Reviewing the Antioquia batholith and satellite bodies: a record of Late Cretaceous to Eocene syn- to post-collisional arc magmatism in the Central Cordillera of Colombia

The Antioquia batholith represents the magmatic record of the interaction between the Farallón and Caribbean plates with the NW part of the South American Plate during the Meso-Cenozoic. Several authors have reported zircon U-Pb ages and whole rock geochemistry in order to constrain the crystallization history of this batholith and its formation conditions. The present work aims to gather the existing data with new data obtained from the Ovejas batholith and La Unión stock, both genetically related to the main intrusion. Gathering our new data with information obtained in previous works, we conclude that the Antioquia batholith was constructed by successive pulses from ca. 97 to 58 Ma in an arc-related setting. The initial pulses are related to syn-collisional tectonics, during the early interaction between the Farallón plate and NW South America. The final pulses, that record Eocene ages, are related to a post-collisional setting, similar to that recorded in other plutons of the Paleogene magmatic arc of the Central Cordillera.

In this paper, we present new U-Pb crystallization ages from one of the earliest (La Unión stock) and intermediate (Ovejas batholith) pulses of the Antioquia batholith, and also provide new whole rock geochemistry. This information combined with a compilation of available data obtained from previous works, will allow us to outline the crystallization history of the Antioquia batholith in relation with the Meso-Cenozoic subduction setting of the NW corner of the South American Plate, tracking the thickening that experienced the margin during the Late Cretaceous and lasted until the Eocene.

Geological setting
Three N-NE trending Cordilleras built the Andes of Colombia. The Eastern Cordillera, mainly constituted by a Proterozoic metamorphic basement covered by highly deformed Paleozoic to Cenozoic sedimentary sequences (Villamil, 1999;Sarmiento-Rojas et al., 2006). This cordillera is separated from the Central Cordillera by the Magdalena River Valley, which in turn consists of Permo-Triassic gneisses, migmatites and amphibolites (Martens et al., 2014) and Jurassic schists belts (Blanco-Quintero et al., 2014;Bustamante et al., 2017) intruded by Jurassic (Cochrane et al., 2014;Bustamante et al., 2016) and Cretaceous to Paleogene arc-related plutons respectively (Bayona et al., 2012;Bustamante et al., 2017). The northernmost exposure of the latter magmatic belt continues under the Lower Magdalena Valley, represented by the Bonga pluton (Mora-Bohórquez et al., 2017). The Cauca River Valley separates the Central Cordillera from the Western Cordillera which includes Late Cretaceous oceanic rocks accreted to the South American plate during Early Cretaceous (Kerr et al., 1997;Villagómez and Spikings, 2013), then intruded by Miocene plutons and covered volcanic rocks from intermediate to tholeiitic character (Bissig et al., 2017;Restrepo and Toussaint, 1990).

I. Introduction
Granite batholiths are found in continental magmatic arcs around the world and constitute the main vestiges of subduction-related settings (Best, 2013). These are constructed over time spans from 10 5 to 10 6 years by the incremental assembly of small magma batches (Coleman et al., 2004;Annen et al., 2015).
In that sense, they can record significant changes in the tectonic style of convergent margins through time, identified when U-Pb geochronology in zircons and whole rock geochemistry is combined and its spatial distribution is considered. The whole Andean chain includes several Meso-Cenozoic granitoids that record the continuous subduction setting that has molded the western margin of South America since the breakup of Pangea during the Triassic (Ramos, 2009;Ramos and Aleman, 2000). Hence, studying these granitoids may help to unravel evolution of the continental margin.
A major arc-continent collisional event took place in the western margin of northern South America related to its interaction with the Caribbean Large Igneous Province during Late Cretaceous (Cardona et al., 2011;Villagómez et al., 2011;Bayona et al., 2012;Spikings et al., 2015;Jaramillo et al., 2017). A contemporaneous granitic magmatism appeared in the Central Cordillera represented by the intrusion of the Antioquia batholith, a granodiorite to tonalite pluton formed by multiple pulses from ca. 90 to 60 Ma (Ibáñez-Mejía et al., 2007;Restrepo-Moreno et al., 2009;Ordóñez and Pimentel, 2001;Ordóñez-Carmona et al., 2006;Leal-Mejía, 2011;Villagómez et al., 2011). This was succeeded by a Paleogene post-collisional magmatic arc which includes the Eocene portion of the Antioquia batholith (Leal-Mejía, 2011;Bayona et al., 2012;Bustamante et al., 2017). The later suggests that the continental margin was subjected to a progressive thickening since its interaction with the Farallón plate, and that may be recorded by the Antioquia batholith.
However, geochemical and geochronological data from this batholith are limited to scarce international works presenting extensive formation ages and discussing the origin of the Antioquia Batholith in a long term tectonic model including both the transition from Nazca-dominated to Caribbeandominated tectonics. 84 Reviewing the Antioquia batholith and satellite bodies... (Vallejo et al., 2009). These are the main vestiges of a well established subduction zone on the western margin of South America that lasted until at least the middle Eocene ( Fig.1), when magmatism stopped due to difficulties of the Caribbean plateau to subduct and the northward migration of the Caribbean and South America plates (Aspden et al., 1987;Pindell et al., 2005;Spikings et al., 2005;Vallejo et al., 2009;Cardona et al., 2010;Villagómez et al., 2011;Bayona et al., 2012).

