2006 SNSM Correlac Tecton Corteza Pre-Mesoz Colombia

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Journal of South American Earth Sciences 21 (2006) 337–354

Tectonic correlations of pre-Mesozoic crust from the northerntermination of the Colombian Andes, Caribbean region

Agustin Cardona Molina a,*,1, Umberto G. Cordani a,1, William D. MacDonald b

a University of Sao Paulo, Brazil. Rua do Lago 562, CEP 05508-080, Sao Paulo, SP, Brazilb State University of New York, Binghamton, NY 13902, USA

Received 1 October 2004; accepted 1 December 2005

Abstract

Reconnaissance zircon U/Pb SHRIMP, Ar–Ar, and Sm–Nd geochronology, petrological, and geochemical data were obtained fromselected localities of two pre-Mesozoic metamorphic belts from the northern termination of the Colombian Andes in the Caribbeanregion. The older Proterozoic belt, with protoliths formed in a rift- or backarc-related environment, was metamorphosed at 6–8 kband 760–810 �C during Late Mesoproterozoic times. This belt correlates with other high-grade metamorphic domains of the Andeanrealm that formed a Grenvillian-related collisional belt linked to the formation of Rodinia. The younger belt was formed over a conti-nental arc at <530–450 Ma in a Gondwanide position and metamorphosed at 5–8 kb and 500–550 �C, probably during the Late Paleo-zoic–Triassic, as part of the terranes that docked with northwestern South America during the formation of Pangea. A Mesozoic Ar–Artectonothermal evolution can be related to regional magmatic events, whereas Late Cretaceous–Paleocene structural trends are related tothe accretion of the allocthonous Caribbean subduction metamorphic belts. Lithotectonic correlations with other circum-Caribbean andsouthern North American pre-Jurassic domains show the existence of different terrane dispersal patterns that can be related to Pangea’sbreakup and Caribbean tectonics.� 2006 Published by Elsevier Ltd.

Keywords: Geochronology; Geochemistry; Metamorphism; Correlations; Caribbean; Rodinia; Pangea

Resumen

Analisis geocronologicos, petrologicos y geoquımicos fueron realizados en dos cinturones metamorficos Pre-Mesozoicos, localizadosen la terminacion de los Andes Colombianos. Los resultados indican la existencia de un cinturon Mesoproterozoico tardıo, con protol-itos formados en un ambiente de rift o backarc, y metamorfoseados en condiciones de 6–8 kb y 760–810 �C. Este cinturon es correlac-ionable con otros dominios metamorficos localizados en los Andes Colombianos, que en conjunto forman un cinturon Grenvilliano,relacionado con la formacion de Rodinia. El otro cinturon harıa parte de un arco magmatico continental formado en la margen deGondwana a <530–450 Ma, y serıa metamorfoseado en condiciones de 5–8 kb y 500–550 �C posiblemente durante el Permo-Triasico.Este evento estarıa relacionado con la acrecion de terrenos en la margen continental Suramericana, durante la formacion de Pangea.La evolucion tectono-termal registrada por la geocronologia Ar–Ar muestra un evento del Mesozoico Medio relacionado con actividadmagmatica regional, y otro Cretacico tardıo, asociado a la acrecion de los cinturones metamorficos de la placa del Caribe. Las correlac-iones geologicas con otros domınios Pre-Mesozoicos del Caribe y del sur de Norte America, muestran la existencia de procesos de dis-persion de terrenos, relacionados con la separacion de Pangea y la evolucion Meso-Cenozoica del Caribe.� 2006 Published by Elsevier Ltd.

0895-9811/$ - see front matter � 2006 Published by Elsevier Ltd.

doi:10.1016/j.jsames.2006.07.009

* Corresponding author.E-mail address: [email protected] (A.C. Molina).

1 Present address: Smithsonian Tropical Research Institute, Balboa,Ancon, Republic of Panama.

1. Introduction

The pre-Mesozoic tectonic evolution of the northernAndes is recorded in various tectonostratigraphic terranes

mailto:[email protected]

Fig. 1. Pre-Mesozoic terrane and crust exposures from the NorthernAndes (soft gray). Northernmost Andean massifs are also included: (1)Sierra Nevada de Santa Marta, (2) Guajira Serranias. L-A, Loja-Amotape; T, Tahamı; CH, Chibcha; M-C, Merida-Caparo; C-T, Cauca-gua-Tinaco. Amazon Craton is hatched.

338 A.C. Molina et al. / Journal of South American Earth Sciences 21 (2006) 337–354

(Fig. 1) that were accreted to the continent in Proterozoicto Mesozoic times (Restrepo and Toussaint, 1988; Bellizziaand Pimentel, 1994; Litherland et al., 1994). These terranesbear some of the effects of tectonic interactions recorded ineastern North America and western South America fromLate Proterozoic to Late Paleozoic times during the devel-opment of the Rodinia, Gondwana, and Pangea supercon-tinents (Rowley and Pindell, 1989; Restrepo-Pace et al.,1997; Keppie and Ramos, 1999). The northern terminationof the Andes was affected by complex Meso-Cenozoiccrustal redistributions of the pre-Mesozoic crust, associat-ed with the development of the Caribbean plate since thebreakup of Pangea.

The present study provides new petrological, geochro-nological, and geochemical data from representative out-crops of the pre-Mesozoic basement domains of isolatedmassifs in the northern termination of the ColombianAndes in the Caribbean region (Fig. 1). These newresults, combined with other available data, permit therecognition of the tectonic development of two metamor-phic belts of Proterozoic and Paleozoic ages and corre-lates them in a terrane perspective. Insights intopatterns of Meso-Cenozoic terrane dispersion emergefrom the distribution of these and correlated crustaldomains in the Caribbean realm.

The next sections provide more details regarding theregional tectonic framework and geology of the two mainmetamorphic belts that characterized the composite pre-Mesozoic domain from the Sierra Nevada de Santa Martaand Guajira massifs, incorporating new petrological, geo-chemical, and geochronological data from selected locali-ties of the different units.

2. Geological setting

The northern termination of the Andean chain inColombia is characterized by several isolated massifs(Fig. 1). This configuration is related to the multiple plateboundaries and associated Meso-Cenozoic escape andtranspressive tectonics that accompanied Andean terraneaccretionary events and the NE migration of the CaribbeanPlate in an oblique regime (Pindell, 1994; Colletta et al.,1997; Taboada et al., 2000).

The massifs (Sierra Nevada de Santa Marta and severalsmaller serranias of the Guajira Peninsula, Figs. 2 and 3)are composed of three correlatable lithotectonic belts(Alvarez, 1971; MacDonald et al., 1971; Tschanz et al.,1974), which from NW to SE include (1) Cretaceous low-grade volcanosedimentary metamorphic rocks, with inter-calated mafic and ultramafic plutonic rocks, related to asubduction front formed as part of the allocthonous Carib-bean plate arc domains (MacDonald et al., 1971; Pindell,1994; Ave Lallement, 1997); (2) a composite pre-Mesozoicdomain, with Proterozoic high-grade rocks and a youngeramphibolite facies belt, considered as lateral extensions ofthe two main continental crustal terranes that constitutethe basement of the Eastern and Central cordillerasof the Colombian Andes (Alvarez, 1971; Toussaint,1993); and (3) an undeformed to weakly deformed belt ofMesozoic sedimentary rocks, with the same depositionalpatterns as the autocthonous South American margin(MacDonald, 1965).

3. Analytical techniques

3.1. Geochemistry

Fourteen whole-rock samples were analyzed for majorelements, trace elements, and rare earth elements (REE)by XRF and ICP-OES in the chemical laboratory of theGeoscience Institute of the University of Sao Paulo. Theobtained data appear in Table 1.

Sample preparation included pressed powder pellets andfused glass discs for major and trace element determinationand dissolution and cationic exchange column separationsfor REE. X-ray flourescence analyses were done in a wave-length-dispersive Philips PW 2400 XRF spectrometer, andICP-OES occurred within the sequential spectrometerARL 3410 equipped with an ultrasonic CETAC Inc. nebu-lizer, model U-5000AT, and follows the procedures pre-sented by Mori et al. (1999) and Navarro et al. (2002).

Amphibole and plagioclase mineral pairs from threesamples were analyzed with the electronic microprobeJEOL JXA-8600 from the same institute; results appearin Table 2. Additional amphibole grain separates fromthe same samples also were analyzed in the same micro-probe and are available on request. The sample currentwas 20 nA, and 15 kV was the accelerating voltage, witha beam diameter of 5 nm. Analyses were done on core,border, and intermediate areas of the grains. Amphibole

Fig. 2. Geological map of the Sierra Nevada de Santa Marta modified after Tschanz et al. (1974) including sampled areas. 1, Dibulla gneiss; 2, anorthosite(Los Mangos granulite); 3, Sevilla Complex.

