Precise ID-TIMS U–Pb baddeleyite ages (1110–1112 Ma) for the Rincón del Tigre–Huanchaca large igneous province (LIP) of the Amazonian Craton: Implications for the Rodinia supercontinent

High quality U–Pb (ID-TIMS) baddeleyite ages define the timing of crystallization of the Rincón del Tigrelayered intrusion (1110 ± 2 Ma) and the Huanchaca mafic suite (1112 ± 2 Ma) in the Bolivian Precambrian shield – SW portion of the Amazonian Craton. The identical ca. 1110–1112 Ma ages obtained foreach (about 500 km apart) suggest these belong to a previously unrecognized LIP. The large area of dis-tribution and the intraplate geochemistry for the 1110 Ma Huanchaca–Rincón del Tigre rocks support arelationship with mantle plume activity pre-dating Rodinia breakup. Contemporary anorogenic magmatism in Amazonia is probably linked to crustal melting caused by the LIP. The newly identified 1110 MaLIP has a tight age match with intraplate magmatism in the Congo, Kalahari and Indian cratons, and the Keweenawan event of central Laurentia among others. While a reconstruction history of Amazonia andLaurentia is still a matter of debate on paleomagnetic grounds, a reconstruction link with other crustalblocks remains possible

The 1590-1520 Ma Cachoeirinha magmatic arc and its tectonic implications for the Mesoproterozoic SW Amazonian craton crustal evolution

Isotopic and chemical data of rocks from the Cachoeirinha suite provide new insights on the Proterozoic evolution of the Rio Negro/Juruena Province in SW Amazonian craton. Six U-Pb and Sm-Nd analyses in granitoid rocks of the Cachoeirinha suite yielded ages of 1587-1522 Ma and T DM model ages of 1.88-1.75 Ga (EpsilonNd values of -0.8 to +1.0). In addition, three post-tectonic plutonic rocks yielded U-Pb ages from 1485-1389 Ma (T DM of 1.77-1.74 Ga and EpsilonNd values from -1.3 to +1.7). Variations in major and trace elements of the Cachoeirinha suite rocks indicate fractional crystallization process and magmatic arc geologic setting. These results suggest the following interpretations: (1) The interval of 1590-1520 Ma represents an important magmatic activity in SW Amazonian craton. (2) T DM and arc-related chemical affinity supportthe hypothesis that the rocks are genetically associated with an east-dipping subduction zone under the older (1.79-1.74 Ga) continental margin. (3) The 1590-1520 Ma age of intrusive rocks adjacent to an older crust represents similar geological framework along the southern margin of Baltica, corroborating the hypothesis of tectonic relationship at that time

Precise ID-TIMS U–Pb baddeleyite ages (1110–1112 Ma) for the Rincón del Tigre–Huanchaca large igneous province (LIP) of the Amazonian Craton: Implications for the Rodinia supercontinent

High quality U–Pb (ID-TIMS) baddeleyite ages define the timing of crystallization of the Rincón del Tigrelayered intrusion (1110 ± 2 Ma) and the Huanchaca mafic suite (1112 ± 2 Ma) in the Bolivian Precambrian shield – SW portion of the Amazonian Craton. The identical ca. 1110–1112 Ma ages obtained foreach (about 500 km apart) suggest these belong to a previously unrecognized LIP. The large area of dis-tribution and the intraplate geochemistry for the 1110 Ma Huanchaca–Rincón del Tigre rocks support arelationship with mantle plume activity pre-dating Rodinia breakup. Contemporary anorogenic magmatism in Amazonia is probably linked to crustal melting caused by the LIP. The newly identified 1110 MaLIP has a tight age match with intraplate magmatism in the Congo, Kalahari and Indian cratons, and the Keweenawan event of central Laurentia among others. While a reconstruction history of Amazonia andLaurentia is still a matter of debate on paleomagnetic grounds, a reconstruction link with other crustalblocks remains possible

THE RIO APA CRATON IN MATO GROSSO DO SUL (BRAZIL) AND NORTHERN PARAGUAY: GEOCHRONOLOGICAL EVOLUTION, CORRELATIONS AND TECTONIC IMPLICATIONS FOR RODINIA AND GONDWANA

