Fracturing of the Panamanian Isthmus during initial collision with

David W. Farris1, Carlos Jaramillo2, German Bayona2,3, Sergio A. Restrepo-Moreno2,4, Camilo Montes2,3, Agustin Cardona2,3, Andres Mora5, Robert J. Speakman6, Michael D. Glascock7, and Victor Valencia8 1Florida State University, Department of Earth, Ocean, and Atmospheric Sciences, Tallahassee, Florida 32306, USA 2Smithsonian Tropical Research Institute, Unit 0948, APO AA 34002-0948, USA 3Corporación Geológica ARES, Calle 44A N. 53-96 Bogotá, 4University of Florida, Department of Geological Sciences, Gainesville, Florida 32611, USA 5Instituto Colombiano del Petroleo, Ecopetrol, Bucaramanga, Colombia 6Smithsonian Institution, Museum Conservation Institute, Washington, D.C. 20012, USA 7University of Missouri, Archaeometry Laboratory, Columbia, Missouri 65211, USA 8University of Arizona, Department of Geosciences, Tucson, Arizona 85721, USA

ABSTRACT tle-wedge−derived subduction zone magmas Tectonic collision between South America and began at 23–25 Ma. The collision is (Pearce and Peate, 1995). signifi cant because it ultimately led to development of the Panamanian Isthmus, which in turn Within the Canal Zone, volcanic rocks had wide-ranging oceanic, climatic, biologic, and tectonic implications. Within the Panama younger than 24 Ma range from basalt to Canal Zone, volcanic activity transitioned from hydrous mantle-wedge−derived arc magma- dacite in composition, but are signifi cantly less tism to localized extensional arc magmatism at 24 Ma, and overall marks a permanent change hydrous and exclusively tholeiitic. Rock types in arc evolution. We interpret the arc geochemical change to result from fracturing of the within the younger group are bimodal with Panama block during initial collision with South America. Fracturing of the Panama block individual units dominated by either silicic led to localized crustal extension, normal faulting, sedimentary basin formation, and exten- tuffs and welded units (Las Cascadas Forma- sional magmatism in the Canal Basin and Bocas del Toro. Synchronous with this change, both tion) or basalt to basaltic-andesite lava fl ows Panama and inboard South America experienced a broad episode of exhumation indicated by and intrusive sills (Pedro Miguel Formation). (U-Th)/He and fi ssion-track thermochronology coupled with changing geographic patterns of Hornblende and other hydrous minerals are sedimentary deposition in the Colombian Eastern Cordillera and Llanos Basin. Such observa- absent. In comparison with earlier arc rocks tions allow for construction of a new tectonic model of the South America–Panama collision, (Bas Obispo Formation and older), northern uplift and Panama orocline formation. Finally, synchroneity of Panama arc Canal Zone volcanism exhibits low LILEs, chemical changes and linked uplift indicates that onset of collision and Isthmus formation higher HREEs and Ti, and a signifi cantly began earlier than commonly assumed. decreased Ta anomaly (Fig. 2A). Trace element ratios are tracers of volcanic- INTRODUCTION PANAMA ARC EVOLUTION WITHIN rock tectonic and mantle environments, and Yb The Isthmus of Panama fully separated the THE CANAL ZONE normalization allows one to see through frac- Sea and Pacifi c Ocean by 3–3.5 Ma The Panama arc formed on the trailing edge tionation processes (Pearce and Peate, 1995; (Keigwin, 1978; O’Dea et al., 2007) and is of the at ca. 75–65 Ma (Buchs Wegner et al., 2011). Welch two-sample t-tests inferred to result from collision between South et al., 2010). Wörner et al. (2009) and Wegner indicate that arc groups identifi ed in Figure 2 America and the Panama block (Trenkamp et et al. (2011) divide arc activity into a depleted have unique element ratio sets, suggesting that al., 2002; Coates et al., 2004) (Fig. 1). However, Late Cretaceous–Eocene initial episode and the mantle environment changed over time this closure date is based on evolutionary diver- an enriched Miocene arc. Modern magmatism (Table DR2). In the Panama arc, ratios such gence of marine organisms and therefore must exists only west of the Canal Zone and consists as La/Yb, Th/Yb, Hf/Yb, and Ta/Yb exhibit an be a minimum age. Other evidence on when of a <2–3 Ma adakitic suite attributed variously increase and change in slope at 24 Ma (Fig. 2B), Isthmus formation began comes from shallow- to slab melting (Defant et al., 1992), a slab with Ta/Yb being the single best discriminator ing sequences in Panamanian and Colombian window (Abratis and Wörner, 2001; Wegner of this change. In rocks younger than 24 Ma, bathyal sedimentary basins at 14.8–12.8 Ma et al., 2011), or subduction erosion (Goss and the Ta/Yb ratio is >0.1. Ba/Yb is also effective (Duque-Caro, 1990; Coates et al., 2004) and Kay, 2006). at discriminating between rocks younger than folded and thrusted Upper Miocene strata in We report that depleted-type volcanic and 24 Ma in the Canal Zone, with younger rocks eastern Panama (Mann and Kolarsky, 1995). plutonic rocks persist until 25 Ma within the showing a distinct depletion (Fig. 2C). Con- These observations document that signifi cant central Zone. Older arc rocks versely, Miocene arc rocks elsewhere in Panama contraction in eastern Panama occurred since are heterogeneous and consist of plutonic and show a progressive increase in Ba/Yb and fl uid- the Middle Miocene, but do not put a fi rm limit extrusive rocks that range from calc-alkaline to mobile elements in general. on when or how the collision between South tholeiitic and basaltic to andesitic in composi- America and the Panama block initiated. We tion. These rocks are dominantly hornblende- 1GSA Data Repository item 2011297, a descrip- suggest that collision initiated at 23–25 Ma bearing (Rooney et al., 2010), have a large Ta tion of geochemical (INAA and XRF) and geochro- when South America fi rst impinged upon Pan- anomaly, exhibit relative enrichment in fl uid- nologic (U-Th/He) methods, a statistical analysis of ama arc crust as observed by distinct Panama mobile large ion lithophile elements (LILEs) the geochemical data, and data tables of the low- arc chemical changes, broad exhumation of (e.g., Cs, Rb, Ba), and have moderate heavy rare temperature thermochronology presented in the pa- per, is available online at www.geosociety.org/pubs/ the northern Andes and Panama, and extensive earth element (HREE) concentrations (Fig. 2A; ft2011.htm, or on request from editing@geosociety 1 foreland deposition in the distal Llanos Basin of Table DR1 in the GSA Data Repository ). Such .org or Documents Secretary, GSA, P.O. Box 9140, Colombia (Fig. 1). characteristics are indicative of hydrous man- Boulder, CO 80301, USA.