Fig. 3. Geological map of the Guajira Peninsula, modified after Alvarez (1971), including sampled areas. Samples for geochronology: 1, A99; 2, Jojon-1;3, Siap 1; 4, A83, A91; 5, A95.

A.C. Molina et al. / Journal of South American Earth Sciences 21 (2006) 337–354 339

compositions were calculated following IMAA (Leakeet al., 1997) with the AMPH program (Yavafuz, 1999)and the free Internet amphibole calculation spreadsheetfor Excel (http://www.abdn.ac.uk/geology/profiles/analysis/software/amphibole-names.xls). Metamorphic conditionswere defined by comparing the results from different

empirical and experimental amphibole and amphibole-pla-gioglase thermobarometers, after Fershater (1990), Ham-marston and Zen (1986), Hollister et al. (1987), Johnsonand Rutherford (1989), Schmidt (1992), and Holland andBlundy (1994) for the high-grade rocks. The proceduresof Plyusnina (1982) and Fershater (1990) were taken into

http://www.abdn.ac.uk/geology/profiles/analysis/software/amphibole-names.xls

http://www.abdn.ac.uk/geology/profiles/analysis/software/amphibole-names.xls

Table 1Major and trace element data from the studied samples

Sample A46 A49 A54 A58 A60 A53 A56 A59 Jojon-1 A81 A82 A83 A88 A91 A97Unit Dibulla

gneissDibullagneiss

Dibullagneiss

Dibullagneiss

Dibullagneiss

Dibullagneiss

Dibullagneiss

Dibullagneiss

Jojoncitogneiss

MacuiraFormation

MacuiraFormation

MacuiraFormation

MacuiraFormation

MacuiraFormation

MacuiraFormation

Rock Felsic Felsic Felsic Felsic Felsic Mafic Mafic Mafic Gneiss Schist Schist Schist Schist Schist Schist

SiO2 71.58 71.65 74.68 75.66 71.87 46.82 46.72 46.03 72.45 59.07 51.84 57.68 50.83 51.12 48.85Al2O3 12.25 12.68 12.24 11.59 12.25 14.73 15.27 15.29 12.58 15.88 17.05 17.5 15.93 17.9 15.57MnO 0.043 0.056 0.026 0.031 0.055 0.216 0.194 0.175 0.033 0.112 0.144 0.101 0.165 0.128 0.209MgO 0.28 12.68 0.21 0.35 0.39 6.89 6.92 7.45 0.1 3.38 5.46 2.98 6.84 4.7 6.75CaO 1.24 1.15 0.9 0.91 1.12 7.32 7.29 9.03 0.84 6.58 7.62 6.46 10.84 7.67 10.19Na2O 2.33 2.42 2.78 2.71 2.31 3.12 2.88 2.95 2.52 4.21 4.54 4.92 3.4 4.95 2.97K2O 5.62 5.74 5.12 4.7 5.65 1.86 2.49 2.31 5.9 0.82 1.03 0.81 0.86 0.72 0.41TiO2 0.476 0.48 0.251 0.277 0.512 1.228 1.23 1.532 0.333 0.709 0.866 0.673 0.32 1.384 0.694P2O5 0.086 0.093 0.046 0.05 0.102 0.251 0.228 0.287 0.038 0.153 0.427 0.246 0.268 0.698 0.01Fe2O3 3.48 3.63 2.15 1.75 3.86 13.82 12.63 12.56 3.47 7.09 8.59 6.49 8.07 8.24 12.83LOI 0.4 0.5 0.39 0.45 0.42 2.15 3.5 1.1 0.3 1.04 1.5 1.01 1.38 1.53 0.61Total 97.79 98.79 98.79 98.48 98.54 99.22 99.35 98.71 98.56 99.04 99.07 98.87 98.9 99.04 99.09

Ba 506 620 634 580 593 494 448 348 1013 1012 979 583 879 582 143Ce 117 163 112 75 151 70 136 86 116 53 33 36 105 63 17Cl <237 386 <237 <237 <237 1304 584 860 253 517 472 <237 <237 <237 <237Co 38 51 55 48 39 45 45 59 77 61 49 26 39 32 47Cr 17 17 <4 18 7 244 298 332 11 119 118 62 131 163 61Cu 3 3 4 7 2 15 17 51 3 7 7 4 5 38 8F 328 1036 <214 469 768 5272 6053 8380 <214 437 273 <214 <214 350 300Ga 21 22 19 16 21 22 19 19 21 17 17 19 15 19 17La 62 85 60 38 69 34 50 32 63 21 21 <19 60 32 <19Nb 17 27 7 10 22 10 11 10 10 4 4 3 1 8 2Nd 48 88 58 19 83 46 46 46 46 26 21 8 57 28 20Ni 3 4 7 7 4 80 96 122 3 53 56 27 61 77 39Pb 18 45 40 37 31 21 13 27 30 24 15 16 13 14 16Rb 237 301 153 118 266 80 122 96 172 7 6 5 6 5 2S <30 <30 <30 <30 <30 163 49 122 <30 <30 <30 <30 <30 <30 <30Sc 5 7 3 <3 6 30 27 30 4 20 18 17 32 21 44Sr 73 80 78 91 84 155 128 141 105 1016 999 775 866 1076 250Th <2 51 7 <2 28 3 <2 <2 8 <2 <2 <2 <2 <2 <2U 2 3 2 2 2 2 2 2 2 <2 <2 <2 <2 <2 3V 16 17 <6 6 13 201 156 198 <6 98 92 114 130 144 285Y 80 111 33 9 97 50 71 66 41 24 22 14 18 17 20Zn 59 74 40 28 74 238 248 166 66 104 106 74 94 85 133Zr 466 507 275 281 490 136 141 154 448 101 98 96 44 107 39Hf 14 16 8.7 5.98 16 2.28 2.8 2.7 3 3.1 N.D. 2.9 1.8 3.1 1.2La 65.5 86.4 76 65.5 79.3 30.4 56.2 35.1 63.3 9.78 N.D. 17.5 65.8 34.6 5.6Ce 126 178 143 126 170 64.4 134 82.3 123 21.6 N.D. 33.3 116 67.9 13.1Nd 59.6 85.6 56.7 59.6 78.8 31.6 58.9 45 56 13.5 N.D. 16.8 46.7 33.7 9.21Sm 13.7 19.4 9.97 13.7 17.3 7.02 11.7 10.3 11.2 3.19 N.D. 3.22 6.15 5.87 2.45Eu 1.71 2.04 1.52 1.71 1.79 1.52 1.77 2.04 1.52 1.15 N.D. 1.3 1.65 1.9 0.87Gd 14.3 20.3 8.69 14.3 17.6 8.04 11.2 11.3 10.5 3.32 N.D. 3.05 4.69 5.02 3.2Dy 15.7 22.6 7.59 15.7 19.7 9.23 12.8 12.5 9.36 3.83 N.D. 2.83 3.64 3.66 3.75Er 9.47 12.9 4.03 9.47 11.4 5.44 7.56 7.24 4.62 1.9 N.D. 1.9 1.84 1.78 2.32Yb 7.84 10.5 3.12 7.84 9.89 4.99 7.64 6.62 3.44 1.63 N.D. 1.63 1.48 1.41 2.02Lu 1.08 1.43 0.47 1.08 1.37 0.75 1.11 0.97 0.49 0.25 N.D. 0.25 0.22 0.21 0.31

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Table 2Representative electronic microprobe chemical data and amphibole-plagioclase chemical calculation

Amphibole A59-1-C A59-1-R A59-2-C A-59-2-R A59-3-C A59-3-R A59-4-C A59-4-R A59-5-C A59-5-R A59-6-R A69-6-R A59-7-C A59-7-R A59-8-C A59-8-R