The Rio Apa cratonic fragment crops out in Mato Grosso do Sul State of Brazil and in northeastern Paraguay. It comprises Paleo-Mesoproterozoic medium grade metamorphic rocks, intruded by granitic rocks, and is covered by the Neoproterozoic deposits of the Corumbi and Itapocurni Groups. Eastward it is bound by the southern portion of the Paraguay belt. In this work, more than 100 isotopic determinations, including U-Pb SHRIMP zircon ages, Rb-Sr and Sm-Nd whole-rock determinations, as well as K-Ar and Ar-Ar mineral ages, were reassessed in order to obtain a complete picture of its regional geological history. The tectonic evolution of the Rio Apa Craton starts with the formation of a series of magmatic arc complexes. The oldest U-Pb SHRIMP zircon age comes from a banded gneiss collected in the northern part of the region, with an age of 1950 +/- 23 Ma. The large granitic intrusion of the Alumiador Batholith yielded a U-Pb zircon age of 1839 +/- 33 Ma, and from the southeastern part of the area two orthogneisses gave zircon U-Pb ages of 1774 +/- 26 Ma and 1721 +/- 25 Ma. These may be coeval with the Alto Terere metamorphic rocks of the northeastern corner, intruded in their turn by the Baia das Garcas granitic rocks, one of them yielding a zircon U-Pb age of 1754 +/- 49 Ma. The original magmatic protoliths of these rocks involved some crustal component, as indicated by the Sm-Nd TDm model ages, between 1.9 and 2.5 Ga. Regional Sr isotopic homogenization, associated with tectonic deformation and medium-grade metamorphism occurred at approximately 1670 Ma, as suggested by Rb-Sr whole rock reference isochrons. Finally, at 1300 Ma ago, the Ar work indicates that the Rio Apa Craton was affected by widespread regional heating, when the temperature probably exceeded 350 degrees C. Geographic distribution, age and isotopic signature of the fithotectonic units suggest the existence of a major suture separating two different tectonic domains, juxtaposed at about 1670 Ma. From that time on, the unified Rio Apa continental block behaved as one coherent and stable tectonic unit. It correlates well with the SW corner of the Amazonian Craton, where the medium-grade rocks of the Juruena-Rio Negro tectonic province, with ages between 1600 and 1780 Ma, were reworked at about 1300 Ma. Looking at the largest scale, the Rio Apa Craton is probably attached to the larger Amazonian Craton, and the actual configuration of southwestern South America is possibly due to a complex arrangement of allochthonous blocks such as the Arequipa, Antofalla and Pampia, with different sizes, that may have originated as disrupted parts of either Laurentia or Amazonia, and were trapped during later collisions of these continental masses.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Brazilian National Research Council (CNPq)[302851/2004]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Brazilian National Research Council (CNPq)[471585/2007]Brazilian National Research Council (CNPq)[302917/2009-8]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Geochemical characterization of a reconstructed 1110 Ma Large Igneous Province

1110 Ma Large Igneous Province (LIP) fragments in the Kalahari craton, southern Africa (Umkondo LIP); Dronning Maud Land, Antarctica; Bundelkhand portion of Indian craton (Mahoba dolerite dykes); Congo craton (Huila-Epembe dolerite dykes); and Amazonia (Rincon del Tigre-Huanchaca LIP) have been reconstructed as a single LIP with plume centre beneath the NW part of the Kalahari Craton. This paper offers the best estimates for the paleoposition of the Indian and Amazonian cratons along with conjoined Kalahari-SF/Congo reconstruction. This 1110 Ma mafic magmatism is dominantly tholeiitic, ranging from basalt to andesitic basalt in composition, generated over a range of mantle melting depths [(Gd/Yb)N = 1.2-2.3], exhibit low to high contamination with crustal components (negative Nb anomalies, eNd (0 to -12), and elevated Th/Yb). The data fall into two Groups based on TiO2 content, with Group 1 (low Ti) of andesitic basalt composition, and Group 2 (high Ti) exhibiting a basaltic affinity. Group 1 magmas were generated in the spinel lherzolite field followed by significant contamination likely during passage through metasomatised lithospheric mantle in crustal magma chambers. A greater melting depth reaching into the garnet lherzolite field is proposed for the Group 2 magmas. The majority of Group 2 units are located in the Kalahari and Congo cratons, and this reflects onset of deeper melting closer to the interpreted plume axis in our reconstruction

The 1420 Ma Indiavai Mafic Intrusion (SW Amazonian Craton): Paleomagnetic results and implications for the Columbia supercontinent

The configuration and the timing of assembly and break-up of Columbia are still matter of debate. In order to improve our knowledge about the Mesoproterozoic evolution of Columbia, a paleomagnetic study was carried out on the 1420 Ma Indiavai mafic intrusive rocks that crosscut the polycyclic Proterozoic basement of the SW Amazonian Craton, in southwestern Mato Grosso State (Brazil). Alternating field and thermal demagnetization revealed south/southwest ChRM directions with downward inclinations for sixteen analyzed sites. These directions are probably carried by SD/PSD magnetite with high coercivities and high unblocking temperatures as indicated by additional rock magnetic tests, including thermomagnetic data, hysteresis data and the progressive acquisition of isothermal remanent magnetization. Different stable magnetization components isolated in host rocks from the basement 10 km NW away to the Indiavai intrusion, further support the primary origin of the ChRM. A mean of the site mean directions was calculated at Dm = 209.8 degrees, Im = 50.7 degrees (alpha(95) = 8.0 degrees, K = 22.1), which yielded a paleomagnetic pole located at 249.7 degrees E, 57.0 degrees S (A(95) = 8.6 degrees). The similarity of this pole with the recently published 1420 Ma pole from the Nova Guarita dykes in northern Mato Grosso State suggests a similar tectonic framework for these two sites located 600 km apart, implying the bulk rigidity of the Rondonian-San Ignacio crust at that time. Furthermore these data provide new insights on the tectonic significance of the 1100-1000 Ma Nova Brasilandia belt-a major EW feature that cuts across the basement rocks of this province, which can now be interpreted as intracratonic, in contrast to previous interpretation. From a global perspective, a new Mesoproterozoic paleogeography of Columbia has been proposed based on comparison of these 1420 Ma poles and a 1780 Ma pole from Amazonia with other paleomagnetic poles of similar age from Baltica and Laurentia, a reconstruction in agreement with geological correlations. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.FAPESPFAPESP [07/53177-4, 07/59531-4, 11/50887-6]CNPq [554458/2005-5, 302917/2009-8]CNPqSwedish Research Council (VR)Swedish Research Council (VR