogeographic constraints suggest collisional interactions with the Sveconorwegian province of as a feasible tectonic scenario. Previous to the early collisional stage and inception of the Putumayo Orogen, a fringing-arc system was developed outboard of Amazonia’s leading margin during Mesoproterozoic times from ~1.3 to 1.1 Ga. It was within this hypothetical parautochthonous arc system were the protoliths for metaigneous and metavulcanosedimentary units found in the inliers of Colombia and Mexico could possibly have originated, defining a commonly evolving Oaxaquian-Colombian fringing-

1 arc system prior to Rodinia’s final assembly. This interpretation finds further support in the analysis of ~500 detrital zircons from Grenville-age metasedimentary units of the Colombian Andes which reveal that protolith sedimentation occurred during late Mesoproterozoic times and was exclusively derived from erosion of Mesoproterozoic sources. Contrasting differences with detrital zircon age spectra of metasediments recovered in core samples from the foreland basement, specifically the paucity of Paleoproterozoic detritus sourced from cratonic Amazonia, suggests a sedimentary disconnect between Mesoproterozoic arc-related basins and those developed on the continental margin shortly before or relatively synchronous with collisional interactions affecting the Putumayo orogen.

Keywords: South America, Amazonia, Putumayo Orogen, Rodinia, U-Pb Geochronology

1. Introduction The recognition of mobile belts and tectonometamorphic provinces in is key for the study and accurate geological reconstruction of ancient orogenic belts, where sea-floor magnetic stripes are no longer available and reliable paleomagnetic data for specific blocks and geological time periods is limited. For these reasons, reconstructions of Proterozoic and paleogeographic connections between different cratons heavily rely on geological correlations drawn upon finely resolved geochronological data and isotope geochemistry signatures. However, any attempt made to reconstruct such old orogens has to deal with the problems of younger crustal reworking, extensive sedimentary cover, and marginal processes that fragments of to redistribute them amongst other cratons as allochtonous blocks.

The Amazon is the largest of the Precambrian blocks that constitute the South American platform (Tassinari and Macambira, 1999), and its role in the cycle during the history of the Earth has for long been inferred (Cordani et al., 2009). However, there are still sizable areas that remain poorly or totally unknown as a result of

2 dense vegetation cover, heavy tropical weathering, and the development of Phanerozoic intracratonic or Andean-related sedimentary basins (Figure 1). Many reconstructions for the early Neoproterozoic supercontinent Rodinia predict collisional interactions between a Laurentia-Baltica-Amazonia triple joint along Grenville-age (sensu lato) orogenic belts (e.g. Dalziel, 1991; Hoffman, 1991 or Li et al., 2008 for a recent review) but precise correlations between the dismembered orogenic segments are still a matter of debate and are specially undermined by the particular lack of geochronological and petrologic information from key regions of Amazonia like its northwestern margin. The north Andean foreland basins, comprising part of northern , eastern Colombia, eastern Ecuador and eastern Peru (Figure 1), represent an area in excess of 800.000 km2 of covered cratonic crust that is still very poorly know, and with the exception of some well data presented by Kovach et al. (1976) and Feo-Codoecido et al. (1984) nothing else is know about the geochronology of this vast area.

The main objective of this paper is to present new U-Pb geochronological results from Proterozoic basement rocks of northwestern South America, along a NW-SE transect that covers most of the width of southern Colombia, ranging from exposures of cratonic Amazonia to reworked blocks included in the Andean orogen (Figure 2). In addition to new data acquired from the Colombian cordilleran inliers and the western Guyana shield area, we present the first zircon U-Pb ages obtained from basement drilling-core samples of the north Andean foreland basins. Our results comprise the first geochronological evidence for the existence of a previously unrecognized segment of late Meso- to early Neoproterozoic (Grenville-age) orogenic belt underlying these basins, herein termed the Putumayo Orogen, and propose a distinct geological evolution with respect to its direct Amazonian analog the Sunsas-Aguapei orogen. Recognition of this belt provides a cratonic reference frame that places a link between the Andean cordilleran inliers and autochthonous Amazonia basement, and permits further comparisons with other supposedly peri-Gondwanan blocks with proposed Amazonian ancestries or affinities.

The word “Putumayo” makes reference to the name of a foreland basin in the Northern Andes of Colombia (Figure 2), from which the well samples presented in this study were

3 retrieved. This basin is termed after the name of the river that delimits most of the Colombian-Peruvian political border, and runs east from the southern Andes of Colombia to merge with the in Brazilian territory. The word “Putumayo” itself comes from the Quechua, the most widely spoken language among the Andean indigenous people of South America, and it means “gushing-” or “rapidly-flowing river”.

2. Geological Setting: The Amazon Craton is subdivided in six different Precambrian provinces (Figure 1), spanning over 2 Ga of Earth’s history. They are 1) the Central Amazonian Province (CA) formed during the time interval between ~3.0 - 2.5 Ga, 2) the early Paleoproterozoic Maroni-Itacaiunas Province (MI) formed in the period from ~2.2 - 1.95 Ga, 3) the Paleoproterozoic Ventuari-Tapajos Province (VT) which evolved from ~1.95 to 1.8 Ga, 4) the Paleo- to Mesoproterozoic -Juruena Province (RNJ) formed during the interval ~1.8 – 1.55 Ga, 5) the Mesoproterozoic Rondonia-San Ignacio Province (RSI) from ~1.55 – 1.3Ga and 6) the Late Mesoproterozoic Sunsas-Aguapei Province (SA) that evolved in the interval ~1.3 – 1.0 Ga. There are many recent reviews dealing with the long-term evolution of the Amazon Craton and the distribution of the different mobile belts, for a more detailed discussion the reader is referred to the works of Teixeira et al. (1989), Tassinari and Macambira (1999), Santos et al. (2000), Santos et al. (2008) and Cordani and Teixeira (2007). In general, it is believed that after the amalgamation of two Archean microcontinents namely Carajás-Iricoumé and Imataca during the Transamazonian (MI province), the remaining of the Paleoproterozoic belts, the VT and RNJ, evolved trough the continuous accretion of juvenile intraoceanic arcs to this proto-Amazonian nucleus. These two provinces are dominated by gneissic of granitic composition and crosscutting intermediate to felsic plutons, which display predominantly mantle-derived isotopic signatures Tassinari and Macambira (1999). The last two provinces located towards the southwestern margin of the craton, the Rondonia-San Ignacio and the Sunsas-Aguapei, are the result of accretionary and collisional characterized by arc-continent and continent-continent collisions throughout the Mesoproterozoic, resulting in restricted episodes of crustal growth and extensive reworking (Litherland and Bloomfield, 1981; Litherland et al. 1989; Sadowski

4 and Bettencourt, 1996; Cordani and Teixeira, 2007; Bettencourt et al., 2010; Teixeira et al. 2010). Collisional tectonics affecting Amazonia during the late Mesoproterozoic have been used as evidence for the participation of this craton during the amalgamation of Rodinia.

3. The Proterozoic of NW South America: 3.1. Cratonic Amazonia: The last outcrops of the Amazon Craton in northwestern South America can be found in the and Amazonas regions of eastern Colombia, western Venezuela and northwestern (Figures 1; 2). Most of the geological mapping on the Colombian side along with the only available geochronological study were conducted during the PRORADAM project (acronym for “Proyecto Radargrametrico del Amazonas”) from 1974 to 1979 (see Galvis et al., 1979; Priem et al., 1982; PRORADAM, 1979). However, no recent geochronological work has been carried out in the area and this is probably still one of the most poorly known portions of the Precambrian basement of South America. The craton in this region consists of deeply eroded, gneissic/migmatitic terranes of dominantly granitic composition, interpreted as the northwestern extension of the wider Rio Negro-Juruena and Ventuari-Tapajos provinces (Tassinari et al., 1996). In Colombian territory, all the basement exposures on the eastern portion of the country are collectively mapped as the “Mitu migmatitic complex” (Galvis et al. 1979; Priem et al. 1982; Gomez et al. 2007), where the dominantly felsic and yield Rb- Sr isochron ages of ca. 1.55Ga. This basement complex is intruded by undeformed , some of them displaying rapakivi textures like the Parguaza batholith of western Venezuela (Gaudette et al., 1978), and is locally covered under metasedimentary supracrustal sequences of the La Pedrera formation. Undeformed biotite from the Guainia and Vaupes departments yield crystallization ages between 1.55 and 1.48Ga, obtained by multigrain TIMS U-Pb analyses in zircon (Priem et al., 1982). In some areas, predominantly in southern Colombia, a sequence of early Neoproterozoic vulcanosedimentary rocks of the Piraparana Formation is found covering the Mesoproterozoic basement where an interbeded rhyodacitic flow has been dated by Rb- Sr at 920 Ma.

5 Despite the lack of direct geochronological evidence, it has been assumed that the Paleo- to early Mesoproterozoic provinces of the Amazon craton extend beneath the north Andean foreland basins until they meet the Andes (Figures 1 and 2), where they are thought to be truncated by exotic terranes of “Grenvillean-affinity” accreted to the continental margin during inferred collisional interactions with Laurentia (Forero-Suarez 1990; Gómez et al. 2007; Kroonenberg, 1982).

3.2. North Andean inliers: Along the Andean orogen, isolated inliers of Proterozoic gneisses and are long known in Colombia and they have been the focus of intensive research (MacDonald and Hurley 1969; Tschanz et al. 1974; Kroonenberg 1982; Priem et al. 1989; Restrepo-Pace et al. 1997; Ruiz et al., 1999; Ordonez-Carmona et al. 1999; Ordonez-Carmona et al. 2002; Cordani et al. 2005; Cardona-Molina et al. 2006; Cardona et al. 2010, among others). However, as shown in a recent compilation of the available isotopic data presented by Ordonez-Carmona et al. (2006), it is evident that precise geochronological data for many of the exposed units is still lacking.

Recent paleomagnetic data acquired in the Colombian and Venezuelan Andes has shown the strong fragmentary character of the pre- basement that underlies the Eastern and Central Cordilleras of Colombia, the Santa Marta massif, and the Merida Andes and Perija Range of Venezuela (Bayona et al. 2010; Bayona et al., 2006). It was shown by these authors that different -bounded blocks in the Cordillera, some of them associated with Proterozoic basement inliers, have suffered significant trench-parallel latitudinal transport of differential magnitudes at least since times. These data most likely preclude the idea of the “Garzon-Santa Marta granulite belt” as a coherent Precambrian terrane constituting the basement of the Eastern Andes of Colombia (Kroonenberg 1982; Restrepo-Pace et al. 1997). Some of these blocks, as it’s the case of the Santa Marta Massif, show displacements in excess of 100Km in magnitude with respect to a dynamic South America reference framework (see Figure 7 in Bayona et al. 2010) while others, as the Garzón massif, are considered as being relatively stable with respect to non-remobilized South America at least since Paleozoic times (Cardona et al.

6 2010; Toussaint, 1993). The cordilleran inliers sampled for the present study, the Garzón, La Macarena and Las Minas massifs, represent the southernmost inliers found in the Colombian Andes, located at approximately the same modern latitude as the wells sampled from the Putumayo basin.

3.2.1. Garzón Massif: This basement inlier located in the southern portion of the Eastern Cordillera of Colombia (Figures 1 and 2) constitutes the largest exposure of Precambrian crust in the northern Andes. Based on regional mapping and mesoscopic characteristics of the different metamorphic rocks, it has been informally subdivided in four lithostratigraphic units shown in Figure 2b (Jimenez Mejia et al., 2006): 1) Las Margaritas migmatites, a metasedimentary unit located along the eastern side of the massif dominated by metasedimentary gneisses and migmatites with mineral assemblages indicative of amphibolite-facies metamorphic conditions; 2) El Vergel granulites, a unit dominantly composed by felsic granulites and garnetiferous paragneisses with subordinate mafic granulites. This unit covers most of the western flank of the massif and is in contact with the Las Margaritas migmatites along the east-verging Las Hermosas reverse fault (Figure 2b); 3) El Recreo , an orthogneissic unit of interpreted anatectic origin, and 4) the Guapotón-Mancagua orthogneiss, a biotite-amphibole gneiss of granitic composition that outcrops along the western margin of the massif and displays a foliation that is concordant with that of the El Vergel granulites. In some literature the first three units are also referred to as the “Garzon Group” (Kroonenberg, 1982; Restrepo-Pace et al. 1997). Geochronological data available for this massif comes from the early works of Alvarez and Cordani (1980) and Priem et al. (1989), followed by Restrepo-Pace et al. (1997) and Cordani et al. (2005), the last one being the most comprehensive so far and containing the first U-Pb SHRIMP data obtained from the Precambrian of the northern Andes. These last authors report an age of 1015±7.8 Ma for prismatic zircons extracted from a discordant leucosome of the Las Margaritas migmatites unit, which they interpret as an anatectic event caused by decompression melting; for the Guapoton-Mancagua orthogneiss they obtained an age of 1000±25 Ma from metamorphic zircon overgrowths (5 analyses) and an age of 1158±22 Ma for the magmatic precursor (3 analyses); and

7 finally, for the El Vergel granulites, zircons analyzed resulted in a complex concordia plot from which a reliable age of metamorphism could not be extracted due to the mixed effects of inheritance and superposed Pb-loss. With the exception of samples disturbed by Phanerozoic thermal events, most of the Ar-Ar results from this massif cluster around 970 to 910 Ma (Restrepo-Pace et al., 1997; Cordani et al., 2005).

3.2.2. Serrania de la Macarena uplift: The geology of the Macarena range (Fig 2) was originally studied by Augusto Gansser (in Trumpy 1943), who described its basement as an association of mica-schists and alkali-feldspar gneisses, hornblende gneisses, and highly deformed syenogranitic gneiss (Trumpy 1943, pp 1282). The Precambrian nature of these rocks was established based on stratigraphic relations with the Güejar group, a clastic sedimentary unit composed of micaceous and qz-rich which rests unconformably on the metamorphic basement and contains trilobites determined as Cambro-Ordovician in age (Harrington and Kay, 1951). However, previous to this study, no radiometric ages had been obtained for the crystalline basement of this range. Toussaint (1993) suggested that the basement of this sierra could potentially be correlated with the Garzon massif as part of a larger crustal block accreted to Amazonia during Precambrian times (the so-called Andaqui terrane), but this hypothesis is based only on stratigraphic observations that correlate the sedimentary sequence of the Güejar series with Lower Ordovician units of the Ariari limestone and the Ordovicico del Rio Ambica that rest unconformably on metamorphic rocks of the Garzon group (Trumpy, 1943).

3.2.3 Las Minas Massif: The Serrania de Las Minas is a NE trending elongated range of about 17 Km in length and 6 Km in width, located only 20 Km west of the Garzon Massif (Figure 2b). Structurally, this range is located along the axis of a pop-up structure bounded on both sides by reverse faults that thrust the Las Minas migmatites and gneisses onto Tertiary alluvial deposits of the Magdallena valley to the east, and over Jurassic volcanosedimentary sequences of the Saldaña Formation to the west (Figure 2b). The stratigraphic succession in this range comprises a high-grade metamorphic basement

8 overlain by clastic sedimentary sequences of Graptolite-bearing Ordovician shales and sandstones of the El Higado Formation (Mojica et al. 1987). In some locations, this sequence appears intruded by granitic plutons of Jurassic age (Cardona et al. unpublished). The only geochronological analysis available for the metamorphic rocks of this area is an hornblende Ar-Ar age obtained from an amphibolite (Restrepo-Pace et al. 1997, sample HP-3) which defines a cooling age of 911±2 Ma similar to other K- Ar and Ar-Ar cooling ages reported for the Garzon massif (Priem et al. 1989; Restrepo- Pace et al. 1997; Cordani et al., 2005).

From transects performed during the present study, the metamorphic sequence was identified as a series of stromatic migmatites overlying a metaigneous unit characterized by porphyroclastic augen-gneisses of granitic composition. Most of the observed migmatites are stromatic metatexites with apparent low degrees of partial melting, whose metasedimentary origin is evidenced by relict sedimentary structures such as cross- bedding observed in psammitic resistant layers that did not undergo anatexis. The disposition of the granitic leucosomes, parallel to subparallel with respect to the dominant metamorphic foliation in the gneisses and the overall morphology of the migmatites, suggests that shearing and deformation occurred in simultaneous with the melting event (e.g. Kemp and Gray 1999). Foliations measured in the gneisses and the migmatites reveals folding about an axis oriented at ~220/10 (Figure 2b).

4. Analytical Methods: U/Pb Zircon Geochronology by LA-MC-ICP-MS Zircon separates from drilling-core and outcrop samples were obtained by standard methods combining jaw crushing, roller-mill pulverizing, water-table concentration, magnetic separation using a Frantz® LB-1 barrier separator, and final heavy-liquid separation using 3,32g/cm3 Methylene Iodide. For zircons extracted from igneous and metamorphic rocks, approximately 50 to 100 individual grains were handpicked, mounted in epoxy, polished, carbon-coated and imaged with SEM cathodoluminescence (CL) prior to analysis. Zircons from sedimentary / metasedimentary samples to be analyzed for detrital zircon (DZ) provenance were mounted randomly following the procedures of Gehrels et al. (2006). All U-Th/Pb isotopic measurements were performed

9 by LA-MC-ICP-MS at the LASERCHRON center facilities in the University of Arizona following the procedures presented by Gehrels et al. (2008) for analyses obtained using the GV-Instruments Isoprobe MC-ICP-MS. However, most of the analyses were obtained using a NU-instruments HR-MC-ICP-MS coupled to a New Wave UP193HE Excimer laser operating at a wavelength of 193 nm. Details about the analytical procedures followed are described in the appendix. Both multicollector blocks are capable of simultaneously measuring 238U, 232Th, 208Pb, 207Pb, and 206Pb isotopes in faraday cups while 204Pb is always measured in a channeltron® detector or an ion-multiplier. This configuration was utilized for analyses performed using ablation spot-sizes between 40µm and 22µm in diameter. Alternatively, in very complexly zoned zircons, we utilized 10µm or 18µm laser spot-sizes in which case masses 208, 207, 206 and 204 were all measured in ion-multipliers in order to allow reliable measurement of the Pb isotopes with low ablation volumes, following procedures similar to those presented by Johnston et al. (2009).

