Tracking Exhumation of Andean Ranges Bounding the Middle Magdalena Valley Basin, Colombia
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Tracking exhumation of Andean ranges bounding the Middle Magdalena Valley Basin, Colombia Junsheng Nie1,2, Brian K. Horton1,3, Andrés Mora4, Joel E. Saylor1, Todd B. Housh1, Jorge Rubiano4, and Julian Naranjo4 1Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78712, USA 2National Laboratory of Western China’s Environmental Systems, Ministry of Education, Lanzhou University, Lanzhou, Gansu 730000, China 3Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78712, USA 4Instituto Colombiano del Petróleo, Ecopetrol, Bucaramanga, Colombia ABSTRACT ous rocks (Aspden and McCourt, 1986; Aspden The shortening history of the Andes is important for understanding retroarc deformation et al., 1987; Gómez et al., 2005). The Eastern along convergent margins and forcing mechanisms of Cenozoic climate. However, the tim- Cordillera has continental-affi nity basement ing of uplift in the northern Andes is poorly constrained, with estimates ranging from Cre- of Proterozoic–Paleozoic age that is mostly taceous to Pliocene. Detrital zircon U-Pb ages from the Middle Magdalena Valley Basin in covered by Paleozoic–Mesozoic strata (Dengo Colombia reveal two provenance shifts during Cenozoic time. The fi rst shift occurs between and Covey, 1993; Gómez et al., 2005; Chew et early and late Paleocene strata, where U-Pb results show a switch from Proterozoic-dom- al., 2007). To the east of these ranges and the inated to Phanerozoic-dominated age spectra. We attribute this change to uplift-related Llanos foreland basin is the Amazonian craton, exhumation of the Central Cordillera. The second shift occurs between middle-late Eocene consisting of several terranes accreted to an and late Oligocene strata, where increased Grenville ages and diminished Mesozoic ages can Archean nucleus. be linked to uplift of the Eastern Cordillera. Our results show that signifi cant pre-Neogene Cenozoic strata in the Middle Magdalena deformation affected the northern Andes, underscoring the potential importance of Andean Valley Basin consist of the Lisama, La Paz, uplift on the dynamics of Paleogene climate. Esmeraldas, Mugrosa, Colorado, Real, and Mesa Formations. Ages of Paleocene–middle INTRODUCTION Cenozoic accretion (McCourt et al., 1984; Miocene units are based on palynology and Despite decades of research, the forcing Dengo and Covey, 1993). invertebrate fossils (Hopping, 1967; Nuttall, mechanisms for Cenozoic cooling remain elu- Detrital zircon U-Pb age analyses have 1990; Gómez et al., 2005). Ages for late Mio- sive (Zachos et al., 2001). Intensifi ed chemi- proven useful in defi ning the provenance his- cene–Pliocene units are based on intercalated cal weathering associated with tectonic uplift tory of sedimentary basins and tracking exhu- tuffs (Gómez et al., 2005). (Raymo and Ruddiman, 1992) has been sug- mation of sediment source regions. In this study The Paleocene Lisama Formation transition- gested as the most plausible cause for the cool- we evaluate erosional exhumation of the Central ally overlies the Maastrichtian shallow-marine ing trend in Cenozoic climate. Previous efforts Cordillera and Eastern Cordillera using detri- Umir Formation and records regressive sedi- have focused on the role of plateau uplift in Asia tal zircon U-Pb geochronology from Cenozoic mentation in deltaic and alluvial plains (Gómez (Raymo and Ruddiman, 1992; Garzione, 2008). strata in the intermontane Middle Magdalena et al., 2005). The middle to late Eocene La Paz However, South America has the highest non- Valley Basin of the Colombian Andes (Fig. 1). Formation consists of amalgamated channel collisional plateau and longest latitudinal range Potential source regions (Horton et al., 2010; sandstones and minor mudstones that uncon- of Earth’s mountain belts; if proven to have initi- see the GSA Data Repository1), including the formably overlie the Lisama Formation. Eocene ated during the Paleogene, the Andes could be Western Cordillera, Central Cordillera, Eastern strata were deposited in a fl uvial setting and indi- an important force for Cenozoic climate cool- Cordillera, and Amazonian craton, have diag- cate transformation of the Middle Magdalena ing. Although pre-Neogene shortening and nostic basement ages, allowing us to recognize Valley Basin into a nonmarine basin (Gómez uplift has been proposed for the central Andes provenance shifts recorded by sediments of the et al., 2005). The early Oligocene Esmeraldas based on integrated stratigraphic and structural Middle Magdalena Valley Basin (Fig. 2). Formation is also composed of broadly lenticu- considerations (Horton et al., 2001; DeCelles lar fl uvial