Antioquia batholith and related stocks
The Antioquia batholith is the only Late-Cretaceous intrusive body recognized in the Central Cordillera of Colombia and constitutes the first record of the continental arc magmatism in NW South America after ca. 20 m.y. of magmatic quiescence .
Along decades, different geochronometers as U-Pb, 40 Ar/ 39 Ar, K-Ar, U-Th/He, Fission tracks, Re/Os and Rb/Sr have been used on the Antioquia Batholith, obtaining a considerable dataset. A review of all available geochronological ages are listed in table 1, where basic data are gathered including sampling site, method, material, error, among others.
In order to establish the formation age of the batholith, extensive U-Pb geochronological studies in zircon, using different techniques (LA-ICP-MS, TIMS and SHRIMP) have been performed ( Fig. 2; Table 1). U-Pb have yielded crystallization ages between 97 and 58 Ma (Fig. 3;Ordóñez-Carmona et al., 2006;Correa et al., 2006;Restrepo-Moreno et al., 2007;Ibáñez-Mejía et al., 2007;Leal-Mejía, 2011;Villagómez et al., 2011). The whole intrusive complex has a scanty compositional variation, ranging from granodiorite to tonalite with minor gabbroic facies (Feininger and Botero, 1982). Five spatially related satellite stocks have also been related to this major Cretaceous magmatic body. These satellite stocks are known as the Altavista, La Culebra, Ovejas, La Unión and San Diego. Their compositions range from granite to granodiorite, except the San Diego stock which has a gabbroic composition (Fig. 3A). Based on extensive zircon U-Pb data, Leal-Mejía (2011) defined four main pulses which constructed the Antioquia batholith (i) An older pulse between   Abbreviation: FID: Figure Restrepo, 1991;11. Sáenz et al., 1996;12. Toro et al., 2006;13. Villagómez and Spikings, 2013;14. Villagómez, 2010;15. Villagómez et al., 2011;16. Correa et al., 2006;17. Cochrane, et al., 2014;18. Restrepo, et al., 2012;19. Zapata et al., 2017. 95 and 87 Ma located to the south of the batholith, including the San Diego and Altavista stocks; (ii) a second pulse between 89 and 82 Ma, mainly located on the margins of the pluton, including La Culebra and a more felsic facies of the Altavista stocks; (iii) a third pulse between 81 and 72 Ma that includes the Ovejas stock; (iv) the fourth and youngest pulse of Eocene age (~63 to 58 Ma) is identified in the central-eastern portion of the batholith (Fig. 3B). This last magmatic pulse is also correlatable with other plutons located south on the Central Cordillera such as Hatillo, Manizales, El Bosque, Norcasia and Sonsón (Bayona et al., 2012;Bustamante et al., 2017) and the Santa Marta batholith and the Parashi stock located at the Colombian caribbean (Cardona et al., 2011;Cardona et al., 2014;Salazar et al., 2016).