All errors reported in the data tables are analytical only. Systematic errors for the measurement of the 206Pb/207Pb ratios on the Sri Lanka (SL2) standard varied for each analytical session, but were normally between 0.8 and 1.2 %. Final ages reported in the concordia plots and discussed throughout this paper represent 2σ confidence-limit total errors, and account for the quadratic propagation of both the analytical and systematic uncertainties. Concordia plots, age calculations and probability density diagrams were plotted at a 1σ uncertainty using the Isoplot Excel® macro of Ludwig (2003).

For metasedimentary samples, analyses of inherited cores were performed carefully using the CL images in order to avoid areas of obvious metamorphic recrystallization. However, as will be evident from the concordia plots below, some of the analyses show departures from concordia along a discordia chord that goes towards the age of the metamorphic overprint while others are apparently affected by normal (young) Pb-loss events. Knowing this, caution must be taken when interpreting one-dimensional probability density plots that consider only one isotopic ratio for the calculation of the best age (i.e. 206Pb/207Pb in this case), as Pb-loss events at non-zero ages can generate

10 “false” distribution peaks and lead to misinterpreting detrital zircon signatures (as illustrated by Nemchin and Cawood, 2005). For the probability density plot of each sample presented here (Figure 8), we took an approach similar to Collins et al. (2007) and plotted both the entire dataset of each sample (shaded in red), and the data filtered at <5% discordance (black solid line). Although some of the smaller peaks that are present in the plots of the entire dataset disappear when the data is filtered, the position of the dominant peaks and their correspondent age maxima do not show any significant variation, which gives further confidence in the robustness of the obtained DZ data.

5. Samples description and geochronological results: For the present study we analyzed samples of a) gneisses, granulites and migmatites collected from three Cordilleran Inliers of the Northern Andes (the Garzón, Macarena and Las Minas massifs); b) drilling-core samples of deep exploratory wells that pierced the crystalline basement of the Putumayo foreland basin of Colombia, east of the frontal thrust systems of the northern Andes, and c) undeformed or slightly deformed intrusive rocks from the northwesternmost cratonic exposures in the Amazonas region of Colombia. Sample locations and other geographic names referenced in the text are shown in Figures 1 and 2.

5.1. Cordilleran Inliers: Seven samples collected in three of the basement inliers were analyzed (Figure 2), three of them from the Garzón massif (MIVS-11, MIVS-26 and CB-002), one from the Serrania de la Macarena range (Macarena-2), and the other three from Las Minas massif (MIVS-37a and MIVS-41 and CB-006). One sample from the La Plata orthogneiss in the Central Cordillera, a metamorphic unit of alleged Precambrian age (Gómez et al. 2007; Priem et al. 1989) was also analyzed but given the Upper Permian age of crystallization obtained it will not be discussed further (Ibanez-Mejia, unpublished).

5.1.1. Garzón Massif: Sample MIVS-11 was collected from the El Vergel granulites unit, approximately 7 Km southeast of the Garzón municipality along the road that connects Garzón with the town

11 of El Recreo (Figure 2b). It is a hyperstene-hornblende-K feldspar-plagioclase- felsic granulite, with slight amphibolite-facies retrograde overprint. Zircons recovered from this sample were mostly rounded to subrounded in shape, colorless to light pink, with 1:1 to 1:3 width:length ratios and generally smaller than 300µm in size. CL imaging shows that most of them exhibit textures indicative of growth and/or recrystallization under metamorphic conditions (inset, Figure 3a) evidenced by relatively homogeneous grains displaying only weak sector-zonation (Corfu et al. 2003), or rims with no internal structure that appear as overgrowths around more complexly zoned cores. U-Pb isotopic analyses of the metamorphic overgrowths are all concordant (Figure 3a), and yield an age of 992±10 Ma (MSWD=0.32, 27 analyses) that is interpreted as the timing of granulite- facies metamorphism for this unit. Uranium concentrations range between 200 and 600 ppm with fairly low U/Th ratios between 1 and 2. A 206Pb/207Pb weighted mean age of the same 27 grains results in an age of 995±10 Ma that is in excellent agreement with the concordia age. As described above, many of the grains contain xenocrystic cores, some of which are characterized by an oscillatory zoning typical of magmatic zircons while others exhibit complex chaotic zoning patterns. The wide range of ages obtained for these xenocrysts, ranging from ca. 1011 to 1490 Ma (Repository Data), reflects the detrital nature of these grains inherited from a volcanosedimentary protolith. A total of 89 detrital core analyses were performed, 62 of which are <5% discordant. The pattern is characterized by a multi-modal age peak distribution dominated exclusively by Mesoproterozoic grains, with the most prominent maxima at ca. 1120, 1300, 1370 and 1450 Ma. A maximum age of deposition for the sedimentary protolith is estimated from the two youngest, >95% concordant grains with ages of 1115±10 and 1118±22 Ma respectively (1σ, total error). This places a limit for the age of sedimentation that is thus constrained between the age of the youngest grain (1115±10 Ma), and the age of metamorphism (992±10 Ma).

Sample MIVS-26 was collected in a small quarry close to the Guapotón municipality (Figure 2b). It corresponds to an augen orthogneiss with centimetric K-feldspar porphyroclasts in a matrix of finer-grained quartz, plagioclase, biotite and hornblende aligned defining the metamorphic foliation. Although no quantitative P-T estimates of

12 metamorphism are available for this unit, the mineral assemblage suggests amphibolite- facies conditions (Jimenez Mejia et al. 2006; Kroonenberg, 1982). No evidence for partial melting was observed in this outcrop. Zircons from this sample are mostly uncolored, ranging in size from ~150 to 300µm, with width:length ratios of 1:2 to 1:3. CL imaging of 50 handpicked grains shows that they consist of oscillatory-zoned igneous cores rimmed by more homogeneous, unzoned, metamorphic overgrowths (inset, Figure 3b). All of the concordant U-Pb analyses from the igneous cores yield an age of 1136±11 Ma with an MSWD=0.84 (Figure 3b, 24 analyses less than 5% discordant). This age is thought to represent the time of crystallization for the igneous protolith, and is within error of the SHRIMP age of 1158±22Ma reported by Cordani et al. (2005) for this same unit. Analyses performed on the rims result in an age of 990±12 Ma (MSWD=1.15), calculated from 15 rim analyses that are less than 5% discordant. We interpret this age to reflect the timing of peak metamorphism of this metagranite which is synchronous with granulitization of the El Vergel unit (obtained from samples MIVS-11 and CB-002), and slightly younger but more precise (although within error) than the 1000±25Ma age reported by Cordani et al. (2005). Nine analyses were not considered for the calculation of either the igneous or metamorphic age, as they possibly represent mixtures between the core and the rim during ablation or partial Pb-loss by recrystallization. These analyses are shown in light gray in Figure 3b.

Sample CB-002 is a leucocratic gneiss also collected from the El Vergel granulites unit, along the road that connects the towns of Garzón and Guadalupe (Figure 2b). This outcrop consists of sillimanite-bearing quartz-feldspar gneisses with biotite as the only ferromagnesian bearing phase also interpret to be of metasedimentary origin. Zircons from this sample are mostly uncolored, but relatively more prismatic than those of sample MIVS11 displaying width:length ratios from 1:3 to 1:5. CL imaging shows a wide variety of internal grain morphologies similar to sample MIVS11, although elongated zircons with igneous zoning are more abundant. This sample shows evidence of extensive solid- state recrystallization of inherited zircon cores by the granulite-facies metamorphic event, observed as widespread “ghost” oscillatory zoning patches in recrystallized portions of zircon grains and the presence of recrystallization fronts (e.g. Hoskin and Black, 2000).

13 This feature is also evident in the U-Pb systematics, where ages obtained from these recrystallized areas show some “memory” of their original age component, and are slightly shifted away from the age of metamorphism towards older ages. The analysis of 10 metamorphic overgrowths and individual crystals that display homogenous, bright and unzoned textures under CL, are all concordant and consistent with an age of 992±10 Ma (MSWD=0.3) for the metamorphism. This age is equivalent within error to the metamorphic ages obtained from the other two samples of the Garzón massif described above. For the analysis of the detrital component, given the strong metamorphic overprint observed in the zircon cores, a more cautious approach was taken for this sample. Analytical spots where carefully selected away from areas where recrystallization is evident and placed in cores where pre-existent zoning is better preserved. Additionally, results plotted in the probability plot if Figure 8 were filtered to discard xenocryst grains whose calculated 206Pb/207Pb age overlaps within analytical error with the abovementioned age of metamorphism in an attempt to reduce the “noise” introduced by recrystallization. All analytical data, including that of those grains that were excluded from plotting, are reported in the repository data table. The detrital age spectrum for this sample shows a multi-modal age peak distribution of early Mesoproterozoic components similar to sample MIVS-11, with peak modes at ca. 1340, 1420, 1450 and 1480 Ma (Figure 8). Considering that young detrital cores whose ages overlap within error with the age of metamorphism were discarded, the maximum depositional age obtained with the remaining grains is a conservative estimate for the maximum age of sedimentation. The youngest four, <5% discordant grains, have ages of 1011±10, 1013±10, 1014±11 and 1014±11 (1σ, total error), respectively. This gives us confidence to place the age of deposition for the sedimentary protolith between 1013±11 (Weighted mean of the 4 youngest analyses) and the age of metamorphism at 992±10 Ma.

5.1.2. Serrania de la Macarena uplift: One sample was analyzed from the metamorphic basement of this sierra (Macarena-2). It consists of a melanocratic biotite-epidote-microcline-plagioclase-qz mylonitic gneiss with abundant sphene, suggestive of dynamic metamorphism under at least upper- -facies conditions. Sub-grain rotation deformation mechanisms observed in qz

14 and feldspar crystals suggest intermediate temperatures for the mylonitization event possibly within the 400-600°C temperature range, but that did not generate a strong metamorphic imprint on U-Pb systematics of the analyzed zircon crystals (Figure 4). CL images from handpicked zircons show that most of the grains have oscillatory-zoned textures indicative of igneous crystallization (inset, Figure 4). Most of the point analyses performed were >95% concordant, and a concordia age calculated with 19 individual analyses yields a value of 1461±15 Ma (MSWD=0.37) for the igneous precursor of these . In some grains, the normal igneous textures appear to be partially obliterated by partial recrystallization of the zircons (possibly during the mylonitization event), but spot analyses performed in these areas resulted in only slightly discordant ages that are very close to those obtained from the unaffected portions of the grains. This age of 1.46 Ga, along with a protolith age of ca. 1.5 Ga reported for an orthogneiss of the Serrania de San Lucas massif (Ordonez-Carmona et al. 2009), are the oldest protolith ages known for metaigneous units of the north Andean inliers to date. No units of similar age have been found in the Garzon massif, where zircons of this age are only found as detrital components in the metasedimentary units presented in this paper. Although this age does not conclusively confirm or preclude correlations that suggest the basement of this sierra to be part of the Andaqui terrane along with the Garzon massif (Ramos, 2010; Toussaint, 1993), the protolith of these mylonites and correlative units may have served as a source for the ca. 1.45 Ga detritus found in metasedimentary units of the Garzon group. It should also be noted that igneous or metamorphic rocks of similar age have also not been found in either cores or outcrops of the stable cratonic area or basement cores as will be shown below.

5.1.3. Las Minas Massif: Three samples were analyzed from the Minas massif: MIVS-41, collected from the granitic augen-gneiss that forms the core of the massif; CB-006, a biotite-rich melanosome from a metasedimentary in proximity to the orthogneissic unit; and MIVS-37a, collected from an outcrop of metasedimentary qz-feldspar migmatitic gneisses on the northern termination of the range (Figure 2b).

15 Sample MIVS-41 is a hornblende-biotite-microcline-plagioclase-quartz augen-gneiss that forms the core of the massif and is well exposed along the Zancudo creek that drains the eastern portion of the Sierra. Along this creek, outcrops of granitic gneiss are apparently overlain by metasedimentary migmatites although the contact between the two units was not observed. Zircons from this sample are light pink in color, have width:length ratios between 1:3 and 1:4, and reach up to 400µm in length. Internal grain structures are dominated by igneous oscillatory-zoning, which in some grains is affected by partial recrystallization caused by the amphibolite-facies metamorphic event (Figure 3d). U-Pb analyses performed on the igneous cores reveal a mid-Mesoproterozoic age for the magmatic precursor of the gneiss, calculated at 1326±13 Ma using 23 analyses that are less than 5% discordant. There is a subset of analyses that, although <5% discordant, clearly define a mixing chord between the age of the igneous precursor and the age of metamorphism, demonstrating that the recrystallization mantles that surround the igneous grains are zones where only partial resetting of the U-Pb systematics took place. This clearly exemplifies how individual spot ages that lie along this chord, although overlapping the concordia within error, lack any geological meaning by themselves as they represent mixing between two end age-components and not a real tectonothermal episode. Using the ion-counter configuration we were able to obtain a group of concordant analyses from thin, unzoned, brighter metamorphic overgrowths, which yield an age of 991±12 Ma for the metamorphic event (8 analyses, MSWD=1.08). This age is basically the same within error with respect to the age of granulite-facies metamorphism previously shown from samples of the Garzon massif. Granitic protolith ages of ca. 1.3 Ga have not been found anywhere else in the Andean inliers, but zircons of this age are widespread in the many of the metasedimentary samples discussed throughout this paper (Figure 8).

Sample CB-006 was also taken along the Zancudo creek, a few tens of meters downstream (east) from the location where the MIVS-41 sample was collected. In this location, metatexic migmatites of metasedimentary origin display well developed stromatic structures, characterized by an interleaving of 5 to 10 cm thick granitic leucosomes with laterally persistent bands of biotite-hornblende gneisses. The sample

16 analyzed corresponds to a sillimanite-bearing biotite rich gneiss with amphibole and clinopyroxene interpreted to be a melanosome for these migmatite. Zircons recovered are mostly rounded to subrounded in shape, displaying width:length ratios of 1:2 to 1:3 and average sizes between 50 and 250 µm and CL imaging showed that most of the grains have xenocrystic cores surrounded by bright, unzoned overgrowths presumably developed during metamorphism and partial melting. Interestingly in this sample, the majority of the xenocrysts are characterized by textures indicative of growth under metamorphic conditions (sector-zoning, inset Figure 3e), and low-U concentrations typically between 70 and 250 ppm (see supplementary data). This observation contrasts with all the other metasedimentary samples presented in this study, where most of the xenocrystic cores display textures indicative of igneous conditions of crystallization. The probability age plot for the detrital component shows an almost unimodal age distribution, dominated by a restricted population within the range from 1100 to 1200 Ma (Figure 8). Grains that fall outside of this range typically have magmatic zoning, but some of them are also low in uranium. This is the case of the youngest detrital grain analyzed which, with an U content of only 83 ppm, results in an rather imprecise age of 1023±81. A weighted mean age calculated using the youngest 4 grains constrains the maximum timing of deposition for the sedimentary protolith to 1086±34 (2-sigma).

Sample MIVS-37a was collected from the northwestern termination of basement exposures in the Las Minas massif. It consists of a leucocratic, quartz-feldespar migmatitic gneiss with biotite (extensively retrograded to chlorite) as the only ferromagnesian metamorphic phase. The outcrop is crosscut by a series of slightly folded mafic dikes of unknown age. The processed sample is a paleosome from these migmatites in a portion where leucocratic veins are scarce, selected in order to obtain inherited zircons that represent the detrital provenance of the sedimentary precursor. CL imaging showed that most of the grains have igneous growth-zoning patterns and resorption textures, but lack evident metamorphic overgrowths or extensive recrystallization. U-Pb analyses confirm that the zircon grains are detrital in character and that zircon did not recrystallized during the metamorphic event but, instead, was probably resorbed during anatexis as a result of high-temperatures and Zr subsaturation in the partial melts. The

17 age spectra obtained, considering all the analyzed grains, ranges from 1005±23 Ma to 1516±21 Ma. The dominant distribution range has a peak maximum at ca. 1490 Ma, while grains that fall out of this range constitute small subsidiary peaks at ~1160 and ~1210. The youngest grain analyzed, slightly more than 5% discordant, has a 206Pb/207Pb calculated age of 1005±23 Ma. However, maximum depositional ages inferred from only one analysis that does not form part of a grain population are not always reliable. For this reason, we adopt an age of 1157±27 as a conservative estimate of maximum protolith deposition, calculated as the weighted mean of the youngest, <5% discordant, two grains of the distribution that form part of a coherent population.

5.2. The Basement underlying the Foreland Basins: The North Andean foreland basins of Colombia can broadly be divided in two sub-basin, namely the Putumayo to the south which represents the northern extension of the Marañon-Oriente basins of Peru and Ecuador, and the to the north that continues northeastward into Venezuelan territory (Figures 1 and 2). These two basins are separated by a series of NW trending basement structures, the Macarena-Chiribiquete structural high and the Vaupes arch, which define the elongated Vaupes-Amazonas intracratonic basin extending from the borders with Peru and Brasil in southeastern Colombia to the Serrania de la Macarena uplift next to the Andean chain. These basement–arch structures, roughly located along the southern and northern margins of the Güejar-Apaporis (Figure 2), are readily observed in the Bouger gravimetric anomalies map of Colombia (available free for download at the Colombian National Hydrocarbons Agency webpage, www.anh.gov.co). This structure has been interpreted as the expression of a lower Paleozoic graben that trends NW-SE and controlled the sedimentation of the Lower Paleozoic Araracuara Formation (Cáceres et al. 2003).

