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Brazilian Journal of Geology

Print version ISSN 2317-4889On-line version ISSN 2317-4692

Braz. J. Geol. vol.46  supl.1 São Paulo June 2016

http://dx.doi.org/10.1590/2317-4889201620150012 

ARTICLE

U-Pb zircon ages of rocks from the Amazonas Territory of Colombia and their bearing on the tectonic history of the NW sector of the Amazonian Craton

Idades U-Pb em zircão de rochas do Território Amazonas da Colômbia e sua relevância para a história tectônica do setor NW do Cráton Amazônico

Umberto Giuseppe Cordani1  *

Kei Sato1 

Walter Sproessner1 

Fabiana Santos Fernandes1 

1Institute of Geosciences, Universidade de São Paulo - USP, São Paulo (SP), Brazil. E-mails: ucordani@usp.br, keisato@usp.br, wmsproes@usp.br, fabianaf00@yahoo.com.br

ABSTRACT:

Here we report the results of several U-Pb zircon ages, made to generate an integrated history for the Rio Negro-Juruena tectonic province, for the northwestern part of the Amazonian ­Craton. This region comprises granitoid rocks, described as calc-alkaline syntectonic gneisses, granites and migmatites, affected by medium level amphibolite facies metamorphism. The new measurements, with the available Rb-Sr and K-Ar ages, indicate the formation of these rocks within a series of essentially juvenile magmatic arcs, that are closely related with subduction. Sm-Nd analyses indicate that all samples, regardless of their zircon ages, yielded TDM model ages roughly between 1.9 and 2.2 Ga, suggesting the absence of a much older source material. In the northeastern part (areas of Puerto Inírida and San Carlos), the Atabapo belt comprises rocks formed within a period of about 60 Ma, from 1800 to 1740 Ma. In the southwestern region, including the towns of Mitú and Iauaretê, the granitoids formed in the Vaupés belt between 1580 and 1520 Ma. Finally, the available K-Ar measurements indicate the onset of the Nickerie-K'Mudku intraplate heating event, with temperature above 300oC within the entire region at 1200 - 1300 Ma.

KEYWORDS: Amazonian Craton; Rio Negro-Juruena province; geochronology; zircon ages; tectonic history

RESUMO:

Este trabalho inclui diversas idades U-Pb SHRIMP e LA_ICP-MS em zircão, produzidas para contribuir com o conhecimento da história geológica da província tectônica Rio Negro-Juruena na parte noroeste do Craton Amazônico. A região é constituída por rochas granitoides, descritas como gnaisses, granitos e migmatitos cálcio-alcalinos, afetadas por metamorfismo de fácies anfibolito, em nível crustal médio. As novas datações, com as idades K-Ar e Rb-Sr previamente existentes, indicam a formação dessas rochas numa série de arcos magmáticos essencialmente juvenis, associados a processos de subducção. A sistemática Sm-Nd indica que todas as amostras analisadas, quaisquer que sejam as suas idades, apresentam idades modelo TDM entre 1,9 e 2,2 Ga, sugerindo ausência de material crustal mais antigo. Na parte nordeste (áreas de Puerto Inírida e San Carlos), a Faixa Atabapo inclui rochas formadas num período de 60 Ma, entre 1800 e 1740 Ma. Na parte sudoeste, que inclui as vilas de Mitú e Iauaretê, os granitoides foram formados entre 1580 e 1520 Ma na Faixa Vaupés. Finalmente, as idades K-Ar disponíveis indicam o advento do importante aquecimento intraplaca cobrindo a região inteira, acima de 300oC, denominado Nickerie-K'Mudku, com ca. 1200 - 1300 Ma.

PALAVRAS-CHAVE: Craton Amazônico; Província Rio Negro-Juruena; Geocronolgia; Idades em zircão; História tectônica

INTRODUCTION

A first attempt towards a geochronological reconnaissance study of the Amazonian Craton was made in the late 1970's (Cordani et al. 1979), after comprehensive geological mapping through the RADAM program of the Brazilian government. In contrast from the previous fixistic tectonic models for that cratonic area, these authors adopted a mobilistic interpretation. Some proterozoic tectonic provinces were envisaged, growing successively around an ancient nucleus located in the central part of the craton. One of them, including the Amazonian region of eastern Colombia, SW Venezuela and NW Brazil, was named Rio Negro-Juruena tectonic province.

At the time of the initial work, only Rb-Sr and K-Ar ages were available. Cordani et al. (1979) reported ages between 1700 and 1500 Ma for the tectonic events within that province. A later increase of available rock ages in Amazonia permitted marked progress in understanding the region (see e.g, comprehensive reviews by Teixeira et al. (1989), Tassinari (1996), Tassinari and Macambira (1999) and Cordani et al. (2000).

With the increasing use of U-Pb zircon ages in recent years, some alternative interpretations for the tectonic evolution of the Amazonian Craton were presented (e.g. Santos et al. 2000, Santos 2003, Cordani and Teixeira 2007). Boundaries of the tectonic domains were altered, and names were changed, but the mobilistic frame was always maintained. Based on Nd isotopic work, Cordani and Teixeira (2007) suggested that the tectonic evolution of the SW half of the Amazonian Craton was accretionary. They proposed that the craton grew by the stacking of successive magmatic arcs originating from subduction zones, from 2000 to1500 Ma. Within the Rio Negro-Juruena province, unequivocal evidence of continental material older than 2000 Ma has not been found.

Figure 1 illustrates the interpretation given by Cordani et al. (2000), with the location of the study area. The first geochronological ages in that region were determined by Pinson et al. (1962), who dated the alkaline rocks of São José del Guaviare by the K-Ar method, back to an ordovician age (about 480 Ma). During the 1970's and the 1980's, the Geological Survey of Colombia, INGEOMINAS, made an extensive reconnaissance geological mapping of the country (PRORADAM 1979). Priem et al. (1982) performed a relevant geochronological study of that area, primarily using Rb-Sr and K-Ar methods. Around the same time, important reconnaissance works were carried out in Brazil and Venezuela by the respective geological surveys, to assess the potential of the region for mineral exploration.

Figure 1: Tectonic provinces of the Amazonian Craton, with location of the study area. 

Our original focus in this work was the poorly known region of the Amazonas Territory of Colombia, located in the NW part of the Rio Negro-Juruena Province of Cordani et al. (1979). We later enlarged the area of interest to involve large parts of SW Venezuela and NW Brazil. In these countries, a few important geochronological works by Fernandes et al. (1976), Pinheiro et al. (1976), Gaudette and Olszewski (1985), and Barrios et al. (1985 and 1986) made several age determinations for the existent governmental mapping projects. Our consolidated study area (Fig. 2) includes the international boundaries of Colombia with Venezuela and Brazil. The terrain of the entire territory was completely shaped by erosion, and the present land surface is a widespread peneplain. Granitic and gneissic rocks, deformed or not, and frequently migmatitic, are largely predominant. In a general way, these regional rocks were formed by tectono-magmatic and metamorphic processes related to medium-grade metamorphic environments. Supracrustal rocks and intraplate volcanic-sedimentary sequences occur in restricted areas.

Figure 2: NW Corner of the Amazonian Craton. Location of samples analysed by the U-Pb and Sm-Nd methods. 

During the 1980's, Priem et al. (1982) and Gaudette and Olszewski (1985) produced a few U-Pb zircon analyses, using conventional TIMS studies. Important geochronological papers were later produced, including work by Tassinari et al. (1996), using SHRIMP, and by Sato and Tassinari (1997), using Sm-Nd model ages. Tassinari (1996) prepared a complete synthesis of all available geochronological ages in the Brazilian territory. In the last 10 to 20 years, additional U-Pb zircon work has been performed, such as studies by Santos et al. (2000), Santos (2003), Almeida (2006), and, more recently, Ibañez et al. (2011), who presented a few U-Pb zircon determinations by LA-ICP-MS.

The aim of the present work was to produce a tentative integrated picture of the tectonic evolution of the NW part of the Amazonian Craton. Following the analyses of about 20 samples of granitoid rocks from the INGEOMINAS collection, we report the results of geochronological and isotopic measurements using accurate U-Pb zircon ages, measured by the SHRIMP or LA-ICP-MS methods. Despite the reasonable amount of available geochronological data, this project remains a very preliminary reconnaissance work, because the covered basement area exceeds 200,000 km2 and only around 30 precise U-Pb zircon ages exist. This work includes the results of several new Sm-Nd isotopic measurements and some new Rb-Sr analyses which were included in the available isochron diagrams constructed from works of Priem et al. (1982) and others. Our regional interpretations consider all available geochronological controls, by K-Ar and Rb-Sr methods. As more than 100 ages by Rb-Sr dating are available for the study area, we tried to select the most significant ages in terms of interpretative results. Figure 3 shows the location of 97 rock samples with Rb-Sr determinations. Their ages are described in a series of Rb-Sr isochron diagrams (Fig. 9) and will be properly discussed later. Overall, these data have helped us to obtain a suitable perspective for interpreting the tectonic history of the region.

Figure 3: Location of samples analysed by the Rb-Sr method. 

ANALYTICAL METHODS

All K-Ar and most Rb-Sr dates considered in this work were obtained during the 1970's and 1980's from laboratories in Amsterdam (Priem et al. 1982) and São Paulo (Barrios et al. 1985, Fernandes et al. 1976, Pinheiro et al. 1976). Analytical procedures can be found in the indicated references. Andrade-Santos (2010) obtained 10 additional Rb-Sr whole-rock measurements at the São Paulo laboratory (CPGeo-USP). Analytical procedures are the same as indicated by Tassinari (1996). The instrument used was a Finnegan-MAT 262, with five Faraday collectors operated in a static way. Table 1 provides the analytical data for the 97 Rb-Sr measurements considered in this work.