SiO2 42.45 42.37 42.19 41.59 41.50 41.55 42.45 41.41 41.05 41.63 41.17 41.51 41.27 41.37 41.50 41.44TiO2 1.62 1.40 1.69 1.63 1.73 1.97 1.76 1.66 1.81 1.95 1.65 1.50 2.13 1.43 1.75 2.00Al2O3 11.29 11.26 11.68 11.19 11.74 11.75 11.77 12.08 11.94 12.00 11.86 12.06 12.08 12.41 11.86 11.50FeO 16.45 16.42 16.20 16.06 15.70 15.70 15.26 15.12 15.76 15.52 15.92 15.70 15.79 15.57 16.36 15.51MnO 0.27 0.28 0.22 0.29 0.21 0.247 0.24 0.28 0.18 0.26 0.23 0.22 0.27 0.25 0.26 0.31MgO 11.17 11.06 11.04 11.37 11.23 11.43 11.38 10.96 10.99 11.06 11.15 11.06 10.82 10.97 11.12 11.19CaO 10.79 11.02 10.77 11.03 10.97 11.08 11.28 11.20 11.14 10.95 10.82 11.26 11.03 11.19 10.80 10.86Na2O 1.90 1.81 1.85 2.02 1.94 2.07 1.85 1.96 2.05 2.07 2.07 1.97 1.92 1.99 1.99 1.95K2O 1.57 1.56 1.54 1.51 1.63 1.59 1.58 1.69 1.66 1.58 1.66 1.62 1.75 1.62 1.66 1.57F 1.64 1.25 1.09 1.47 1.36 1.60 0.93 1.15 1.67 1.64 1.33 1.11 1.34 1.55 1.54 1.51Cl 0.15 0.17 1.09 0.15 0.18 0.193 0.20 0.23 0.18 0.21 0.16 0.19 0.18 0.19 0.20 0.19Total 99.30 98.65 98.44 98.29 98.19 98.73 98.51 97.73 98.43 98.59 98.02 98.20 98.58 98.54 99.05 98.03

Si 6.55 6.48 6.55 6.39 6.52 6.44 6.50 6.47 6.49 6.50 6.50 6.37 6.33 6.47 6.46 6.47Al 2.02 2.00 2.02 2.02 2.06 2.04 2.01 2.23 2.05 2.05 2.05 2.20 2.18 2.23 2.04 2.04Ti 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.12 0.23 0.12 0.12 0.24Fe2+ 1.94 1.74 1.94 1.92 1.84 1.94 1.80 1.88 1.79 1.99 1.99 1.61 1.94 1.88 1.81 1.93Fe3+ 0.15 0.32 0.15 0.17 0.16 0.03 0.15 0.10 0.19 0.00 0.00 0.34 0.00 0.10 0.28 0.04Mg 2.56 2.53 2.56 2.55 2.61 2.58 2.54 2.35 2.36 2.60 2.60 2.55 2.30 2.35 2.58 2.59Ca 1.67 1.82 1.67 1.84 1.70 1.85 1.83 1.86 1.86 1.70 1.70 1.83 1.82 1.86 1.69 1.69Na 0.30 0.30 0.30 0.60 0.31 0.61 0.30 0.31 0.61 0.61 0.61 0.30 0.30 0.31 0.31 0.31K 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20F 0.49 0.49 0.49 0.49 0.50 0.50 0.00 0.50 0.50 0.50 0.50 0.49 0.49 0.50 0.50 0.50Total 16.00 16.00 16.00 16.30 16.02 16.31 15.45 16.02 16.17 16.27 16.27 16.01 15.79 16.02 15.99 16.01

Plagioclase A59-1-C A59-1-R A59-2-C A-59-2-R A59-3-C A59-3-R A59-4-C A59-4-R A59-5-C A59-5-R A59-6-C A69-6-R A59-7-C A59-7-R A59-8-C A59-8-R

SiO2 60.642 61.425 59.870 59.584 59.270 60.179 58.872 59.686 59.112 59.563 59.092 59.874 60.391 60.496 59.604 60.154Al2O3 24.281 24.390 25.153 24.695 25.374 25.216 25.100 25.055 25.275 25.089 25.106 25.083 24.797 24.743 24.828 24.281CaO 5.885 5.805 7.024 6.515 7.112 6.691 6.758 6.694 6.921 6.994 7.075 6.661 6.175 6.239 6.930 6.233Na2O 7.786 8.180 7.425 7.934 7.341 7.750 7.444 7.682 7.583 7.489 7.380 7.573 7.924 7.845 7.526 7.779K2O 0.429 0.086 0.194 0.194 0.264 0.071 0.263 0.185 0.073 0.203 0.235 0.105 0.094 0.230 0.277 0.158Total 99.023 99.886 99.666 98.922 99.361 99.907 98.437 99.302 98.964 99.338 98.888 99.296 99.381 99.553 99.165 98.605

Si 10.88 10.91 10.74 10.69 10.63 10.72 10.70 10.71 10.64 10.66 10.56 10.73 10.80 10.81 10.71 10.83Al 5.13 5.11 5.24 5.29 5.36 5.29 5.29 5.30 5.36 5.34 5.34 5.30 5.23 5.21 5.25 5.15Ca 1.13 1.11 1.26 1.34 1.37 1.28 1.30 1.29 1.34 1.34 1.37 1.28 1.18 1.19 1.33 1.20Na 2.71 2.82 2.77 2.57 2.55 2.68 2.58 2.67 2.65 2.60 2.58 2.63 2.75 2.72 2.62 2.72K 0.10 0.02 0.05 0.07 0.06 0.02 0.06 0.04 0.02 0.05 0.05 0.02 0.02 0.05 0.06 0.04Total 19.95 19.96 20.05 19.96 19.97 19.98 19.92 20.00 20.01 19.98 19.89 19.95 19.97 19.98 19.98 19.93

Ab 69 71 68 64 64 67 66 67 66 65 64 67 70 69 65 69An 29 28 31 34 34 32 33 32 33 34 34 33 30 30 33 30Or 2 0 1 2 2 0 2 1 0 1 1 1 1 1 2 1

Amphibole A28-1-C A28-1-R A28-2-C A28-2-R A28-3-C A28-3-R A28-3-I A28-3-I A28-3-I A28-4-C A28-B-4 A28-5-C A28-5-R A28-6-C A28-6-R

SiO2 42.228 42.300 44.253 43.273 43.886 51.682 44.273 42.175 44.008 44.087 44.148 44.708 44.599 42.033 42.944TiO2 0.698 0.852 0.510 0.592 0.602 0.040 0.356 0.671 0.605 0.515 0.679 0.646 0.589 0.602 0.731Al2O3 13.787 12.621 10.637 10.877 11.304 3.304 10.949 12.791 10.201 10.574 10.742 10.196 10.190 13.944 13.155

(continued on next page)

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Table 2 (continued)

Amphibole A28-1-C A28-1-R A28-2-C A28-2-R A28-3-C A28-3-R A28-3-I A28-3-I A28-3-I A28-4-C A28-B-4 A28-5-C A28-5-R A28-6-C A28-6-R

FeO 15.884 16.465 15.595 15.380 16.559 14.139 15.706 16.462 15.888 15.913 15.716 15.651 15.628 15.703 15.661MnO 0.304 0.247 0.291 0.277 0.332 0.343 0.291 0.272 0.346 0.344 0.323 0.281 0.335 0.289 0.350MgO 9.823 10.096 11.082 10.733 9.991 13.982 10.916 9.989 10.831 10.924 10.955 11.460 11.299 9.901 10.346CaO 11.443 11.697 11.491 11.101 11.429 12.148 11.413 11.409 11.232 11.562 11.379 11.596 11.469 11.329 11.431Na2O 1.322 1.183 1.063 1.003 0.968 0.202 1.185 1.170 0.886 0.989 1.126 1.012 1.040 1.237 1.215K2O 1.034 0.904 0.643 0.733 0.801 0.101 0.800 0.880 0.662 0.636 0.700 0.646 0.600 1.020 0.885F 0.122 0.154 0.052 0.068 0.000 0.000 0.009 0.006 0.129 0.000 0.024 0.118 0.102 0.000 0.000Cl 0.000 0.023 0.001 0.050 0.000 0.000 0.013 0.002 0.015 0.032 0.021 0.015 0.007 0.015 0.011Total 96.646 96.542 95.622 94.087 95.872 95.941 95910 95.827 94.803 95.577 95.815 96.33 95.857 96.075 96.73

