Geological Society of America Bulletin, published online on 13 January 2012 as doi:10.1130/B30528.1 Geological Society of America Bulletin Evidence for middle Eocene and younger land emergence in central Panama: Implications for Isthmus closure Camilo Montes, A. Cardona, R. McFadden, S.E. Morón, C.A. Silva, S. Restrepo-Moreno, D.A. Ramírez, N. Hoyos, J. Wilson, D. Farris, G.A. Bayona, C.A. Jaramillo, V. Valencia, J. Bryan and J.A. Flores Geological Society of America Bulletin published online 13 January 2012; doi: 10.1130/B30528.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. 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Notes Advance online articles have been peer reviewed and accepted for publication but have not yet appeared in the paper journal (edited, typeset versions may be posted when available prior to final publication). Advance online articles are citable and establish publication priority; they are indexed by GeoRef from initial publication. Citations to Advance online articles must include the digital object identifier (DOIs) and date of initial publication. Copyright © 2012 Geological Society of America Geological Society of America Bulletin, published online on 13 January 2012 as doi:10.1130/B30528.1 Evidence for middle Eocene and younger land emergence in central Panama: Implications for Isthmus closure Camilo Montes1,2,†, A. Cardona1,3, R. McFadden1, S.E. Morón1, C.A. Silva1, S. Restrepo-Moreno1,4, D.A. Ramírez1, N. Hoyos1, J. Wilson1, D. Farris5, G.A. Bayona6, C.A. Jaramillo1, V. Valencia7, J. Bryan8, and J.A. Flores9 1Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancón, Republic of Panamá 2Geociencias, Universidad de los Andes, Calle 1A # 18A-10, Edifi cio IP, Bogotá DC, Colombia 3Ingenieria de Petroleos, Universidad Nacional de Colombia, Carrera 80 No. 65-223, Medellín, Colombia 4Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, 24 Florida 32611, USA 5Department of Earth, Ocean and Atmospheric Science, Florida State University, 1017 26 Academic Way, Tallahassee, Florida 32306-4520, USA 6Corporación Geológica Ares, Calle 44A # 53-96, Bogotá, Colombia 7Department of Geosciences, University of Arizona, Gould-Simpson Building #77, 1040 E Street, Tucson, Arizona 85721, USA 8Geology/Oceanography, Northwest Florida State College, 100 College Boulevard, Niceville, Florida 32578, USA 9Facultad de Ciencias, Departamento de Geología, Universidad de Salamanca, 37008 Salamanca, Spain ABSTRACT low ~40 °C between 12 and 9 Ma. Cooling is et al., 1996; Kameo and Sato, 2000; Beu, 2001; linked to exhumation by an angular uncon- Newkirk and Martin, 2009). Some of the evi- The rise of the Isthmus of Panama, linked formity that separates the deformed basement dence for timing, however, may also be inter- to a number of climatic, paleoceanographic, complex below from mildly deformed, upper preted to show no causal relationship to isthmus and biological events, has been studied mostly Eocene to Oligocene terrestrial to shallow- closure (see review by Molnar, 2008), partially from indirect, often distal, geochemical and marine strata above. Exhumation and erosion because most studies rely on distal records of biotic evidence. We have upgraded existing of the basement complex are independently isotopic, chemical, or faunal changes, which are geologic mapping in central Panama with confi rmed by lower Miocene strata that have then correlated to a Pliocene isthmus closure. more than 2000 fi eld stations, over 40 petro- a detrital zircon signature that closely fol- The paleogeographic evolution of the isthmus graphic analyses, and more than 30 new lows the central Panama basement complex strait can additionally be constrained using: geochronological and thermo chrono logi- age distribution. These results greatly restrict (1) land-mammal isthmian faunas (Whitmore cal analy ses. This data set suggests that the the width and depth of the strait separating and Stewart, 1965; Kirby and MacFadden, isthmus was an uninterrupted chain above southern Central America from South Amer- 2005) that call for a peninsula connected to sea level from late Eocene until at least late ica, and challenge the widely accepted notion North America by the early Miocene; (2) geo- Miocene times. The basement complex of cen- that the Central American Seaway closed in chemistry of isthmian volcanic products that tral Panama is a folded-faulted, ~3-km-thick late Pliocene time, when the ice age began. suggest an early Miocene initiation of colli- arc sequence, intruded by granitoid