Table 1: Rb-Sr analytical data for the rock samples included in Fig. 3

Sample Location Rb, ppm Sr, ppm 87Rb/86Sr 87Sr/86Sr References
San Carlos
UNH30 San Carlos, Venezuela 411 83 14.870 1.03800 1
UNH31 San Carlos, Venezuela 396 87.5 13.470 1.00700 1
UNH34A San Carlos, Venezuela 264 349 2.195 0.75190 1
UNH34B San Carlos, Venezuela 254 324 2.277 0.75630 1
5414 San Carlos, Venezuela 261 323 2.350 0.75570 2
5415 San Carlos, Venezuela 269 229 3.420 0.77790 2
J-205 San Felipe, Colombia 227.5 286.7 2.307 0.75650 6
PRA-16 San Felipe, Colombia 348 99.3 10.340 0.91973 3
PRA-20 Rio Negro,Colombia 279 93.5 8.780 0.89308 3
PRA-21 Rio Negro,Colombia 293 177 4.850 0.81300 3
PRA-23 Rio Negro,Colombia 217 356 1.770 0.74388 3
PRA-29 San Felipe, Colombia 183 224 2.380 0.75699 3
Puerto Inírida
PRA-30 Puerto Inírida, Colombia 351 316 3.050 0.76941 3
PRA-32 Puerto Inírida, Colombia 372 253 4.310 0.79862 3
PRA-33 Puerto Inírida, Colombia 376 126 8.790 0.89272 3
PRA-34 Puerto Inírida, Colombia 370 134 8.140 0.87994 3
PRA-35 Puerto Inírida, Colombia 363 144 7.440 0.86444 3
PRA-37 Puerto Inírida, Colombia 266 359 2.150 0.75248 3
PR-3141 Puerto Inírida, Colombia 389.2 180.5 6.322 0.83872 6
São Gabriel + Içana River
RM-O2 A São Gabriel da Cachoeira, Brazil 252.1 232.9 3.156 0.77730 4
RM-O2 A1 São Gabriel da Cachoeira, Brazil 258.3 205.4 3.669 0.78420 4
RM-02 A2 São Gabriel da Cachoeira, Brazil 288.9 198.6 4.249 0.79700 4
RM-02 A3 São Gabriel da Cachoeira, Brazil 289.8 214.3 3.947 0.78800 4
RM-O2 A4 São Gabriel da Cachoeira, Brazil 268.5 222.1 3.542 0.78240 4
IÇ-12 Içana river, Brazil 290.8 167.9 5.064 0.80620 4
IÇ-15 Içana river, Brazil 308.3 119.3 7.591 0.85500 4
IÇ-29 Içana river, Brazil 340.5 100.3 10.013 0.89660 4
IÇ-35 Içana river, Brazil 344.5 98.5 10.319 0.89970 4
PT-10-Mi8 Içana river, Brazil 659.4 168.5 11.565 0.91700 4
Negro River
PRA-22 Guainia river, Colombia 215 156 3.988 0.80576 3
PRA-24 San Felipe, Colombia 303 106 8.271 0.91560 3
PRA-25 Negro river, Colombia 211 172 3.549 0.79603 3
PRA-26 Negro river, Colombia 245 165 4.296 0.81348 3
PRA-27 Negro river, Colombia 260 163 4.615 0.82460 3
J-199 Negro river, Colombia 406.8 154.7 7.611 0.89623 6
PRA-19 Negro river, Colombia 249 146 5.000 0.82784 3
UNH-19 Casiquiare river, Venezuela 165 150 3.225 0.78860 1
UNH-21A Casiquiare river, Venezuela 279 71.8 11.570 0.99060 1
UNH-21B Casiquiare river, Venezuela 271 70.2 11.500 0.99860 1
UNH-22 Casiquiare river, Venezuela 216 231 2.729 0.76970 1
UNH-23 Casiquiare river, Venezuela 226 148 4.473 0.82060 1
UNH-24 Casiquiare river, Venezuela 132 437 0.877 0.72660 1
UNH-25A Casiquiare river, Venezuela 179 344 1.509 0.73920 1
UNH-25B Casiquiare river, Venezuela 191 342 1.622 0.74270 1
UNH-26 Casiquiare river, Venezuela 149 503 0.861 0.72470 1
Caquetá River
PRA-51 Caquetá river, Colombia 505 105 14.410 1.01970 3
PRA-52 Caquetá river, Colombia 268 131 6.030 0.83422 3
PRA-53 Caquetá river, Colombia 406 68.4 17.850 1.09820 3
PRA-50 Araracuara, Colombia 327 86.2 11.270 0.97398 3
EP-2 Araracuara, Colombia 274.7 60.9 13.446 1.00664 6
Rio Atabapo
PRA-31 Inírida river, Colombia 211 221 2.790 0.77596 3
PRA-36 Inírida river, Colombia 247 180 4.010 0.80642 3
UNH-68 A Atabapo river, Venezuela 239 151 4.631 0.82730 1
UNH-68 B Atabapo river, Venezuela 252 149 4.952 0.83170 1
UNH-69 Atabapo river, Venezuela 281 160 5.133 0.83610 1
UNH-70 Atabapo river, Venezuela 234 210 3.251 0.78880 1
UNH-72 Atabapo river, Venezuela 242 173 4.076 0.81010 1
5511 Atabapo river, Venezuela 222 166 3.920 0.79750 2
5523 Atabapo river, Venezuela 248 164 4.440 0.81900 2
5480 Atabapo river, Venezuela 287 135 6.240 0.86300 2
5506 Atabapo river, Venezuela 280 153 5.370 0.84300 2
5507 Atabapo river, Venezuela 326 108 8.980 0.93570 2
5528 Atabapo river, Venezuela 264 156 4.970 0.83410 2
5532 Atabapo river, Venezuela 179 179 3.900 0.80610 2
2439 Atabapo river, Venezuela 241 191 3.680 0.79720 2
10514 Atabapo river, Venezuela 190 211 2.630 0.77870 5
BA54 Atabapo river, Venezuela 273 148 5.430 0.84350 5
Região Mitú - Iauaretê
PRA-1 Mitú, Colombia 280 151 5.410 0.82390 3
PRA-2 Mitú, Colombia 273 153 5.220 0.82820 3
PRA-3 Mitú, Colombia 312 111 8.290 0.88956 3
PRA-4 Mitú, Colombia 238 100 6.970 0.86076 3
PRA-14 Vaupés river, Colombia 327 117 8.260 0.88758 3
PRA-44 A Papuri river, Colombia 166 307 1.570 0.74145 3
PRA-44 B Papuri river, Colombia 174 301 1.670 0.74335 3
PRA-45 Papuri river, Colombia 153 353 1.260 0.73393 3
PRA-46 Papuri river, Colombia 184 291 1.840 0.74659 3
PRA-47 Papuri river, Colombia 166 321 1.500 0.73938 3
PRA-48 Papuri river, Colombia 174 292 1.730 0.74455 3
PRA-49 Papuri river, Colombia 201 324 1.800 0.74629 3
PA-01 Iauaretê, Brazil 336.6 156.8 6.301 0.84740 4
PA-08 Papuri river, Brazil 112.6 451.6 0.723 0.72210 4
PA-35 Papuri river, Brazil 62.4 386.8 0.467 0.71560 4
UA-02 Iauaretê, Brazil 384 189.9 5.929 0.83670 4
UA-18 Iauaretê, Brazil 214.4 250.6 2.490 0.75910 4
UA-39 Uaupés river, Brazil 171.5 515.3 0.965 0.72650 4
UA-41 Uaupés river, Brazil 162.2 341.6 1.379 0.73680 4
AH-1212 A Vaupes river, Colombia 161.8 76.7 6.181 0.83691 6
AH-1213 A Vaupes river, Colombia 115.9 159.2 2.118 0.75528 6
AH-1231 Mitú, Colombia 334.2 223 4.376 0.79724 6
HB-653 Vaupes river, Colombia 78.1 220.4 1.028 0.73392 6
Ventuari River
8697 Minicia, Venezuela 132 169 2.272 0.76090 1
8698A Ventuari river, Venezuela 150 339 1.287 0.73740 1
8698B Ventuari river, Venezuela 128 229 1.629 0.74340 1
8722 Ventuari river, Venezuela 162 298 1.581 0.74580 1
8724 Ventuari river, Venezuela 116 504 0.669 0.71980 1
8727 Ventuari river, Venezuela 161 296 1.576 0.74180 1
8699 Macabana, Venezuela 300 198 4.451 0.82150 1

References: 1 - Gaudette, Olszewski Jr. 1985; 2 - Barrios et al. 1985; 3 - Priem et al. 1982; 4 - Fernandes et al. 1976; 5 - Barrios 1983; 6 - This work.

A few Sm-Nd measurements, reported by Sato and Tassinari (1997), were produced at the CPGeo-USP, by using the same instrument used for the Rb-Sr measurements. Sixteen measurements, reported by Andrade-Santos (2010), were later made in the same laboratory by employing 149Sm and 150Nd spikes, as well as elemental separation by AG50WX8 and LN Spec resins (Sato et al. 1995). All Sm-Nd analyses available for the studied area are included in Table 2.

Table 2: Sm-Nd analytical data. 

*T1: estimated age; NA: Not applicable.

Several U-Pb zircon ages, obtained by TIMS, were available from the works of Priem et al. (1982) and Gaudette and Olszewski (1985). Santos et al. (2000) and Ibañez et al. (2011) produced additional U-Pb ages by Pb evaporation, SHRIMP or LA-ICP-MS. All them are displayed in Table 3. Analytical procedures are provided in the respective references.

Table 3: U-Pb ages already available for the region, obtained by means of different methods. 

Number Location Rock type Method Age, MA Reference
8697-8679 Minícia Migmatite TIMS 1859 Gaudette and Olszewski 1985
6580-6085 Casiquiare River Tonalite SHRIMP 1834 ± 18 Tassinari et al. 1996
8699 Macabana Augen-gneiss TIMS 1823 Gaudette and Olszewski 1985
MS-63 Iã-Mirim River Monzogranite SHRIMP 1810 ± 09 Santos et al. 2000
PR-3215 Araracuara Syenogranite ICP-MS 1756 ± 08 Ibañez-Mejia et al. 2011
J-263 Araracuara Syenogranite ICP-MS 1732 ± 17 Ibañez-Mejia et al. 2011
UA-39 Uaupés River Qartz-diorite TIMS 1703 ± 07 Tassinari et al. 1996
CRJ-19 Apaporis River Syenogranite ICP-MS 1593 ± 06 Ibañez-Mejia et al. 2011
PR-3092 Apaporis River Syenogranite ICP-MS 1578 ± 27 Ibañez-Mejia et al. 2011
UAH-1216 Vaupés River Monzogranite ICP-MS 1574 ± 10 Ibañez-Mejia et al. 2011
PRA-4 Mitu Granite TIMS 1552 ± 34 Priem et al. 1982
AH-1419 Apaporis River Monzogranite ICP-MS 1530 ± 21 Ibañez-Mejia et al. 2011
PA-22 Papuri River Granite SHRIMP 1521 ± 13 Tassinari et al. 1996
AF-151 Içana River Two mica-granite Pb evap. 1521 ± 32 Almeida et al. 1997
AF-1 São Gabriel Granite with titanite TIMS 1518 ± 25 Santos et al. 2000
PRA-21 Guainia River Granite TIMS 1480 ± 70 Priem et al. 1982

For U-Pb dating in this work, zircon grains were extracted by standard crushing, milling, sieving (0.150 - 0.063 µm), Wilfley table, Franz and heavy liquid techniques. Extracted grains were set in an epoxy disk and polished to reveal half sections. Reflected, transmitted and cathodoluminescence (CL) images were obtained by SEM and XMAX CL detectors.

Eight U-Pb dates were obtained by SHRIMP II at the GeoLab-IGc-USP (Sato et al. 2014). Mounts were gold-coated, and dating was performed with the standard Temora2 for age reference and SL13 for uranium composition. Acquisition was obtained by following the procedure described in Williams (1998). Individual ages were determined from six successive MS scans. Correction for common Pb was made based on the measured 204Pb. The typical error component for 206Pb/238U ratios is less than 2%. Data were reduced by using SQUID 1.06. Concordia diagrams were plotted with ISOPLOT 4 (Ludwig 2009). Analytical results are included in Annex I.

Seven U-Pb zircon ages were determined by a Neptune ICP-MS instrument coupled with an excimer laser ablation system. Khan titanite standard was utilized for mass bias correction and the GJ standard was utilized for zircon. Residual common Pb was corrected by using the terrestrial composition reported by Stacey and Kramer (1975). Analytical results are included in Annex II. However, these U-Pb LA-ICP-MS analyses were done in 2009, at the very beginning of the use of our instrument, when we were still dealing with the calibration of it. Now we do not have the complete knowledge of the analytical conditions of that time, when the software was set up for detrital zircon and was not optimized for crystallization ages. The Concordia diagrams of Fig. 7 are rather odd. Several measurements indicate reverse discordance, which may have been caused by inadequate adjustment of the detectors, or to some inadequacy of the 204Pb correction, when the 204 peak may have been not properly stabilized, or perhaps to some Hg interference not detected. We are keeping the diagrams as they were produced in 2009, and the rather imprecise calculated ages are only used in this paper as indicators for the regional interpretation.

NEW U-Pb ZIRCON AGES

Figure 2 illustrates the study area and location of samples with U-Pb zircon ages, 15 of which were produced in this work. Cathodoluminescence (CL) images of some selected zircons dated by SHRIMP are shown in Figs. 4A to 4H. The resulting Concordia diagrams are provided in Figs. 5A to 5H.

Figure 4: Example of zircons dated by the shrimp method. (A) Sample J-36; (B) Sample J-127; (C) Sample PR-3141; (D) Sample EP-2; (E) Sample J-84; (F) Sample PR-3001; (G) Sample J-199; (H) Sample HB-667. 

Figure 5: Concordia diagrams for the samples dated by shrimp. (A) J-36 Paragneiss; (B) J-127 Orthogneiss; (C) PR-3141M Orthogneiss; (D) EP-2 Orthogneiss; (E) J-84 Monzogranite; (F) J-84 Monzogranite; (G) J-199 Orthogneiss; (H) HB-667 Monzogranite. 

J-36 - Muscovite-chlorite paragneiss - Vaupés River, near Mitú, Colombia

Sample J-36 is a fine-grained muscovite-chlorite paragneiss, with a granolepidoblastic structure and centimetric porphyroblasts of plagioclase. Zircons from this rock range in size from 70 to 220 µm and exhibit length to width ratios from 2:1 to 3:1. CL images reveal oscillatory zoning (e.g. zircon 10.1 of Fig. 4A). This rock is a paragneiss; however, only 13 zircons were dated, which is too few to analyse the statistical significance of the detrital zircons distribution. The Concordia diagram (Fig. 5A) shows that many of the analytical points are discordant. Only 5 of them are relatively close to the Concordia, with ages between 1800 and 1000 Ma. Zircons 4.1 (6/38 age of 2094 ± 17 Ma) and 13.1 (6/38 age of 2089 ± 16 Ma) indicate the possible existence of much older sources.

J-127 - Tonalitic orthogneiss - Caño Naquen, Guainia River, Colombia

Sample J-127 is a coarse-grained tonalitic orthogneiss with biotite, hornblende and some muscovite. Zircons are euhedral and well preserved, presenting a prismatic habit. The length to width ratios range from 0.5:1 to 4:1, and lengths range from 0.12 to 0.37 µm. CL images reveal a complex to well-developed oscillatory zoning (e.g.. zircons 7.1 and 1.1 of Fig. 4B. The Concordia diagram (Fig. 5B) indicates a good-quality crystallization age of 1775.3 ± 7.7 Ma (MSWD = 1.2, n = 16 ) for the protolith.

PR-3141 - Biotite gneiss - Caño Cuaubén, near Puerto Inírida, Colombia

Sample PR-3141 is a fine-grained foliated biotite gneiss, very likely an orthogneiss, with a granolepidoblastic structure. Zircons of this rock are euhedral with a prismatic to sub-rounded habit. They range in length from 0.150 to 0.290 µm, with length to width ratios from 2:1 to 3:1. CL images reveal a complex to well-developed oscillatory zoning in most of the grains (e.g. zircons 6.1 and 9.1 in Fig. 4C). The Concordia diagram (Fig. 5C) shows a few discordant grains, but 15 grains near the Concordia, yield an age of 1501.0 ± 9.5 Ma (MSWD = 1.08, n = 15), which can be attributed to magmatic crystallization.

EP-2 - Biotite-gneiss - Caquetá River, near Araracuara, Colombia

Sample EP-2 is a probable biotite-muscovite orthogneiss, with a fine-grained granoblastic structure. Zircons of this sample are euhedral to subhedral, mostly with a prismatic habit. They range in size from 0.1 to 0.3 µm and have length to width ratios from 1:1 to 3:1. CL images reveal mostly oscillatory zoning (e.g. zircon 2.1 of Fig. 4D). Some points are discordant in the Concordia diagram (Fig. 5D), but a group of 10 grains located very close to the Concordia indicate an age of 1721.0 ± 9.6 Ma (MSWD = 1.8, n = 10) which is attributed to the crystallization of the igneous protolith.

J-84 - Monzogranite - Raudal Morroco, Inírida River, Colombia

Sample J-84 is a coarse-grained faneritic monzogranite with centimetric K-feldspar. Zircons of this rock are euhedral with a prismatic to sub-rounded habit. They range in length from 110 to 370 µm, with length to width ratios from 2:1 to 7:1. CL images reveal either sector or oscillatory zoning in most of the grains (e.g. zircons 2.1 and 3.1 of Fig. 4E). The Concordia diagram (Fig. 5E) indicates discordance of several grains. However, the age calculation for 12 zircons near the upper intercept yield a reasonable crystallization age of 1507 ± 22 Ma (MSWD = 4.7, n = 13).