Many exploratory wells in the foreland basins of Colombia have drilled below the unconformity between the crystalline basement and the overlying Phanerozoic sedimentary cover, but unfortunately not many of them have retrieved core samples. The depth to the crystalline basement is highly variable, depending on the relative position of each well with respect to the horst/graben basement structures. However, the crystalline

18 basement is generally shallower in the Putumayo basin in comparison to the Llanos. In the Putumayo basin, on those wells where basement cores have been recovered, rocks directly overlie the Precambrian units whereas a pile in excess of 1Km in thickness has been drilled in several locations around the . For this reason, it is more common to find wells piercing the crystalline basement and recovering cores in the Putumayo area than in the Llanos.

For the purposes of this study, we sampled six different exploratory wells that recovered core samples from the crystalline basement of the Putumayo Basin. From north to south they comprise the Payara-1, La Rastra-1, Solita-1, Mandur-2, Caiman-3, and Mandur-3 wells (Figure 2), which drilled through basement rocks below depths of 3492’ft, 3087’ft, 3675’ft, 5613’ft, 7704’ft and 7508’ft, respectively. These are not the only wells that reached the crystalline basement in the region but, to our knowledge, are most of those (if not the only ones) that recovered cores that are accessible for sampling. These cores represent the only available means to study the petrology and geochronology of the basement of the proximal Andean foreland in Colombia. Samples processed from the Mandur-3 and La Rastra-1 wells did not yield zircons concentrates so they will not be discussed further. They are an epidote-amphibolite -facies metabasite rock, and a kyanite- bearing grt-cpx-amph-bt-plag-qz melanocratic schist. These two samples are being analyzed by other methods and will be presented in a future paper.

5.2.1. Putumayo Basin Basement Cores: The Payara-1 well was drilled in the northern part of the basin and is the northernmost of the basement wells presented in this study (Figure 2a). It drilled through a 3492’ft thick Meso- Cenozoic sedimentary succession to finally pierce the crystalline basement along the western flank of the Macarena arch. The core sample consists of a granulite-facies Opx-Sil-Grt-Amph-Bt-Plag-Qz migmatitic gneiss (Figure 5a), and the occurrence of feldspar-quartz symplectites intergrown with fleaky biotite is suggestive of reactions involving biotite dehydration melting (Waters, 2001). CL images of zircons recovered from this sample all have oscillatory-zoned cores that indicate formation under igneous conditions, which in turn appear mantled by a thin rim of unzoned bright metamorphic

19 zircon (inset, Figure 6a). Small zircons grains tend to show a subtle fading of the original igneous growth zoning which can be due to the effect of partial solid-state metamorphic recrystallization under granulite-facies conditions (e.g. Connelly, 2001). This observation is supported by the U-Pb isotopic data, where it is evident that spot analyses performed in smaller grains are slightly discordant and lying along a chord that joins the bigger, well zoned, and isotopically concordant cores in the upper discordia intercept with the age of the metamorphic overgrowths in the lower intercept (Figure 6a). Calculation of a concordia age using 16 core analyses that are <3% discordant yields a value of 1606±16 Ma (MSWD=0.97) for the crystallization of the igneous protolith. Given the thin width of the metamorphic overgrowths (<30µm), analyses were performed using an 18µm diameter spot size with the ion-counter configuration. Seven analyses were acquired from these overgrowths, four of them being <4% discordant. One is 10% normal discordant, another one is 8% reverse discordant, and the last one is 5% discordant but is significantly older than the others and lying along a chord that goes towards the age of the igneous cores. We interpret this last analysis as a mixed ablation spot. The four <4% discordant analyses yield an age of 986±16 Ma (MSWD=0.49) for the granulite-facies event, considered to be the best estimate for the age of metamorphism of this gneiss. A 206Pb/207Pb weighted mean age of the 6 non-mixed analyses defines an equivalent but less-precise age of 985±23 Ma (MSWD=0.70), but as in previous samples the concordia age is preferred. Note the very low U concentrations measured on the overgrowths, estimated between 15 and 20 ppm (supplementary data). This result demonstrates the occurrence of Grenville-age granulite-facies reworking of Amazonia’s late Paleoproterozoic crust, just east of the Garzon massif in the proximal foreland basement.

The Solita-1 well was drilled in the central part of the basin, coring basement rocks of the Florencia arch below a 3675’ft thick sequence of Cenozoic clastic rocks. The analyzed sample consists of strongly deformed Amph-Bt-Ep-Plag-Qz migmatitic gneisses, which suggests syn-deformational metamorphism and melting under amphibolite facies conditions. The folded leucosomes and the foliation of these migmatites appear crosscut by discrete blastomylonitic zones along which euhedral amphiboles and subhedral pyroxenes attain larger grain sizes than the regional metamorphic phases of the

20 migmatite. It is unclear whether if the mylonitization event is somehow related to the phase of regional metamorphism and anatexis (slightly postdating it) or if it is a considerably younger event that was not recorded in the zircon U-Pb system of the non- mylonitized rock. Recovered zircons are small in size, generally <150µm in length, displaying 1:2 to 1:4 width:length ratios. Most of the crystals are cloudy with reddish and brownish colors and show strong suppression of their CL emission, observations that suggest a considerable degree of metamictization (inset, Fig 6a). Xenocrystic cores are common in most of the imaged crystals and U-Pb analyses performed on zircons from this sample produce a quite complex concordia plot. Most of the spots placed on the dark overgrowths appear to be aligned defining a discordia chord with an upper intercept of 1044±26 Ma and a lower intercept trending towards recent Pb-loss (Figure 6b). This upper intercept, considered to represent the age of metamorphism and melting, is calculated using 12 analyses that are less than 30% discordant, and anchoring the lower intercept at 6 Ma. Two important geological events that affected the western Putumayo basin justify the lower-intercept anchoring of the discordia to late Miocene times, as they may be responsible for the observed Pb loss: 1) Hydrothermal water circulation from the Cordillera towards the foreland during Oligo-Miocene Andean uplift pulses and orogenic development (Parra et al. 2009), and 2) thermal effects and hydrothermal water circulation during nearby late Miocene mafic magmatism. In the Orito oil field, gabbroic dikes are known to cut the Cretaceous sequence of the southwestern Putumayo basin where they have been dated at 6.1±0.7 Ma by Amphibole K-Ar (Vasquez et al. 2009). A weighted average age calculated using 11 analyses that are <20% discordant produces an undistinguishable age of 1046±25 Ma for the migmatization event. Ellipses shown in blue in Figure 6b represent analyses that are either xenocrystic cores or ablation spots that represent mixtures between the inherited component and the ca. 1.05 Ga overgrowths. Older ages, with ages of 1.73 and 1.85 Ga, are interpreted as detrital grains from a sedimentary protolith. Some of the mixed analyses appear to be aligned along a chord that joins the metamorphic age and a presumable ca. 2.0 Ga component.

The Mandur-2 well cored a depth interval between 5690’ and 5708’ beneath the west- central part of the basin, and consists of an intercalation of melanocratic migmatitic

21 gneisses and centimetric to decimetric coarse-grained leucocratic veins and dikes of granitic composition (Figure 5b). Given the size of the granitic layers and the lack of evident melanosomes and/or reaction margins (selvedges) along the contact with the surrounding gneiss, we interpret these dikes as granitic melts injected into the melanocratic gneisses within a regional migmatitic terrain, but bearing no genetic relation (as derivation through partial melting) with its more mafic gneissic host rock. The granites display clear textures of crystallization from a silicate melt but also display flow and shearing textures indicative of injection and crystallization under differential stress conditions. These dikes are petrographically classified as syenogranites, composed mostly by microcline and quartz with subordinate plagioclase and muscovite. The melanocratic host rocks for the dikes are Amph-Bt-Plag-Qz gneisses that also underwent some degree of partial melting during the metamorphic peak at least under amphibolite facies conditions. Thin leucocratic stromata were developed parallel to the foliation of the gneisses, and their white color contrasts with the pinkish tone of the syenogranitic dikes. Additionally, these elongated patches of partial melt (neosome) are trondjhemitic in composition, completely lacking any K-feldspar in contraposition to the microcline-rich granitic dikes. We thus interpret the overall stromatic morphology as the result of layer- parallel injection of the syenogranitic melt, although the presence of thin trondhjemitic neosomes in the gneisses also evidences some degree of partial melting of the host rocks.

We analyzed two separate samples from this core; one zircon concentrate was obtained from a sample of an approximately 70 cm thick coarse-grained leucocratic dike, and the other from the host melanocratic amphibole-gneisses. Zircons from the gneiss display complex internal morphologies under CL (inset, Figure 6c), characterized by cores with oscillatory zoning patterns that are enclosed by low-luminescent, high-U rims inferred to have crystallized under metamorphic conditions. Textures indicative of solid-state recrystallization were also observed, evidenced as bright margins with lobate terminations inboard of the metamorphic overgrowths that clearly crosscut the primary igneous zonation of the cores. These rims resemble the recrystallization fronts studied by Hoskin and Black (2000). Isotopic analyses performed on the low-luminiscent metamorphic overgrowths are concordant to moderately discordant (Figure 6c), yielding

22 an upper discordia intercept age of 1019±23 Ma (MSWD=0.62) for the amphibolites- facies event similar to that found in the Solita-1 well but older than the granulite-facies imprint dated from the Payara-1 well. Analyses of the xenocryst cores are more variable, depending primordially on the internal structure of each grain. Most of the cores with oscillatory-zoned textures appear to pertain to a single population variably affected by Pb-loss effects, defining a discordia chord with a latest Paleoproterozoic upper-intercept age of 1601±28 Ma (MSWD=0.62). Cores with non-oscillatory zoned textures yield older ages up to 1713 Ma, which can be inherited from a vulcanosedimentary protolith. Finally, analyses performed on the bright luminescent areas showed mixed ages between the inherited components and those of the metamorphic rims (gray ellipses in Figure 6c), interpreted as mixed ablation spots and/or partial metamorphic recrystallization of inherited zircon cores.

Zircons from the leucocratic sills are mostly elongated and prismatic, displaying width:length ratios between 1:3 and 1:5. Some of the grains were broken during sample processing due to their big sizes of at least 500µm in length. Internal CL images showed that the grains have oscillatory-zoned textures indicative of crystallization from a melt, but some internal complexities are apparent from the presence of bright rims surrounding darker cores which sometimes appear to truncate previous zoning patterns (inset, Figure 6d). Around 60 U-Pb spots were performed over the different textural areas and complexities of the grains but they produced a fairly simple plot (Figure 6d), with most of the analyses overlapping concordia within error and defining a rather homogeneous population with few analyses affected by Pb-loss (gray ellipses) and others evidencing some degree of inheritance from an older component (blue ellipses). An homogeneous population defined by 52 analyses that are <6% discordant produced a concordia age of 1017±10 Ma with an MSWD=0.66. This age, interpreted as reflecting the timing of crystallization of the granitic melt, is more precise but still within error with respect to the age of metamorphism measured from the zircons overgrowths of the host gneisses previously described. We thus consider that regional metamorphism and injection of granitic melt were relatively synchronous in this area of the basin (within analytical error), and that this age of 1017±10 may also be a better estimate for the amphibolite-

23 facies metamorphism of the gneisses. These geochronological evidences further support the textural interpretations presented above with regards to the temporal relations between metamorphism, partial melting and injection of syenogranitic sills observed in the core sample.

The Caiman-3 well cored approximately 30 feet of basement in the southwestern part of the basin, sampling a depth interval between 7704’ and 7731’ just below the unconformity with the overlying Cretaceous strata. This 27 ft long core broadly consists of two different rock types: An upper part of felsic migmatites (Figure 5c), and a lower part of leucogranites that crosscut the foliation of the metamorphic host rocks (Figure 5d). The migmatites display leucosomes that are sub-parallel with respect to a foliation defined by the orientation of biotites, quartz and plagioclase, and judging by the relative proportions of leucosome with respect to the apparent paleosome this could tentatively be classified as a diatexite. However, as this rock was located just a couple meters below the Cretaceous paleosurface, the entire core is intensively weathered making more detailed petrographic observations impossible. Zircons extracted from a segment of the core between 7718.5’ and 7719’ (corresponding to Figure 5c) have rounded to sub-rounded external shapes and length:width ratios from 1:1 to 2:1. CL images revealed a complex internal morphology for the imaged grains, characterized by cores with oscillatory-zoning that are mantled by low luminescent thin metamorphic rims (inset, Fig 6e). Individual grains are generally not larger than 110µm, and metamorphic rims do not exceed 20µm in thickness. We performed 85 spot analyses in the xenocrysts utilizing a 30µm laser diameter, and 20 analyses on the overgrowths using a 10µm laser-beam diameter on ion- counter configuration. From the rim analyses, only 12 clustered around an age of ~990Ma while the remaining gave ages that were much older, reflecting partial zircon recrystallization and/or mixing of old core material in the ablation sites. Figure 6e shows the concordia plot for this sample, where green ellipses refer to analyses performed using the 10µm spot-size; red ellipses refer to <5% discordant analyses performed with a 30µm diameter beam, and gray ellipses are >5% discordant analyses also with a 30µm beam. A concordia age calculated from the rims data yields a value of 989±14Ma (MSWD=0.7), interpreted as the age of the metamorphic event. From the xenocryst core results 11

24 grains with >30% discordance were discarded from ploting, while the remaining 74 revealed that all the zircons analyzed were derived from late Paleproterozoic to early Mesoproterozoic source areas like those found in the northwestern Amazon Craton. From the concordia plot of Figure 6e it can readily be observed that many of the analyzed xenocrysts have been affected by varying degrees of Pb-loss, possibly by partial recrystallization during the metamorphic event. If the observed discordance is in effect related to metamorphism, individual ellipses could conceivably be displaced from their “true” age towards slightly younger apparent 206Pb/207Pb ages if they lie along a discordia chord that is subparalel to concordia joining the original age of each individual grain (as the upper intercept) with the age of the metamorphic event in the lower intercept (e.g. Nemchin and Cawood, 2005). This effect however, although difficult to quantify, would only reinforce the observation that all of the detrital grains analyzed have crystallization ages older than about 1.45 Ga as any “partially reset” ages would yield slightly older upper intercepts if the Pb-loss event goes through 0.99 Ga (age of metamorphism) instead of being projected through the origin. The diverse range of ages obtained for the xenocrystic cores reflects the detrital nature for the protolith of this rock, providing valuable information about the provenance of this unit. The age spectrum, which is shown in Figure 9, is dominated by peak modes at ca. 1470 Ma, 1500 Ma, 1570Ma, and in the range 1650-1680Ma.

The second sample analyzed from the Caiman-3 well, corresponding to the lower segment of leucogranites, was taken from the depth interval between 7728.5’ and 7729’. It is petrographically classified as a monzogranite with muscovite and it crosscuts the foliation of the migmatites described above. Zircons recovered have more elongated and prismatic shapes than those from the migmatites, display width:length rations between 1:2 and 1:4, and are in this case characterized by bright overgrowths enclosing darker xenocryst cores with crystal terminations that tend to be sharper in comparison to the rounded edges of the zircons from the host migmatite (inset, Figure 6f). Additionally, some of the overgrowths were observed to have oscillatory-zoning patterns, indicating crystallization from a melt. Analyses from this sample were carried out the same way as in zircons from the migmatites, using 10µm ion-counter configuration for the rims and

25 30µm faraday configuration for the cores. Twenty-three spots were analyzed from the overgrowths but only 7 of them were younger than ~1Ga, reflecting significant mixing of older material in most of the ablation pits. Those 7 rim analyses are mostly <5% discordant yielding a concordia age of 952±21 Ma (MSWD=0.98) for the crystallization event, confirming the textural relationships observed from the core as the leucogranites are in fact younger (and distinct within error) than the host felsic migmatites. This age of crystallization is important as it places a minimum age for pervasive deformation in this region of the basement, and is comparable to ages reported for postectonic pegmatitic dikes in the Mexican inliers (Solari et al., 2003). From the xenocryst cores, 61 out of the 84 analyses performed are <5% discordant and they yield ages ranging from ca. 1440 to 1700 Ma with distribution peak maxima at ~1460, ~1490, ~1530, ~1615 and ~1677 Ma. This age distribution closely resembles that of the migmatites from this same well (Figure 8), suggesting that these leucogranites may represent anatectic melts derived from metasediments similar or related to those of the host rocks.

5.3. Cratonic exposures: Samples analyzed from outcrop exposures of the Amazon Craton in eastern Colombia are all undeformed or sheared rocks, analyzed in order to constrain a minimum age of significant metamorphism and deformation within this largely unknown portion of the shield. They are subdivided into the Araracuara granitoids, collected from a basement along the Yari and Caqueta Rivers in proximity to the Araracuara Indigenous settlement, and the Mitu-Taraira granitoids, outcropping in easternmost Colombia in the Vaupes department along the Vauper and Apaporis rivers (Fig2).