Si 6.297 6.332 6.614 6.569 6.582 7.586 6.608 6.328 6.636 6.601 6.592 6.633 6.645 6.277 6.358Al 0.078 0.096 0.057 0.068 0.068 0.004 0.040 0.076 0.069 0.058 0.076 0.072 0.066 0.068 0.081Ti 2.423 2.227 1.874 1.946 1.998 0.572 1.926 2.262 1.813 1.866 1.890 1.783 1.789 2.454 2.295Fe2+ 0.593 0.650 0.673 0.732 0.596 0.350 0.633 0.754 0.762 0.697 0.674 0.707 0.712 0.680 0.685Fe3+ 1.388 1.411 1.276 1.220 1.481 1.385 1.327 1.312 1.241 1.295 1.288 1.235 1.235 1.281 1.253Mg 0.038 0.031 0.037 0.036 0.042 0.043 0.037 0.035 0.044 0.044 0.041 0.035 0.042 0.037 0.044Ca 2.184 2.253 2.469 2.429 2.234 3.060 2.429 2.234 2.435 2.439 2.439 2.535 2.510 2.204 2.283Na 1.828 1.876 1.840 1.805 1.836 1.910 1.825 1.834 1.815 1.855 1.820 1.843 1.831 1.812 1.813K 0.382 0.343 0.308 0.295 0.281 0.057 0.343 0.340 0.259 0.287 0.326 0.291 0.300 0.358 0.349Total 15.210 15.219 15.148 15.101 15.118 14.968 15.168 15.174 15.074 15.142 15.146 15.134 15.131 15.171 15.162

Plagioclase A28-1-C A28-1-R A28-2-C A28-2-R A28-3-C A28-3-R A28-4-C A28-4-R A28-5-C A28-5-R A28-6-C A28-6-R A28-7-C A28-7-R A28-8-C

SiO2 61.834 57.936 60.961 59.191 60.086 61.543 62.107 59.66 58.772 60.384 61.452 60.042 60.872 60.28 61.236Al2O3 24.187 24.865 23.956 24.799 24.696 23.656 23.47 24.664 24.948 24.907 24.035 24.917 24.323 24.285 23.679CaO 5.44 6.845 5.567 6.236 6.233 4.955 4.802 6.344 6.772 6.546 5.45 5.889 5.464 5.25 5.274Na2O 8.281 7.277 8.325 7.584 8.013 8.376 8.663 7.558 7.475 7.697 8.332 7.768 8.297 7.936 8.42K2O 0.11 0.101 0.089 0.22 0.092 0.287 0.095 0.353 0.096 0.112 0.135 0.389 0.142 0.419 0.106Total 99.949 97.738 98.993 98.366 99.225 99.056 99.16 98.784 98.212 99.815 99.609 99.267 99.141 98.369 98.832

Si 10.969 10.620 10.935 10.729 10.778 11.021 11.083 10.761 10.668 10.766 10.953 10.770 10.897 10.887 10.993Al 5.056 5.372 5.064 5.297 5.220 4.992 4.936 5.243 5.337 5.233 5.049 5.267 5.131 5.169 5.010Ca 1.034 1.344 1.070 1.211 1.198 0.951 0.918 1.226 1.317 1.250 1.041 1.132 1.048 1.016 1.014Na 2.848 2.586 2.895 2.665 2.786 2.908 2.997 2.643 2.631 2.660 2.879 2.701 2.880 2.779 2.930K 0.025 0.024 0.020 0.051 0.021 0.066 0.022 0.081 0.022 0.025 0.031 0.089 0.032 0.097 0.024Total 19.940 19.999 19.991 19.981 20.016 19.970 19.959 19.980 19.990 19.960 19.977 19.992 19.993 19.966 19.979

Ab 26 34 27 31 30 24 23 31 33 32 26 29 26 26 26Na 73 65 73 68 70 74 76 67 66 68 73 69 73 71 74Or 1 1 1 1 1 2 1 2 1 1 1 2 1 2 1

Amphibole A91-1-C A91-1-R A91-2-C A91-3-C A91-3-R A91-5-C A91-5-R A91-6-C A91-6-R A91-7-R

SiO2 41.090 40.644 49.880 42.128 42.717 40.231 42.830 40.525 39.887 52.580TiO2 0.674 0.565 0.161 0.463 0.542 0.596 0.438 0.399 0.616 0.039Al2O3 14.907 14.213 4.939 13.677 11.869 14.800 11.771 14.363 14.149 2.744FeO 16.400 17.820 12.877 16.040 16.594 17.237 16.564 17.428 17.802 11.354

342A

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MnO 0.307 0.311 0.344 0.314 0.260 0.290 0.327 0.256 0.238 0.304MgO 8.952 8.795 14.555 9.887 10.206 8.981 10.211 8.952 8.729 16.227CaO 11.167 11.112 11.703 11.182 11.243 11.133 11.217 11.182 11.011 11.917Na2O 1.695 1.680 0.802 1.506 1.439 1.568 1.484 1.578 1.593 0.458K2O 0.634 0.681 1.121 0.438 0.329 0.630 0.286 0.714 0.648 0.061F 0.000 0.000 0.000 0.000 0.081 0.125 0.000 0.115 0.000 0.016Cl 0.009 0.014 0.000 0.028 0.014 0.000 0.003 0.000 0.004 0.002Total 95.835 95.835 95.381 95.662 95.296 95.591 95.130 95.512 94.677 95.701

Si 6.177 6.137 7.320 6.294 6.426 6.069 6.446 6.134 6.091 7.613Al 0.076 0.064 0.018 0.052 0.061 0.068 0.050 0.045 0.071 0.004Ti 2.641 2.529 0.854 2.408 2.104 2.631 2.088 2.562 2.546 0.468Fe2+ 0.642 0.850 0.351 0.800 0.816 0.916 0.817 0.852 0.928 0.460Fe3+ 1.420 1.400 1.229 1.203 1.271 1.259 1.268 1.354 1.345 0.914Mg 2.006 1.980 3.185 2.202 2.289 2.020 2.291 2.020 1.987 3.503Ca 1.798 1.798 1.840 1.790 1.812 1.799 1.809 1.813 1.801 1.849Na 0.494 0.492 0.228 0.436 0.420 0.459 0.433 0.463 0.472 0.129K 0.122 0.131 0.210 0.083 0.063 0.121 0.055 0.138 0.126 0.011Total 15.375 15.381 15.235 15.270 15.261 15.342 15.255 15.381 15.369 14.951

Plagioclase A91-1-C A91-1-R A91-2-C A91-3-C A91-3-R A91-5-C A91-5-R A-91-6-C A-91-6-R A-91-7-R

SiO2 70.554 61.836 60.996 61.654 61.034 60.928 61.148 62.628 61.337 61.103Al2O3 17.757 23.043 23.884 23.048 23.790 24.100 23.144 22.262 23.806 23.406CaO 3.719 4.569 5.343 4.676 5.383 5.483 4.681 3.540 5.174 5.329Na2O 6.793 8.765 8.152 8.436 8.248 8.228 8.585 9.222 8.315 8.218K2O 0.043 0.069 0.066 0.208 0.113 0.097 0.048 0.265 0.102 0.094Total 98.902 98.438 98.522 98.210 98.706 98.947 97.764 98.167 98.937 98.319

Si 12.331 11.126 10.973 11.123 10.975 10.931 11.082 11.290 11.001 11.027Al 3.657 4.886 5.064 4.900 5.041 5.095 4.943 4.730 5.032 4.978Ca 0.696 0.881 1.030 0.904 1.037 1.054 0.909 0.684 0.994 1.030Na 2.302 3.058 2.843 2.951 2.875 2.862 3.016 3.223 2.891 2.875K 0.010 0.016 0.015 0.048 0.026 0.022 0.011 0.061 0.023 0.022Total 18.996 19.967 19.924 19.926 19.955 19.964 19.961 19.987 19.941 19.932

Ab 23 22 26 23 26 27 23 17 25 26An 77 77 73 76 73 73 77 81 74 73Or 0 0 0 1 1 1 0 2 1 1

Labels includes sample number: c, core; r, rim; i, intermediate. A49 (Dibulla gneiss), A28 (Sevilla Complex), A91 (Macuira Formation).

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Table 4Sm-Nd analytical data from the studied samples

Sample#

Rock type Unit 147Sm/144Nd

143Nd/144Nd

TDm €(0)

A95 Muscoviteschist

MacuiraFormation

0.16161 0.512111 1.45 10.28

Siap-1 Granodiorite Siapanagranodiorite

0.1327 0.512260 1.46 7.37


consideration in analyzing the lower-grade greenschist-am-phibolite rocks. Holland and Blundy’s (1994) thermometerwas not employed for the greenschist and amphibolitefacies rocks, because it overestimates temperature values(John et al., 1999). The results represent probable intervalsof P–T conditions, considering the differences in their inter-nal errors and calibrations.