PR-3001 - Biotite-chlorite gneiss - Caño Cuduyarí, Vaupés River, near Mitú, Colombia

Sample PR-3001 is a coarse-grained biotite-chlorite gneiss, possibly an orthogneiss, with a granolepidoblastic structure. Zircons are euhedral to subhedral, and most have prismatic habit. They range in size from 110 to 400 µm and have length to width ratios from 1:1 to 3:1. CL images reveal mostly complex and well-developed oscillatory zoning (e.g. zircons 2.1 and 5.1 in Fig. 4F). In the Concordia diagram (Fig. 5F) zircons are mostly concordant. Age calculation of 12 selected zircon grains indicates a crystallization age of 1769 ± 33 Ma (MSWD = 1.9, n = 12).

J-199 - Biotite-hornblende orthogneiss - Negro river, north of San Carlos, Colombia/Venezuela

Sample J-199 is a biotite-hornblende orthogneiss rich in quartz, with a fine-grained lepidonematoblastic structure. Zircons from this rock range in size from 90 to 170 µm and have length to width ratios of less than 2:1. CL images reveal either sector or oscillatory zoning (e.g. zircons 6.1 and 3.1 in Fig. 4G). Zircons are mostly concordant. The age calculation for the Concordia diagram (Fig. 5G) indicates a quite precise crystallization age of 1796.1 ± 3.7 Ma (MSWD = 1.5, n = 12).

HB-667 - Monzogranite - Raudal Carurú, Vaupés River, near Iauaretê, Brazil/Colombia

Sample HB-667 is a coarse grained faneritic monzogranite with biotite, hornblende and centimetric microcline phenocrysts. Zircons of this rock are subhedral with a sub-rounded habit. They range in length from 100 to 400 µm, with length to width ratios from 1:1 to 3:1. CL images reveal a complex oscillatory zoning in most of the grains (e.g. zircons 6.1 and 4.1 of Fig. 4H). Analyses of 12 concordant zircons (Fig. 5H) indicates a precise crystallization age of 1778.8 ± 5.9 Ma (MSWD = 1.4, n = 12).

The following U-Pb dates, obtained by WS, were reported in a preliminary form by Andrade-Santos (2010). Figure 2 shows the locations of the samples. Figs. 4A to 4G provides CL images of some selected zircons, and Figs. 5A to 5G the resulting Concordia diagrams.

AH-1213A - Biotite-hornblende orthogneiss - Raudal Tucunaré, Vaupés, SE of Mitú, Colombia

Sample AH-1213A is a biotite-hornblende orthogneiss characterized by a fine to medium grained granoblastic structure, with some lepidoblastic portions. Zircons from this rock range in size from 100 to 390 µm, with length to width ratios ranging from 1.5:1 to 4:1. The zircons are generally anhedral to subhedral and medium rounded. CL images reveal sector zoning (e.g. zircon 12, Fig. 6A). Analyses of 26 zircons yield a crystallization age for the protolith of 1736 ± 19 Ma (MSWD = 0.08, Fig. 7A).

Figure 6: Example of zircons analysed by LA-ICP-MS method. (A) Sample AH-1213A; (B) Sample AH-1231; (C) Sample AH-1248; (D) Sample J-42; (E) Sample J-98; (F) Sample J-159; (G) Sample PR-3228. 

Figure 7: Concordia diagrams for the samples dated by LA-ICP-MS. (A) AH-1213A Orthogneiss; (B) AH-1231 Monzogranite; (C) AH-1248 Paragneiss; (D) J-42 Paragneiss; (E) J-98 Monzogranite; (F) PR-3001 Orthogneiss; (G) PR-3228 Paragneiss. 

AH-1231 - Monzogranite - Serrania Mitu, Colombia

Sample AH-1231 is a monzogranite with a medium to coarse-grained faneritic structure. Zircons are euhedral to subhedral, with a prismatic habit. They range in size from 200 to 400 µm and have length to width ratios from 1.5:1 to 2:1. CL images reveal mostly complex sector and oscillatory zoning (e.g. zircons 8 and 10 in Fig. 6B). Analyses of 23 selected zircons reveal concordance and a crystallization age of 1510 ± 26 Ma (MSWD = 0.15, Fig. 7B).

AH-1248 - Paragneiss - Caño Chaquita, Atabapo River, near Puerto Inírida

Sample AH-1248 is a paragneiss with a fine-grained structure and some muscovite. Zircons of this sample are euhedral, mostly with a prismatic habit. They range in size from 100 to 230 µm and have length to width ratios from 2:1 to 6:1. CL images reveal mostly oscillatory zoning (Fig. 6C). Analyses of 37 selected zircons reveal that most are discordant. Those close to the Concordia were plotted (Fig. 7C), with most being located between 1120 and 1550 Ma. One of the grains is located at about 650 Ma and its age and tectonic significance must be investigated further.

J-42 - Paragneiss - Mitú, Colombia

Sample J-42 is a paragneiss characterized by a medium to coarse-grained texture with some centimetric K-feldspar phenocrysts. Zircons of this rock are subhedral and medium rounded. They range in length from 120 to 260 µm, with length to width ratios from 1.5:1 to 2:1. CL images reveal sector and oscillatory zoning in most grains (e.g. zircons 13 and 9, Fig. 6D). Twenty-five detrital zircons were analyzed. Several grains are not far from the Concordia (Fig. 7D), located between 700 and 1900 Ma. Possible Neoproterozoic sources have not been identified in the area, and this metasedimentary unit must be investigated further.

J-98 - Monzogranite - Caño Nabuquén, Inírida River

Sample J-98 is a monzogranite comprised of medium- to coarse-grained faneritic rock. Zircons from this rock are mostly euhedral with a prismatic habit, sizes ranging from 100 to 320 µm, and length to width ratios from 1.6:1 to 3:1. CL images reveal oscillatory zoning in most grains with well preserved cores (e.g. zircon 2 in Fig. 6E). Twenty zircons were analysed, and a few of them are discordant. Fifteen grains close to the Concordia indicate a crystallization age of 1752 ± 21 MA (MSWD = 0.13, Fig. 7E)

J-159 - Tonalite - Serrania de Naquén, Guainia River, Colombia

Sample J-159 is a tonalite characterized by a medium to coarse-grained faneritic texture, with some muscovite. Zircons are mostly euhedral and well preserved, with a prismatic habit. Length to width ratios range from 1:1 to 3:1, and lengths range from 120 to 310 µm. CL images reveal a complex to well-developed oscillatory zoning (Fig. 6F). Analyses of 26 zircons revealed that most are concordant, with a crystallization age of 1770 ± 40 Ma (MSWD = 0.21, Fig. 7F).

PR-3228 - Paragneiss - Rio Mesai, Yarí, N of Araracuara, Colombia

Sample PR-3228 is a biotite gneiss, with microcline and some chlorite, characterized by a fine to medium granoblastic structure. Zircons of this rock are euhedral to subhedral with a prismatic habit. They range in length from 70 to 250 µm with length to width ratios from 1,3:1 to 4:1. CL images reveal a complex oscillatory zoning in most of the grains (e.g. zircon 3, Fig. 6G) and some complex sector zoning. Thirty-eight zircons were analyzed and plotted in Fig. 7G. Although most of the zircons are discordant, nine grains are nearly concordant and yield detrital ages between 1800 and 1300 Ma. Older grains were not found.

SAMARIUM-NEODYMIUM MEASUREMENTS

Twenty-two Sm-Nd model ages are currently available for the study region (see Fig. 2 for sample locations and Tab. 2 for the analytical data). Twelve of these samples (described above) were also dated by the U-Pb zircon method.

Most samples yield very similar paleoproterozoic TDM model ages (ca. 1.9 - 2.2 Ga, Tab. 2) although their U-Pb zircon ages varied within the 1800 - 1500 MA interval. Their calculated εNd(TDM) values were also similar (positive values of 3.0 - 3.5), suggesting formation from the same juvenile source material. Given that the εNd(T1) values of the granitoid rocks are near zero or slightly negative, the possible presence of much older source material is improbable. This finding reinforces the idea of accretion though subduction during the Proterozoic, as well as the presence of juvenile magmatic arcs in this part of the Rio Negro-Juruena province.

There is marked similarity in all trends in the Nd isotopic evolution diagram for the 11 granitoid rocks dated by the U-Pb zircon method (Fig. 8). Rocks with ages in the 1800 - 1750 Ma range exhibit εNd(T1) values close to zero, but 2 younger rocks (J-84 and PR-3141, ages around 1550 Ma) have moderately negative values. We suggest that these younger granitic rocks could have originated from the melting or complete reworking of the accretionary crustal material that formed about 200 to 250 Ma earlier.

Figure 8: Nd evolution diagram. 

INTERPRETATION OF THE RADIOMETRIC AGES

General remarks

A total of 97 granites, gneisses and migmatites within the studied region were analysed by the Rb-Sr method and selected for further interpretation (Fig. 3, Tab. 1). Some of the analyses were performed recently by the CPGeo-USP, but most of them were taken from the literature (Gaudette and Olszewski 1985, Priem et al.1982, Barrios et al.1985, Fernandes et al.1976, Pinheiro et al. 1976). An interpretative exercise was made to verify the possible temporal relationship among granitoid rocks located close enough to have been subjected to the same geological history. Potentially related samples were identified in eight areas (different colors in Fig. 3, Ventuari River, Atabapo River, Negro-Casiquiare Rivers, Puerto Inírida, San Carlos, Mitu-Iauaretê, Caquetá River and São Gabriel + Içana River).

Analytical points of the potentially related samples were included in isochron diagrams (Fig. 9A-H), each of which obtained in different works from different laboratories, with different equipment and precision levels. To "normalize" the calculations, we fixed the same values to the experimental errors of the calculated 87Rb/86Sr (3%) and 87Sr/86Sr (0.25%) results. This approach should minimize the preference for precise analytical results during the Isoplot calculations. As the granitoid samples in each diagram are not strictly cogenetic, the calculated isochron ages should be viewed as rough approximations for interpreting the overall tectonic history. Analytical points in all diagrams (Fig. 9) show reasonable alignments. As the calculated best-fit lines could be broadly interpreted as "isochron ages", with probable geological significance, they are referred as "reference isochrons". We speculate that these lines indicate, for each area, a regional event of Sr homogenization for the whole-rock system.

Figure 9: Rb-Sr whole-rock isochron diagrams. (A) Ventuari River; (B) Atabapo River; (C) Negro and Casiquiare rivers; (D) Puerto Inírida; (E) San Carlos; (F) Mitú-Iauaretê; (G) Caquetá River; (H) San Gabriel + Içana River. 

Atabapo belt

Gaudette and Olszewski (1985) collected seven samples of granitic-migmatitic rocks from the NE part of the study area along the Ventuari River between Minicia and Macabana (Venezuela). These rocks are located along a reference isochron of 1837 ± 87 Ma, with a low initial 87Sr/86Sr ratio of 0.7021 (Fig. 9A). Analysis of the same rocks by U-Pb zircon (TIMS) revealed concordant values of 1859 Ma at Minicia and 1823 Ma at Macabana (Tab. 3). Several authors (Gaudette and Olszewski 1985, Priem et al. 1982, Barrios et al.1985), collected 17 samples of granitoid rocks along the Atabapo River (Tab. 1). Their isochron diagram (Fig. 9B) indicated an apparent age of 1749 ± 92 Ma, with an initial 87Sr/86Sr ratio of 0.7073. A similar age span (1787 ± 53 Ma), with an initial 87Sr/86Sr ratio of 0.7025 (Fig. 9C), was obtained for samples from the Negro and Casiquiare Rivers, by Priem et al. (1982), Gaudette and Olszewski (1985), and the present work (Tab. 1).

Four isolated samples of granitoid rocks collected along the Inírida and Guainia Rivers yielded precise U-Pb zircon ages in the same range (Fig. 2, Tab. 3): J98(1772 ± 15 Ma), J-127 (1772 ± 4 Ma), J-159 (1785 ± 6 Ma) and J-199 (1796 ± 4 Ma). Considering the isolated U-Pb zircon ages and the Rb-Sr reference isochrones (Fig. 9B and 9C), we provisionally name this granitoid region of the Rio Negro-Juruena province as the "Atabapo belt". We propose that a series of orogenic pulses, lasting at least 60 Ma, from 1800 to 1740 Ma, in the late Paleoproterozoic (Statherian), was responsible for the development of this belt in the NE part of the study area.

We constructed another isochron diagram (Fig. 9D) from data of six samples of a non-deformed granite (Priem et al. 1982), and one sample of the present work (Tab. 1), obtained within the same corner near Puerto Inírida. The apparent age of these samples was 1476 ± 68 Ma, with an initial 87Sr/86Sr ratio of 0.7064. One sample of the present work (Tab. 1) and seven previously obtained granitic samples (Gaudette and Olszewski 1985, Priem et al. 1982, Barrios et al. 1985), all collected near the town of San Carlos at the Negro River, yielded an age of 1521 ± 52 Ma, with an initial 87Sr/86Sr ratio of 0.7051 (Fig. 9E). Three isolated granitic samples within the same region were dated by the U-Pb method (PR-3141: 1500 ± 9 Ma, J-84: 1507 ± 19 Ma, and PRA-2: 1480 ± 70 Ma; Tab. 3). The results confirm the intrusive age of some granitic intrusions into the Atabapo belt at about 1500 Ma, within the Mesoproterozoic (Calymmian).