sandstones, but with a much higher and Horton, 2003; Horton, 2005; McQuarrie GEOLOGIC SETTING proportion of fi ne-grained overbank deposits. In et al., 2005), the uplift history of the northern Three ranges in the Colombian Andes (West- the late Oligocene Mugrosa Formation, abun- Andes remains poorly understood. For the East- ern Cordillera, Central Cordillera, Eastern Cor- dant well-developed pedogenic features have ern Cordillera of Colombia, initial uplift ages of dillera) are separated by the Magdalena and overprinted channel sandstones and fl oodplain latest Cretaceous, middle Eocene, late Eocene– Cauca valleys (Fig. 1). The Western Cordillera mudstones. Available paleocurrent data indicate early Oligocene, and middle Miocene–Pliocene is composed of Late Cretaceous–Cenozoic dominantly eastward fl ow in the La Paz and (Dengo and Covey, 1993; Hoorn et al., 1995; igneous rocks of oceanic affi nity (McCourt et Esmeraldas Formations (Gómez et al., 2005); Gregory-Wodzicki, 2000; Gómez et al., 2003; al., 1984; Aspden and McCourt, 1986). The the Mugrosa Formation mainly shows a strike- Bayona et al., 2008; Parra et al., 2009; Horton Central Cordillera has mixed continental and perpendicular, westward or eastward direction. et al., 2010) have all been proposed using strati- oceanic basement that is intruded and over- The contact with the early–middle Miocene graphic and thermochronological data. Esti- lapped by numerous Jurassic–Cretaceous igne- Colorado Formation is transitional, with con- mates for initial uplift of the Central Cordillera, tinued evidence for extensive pedogenesis and based primarily on sedimentological evidence, 1GSA Data Repository item 2010122, review of upward coarsening to alluvial-fan boulder con- range from mid-Cretaceous to early Cenozoic basement ages of potential source regions, supple- glomerates at the top. The late Miocene Real (Cooper et al., 1995; Villamil, 1999; Gómez mentary method, and U-Pb geochronologic analy- Formation is distinguished from the Colorado ses, is available online at www.geosociety.org/pubs/ et al., 2005; Jaimes and de Freitas, 2006). For ft2010.htm, or on request from editing@geosociety Formation by a greater proportion of volcanic the Western Cordillera, available studies sug- .org or Documents Secretary, GSA, P.O. Box 9140, and igneous detritus, along with northward- gest initial uplift during Late Cretaceous–early Boulder, CO 80301, USA. directed paleocurrents (Gómez et al., 2005). © 2010 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, May May 2010; 2010 v. 38; no. 5; p. 451–454; doi: 10.1130/G30775.1; 2 fi gures; Data Repository item 2010122. 451 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/38/5/451/3539099/451.pdf by guest on 02 October 2021 Figure 1. A: Map showing tectonomorphic provinces of northern Andes. B: Simplifi ed geologic map of Middle Magdalena Valley Basin (MMVB). C: Simplifi ed cross section across MMVB. S—Santander massif; P—Panama arc; WC—Western Cordillera; CC—Central Cordillera; EC—Eastern Cordillera. METHODS age probability diagram and age histogram for Oligocene−late Miocene record. For the upper Medium- and coarse-grained sandstones each sample (Fig. 2). Following previous stud- Mugrosa (U08025, late Oligocene), lower Colo- were collected from the eastern limb of the ies, age peaks on age probability diagrams are rado (M09, early Miocene), upper Colorado Nuevo Mundo syncline, a type locality for considered signifi cant only if defi ned by three (U08027, middle Miocene), and lower Real Cenozoic fi ll of the Middle Magdalena Val- or more analyses (e.g., Dickinson and Gehrels, (U08028; late Miocene) samples, (1) Grenville ley Basin (Gómez et al., 2005) (Fig. 1C). We 2008). This approach minimizes the likelihood ages (1200–900 Ma) become more abundant obtained eight samples from fi ve exposed for- of erroneously identifying source terranes based and (2) Late Jurassic–Early Cretaceous ages mations (Fig. 1C). Detrital zircon grains were on ages affected by Pb loss in young grains or (150–100 Ma) are eliminated. separated by standard heavy liquid techniques, discordance in older grains. selected randomly, and analyzed by laser- DISCUSSION AND CONCLUSIONS ablation–inductively coupled plasma–mass RESULTS Detrital zircon U-Pb ages from the Middle spectrometry in the Department of Geological The lower Lisama sample (RS0114091, early Magdalena Valley Basin reveal two age popula- Sciences at the University of Texas at Austin. Paleocene) has no signifi cant zircon age popula- tion shifts during the Cenozoic. The fi rst occurs Analyses and associated age calculations fol- tions younger than 500 Ma; instead, most ages between early and late Paleocene strata, where lowed methods outlined in the Data Repository, are