3.2. Geochronology: radiometric methods

U–Pb determinations from 25 single zircon crystals fromtwo samples were carried out with the sensitive high reso-lution ion microprobe (SHRIMP II) of the Chinese Acad-emy of Geological Sciences. Zircons were hand picked andmounted on epoxy resin for the isotopic measurements.Because of effects, such as the differential yield of metaland oxide species between elements during sputtering, inter-element ratios are calibrated with a standard when theratios are known by isotope dilution thermal ionizationmass spectrometry (IDTIMS). Details of analytical proce-dures, including calibration methods, are fully presentedby Stern (1998). 206Pb/238U ratios have an error component(typically 1.5–2.0%) from calibration of the measurementsusing the standard zircons. U abundance and U/Pb ratioswere calibrated against 238 ppm U, 572 Ma fragments ofthe single crystal SL13 zircon standard. All errors also takeinto account nonlinear fluctuations in ion counting ratesbeyond that expected from counting statistics (e.g., Stern,

Table 3Zircon U/Pb SHRIMP analytical data from analyzed samples

Analysis % 206Pbc ppmU

ppmTh

232Th/238U

ppm206Pb*

Measured238/206

% err M20

A-19. Paragneiss

1 0.81 160 42 0.27 24.8 5.550 2.7 0.02 0.02 807 5 0.01 116 5.990 1.9 0.03 0.27 260 65 0.26 43.4 5.150 2.0 0.04 1.05 113 70 0.63 23.1 4.212 2.1 0.05 1.47 269 87 0.34 20.1 11.520 2.0 0.06 0.97 135 97 0.74 25.3 4.582 2.1 0.07 0.62 150 89 0.61 22.6 5.72 0 2.1 0.08 1.61 165 43 0.27 14.4 9.85 0 2.1 0.09 0.49 212 92 0.45 30.1 6.070 2.0 0.0

10 0.53 323 28 0.09 33.6 8.270 2.3 0.011 0.57 140 50 0.37 24.2 4.960 2.1 0.012 2.03 74 56 0.79 12.7 4.980 2.2 0.013 0.06 29 10 0.35 3.96 6.200 2.7 0.014 0.36 184 80 0.45 33.4 4.744 2.0 0.015 0.53 439 101 0.24 56.7 6.660 1.9 0.0

Siap-1. Granodiorite

1 1 408 79 0.2 60 6.890 2.4 0.02 0 438 42 0.1 85 4.416 2.0 0.03 1 597 208 0.4 14 36.320 2.1 0.04 2 389 173 0.5 9 38.590 2.2 0.05 0 2330 764 0.3 56 35.720 2.0 0.07 0 326 98 0.3 41 6.870 2.0 0.08 1 759 146 0.2 17 38.210 2.1 0.09 0 664 206 0.3 14 39.840 2.2 0.0

10 0 139 87 0.7 9 13.650 2.2 0.0

Ratios and 206Pb/238Pb are corrected after measured Pb204.

1998). Pooled dates calculated herein are weighted mean206Pb/238U dates (inverse-variance weighted at two-sigmalevel and rounded to the nearest million year), followingcorrection for common Pb based on measured 204Pb. Theanalytical results appear in conventional diagrams inFig. 8a and b and Table 3.

Two Sm–Nd whole-rock analyses at the Center of Geo-chronological Research of the University of Sao Paulo(CPGeo-USP) follow the procedures described by Satoet al. (1995). Isotopic ratios of 143Nd/144Nd were obtainedin a multicollector mass spectrometer with analytical preci-sion of 0.014% (2r). Experimental error for the147Sm/144Nd ratios is on the order of 0.5%. La Jolla andBCR-1 standards yield, respectively, 143Nd/144Nd =0.511849 ± 0.000025 (1r) and 0.512662 ± 0.000027 (1r)during the analysis period. Single-stage Sm–Nd TDM modelages were calculated following De Paolo (1988) and appearin Table 4.

easured7/206

%err

207r/235 %err

206r/238

%err

errcorr

206Pb/238UAge

±

750 1.5 1.682 4.2 0.1787 2.7 0.63 1060 267350 1.2 1.689 2.3 0.1670 1.9 0.85 995 18795 1.9 2.060 3.1 0.1936 2.0 0.66 1141 21869 1.5 2.53 4.5 0.2349 2.1 0.47 1360 26616 1.9 0.589 6.6 0.0855 2.1 0.31 529 10840 1.7 2.261 4.1 0.2161 2.1 0.51 1261 24774 1.5 1.730 3.8 0.1736 2.1 0.55 1032 20670 2.7 0.744 7.7 0.0999 2.2 0.28 614 13713 1.4 1.521 3.4 0.1640 2.0 0.59 979 18713 1.3 1.109 3.3 0.1203 2.3 0.70 732 16810 1.4 2.105 3.0 0.2004 2.1 0.69 1177 22914 3.6 2.02 8.6 0.1969 2.3 0.27 1158 25844 3.4 1.862 4.4 0.1611 2.7 0.61 963 248343 1.2 2.327 2.9 0.2100 2.0 0.70 1229 237137 0.99 1.379 2.7 0.1494 1.9 0.73 898 16

840 2.4 1. 4693 4.0 0.1434 2.4 0.59 864 19880 1.3 2. 7144 2.4 0.2262 2.0 0.84 1.315 24511 1.9 0. 1643 5.7 0.0273 2.1 0.37 173.5 4515 2.3 0. 1305 10.2 0.0255 2.2 0.21 162.0 4486 1.0 0. 1820 2.5 0.0279 2.0 0.82 177.7 4697 0.93 1. 3720 2.3 0.1453 2.1 0.89 875 17509 1.6 0. 1680 3.8 0.0260 2.1 0.54 165.7 3512 1.8 0. 1695 3.6 0.0250 2.1 0.59 159.3 3573 2.2 0. 5554 3.4 0.0731 2.2 0.65 454.6 9.7


Ar–Ar laser step-heating analyses on four micas (3 bio-tites and 1 muscovite) and five amphiboles were carried outfollowing the standard procedures of the Ar–Ar laboratoryof CPGeo-USP (Vasconcelos et al., 2002). Several grains ofeach sample were irradiated in the nuclear reactor IEA-R1of the Brazilian Institute of Nuclear Research (IPEN),together with Fish Canyon sanidine standards. Three ofthe irradiated grains for each of the samples then wereselected for Ar–Ar analyses. During the successive incre-mental heating steps, the released gas was purified in anultravacuum system, and the 40Ar/39Ar ratios were mea-sured in a high sensibility mass spectrometer MAP-215-50. The Ar–Ar age spectra of the analyzed samples appearin Fig. 6, and the complete analytical data are available onrequest.

For all radiometric data, the decay constants employedare from Steiger and Jager (1977). The U–Pb were calculat-ed using the Isoplot/Ex 2.1 program of Ludwig (2002).Ar–Ar analytical data are available on request.

4. Proterozoic belt

High-grade metamorphic rocks of Proterozoic age fromthe Sierra Nevada de Santa Marta and Guajira regionshave been recognized since the early 1970s (MacDonaldand Hurley, 1969; Banks, 1975; Tschanz et al., 1974) andrelated to a correlated fragmented belt widespread in theEastern Colombian Andes (Toussaint, 1993; Cordaniet al., 2005).

In the Sierra Nevada de Santa Marta region (Fig. 2),banded high-grade Proterozoic metamorphic rocks ofgranulite facies and associated metamorphosed anorthosi-tic bodies are grouped within Los Mangos granulites(Tschanz et al., 1969). The NE segment of this unit isnamed the Dibulla gneiss (MacDonald and Hurley,1969). It is a centimetric to decametric banded metamor-phic rock, with local nebulitic structures. Two types of fel-sic quartz–feldespathic bands are common. The first showsa strong lineation fabric, with ribbon and ameboidmesoperthitic feldspar (plagioclase 10–20%, K-feldspar30–40%) with mirmekitic texture, quartz (30–50%), andbrown biotite (0–5%), as well as zircon, monazite, andopaques as mineral accessories. The other band lacksmineral fabric and is more K-feldspar rich; it presentsgraphic textures, as well as embayed and corroded grains,that are common on rocks affected by partial fusion(Sawyer, 1999). The mafic amphibolite bands exhibitbrown amphibole and biotite, defining a clear mineral lin-eation with quartz and elongated plagioclase and minoropaques.

Amphibole and plagioglase chemistry from an amphib-olite sample were analyzed. The amphiboles are calcic andshow no chemical zonation; plagioclase is andesine (An28–32). Comparative amphibole and amphibole-plagioclasethermobarometry (see ‘‘Analytical Techniques’’ for the cal-ibrations used) yields P–T conditions of 6–7.6 kb and tem-peratures of 760–810 �C, the latter based on Holland and

Blundy’s (1994) calibration. The metamorphic conditionsare characteristic of an amphibolite–granulite facies transi-tion, close to the dry melting of biotite (Bucher and Frey,1994; Johannes and Holtz, 1996) and compatible with theobserved (nebulitic) structures and textures of the differentfelsic bands, which are similar to the high-temperaturedeformation and partial fusion evidence provided bySawyer (1999) and Passchier and Trouw (1996).