Vaupés belt

Priem et al. (1982), Pinheiro et al. (1976) and Santos (2003) obtained and dated 27 samples of granitoid rocks from central area of the study region, between the villages of Mitú, Colombia, and Iauaretê, Brazil. A few samples from the same area were analysed by us (Tab. 1). A reference isochron (Fig. 9F) seems to indicate a mesoproterozoic ( calymmian) Sr homogenization event at 1529 ± 43 Ma with an initial 87Sr/86Sr ratio of 0.7067. Within the same area, there are 8 U-Pb zircon ages (see Fig. 2 and Tab. 3). Four of them are clearly older, and have statherian apparent ages (AH-1213A: 1746 ± 8 Ma; PR-3001: 1740 ± 5 Ma; J-36: 1739 ± 38 Ma; HB-667: 1778 ± 4 Ma), whereas the 4 other are within the same age range as the Rb-Sr isochron (AH-1231: 1555 ± 7 Ma; AH-1216: 1574 ± 10 Ma; PA-SP-22: 1521 ± 13 Ma; PRA-4: 1552 ± 34 Ma). In this region, the younger granitoid rocks are described as calc-alkaline syntectonic gneisses and migmatites affected by medium-level amphibolite facies metamorphism (Priem et al. 1982, Santos 2003). Thus, we may conclude that the results of the Rb-Sr systematics indicate an episode of Sr isotopic homogenization of mesoproterozoic age related to that specific orogenic pulse.

We provisionally name this area "Vaupés belt". We postulate that the belt developed from a series of orogenic pulses in the Calymmian, with duration of at least 60 Ma, between 1580 and1520 Ma. Older statherian granitoid rocks in the region (U-Pb zircon age ~ 1750 Ma) may be considered as basement inliers. These rocks must have been involved within the younger calymmian metamorphism. A few younger and undeformed granitic rocks, whose points lie within the same reference isochron, could represent post-tectonic granitic batholiths.

Four samples by Priem et al. (1982) and one by us were obtained from the SW of the study area, near Araracuara. The reference isochron with these samples indicated an apparent age of 1557 ± 41 Ma, with an initial 87Sr/86Sr ratio of 0.7050 that was fixed in the age calculation (Fig. 9G). Older ages in the same area were obtained by Ibañez et al. (2011) from two syenogranitic gneisses (PR-3215: 1756 ± 8 Ma; J-263: 1732 ± 17 Ma) and sample EP-2 from this work 1725 ± 10 MA (Fig. 2 and Tab. 3). As was the case in the central Mitú-Iauaretê region, these older rocks could represent statherian basement rocks within younger mesoproterozoic metamorphic gneisses. However, for the same region, along the Apaporis river, the same authors encountered three other rocks with younger ages (CRJ-19: 1593 ± 6 Ma; PR-3092: 1578 ± 27 Ma; AH-1419: 1530± 21 Ma), reinforcing the idea of the existence of a Vaupés tectonic-metamorphic belt of calymmian age.

Regional thermal evolution

The initial Sr87/Sr86 ratios encountered in the reference isochrones of Figs 9A to 9G (0.702 - 0.708), are considered relatively low and indicate an important participation of juvenile material. This possibility is supported by the Sm-Nd systematics. The only exception to the relatively low initial ratios was observed for samples from the Brazilian region along the Içana River and near the town of São Gabriel da Cachoeira (Fig. 9H). In this case, the reference isochron of 11 points yielded an apparent age of 1203 ± 58 Ma with a very high initial 87Sr/86Sr close to 0.72. This age, much younger than what was encountered for most domains within the study area, should be related to a very strong regional heating that imposed Sr isotopic redistribution in the whole-rock samples. This condition seems to have been localized to an elongated area separating the Atabapo and Vaupés belts (Fig.3), affected respectively by metamorphic belts with statherian and calymmian age.

About 100 K-Ar measurements, predominantly from micas, were made a few decades ago in rock samples from the study area. Complete analytical data of these measurements and sample locations can be found in Priem et al. (1982) for Colombia, Barrios et al. (1985) for Venezuela and Tassinari (1996) for Brazil. A histogram of all available apparent K-Ar ages (Fig.10) reveals that the ages are concentrated within the 1200 - 1400 Ma interval. This result reflects regional heating above 350 - 400oC, which affected the entire territory of Figure 2 and beyond, covering much of the Amazonian Craton. This regional heating was first observed in the 1960's (Priem et al. 1971) and is called the Nickerie thermo-tectonic episode in Suriname and K'Mudku in the Guyana Republic (Gibbs, Barron 1993). Cordani et al. (2010) attempted a comprehensive review and tentative interpretation of this major intraplate heating episode, whose duration may have been of 100-to-200 Ma. It is clear that this mesoproterozoic thermal episode was pervasive and widespread in the Amazonian Craton.

Figure 10: Histogram of K-Ar ages on micas. 

TECTONIC HISTORY OF THE NW AMAZONIAN CRATON

General considerations

Robust geochronological tools are required when synthesizing the tectonic evolution of a very large region where basic geologic information is quite rare. Here, we employ four radiometric methods, each with its own interpretative value and tectonic significance. U-Pb measurements, either SHRIMP, ICP or TIMS, are essential for any geochronological work, because they produce significant punctual ages. However, alone, these measurements do not provide an entire geological history. They may indicate several magmatic events localized in time, but not their integration into a complete regional tectonic evolution. Rb-Sr whole-rock isochrones are less precise, but they indicate the timing of relevant episodes of Sr isotopic homogenization, related to medium- to high-grade metamorphic episodes. Sm-Nd model ages give insight into the type of the regional tectonic processes (e.g. intraplate or subduction-related, accretionary or collisional, juvenile or reworked). Finally, K-Ar ages, especially of micas, are related to the final cooling of the region, usually with respect to the principal episode of cratonization, or, alternatively, to some episodes of major intraplate crustal heating above 350 - 400oC.

According to Cordani and Teixeira (2007), the Rio Negro-Juruena tectonic province of the Amazonian Craton (1.78 - 1.55 Ma) was formed by continued soft-collision/accretion processes driven by subduction, which produce a very large "basement" with the predominance of granitoid rocks, many of them with a juvenile-like Nd isotopic signature. Clear evidence of archean or paleoproterozoic basement has not yet been found in this region. This province is considered to be basically accretionary, formed from the complex juxtaposition of tectonic units, including intra-oceanic material, but also containing Cordilleran-type granites, collisional-type belts, volcanic-sedimentary basins, as well as post-tectonic and anorogenic-type complexes.

Summary of the tectonic history

Considering the geochronological pattern encountered in the Atabapo belt, we agree with Gaudette and Olszewski (1985), Barrios et al. (1985) and Cordani et al. (2000) that the possible NE boundary of the Rio Negro-Juruena province with the older Ventuari-Tapajós province would be located close to or along the Atabapo River (Fig. 2 and 3). The U-Pb zircon SHRIMP measurements indicate the formation of a series of statherian magmatic arcs in that region, in which juvenile and possibly intra-oceanic material predominates. Closely related to subduction, these magmatic arcs piled up by soft-collision episodes and successive stacking from SW to NE, encompassing a period of about 60 Ma.

In the SW region, comprising the Mitú-Iauaretê and Caquetá River areas, calymmian granitic and gneissic rocks formed between 1580 and 1500 Ma within the Vaupés belt. These calymmian ages can be confirmed by the U-Pb zircon ICP-MS ages obtained by Ibañez et al. (2011) on granitic rocks collected along the Apoporis River (see Fig. 2), well inside the younger belt. Results of the Sm-Nd systematics for rocks of the Vaupés belt indicate the presence of substantial juvenile material. An important time-gap of 150-to-200 Ma exists between the youngest rocks of the Atabapo belt (1740 Ma) and the oldest rocks of the Vaupés belt (1580 Ma). The latter are products of a second orogenic pulse within the same Rio Negro-Juruena tectonic province. Thus, there is ample time for cratonization of the first series of tectonic belts before the stacking of the second series of possibly accretionary belts in Mesoproterozoic time. At the NE corner, a cratonized 1740 - 1800 Ma basement was intruded by granitic batholiths at 1550 Ma, which may correspond to the reflection of the orogenic pulse occurring at that time to the SW. However, at the SW corner, the second 1580 - 1500 Ma orogenic pulse includes parts of possibly retrogressed basement inliers with ages of about 1750 Ma.

Gorayeb et al. (2005) showed that the NW part of the Rio Negro-Juruena province continues to the SE below the Solimões sedimentary basin, where its basement presents a few U-Pb zircon evaporation ages in the 1800 - 1550 Ma range. Geochronological control in the SE half of the province, in Mato Grosso, Brazil, shows that the ages of the granitoid rocks decrease from NNE to SSW. Near the boundary with the older Ventuari-Tapajós province, in the region of Alta Floresta, Santos (2003) encountered ages of 1780 Ma in the São Romão and São Pedro granites. On the other side, near the border with the Rondonian-San Ignacio belt, in the Alto Jauru region of Mato Grosso, Geraldes et al. (2001) reported the age of the Cachoeirinha magmatic arc as 1590 Ma. We found a comparable age pattern for the NW part of the Amazonian Craton (Fig. 3), where calc-alkaline orogenic type rocks yielded ages of 1800-to-500 Ma, decreasing from the NE (Atabapo belt) to the SW (Vaupés belt).

Thermal history

Finally, a peculiar but remarkable aspect of the tectonic evolution of this area is the widespread Nickerie-K'Mudku intraplate mid-proterozoic regional heating. This phenomenon affected all the rock units of the study area, from about 1400-to-1200 Ma (see histogram of Fig. 10). This regional heating episode, with temperatures exceeding 300oC, was uniform and affected the entire crust of the study area. The episode affected very large parts of the Amazonian Craton, and its duration may have been on the order of 100 - 200 Ma. All the rock ages determined by U-Pb zircon measurements are much older (1800 - 1500 Ma). Regardless of their ages, all rocks were affected in the same way. Therefore, none of the K-Ar apparent ages likely represents a primary magmatic age of the corresponding dated rock. Considering the Rb-Sr systematics of the region, the Rb-Sr reference isochron age (1200 ± 60 Ma) and the high initial 87Sr/86Sr ratio (~ near 0.720; Fig. 3 and 9G), we can make some additional speculations from the K-Ar ages. Rocks in the area of São Gabriel da Cachoeira and the Içana River, in NW Brazil, are well within the Rio Negro-Juruena province, and very likely have primary ages between 1800 and 1500 MA, as suggested by the U-Pb zircon ages. However, the rocks were perhaps heated to as high as 600oC, which would be necessary to produce the observed widespread Sr isotopic homogenization in the whole-rock systems. This very high heating event seems to have been restricted to the territory located more or less between the Atabapo and Vaupés belts (see Fig. 3).

CONCLUSIONS

From the currently available data, we suggest the following possible tectonic-thermal history for the overall region:

  • 1. Formation of the first orogenic pulse of the province, the Atabapo belt, with stacking of magmatic arcs of the Atabapo-Negro-Casiquiare region against the cratonic area formed by the Ventuari-Tapajós continent, at 1800 - 1740 Ma.

  • 2. Formation of the second orogenic pulse related to the Vaupés belt, with stacking of the Mitú-Iauretê and Caquetá magmatic arcs against the already cratonized area of the first pulse, at 1580 - 1500 Ma.

  • 3. Onset of the Nickerie-K'Mudku intraplate regional heating to above 300oC within the entire region at 1200 - 1300 Ma, but attaining 600oC in the belt separating the first (Atabapo) and second (Vaupés) orogenic pulses.

  • 4. The probable existence of younger metasedimentary units such as the paragneisses J-36, J-42, AH-1248 and PR-3228, which contain young detrital zircons of meso and neoproterozoic age, should be investigated.

ACKNOWLEDGEMENTS

We acknowledge help received from the staff of the Geochronology Research Center (CPGeo -USP), especially Ivone Sonoki for geochronological calculations and Vasco Loios for zircon s eparation. We thank geologist Guilherme Andrade Santos for his aid during the preliminary phase of the work. W.R. Van Schmus and M. Ibañez-Mejia are acknowledged for their much appreciated and important revision of the original version of our manuscript. INGEOMINAS of Colombia provided the samples and valuable geological information for this research. Financial support was received from FAPESP through grant 2013/12754-0 to UGC.

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Annex I

Annex I: Isotope ratio data for samples analysed by LA-ICP-MS method. 