© 2011 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. GEOLOGY,Geology, November November 2011; 2011 v. 39; no. 11; p. 1007–1010; doi:10.1130/G32237.1; 4 fi gures; Data Repository item 2011297. 1007 Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/39/11/1007/3538911/1007.pdf by Smithsonian Institution Lib user on 18 September 2018 Geochemical samples 80oW Caribbean plate Paleocene-Olig. Arc A 100 Paleocene-Olig. Arc Figure 2. Instrumental neutron activation Canal Zone N. Panama Bocas del Toro deformed belt Canal Zone A Western Panama Bocas del Toro analysis (INAA) trace element geochemis- Darien Western Panama try from the Panama arc (see Table DR1). Ranges A: Averaged trace element geochemistry o Panama block 8 N 10 from different temporal and spatial groups of Panama arc rocks. Shaded red/blue fi elds Coiba Sandra Rift Plateau Extensional arc indicate the full data range for early arc and Cocos Ridge >8 Ma Llanos Basin volcanism Canal Zone, respectively. N-MORB—normal Ridge Fig. 4 Cocos Thermochronology sites 1 mid-oceanic-ridge basalt. B: La/Yb versus

Panama Fracture Zone plate Malepo sample / N-MORB Mamoní batholith Ta/Yb with individual samples plotted. Re- >8–9 Ma Cerro Petaquilla gressions through the early and youngest South American Central Cordillera Post-Oligocene decrease plate Sierra Nevada S.M. arc groups intersect at Ta/Yb = 0.1. In Ca- Eastern Cordillera in subduction signal Nazca plate 500 km nal Zone rocks, this boundary is crossed at 0.1 Rb Th Ta La Sr Zr Sm Ti Dy Lu 80oW Caribbean plate (Stationary) Cs Ba Nb K Ce Nd Hf Eu Tb Yb 23–25 Ma and corresponds to a permanent BV change in arc chemistry. C: Ba/Yb versus v Volcanic Zones of Extension 100 v Bocas Canal Zone depleted Hydrous Ta/Yb with individual samples. Canal Zone v del Toro arc magmatism B arc mantle-wedge v defoN. Pan Underthrust volcanic rocks have sharply lower Ba/Yb ra- v magmatism Progressive rmed belt ama tios indicative of general large ion lithophile CaribbeanNorthward lithosphere mantle o v v v migrated 10 8 N v terranes enrichment element (LILE) depletion. D: Shervais (1982) v Zone of tectonic discrimination diagram. Canal Zone Coiba contraction 24–0 Ma Plateau Sandra Rift submarines volcanic formations (Fm.) transition from

South Yb La / y=53.9x - 2.0 America 1 R2= 0.92 arc tholeiites to extensional products af- ter 25 Ma. Rocks from Bocas del Toro also Extinct 65–25 Ma Similar Panama Fracture Zone (9–0 Ma) (9–0 Zone Fracture Panama Malpelo 21 mm/yr Ridge at 8–9 Ma y=17.8x + 1.9 enrichment trends exit plot in the extensional fi eld. MORB—mid- 2 for Th/Yb and Hf/Yb ratios 0.1 R = 0.17 oceanic-ridge basalt; BAB—backarc basin;

Cocos Ridge 10 Ma lithosphere v 25–27 Ma CFB—continental fl ood basalt. Subducted oceanic v reconstruction v Canal Zone C Cocos-Nazca spreading center 200 km Volcanic (210 arc km of S. American (Bas Obispo Fm.) (active until present) displacement) 1000 o C 80 W < 24 Ma Central AmericanCaribbean plate v (Stationary in Indo-Atlantic LILE depleted v hot spot reference frame) Underthrust Caribbean 100 Canal Zone v lithosphere volcanism

Ba / Yb Ba / marine fossil assemblages (Kirby et al., 2008). v v Pen Wegner et al. (2011) Both sedimentary and volcanic units within 8oN v insula Late Oligocene v 10 Paleocene-Olig. Arc v Canal zone arc Canal Zone the basin are cut by a pervasive orthorhombic v “standard arc volcanism” Bocas del Toro fault set. In general, earlier faults have normal v Western Panama s 1 movement and are cut by later strike-slip faults ubmarine South 0.01 0.10 1.00 10.00 America Ta / Yb related or synthetic to the active right-lateral 500 21 mm/yr Arc Pedro Miguel fault (Rockwell et al., 2010). The Farallon plate Tholeiite MORB/BAB/CFB D 25 Ma 400 27–25 largest normal faults are parallel to the Canal Subducted oceanic reconstruction Ma 20–15 Ma Basin axis and have drill core−constrained 200 km lithosphere (525 km of S. American displacement) 300 vertical offsets of >100 m on individual faults