Due to their metamorphic character, the interpretationof the obtained geochemical data is based on immobile ele-ments (Wilson, 1989), whereas the variable thickness of themetamorphic bands may be related to an inherited strati-graphic character from the protolith (Passchier et al.,1990).

The five analyzed quartz-feldspathic bands (Table 1)show high SiO2 values of 71–75% and high K2O/Na2O(�2.4). The REE elements from four of the anisotropicbands (Fig. 5a) are enriched (RREE > 312 ppm) and showstrongly negative slopes (La/YbN = 5.19–15.76) and a well-defined Eu anomaly. These patterns are typical of theupper continental crust and indicate extensive intracrustaldifferentiation (Taylor and Mclennan, 1985). A massive fel-sic rock shows lower REE values (RREE > 136,46), isdepleted in HREE, and exhibits a positive Eu anomaly,which might suggest a cumulatic origin (Cullers and Graf,1984; Sawyer, 1987). Three amphibolites from the maficbands show Cr concentrations > 100 ppm and Cr/Niratios > 1, which suggest a magmatic origin for the proto-liths (Walker et al., 1960; Leake, 1964). The REE are high,with RREE > 163, a negative slope (La/Yb)N = 3.4–5.6,and a flat HREE pattern (Fig. 5b). These patterns, com-bined with the Y, Sc, Zr, Ni, and Cr values, are similarto the continental tholeiitic basalts and suggest that themagmas could have formed at shallow depths in the spinelor plagioclase stability field (Pearce, 1982; Wilson, 1989).The Nb/La ratio (0.25–0.33) and relative Nb and Ti nega-tive anomalies may be related to an enriched mantle withsome crustal contamination (Culshaw and Dostal, 1997;Li et al., 2000). According to these geochemical patterns,the association with recycled upper continental crust rocks(associated felsic bands), and the Ti–V discriminationdiagram (not included; after Shervais, 1982), the tectonicsetting for the amphibolites is considered to have been a riftor backarc basin.

An anorthosite body that shows an intrusive relation toLos Mangos granulite, located SW of the Dibulla gneiss,was also sampled. This rock shows a weak mineral linea-tion and granoblastic and polygonal textures. Plagioclase(�An40) represents 85–98%, and mafic minerals are totallyreplaced by epidote, chlorite, biotite, and amphibole andrelated to a later hydrothermal event. Both plagioclasetextures and andesine composition suggest they metamor-phosed at high-grade conditions, probably in the granulitefacies (Kruhl and Huntenmann, 1991; Ashwall, 1993).

In the Guajira region (Fig. 3), Proterozoic rocks areincluded in the Jojoncito gneiss, with associated metasedi-mentary and amphibolitic rocks (Alvarez, 1967; Banks,

Fig. 4. Amphibole-plagioclase thermobarometer of Plyusnina (1982).


1975). The Jojoncito gneiss is a quartz-feldspathic rockwith strong mineral lineation, composed of quartz (32–50%), mesoperthitic K-feldspar (29–40%), plagioclase(An10–20), biotite less than 1%, and zircon, monazite, andopaque minerals as accessories. Its textural characteristicsare similar to those found in the Dibulla gneiss. The maingeochemical patterns (Table 1) and REE trend of one ana-lyzed sample shows the same upper crustal pattern foundon the Dibulla gneiss (Fig. 5a), which suggests the presenceof a similar, highly evolved crustal signature.

New and available geochronological data from thegneissic rocks of these two regions is presented in Cordaniet al. (2005) and summarized here. Both the Dibulla andJojoncito gneisses show a metasedimentary character, witha few magmatic-related Mesoproterozoic sources, ofbetween 1.55 and 1.25 Ga. They seem to have been affectedby two metamorphic events at approximately 1.14 and1.0 Ga. These patterns limit basin formation to the range1.25–1.14 Ga. Sm–Nd crustal residence ages from bothregions are between 1.5 and 1.9 Ga and suggest that theprotoliths for the paragneisess are a mix of juvenile Meso-proterozoic and older rocks (Restrepo-Pace et al., 1997;Ordonez et al., 1999).

Two Ar–Ar ages from one biotite and an amphiboleof an anorthosite sample associated with Los Mangosgranulite were obtained during this work. The biotiteyields irregular spectra (Fig. 6a and b) with plateaus inthe intermediate stages between 50 and 70 Ma. Theamphibole shows a more complex spectra. Both biotiteand amphibole replace higher grade minerals and formedin a superimposed hydrothermal event. The variability ofthe spectra may be related to the hydrothermal origin ofthe minerals, and the constrained Paleocene ages are sim-ilar to the age of magmatic plutons in the region(Tschanz et al., 1974).

5. Paleozoic belt

Amphibolite facies metamorphic rocks are exposed inboth the Sierra Nevada and Guajira regions, NW of thehigh-grade Proterozoic rocks. The units are named SevillaComplex and Macuira Formation (MacDonald, 1965;Tschanz et al., 1974), respectively (Figs. 2 and 3). The mainlithology includes paragneisses, amphibolites, amphibole-biotite schists, and mica schists. A superimposed myloniticfabric in the greenschist facies is common, with some low-strain zones preserving the former higher grade metamor-phism. These rocks are intruded by Late Jurassic granitoidsand undeformed Eocene granitoids (MacDonald, 1965;Lockwood, 1966; Alvarez, 1967; Tschanz et al., 1969).Geological relations with Proterozoic rocks are tectonicand, in the Santa Marta region, have been related to syn-tectonic granitoids (Tschanz et al., 1974).

Samples from amphibole-biotite and muscovite schistfrom the low-strain zones, a mylonitic garnet paragneiss,and an undeformed Jurassic granitoid related to the twounits were analyzed. Amphibole-plagioclase thermobarom-

etry from two amphibole-biotite schist samples of the Sevil-la Complex and Macuira Formation was undertaken. TheSevilla Complex amphiboles are mainly magnesiohorn-blende and actinolite, with variable Si and Al contents.Calculated pressures are in the range of 5–8 kb (Fig. 4),as shown by Plyusnina’s (1982) and Fershater’s (1990) cal-ibrations. Temperature is more precise, with valuesbetween 490 and 550 �C in Plyusnina’s (1982) and Spear’s(1980) calibrations, as a consequence of the more restrictedplagioclase composition (An26–An33). The Macuira schistcontains magnesiohornblende and tschermackite amphibo-les, with plagioclase varying between An17–An33 and thesame thermobarometrical pattern using both calibrations,with pressures of 6–9 kb and temperatures of 500–550 �C(Fig. 4). Actinolite is observed as small blebs in the coresof some crystals.

The variability in calculated pressures is probably relat-ed to disequilibrium associated with continued amphibolecrystallization (Villa et al., 2000; Bellot et al., 2003),whereas the actinolite blebs are related to the Ca-amphi-bole miscibility gap common in middle-pressure metaba-sites (Begın and Carmichael, 1992). Together, they maybe related to a prograde metamorphism toward amphibo-lite facies of the intermediate pressure baric type. Local ret-rograde greenschist evidence appears in some rims thatshow amphiboles with actinolite compositions, as well asthe presence of chlorite.

Geochemical data from the Macuira Formation wasinterpreted following the same criteria used for the Dibullagneiss. Five amphibole schist samples from the MacuiraFormation (Table 1) show silica contents of 48–59% andlow MgO and TiO2 values. They follow a general calc-alka-line trend in the AFM diagram (not included) and corre-spond to andesite basalts and andesites. The REEpatterns have negative slopes, with strong LREE enrich-ment [(La/Yb)N ratios of 1.7–38 and (La/Sm)N of 1.3–6.1], low HREE and Y values, and an almost lack of Euanomaly (Fig. 5c). The low HREE and Y values, togetherwith the high Cr and Ni values (>26 ppm) and high Sr(250–1076 ppm) suggest plagioclase fusion in the source

Fig. 5. REE geochemical data normalized to chondrite (C1). (a) Quartz-feldespathic rocks from the Dibulla (romba) and Jojoncito gneises (cross),(b) amphibolite bands from the Dibulla gneiss, (c) amphibole schists fromthe Sevilla Complex.


and a restite with garnet, amphibole, and clinopyroxene(Martin, 1999). The LREE enrichment correlates with theincrease in SiO2, and the decrease in MgO can be relatedto fractional crystallization of pyroxene, titanite, and prob-ably hornblende (Wilson, 1989).