Sample Spot Ratios Ages 206/238
207/235 1σ err 206/238 1σ err coef. corr 238/206 1σ err 207/206 1σ err 208/206 1σ err T206/238 1σ err T207/206 1σ err 207/206
AH1213A 9.1 4.3892 0.1505 0.2985 0.0031 0.940 3.3504 0.0342 0.1067 0.0034 0.2088 0.0043 1.684 0.015 1.743 0.059 96
AH1213A 11.1 4.4771 0.1615 0.3002 0.0033 0.600 3.3316 0.0367 0.1082 0.0039 0.1005 0.0273 1.692 0.016 1.769 0.065 95
AH1213A 12.1 4.4426 0.1415 0.3007 0.0028 0.920 3.3257 0.0312 0.1072 0.0031 0.1707 0.0728 1.695 0.014 1.752 0.054 96
AH1213A 3.1 4.4305 0.1466 0.3022 0.0029 0.960 3.3091 0.0323 0.1063 0.0033 0.0642 0.0024 1.702 0.015 1.737 0.056 97
AH1213A 4.1 4.4941 0.1577 0.3061 0.0032 0.840 3.2669 0.0343 0.1065 0.0036 0.1860 0.0089 1.721 0.016 1.740 0.062 98
AH1213A 13.1 4.5635 0.1892 0.3139 0.0040 0.660 3.1862 0.0407 0.1055 0.0044 0.1462 0.0255 1.760 0.020 1.722 0.076 102
AH1213A 8.1 4.3386 0.1450 0.2947 0.0029 0.920 3.3936 0.0332 0.1068 0.0032 0.2295 0.0115 1.665 0.014 1.745 0.055 95
AH1213A 7.1 4.5632 0.1486 0.3087 0.0030 0.830 3.2399 0.0312 0.1072 0.0033 0.1839 0.0278 1.734 0.015 1.753 0.056 98
AH1213A 5.1 4.4900 0.1499 0.3088 0.0031 0.940 3.2387 0.0321 0.1055 0.0034 0.1804 0.0474 1.735 0.015 1.722 0.060 100
AH1213A 1.1 4.6893 0.1520 0.3212 0.0031 0.970 3.1133 0.0297 0.1059 0.0033 0.0560 0.0033 1.796 0.015 1.730 0.057 103
AH1213A 16.1 4.6858 0.1311 0.3223 0.0035 0.940 3.1023 0.0340 0.1054 0.0028 0.1857 0.0110 1.801 0.017 1.722 0.049 104
AH1213A 17.1 4.6575 0.1364 0.3227 0.0037 0.900 3.0988 0.0355 0.1047 0.0030 0.1521 0.0417 1.803 0.018 1.709 0.052 105
AH1213A 10.1 4.7158 0.1506 0.3231 0.0030 0.780 3.0951 0.0289 0.1059 0.0031 0.2427 0.0151 1.805 0.015 1.729 0.055 104
AH1213A 12.2 4.7058 0.1211 0.3243 0.0032 0.570 3.0831 0.0303 0.1052 0.0026 0.2174 0.0201 1.811 0.016 1.718 0.045 105
AH1213A 20.2 4.7240 0.1296 0.3262 0.0035 0.660 3.0652 0.0325 0.1050 0.0027 0.2032 0.0035 1.820 0.017 1.715 0.048 106
AH1213A 19.1 4.7352 0.1239 0.3288 0.0033 0.880 3.0413 0.0303 0.1044 0.0026 0.0795 0.0070 1.833 0.016 1.705 0.045 107
AH1213A 21.1 4.7694 0.1408 0.3299 0.0039 0.940 3.0312 0.0357 0.1049 0.0030 0.0616 0.0657 1.838 0.019 1.712 0.053 107
AH1213A 20.1 4.7958 0.1337 0.3317 0.0036 0.890 3.0152 0.0327 0.1049 0.0028 0.1516 0.0099 1.846 0.017 1.712 0.050 107
AH1213A 10.2 4.8165 0.1201 0.3333 0.0032 0.990 2.9999 0.0284 0.1048 0.0025 0.2440 0.0453 1.855 0.015 1.711 0.044 108
AH1213A 18.1 4.8432 0.1266 0.3338 0.0034 0.970 2.9956 0.0301 0.1052 0.0026 0.2042 0.0045 1.857 0.016 1.718 0.046 108
AH1213A 13.2 4.9062 0.1458 0.3352 0.0040 0.960 2.9832 0.0352 0.1061 0.0031 0.1291 0.0184 1.864 0.019 1.734 0.054 107
AH1213A 14.1 4.9491 0.1284 0.3384 0.0034 0.990 2.9555 0.0298 0.1061 0.0027 0.2513 0.0346 1.879 0.017 1.733 0.047 108
AH1213A 11.2 4.9057 0.1432 0.3395 0.0039 0.970 2.9459 0.0341 0.1048 0.0031 0.1282 0.0151 1.884 0.019 1.711 0.054 110
AH1213A 15.1 5.0493 0.1352 0.3471 0.0036 0.960 2.8808 0.0302 0.1055 0.0027 0.1168 0.0255 1.921 0.017 1.723 0.048 111
AH1213A 6.1 4.3024 0.1376 0.2898 0.0028 0.370 3.4501 0.0336 0.1077 0.0033 0.2560 0.0032 1.641 0.014 1.760 0.057 93
AH1213A 2.1 3.7228 0.1492 0.2706 0.0033 0.880 3.6957 0.0445 0.0998 0.0040 0.0758 0.0247 1.544 0.016 1.620 0.072 95
AH 1231 13.1 3.4623 0.1005 0.2669 0.0029 0.860 3.7461 0.0402 0.0941 0.0025 0.2184 0.0887 1.525 0.015 1.510 0.051 101
AH 1231 4.3 3.4966 0.1142 0.2669 0.0031 0.890 3.7472 0.0438 0.0950 0.0030 0.3226 0.0533 1.525 0.016 1.529 0.060 99
AH1231 7.1 3.3965 0.2637 0.2667 0.0040 0.530 3.7499 0.0569 0.0924 0.0075 0.5288 0.0169 1.524 0.021 1.475 0.151 103
AH1231 1.1B 3.2974 0.2081 0.2718 0.0033 0.840 3.6786 0.0443 0.0880 0.0059 0.2046 0.0224 1.550 0.017 1.382 0.130 112
AH 1231 15.1 3.5769 0.1154 0.2735 0.0032 0.780 3.6567 0.0430 0.0949 0.0028 0.3062 0.0531 1.558 0.016 1.525 0.056 102
AH 1231 8.2 3.5681 0.1054 0.2741 0.0030 0.930 3.6484 0.0400 0.0944 0.0026 0.1442 0.0685 1.562 0.015 1.516 0.051 102
AH 1231 9.1 3.5838 0.1083 0.2744 0.0030 0.800 3.6439 0.0404 0.0947 0.0027 0.2152 0.0839 1.563 0.015 1.522 0.054 102
AH 1231 6.2 3.6575 0.2077 0.2750 0.0051 0.370 3.6364 0.0678 0.0965 0.0058 0.3662 0.0210 1.566 0.026 1.557 0.113 100
AH 1231 12.1 3.6004 0.1679 0.2755 0.0043 0.520 3.6303 0.0565 0.0948 0.0046 0.3525 0.0120 1.568 0.022 1.524 0.091 102
AH 1231 7.2 3.6374 0.1325 0.2770 0.0035 0.960 3.6099 0.0461 0.0952 0.0033 0.3690 0.0171 1.576 0.018 1.533 0.065 102
AH 1231 10.1 3.6636 0.1434 0.2783 0.0038 0.730 3.5926 0.0489 0.0955 0.0037 0.4439 0.0353 1.583 0.019 1.537 0.071 102
AH 1231 1.3 3.6444 0.1996 0.2795 0.0051 0.860 3.5777 0.0657 0.0946 0.0056 0.5027 0.0624 1.589 0.026 1.519 0.115 104
AH1231 2.1 3.6879 0.2044 0.2851 0.0026 0.980 3.5077 0.0319 0.0938 0.0052 0.2085 0.0050 1.617 0.013 1.505 0.104 107
AH 1231 11.1 3.6759 0.1043 0.2826 0.0030 0.950 3.5392 0.0377 0.0944 0.0025 0.1908 0.0655 1.604 0.015 1.515 0.049 105
AH 1231 14.1 3.5750 0.1042 0.2742 0.0030 0.980 3.6469 0.0393 0.0946 0.0025 0.1895 0.0676 1.562 0.015 1.519 0.051 102
AH1231 3.1 3.8222 0.2374 0.2901 0.0033 0.160 3.4473 0.0398 0.0956 0.0060 0.1232 0.0386 1.642 0.017 1.539 0.124 106
AH1231 2.2 1.6920 0.1370 0.1430 0.0022 0.550 6.9950 0.1063 0.0858 0.0070 0.4270 0.0723 0.861 0.012 1.335 0.156 64
AH1231 4.2 3.1451 0.1859 0.2465 0.0024 0.960 4.0574 0.0400 0.0926 0.0053 0.1447 0.0381 1.420 0.012 1.479 0.109 96
AH1231 4.1 3.2009 0.1919 0.2498 0.0026 0.610 4.0029 0.0422 0.0929 0.0057 0.1463 0.0098 1.438 0.014 1.486 0.117 96
AH 1231 16.1 2.8970 0.0846 0.2272 0.0024 0.990 4.4022 0.0472 0.0925 0.0025 0.2449 0.0105 1.320 0.013 1.478 0.051 89
AH1231 1.2N 3.7190 0.4141 0.2860 0.0077 0.190 3.4966 0.0937 0.0943 0.0127 0.3542 0.0479 1.621 0.039 1.514 0.260 107
AH1231 8.1 3.9770 0.4464 0.2887 0.0078 0.640 3.4637 0.0933 0.0999 0.0124 0.4023 0.0413 1.635 0.039 1.622 0.246 100
AH1231 6.1 3.0984 0.2348 0.2777 0.0039 0.010 3.6011 0.0505 0.0809 0.0064 0.3837 0.0319 1.580 0.020 1.220 0.157 129
AH 1248 27.1 2.6027 0.1252 0.2195 0.0040 0.999 4.5552 0.0840 0.0860 0.0045 0.0993 0.0323 1.279 0.022 1.338 0.104 95
AH 1248 15.1 2.7574 0.0560 0.2239 0.0021 0.990 4.4655 0.0412 0.0893 0.0020 0.2537 0.0357 1.303 0.011 1.411 0.044 92
AH 1248 8.2 2.6882 0.0529 0.2255 0.0020 0.760 4.4340 0.0401 0.0864 0.0018 0.1131 0.0105 1.311 0.011 1.348 0.041 97
AH 1248 16.1 2.8489 0.0646 0.2276 0.0024 0.990 4.3940 0.0454 0.0908 0.0019 0.1050 0.0240 1.322 0.012 1.442 0.040 91
AH 1248 5.3 3.5078 0.0801 0.2705 0.0028 0.920 3.6973 0.0388 0.0941 0.0023 0.3393 0.0270 1.543 0.014 1.509 0.046 102
AH 1248 21.1 3.5092 0.0693 0.2757 0.0026 0.900 3.6269 0.0342 0.0923 0.0019 0.0866 0.0710 1.570 0.013 1.474 0.040 106
AH 1248 5.2 3.6181 0.0810 0.2776 0.0028 0.990 3.6028 0.0365 0.0945 0.0024 0.5054 0.1721 1.579 0.014 1.519 0.048 103
AH 1248 28.1 0.9198 0.0532 0.1075 0.0022 0.830 9.2985 0.1925 0.0620 0.0035 0.8023 0.1539 0.658 0.013 0.675 0.115 97
AH1248 1.1 2.0763 0.0932 0.1904 0.0021 0.960 5.2519 0.0585 0.0791 0.0038 0.4334 0.0841 1.124 0.012 1.174 0.112 95
AH 1248 22.1 2.1424 0.1203 0.1941 0.0039 0.880 5.1517 0.1023 0.0800 0.0046 0.1147 0.0517 1.144 0.021 1.198 0.116 95
AH 1248 17.1 3.3368 0.0652 0.2636 0.0024 0.360 3.7938 0.0338 0.0918 0.0019 0.1028 0.0516 1.508 0.012 1.464 0.041 103
AH 1248 19.1 0.5142 0.0127 0.0570 0.0006 0.970 17.5393 0.1870 0.0654 0.0016 0.0648 0.0146 0.357 0.004 0.787 0.050 45
AH 1248 23.1 0.5174 0.0347 0.0731 0.0017 0.950 13.6830 0.3264 0.0513 0.0031 0.3040 0.0414 0.455 0.010 0.256 0.137 177
AH 1248 1.2 1.4083 0.0938 0.1192 0.0029 0.980 8.3870 0.2073 0.0857 0.0061 0.5170 0.0834 0.726 0.017 1.331 0.143 54