V (ppm) V 200 Canal Zone (Lutton and Banks, 1970). Figure 1. A: Modern tectonic map with lo- Bas Obisbo Fm. cation of geochemical samples and low- Pedro Miguel Fm. Another volcanic sequence of note is from temperature thermochronology profi le sites. 100 OIB Bocas del Toro Bocas del Toro (Fig. 1A). This group shares S.M.—Santa Marta. B: Tectonic reconstruc- 12 Ma Valiente Fm. geochemical characteristics of Canal Zone tion at 10 Ma. This is an intermediate step 0 0 4000 8000 12000 16000 rocks with moderate enrichment in compatible in the collision between South America and Ti (ppm) Panama. The Panama block has fractured, elements such as HREEs and Ti; however, they resulting in two zones of extension (Canal are distinct with strongly enriched LILEs and Zone and Bocas del Toro) and one zone of shoshonitic, with >4 wt% K2O at 52 wt% SiO2. contraction in eastern Panama. Also, the a signifi cant drying out of the mantle source In terms of rock type, they consist of glassy North Panama deformed belt has partially formed and a seaway >200 km wide sepa- after 25 Ma. basaltic to andesitic blocky lava fl ows interbed- rates Panama and South America. C: Tec- Canal Zone volcanic units are interbedded ded with marine sandstones cut by normal faults tonic reconstruction at 25 Ma. This imme- within well-dated Canal Basin sedimentary and range in age from 12 to 8 Ma (Coates et diately precedes collision between Panama rocks. Sr isotope dating places the depositional al., 2003). This group also plots within an exten- arc crust and South America. Previously, un- modifi ed Caribbean crust was underthrust contact of the terrestrial volcanic Las Cascadas sional tectonic environment (Fig. 2D). beneath South America. Formation and the overlying marine sedimen- tary Culebra Formation at 23 Ma (Kirby et al., EXHUMATION AND CHANGING 2008). Rooney et al. (2010) reported an Ar/Ar DEPOSITIONAL PATTERNS Canal Zone rocks also show the 24 Ma tran- age of Bas Obispo Formation equivalents (Cerro Exhumation and changing depositional pat- sition on the V versus Ti tectonic discrimina- Patacon) to be 25.37 ± 0.13 Ma. Geochemical terns in the northern Andes and Panama are tion diagram of Shervais (1982) (Fig. 2D). Bas data (Ta/Yb ratios >0.1) indicate that the Las synchronous with geochemical changes in the Obispo Formation rocks plot within the arc Cascadas Formation is the fi rst younger arc unit Panama arc. Apatite-zircon (U-Th)/He and tholeiite fi eld, whereas younger Pedro Miguel within the Canal Zone and so the transition is fi ssion-track thermochronology collected from Formation rocks fall within the backarc basin constrained to 25–23 Ma. the Colombian northern Andes and Panama fi eld. Las Cascadas Formation rocks are too Canal Zone arc chemistry change also coin- indicate a broad exhumation pulse at 22–28 Ma, silicic, and thus are not plotted. The V versus cides with formation of the Canal Basin. The with most data near 25 Ma (Fig. 3). Onset and Ti diagram is sensitive to changes in source basin is shallow and oriented perpendicular to intensity of this event was derived from verti- oxygen fugacity, and coupled with the decrease the axis of the Isthmus. It is important because cal sample profi les collected through igneous in Ba/Yb and loss of hydrous minerals suggests it preserves unique Miocene terrestrial and suites in Panama (Mamoni and Petaquilla),

1008 GEOLOGY, November 2011 Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/39/11/1007/3538911/1007.pdf by Smithsonian Institution Lib user on 18 September 2018 3800 western fl anks (Gomez et al., 2005; Parra et al., are explainable by low degrees of decompres- 23–25 Ma Inflection 2009). Also at this time, the Llanos Basin propa- sion melting in compositionally similar astheno- 3400 point in Panama arc chemistry gated over 200 km to the east, refl ecting onset of sphere (Fig. 2). Similar variations within exten- 3000 Eastern Cordillera deformation (Bayona et al., sional arcs have been observed in the northern 2600 2008; Parra et al., 2009) (Fig. 4). Marianas (Lin et al., 1989). 2200 The standard interpretation of extensional arc DISCUSSION magmatism is trench rollback−coupled backarc 1800 Thermochronology Sites Mamoni Batholith Overall, our goal is to link geochemical extension and trenchward arc migration (Ewart (A-He)