5.3.1. Araracuara Granitoids: Sample PR-3215 is classified as a sheared biotite syenogranite. It is composed of quartz, alkaline feldspar, plagioclase, brown biotite with occasional chloritized margins, and sporadic epidote (seemingly pistacite). Two generations of K-feldspar are observed in the thin section, a probably older generation of orthoclase showing evidence of strong cataclastic deformation, while the more abundant microcline is coarser-grained and appears less deformed. Twinned microcline megablasts are common and display

26 poikilitic textures, containing inclusions of plagioclase, quartz and less frequently biotite. Some crystals of plagioclase included or in direct contact with the K-feldspar exhibit myrmekitic textures, and quartz crystals appear elongated, displaying ondulose extinction and contorted margins. These observations altogether suggest that the granitic rock has been deformed under dynamic low- to intermediate-temperature metamorphic conditions resulting in grain-size reduction and orienting of the quartz crystals, recrystallization of orthoclase as microcline, and are responsible for the partial replacement of plagioclase for K-feldspar observed as myrmekitic structures. Solid-state recrystallization may have occurred in a temperature range between 400-450°C, constrained by the observed deformation mechanisms of quartz and feldspars (Passchier and Trouw, 2005). U-Pb geochronological data obtained from zircons of this sample all define a single population with variable degrees of Pb-loss (Figure 7a), with no evidence for the presence of older inherited material. CL images obtained from the analyzed grains (inset, Figure 7a) show internal oscillatory zoning textures typical of zircons crystallized from a melt, and many of the grains seem to be affected by significant metamictization. A concordia age calculated using the 14 most concordant analyses (<2% discordant) yields a value of 1756±18Ma (MSWD=0.98), equivalent to a 206Pb/207Pb weighted mean age of 1750±18Ma (MSWD=0.43) calculated using the entire dataset. The metamorphic conditions that affected the original granitic rock were not of sufficient grade to induce zircon recrystallization and/or formation of metamorphic overgrowths, and we consider the age of 1756±18 Ma as reflecting the age of crystallization of the granitic protolith.

Sample J-263 has essentially the same mineralogy as sample PR-3215 but it is less affected by cataclasis and recrystallization. Orthoclase is more abundant that microcline, and other deformational features like myrmekites and grain-size reduction are less widespread. Original igneous textures such as dominantly euhedral plagioclase surrounded by anhedral quartz grains filling spaces are better preserved, evidencing their igneous origin (Vernon, 2004). Zircons from this sample also show oscillatory zoning under CL (inset, Figure 7b) and are strongly metamictic. All but one of the analyzed grains are slightly to significantly discordant, thus not allowing the calculation of a concordia age. A 206Pb/207Pb weighted mean calculation for 16 grains that are less than

27 10% discordant yields an age of 1732±24Ma (MSWD=0.66), which is interpreted as the age of crystallization of the syenogranite. As in the previous sample, no inheritance was observed in the grains selected for analysis.

The age of the metamorphic event that affected the granitoids of the Araracuara area is constrained between the crystallization ages discussed above and K-Ar cooling ages of around 1320-1340 Ma obtained in micas from nearby rocks (samples PRA-51 and PRA- 53 of Priem et al. 1982). No precisions about the age of metamorphism can be made based on the zircon U-Pb data presented here.

5.3.2. Mitu-Taraira Granitoids: Granitoids selected from the Mitu and Taraira regions of Colombia are all petrographically very similar, characterized by porphyritic granitoids with subordinate mafic minerals like biotite and amphibole as the only ferromagnesian-bearing phases. Perthitic textures are common in the feldspars and amphiboles display optical properties of the Riebeckite-Arfvedsonite series, indications of the strong alkalic character of these intrusives. Zircons from all the samples are mostly prismatic displaying width:length ratios between 1:3 and 1:7, with U contents that typically range from ~60 to ~1500 ppm. Inheritance is common in all the samples.

Crystallization ages calculated from these granites are also very similar, falling within a restricted range from 1530 to 1588 Ma (Figures 7c, d, e, f). Sample AH-1216 from the Vaupes River SE of Mitu yields a concordia age of 1574±16 Ma (MSWD=0.37) calculated from seven concordant analyses, with most of the inherited cores defining a rather coherent population at ~1780 Ma. Most of the analyzed spots from the igneous portions of the grains are affected by modern Pb-loss and are shown in gray in Figure 7c. A 206Pb/207Pb weighted mean age calculated using all the analyzed spots, including those that are >5% discordant, produces an undistinguishable age of 1574±17 Ma with an MSWD=0.20. Sample PR-3092 from the Lerida settlement along the Apaporis River produced a complex concordia, as strong metamictization of the grains resulted in significant Pb-loss and discordance. Nine grains that are less than 10% discordant define

28 a 206Pb/207Pb weighted mean age of 1578±30 Ma (MSWD=0.76), and most of the inherited grains cluster around ~1800 Ma. This sample has the oldest zircons analyzed in the present study, with three xenocrysts that yield early Paleoproterozoic ages between 2.1-2.3 Ga and two others with late Archean ages around 2.6 Ga. Zircons from sample AH-1419, collected from the Raudal Cupay in the Apaporis River proven to be mostly concordant (Figure 7e). Analyses from 11 igneous crystals and/or overgrowths yields a 206Pb/207Pb weighted mean age of 1530±24 Ma (MSWD=0.32) while most of the xenocryst cores have ages between 1.70 and 1.86 Ga. There is another set of inherited ages that defines a younger cluster at ~1.59 Ga. Finally, sample CJR-19 from the Raudal La Libertad on the Apaporis River yields a 206Pb/207Pb weighted mean crystallization age of 1588±21 Ma (MSWD=1.03) calculated using 35 analyses performed in oscillatory- zoned grains and overgrowths as revealed by CL imaging. Analyses performed in areas interpreted as inherited xenocrysts are in some cases as old as ~1.9Ga, but some others show a significant age overlap with spots interpreted as reflecting granitoid crystallization. However, age calculation using the zircon-age extractor algorithm of Isoplot results in an undistinguishable age of 1591 +20/-4 Ma, obtained from a coherent group of 44 analyses. It is possible that some of the xenocryst analyses that are slightly older than the crystallization ages only represent mixed ablation spots between the xenocryst and the magmatic overgrowths. This sample corresponds to the series of granites that conform the basement for the metasediments of the Serrania del Taraira, thus placing a maximum age of 1.58 Ga for the deposition of these supracrustal sequences. These stratigraphic and age constraints preclude correlations that suggest affinity of these metasedimentary sequences with the Group (Galvis et al., 1979), given its exclusively Paloproterozoic age (Santos et al., 2003).

6. Discussion. Proposed evolution of the Putumayo orogen within a Rodinian context: The participation of the Amazon Craton during the assembly of the Rodinia supercontinent has for long been inferred, using the Bolivian-Brazilian Sunsas-Aguapei orogenic belt as a tie to other Grenville-age orogenic segments worldwide (Cordani et al. 2009; Hoffman, 1991; Li et al. 2008). Continuation of this Meso- Neoproterozoic belt

29 towards the northwest extending beneath the Amazon River graben and the north Andean foreland basins has commonly been inferred by some authors, but this assumption has so far only been based on indirect evidence. Observations used to support this idea are 1) the widespread occurrence of ~1Ga zircon populations in parautochthonous lower Paleozoic sequences of the Peruvian Andes (Cardona et al. 2009; Chew et al. 2007, 2008; Cordani et al. 2010), and 2) the occurrence of Grenville-age inliers in the Andes of Colombia (Fuck et al. 2008; Li et al. 2008; Restrepo-Pace et al. 1997). However, the complex tectonic evolution of the northern Andes characterized by semi-continuous and superposed extensive terrane transfer and accretion throughout the Phanerozoic (Aspden et al. 1987; Bayona et al. 2006, 2010; Forero-Suarez, 1990; McCourt et al. 1984; Ramos, 2010; Toussaint, 1993), casts doubts on the direct correlation between the basement blocks exposed in the cordillera and that of its related foreland basins. The geochronological results presented in this paper provide, for the first time, direct evidence that demonstrates the existence of an autochthonous Grenville-age orogenic belt along the northwestern margin of Amazonia, which serves both as a basis for global intercratonic correlations and as a reference against which the Cordilleran inliers and other supposedly peri-Amazonian blocks can be compared. As will be further expanded below, our interpretations of the geological and geochronological data obtained from this study favor a tectonic model for the evolution of NW Amazonia’s Mesoproterozoic margin that is very different from that of the Sunsas-Aguapei orogen. Consequently, we propose the name Putumayo orogen for a distinct segment of a Grenville-age mobile belt in northern South America, whose paleogeographic reconstruction and global tectonic implications should also be different to the Sunsas belt, according to the nature and timing of the major geologic events that locally characterized its evolution. We propose a two-stage metamorphic history for the development of this orogen, characterized by initial accretionary orogenesis followed by final ocean closure and continent-continent collision. The following discussion will be subdivided in four temporal intervals, roughly following the paleogeographic model presented in Figure 10. They include: 1) Pre- Rodinian framework: the peri-Amazonian “Oaxaquian-Colombian” arc phase, 2) Rodinia assembly initiation: early arc and terrane accretions onto Amazonia’s margin, 3) Rodinia final assembly: the Putumayo-Sveconorwegian orogeny; and 4) some observations on

30 regional cooling and post-collisional evolution. A correlation chart comparing the timing of major geological events in the different blocks considered for the tectonic reconstruction and discussed throughout the text is presented in Figure 9.

6.1. Pre-Rodinian framework (~1.3-1.08 Ga): The position of Amazonia during this time period is constrained by few paleomagnetic poles obtained in the SW portion of the Amazon craton that suggest an oblique collision between Laurentia and Amazonia along the Llano-Rondonia segments at ca. 1.2 Ga (Tohver et al. 2002), and a continued strike-slip displacement that juxtaposes the same SW margin of Amazonia against the SE Appalachian margin at ca. 1.15 Ga (D'Agrella- Filho et al., 2008). Additional geochemical/geochronological evidence supporting this model is the presence of exotic, Amazonian-affine crust in the Blue Ridge /Mars hill inlier of the southern Appalachians (Loewy et al. 2003; Tohver et al. 2004a). Structural data for both of the supposedly colliding margins agrees with a sinistral-shearing kinematic history in both the Llano and the Blue Ridge segments, the later coinciding with the final of the Nova Brasilandia intracontinental rift of central-western Brazil (Tohver et al. 2004b). Significant deformation in both segments is culminated by the occurrence of undeformed, postectonic intrusions, represented by the Sunsas suite dated at 1076±18 Ma in the Sunsas-Aguapei belt (U-Pb SHRIMP age by Boger et al. 2005) and undeformed rhyolitic dikes dated at 1098±10 Ma by ID-TIMS in the eastern Llano uplift (Mosher, 1998; Walker, 1992).

The relative position and interaction of Baltica with respect to Laurentia during this period is better understood, constrained by both paleomagnetic and geologic data (Cawood and Pisarevsky, 2006; Cawood et al. 2010; Pisarevsky et al. 2003 and references therein). Prior to ~1.25Ga, Baltica is though to have been attached to the modern eastern coast of Greenland along the northern Timanian margin (Figure 10a), before it started a late Mesoproterozoic ~90 degrees clockwise rotation on its way to its final Rodinia position (Cawood and Pisarevsky, 2006). This rifting and rotation is responsible for the opening of the so-called Asgard sea, where a subduction complex was established along the Laurentian margin giving birth to the Neoproterozoic Valhalla

31 orogen (Cawood et al. 2010). During this rotation, a passive margin system is established along Baltica’s trailing edge and accretionary tectonics were triggered along its leading edge during the early stages of the Sveconorwegian orogeny (Bingen et al. 2008b; Bogdanova et al. 2008).

6.1.1. Geochronological structure of Amazonia’s continental leading margin: U-Pb zircon geochronological results presented in this study confirm the early Meso- to late Paleoproterozoic character of the crystalline basement exposed in the eastern Colombian lowlands. Undeformed alkaline granitoids with crystallization ages between 1.53-1.58 Ga intrude a basement that is predominantly equal or older than ca. 1.7Ga old, considering the ages of inherited zircon xenocrysts in the Mesoproterozoic intrusives (Figure 7) and in accordance with a SHRIMP U-Pb age of 1703±7 Ma from a nearby biotite qz-diorite along the Colombian-Brazilian border (Tassinari et al. 1996). Further west, in the Araracuara basement window, deformed granitoids yield U-Pb ages of 1732±24 and 1756±18 Ma, evidencing the extent of the Paleoproterozoic basement in eastern Colombia. All these results are broadly in agreement with a NW extension of the Rio Negro-Juruena province from Brazil towards Colombian territory (Tassinari and Macambira, 1999), where early Mesoproterozoic undeformed granites intrude Paleoproterozoic gneisses and deformed granitoids. These intrusive suites are possibly similar in nature to the ~1.5 Ga anorogenic granitic complexes that are widespread in the RNJ province and western Amazonia in general (e.g. Parguaza Batholith in Venezuela, Gaudette et al. 1978; Rio Crespo intrusive suite of Rondonia, Bettencourt et al. 2010; among many others as summarized by Dall'Agnol et al. 1999).

Furthermore, latest Paleoproterozoic protolith ages obtained from drilling-well cores of migmatitic gneisses underlying the Putumayo foreland (wells Mandur-2 and Payara-1, Figure 6) suggest that, previous to the inception of the Putumayo orogen, the Paleoproterozoic basement of NW Amazonia extended all the way towards the cratonic margin (today’s limits with the Cordillera, covered under the Andean foreland). This observation contrasts with the regional structure mapped in SW Amazonia, where the Rondonia-San Ignacio Mesoproterozoic orogen lies outboard of the Rio Negro-Juruena

32 province and separates it from the Sunsas-Aguapei orogen (Cordani and Teixeira, 2007). It is interesting to note the conspicuous lack of evidence for zircon-forming events throughout most of the Mesoproterozoic in samples analyzed from the Putumayo basement. While during this period SW Amazonia’s margin is characterized by voluminous arc-related magmatism and crustal growth by accretion of island arcs and continental terranes (Bettencourt et al. 2010; Cordani and Teixeira, 2007), autochthonous NW Amazonia seems to have experienced a completely different geological history in a tectonically more stable setting, conceivably as a wide back-arc or a passive margin.

6.1.2. Basins and sedimentation in Amazonia’s continental margin: The geological knowledge of the Proterozoic basins and sedimentary successions in NW South America is very limited. The only Proterozoic sedimentary units that have been described to date are metasediments from the Taraira, Caranacoa and Naquen ranges of eastern Colombia (of unknown age, but arguably younger than 1.5Ga given the new ages presented here from granites of the Taraira area), and the volcanosedimentary Piraparana Formation of Priem et al. (1982). Cawood et al. (2007) suggested a possible correlation between the Piraparana formation of eastern Colombia with cratonic-cover and rift sequences of Rondonia (Huanchaca and Aguapei groups). However, these sequences in the Bolivia-Brazil area are interpreted as intracratonic or supracrustal in nature, deposited in an intracontinental-rift and/or passive-margin settings prior to the Sunsas collisional phase (Teixeira et al. 2010). Rhyodacitic lavas included in the Piraparana formation have been dated at ca. 920 Ma by Rb-Sr (Priem et al. 1982), younger that the depositional ages inferred for the passive-margin and rift sequences in the Sunsas region and postdating collisional orogenesis recorded in the Putumayo orogen. Instead of a marginal cratonic cover, we propose that the Piraparana formation could represent either 1) foreland basin deposits related to Putumayo orogenic development inboard in Amazonia, or 2) Neoproterozoic syn-rift sedimentation and volcanism associated with early extensional events of the Neoproterozoic Güejar-Apaporis graben preceding the collapse of the Putumayo orogen and related Grenville-age belts. Only detailed sedimentary provenance studies in the Piraparana formation will allow us to test these hypotheses.

33 Metasedimentary migmatites recovered in the Caiman-3 well show detrital zircon age spectra indicative of provenance from the cratonic interior, dominated by Rio Negro- Juruena and Ventuari-Tapajos -like ages (Figure 8). Distribution peak maxima at ca. 1470, 1500, 1570, 1650-1670 and 1880 Ma, with more than 50% of the analyzed grains on the Paleoproterozoic side of the spectrum, are completely different from the patterns observed in metasediments associated with the Cordilleran terranes, where no grains older than 1.51 Ga were found in the more than 400 individual zircons analyzed. Maximum depositional ages for the sedimentary protolith of these migmatites are calculated at 1444±15 Ma (1σ, total error) from the age of the youngest grain of the >95% concordant xenocryst analyses. Although the age of deposition of the protolith is loosely bracketed between this age and the metamorphism at 989±14 Ma (Figure 6e), sedimentation clearly post-dates the protoliths of the Mandur-3 and Payara-1 gneisses, implying that these migmatites represent a metamorphosed Mesoproterozoic sedimentary cover of the Paleoproterozoic marginal basement in the area. It is also entirely possible that deposition of this sedimentary sequence occurred later than 1.44 Ga, in a location where syn-sedimentary arc influence was negligible or non-existent and only cratonic- like ages are recorded in the zircon age spectra.