AH 1248 24.1 1.4580 0.1039 0.1385 0.0034 0.980 7.2213 0.1787 0.0764 0.0047 0.2162 0.0689 0.836 0.019 1.105 0.121 75
AH 1248 15.2 1.5525 0.1207 0.1468 0.0039 0.980 6.8109 0.1802 0.0767 0.0049 0.3055 0.0364 0.883 0.021 1.113 0.121 79
AH 1248 17.2 1.7359 0.1106 0.1514 0.0035 0.800 6.6052 0.1532 0.0832 0.0051 0.1521 0.0408 0.909 0.020 1.273 0.118 71
AH 1248 20.1 1.2965 0.0383 0.1519 0.0018 0.840 6.5842 0.0797 0.0619 0.0018 0.1032 0.0416 0.911 0.010 0.671 0.066 135
AH 1248 25.1 1.7489 0.1193 0.1635 0.0041 0.960 6.1161 0.1524 0.0776 0.0045 0.1650 0.0220 0.976 0.022 1.136 0.113 85
AH 1248 14.1 2.2216 0.0452 0.1839 0.0017 0.850 5.4385 0.0509 0.0876 0.0019 0.3575 0.3714 1.088 0.009 1.374 0.042 79
AH 1248 12.1 2.1552 0.0542 0.1867 0.0022 0.940 5.3559 0.0621 0.0837 0.0018 0.1021 0.0150 1.104 0.011 1.286 0.042 85
AH 1248 26.1 2.1568 0.1129 0.1896 0.0036 0.980 5.2733 0.1006 0.0825 0.0047 0.1702 0.1228 1.119 0.020 1.257 0.121 89
AH 1248 13.1 2.3148 0.0510 0.1987 0.0020 0.660 5.0334 0.0496 0.0845 0.0018 0.1299 0.1006 1.168 0.010 1.304 0.041 89
AH1248 4.1 1.9494 0.0847 0.2236 0.0022 0.970 4.4725 0.0447 0.0632 0.0026 0.0455 0.0077 1.301 0.012 0.716 0.086 181
AH 1248 29.1 2.2456 0.1414 0.2256 0.0051 0.910 4.4317 0.1005 0.0722 0.0041 0.3780 0.0620 1.312 0.027 0.991 0.114 132
AH1248 8.1 1.9075 0.0816 0.2336 0.0022 0.640 4.2804 0.0403 0.0592 0.0025 0.0976 0.0173 1.353 0.011 0.575 0.090 235
AH1248 11.1 2.5229 0.1108 0.2733 0.0026 0.010 3.6584 0.0353 0.0669 0.0029 0.1916 0.0352 1.558 0.013 0.836 0.092 186
AH1248 2.1 2.5165 0.1103 0.2735 0.0027 0.730 3.6559 0.0365 0.0667 0.0028 0.1505 0.0565 1.559 0.014 0.829 0.086 187
AH1248 5.1 3.1815 0.1670 0.2758 0.0033 0.960 3.6262 0.0438 0.0837 0.0043 0.2857 0.0410 1.570 0.017 1.285 0.098 122
AH1248 9.1 2.5528 0.1216 0.2867 0.0030 0.900 3.4876 0.0359 0.0646 0.0031 0.1155 0.0058 1.625 0.015 0.760 0.101 213
AH 1248 18.1 3.1811 0.0613 0.2885 0.0026 0.900 3.4667 0.0312 0.0800 0.0017 0.1760 0.0505 1.634 0.013 1.197 0.047 136
AH 1248 2.2 3.1259 0.1857 0.2899 0.0062 0.900 3.4491 0.0734 0.0782 0.0045 0.0696 0.0063 1.641 0.031 1.152 0.114 142
AH1248 10.1 3.1388 0.1773 0.2935 0.0037 0.930 3.4072 0.0433 0.0776 0.0045 0.3933 0.0790 1.659 0.019 1.136 0.116 146
AH1248 7.1 3.4501 0.1561 0.3032 0.0031 0.999 3.2984 0.0342 0.0825 0.0034 0.0330 0.0107 1.707 0.015 1.258 0.081 135
AH 1248 21.2 3.6313 0.2122 0.3031 0.0063 0.990 3.2990 0.0682 0.0869 0.0050 0.0730 0.0791 1.707 0.031 1.358 0.109 125
J42 1.2 4.7215 0.2119 0.3177 0.0037 0.999 3.1478 0.0369 0.1078 0.0044 0.0658 0.0037 1.778 0.018 1.762 0.075 100
J42 1.1 4.7981 0.2020 0.3188 0.0036 0.999 3.1372 0.0352 0.1092 0.0047 0.1133 0.0297 1.784 0.018 1.786 0.079 99
J 42 2.2 4.9001 0.1492 0.3219 0.0027 0.950 3.1070 0.0257 0.1104 0.0033 0.1864 0.0116 1.799 0.013 1.806 0.053 99
J 42 19.2 4.9645 0.1530 0.3335 0.0029 0.990 2.9982 0.0257 0.1080 0.0034 0.1387 0.0193 1.856 0.014 1.765 0.059 105
J 42 16.1 5.0756 0.1448 0.3423 0.0026 0.950 2.9215 0.0225 0.1075 0.0030 0.1556 0.0045 1.898 0.013 1.758 0.051 107
J 42 15.1 5.2269 0.1760 0.3427 0.0032 0.999 2.9181 0.0273 0.1106 0.0038 0.1667 0.0101 1.900 0.015 1.810 0.063 104
J42 2.1 5.2365 0.2422 0.3521 0.0045 0.930 2.8400 0.0361 0.1079 0.0048 0.1894 0.0056 1.945 0.021 1.764 0.083 110
J 42 14.1 5.0948 0.1527 0.3444 0.0028 0.980 2.9040 0.0239 0.1073 0.0034 0.1827 0.0391 1.908 0.014 1.754 0.060 108
J 42 20.1 5.2084 0.1483 0.3486 0.0027 0.840 2.8690 0.0221 0.1084 0.0031 0.1791 0.0053 1.928 0.013 1.772 0.052 108
J42 8.1i 1.0815 0.0465 0.1203 0.0013 0.980 8.3139 0.0915 0.0652 0.0026 0.1043 0.0034 0.732 0.008 0.781 0.084 93
J42 3.1 1.5682 0.0660 0.1514 0.0017 0.980 6.6067 0.0730 0.0751 0.0030 0.0578 0.0071 0.909 0.009 1.072 0.080 84
J42 5.1B 1.6932 0.0720 0.1646 0.0018 0.950 6.0746 0.0663 0.0746 0.0030 0.0536 0.0011 0.982 0.010 1.058 0.081 92
J42 9.1i 3.5188 0.1963 0.2674 0.0040 0.980 3.7392 0.0563 0.0954 0.0052 0.2362 0.0129 1.528 0.020 1.537 0.101 99
J 42 12.1 3.7369 0.1076 0.2911 0.0022 0.950 3.4353 0.0262 0.0931 0.0026 0.0687 0.0169 1.647 0.011 1.490 0.053 110
J 42 13.1 4.3371 0.1177 0.3066 0.0022 0.960 3.2620 0.0237 0.1026 0.0028 0.0695 0.0051 1.724 0.011 1.672 0.051 103
J42 4.1 2.4059 0.1514 0.1955 0.0031 0.990 5.1142 0.0798 0.0892 0.0044 0.1213 0.0137 1.151 0.016 1.409 0.087 81
J42 6.1f 2.2598 0.0894 0.2137 0.0022 0.999 4.6793 0.0483 0.0767 0.0030 0.0662 0.0018 1.249 0.012 1.113 0.080 112
J42 7.1 4.8574 0.2512 0.3504 0.0050 0.930 2.8539 0.0409 0.1005 0.0051 0.1647 0.0112 1.936 0.024 1.634 0.095 118
J42 10.1 4.3198 0.1957 0.3550 0.0042 0.980 2.8168 0.0334 0.0883 0.0039 0.1773 0.0525 1.958 0.020 1.388 0.087 141
J42 11.1 4.9637 0.2375 0.3736 0.0048 0.950 2.6764 0.0342 0.0964 0.0044 0.1423 0.0163 2.046 0.022 1.555 0.085 131
J 42 5.2 1.6510 0.0553 0.1796 0.0015 0.520 5.5693 0.0478 0.0667 0.0021 0.0603 0.0047 1.065 0.008 0.828 0.065 128
J 42 9.2 3.5614 0.1132 0.2454 0.0021 0.980 4.0751 0.0348 0.1053 0.0032 0.1070 0.0130 1.415 0.011 1.719 0.056 82
J 42 17.1 1.3116 0.0479 0.1250 0.0012 0.990 7.9969 0.0766 0.0761 0.0021 0.0431 0.0062 0.760 0.007 1.097 0.055 69
J 42 18.1 2.2789 0.0807 0.1821 0.0017 0.990 5.4906 0.0501 0.0907 0.0029 0.1747 0.0268 1.079 0.009 1.441 0.059 74
J 42 19.1 3.3409 0.1108 0.2417 0.0021 0.980 4.1379 0.0366 0.1003 0.0032 0.1493 0.0138 1.395 0.011 1.629 0.059 85
J98 1.1 4.6414 0.2140 0.3165 0.0045 0.950 3.1600 0.0447 0.1064 0.0048 0.1761 0.0048 1.772 0.022 1.738 0.083 101
J98 20.1 4.7344 0.1428 0.3192 0.0031 0.940 3.1325 0.0305 0.1076 0.0033 0.1993 0.0051 1.786 0.015 1.758 0.055 101
J98 15.1 4.7204 0.1503 0.3206 0.0033 0.950 3.1188 0.0318 0.1068 0.0034 0.2588 0.0235 1.793 0.016 1.745 0.058 102
J98 6.1 4.7774 0.2197 0.3216 0.0047 0.900 3.1090 0.0451 0.1077 0.0050 0.1800 0.0084 1.798 0.023 1.761 0.086 102
J98 3.1 4.7700 0.2166 0.3219 0.0046 0.870 3.1069 0.0443 0.1075 0.0051 0.2797 0.0138 1.799 0.022 1.757 0.087 102
J98 19.1 4.8515 0.1454 0.3273 0.0032 0.950 3.0549 0.0295 0.1075 0.0033 0.2414 0.0117 1.826 0.015 1.757 0.056 103
J98 17.1 4.8812 0.1653 0.3326 0.0036 0.910 3.0062 0.0329 0.1064 0.0038 0.2180 0.0098 1.851 0.018 1.739 0.065 106
J98 12.1 4.9617 0.1536 0.3334 0.0033 0.980 2.9994 0.0301 0.1079 0.0034 0.2116 0.0091 1.855 0.016 1.765 0.059 105
J98 2.1 4.6519 0.2234 0.3073 0.0048 0.010 3.2544 0.0510 0.1098 0.0055 0.1979 0.0070 1.727 0.024 1.796 0.093 96
J98 16.1 5.0418 0.1603 0.3374 0.0035 0.880 2.9639 0.0305 0.1084 0.0036 0.2355 0.0150 1.874 0.017 1.772 0.060 105
J98 18.1 5.0217 0.1655 0.3426 0.0037 0.940 2.9189 0.0314 0.1063 0.0038 0.1707 0.0035 1.899 0.018 1.737 0.065 109
J98 11.1 5.2108 0.2332 0.3459 0.0050 0.880 2.8907 0.0420 0.1092 0.0052 0.1748 0.0103 1.915 0.024 1.787 0.087 107
J98 4.1 5.6694 0.2762 0.3953 0.0058 0.999 2.5300 0.0373 0.1040 0.0044 0.5236 0.1065 2.147 0.026 1.697 0.078 126
J98 8.1 3.6780 0.1635 0.2516 0.0034 0.890 3.9753 0.0537 0.1060 0.0047 0.2209 0.0181 1.446 0.018 1.732 0.081 83
J98 14.1 3.8352 0.1195 0.2594 0.0026 0.990 3.8547 0.0386 0.1072 0.0034 0.2576 0.0153 1.487 0.013 1.753 0.059 84
J98 7.1 3.9839 0.1919 0.2719 0.0042 0.980 3.6782 0.0571 0.1063 0.0056 0.2059 0.0054 1.550 0.021 1.737 0.097 89
J98 5.1 4.1932 0.1932 0.2810 0.0041 0.940 3.5583 0.0518 0.1082 0.0051 0.3019 0.0139 1.597 0.021 1.770 0.087 90
J98 21.1 4.3710 0.1312 0.2964 0.0029 0.999 3.3740 0.0327 0.1070 0.0034 0.2366 0.0161 1.673 0.014 1.748 0.059 95
J98 10.1 4.3906 0.1436 0.2975 0.0031 0.970 3.3618 0.0353 0.1071 0.0038 0.2017 0.0065 1.679 0.016 1.750 0.065 95