Elevation (m) Elevation 1400 Cerro Petaquilla changes in the Panama arc with synchronous et al., 1998). However, in the Panama arc we 1000 (Zr-He) exhumation in Panama and the northern Andes propose an alternative interpretation. First, a Central Cordillera 600 (A-He) using a tectonic model that explains both. Unit- transition to backarc magmatism would cre- Sierra Nevada S.M. (Zr-He) based observations indicate that at 23–25 Ma ate a continuous belt of extensional volcanism 200 Eastern Cordillera the Panama arc experienced permanent geo- parallel to the arc. In contrast, extensional mag- (A/Zr-FT) -200 chemical change. Two related events occur at matism is observed only in the Canal Zone 0 102030405060 Age (Ma) this time: (1) progressive mantle enrichment and Bocas del Toro. Second, dominant normal (e.g., La/Yb, Ta/Yb) that affects all younger arc faults within the Canal Zone are perpendicular Figure 3. Low-temperature thermochronol- ogy from Panama and inboard South Amer- rocks, and (2) localized extensional arc magma- to the arc, whereas backarc faulting should be 2 ica (see Tables DR3 and DR4 [see footnote tism. A linear regression fi t (R = 0.92) through arc-parallel. Third, Canal Basin formation is 1]). Ages shown are (U-Th)/He and fi ssion- the younger arc rocks suggests an enriched synchronous with the onset of extensional arc track dates from apatite and zircon sampled mantle source mixed into the subarc environ- magmatism at 24 Ma, and is also arc-perpendic- on vertical profi les through igneous intru- ment beginning at 25 Ma. ular. Thus, our interpretation is that the Panama sive suites. S.M.—Santa Marta. Cooling ages coincide with the Panama arc chemistry in- The enrichment event is compatible with the block underwent localized arc-perpendicular fl ection point at 23–25 Ma. Wegner et al. (2011) division of arc activity into extension. One mechanism is that during Pan- a depleted Late Cretaceous through Eocene ama orocline formation (Silver et al., 1990) the initial arc, an Oligocene lull, and an enriched Isthmus fractured. Basic geometric reconstruc- the Colombian Central Cordillera (Restrepo- Miocene arc. However, Canal Zone observa- tions (Fig. 1B) of the Panama orocline can be Moreno et al., 2009), and the Sierra Nevada de tions sharply delineate the boundary between accomplished with two localized zones of Santa Marta (Cardona et al., 2011), and from the initial and Miocene arc episodes and show extension (Canal Zone and Bocas del Toro) and sedimentary sequences in Colombia’s Eastern that magmatism continues throughout the Oli- one zone of contraction (Darien Ranges). This Cordillera (Mora et al., 2010). Igneous suite gocene, although at a lower volumetric level. method can accommodate crustal-scale bend- crystallization ages vary, but all are Eocene and Throughout the lull, arc magmatism retains a ing by brittle processes and is potentially wide- older except for Petaquilla in Panama (Early Oli- strong subduction signal and geochemical char- spread in the geologic record as the accretion of gocene; Kesler et al., 1977). Different locations acteristics similar to the earlier magmatic peak. ribbon is an important mechanism of experienced varying subsequent levels of exhu- One signifi cant difference between the arc crustal growth (Johnston, 2001). mation, and so the 25 Ma event is manifested chemistry presented here and that of previ- The opposed geometry of the two extensional by different thermochronometers at different ous workers is the identifi cation of localized zones can explain age/chemical variations in locations. Cooling during this episode translates extensional magmatism in the