U-Pb geochronology
This paper presents five new U-Pb (LA-ICP-MS) ages in zircon (crystallization ages) from La Unión Stock and Ovejas Batholith. These ages were obtained at the Laboratorio de Estudios Isotópicos (LEI), Centro de Geociencias (CGEO), Universidad Nacional Autónoma de México (UNAM) following procedures described in Solari et al. (2010). Zircon crystals were separated using conventional techniques of rock crushing, sieving, Frantz isodynamic magnetic separator, panning, and heavy liquid separation. Crystal ablation was performed using an ArF excimer laser (Resolution M-50) operated at 193nm, 5 Hz and ~6 J/cm. The Plešovice reference zircon (ca. 337 Ma; Sláma et al., 2008) was used in combination with NIST 610 standard glass to correct for instrumental drift and down-hole fractionation and to recalculate elemental concentrations, using the UPb.age script for R (Solari and Tanner, 2011) and Iolite (Paton et al., 2010). Because its signal is swamped by the 204 Hg contained in the carrier gases, 204 Pb was not analyzed during this study. Common Pb correction, where needed, was thus performed employing the algebraic method of Andersen (2002). Concordia and age distribution plots, as well as age error calculations, were performed using Isoplot v. 3.70 (Ludwig, 2004).

Whole-rock geochemistry
Whole rock geochemistry was performed on the same samples where U-Pb ages were obtained, except for the A.G.1.6 sample (La Unión Stock), which was completely weathered. Major elements analysis were performed by X-ray fluorescence with a Siemens SRS-300 equipment, following the procedures described by Lozano-Santa Cruz et al. (1995). Trace elements analysis were performed on the LEI by ICP-MS using a Thermo Series XII equipment, under procedures described by Mori et al. (2009). Two additional digestion steps were added in order to achieve complete dissolution of highly refractory minerals (e.g., zircon) as described in Duque-Trujillo et al. (2014). Due to the impossibility of accessing raw data from Leal-Mejía (2011) a graphic comparison was made between the data of this author and the data here presented.

Petrography and geochemistry
Petrographic analyses were performed on four samples from the Ovejas Batholith and one sample from a magmatic mafic enclave. The sample belonging to La Unión Stock could not be analyzed due to its high degree of weathering.
The analyzed samples were classified as granodiorites. Broadly speaking, the samples are hypidiomorphic, equigranular, coarse to medium grained. These are mainly composed of quartz, plagioclase, K-feldspar, hornblende, and biotite. Magmatic mafic enclaves are common, and those present the same mineralogical composition as the main magmatic mass with a high content of mafic minerals.
Plagioclase is usually classified as andesine although compositional zonation is frequent. K-feldspar is classified as orthoclase. The amphibole, classified as hornblende, usually presents a genetic relationship with biotite in clusters of crystals. The amphibole and biotite are frequently altered to chlorite and present local replacements to epidote-clinozoisite. These observations agree with the results obtained by Feininger and Botero (1982) and Álvarez (1983) for the Antioquia Batholith. Those authors, based on a large data-set, found that the petrographic characteristics of the main granitic mass of the Antioquia Batholith are very homogeneous, with a ~97% of the samples classified as granodiorites to tonalities.
Four samples of the Ovejas Batholith were geochemically analyzed and their results are presented in table. 2. Three samples correspond to the main granodioritic mass of the Ovejas Batholith and one sample from a mafic enclave. Samples belonging to the granodioritic mass were classified as quartzdiorites and diorites, meanwhile the mafic enclave fall in the gabbro field (Fig. 4A). SiO 2 vary from 61.9 to 66.7 wt%, while K 2 O content is almost invariant around ~1.8 wt% for the granitic samples, which fall in the calc-alkaline series of medium K (Fig. 4B). The mafic enclave has 52.3% of Si 2 O and higher K 2 O, locating the sample on the Shoshonitic series. MgO values range from 1.5 to 2.3 wt% in the granitic samples, and have a value of 4.1 wt% for the mafic enclave. Al 2 O 3 values range from 16.2 to 17.0 wt% within the granitic samples, and 17.9 wt% for the mafic enclave. From the four analyzed samples, two samples, (the mafic enclave and one granitic sample) fall in the metaluminous field, meanwhile the other two granitic rocks fall into the peraluminous field (Fig. 4C).
Primitive mantle-normalized multi-element diagrams for the Ovejas Batholith rocks are characterized by an enrichment of the Large Ion Lithophile Elements (LILE) over the High Field Strength Elements (HFSE) (Fig. 5A, C). These patterns are also characterized by negative Nb-Ta, La-Ce and Ti anomalies, and positive Pb, and Zr-Hf anomalies (Fig. 5A, C). Although the mafic enclave has a similar pattern as the granitic rocks, it differs from those in some aspects, especially those related to less differentiated rocks (e.g., Zr-Hf anomaly, which is negative in the mafic enclave and positive in the granitic rocks).
Chondrite-normalized REE patterns show a well-defined LREE enrichment ([La/Yb] N ratios vary from 6.4 to 8.6 in granitic rocks and 3.8 for the mafic enclave) and an almost flat HREE pattern ([Gd/Yb] N ratios vary from 1.58 to 1.70 in granitic rocks and 1.51 for the mafic enclave) (Fig. 5B, D, E and F). Unless all samples have similar patterns, La/Yb ratios show that the mafic enclave rock is less depleted in REE than the granitic samples (Fig. 5B, D and E). Eu anomaly is present in three from the four analyzed samples (Fig. 5B). The mafic enclave shows a well-defined negative anomaly (Eu/Eu*=0.68), meanwhile the granitic rocks all samples have positive anomalies (Eu/Eu* from 1.03 to 1.42) (Fig. 5G).