Such distinctive chemical trends, including the REE pat-tern, presence of negative Nb and Ti anomalies, andHFSE/REE ratio, suggest calc-alkaline series rocks or evenadakites, formed in subduction-related environments ofcontinental magmatic arcs (Pearce, 1982; Cullers and Graf,

1984; Wilson, 1989; Defant and Drummond, 1990; Tats-umi and Eggins, 1995).

5.1. Geochronology

Previous geochronological data from these units includeamphibole and mica K–Ar Jurassic and Eocene ages ofmetamorphic rocks and cross-cutting intrusives (MacDon-ald, 1965; Lockwood, 1966; Alvarez, 1967; Tschanz et al.,1974). For this work, 25 U–Pb SHRIMP zircon analyseswere obtained from a mylonitized garnetiferous paragneiss(garnets broken and partially replaced by mylonitic fabric)of the Sevilla Complex (15) and an undeformed Siapanagranodiorite that intrudes the Macuira Formation (10).Ar–Ar step-heating ages were obtained on 4 amphiboles,2 biotites, and 1 muscovite from five schist samples of theMacuira Formation (4) and Sevilla Complex (1), as wellas 1 biotite from the granodiorite analyzed for U/Pb.

Fig. 7a shows conventional U–Pb concordia diagramfor zircons from a paragneiss of the Sevilla Complex(A19). The analyzed zircons show variable and roundedshapes, which may be related to a sedimentary provenance.Th/U ratios of most of the analyzed zircons are >0.2 (Table3), suggesting that the source for the sediments includedmany magmatic rocks (Beloussova et al., 2002).238U/206Pb ages are widespread along the concordia from500 to 1400 Ma (Table 3). Six zircons show Proterozoicages between 1380 and 1120 Ma, with two grains showinga 1244 ± 23 Ma age and three older than 1185 ± 25 Ma.The other six zircons show 920–1080 Ma ages. YoungerNeoproterozoic and Cambrian concordant ages are alsopresent, with values of 529 ± 10 Ma, 614 ± 13 Ma, and732 ± 16 Ma. These data are related to the sedimentarysources, constraining a maximum Cambrian age for thedeposition of the sedimentary protolith of the paragneiss.

Fig. 7b shows U/Pb data from 10 equant and prismaticzircons with well-developed faces from the Siapana grano-diorite (Siap 1). The cathodoluminescence images showoscillatory zoning patterns typical of magmatic zircons,as well as older cores with strong luminescence. Five zirconcrystals with oscillatory zoning plot within the concordiawith a weighted 206Pb/238U age of 167 ± 9.4 Ma. The coresfrom three grains yield older concordant ages of870 ± 25 Ma, 1311 ± 26 Ma, and 456 ± 9.7 Ma, and theremaining two show evidence of ancient Pb-loss. The Th/U ratios of all zircons are >0.2, typical of magmatic zircons(Beloussova et al., 2002). A Sm–Nd analysis from thisgranitoid sample yields CNd calculated for a 167 Ma crys-tallization age of �5.90 and TDM = 1.45. Moreover, amuscovite schist sample from the Macuira Formationshows a TDM Sm–Nd model age of 1.47. These data, whencombined with the presence of inherited zircons, clearlypoint to a crustal contribution for the magma genesisand the relevance of the regional Proterozoic ages.

Three biotite grains from the same sample of the Siapanagranodiorite yield well-defined and coherent plateau agesaround 156 Ma (Fig. 7c). Such Jurassic ages are related


to cooling at temperatures of 300 ± 50 �C, indicating thatthe relatively rapid cooling may be related to an emplace-ment into upper crustal levels.

Three amphibole and three biotite grains from anamphibolitic schist of the Sevilla Complex (A28) show evi-dence of a two-stage Ar–Ar thermal evolution (Fig. 6d ande). The amphiboles define plateau and pseudoplateau agesin the intermediate steps between 180 and 185 Ma, as wellas some complex spectra with older apparent ages around220–230 Ma. In contrast, the biotite grains show a staircasepattern, forming plateau and pseudoplateau early Tertiaryages. Such patterns indicate the presence of an importantTriassic–Jurassic thermal event, recorded by partial argonloss in the amphiboles, and a second Paleocene perturba-

Fig. 6. 40Ar–39Ar age spectra. Experimental temperatures increase from left tAmphibole from anorthosite (A77) of Los Mangos granulite, (b) biotite frogranodiorite (Siap 1), (d) amphibole from schist of the Sevilla Complex (A28)schist of the Macuira Formation (A83), (g) biotite from schist of the Macuira(A91), (i) amphibole from schist of the Macuira Formation (A99), and (j) mu

tion that attained temperatures of 300–350 �C, releasingAr from the biotites.

The amphibole grains from the Macuira Formationamphibole schist samples (A-83 and A-91, Fig. 7f and h)show a staircase pattern between 100 and 220 Ma, with lat-er steps yielding apparent ages of 160 and 220 Ma. In con-trast, amphibole A-99 shows plateau and pseudoplateauages between 150 and 160 Ma (Fig. 7i). Biotite from sampleA-83 (Fig. 7g) also shows a younger staircase pattern, withone of the grains indicating a plateau age of 79.0 ± 05 Ma.However, a muscovite from micaschist sample A-95(Fig. 7j) of the Macuira Formation shows irregular spectrawith staircase patterns and late step apparent ages near160 Ma.

o right. Each analysis corresponds to three grains of the same sample. (a)m anorthosite (A77) of Los Mangos granulite, (c) biotite from Siapana, (e) biotite from schist of the Sevilla Complex (A28), (f) amphibole from

Formation (A83), (h) amphibole from schist of the Macuira Formationscovite from schist of the Macuira Formation.

Fig. 7. Conventional zircon U/Pb concordia plot from a paragneiss of the(a) Sevilla Complex and (b) Siapana granodiorite.


Ar–Ar staircase patterns indicate partial argon losscaused by thermal events, whereas older ages from thehigh-temperature stages of the spectra are considered min-imum ages for the original formation of the minerals(McDougall and Harrison, 1999). Collectively, these datasuggest the presence of possible Triassic–Jurassic andPaleocene thermal perturbations.

Fig. 8. (a) Permo-Triassic and (b) actual distribution of Pre-Mesozoic terraneCaribbean, including geographic localities discussed in text. Modified from StewLA, Loja-Amotape; T, Tahamı; Ch, Chibcha; M-C, Merida Caparo; C-T,Mixteca; S, Socorro Complex. Localities: (1) Sierra Nevada de Santa Marta, (2Bonaire. Amazon Craton is hatched.

6. Tectonic implications and correlations

Two correlated pre-Mesozoic metamorphic belts char-acterize the basement of the northern termination of theColombian Andes: an older one including the Dibullaand Jojoncito gneisses, and a younger one including theSevilla and Macuira schists.

Within the older belt, the field relations (mafic and felsicbands) and geochemical patterns can be related to volca-nosedimentary protoliths formed in a continental rift orbackarc environment. The presence of anorthosite bodiesmay be related to this type of continental extensional envi-ronment (Ashwall, 1993). Petrographic textures of the dif-ferent rocks and amphibole-plagioclase thermobarometryindicate that these rocks metamorphosed in amphibolite–granulite conditions and were accompanied by partialfusion.

The temporal constraints and tectonic interpretationsfrom these Proterozoic basement units presented by Corda-ni et al. (2005), when integrated with the data presentedhere, show Mesoproterozoic zircon sources that can berelated to the SW Amazon Craton margin. The availableage data indicate that original rift or backarc basin forma-tion may have taken place at 1.25–1.16 Ga (younger detri-tal and metamorphic zircons); a first regionalmetamorphism followed at approximately 1.14 in a formerCordilleran orogen with associated arc magmatism, and amajor continental collision event followed at 1.0 Ga, pro-ducing high-grade regional metamorphism. Similar tempo-ral and metamorphic characteristics occur in the otherProterozoic exposures from the Eastern Colombian Andesand within the Chibcha terrane and paraauthoctonousGarzon Massif (Cordani et al., 2005; Restrepo-Paceet al., 1997; Ordonez et al., 1999; Ordonez, 2001; Fig. 8),which suggests these domains and other similar fragmentsfrom the Southern Andes and Mexico (Wasteneys et al.,1995; Keppie and Ortega-Gutierrez, 1999; Ruiz et al.,1999; Solari et al., 2003; Loewy et al., 2004) were partof a larger Mesoproterozoic Grenvillian collisional belt

s and crustal exposures from the Northern Andes, Central America, andart et al. (1999) and Elıas-Herrera and Ortega-Gutierrez (2002). Terranes:

Caucagua-Tinaco; Co, Chortis; Y-M, Yucatan-Maya; O, Oaxaquia; M,) Guajira Massif, (3) Paraguana Peninsula, (4) Toas Island, (5) Perija, (6)


(Cordani et al., 2005) related to Rodinia formation and thejuxtaposition of the western Amazonian Craton with Laur-entia (Hoffman, 1991).