Canal Zone and that Bocas del Toro is in an extensional zone to exhumation rates of 0.6–0.8 km/m.y. (Fig. 3). Bocas del Toro. Within the Canal Zone, this “tip” whereas the Canal Zone is in a “mouth.” This exhumation pulse correlates with the arc interpretation is supported by sharp decreases in Volcanism at an extensional zone tip should be geochemical change in Panama and the onset of fl uid-mobile elements, tectonic discrimination younger and result from less mantle melting, localized extensional magmatism. diagrams, and fl attened REE curves. Onset of with which observations are consistent. Also indicative of Andean orogenesis at extensional Canal Zone volcanism is also asso- Exhumation in Panama and the northern this time are changing patterns of erosion and ciated with extensive normal faulting and basin Andes is synchronous with onset of Canal Zone deposition inboard of the Panama block. In the formation. Our preferred model is extension- extensional magmatism shortly after 25 Ma. Our Eastern Cordillera, Middle Eocene continental induced decompression melting of the subarc preferred explanation is the onset of collision deposition covered broad areas. By Late Oligo- asthenosphere, in which high degrees of shallow between South America and Panama arc crust. cene, the Eastern Cordillera underwent exhu- partial melting caused fl uid and LILE depletion Collision with South America is the dominant mation and erosion (Mora et al., 2010) coupled in Canal Zone rocks. Strong LILE enrichments explanation for the Panama orocline (Silver et al., with synorogenic deposition on its eastern and with similar Yb concentrations at Bocas del Toro 1990) and can also explain the localized zones of extension within the Panama arc. Other infl u- ences for exhumation and arc change include a 10-50 Ma sedimentary record f 25–30 Ma westward increase in South American 10 Ma End of Onset o Atrato fault deposition Accreted deposition foreland plate motion (no-net-torque reference frame; Canal Zone (Panama-South 30 N. Panama America suture) Caribbean Subariel exposure Silver et al., 1998) and/or the 23 Ma fi ssion- deformed zone (extensional zone) crust and arcs 50 0 Llanos Basin ing of the Farallon plate (Lonsdale, 2005). The Panama block 40 Caribbean Guyana craton motion of South America is almost certainly the Plate Darien ranges Central Eastern Depth (km) vertical exaggeration = 1 (contractional zone) Cordillera Cordillera driver of broad Andean tectonic trends, and the 100 23 Ma exhumation event is observed throughout Figure 4. Modern cross section through Panama and South America. Location is shown in western South America (Mora, 2010). However, Figure 1A. Gray bars indicate sedimentary depositional history. Panama and the northern inboard of Panama, the Central/Western Cordil- Andes form a bivergent orogen, with the N. Panama deformed belt and Llanos Basin forming opposing thrust belts. Exhumation and eastward Llanos Basin propagation is synchronous leras are defl ected northward, and the width of with Panama arc geochemical change and is interpreted to result from accretion of Panama the Colombian orogenic belt is almost twice that arc crust to South America at 23–25 Ma. farther south in Ecuador, suggesting a causative

GEOLOGY, November 2011 1009 Downloaded from https://pubs.geoscienceworld.org/gsa/geology/article-pdf/39/11/1007/3538911/1007.pdf by Smithsonian Institution Lib user on 18 September 2018 relationship. Overall, our preferred interpretation Defant, M.J., Jackson, T.E., Drummond, M.S., de Boer, can Association of Petroleum Geologists Bulletin, is that South America surged westward at the J.Z., Bellon, H., Feigenson, M.D., Maury, R.C., and v. 94, p. 1543–1580, doi: 10.1306/01051009111. Stewart, R.H., 1992, The geochemistry of young O’Dea, A., Jackson, J.B.C., Fortunato, H., Smith, J.T., end of the Oligocene and collided with Panama volcanism throughout western Panama and south- D’Croz, L., Johnson, K.G., and Todd, J.A., 2007, arc