U-Pb geochronology
Zircon U-Pb crystallization ages (Table 3) were obtained by the LA-ICP-MS method in five samples ( Fig. 6 and 7). One of them corresponds to the La Unión Stock, and four to the Ovejas Batholith. In order to obtain the age of the last crystallization event, the preferred ablation target were crystal borders; nevertheless, some cores were analyzed in order to identify possible inherited ages.

La Unión Stock
One sample (AG 1.6) was analyzed for this pluton. Cathodoluminescence (CL) images show thin concentric overgrowths around ante-crystals (Fig. 6). Twenty-six analysis from this sample yield a weighted mean 238 U/ 206 Pb age of 97.2±0.6 Ma (Fig. 6). This age is dominated by the age of the magmatic overgrowths, leading to interpret this as the age of the latest magmatic activity during the La Unión Stock magmatism. Zircon cores yield ages only ~4 Ma older than the overgrowths (102-100 Ma).

Ovejas Batholith
Four samples were analyzed for the Ovejas Batholith (AG 1.1, 1.2, 1.3 and 1.4) (Fig. 3). CLimages show mostly thin concentric overgrowths around an older core (Fig. 7). Although most of the analytical spots were located on zircons overgrowths, some of them were located on the cores (Fig. 7). Single-spot U-Pb ages obtained from the Ovejas Batholith samples yield ages between 85 and 66 Ma (Fig. 7); meanwhile, intercept ages fall between 76.9 and 73.3 Ma (Fig. 7). A weighted mean age calculated using those four ages yield an age of 75.2 Ma (MSWD=0.47).
Although intercept ages from the Ovejas Batholith clearly define a coherent unique age for this magmatism, sample AG 1.1 has three zircons with ages ~10 M.y. younger (66-62 Ma) than the intercept age calculated for that sample. It is plausible that these zircons represent a later magmatic pulse which had affected part of the Ovejas Batholith between 66 and 64 Ma.
FIG. 5. Trace element diagrams for samples from ovejas Batholit (in red) and mafie enclave (in blue). A. Trace element (PRIMA normalized, Wood, 1979); B. REE normalized diagram (normalized using Boynton, 1984) spider-diagram from the Ovejas Batholith; C-D. Ovejas Batholith trace elements spider-diagrams compared with Leal-Mejía (2011); Antioquia Batholith data; E-G. Trace elements ratio for the Ovejas Batholith and Antioquia Batholith from Almeida and Villamizar (2012) in grey color.  (Bustamante et al., 2017) and the Caribbean region . According to such age distribution exposed over the present work, we propose to challenge previous geological models which suggest a southward magmatic migration during Paleogene (Ordóñez et al., 2001;Cardona et al., 2012;Pindell and Kennan, 2009;Pindell et al., 1998Pindell et al., , 2006. Instead, we propose that continental arc magmatism was stationary during upper Cretaceous, forming the Antioquia Batholith, whereas its Paleogene pulse, ~10 Ma after the mentioned magmatic hiatus, was formed on the eastern side and share geochemical features with other Paleogene post-collisional plutons of the Central Cordillera (Bustamante et al., 2017). Further Miocene rotation of the Sierra Nevada de Santa Marta located northern of Colombia (Montes et al., 2010) and the oblique convergence between South America and the Caribbean Plate may have dispersed the Eocene granitoids from its former position , which in turn, may explain the magmatic gap between the Central Cordillera and the Sierra Nevada de Santa Marta (Fig. 1). The coincidence of the aforementioned ~10 m.y. magmatic hiatus with increasing Sr/Y ratios, suggest that the collision of the Caribbean plateau with NW South America may have caused such period of magmatic quiescence.