6.2. The Oaxaquian-Colombian fringing-arc system (1.30-1.10 Ga): Proterozoic basement blocks found in Mexico are included in the units known as the Novillo gneiss, Huiznopala gneiss, the Oaxacan complex, and the Guichicovi complex (Figure 1 in Keppie and Ortega-Gutierrez, 2010). These inliers are characterized by a similar Proterozoic history consisting in intrusion of granitoids with arc and backarc chemical affinities during the interval ~1.3 to 1.15 Ga, intrusion of AMC (Anorthosite- Mangerite-Charnokite) complexes around 1.01 Ga, and high-grade granulite-facies metamorphism at around 0.99 Ga (Cameron et al., 2004; Keppie and Ortega-Gutierrez, 2010; Solari et al. 2003; Weber and Hecht, 2003; Weber and Kohler, 1999). In contrast to Mexico, few Proterozoic meta-igneous units have been identified in the Colombian Andes, where they are only represented by the Guapoton orthogneiss (Cordani et al.,2005), Las Minas orthogneiss and La Macarena mylonites (this study), and the San Lucas orthogneiss of Ordoñez-Carmona et al. (2009). Most of the Proterozoic units

34 outcropping in the Colombian inliers are metasedimentary or metavolcanic in nature (Kroonenberg, 1982). Similarities in Pb isotopic compositions, U-Pb ages of granulite- facies rocks, and Paleozoic fossil faunas from Colombia and Mexico, led Ruiz et al. (1999) to suggests a correlation between the Proterozoic inliers of these two regions specially between the Garzon, Santa Marta and Guichicovi inliers, correlation that has found further support with recent zircon Hf isotopic data (Weber et al. in press).

In many Mesoproterozoic paleogeographic reconstructions, Oaxaquia is commonly positioned along the northwestern margin of Amazonia in close association with the Colombian Andean inliers, where it is thought to have evolved as a parautochthonous arc complex latter to be trapped between colliding continental blocks during the assembly of Rodinia (Bogdanova et al. 2008; Cardona et al. 2010; Keppie et al. 2001; Keppie and Dostal, 2007; Keppie and Ortega-Gutierrez, 2010; Keppie and Ramos, 1999; Li et al. 2008). Figure 11 presents a schematic reconstruction for the tectonic configuration of proto- NW South America, in which we include the Colombian cordilleran inliers and the Mexican terranes as part of a commonly evolving “Oaxaquian-Colombian” peri- Amazonian fringing arc system located outboard of Amazonia’s leading edge (Figure 10a). According to Busby et al. (1998), long-lived convergent margins facing a large ocean basin may evolve through three distinct phases, (1) a strongly extensional intraoceanic-arc phase, (2) a mildly extensional arc system, and (3) a compressional continental arc phase following accretion of the fringing-arc terranes. We propose that the Oaxaquian-Colombian fringing arc may have evolved in a similar fashion, as many of these stages can be identified from its Mesoproterozoic geological record. Initiation of the strongly extensional arc phase is represented by the occurrence of 1.3 Ga rift related basalts (now transformed into mafic granulites) of the north Oaxaca complex (Keppie and Dostal, 2007) and bimodal igneous suites with backarc geochemical signatures of the Novillo gneiss (Keppie and Ortega-Gutierrez, 2010). Rifting from Amazonia was shortly followed by the development of an intraoceanic arc (phase 2), characterized by widespread arc-related juvenile magmatism between 1.3 and 1.2 Ga in Oaxaquia (Keppie et al. 2001; Keppie and Ortega-Gutierrez, 2010; Weber and Hecht, 2003; Weber and Kohler, 1999)Weber et al. in press), which then evolved towards a more mature arc as

35 reflected by granites displaying more crustal isotopic compositions like the 1.15 Ga protolith of the Guapoton orthogneiss in the Garzon massif (Restrepo-Pace et al. 1997). Associated to this phase may start the accumulation of thick vulcanosedimentary sequences included within the Garzon group, now represented by thrust slices of the El Vergel migmatites in which metasedimentary felsic granulites yield calculated maximum depositional ages around 1.12 Ga (e.g. sample MIVS-11). Metasedimentary units included in the Garzon and Las Minas massifs of southern Colombia all have maximum protolith depositional ages within the range 1.0 to 1.12 Ga, and they are interpreted as syn-collisional to slightly pre-collisional basins (similar to Assemblage 1 and 2 basins of Cawood et al. 2007) developed in close proximity to a convergent margin. Detrital zircon signatures from these units can be explained in terms of derivation from granitic plutons included within the same Oaxaquian-Colombian arc terrane, with no detritus sourced from continental Amazonia crust evidenced by the paucity of older than 1.5 Ga (Rio Negro-Juruena –like) ages observed in the spectrum (Figure 8). The absence of Paleoproterozoic detritus in these units, both pre- and syn-collisional could be explained in at least two ways: First, in terms of a high-standing continental arc acting as a topographic barrier preventing detritus of the cratonic interior from reaching a forearc basin, and 2), that there was truly a disconnect in the sedimentary systems between arc- related basins and those formed along the stable continental margin. In the second case, these basins could conceivably be separated by a wide back-arc developed behind a fringing-arc complex (Figure 11). It should be noted that there is a slight overlap in the age distribution spectra between the metasediments with craton-like signatures of the Caiman-3 migmatites discussed above and those from the Garzon and Las Minas massifs, spanning the age range from 1.46 to 1.50 Ga (Figure 8). There are many lines of evidence that support the presence of older continental material to be present within the parautochthonous terranes; Recently reported orthogneisic units with protolith ages around 1.5 Ga in the San Lucas Massif (Ordoñez-Carmona et al. 2009), and protolith crystallization ages of 1.46 Ga from metaigneous mylonites of the Macarena range from this study, comprise direct evidence for the presence of such old blocks within the Colombian terranes. We suggest that initial rifting of the Oaxaquian-Colombian arc from Amazonia during the initial extensional phase may have detached fragments of older

36 continental crust and incorporated them within the basement of the intraoceanic arc (Figure 11), so differences in Nd and Hf isotope compositions between the different orthogneissic units could also be explained in terms of different crustal contamination histories related to along-strike variations in the nature of the basement that makes up each segment of the arc (i.e. segments built up only by juvenile rocks vs. segments which have incorporated older Proterozoic basement of Amazonia following initial arc rifting).

Based on Hf isotope systematics in zircons, Weber et al. (submitted) identified two different reservoirs that took part in the evolution of Oaxaquia: First, what they term “typical Oaxaquia”, comprised by juvenile intrusives of an early intraoceanic arc which yield high positive εHf initial values (orthogneisses of the Oaxaca complex and the Novillo gneiss), and second, crustal slices with an older cratonic Amazonian component that yield mixed initial εHf compositions between a juvenile and a more evolved component (the Huiznopala and Guapoton orthogneisses). Following from this distinction, these authors propose that typical Oaxaquia crust evolved as an intraoceanic arc outboard of Amazonia, whereas the less radiogenic arc-related intrusives of the Huiznopala and Guapoton orthogneisses were developed along and active continental margin built on cratonic Amazonia crust. Geochronological results from core samples recovered in the Putumayo basin basement presented in this study do not support the existence of a late Mesoproterozoic active margin developed in autochthonous Amazonia crust. Instead, our data suggest that the cratonic margin of northwestern South America is characterized by late Meso- to early Neoproterozoic metamorphic reworking of late Paleoproterozoic basement and associated Mesoproterozoic cover sequences, with no magmatic events identified within this range. In our reconstruction (Figure 10), we include all the late Mesoproterozoic Colombian and Mexican inliers in a common fringing arc system outboard of Amazonia instead of separated in two sub parallel arcs.

Following this period of intensive arc plutonism, there is an interval of magmatic quiescence that spanned the age range between 1100 and 1050 Ma and is present both in Oaxaquia and the Colombian terranes (Figure 9). One possible scenario for the sudden shutting down of magmatism could be a drastic change of stress regimes along the arc,

37 switching from a mildly extensive to a compressive regime (moving from phase 2 to phase 3) that could have resulted in increased plate coupling along the margin, continent- directed trench migration, and final collapse of the fringing arc against the continental margin (e.g. Busby, 2004). This transition between intraoceanic arc magmatic activity and terrane accretion marks the initiation of collisional events recorded in the Putumayo orogen.

6.3. Rodinia assembly initiation: terrane and arc accretion onto Amazonia’s margin (1.07-1.01 Ga): Although mostly obliterated by the later ca. 0.99 Ga granulite-facies overprint, there is textural and geochronological evidence supporting the existence of an early metamorphic event between 1.05 and 1.01 Ga, both in the cordilleran inliers (Cordani et al. 2005; Jimenez Mejia et al. 2006) and in the basement of the Putumayo basin (this study). Migmatization of the Las Margaritas unit in the eastern side of the Garzon massif is constrained to 1015±7.8 Ma by SHRIMP U-Pb dating of zircons from a leucosome and 1034±16 Ma by a Sm-Nd garnet-whole rock isochron, although additional Sm-Nd data evidences that the ~990 Ma event is locally present within this unit as well (Cordani et al. 2005). In the basement of the Putumayo basin, the amphibolite-facies metamorphic event identified in the Mandur-2 and Solita-1 wells yields ages of 1017±10 Ma and 1044±26 Ma, respectively (Figure 9), and in the Guamoco area of the Colombian Central Cordillera just south of the Serrania de San Lucas an orthogneiss unit with protolith ages of ca. 1.28 Ga was also affected by metamorphism at 1.04 Ga (Victor Valencia, personal communication). Late Mesoproterozoic tectonothermal events constrained between 1.1 and 1.07 Ga are also known from the northern Oaxaca complex (Solari et al. 2003); Weber et al. submitted), where they have received the name of Olmecan orogeny. These migmatization ages are interpreted in terms of accretion of the Oaxaquian-Colombian arc onto Amazonia continental margin, probably along a series of slightly diachronous soft- collision events. Amalgamation of the fringing terranes against Amazonia was possibly shortly followed by slab-break off and melting of the lower crust, leading to the generation of AMC intrusive complexes that are widespread amongst the Oaxaquian

38 terranes (Weber et al. submitted) and which are possibly also recorded in the Sierra Nevada de Santa Marta massif in the northernmost Colombian Andes.

In Baltica, metamorphism of the Bamble and Kongsberg tectonic wedges marks the timing of early terrane accretions onto Fennoscandian crust through the collision of Telemarkia against the Idefjorden terrane (the Arendal phase, Bingen et al., 2008b). The Bamble and the Kongsberg terranes comprise variably metamorphosed supra-subduction complexes whose metamorphic ages constrain the age of collision between ~1140 and 1090 Ma, earlier than the initial accretions along Amazonia’s margin as recorded in the Putumayo Orogen and Oaxaquia. Additionally, marked differences that exist between the detrital zircon age spectra of Telemarkia’s metasedimentary units (Bingen et al. 2001; Bingen et al. 2003), and those from NW autochtonous/parautochtonous Amazonia (Cardona et al. 2010; this study) lead us to conclude that regardless of the exotic or indigenous origin of Telemarkia with respect to Fennoscandia, an Amazonian ancestry for this terrane and its subsequent accretion to Baltica by early collisional interactions with Amazonia at ca. 1.1 Ga are both unlikely.

6.4. Final Rodinia assembly: maximum convergence along the Putumayo- Sveconorwegian orogen (1.00-0.98 Ga): As it was mentioned before, collisional interaction between Baltica and Amazonia during the early Neoproterozoic agglomeration of Rodinia have already been suggested by previous authors (Bingen et al. 2008b; Bogdanova et al. 2008; Cardona et al. 2010; Keppie and Dostal, 2007; Li et al. 2008). However, geological evidence to support this correlation was previously not available from the Amazonian side, given that the only previously known outcrops of Grenville-age crust were Cordilleran inliers whose autochthonous character with respect to non-remobilized NW Amazonia was uncertain. New U-Pb data presented here demonstrates the existence of a Grenville-age orogenic belt in NW South America, buried under Andean foreland basin sequences, and for the first time provides a link between granulite-facies tectonothermal events occurring in NW cratonic Amazonia, the Colombian inliers, Oaxaquia, and the Sveconorwegian orogen (Figure 9).

39

As noted by Bogdanova et al. (2008), paleogeographic reconstructions between Laurentia and Baltica imply the necessity of a “third continent” in order to explain some periods of the Sveconorwegian orogeny, and they suggest collision with Amazonia as a feasible tectonic scenario. Additionally, these authors also point that the chronology of the final granulite-facies event in the Sveconorwegian indicates that crustal shortening was still underway along this orogen while extensional regimes were already dominating the Grenville margin (Gower and Krogh, 2002; Gower et al. 2008), so in addition of the third continental mass needed in order satisfy late-Sveconorwegian orogenic events, this third continent needs to fulfill certain geological requirements in terms of the chronology for the final collision-related metamorphism. All of the Oaxaquian inliers show evidence of an early Neoproterozoic granulite-facies tectonothermal event at ca. 990 Ma (Cameron et al. 2004; Keppie and Ortega-Gutierrez, 2010; Lawlor et al. 1999; Ruiz et al. 1999; Solari et al. 2003; Weber and Kohler, 1999) known as the Zapotecan event, which is also coincident with the age of the granulite-facies metamorphism from the Garzon Massif (El Vergel granulites, Figure 3a and c; Guapoton-Mancagua orthogneiss, Figure 3b), Las Minas orthogneiss (Figure 3d), and is also recorded in ortho- and para-migmatites of the Putumayo basin basement (Payara-1 and Caiman-3 wells, Figure 6). In line with these chronological evidences, our reconstruction displays final collisional between Baltica and Amazonia along a juxtaposed Sveconorwegian-Putumayo orogenic belt at ca. 990 Ma, defining a separate belt with a structural trend that lies almost orthogonal with respect to the Sunsas-Grenville orogenic tract (Figure 10). Continuation of the Putumayo Orogen towards the (actual) northeast, underlying the foreland Llanos basins of northern Colombia and Venezuela still awaits for conclusive evidence, although there are observations that may suggest it is so. Occurrences of possible Grenville-age orogenic rocks in Venezuela are expressed as: 1) The presence of the high-grade “Nirgua complex” inlier of the southern Merida Andes, consisting of mafic and felsic charnockites crosscut by ultramafic dykes resembling granulitic complexes of the Colombian Andes, and 2) A wide variety of high-grade rocks that occur as xenoliths in Oligo-Miocene diatremes, in drilling wells from the La Vela Gulf, and boulders in Paleocene and Miocene conglomerates (Grande and Urbani 2009 and references therein).

40 Additionally, the occurrence of feldspar K-Ar cooling ages of ca. 1.0 Ga in samples from drilling-well cores in eastern Venezuela (locations in Figure 1) also records the extension of the Grenville-age heat pulse towards this portion of South America (Feo-Codecido et al. 1984)

Cameron et al. (2004) noted that there is no obvious variation in ages for the granulite- facies event in Oaxaquia with respect to geographical position, observation that also holds for the available U-Pb ages of high-grade metamorphism in the Colombian massifs and the Putumayo basin basement. With the exception of the Zancudo migmatites (CB- 006, Figure 3e), ages presented in this study for the early-Neoproterozoic metamorphic event all fall in a restricted range between 986 and 992 Ma, indistinguishable from each other within analytical error. These observations suggest that the character of the collision between Baltica and Amazonia was relatively close to frontal between the proto- margins. Following collision, shortening and crustal thickening may have continued in the orogen, identified in the Sveconorwegian belt as continued deformation along the zone between 980-970 Ma, propagation of the foreland, and -facies metamorphism on the “eastern segment” at 970 Ma (Johansson et al. 2001), also coinciding with the early stages of intrusion of mafic dikes related to the Blekinge- Dalarna dolerite swarm (Soderlund et al. 2005). Late tectonothermal events with similar ages are also recorded along the margin of Amazonia, where metatexic migmatites of the Las Minas massif yield ages of 972±14 for the anatectic event, similar to other ages of ~0.97 found elsewhere in Oaxaquia (Cameron et al., 2004; Weber et al. in press). In the Putumayo basin, the undeformed leucogranite that crosscuts the foliation of the migmatites in the Caiman-3 well provides a minimum age of 952±21 Ma for pervasive deformation in this sector of the Putumayo orogen. This age is similar to that obtained for undeformed granitic pegmatites in Oaxaquia, constrained to ca. 0.97 Ga as discussed by Solari et al. (2003).

6.5. Post-collisional events and regional cooling (post 0.97 Ga): In different locations of the Colombian Andes, medium- to low-temperature cooling of the high-grade basement of the cordilleran inliers is constrained by K-Ar and Ar-Ar data.

41 Although ages spread over a wide range from ~1028 to ~561 Ma, most of them cluster in a restricted range from 970 to 910 Ma (Cordani et al. 2005; Restrepo-Pace et al. 1997) implying relatively fast rates of exhumation for the orogenic rocks. Metamorphic rims in zircons from the Santander and Jojoncito paragneisses yield U-Pb ages of metamorphism at 864±66Ma and 916±19Ma respectively (Cordani et al. 2005), much younger than any of the other Proterozoic metamorphic events recorded elsewhere in the Colombian Andes. Although inherited zircon analyses from the detrital protolith of these gneisses display age peaks that resemble those from other metasedimentary units presented in this study there is an important difference, and its the presence of detrital grains with ages equivalent to the metamorphic events described from the Garzon and Las Minas massifs at ca. 980 and 1020-1050 Ma. We suggest that the sedimentary protoliths of these paragneisses were deposited later than ~970 Ma in basins internal to the orogen (equivalent to assemblage 3 basins of Cawood et al. 2007), by reworking of older Putumayo metaigneous and metasedimentary units such as those found in the Garzon and Minas massifs. In that case, low-P/high-T metamorphic events at ca. 920 and 860 Ma could be interpreted as related to early phases of crustal extension within the mountain chain, possibly in a basin and range-like setting during initial orogenic collapse. An analog for this may be the case of the Swedish “eastern segment” where steep normal faults and core-complex structures developed between 960 and 900 Ma recording pulses of extension and collapse in the Sveconorwegian orogen (Bingen et al., 2008b).