bod- sion with South America (Farris et al., 2011); ies and onlapped by mildly deformed upper INTRODUCTION and (3) regional palinspastic reconstructions Eocene and Oligocene strata. Six U/Pb zir- (Wadge and Burke, 1983; Pindell and Ken- con ages in the granitoids—along with pub- The emergence of the Isthmus of Panama and nan, 2009) that allow only a narrow gap, or no lished geochronological data—reveal intense separation of Pacifi c-Caribbean waters has been gap, between the Central American volcanic late Paleocene to middle Eocene magmatism interpreted as the trigger for major climatic and arc and northwestern South America during (58–39 Ma), a temporary cessa tion of mag- biotic changes, including the onset of North- Neogene times, albeit with no information on matic activity between 38 and 27 Ma, and ern Hemisphere glaciations, the strengthening the degree of land emergence. Molecular biol- renewed magmatism between 25 and 15 Ma of the Gulf Stream current (e.g., Burton et al., ogy studies of saltwater-intolerant frogs (Weigt in a position ~75 km south of the former 1997; Haug et al., 2001; Lear et al., 2003), the et al., 2005), freshwater fi sh (Bermingham and magmatic axis. Thermochronological analy- Great American Interchange of land mammals Martin, 1998), and plants (Cody et al., 2010) al- ses in zircon (eight U-Th/He ages), and in (Marshall et al., 1982), and an increase in Carib- low early exchange times in the middle to late apatite crystals (four U-Th/He ages and nine bean molluscan diversity (Jackson et al., 1993). Miocene, well before the presumed formation fi ssion-track ages) obtained from a subset of Isotopic, geochemical, and faunal changes in of the land bridge. An understanding of the tim- 58–54 Ma granitoid bodies record a concor- sedimentary strata on both sides of the isthmus ing and extent of emergence in the central part dant Lutetian-age (47–42 Ma) cooling from have been used to indirectly narrow the tim- of the isthmus from its onshore geologic record ~200 °C to ~70 °C in ~5 m.y., and cooling be- ing of emergence and closure to between ca. 7 is therefore a fundamental component of global and 3.5 Ma (Keigwin, 1978, 1982; Duque- paleoceanographic and paleoclimatic modeling, †E-mail: [email protected] Caro, 1990; Coates et al., 1992, 2004; Collins molecular biology, and biogeography efforts. GSA Bulletin; Month/Month 2012; v. 1xx; no. X/X; p. 1–20; doi: 10.1130/B30528.1; 10 fi gures; 4 tables; Data Repository item 2012073. For permission to copy, contact [email protected] 1 © 2012 Geological Society of America Geological Society of America Bulletin, published online on 13 January 2012 as doi:10.1130/B30528.1 Montes et al. The purpose of this paper is to: (1) docu- detrital geochronology signature preserved in on opposite sides of the small Canal Basin, lo- ment the timing and style of deformation in lower Miocene strata. We interpret these data as cated at the apex of its curvature. Immediately the isthmus using geologic mapping; (2) bet- the record of middle Eocene and younger defor- east of the Canal Basin, and unlike the rest of ter document the timing of magmatic activity mation, exhumation, and erosion processes in the actively volcanic Central American geologic in the isthmus using U/Pb geochronology, and the Isthmus of Panama, which greatly restricted province, an ~300-km-long, curvilinear, basin- the role of these magmatic products in isthmus the width of the seaway separating the Pacifi c range pair with no active volcanism (Chucu- emergence using thermochronological data; and Caribbean waters since at least early Mio- naque–San Blas) traces the northwest-trending and (3) study the origin and provenance rec- cene times. segment of the curvature. ord of Eocene to Miocene terrestrial deposits The stratigraphy of the isthmus can be sepa- (e.g., Gatuncillo and Cucaracha Formations; GEOLOGIC SETTING rated in two main sequences: (1) an older base- Woodring, 1957). Here, we fi rst refi ne existing ment complex consisting of basalt, diabase, and mapping and lithological and geochronological The Isthmus of Panama is located east of the basaltic andesite rocks, interbedded with pelagic characterization of the volcaniclastic and plu- easternmost Central American modern volcano sediments (chert and siliceous limestone), in- tonic basement, and the overlying sedimentary El Valle Volcano (de Boer et al., 1991; Defant truded by plutonic bodies ranging from grano- and volcaniclastic cover in central Panama.
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