J98 13.1 4.4905 0.1754 0.3016 0.0038 0.290 3.3157 0.0418 0.1080 0.0045 0.3164 0.0163 1.699 0.019 1.766 0.076 96
J 159 5.1 4.8326 0.2042 0.3226 0.0032 0.850 3.0999 0.0307 0.1086 0.0045 0.1985 0.0313 1.802 0.016 1.777 0.078 101
J 159 12.3 4.8640 0.1167 0.3262 0.0026 0.890 3.0653 0.0247 0.1081 0.0025 0.0334 0.0187 1.820 0.013 1.768 0.042 102
J 159 7.1 5.0194 0.1403 0.3288 0.0033 0.990 3.0413 0.0303 0.1107 0.0032 0.2024 0.0189 1.833 0.016 1.811 0.052 101
J 159 1.1 5.0358 0.2466 0.3308 0.0038 0.710 3.0232 0.0351 0.1104 0.0052 0.2136 0.0362 1.842 0.018 1.806 0.084 101
J 159 14.1 4.9381 0.1271 0.3317 0.0030 0.810 3.0146 0.0269 0.1080 0.0028 0.1653 0.0130 1.847 0.014 1.765 0.047 104
J 159 19.1 4.9322 0.1247 0.3334 0.0029 0.950 2.9996 0.0258 0.1073 0.0026 0.1971 0.0126 1.855 0.014 1.754 0.045 105
J 159 15.1 5.0149 0.1350 0.3351 0.0032 0.880 2.9839 0.0286 0.1085 0.0030 0.1867 0.0513 1.863 0.015 1.775 0.050 104
J 159 16.1 4.9910 0.1375 0.3358 0.0032 0.960 2.9782 0.0288 0.1078 0.0030 0.2188 0.0139 1.866 0.016 1.763 0.050 105
J 159 18.1 5.0169 0.1540 0.3364 0.0037 0.470 2.9727 0.0331 0.1082 0.0035 0.1971 0.0071 1.869 0.018 1.769 0.059 105
J 159 21.1 5.0023 0.1344 0.3373 0.0032 0.920 2.9643 0.0279 0.1075 0.0028 0.2426 0.0268 1.874 0.015 1.758 0.048 106
J 159 22.1 5.0482 0.1606 0.3389 0.0040 0.920 2.9511 0.0344 0.1080 0.0036 0.2103 0.0079 1.881 0.019 1.767 0.061 106
J 159 17.1 5.1166 0.1355 0.3412 0.0032 0.940 2.9311 0.0276 0.1088 0.0030 0.2528 0.0196 1.892 0.016 1.779 0.051 106
J 159 20.1 5.1348 0.1382 0.3439 0.0033 0.880 2.9075 0.0275 0.1083 0.0029 0.2358 0.0063 1.906 0.016 1.771 0.050 107
J 159 12.1 5.1990 0.2197 0.3472 0.0033 0.850 2.8802 0.0272 0.1086 0.0044 0.1218 0.0147 1.921 0.016 1.776 0.074 108
J 159 13.1 5.2973 0.2405 0.3447 0.0037 0.860 2.9012 0.0313 0.1115 0.0050 0.1542 0.0175 1.909 0.018 1.823 0.083 104
J 159 8.1 5.1945 0.2308 0.3460 0.0035 0.920 2.8904 0.0293 0.1089 0.0046 0.1722 0.0078 1.915 0.017 1.781 0.077 107
J 159 2.1 5.2970 0.2157 0.3468 0.0032 0.840 2.8833 0.0267 0.1108 0.0044 4.4055 25.6843 1.919 0.015 1.812 0.072 105
J 159 4.1 5.3876 0.2929 0.3488 0.0046 0.120 2.8670 0.0381 0.1120 0.0061 0.2355 0.0252 1.929 0.022 1.833 0.099 105
J 159 10.1 5.2967 0.2366 0.3518 0.0036 0.600 2.8423 0.0292 0.1092 0.0048 0.2657 0.0213 1.943 0.017 1.786 0.079 108
J 159 11.1 5.2603 0.2206 0.3520 0.0033 0.870 2.8406 0.0267 0.1084 0.0043 0.1110 0.0059 1.944 0.016 1.772 0.072 109
J 159 3.1 5.4434 0.2317 0.3559 0.0035 0.970 2.8098 0.0275 0.1109 0.0047 0.1961 0.0077 1.963 0.017 1.815 0.076 108
J 159 9.1 5.4885 0.2738 0.3597 0.0043 0.760 2.7802 0.0333 0.1107 0.0055 0.2012 0.0087 1.981 0.020 1.810 0.091 109
J 159 2.2 5.6415 0.1212 0.3723 0.0027 0.999 2.6857 0.0197 0.1099 0.0026 0.1642 0.0598 2.040 0.013 1.798 0.043 113
J 159 6.1 5.5019 0.2485 0.3634 0.0038 0.940 2.7521 0.0286 0.1098 0.0048 0.1624 0.0039 1.998 0.018 1.796 0.080 111
J 159 7.1 4.6764 0.2353 0.3053 0.0037 0.970 3.2752 0.0394 0.1111 0.0057 0.1356 0.0172 1.718 0.018 1.817 0.093 94
J 159 12.2 5.2594 0.1363 0.3482 0.0032 0.790 2.8718 0.0261 0.1095 0.0029 0.0944 0.0497 1.926 0.015 1.792 0.048 107
PR3228 9.1 0.9998 0.0568 0.0787 0.0018 0.990 12.7128 0.2885 0.0922 0.0052 0.1266 0.0147 0.488 0.011 1.471 0.107 33
PR3228 20.1 1.0403 0.0357 0.0853 0.0012 0.990 11.7205 0.1610 0.0884 0.0024 0.2415 0.0626 0.528 0.007 1.392 0.052 37
PR3228 27.1 1.0580 0.0270 0.0887 0.0008 0.990 11.2717 0.1025 0.0865 0.0022 0.1837 0.0307 0.548 0.005 1.349 0.049 40
PR3228 24.1 1.3841 0.0377 0.1064 0.0010 0.999 9.4017 0.0926 0.0944 0.0024 0.0815 0.0188 0.652 0.006 1.516 0.048 42
PR3228 2.2 1.4504 0.0405 0.1086 0.0011 0.999 9.2042 0.0908 0.0968 0.0030 0.2593 0.0257 0.665 0.006 1.564 0.059 42
PR3228 1.1 1.5898 0.0609 0.1159 0.0016 0.970 8.6248 0.1206 0.0994 0.0040 0.2283 0.0150 0.707 0.009 1.614 0.075 43
PR3228 7.1 1.7215 0.0683 0.1266 0.0018 0.630 7.8981 0.1103 0.0986 0.0040 0.1141 0.0215 0.769 0.010 1.598 0.074 48
PR3228 24.2 2.1287 0.0471 0.1626 0.0013 0.990 6.1484 0.0502 0.0949 0.0024 0.0819 0.0314 0.971 0.007 1.527 0.048 63
PR3228 15.1 2.2896 0.0527 0.1731 0.0014 0.999 5.7765 0.0471 0.0959 0.0024 0.1140 0.0251 1.029 0.008 1.546 0.047 66
PR3228 1.2 2.5180 0.0720 0.1795 0.0019 0.990 5.5713 0.0583 0.1017 0.0031 0.1877 0.0197 1.064 0.010 1.656 0.056 64
PR3228 12.2 2.5964 0.0744 0.1848 0.0021 0.999 5.4098 0.0601 0.1019 0.0028 0.1960 0.0075 1.093 0.011 1.659 0.051 65
PR3228 4.2 2.5545 0.0657 0.1850 0.0017 0.990 5.4068 0.0507 0.1002 0.0026 0.2197 0.0295 1.094 0.009 1.627 0.050 67
PR3228 21.1 2.9789 0.0796 0.2205 0.0023 0.999 4.5345 0.0468 0.0980 0.0026 0.2560 0.0552 1.285 0.012 1.586 0.050 81
PR3228 2.5 3.1696 0.1183 0.2273 0.0029 0.750 4.3992 0.0565 0.1011 0.0037 0.1791 0.0053 1.320 0.015 1.645 0.068 80
PR3228 4.1 3.4902 0.1380 0.2421 0.0036 0.950 4.1301 0.0610 0.1045 0.0042 0.2257 0.0062 1.398 0.019 1.706 0.075 81
PR3228 8.1 3.4189 0.1235 0.2464 0.0030 0.960 4.0585 0.0501 0.1006 0.0036 0.1690 0.0033 1.420 0.016 1.636 0.067 86
PR3228 12.1 3.6555 0.1447 0.2571 0.0038 0.780 3.8903 0.0576 0.1031 0.0042 0.1602 0.0066 1.475 0.020 1.681 0.075 87
PR3228 2.1 3.8671 0.1561 0.2680 0.0044 0.950 3.7316 0.0612 0.1047 0.0047 0.2507 0.0204 1.531 0.023 1.708 0.083 89
PR3228 29.1 3.7695 0.0768 0.2720 0.0021 0.999 3.6763 0.0280 0.1005 0.0025 0.1416 0.0055 1.551 0.011 1.633 0.048 94
PR3228 14.1 3.7014 0.0929 0.2760 0.0024 0.980 3.6236 0.0319 0.0973 0.0027 0.2171 0.1298 1.571 0.012 1.573 0.051 99
PR3228 11.1 4.0880 0.1581 0.2854 0.0041 0.920 3.5034 0.0500 0.1039 0.0041 0.2180 0.0116 1.619 0.020 1.694 0.072 95
PR3228 13.1 4.2934 0.1629 0.3002 0.0041 0.600 3.3308 0.0454 0.1037 0.0040 0.3139 0.0267 1.692 0.020 1.692 0.071 100
PR3228 3.2 4.3267 0.1097 0.3073 0.0027 0.990 3.2541 0.0289 0.1021 0.0026 0.1883 0.0165 1.727 0.013 1.663 0.046 103
PR3228 11.2 4.7007 0.1221 0.3252 0.0031 0.990 3.0748 0.0295 0.1048 0.0029 0.1846 0.0408 1.815 0.015 1.711 0.051 106
PR3228 16.1 2.9286 0.0705 0.2320 0.0019 0.960 4.3104 0.0360 0.0916 0.0021 0.0387 0.0061 1.345 0.010 1.458 0.045 92
PR3228 18.1 3.2095 0.0843 0.2598 0.0022 0.980 3.8495 0.0329 0.0896 0.0022 1.6957 0.4373 1.489 0.011 1.417 0.045 105
PR3228 25.1 2.6141 0.0663 0.2190 0.0020 0.990 4.5657 0.0414 0.0866 0.0022 0.1867 0.0407 1.277 0.010 1.351 0.047 94
PR3228 6.1 0.7243 0.0267 0.0686 0.0009 0.990 14.5813 0.1837 0.0766 0.0029 0.3004 0.0249 0.428 0.005 1.111 0.077 38
PR3228 5.1 1.1994 0.0453 0.1026 0.0013 0.970 9.7436 0.1253 0.0848 0.0031 0.1262 0.0103 0.630 0.008 1.310 0.073 48
PR3228 13.2 1.6609 0.0653 0.1430 0.0020 0.980 6.9931 0.0980 0.0842 0.0025 0.2686 0.3766 0.862 0.011 1.298 0.052 66
PR3228 14.2 1.9140 0.0490 0.1578 0.0015 0.960 6.3356 0.0585 0.0879 0.0022 0.1662 0.0535 0.945 0.008 1.381 0.049 68
PR3228 17.1 2.1306 0.0529 0.1803 0.0015 0.860 5.5465 0.0475 0.0857 0.0021 0.1174 0.0155 1.069 0.008 1.332 0.048 80
PR3228 18.2 3.3986 0.0766 0.2817 0.0024 0.930 3.5494 0.0297 0.0875 0.0020 1.9408 0.1997 1.600 0.012 1.371 0.045 116
PR3228 19.1 1.0006 0.0437 0.1013 0.0015 0.990 9.8723 0.1434 0.0716 0.0021 0.6122 0.0945 0.622 0.008 0.976 0.051 63
PR3228 22.1 1.6197 0.0495 0.1391 0.0017 0.999 7.1872 0.0859 0.0844 0.0024 1.2693 0.4022 0.840 0.009 1.302 0.051 64
PR3228 23.1 2.8549 0.0699 0.2194 0.0019 0.980 4.5586 0.0400 0.0944 0.0022 0.1172 0.0054 1.279 0.010 1.516 0.044 84
PR3228 26.1 2.0026 0.0480 0.1772 0.0015 0.760 5.6433 0.0480 0.0820 0.0020 0.1688 0.0349 1.052 0.008 1.245 0.047 84
PR3228 28.1 2.0427 0.0451 0.1811 0.0014 0.970 5.5213 0.0436 0.0818 0.0019 0.1032 0.0100 1.073 0.008 1.241 0.046 86