Whole rock geochemical results from the Ovejas Batholith indicate an arc related setting for this pluton according to the Nb, Ti and Ta negative anomalies (Fig. 5) as well as the LREE/HREE ratios ([La/Yb] N from 6.4 to 8.6). We compared our results with geochemical analyses obtained in previous works of the Antioquia Batholith (Botero, 1963;Feininger and Botero, 1982;González, 1980;Álvarez, 1983;Sáenz, et al., 2003;Villagómez, 2010;Almeida and Villamizar, 2012). Such compilation, however, lacks of the raw data and trace and REE analyses, and only eight of them are complete (Almeida and Villamizar, 2012). Analytical data obtained by Leal-Mejía (2011) are also included in this compilation by graphical comparison because the absence of the raw data.
Primordial mantle-normalized trace-element trends exhibit a clear enrichment in LILE over HFSE (   figure 5F. Nb, Ta and Ti negative anomalies, and Zr, Hf positive anomalies are identifiable (Fig. 5A). Chondritenormalized REE patterns show enrichment in LREE versus HREE with similar patterns as those obtained for the Ovejas Batholith. Nevertheless, Antioquia batholith has less steep MREE-HREE patterns, indicated by the Gd/Yb ratio.
Some authors consider these and other plutons in Aruba, Curaçao, Pujilí, Guajira, among others, as belonging to the tonalite-trondhjemite-granodiorite series or having an adakitic affinity (e.g., Wright and Wyld, 2011;Whattam and Stern, 2015). Pindell and Kennan (2009) consider that this series of plutons are so close to the Caribbean-South American Plate boundary and cast doubt on the normal arc setting for these rocks, suggesting the melting of a slabtip during subduction initiation. Conversely, we claim for a primitive continental arc setting for the Antioquia batholith and its satellite bodies based on the aforementioned geochemical evidences. Such magmatic arc is recording an increasing in its maturity with time as suggested in the Rb/Zr versus Nb ratios (Fig. 8). Elliot et al. (1997) observed that incompatible elements like Ba and Th can be used as tracers of fluids derived from subducting slabs. In that sense, the high Ba/Th (~111 to 185) ratios of the Antioquia batholith are indicative of a continental arc where the slab derived fluids are increasing with maturity (Fig. 8). The stationary character of the magmatism represented by the Antioquia batholith, indicates that the subduction components (hydrous fluids) involved in the petrogenesis of these magmas would have changed locally, and are not related to the migration of the magmatic arc away from the trench.

Conclusions
Syn-to post-collisional tectonics characterized the NW margin of South America since the Late Cretaceous to the Eocene, mainly influenced by the interaction of the Farallón and Caribbean plates with this margin. The Antioquia batholith, built by successive magmatic pulses for ca. 40 m.y., constitutes one of the main magmatic records of this tectonic scenario. Its crystallization history can be inferred according to new and already published U-Pb ages, whereas the whole rock geochemistry suggests that this magmatism is arc-related and that its locus may have been relatively stationary since no evidences of arc migration are recorded.
The latest magmatic phases of the Antioquia Batholith, Paleogene in age, constitute part of a magmatic arc that includes other small volume FIG. 8. Rb/Zr versus Nb diagram (Brown et al., 1984). Data from samples belonging to the Antioquia batholith from: Whatam and Stern (2015), blue dots; Almeida and Villamizar (2012), red dots; Villagómez (2010), green dots; this work, gray dots.
plutons currently located at the Colombian Caribbean. This formerly arc would have been disrupted and dispersed by the interaction between the NW margin of South America and the Caribbean Plate which lead to rotation and translation of cortical blocks as well as basin formation.