crust. Due to arc crust unsubductability, the eastern Costa Rica: An overview: The Geological Environmental change preceded Caribbean ex- Panama block detached from the Caribbean plate Society of London Journal, v. 149, p. 569–579, doi: tinction by 2 million years: Proceedings of the Na- and was thrust over it, leading to the formation 10.1144/gsjgs.149.4.0569. tional Academy of Sciences of the United States Duque-Caro, H., 1990, stratigraphy, pale- of America, v. 104, no. 13, p. 5501–5506, doi: of the North Panama deformed belt. The North oceanography and paleobiogeography in north- 10.1073/pnas.0610947104. Panama deformed belt and Llanos Basin form west South America and the evolution of the Oldow, J.S., Bally, A.W., and Ave Lallemant, H.G., opposite verging fold-and-thrust belts occurring Panama Seaway: Palaeogeography, Palaeocli- 1990, Transpression, orogenic fl oat, and litho- matology, Palaeoecology, v. 77, p. 203–234, doi: spheric balance: Geology, v. 18, p. 991–994, doi: ~500 km on either side of the Panama–South 10.1016/0031-0182(90)90178-A. 10.1130/0091-7613(1990)018<0991:TOFALB America suture (the Atrato fault; Trenkamp et al., Ewart, A., Collerson, K.D., Regelous, J.I., Wendt, J.I., and >2.3.CO;2. 2002) (Fig. 4). Between the bivergent thrust belts, Niu, Y., 1998, Geochemical evolution within the Parra, M., Mora, A., Jaramillo, C., Strecker, M.R., Sobel, heterogeneous basement blocks exhibit near- Tonga-Kermadec-Lau arc-back-arc systems: The E.R., Quiroz, L., Rueda, M., and Torres, V., 2009, role of varying mantle wedge composition in space Orogenic wedge advance in the northern Andes: synchronous exhumation at 23–25 Ma, sugges- and time: Journal of Petrology, v. 39, p. 331–368, Evidence from the Oligo-Miocene sedimentary tive of a regional detachment at depth. Bivergent doi: 10.1093/petrology/39.3.331. record of the Medina Basin, Eastern Cordillera, orogenic fl oat (Oldow et al., 1990) could produce Gomez, E., Jordan, T.E., Allmendinger, R.W., and Colombia: Geological Society of America Bul- Cardozo, N., 2005, Development of the Colom- letin, v. 121, p. 780–800, doi: 10.1130/B26257.1. such widespread exhumation. Finally, we pro- bian foreland-basin system as a consequence of Pearce, J.A., and Peate, D.W., 1995, Tectonic implica- pose that the semirigid beam of Panama arc crust diachronous exhumation of the northern Andes: tions of the composition of volcanic arc mag- fractured and underwent rotation in response Geological Society of America Bulletin, v. 117, mas: Annual Review of Earth and Planetary Sci- p. 1272–1292, doi: 10.1130/B25456.1. ences, v. 23, p. 251–285, doi: 10.1146/annurev.ea to collision with South America, leading to the Goss, A.R., and Kay, S.M., 2006, Steep REE patterns .23.050195.001343. observed zones of extensional magmatism. and enriched Pb isotopes in southern Central Restrepo-Moreno, S.A., Foster, D.A., Stockli, D.F., American arc magmas: Evidence for forearc and Parra-Sanchez, L.N., 2009, Long-term ero- ACKNOWLEDGMENTS subduction erosion?: Geochemistry, Geophysics, sion and exhumation of the Altiplano Antioqueño, This contribution to the Panama Canal Project (PCP) Geosystems, v. 7, Q05016, 20 p. northern Andes (Colombia) from apatite (U-Th)/ was supported by National Science Foundation (NSF) Johnston, S.T., 2001, The Great Alaskan Terrane Wreck: He thermochronology: Earth and Planetary Sci- PIRE grant 0966884 (OISE, EAR, DRL). Funding also Reconciliation of paleomagnetic and geologic ence Letters, v. 278, p. 1–12. came from NSF grant DEB-0733725, the Smithson- data in the northern Cordillera: Earth and Plan- Rockwell, T.K., Bennett, R.A., Gath, E., and France- ian Institution, the Panama Canal Authority, Mr. Mark etary Science Letters, v. 193, p. 259–272, doi: schi, P., 2010, Unhinging an indenter: A new Tupper, the National Geographic, SENACYT, and 10.1016/S0012-821X(01)00516-7. tectonic model for the internal deformation of Ricardo Perez SA. 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