Annex II

Annex II: Isotope ratio data for samples analysed by SHRIMP method (errors are 1s unless otherwise specified). 

Spot Name ppm U ppm Th 232Th /238U ppm Rad 206Pb 204corr 206Pb /238U Age 1σ err 204corr 207Pb /206Pb Age 1σ err % Disc 4corr 207r /206r % err 4corr 207r /235 % err 4corr 206r /238 % err Err corr
J36-1.1 373 120 0.33 64.6 1154.0 10.3 1637 61 42 .1007 3.3 2.72 3.4 .1960 1.0 .287
J36-2.1 186 70 0.39 28.0 1036.5 9.9 1047 31 1 .0742 1.5 1.78 1.9 .1744 1.0 .559
J36-3.1 235 98 0.43 56.3 1578.0 14.3 1580 23 0 .0977 1.2 3.73 1.6 .2773 1.0 .632
J36-4.1 230 111 0.50 76.0 2094.2 17.7 2197 8 5 .1376 0.4 7.28 1.1 .3838 1.0 .915
J36-5.1 404 393 1.00 73.9 1228.9 10.7 1543 32 26 .0958 1.7 2.77 2.0 .2100 1.0 .485
J36-6.1 284 197 0.72 74.0 1707.5 14.5 1757 8 3 .1075 0.5 4.49 1.1 .3033 1.0 .903
J36-7.1 287 20 0.07 76.3 1729.3 14.6 2005 13 16 .1233 0.8 5.23 1.2 .3077 1.0 .785
J36-8.1 578 136 0.24 172.2 1908.5 15.7 1651 16 -14 .1014 0.9 4.82 1.3 .3445 1.0 .745
J36-9.1 91 54 0.61 19.9 1455.1 14.6 1514 26 4 .0943 1.4 3.29 1.8 .2532 1.1 .638
J36-10.1 645 418 0.67 180.8 1820.5 15.6 1749 5 -4 .1070 0.3 4.81 1.0 .3263 1.0 .966
J36-11.1 1280 514 0.42 316.5 1546.0 14.2 1524 135 -1 .0948 7.2 3.54 7.2 .2710 1.0 .142
J36-12.1 309 247 0.83 66.8 1438.2 14.6 1700 47 18 .1042 2.5 3.59 2.8 .2499 1.1 .408
J36-13.1 603 236 0.40 198.5 2089.8 16.6 2553 4 22 .1696 0.2 8.95 1.0 .3829 0.9 .969
J127MIZ-1.1 167 124 0.77 45.0 1745.3 15.9 1786 21 2 .1092 1.2 4.68 1.6 .3109 1.0 .663
J127MIZ-1.2 368 83 0.23 105.5 1853.0 17.8 1752 12 -5 .1072 0.6 4.92 1.3 .3330 1.1 .862
J127MIZ-2.1 190 112 0.61 51.3 1755.9 15.2 1787 12 2 .1093 0.6 4.72 1.2 .3131 1.0 .838
J127MIZ-3.1 161 99 0.63 43.6 1754.5 15.5 1781 19 1 .1089 1.0 4.70 1.4 .3128 1.0 .700
J127MIZ-4.1 273 135 0.51 74.0 1768.4 16.3 1781 8 1 .1089 0.5 4.74 1.1 .3156 1.1 .918
J127MIZ-4.2 119 100 0.87 45.0 1997.6 30.5 1919 373 -4 .1175 20.8 5.89 20.9 .3633 1.8 .085
J127MIZ-5.1 136 147 1.12 36.6 1750.3 16.2 1780 15 2 .1089 0.8 4.68 1.4 .3119 1.1 .780
J127MIZ-6.1 140 75 0.55 36.4 1702.2 15.8 1785 14 5 .1091 0.8 4.55 1.3 .3022 1.1 .803
J127MIZ-7.1 188 139 0.77 51.2 1769.4 15.4 1787 14 1 .1093 0.8 4.76 1.3 .3158 1.0 .782
J127MIZ-8.1 132 90 0.71 35.6 1761.5 19.4 1772 12 1 .1084 0.7 4.70 1.4 .3142 1.3 .879
J127MIZ-9.1 152 88 0.60 41.7 1773.8 16.3 1783 32 0 .1090 1.8 4.76 2.1 .3167 1.0 .510
J127MIZ-10.1 220 142 0.67 44.6 1363.0 12.1 1730 14 27 .1059 0.7 3.44 1.2 .2354 1.0 .798
J127MIZ-11.1 149 91 0.63 39.9 1722.2 15.7 1746 39 1 .1068 2.1 4.51 2.4 .3062 1.0 .441
J127MIZ-12.1 184 123 0.69 48.8 1726.9 15.1 1771 17 3 .1083 0.9 4.59 1.4 .3072 1.0 .727
J127MIZ-13.1 115 86 0.77 31.7 1792.0 18.5 1778 14 -1 .1087 0.8 4.80 1.4 .3205 1.2 .838
J127MIZ-14.1 211 199 0.98 55.9 1721.4 14.9 1757 22 2 .1075 1.2 4.54 1.5 .3061 1.0 .638
PR-3141M-2.1 230 165 0.74 50.5 1463.0 12.9 1506 19 3 .0939 1.0 3.30 1.4 .2548 1.0 .702
PR-3141M-3.1 933 258 0.29 194.0 1395.7 11.6 1485 9 6 .0928 0.5 3.09 1.0 .2417 0.9 .897
PR-3141M-4.1 232 284 1.27 43.0 1178.0 12.5 1464 188 24 .0918 9.9 2.54 9.9 .2005 1.2 .116
PR-3141M-5.1 140 130 0.96 31.0 1434.6 13.8 1483 78 3 .0928 4.1 3.19 4.2 .2492 1.1 .253
PR-3141M-6.1 143 124 0.89 33.1 1509.7 14.5 1493 53 -1 .0932 2.8 3.39 3.0 .2639 1.1 .362
PR-3141M-7.1 333 185 0.57 94.0 1820.1 15.7 1550 25 -15 .0961 1.3 4.32 1.7 .3262 1.0 .600
PR-3141M-8.1 175 185 1.09 38.8 1475.1 13.6 1504 15 2 .0938 0.8 3.33 1.3 .2571 1.0 .792
PR-3141M-9.1 262 206 0.81 54.2 1384.0 12.2 1500 19 8 .0936 1.0 3.09 1.4 .2395 1.0 .690
PR-3141M-10.1 295 199 0.70 64.8 1454.1 12.6 1507 31 4 .0940 1.6 3.28 1.9 .2530 1.0 .511
PR-3141M-11.1 131 134 1.06 29.6 1500.9 13.9 1513 19 1 .0943 1.0 3.41 1.5 .2622 1.0 .713
PR-3141M-12.1 143 156 1.13 32.4 1507.7 13.9 1507 16 0 .0939 0.8 3.41 1.3 .2635 1.0 .780
PR-3141M-13.1 234 227 1.00 52.0 1484.5 13.0 1519 10 2 .0945 0.5 3.38 1.1 .2589 1.0 .881
PR-3141M-14.1 226 159 0.73 38.8 1151.4 10.7 1482 55 29 .0927 2.9 2.50 3.1 .1956 1.0 .329
PR-3141M-15.1 288 220 0.79 62.3 1441.6 12.7 1473 26 2 .0923 1.4 3.19 1.7 .2506 1.0 .578
EP2MI-1.1 128 82 0.67 33.3 1707.8 15.7 1738 15 2 .1063 0.8 4.45 1.3 .3033 1.0 .782
EP2MI-2.1 202 93 0.47 48.9 1595.7 14.1 1686 17 6 .1034 0.9 4.00 1.3 .2809 1.0 .741
EP2MI-3.1 620 334 0.56 106.3 1139.5 11.4 1632 68 43 .1004 3.7 2.68 3.8 .1934 1.1 .285
EP2MI-4.1 159 86 0.56 41.5 1697.1 21.7 1677 46 -1 .1029 2.5 4.27 2.9 .3012 1.5 .506
EP2MI-5.1 159 86 0.56 21.2 923.4 8.6 1677 46 82 .1029 2.5 2.18 2.7 .1540 1.0 .373
EP2MI-6.1 586 245 0.43 106.1 1194.6 10.7 1624 76 36 .1000 4.1 2.81 4.2 .2036 1.0 .234
EP2MI-7.1 137 253 1.91 35.1 1683.6 15.3 1715 16 2 .1050 0.9 4.32 1.3 .2984 1.0 .771
EP2MI-8.1 343 198 0.60 89.8 1713.7 14.4 1725 8 1 .1056 0.5 4.43 1.1 .3045 1.0 .904
EP2MI-9.1 279 149 0.55 72.2 1697.8 14.5 1725 10 2 .1056 0.5 4.39 1.1 .3013 1.0 .876
EP2MI-10.1 339 182 0.55 88.2 1702.7 14.3 1721 8 1 .1054 0.4 4.39 1.0 .3023 1.0 .912
EP2MI-11.1 410 239 0.60 98.8 1589.1 13.3 1707 11 7 .1046 0.6 4.03 1.1 .2796 0.9 .841
EP2MI-12.1 592 417 0.73 126.3 1403.2 11.9 1655 44 18 .1017 2.4 3.41 2.6 .2432 0.9 .370
EP2MI-13.1 140 70 0.51 40.2 1861.2 19.1 1742 15 -6 .1066 0.8 4.92 1.4 .3347 1.2 .815
EP2MI-14.1 417 327 0.81 106.9 1682.5 14.2 1717 8 2 .1052 0.4 4.32 1.0 .2982 1.0 .913
EP2MI-15.1 272 288 1.09 70.4 1694.3 14.7 1747 9 3 .1069 0.5 4.43 1.1 .3006 1.0 .886
EP2MI-16.1 254 110 0.45 75.8 1925.1 17.4 1756 11 -9 .1074 0.6 5.15 1.2 .3480 1.0 .869
J-84-1.1 326 436 1.38 56.7 1186.7 41.0 1458 14 23 .0916 0.7 2.55 3.9 .2021 3.8 .981
J-84-2.1 770 224 0.30 168.4 1462.9 49.4 1520 6 4 .0946 0.3 3.32 3.8 .2547 3.8 .997
J-84-3.1 171 155 0.94 41.7 1606.7 54.1 1963 19 22 .1204 1.1 4.70 3.9 .2830 3.8 .962
J-84-3.2 1978 754 0.39 288.9 1003.2 35.0 1411 26 41 .0893 1.4 2.07 4.0 .1684 3.8 .941
J-84-4.1 345 149 0.44 67.5 1320.3 45.2 1504 15 14 .0938 0.8 2.94 3.9 .2273 3.8 .980
J-84-6.1 227 113 0.51 23.3 722.2 26.2 1539 57 113 .0956 3.0 1.56 4.9 .1185 3.8 .785
J-84-7.1 550 163 0.31 89.1 1110.4 38.5 1533 16 38 .0952 0.8 2.47 3.9 .1880 3.8 .977
J-84-8.1 729 186 0.26 155.0 1378.4 49.6 1541 161 12 .0956 8.5 3.14 9.4 .2384 4.0 .423
J-84-9.1 194 141 0.75 42.0 1438.6 49.9 1455 31 1 .0914 1.6 3.15 4.2 .2500 3.9 .922
J-84-10.1 125 219 1.81 21.1 1116.0 39.2 1446 108 30 .0910 5.7 2.37 6.8 .1890 3.8 .559
J-84-1.2 120 195 1.68 26.6 1461.0 49.9 1480 59 1 .0926 3.1 3.25 4.9 .2544 3.8 .775
J-84-11.1 395 171 0.45 83.3 1409.9 47.8 1506 14 7 .0939 0.7 3.16 3.8 .2445 3.8 .981
PR-3001-1.1 291 77 0.27 75.5 1700.5 57.3 1740 8 2 .1065 0.4 4.43 3.9 .3019 3.8 .994
PR-3001-2.1 316 91 0.30 77.9 1614.0 54.4 1708 20 6 .1047 1.1 4.11 4.0 .2845 3.8 .963
PR-3001-3.1 174 68 0.40 46.8 1756.0 58.3 1829 12 4 .1118 0.7 4.83 3.8 .3131 3.8 .986
PR-3001-4.1 467 445 0.98 120.0 1682.3 55.9 1762 10 5 .1078 0.5 4.43 3.8 .2982 3.8 .990
PR-3001-5.1 395 171 0.45 64.4 1115.4 38.7 1506 14 35 .0939 0.7 2.45 3.8 .1889 3.8 .981
PR-3001-6.1 309 64 0.21 62.4 1309.1 44.9 1696 97 30 .1040 5.3 3.23 6.5 .2252 3.8 .585
PR-3001-7.1 171 99 0.60 43.8 1670.9 55.8 1757 21 5 .1074 1.2 4.38 4.0 .2959 3.8 .956
PR-3001-8.1 346 115 0.34 88.6 1665.8 55.4 1734 25 4 .1061 1.3 4.31 4.0 .2949 3.8 .942
PR-3001-9.1 292 73 0.26 77.4 1727.5 57.2 1742 11 1 .1066 0.6 4.52 3.8 .3073 3.8 .987
PR-3001-10.1 564 224 0.41 154.7 1782.3 58.7 1739 10 -2 .1064 0.6 4.67 3.8 .3185 3.8 .989
PR-3001-11.1 1351 401 0.31 319.1 1548.4 51.8 1704 25 10 .1044 1.4 3.91 4.0 .2715 3.8 .941
PR-3001-12.1 607 125 0.21 144.8 1572.2 52.6 1712 13 9 .1049 0.7 3.99 3.8 .2762 3.8 .983
J-199-1.1 537 250 0.48 138.8 1691.0 56.2 1784 10 5 .1091 0.6 4.51 3.8 .2999 3.8 .989
J-199-2.1 309 161 0.54 80.9 1715.2 57.4 1785 9 4 .1091 0.5 4.59 3.8 .3048 3.8 .992
J-199-3.1 276 151 0.56 71.2 1687.6 56.7 1784 11 6 .1091 0.6 4.50 3.9 .2992 3.8 .989
J-199-4.1 439 166 0.39 113.5 1694.3 57.5 1805 7 7 .1103 0.4 4.57 3.9 .3006 3.9 .995
J-199-5.1 300 137 0.47 83.6 1801.0 59.3 1783 16 -1 .1090 0.9 4.84 3.9 .3223 3.8 .975
J-199-6.1 252 108 0.44 71.9 1847.3 60.8 1811 9 -2 .1107 0.5 5.06 3.8 .3318 3.8 .992
J-199-7.1 332 179 0.56 93.7 1797.2 59.3 1807 43 1 .1104 2.4 4.90 4.5 .3215 3.8 .846
J-199-8.1 415 198 0.49 117.6 1839.4 60.4 1802 6 -2 .1102 0.3 5.02 3.8 .3302 3.8 .996
J-199-9.1 269 133 0.51 76.9 1851.1 60.8 1812 7 -2 .1108 0.4 5.08 3.8 .3326 3.8 .994
J-199-10.1 257 120 0.48 72.1 1824.2 60.0 1797 8 -1 .1099 0.4 4.95 3.8 .3271 3.8 .993
J-199-11.1 410 181 0.46 115.9 1833.1 60.2 1790 6 -2 .1094 0.3 4.96 3.8 .3289 3.8 .996
J-199-12.1 533 346 0.67 150.5 1812.5 59.6 1786 27 -1 .1092 1.5 4.89 4.0 .3247 3.8 .931
HB-667-1.1 294 144 0.50 80.5 1782.9 58.9 1770 16 -1 .1083 0.9 4.76 3.9 .3186 3.8 .975
HB-667-1.2 299 109 0.38 76.2 1672.6 55.7 1775 10 6 .1085 0.5 4.43 3.8 .2962 3.8 .990
HB-667-2.1 2075 1012 0.50 311.6 1027.9 35.8 1461 28 42 .0917 1.5 2.19 4.0 .1729 3.8 .931
HB-667-3.1 340 247 0.75 85.7 1590.0 53.6 1761 105 11 .1077 5.7 4.15 6.9 .2797 3.8 .553
HB-667-4.1 368 154 0.43 100.4 1777.7 58.7 1767 7 -1 .1081 0.4 4.73 3.8 .3175 3.8 .995
HB-667-5.1 425 170 0.41 117.5 1799.5 59.2 1788 6 -1 .1093 0.3 4.85 3.8 .3220 3.8 .996
HB-667-6.1 955 468 0.51 264.6 1802.6 59.2 1761 4 -2 .1077 0.2 4.79 3.8 .3226 3.8 .998
HB-667-6.2 222 162 0.75 61.4 1798.4 59.3 1790 8 0 .1094 0.5 4.85 3.8 .3218 3.8 .993
HB-667-7.1 257 109 0.44 71.2 1803.2 59.4 1773 8 -2 .1084 0.4 4.83 3.8 .3228 3.8 .994
HB-667-8.1 400 254 0.66 110.3 1796.8 59.2 1778 6 -1 .1087 0.3 4.82 3.8 .3215 3.8 .996
HB-667-9.1 341 137 0.42 96.1 1830.5 60.2 1801 12 -2 .1101 0.7 4.99 3.8 .3284 3.8 .984
HB-667-10.1 470 407 0.89 130.0 1799.1 59.2 1774 6 -1 .1085 0.3 4.82 3.8 .3219 3.8 .997

Received: June 29, 2015; Accepted: October 08, 2015

*

*Corresponding author.

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