The lower-grade metamorphic belt that includes theSevilla Complex and Macuira Formation shows continen-tal arc geochemical affinities for the protoliths and thermo-barometrical features of Barrovian-type progressiveamphibolite facies metamorphism. This kind of metamor-phism affecting continental arc protoliths is typical of a col-lisional tectonic environment (Best, 2003). The detritalzircon ages of 530 Ma from a paragneiss of the SevillaComplex and the Ordovician inherited zircons from theJurassic Siapana granodiorite that intrudes the MacuiraFormation provide a maximum original age for the proto-liths. The Mesoproterozoic Grenville sources are similar tothose from the older domain. Neoproterozoic and Cambri-an ages of zircons can be related to Gondwanan sourcesand indicate a South American position for this domainduring its original early Paleozoic formation. The Ar–ArLate Jurassic thermal resting ages (�160 Ma) are similarto the crystallization age of the Siapana granodiorite.Moreover, correlatable regional thermal and magmaticevents are recorded in the basement rocks of the EasternAndean domain of Colombia and Venezuela (Espejoet al., 1980).

The metamorphic conditions from the amphibole schistindicates temperatures of 490–550 �C, and Ar–Ar amphi-bole closure temperatures vary between 450 and 550 �Cas a function of its composition (McDougall and Harrison,1999), with magnesiohornblende and actinolite closuretemperatures considered to be approximately 500 �C(Dahl, 1996). Therefore, the older minimum ages of 210–230 Ma yielded by some amphiboles may be linked to cool-ing from the main regional metamorphic event and are sim-ilar to metamorphic cooling ages found in both Venezuelaand central Colombia (Cordani et al., 1985).

The Gondwanan affinity, the apparent older Triassiccooling ages, and the lithostratigraphic and geochronolog-ical similarities suggest a possible correlation with thePaleozoic evolution of the Merida Andes of Venezuela(Lockwood, 1966; Burkley, 1976; Marechal, 1983; Cordaniet al., 1985) that ends with a Late Paleozoic collisionalevent related to the formation of Pangea (for a review,see Aleman and Ramos, 2000).

Permian–Triassic ages have been found in granitoidsfrom the Paraguana Peninsula in the Caribbean region ofVenezuela (Martin, 1968), where geologic relations similarto those of the Guajira Peninsula are common. Similarmagmatic ages and a Late Paleozoic deformational eventare also present in the eastern Colombian Andes, Perijaregion, and Toas Island in the northern end of Lake Mar-acaibo (Espejo et al., 1980; Gonzalez de Juana et al., 1980;Dasch, 1982; Toussaint, 1993), which suggests this tectonicevent was regionally widespread in the northernmost seg-ment of the northern Andes.

The apparent lack of Jurassic thermal and magmaticevents in the Tahami terrane from the Central Colombian

Cordillera prevents lateral correlation of this metamor-phic belt with the Santa Marta and Guajira units(Toussaint, 1993, 1994). Jurassic magmatism correlatablewith the Jojoncito granodiorite is well represented region-ally in plutonic and volcanic units in the studied regions(Tschanz et al., 1974; MacDonald and Opdyke, 1972),as well as in the nearby northeastern Colombian Andeanregion (Dasch, 1982; Steinitz and Maze, 1984; Dorr et al.,1995); thus, these two regions may have been related tothe authocthonous South American continent in theJurassic, where this event is widespread (Aspden et al.,1987).

The Cambrian–Ordovician ages found in the paragneis-ses and Jurassic granitoid are similar to ages found in theCaucagua-Tinaco terrane from the Cordillera de la Costaof Venezuela (Ave Lallement and Sisson, 1993; Ertanet al., 1995; Seyler et al., 1998). This terrane probablyhas been displaced along the continental margin from awestern position compatible with the Colombian massifs(Ave Lallement and Sisson, 1993) and implies the existenceof an important Early Paleozoic domain in northernmostSouth America.

Relations between the Proterozoic and the youngermetamorphic belt are considered tectonic and related toPermian granitoids (Tschanz et al., 1974). The presenceof Mesoproterozoic sources for the Sevilla Complex andMacuira Formation, similar to those from the Dibullaand Jojoncito gneisses and other Grenvillian exposures ofthe Colombian Andes reported by Cordani et al. (2005),suggest the proximity of these belts. According to regionalpaleogeography (Pindell, 1985; Rowley and Pindell, 1989),a Late Paleozoic–Triassic docking event associated withthe formation of Pangea is feasible.

The Meso-Cenozoic tectonic evolution of NW SouthAmerica also is recorded in these fragments. The typicalMid- and Late-Jurassic magmatic and tectonothermalactivity related to active convergence and Pangea disrup-tion found on the northwestern Andes (Aspden et al.,1987; Pindell, 1994) is seen directly in the younger belt, incross-cutting intrusive rocks, the Ar–Ar thermal evolutionof the metamorphic rocks, and the previously availableK–Ar ages (MacDonald, 1964; Lockwood, 1966; Tschanzet al., 1974).

The Cretaceous–Paleocene biotite ages from the low-strain zone schists of the younger Sevilla and Macuirametamorphic belts are older than the reported 48 MaK–Ar ages from regional granitoids (Lockwood, 1966;Tschanz et al., 1974) and may be related to a thermal per-turbation of the greenschist deformational event thatformed high-strain mylonite zones in other parts of theamphibolite facies belt. Moreover, they are temporallycompatible with the second metamorphic event in theCretaceous metamorphic rocks in tectonic contact withthe Sevilla Complex and Macuira Formation (MacDonald,1965; MacDonald et al., 1971; Tschanz et al., 1974) andcould be related to the accretion of the allocthonousCaribbean-related metamorphic belts.


Terrane disruption and dispersal mechanisms are linkedto the evolution of rift and convergent tectonic regions(Gibbons, 1994; Howell, 1995). Within Pangean tectonicreconstructions, northern South America and southernMexico pre-Mesozoic terranes are juxtaposed and/or over-lap (Rowley and Pindell, 1989; Dickinson and Lawton,2001), and Permian-related orogenic events are commonin both regions (Marechal, 1983; Malone et al., 2002;Weber and Cameron, 2003). From the lithostratigraphicrecord of the northernmost Andean massifs, terrane dis-persal associated with Pangea disruption can be inferredfrom the possible correlation of some studied rocks withProterozoic Oaxaquia and Socorro complex rocks, as wellas the similar Jurassic thermal and magmatic record foundin Mexico and Cuba (Renne et al., 1989; Alaniz-Alvarezet al., 1996; Ruiz et al., 1999; Keppie et al., 2004). Dispersalpatterns related to the Meso-Cenozoic oblique migration ofthe Caribbean plate (Pindell, 1994) are envisaged from thepresence of allocthonous domains in the Cordillera de laCosta of Venezuela (Caucagua-Tinaco belt; Ave Lallementand Sisson, 1993; Ertan et al., 1995; Seyler et al., 1998) andthe Eocene conglomerates from the leeward Antilles (Priemet al., 1986). Such allocthonous terranes present some Pro-terozoic and Early Paleozoic ages similar to those reportedfor the Santa Marta and Guajira massifs.

This active continental margin dispersal pattern alsoappears in paleomagnetic data on Jurassic rocks, strati-graphic comparisons of more recent displacements alongrecognized faults, and recent GPS measurements from thisregion (MacDonald and Opdyke, 1972; Tschanz et al.,1974; Thery, 1982; Trenkamp et al., 2002).

Acknowledgements

The authors appreciate support received from the Bra-zilian Ministry of Science and Technology (PRONEX41.96.0899.00) and Sao Paulo State Foundation of Re-search (FAPESP 00/09695-1 and 01/08940-5). Lyu Dunyiis acknowledged for providing SHRIMP facilities at theChinese Academy of Geological Sciences. The staff of theCenter of the Geochronological Research (CP-Geo) andGeochemical Laboratories of the University of Sao Paulois acknowledged for laboratory assistance. Field supportby Andres Bustamante, Pablo Castro, and Daiver Pintowas crucial. Discussions with Cesar Vinasco were very usefulfor elaborating the manuscript. Constructive comments andsuggestions by Andre Steenken and an anonymous journalreferee improved the final version of the manuscript.

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