6.6. Implications for the peri-Gondwanan realm: The existence of a Grenville-age Putumayo Orogen in NW South America has implications for the identification and tracing of peri-Gondwanan blocks in different ways that will only be briefly mentioned here. 1) It provides a cratonic reference for evaluating the affinity of crustal blocks with inferred Amazonian ancestries. For example, it strengthens reconstructions that correlate the Proterozoic inliers of Mexico and Colombia generating a direct link to autochthonous Amazonia crust. 2) It provides a feasible source area for the origin of Grenville-age detritus found in blocks that formed part of or may have interacted with northern Amazonia at some point in their history (e.g. Marañon complex, Cardona et al. 2009; Maya block, Weber et al. 2008; Ganderian-type

42 massifs, Nance et al. 2007, Finnmarkian , Corfu et al. 2007, among others). For example, in an analog way as the Grenville-Sveconorwegian belt shed sediments to the developing Valhalla orogen (Cawood et al. 2010), the Putumayo orogen and its possible northwestward extension towards Venezuela could elegantly explain the spectrum of Grenville-age zircons found in Ganderian-type massifs like NW Iberia / Cadomia, and could also represent a proximal source for early Neoproterozoic detrital white-micas found in these massifs (Gutierrez-Alonso et al. 2005; Nance et al. 2007). Given the differences in timing of the geological events that affected Amazonia during the Meso- Neoproterozoic, further refinement of the geochronological database could potentially allow identifying distinctive fingerprints to separate between Sunsas-like vs. Putumayo- like signatures for Amazonia’s Grenville-age detrital zircon fingerprint.

7. CONCLUSIONS Zircon U-Pb geochronological data presented in this contribution comprises the first evidence for the existence of a Meso- Neoproterozoic (Grenville-age) orogenic belt in autochthonous NW Amazonia, buried underneath Meso-Cenozoic sedimentary sequences of the north Andean Putumayo foreland basin. Samples distributed amongst the Garzon and Minas massifs and the Putumayo foreland basin basement enclose an area of at least ~50.000 Km2 that are underlain by Grenville-age crust, expanding the known extent of metamorphic and deformational effects in northern South America caused by continental collisions during Rodinia assembly. Although many details about the geochemistry, metamorphic petrology and medium- to low-temperature history of the proposed Putumayo Orogen are still to be discovered, the new geochronological data obtained allowed us to identify two distinct tectonometamorphic events of arc-continent and continent-continent collision comprising its evolution. In addition to the differences in timing for the peak metamorphic event with respect to the Sunsas-Aguapei orogen, the conspicuous lack of evidence for Mesoproterozoic zircon-forming events in the Putumayo basement, in turn characterized by Grenville-age reworking of Paleoproterozoic crust, sets clear differences with respect to the Mesoproterozoic evolution of the SW Amazonian margin. As implied in the paleogeographic reconstruction presented in Figure 10, it is suggested that the Guayaquil deflection of the

43 Andean orogen may in some way represent a feature inherited from the Proterozoic tectonic configuration of Amazonia (an hypothetical Guayaquil promontory?), where it may have corresponded to a Mesoproterozoic oroclinal bend that separated the Sunsas margin colliding with Laurentia and the Putumayo margin colliding against Baltica. It should be noted however, that data presented in this study does not necessarily preclude correlations that suggest a long-lasting connection between Amazonia and Baltica throughout the Mesoproterozoic and part of the Paleoproterozoic (i.e. the SAMBA connection. Johansson, 2009), but we chose a paleogeographic model which is in line with independent paleomagnetic (D'Agrella-Filho et al., 2008; Tohver et al., 2002), thermochronologic (Tohver et al., 2006) and isotopic data (Loewy et al., 2003; Tohver et al., 2004a) that constrain collisional interactions between Laurentia and Amazonia during Mesoproterozoic times. Our interpretation of the data provides a testable model for the Proterozoic tectonometamorphic evolution of NW South America, model that will necessarily face changes and refinements as more detailed petrologic and geo- thermochronologic information is gathered from this region.

ACKNOWLEDGEMENTS This research benefited from funding provided by Ecopetrol-ICP, the GSA student grant #9184-09 and a Chevron-Texaco summer grant through the University Of Arizona. The authors would like to thank the Colombian “Instituto Nacional del Petroleo-ICP” and the “Litoteca Nacional de Colombia” for allowing access to the core samples. M.I would specially like to thank Monica Carvalho for her help with text edition and figure elaboration, Camilo Bustamante for assistance during fieldwork, and Ana Milena Rangel for her assistance during core sampling at the Litoteca Nacional. The Laserchron center is partially funded by NSF-EAR grants #0443387 and #0732436. This paper is specially dedicated to the memory of Prof. Dr. Thomas Van der Hammen for his inspiring work about the and the Amazonas region.

44 FIGURE CAPTIONS

Figure 1. Tectonic map of South America illustrating its major Precambrian constituent elements with emphasis on the provinces of the Amazon Carton. Modified from Cordani et al. (2000) and Fuck et al. (2008). The location of the north Andean foreland basins is highlighted along with the location of drilling-wells from which core samples and geochronological data have been obtained. Red dot: Location of the core samples presented in this study. Black dots: core samples presented by other authors; 1, Kovach et al. 1976; 2, Gorayeb et a. 2004; 3 and 4, Feo-Coecido et al. .

Figure 2. Simplified geological map of our study area in south-central Colombia, showing the location of samples described in this study. a) Major pre-Mesozoic features of Colombian geology and location of the Putumayo and Llanos north Andean foreland basins. Modified after Gomez et al. MAP, ANH b) detailed map of the west Garzon and Serrania de las Minas area in the Upper Magdalena Valley. Modified from Gomez et al. Jimenez-Mejia

Figure 3. U-Pb concordia diagrams for samples analyzed from the Garzon and Las Minas cordilleran inliers.

Figure 4. U-Pb concordia diagram for the sample analyzed from the basement of the Serrania de la Macarena

Figure 5. Photographs from some of the drilling-core samples analyzed for the present study. a) Migmatitic gneisses from the Payara-1 well, b) Stromatic migmatites injected by granitic sills from the Mandur-2 well, c) Metasedimentary felsic migmatites from the Caiman-3 well, d) Leucogranites that crosscut the metamorphic foliation of the migmatites in the Caiman-3 well.

Figure 6. U-Pb concordia diagrams for samples analyzed from drilling-core samples of the Putumayo basin basement.

45

Figure 7. U-Pb concordia diagrams for samples analyzed from outcrops of cratonic Amazonia in the Araracuara, Mitu and Taraira areas.

Figure 8. Probability plots for the detrital age components of Mesoproterozoic metasedimentary units included within the Putumayo Orogen, indicating their respective ages of metamorphism measured by zircon U-Pb and calculated protolith maximum depositional ages. Shaded red areas represent the spectra plotted from the entire dataset of each sample while black solid lines show data filtered to <5% discordance. In addition to the metasedimentary samples, the inherited component of anatectic leucogranites found in the Caiman-3 is also plotted along with a synthetic diagram that combines all the individual spot ages analyzed from granitoids of the Mitu-Taraira-Araracuara areas. In the upper portion of the plot, ranges of relevant magmatic activity from the Proterozoic of Mexico and Colombia are shown for comparison (data from Mexico Weber , Weber, Cameron et al. 2004). Colored columns have the same coding as Figure 1 and represent the age ranges for the evolution of the different provinces of the Amazon craton from Tassinari and Macambira 1999.

Figure 9. Events correlation chart for different provinces of Amazonia, Baltica and Laurentia during the time interval from 1200 to 900 Ma, relevant for paleogeographic correlations discussed throughout the paper. References used are listed in the figure. (Cardona et al., 2010; Cordani et al., 2005; Ordonez-Carmona et al., 2006; Restrepo-Pace et al., 1997), (Boger et al., 2005; Cordani et al., 2009; Santos et al., 2008; Teixeira et al., 2010; Tohver et al., 2004b), (Cameron et al., 2004; Keppie and Ortega-Gutierrez, 2010; Solari et al., 2003), (Bingen et al., 2008a; Bingen et al., 2008b; Bogdanova et al., 2008), (Barker and Reed, 2010; Mosher et al., 2008; Reese and Mosher, 2004), (Bartholomew and Hatcher, 2010; Rivers, 1997)

Figure 10. Geological evolution of the Putumayo orogen from the late Mesoproterozoic to early Neoproterozoic and proposed paleogeographic correlations between Amazonia, Baltica and Laurentia. Other blocks and cratons were omitted for implicity. Outline and

46 provinces of Laurentia modified from Cawood et al. (2007); Baltica from Bingen et al. (2008) and Bogdanova et al. (2008); Amazonia from Cordani et al. (2001). See text for discussion and other references used.

Figure 11. Geological sketch for the proposed configuration of the Oaxaquian- Colombian fringing-arc system at 1.15 Ga. Modified from Busby et al. (2004)

REFERENCES Alvarez, J. and Cordani, U.G., 1980. Precambrian basement within the septentrional Andes: Age and geological evolution, 26ieme Congr. Geol. Int., Paris, pp. 10.

Aspden, J., McCourt, W. and Brook, M., 1987. Geometrical control of subduction-related magmatism - The Mesozoic and Cenozoic plutonic history of western Colombia. J Geol Soc London, 144: 893-905.

Barker, D.S. and Reed, R.M., 2010. Proterozoic granites of the Llano Uplift, Texas: A collision-related suite containing rapakivi and topaz granites. Geol Soc Am Bull, 122(1-2): 253-264.

Bartholomew, M.J. and Hatcher, R.D., 2010. The Grenville orogenic cycle of southern Laurentia: Unraveling sutures, , and shear zones as potential piercing points for Amazonia. J S Am Earth Sci, 29(1): 4-20.

Bayona, G. et al., 2010. Paleomagnetic data and K-Ar ages from Mesozoic units of the Santa Marta Massif: A preliminary interpretation for block rotation and translations. Journal of South American Earth Sciences, in press.

Bayona, G., Rapalini, V. and Constazo-Alvarez, V., 2006. Paleomagnetism in Mesozoic rocks of the northern Andes and its implications in Mesozoic tectonics of northwestern South America. Earth, Planets and Space, 58: 1255–1272.

Bettencourt, J.S. et al., 2010. The Rondonian-San Ignacio Province in the SW : An overview. J S Am Earth Sci, 29(1): 28-46. Bingen, B., Andersson, J., Soderlund, U. and Moller, C., 2008a. The Mesoproterozoic in the Nordic countries. Episodes, 31(1): 29-34.

Bingen, B., Birkeland, A., Nordgulen, O. and Sigmond, E., 2001. Correlation of supracrustal sequences and origin of terranes in the Sveconorwegian orogen of SW Scandinavia: SIMS data on zircon in clastic metasediments. Precambrian Res, 108(3-4): 293-318.

47 Bingen, B. et al., 2003. Relations between 1.19-1.13 Ga continental magmatism, sedimentation and metamorphism, Sveconorwegian province, S Norway. Precambrian Res, 124(2-4): 215-241.

Bingen, B., Nordgulen, O. and Viola, G., 2008b. A four-phase model for the Sveconorwegian orogeny, SW Scandinavia. Norw J Geol, 88(1): 43-72.

Bogdanova, S.V. et al., 2008. The (Baltica) before and during the assembly of Rodinia. Precambrian Res, 160(1-2): 23-45.

Boger, S., Raetz, A., Giles, D., Etchart, E. and Fanning, C., 2005. U-Pb age data from the Sunsas region of Eastern Bolivia, evidence for the allochthonous origin of the Paragua Block. Precambrian Res, 139(3-4): 121-146.

Busby, C., 2004. Continental growth at convergent margins facing large ocean basins: a case study from Mesozoic convergent-margin basins of Baja California, Mexico. Tectonophysics, 392(1-4): 241-277.

Busby, C., Smith, D., Morris, W. and Fackler-Adams, B., 1998. Evolutionary model for convergent margins facing large ocean basins: Mesozoic Baja California, Mexico. Geology, 26(3): 227-230.

Cáceres, C., Cediel, F. and Etayo, F., 2003. Mapas de distribución de facies sedimentarias y armazón tectónico de Colombia a través del Proterozoico y del Fanerozoico. Ingeominas, Bogota, 40 pp.

Cameron, K.L. et al., 2004. U-Pb geochronology and Pb isotope compositions of leached feldspars: constraints on the origin and evolution of Grenvillian rocks from eastern and southern Mexico. In: R.P. Tollo, L. Corriveau, J.B. McLelland and G. Bartholemew (Editors), Proterozoic Tectonic Evolution of the Grenville Orogen in North America. Geological Society of America Memoir, pp. 755–769.

Cardona, A. et al., 2010. Grenvillian remnants in the Northern Andes: Rodinian and Phanerozoic paleogeographic perspectives. J S Am Earth Sci, 29(1): 92-104.

Cardona, A. et al., 2009. U-Pb Zircon Geochronology and Nd Isotopic Signatures of the Pre-Mesozoic Metamorphic Basement of the Eastern Peruvian Andes: Growth and Provenance of a Late Neoproterozoic to Carboniferous Accretionary Orogen on the Northwest Margin of Gondwana. J Geol, 117(3): 285-305.

Cardona-Molina, A., Cordani, U.G. and MacDonald, W.D., 2006. Tectonic correlations of pre-Mesozoic crust from the northern termination of the Colombian Andes, Caribbean region. J S Am Earth Sci, 21(4): 337-354.

48 Cawood, P.A., Nemchin, A.A., Strachan, R., Prave, T. and Krabbendam, M., 2007. and detrital zircon record along East Laurentia and Baltica during assembly and breakup of Rodinia. J Geol Soc London, 164: 257-275.

Cawood, P.A. and Pisarevsky, S.A., 2006. Was Baltica right-way-up or upside-down in the Neoproterozoic? J Geol Soc London, 163: 753-759.

Cawood, P.A. et al., 2010. Neoproterozoic orogeny along the margin of Rodinia: Valhalla orogen, North Atlantic. Geology, 38(2): 99-102.

Chew, D., Kirkland, C., Schaltegger, U. and Goodhue, R., 2007. Neoproterozoic glaciation in the Proto-Andes: Tectonic implications and global correlation. Geology, 35(12): 1095-1098.

Chew, D.M. et al., 2008. Detrital zircon fingerprint of the Proto-Andes: Evidence for a Neoproterozoic active margin? Precambrian Res, 167(1-2): 186-200.

Collins, A.S., Santosh, M., Braun, I. and Clark, C., 2007. Age and sedimentary provenance of the Southern Granulites, South India: U-Th-Pb SHRIMP secondary ion mass spectrometry. Precambrian Research, 155(1-2): 125-138.

Connelly, J., 2001. Degree of preservation of igneous zonation in zircon as a signpost for concordancy in U/Pb geochronology. Chem Geol, 172(1-2): 25-39.

Cordani, U.G., Cardona, A., Jimenez Mejia, D.M., Liu, D. and Nutman, A., 2005. Geochronology of Proterozoic basement inliers in the Colombian Andes: tectonic history of remnants of a fragmented Grenville belt Geological Society, London, Special Publications, 246: 329-346.

Cordani, U.G., Fraga, L.M., Reis, N., Tassinari, C.C.G. and Brito-Neves, B.B., 2010. On the origin and tectonic significance of the intra-plate events of Grenvillian-type age in South America: A discussion. J S Am Earth Sci, 29(1): 143-159.

Cordani, U.G. and Teixeira, W., 2007. Proterozoic accretionary belts in the Amazonian Craton The Geological Society of America, Special Publications, 200: 297-320.

Cordani, U.G., Teixeira, W., D'agrella-Filho, M.S. and Trindade, R.I., 2009. The position of the Amazonian Craton in supercontinents. Gondwana Research, 15(3-4): 396- 407.

Corfu, F., Hanchar, J.M., Hoskin, P.W.O. and Kinny, P., 2003. Atlas of zircon textures. In: J.M. Hanchar and P.W.O. Hoskin (Editors), Zircon. Reviews in Mineralogy and Geochemistry. Mineralogical Society of America & Geochemical Society.

Corfu, F., Roberts, R.J., Torsvik, T.H., Ashwal, L.D. and Ramsay, D.M., 2007. Peri- Gondwanan elements in the Caledonian Nappes of Finnmark, Northern Norway:

49 Implications for the paleogeographic framework of the . Am J Sci, 307(2): 434-458.

D'Agrella-Filho, M.S. et al., 2008. Direct dating of paleomagnetic results from Precambrian sediments in the Amazon craton: Evidence for Grenvillian emplacement of exotic crust in SE Appalachians of North America. Earth Planet Sc Lett, 267(1-2): 188-199.

Dall'Agnol, R., Costi, H., Leite, A., Magalhaes, M.d. and Teixeira, N., 1999. Rapakivi granites from Brazil and adjacent areas. Precambrian Research, 95(1-2): 9-39.

Dalziel, I., 1991. Pacific margins of Laurentia and east Antarctica Australia as a conjugate rift pair - Evidence and implications for an Eocambrian supercontinent. Geology, 19(6): 598-601.

Feo-Codoecido, G., Smith, F., Aboud, N. and Di Giacomo, E., 1984. Basement Paleozoic rocks of the Basin, 162. Geological Society of America.

Forero-Suarez, A., 1990. The basement of the Eastern Cordillera, Colombia - An allochthonous terrane in northwestern South America. Journal of South American Earth Sciences, 3(2-3): 141-151.

Fuck, R.A., Brito Neves, B.B. and Schobbenhaus, C., 2008. Rodinia descendants in South America. Precambrian Res, 160(1-2): 108-126.

Galvis, J., Huguett, A. and Ruge, P., 1979. Geologıa de la Amazonia Colombiana. Boletin Geologico del Ingeominas, 22(3): 3-86.

Gaudette, H., Mendoza, V., Hurley, P. and Fairbairn, H., 1978. Geology and age of Parguaza rapakivi granite, Venezuela. Geol Soc Am Bull, 89(9): 1335-1340.

