Abstract
New U-Pb zircon geochronological data integrated with field relationships and an airborne geophysical survey suggest that the Nova Brasilândia and Aguapeí belts are part of the same monocyclic, metaigneous and metasedimentary belt formed in the late Mesoproterozoic (1150 Ma-1110 Ma). This geological history is very similar to the within-plate origin of the Sunsás belt, in eastern Bolivia. Thus, we propose that the Nova Brasilândia, Aguapeí and Sunsás belts represent a unique geotectonic unit (here termed the Western Amazon belt) that became amalgamated at the end of the Mesoproterozoic and originated through the reactivation of a paleo-suture (Guaporé suture zone) in an intracontinental rift environment. Therefore, its geological history involves a short, complete Wilson cycle of ca. 40 Ma. Globally, this tectonic evolution may be related with the final breakup of the supercontinent Columbia. Mafic rocks and trondhjemites in the northernmost portion of the belt yielded U-Pb zircon ages ca. 1110 Ma, which dates the high-grade metamorphism and the closure of the rift. This indicates that the breakup of supercontinent Columbia was followed in short sequence by the assembly of supercontinent Rodinia at ca. 1.1-1.0 Ga and that the Western Amazon belt was formed during the accretion of the Arequipa-Antofalla basement to the Amazonian craton.
Highlights
The Amazonian craton constitutes a central core of the South American continent and it was formed by the amalgamation of Proterozoic accretionary belts that are successively younger toward the southwestern border of the craton (Cordani et al 2000, Santos et al 2000, 2008)
New U-Pb zircon geochronological data integrated with field relationships and an airborne geophysical survey suggest that the Nova Brasilândia and Aguapeí belts are part of the same monocyclic, metaigneous and metasedimentary belt formed in the late Mesoproterozoic (1150 Ma-1110 Ma)
Zircon U-Pb geochronological data and field relationships presented in this contribution are strong evidence for the existence of a continuous intracratonic late Mesoproterozoic orogenic belt (Western Amazon belt) in the southwestern margin of the Amazonian craton
Summary
The Amazonian craton constitutes a central core of the South American continent and it was formed by the amalgamation of Proterozoic accretionary belts that are successively younger toward the southwestern border of the craton (Cordani et al 2000, Santos et al 2000, 2008) (from 1465 to 1110 Ma) and was formed by four orogenies: Santa Helena (1460-1420 Ma), Candeias (1370-1320 Ma), San Andrés (1275 Ma) and Nova Brasilândia (1180-1110 Ma) They postulated the nonexistence of the Paraguá craton, a cratonic fragment that consists of metamorphic basement rocks in the eastern Bolivia Precambrian shield, which was first defined by Litherland et al (1986), and argued that Paraguá “craton” and Amazonia were already close together, as parts of the same continental masses in the middle to late Mesoproterozoic. In the same way, Sadowski and Bettencourt (1996) argued that there is no clear evidence that the Paraguá craton is a unit that is independent from the Amazonian craton, and they consider it to be part of the Amazonian craton that is defined as the Paraguá Block
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