Gehrels, G., Valencia, V. and Pullen, A., 2006. Detrital zircon geochronology by Laser- Ablation Multicollector ICPMS at the Arizona LaserChron Center. In: T.D. Olszewski (Editor), Geochronology Emerging opportunities. Paleontological Society, pp. 67-76.

Gehrels, G.E., Valencia, V.A. and Ruiz, J., 2008. Enhanced precision, accuracy, efficiency, and spatial resolution of U-Pb ages by laser ablation-multicollector- inductively coupled plasma-mass spectrometry. Geochem Geophy Geosy, 9: Q03017.

Gómez, J. et al., 2007. Mapa Geológico de Colombia. Escala 1:2'800.000. . Ingeominas, Bogota.

Gower, C. and Krogh, T., 2002. A U-Pb geochronological review of the Proterozoic history of the eastern Grenville Province. Can J Earth Sci, 39(5): 795-829.

50

Gower, C.F., Kamo, S. and Krogh, T.E., 2008. Indentor tectonism in the eastern Grenville Province. Precambrian Res, 167(1-2): 201-212.

Grande, S. and Urbani, F., 2009. Presence of high-grade rocks in NW Venezuela of possible Grenvillian affinity. In: K.H. JAMES, M.A. LORENTE and J.L. PINDELL (Editors), The Origin and Evolution of the . Geological Society of London Special Publications, pp. 533–548.

Gutierrez-Alonso, G., Fernandez-Suarez, J., Collins, A., Abad, I. and Nieto, F., 2005. Amazonian mesoproterozoic basement in the core of the ibero-Armorican Arc: Ar-40/Ar-39 detrital mica ages complement the zircon's tale. Geology, 33(8): 637-640.

Harrington, H.J. and Kay, M., 1951. Cambrian and Ordovician faunas of eastern Colombia. Journal of Paleontology, 25(5): 655-668.

Hoffman, P., 1991. Did the breakout of Laurentia turn Gondwanaland inside-out. Science, 252(5011): 1409-1412.

Hoskin, P.W.O. and Black, L.P., 2000. Metamorphic zircon formation by solid-state recrystallization of protolith igneous zircon. Journal of Metamorphic Geology, 18(4): 423-439.

Jimenez Mejia, D.M., Juliani, C. and Cordani, U.G., 2006. P-T-t conditions of high-grade metamorphic rocks of the Garzon Massif, Andean basement, SE Colombia. J S Am Earth Sci, 21(4): 322-336.

Johansson, A., 2009. Baltica, Amazonia and the SAMBA connection-1000 million years of neighbourhood during the Proterozoic? Precambrian Res, 175(1-4): 221-234.

Johansson, L., Moller, C. and Soderlund, U., 2001. Geochronology of eclogite facies metamorphism in the Sveconorwegian Province of SW Sweden. Precambrian Res, 106(3-4): 261-275.

Johnston, S., Gehrels, G., Valencia, V. and Ruiz, J., 2009. Small-volume U-Pb zircon geochronology by laser ablation-multicollector-ICP-MS. Chemical Geology, 259(3-4): 218-229.

Kemp, A.I.S. and Gray, C.M., 1999. Geological context of crustal anatexis and granitic magmatism in the northeastern Glenelg River Complex, western Victoria. Australian Journal of Earth Sciences, 46(3): 407-420.

Keppie, J., Dostal, J., Ortega-Gutierrez, F. and Lopez, R., 2001. A Grenvillian arc on the margin of Amazonia: evidence from the southern Oaxacan Complex, southern Mexico. Precambrian Res, 112(3-4): 165-181.

51

Keppie, J.D. and Dostal, J., 2007. Rift-related basalts in the 1.2-1.3 Ga granulites of the northern Oaxacan Complex, southern Mexico: evidence for a rifted arc on the northwestern margin of Amazonia. P Geologist Assoc, 118: 63-74.

Keppie, J.D. and Ortega-Gutierrez, F., 2010. 1.3-0.9 Ga Oaxaquia (Mexico): Remnant of an arc/backarc on the northern margin of Amazonia. J S Am Earth Sci, 29(1): 21- 27.

Keppie, J.D. and Ramos, V.A., 1999. Odyssey of terranes in the Iapetus and Rheic oceans during the Paleozoic. In: J.D. Keppie and V.A. Ramos (Editors), Laurentia- Gondwana Connections Before Pangea. Geological Society of America Special Paper, Boulder, CO.

Kovach, A., Fairbairn, H., Hurley, P., Basei, M. and Cordani, U., 1976. Reconnaissance geochronology of basement rocks from Amazonas and Maranhão basins in Brazil. Precambrian Res, 3(5): 471-480.

Kroonenberg, S., 1982. A Grenvillian granulite belt in the Colombian Andes and its relation to the . Geol Mijnbouw, 61(4): 325-333.

Lawlor, P. et al., 1999. U-Pb geochronology, geochemistry, and provenance of the Grenvillian Huiznopala Gneiss of Eastern Mexico. Precambrian Research, 94(1- 2): 73-99.

Li, Z.X. et al., 2008. Assembly, configuration, and break-up history of Rodinia: A synthesis. Precambrian Res, 160(1-2): 179-210.

Litherland, M. et al., 1989. The Proterozoic of eastern Bolivia and its relationship to the Andean mobile belt. Precambrian Res, 43(3): 157-174.

LITHERLAND, M. and BLOOMFIELD, K., 1981. The Proterozoic history of eastern Bolivia. Precambrian Res, 15(2): 157-&.

Loewy, S., Connelly, J., Dalziel, I. and Gower, C., 2003. Eastern Laurentia in Rodinia: constraints from whole-rock Pb and U/Pb geochronology. Tectonophysics, 375(1- 4): 169-197.

Ludwig, K., 2003. User's manual for Isoplot 3.00. A geochronological toolkit for Microsoft Excel, 4. Berkeley Geochronology Center Special Publication.

MacDonald, W.D. and Hurley, P.M., 1969. Precambrian gneisses from northern Colombia, South America. Geological Society of America Bulletin, 80: 1867- 1872.

52 McCourt, W., Aspden, J. and Brook, M., 1984. New geological and geochronological data from the Colombian Andes - Continental growth by multiple accretion. J Geol Soc London, 141(SEP): 831-845.

Mojica, J., Villaroel, C. and Macia, C., 1987. Nuevos afloramientos fosil ́ıferos del Ordov ́ıcico Medio (Fm El Higado) al oeste de Tarqui, valle superiordelMagdalena (Huila,Colombia). Geologıa Colombiana, 16: 95-97.

Mosher, S., 1998. Tectonic evolution of the southern Laurentian Grenville orogenic belt. Geological Society of America Bulletin, 110(11): 1357-1375.

Mosher, S., Levine, J.S.F. and Carlson, W.D., 2008. Mesoproterozoic : A collisional model for the Grenville-aged orogenic belt in the Llano uplift, central Texas. Geology, 36(1): 55-58.

Nance, R.D. et al., 2007. Neoproterozoic-early Paleozoic paleogeography of the peri- Gondwanan terranes: Amazonian versus West African connections. In: E. Nasser and J.-P. Liégeois (Editors), The Boundaries of the West African Craton. Geological Society of London, Special Publication, pp. 345-383.

Nemchin, A. and Cawood, P., 2005. Discordance of the U-Pb system in detrital zircons: Implication for provenance studies of sedimentary rocks. Sediment Geol, 182(1- 4): 143-162.

Ordonez-Carmona, O., Pimentel, M.M. and De Moraes, R., 2002. Granulitas de Los Mangos: un fragmento grenviliano en la parte SE de la Sierra Nevada de Santa Marta. Revista de la Academia Colombiana de Ciencias Exactas, Fısicas y Naturales, 26(99): 169-179.

Ordonez-Carmona, O., Pimentel, M.M., De Moraes, R. and Restrepo, J.J., 1999. Rocas Grenvillianas en la region de Puerto Berrio – Antioquia. Revista de la Academia Colombiana de Ciencias Exactas, F ́ısicas y Naturales, 23(87): 225-232.

Ordonez-Carmona, O., Restrepo Alvarez, J.J. and Pimentel, M.M., 2006. Geochronological and isotopical review of pre-Devonian crustal basement of the Colombian Andes. J S Am Earth Sci, 21(4): 372-382.

Parra, M. et al., 2009. Orogenic wedge advance in the northern Andes: Evidence from the Oligocene-Miocene sedimentary record of the Medina Basin, Eastern Cordillera, Colombia. Geological Society of America Bulletin, 121(5-6): 780-800.

Passchier, C.W. and Trouw, R.A.J., 2005. Microtectonics. Springer-Verlag, Berlin, 366 pp.

53 Pisarevsky, S.A., Wingate, M.T.D., Powell, C.M., Johnson, S. and Evans, D.A.D., 2003. Models of Rodinia assembly and fragmentation. Geological Society, London, Special Publications, 206(1): 35-55.

Priem, H. et al., 1982. Geochronology of the Precambrian in the Amazonas region of southeastern Colombia (Western Guiana Shield). Geol Mijnbouw, 61(3): 229- 242.

Priem, H., Kroonenberg, S., Boelrijk, N. and Hebeda, E., 1989. Rb-Sr and K-Ar evidence for the presence of a 1.6 Ga basement underlying the 1.2 Ga Garzon-Santa Marta granulite belt in the Colombian Andes. Precambrian Res, 42(3-4): 315-324.

PRORADAM, 1979. La Amazonia Colombiana y sus recursos - Proyecto Radargrametrico del Amazonas. Ingeominas, Bogota, 590 pp.

Ramos, V.A., 2010. The Grenville-age basement of the Andes. J S Am Earth Sci, 29(1): 77-91.

Reese, J. and Mosher, S., 2004. Kinematic constraints on Rodinia reconstructions from the core of the Texas Grenville orogen. Journal of Geology, 112(2): 185-205.

Restrepo-Pace, P., Ruiz, J., Gehrels, G. and Cosca, M., 1997. Geochronology and Nd isotopic data of Grenville-age rocks in the Colombian Andes: new constraints for late Proterozoic Early Paleozoic paleocontinental reconstructions of the Americas. Earth Planet Sc Lett, 150(3-4): 427-441.

Rivers, T., 1997. Lithotectonic elements of the Grenville Province: review and tectonic implications. Precambrian Res, 86(3-4): 117-154.

Ruiz, J., Tosdal, R.M., Restrepo-Pace, P.A. and Murillo-Muñeton, G. (Editors), 1999. Pb Isotope evidence for Colombian-southern Mexico connections in the Proterozoic. GSA Special Paper, 336.

Sadowski, G. and Bettencourt, J., 1996. Mesoproterozoic tectonic correlations between eastern Laurentia and the western border of the Amazon Craton. Precambrian Res, 76(3-4): 213-227.

Santos, J. et al., 2000. A new understanding of the provinces of the Amazon craton based on integration of field mapping and U-Pb and Sm-Nd geochronology. Gondwana Research, 3(4): 453-488.

Santos, J. et al., 2003. Age, source, and regional stratigraphy of the Roraima Supergroup and Roraima-like outliers in northern South America based on U-Pb geochronology. Geol Soc Am Bull, 115(3): 331-348.

54 Santos, J.O.S. et al., 2008. Age and autochthonous evolution of the Sunsas Orogen in West Amazon Craton based on mapping and U-Pb geochronology. Precambrian Res, 165(3-4): 120-152.

Soderlund, U. et al., 2005. U-Pb baddeleyite ages and Hf, Nd isotope chemistry constraining repeated mafic magmatism in the Fennoscandian Shield from 1.6 to 0.9 Ga. Contributions to Minralogy and Petrology, 150(2): 174-194.

Solari, L. et al., 2003. 990 and 1100 Ma Grenvillian tectonothermal events in the northern Oaxacan Complex, southern Mexico: roots of an orogen. Tectonophysics, 365(1- 4): 257-282.

Tassinari, C. and Macambira, M., 1999. Geochronological provinces of the Amazonian Craton. Episodes, 22(3): 174-182.

Tassinari, C.C.G. et al., 1996. Geochronological systematics on basement rocks from the Rio Negro–Juruena Province (Amazonian Craton), and tectonic implications. International Geology Review, 38(2): 161-175.

Teixeira, W. et al., 2010. A review of the tectonic evolution of the Sunsás belt, SW Amazonian Craton. J S Am Earth Sci, 29(1): 47-60.

Teixeira, W., Tassinari, C., Cordani, U. and Kawashita, K., 1989. A review of the geochronology of the Amazonian Craton - Tectonic implications. Precambrian Res, 42(3-4): 213-227.

Tohver, E. et al., 2004a. Terrane transfer during the : tracing the Amazonian ancestry of southern Appalachian basement through Pb and Nd isotopes. Earth Planet Sc Lett, 228(1-2): 161-176.

Tohver, E. et al., 2006. Restored transect across the exhumed Grenville orogen of Laurentia and Amazonia, with implications for crustal architecture. Geology, 34(8): 669-672.

Tohver, E. et al., 2004b. Significance of the Nova Brasilandia metasedimentary belt in western Brazil: Redefining the Mesoproterozoic boundary of the Amazon craton. Tectonics, 23(6): TC6004.

Tohver, E., van der Pluijm, B., Van der Voo, R., Rizzotto, G. and Scandolara, J., 2002. Paleogeography of the Amazon craton at 1.2 Ga: early Grenvillian collision with the Llano segment of Laurentia. Earth Planet Sc Lett, 199(1-2): 185-200.

Toussaint, J.F., 1993. Precámbrico–Paleozóico., Evolución geológica de Colombia. Universidad Nacional de Colombia, Medellin, pp. 129.

55 Trumpy, D., 1943. Pre-Cretaceous of Colombia. Geological Society American Bulletin, 54: 1281-1304.

Tschanz, C., Richard, F.M., Cruz, B.J., Harald, H.M. and Gerald, T.C., 1974. Geologic evolution of the Sierra Nevada de Santa Marta, Northeastern Colombia. Geological Society American Bulletin, 85: 273–284.

Vasquez, M., Altenberger, U. and Romer, R.L., 2009. Neogene magmatism and its possible causal relationship with hydrocarbon generation in SW Colombia. Int J Earth Sci, 98(5): 1053-1062.

Vernon, R.H., 2004. A Practical Guide to Rock Microstructure. Cambridge University Press, 606 pp.

Walker, N., 1992. Middle Proterozoic geologic evolution of Llano Uplift, Texas - Evidence from U-Pb zircon geochronometry. Geol Soc Am Bull, 104(4): 494- 504.

Waters, D., 2001. The significance of prograde and retrograde quartz-bearing intergrowth microstructures in partially melted granulite-facies rocks. Lithos, 56(1): 97-110.

Weber, B. and Hecht, L., 2003. Petrology and geochemistry of metaigneous rocks from a Grenvillian basement fragment in the Maya block: the Guichicovi complex, Oaxaca, southern Mexico. Precambrian Res, 124(1): 41-67.

Weber, B. and Kohler, H., 1999. Sm-Nd, Rb-Sr and U-Pb geochronology of a Grenville terrane in southern Mexico: origin and geologic history of the Guichicovi complex. Precambrian Res, 96(3-4): 245-262.

Weber, B., Valencia, V.A., Schaaf, P., Pompa-Mera, V. and Ruiz, J., 2008. Significance of Provenance Ages from the Chiapas Massif Complex (Southeastern Mexico): Redefining the Paleozoic Basement of the Maya Block and Its Evolution in a Peri-Gondwanan Realm. Journal of Geology, 116(6): 619-639.

56 FIGURE 1

Santa Guajira Northern Andes Marta Wells reported in this article foreland basins Santander A Other wells referenced 4 mazon C 3

San raton Lucas Macarena Garzon CA MI Sao Luis Fig.2 Craton

2 Amazon Graben CA Parnaiba 1 VT RNJ Sao Southern Francisco Peru RSI Craton S Arequipa-Antofalla terrane

Amazonia Geochron. Provinces Paranapanema Central Amazonian CA >2.5 Ga Luis Alves Craton MI Maroni-Itacaiunas 2.2-1.95 Ga Pa Rio de la Ventuari-Tapajos VT 1.95-1.8 Ga Plata Andean deformation front Rio Negro-Juruena Cu RNJ 1.8-1.55 Ga Inferred cratonic limits and other major structural features Rondonia-Sn Ignacio pC massifs exposed in the Andes RSI 1.5-1.3 Ga Other pre-Pan African cratonic blocks Sunsas - Aguapeí Pan African - Brasiliano belts S 1.3-0.9 Ga 0.9-0.6 Ga Figure 2

Early Mesoproterozoic and a) Paleoproterozoic crystalline basement

Late Mesoproterozoic (Grenville-age) Cordilleran Inliers North Andean Orogen Llanos Basin Supracrustal metasedimentary units Paci c of Mesoproterozoic age Lower Paleozoic clastic sequences (Araracuara Formation)

Macarena-2

Güejar - Apaporis inverted (?) Pz Graben Payara-1

La Rastra-1 AH-1216 Mandur-2 Solita-1

Caiman-3 Putumayo Basin PR-3215 Brazil Mandur-3 Ecuador Thin Tertiary PR-3092 cover CJR-19 Foreland Basins AH-1419 J-263

PROTEROZOIC UNITS Serrania de b) Quaternary aluvial El Vergel Granulites Las Minas La Plata 0° Lower/Upper tertiary sandstones Las Margaritas Migmatites Hermosas F. and aluvial deposits Agrado F. MIVS-37a El Pital Group Garzón El Recreo Gneiss Algeciras F. Cretaceous Clastic sequences MIVS-41 GARZON Guapoton-Mancagua orthogneiss CB-006 MIVS-11 Jurassic Vulcanosedimentary n=8 El Recreo Las Minas Migmatites Ks Magdalena River Jurassic Granitoids 180° Tarqui Representative foliations Las Pital F. CB-002 Altamira Minas gneisses and migmatites Permo- Granitoids Municipalities Guadalupe MIVS-26 0 5 10 Rivers Cambro-Ordovician clastic Km Roads a sequences Magdalena Garzon Massif River valley Js FIGURE 3

data-point error ellipses are 68.3% conf. data-point error ellipses are 68.3% conf. a) 0.30 b) 0.23 MIVS-11 MIVS-26 40μm, Faradays, Cores and rims 40μm, Faradays, Mixed ablation spots Felsic Granulite Guapoton Augen-Gneiss “El Vergel Granulites” 1550 0.21 Igneous Protolith Age 0.26 1135 ± 12 Ma (1.1%) 1200 Metamorphic Age 1450 MSWD = 0.96 992 ± 10 Ma (1.01%) MSWD = 0.32 Mean 206/207 (2σ) = 1129 ± 12 1350 0.19 MSWD = 0.49 U 1100

U Mean 206/207 (2σ) = 995 ± 5

MSWD = 0.22 238 238 0.22

1250 Pb/ Pb/ 206 206 0.17 1000 1150

0.18 1050 Metamorphic Overgrowths 0.15 900 990 ± 12 Ma (1.2%) 950 30μm spots, Metamophic rims MSWD = 0.58 40μm, Detrital cores, <5% Disc. 100μm Mean 206/207 (2σ) = 1005 ± 26 100μm 40μm, Detrital cores, >5% Disc. MSWD = 0.19 0.14 0.13 1.4 1.8 2.2 2.6 3.0 3.4 3.8 1.2 1.4 1.6 1.8 2.0 2.2 2.4

CB-002 MIVS-41 Igneous Protolith Age 1400 c) 0.30 d) 0.24 Qz-Feldspar Gneiss Las Minas Augen-Gneiss 1326 ± 13 Ma (1.0%) 1600 MSWD = 0.97 Mean 206/207 (2σ) = 1335 ± 13 MSWD = 0.53 Metamorphic Overgrowths 0.26 0.22 992 ± 12 Ma (1.2%) Metamorphic Overgrowths 1400 MSWD = 0.45 991 ± 12 Ma (1.2%) Mean 206/207 (2σ) = 998 ± 18 MSWD = 1.08 1200

U U 0.22 MSWD = 0.082 0.20 238 238 Mean 206/207 (2σ) = 997 ± 14 1200 MSWD = 0.04 Pb/ Pb/ 1100 206 206 0.18 0.18 1000 1000 18μm spots, Ion-Counters, 0.16 Metamorphic overgrowths 0.14 800 30μm spots, Metamorphic rims 40μm, Faradays, <5% Disc. 40μm, Detrital cores, <5% Disc. 40μm, Faradays, >5% Disc. 100μm 40μm, Detrital cores, >5% Disc. 100μm and mixed analyses 0.10 0.14 0.8 1.8 2.8 3.8 1.4 1.8 2.2 2.6 3.0 . 0.26 e) CB-006 f) MIVS-37a 1700 0.30 Metasedimentary Biotite Gneiss 0.24 Migmatitic Gneiss 1350 (Paleosome) Metamorphic Overgrowths 1500 0.26 0.22 972 ± 14 Ma (1.5%) MSWD = 0.14 1250 Mean 206/207 (2σ) = 977 ± 25

U 0.20 MSWD = 0.057 1300 1150 U 0.22 238 238 Pb/ Pb/

206 0.18 1050 206 1100 0.18

0.16 950 900 0.14

0.14 30μm spots, Metamorphic rims 30μm, Faradays, <5% Disc. 40μm, Detrital cores, <5% Disc. 700 30μm, Faradays, >5% Disc. 100μm 40μm, Detrital cores, >5% Disc. 100μm 0.12 0.10 1.4 1.8 2.2 2.6 3.0 0.5 1.5 2.5 3.5 4.5 207 235 207Pb/235U Pb/ U FIGURE 4

data-point error ellipses are 68.3% conf. 0.29 Macarena-2 Melanocratic mylonitic gneiss 1550 0.27 Igneous Protolith Age 1461 ± 15 Ma (1.0%) MSWD = 0.37 Mean 206/207 (2σ) = 1471 ± 18 U MSWD = 0.17 1450 238 0.25 Pb/ 206

1350 0.23

40μm, Faradays, <5% Disc. 40μm, Faradays, >5% Disc. 100μm 0.21 2.5 2.7 2.9 3.1 3.3 3.5 3.7 3.9 207Pb/235U FIGURE 5

A B

C D FIGURE 6

data-point error ellipses are 68.3% conf. a) 0.32 b) data-point error ellipses are 68.3% conf. Igneous Protolith Age Payara-1 well Solita-1 well <30% Discordant 1606 ± 16 Ma (1.0%) 1700 >30% Discordant 1800 Migmatitic Gneiss Sheared Migmatite Inheritance and mixing MSWD = 0.97 0.3 0.28 Mean 206/207 (2σ) = 1608 ± 15 Metamorphic Overgrowths MSWD = 0.93 to ~2000 Ma 18μm spots, Ion-Counters Mean 206/207 Age (2σ) 40μm, Faradays, <5% Disc. 1044 ± 26 Ma (2.5%) 1400 40μm, Faradays, >5% Disc. MSWD = 0.5 1400 Upper Discordia Intercept 0.24 1046 ± 25 Ma (2.5%)

U 0.2 MSWD = 0.54 U 238

238 1000

Pb/ reference chord

1200 Pb/ 206 0.20 206

box heights are 1σ Metamorphic Overgrowths 0.1 600 1000 1150 0.16 986 ± 19 Ma (1.9%) MSWD = 0.49 1050 800 Mean 206/207 (2σ) = 985 ± 23

MSWD = 0.70 206/207 AGE 950 <20% Disc. 100μm (6 analyses) 100μm 0.12 0.0 1 2 3 4 0 1 2 3 4 5

0.34 c) Mandur-2 well 1800 d) Mandur-2 well Melanocratic Migmatitic Gneiss 0.19 Leucocratic dike 1100 0.30 Protolith Age (Upp. Intercept) Crystallization Age 1601 ± 28 Ma (1.7%) 1600 1017 ± 10 Ma (0.9%) MSWD = 0.62 0.18 MSWD = 0.66 1060 Mean 206/207 (2σ) = 1587 ± 18 0.26 MSWD = 0.67 Mean 206/207 (2σ) = 1014 ± 12 U U MSWD = 0.24 238 238 1400 Pb/ Pb/ 0.17 206 206 0.22 1200 980 Metamorphic Overgrowths Upper Intercept 0.16 0.18 1019 ± 23 Ma (2.2%) 940 1000 MSWD = 0.62 Mean 206/207 (2σ) = 1019 ± 20 MSWD = 0.23 100μm 100μm 0.14 0.15 1 2 3 4 5 1.45 1.55 1.65 1.75 1.85 1.95 2.05 e) 2000 f) 2000 0.36 Caiman-3 well 0.36 Caiman-3 well sample-1 sample-2 Migmatite Leucogranite 0.32 1800 0.32 1800 10μm spots, Ion-Counters 10μm spots, Ion-Counters 30μm, Faradays, <5% Disc. 30μm, Faradays, <5% Disc. 1600 1600 0.28 30μm, Faradays, >5% Disc. 0.28 30μm, Faradays, >5% Disc. U U 1400 1400 0.24 0.24 238 238 Pb/ Pb/ 1200 1200 206 206 0.20 0.20

1000 Metamorphic Overgrowths 1000 0.16 0.16 Crystallization Age 989 ± 14 Ma (1.4%) 952 ± 21 Ma (2.2%) 800 MSWD = 0.7 800 MSWD = 0.98 0.12 0.12 Mean 206/207 (2σ) = 991 ± 13 100μm MSWD = 1.05 100μm Mean 206/207 (2σ) = 950 ± 25 MSWD = 0.91 0.08 0.08 0.5 1.5 2.5 3.5 4.5 5.5 6.5 0.5 1.5 2.5 3.5 4.5 5.5 6.5 207Pb/235U 207Pb/235U FIGURE 7

data-point error ellipses are 68.3% conf. data-point error ellipses are 68.3% conf. 0.36 a) b) 35μm, Faradays, <10% Disc. PR-3215 (Araracuara) 1900 J-263 (Araracuara) 35μm, Faradays, >10% Disc. 0.34 Deformed syenogranite Weakly sheared Syenogranite 1800 0.32 Crystallization Age 1756 ± 18 Ma (1.0%) Crystallization Age 1700 1700 Mean 206/207 (2σ), 16 analyses 0.30 MSWD = 0.98 1732 ± 24 Ma (1.4%) 1600 Mean 206/207 (2σ) = 1750 ± 18 0.28 MSWD = 0.43 MSWD = 0.66 U

U (38 analyses) 238

238 1500 1500 Pb/ 0.26 Pb/ 1400 206 206 0.24 1300 box heights are 1 1820 1300 0.22 0.20 1740

35μm, Faradays, <5% Disc.

1100 35μm, Faradays, >5% Disc. 206/207 Age 1660 0.18 0.16 1.5 2.5 3.5 4.5 5.5 2 3 4 5

0.38 PR-3092 (Mitu) Crystalization, <10% Disc. c) AH-1216 (Mitu) d) Inheritance, <30% Discordant Undeformed Granitoid Undeformed granite >30% Discordant analyses 1900 2400 0.34 0.45 Crystallization Age 35μm, Faradays, <5% Disc. Mean 206/207 (2σ), 9 analyses 35μm, Faradays, >5% Disc. 1578 ± 30 Ma (1.9%) Inheritance and mixing MSWD = 0.76 2000 1700 0.30 0.35 U U 238 238 1600 Pb/ Pb/ 206 0.26 1500 206 0.25

Crystallization Age 1200 box heights are 1 1740 1574 ± 16 Ma (1.0%) 1300 0.22 MSWD = 0.37 0.15 1660 800 Mean 206/207 (2σ) = 1574 ± 17 MSWD = 0.20 1580 (27 analyses) 100μm 206/207 Age 1500 0.18 0.05 2 3 4 5 6 0 2 4 6 8 10 12 14 e) f) 0.38 AH-1419 CJR-19 (Taraira) 0.40 Crystallization 2000 Taraira Granitoid Inheritance 2100 0.36 Undeformed Granitoid

1900 0.36 Crystallization Age Crystallization Age 0.34 35 analyses, Mean 206/207 (2σ) 11 analyses, Mean 206/207 (2σ) 1900 1588 ± 21 Ma (1.3%) 1530 ± 24 Ma (1.6%) MSWD = 1.03 1800 U 0.32 0.32 MSWD = 0.32 U

238 238 1700 Pb/ Pb/ 1700 0.30 206 206

0.28 box heights are 1 box heights are 1 1600 1500 1600 0.28 1640

0.24 1520 1500 1560 0.26

1300 206/207 Age

1440 206/207 Age 1480

0.20 0.24 2 3 4 5 6 7 3 4 5 6 7 207 235 207Pb/235U Pb/ U FIGURE 8

O O-N-H-Gu Periods of relevant Mexico Igneous Activity G Mi Ma MT P Ar Colombia

U-Pb age of JRG-20-96 Metamorphism/ Dibulla Gneiss Anatexis All data (59) <5% Disc. (41)

991±12 Ma Massif Santa MartaSanta

CB-006 El Zancudo Migmatites All data (111) <5% Disc. (102)

972±14 Ma MDA ~1086±34 Ma

MIVS-37a Pital Migmatites All data (70) <5% Disc. (55) Las Minas Massif N.A. MDA ~1150±18 Ma

CB-002 El Vergel Granulites All data (89) <5% Disc. (59)

992±12 Ma MDA ~1013±11Ma

MIVS-11 El Vergel Granulites All data (89)

<5% Disc. (62) Garzón Massif

992±10 Ma MDA ~1115±10 Ma

Caiman-3 Well Leucogranite All data (84) <5% Disc. (61)

952±21 Ma

Caiman-3 Well MDA Migmatite ~1444±9 Ma All data (80) <5% Disc. (63)

989±14 Ma

Mitu-Taraira-Araracuara Craton Granitoids All data (278) <5% Disc. (168) ” Amazonia Basement Amazonia “ in-situ ” Foreland

Amazonia Provinces Sunsas-Putumayo RSI RNJ VTP 1000 1200 1400 1600 1800 2000 Age (Ma) FIGURE 9

NW Amazonia N Andes Foreland Basement Laurentia SE Laurentia NE North Andean Inliers SW Amazonia Mexican Terranes (Autochtonous NW Gondwana) (para-autochtonous terranes) SW Baltica (Llano) (Grenville) 900 Regional cooling and Sveconorwegian localized Low-P Metamorph Dalane phase (Post-collisional Putumayo relaxation and collapse) Extensional Undeformed Leucogranites Phase

SunsasRondônia tin province Post-tectonic pegmatites Falkenberg phase Migmatization granites followed by Payara and Caiman wells Peak Metamorphism Peak Metamorphism Garzon and Las Minas regional cooling “Zapotecan” event

1000 Orogen Agder phase Rigolet Phase Margaritas Migmatites (Garzon) (Main continental Fringing arc /terrane AMCG magmatism collision event) Grenville

collisions initiation (?) Strike-slip continuous deform. (Migmatization Sedimentation Aguapei(Late shearing o shots and nal Ottawan (Arc-related basins) accretion of the “Paragua block”) Mandur and Solita wells) ? Orogen Phase ? ? Post-collisional Post-tectonic Sunsas Granite Suite granites Millions of Years (Ma) Millions of Years 1100 Sunsas group “Olmecan” event Arendal phase

Back-arc Early terrane collisions Adirondian Orogencollisional deformation Orogen sedimentation over Magmatism Arc Magmatism Metamorphic the continental event. Zr rims Arc/Backarc magmatism Garzon Massif margin (?) Dibulla gneiss Accretion of (AMCG suites) (Protolith ages in orthogneisses. older than Metamorphic Bimodal magmatism 1.25 Ga terranes event. Zr rims Passive-margin and Huiznopala, Oaxaca, Novillo) Jojoncito gneiss intra-continental rift and Sedimentation ? Shawinigan Sedimentation sedimentation 1200 phase This Work Boger et al. (2005) Keppie et al. (2009) Bingen et al. (2008)a Barker and Reed Bartholomew et al. This work Cardona et al. (2010) Santos et al. (2008) Cameron et al. (2004) Bingen et al. (2008)b (2010) (2010) Ordonez-Carmona et al (2007) Cordani et al. (2009) Keppie et al. (2003) Bogdanova et al. (2008) Mosher et al. (2004) Tollo et al. (2004) Cordani et al. (2005) Teixeira et al. (2010) Solari et al. (2003) Reese and Mosher Gower and Krogh Restrepo-Pace et al. (1997) Tohver et al. (2004) (2004) (2002) Rivers (1997) McLelland (1996) FIGURE 10 a) b) pre-1.25 Ga Baltica 1.07-1.01 Ga

Newborn Asgard Sea ~1.14 Ga Accretion of non-Amazonian Telemarkia Fennoscandia (Arendal phase)

Ideorden Telemarkia Arc accretion onto Amazonia’s margin. Metamorphism and melting ? under Amphibolite facies “Oaxaquian-Colombian terranes” conditions. Laurentia Fringing arc system A outboard of Amazonia ?

PF GR ? Backarc spreading and BR P sedimentation over APC the continental margin P LLA

~1.15 Ga Metamorphism Nova Brasilandia belt RSI

~1.2 Ga 1000 km 1000 km Amazonia

Laurentia-Amazonia initial collision. Baltica-Amazonia collision initiation close to their nal Rodinia positions. Development of the “Colombian-Oaxaquian”fringing-arc system. Amalgamation of fringing arcs and terranes.

c) 1.00 - 0.98 Ga Archean crust Paleoproterozoic

Valhalla Orogen Asgard Sea Baltica Timanide Margin Laurentia Ideorden terrane

Grenville Province Telemarkia terrane

Eastern Segment Granite-Rhyolite province Blekinge-Dalarna dolerite dike swarm ? Ganderian massifs Avalonian - Cadomian terranes Amazonia

Colombian-Oaxaquian Rondonia-San Ignacio terranes West-Africa Sunsas-Aguapei Putumayo basin basement

Nova Brasilandia cooled below ~500°C A= Adirondacks APC = Argentine Precordillera Terrane BR = Blue Ridge 1000 km GR = Granite-Rhyolite LLA = Llano Segment P = Paragua Terrane PF = Paleoproterozoic underlying the Andean foreland Rodinia fully assembled RSI = Rondonia-San Ignacio Orogen Maximum convergence along the Sveconorwegian-Putumayo orogen

Other blocks were omitted for simplicity. Craton outlines and general geology: Laurentia, Cawood et al. 2007. Baltica, Bogdanova et al. 2008, Bingen et al. 2008, Amazonia, Cordani et al. 2001 FIGURE 11

“Oaxaquia-Colombian terranes” Detritus deposited on Amazonia’s peri-Amazonian fringing arc Paleoproterozoic basement (Cratonic provenance signatures with little @ ~1.15 Ga or no arc in uence) Arc- related volcanosedimentary sequences (”Garzon group”-like) Mildly extensive back-arc Sea Level

Oceanic Crust ? Intrusion of arc plutons with variable older crustal contamination Mid- Mesoproterozoic to (Guapoton and Oaxaquia Paleoproterozoic basement orthogneisses) of the RNJ province