Two stage tectonic history of the SW Amazon craton in the late Mesoproterozoic: identifying a cryptic suture zone

The history of the SW Amazon craton during late Mesoproterozoic times is marked by two separate tectonic events, the first related to collision with southern Laurentia and the second caused by suturing of the Paragua craton. The polycyclic basement rocks of the SW Amazon craton exposed in the Brazilian state of Rondônia were deformed at lower amphibolite conditions during early Grenville times (ca. 1.2-1.15 Ga). This deformation episode is the last of several tectonometamorphic events that affected the granitoid rocks of the Amazon basement throughout the Mesoproterozoic. The southern margin of the Amazon craton during late Mesoproterozoic times is defined by the E-W trending Nova Brasilândia metasedimentary belt, where upper amphibolite to granulite facies rocks from a younger (ca. 1.09 Ga) collisional event are preserved. Temperature-time (T-t) paths for each domain (craton and metasedimentary belt) are constructed using U-Pb, 40Ar/39Ar, and Rb-Sr data for minerals with different blocking temperatures. The T-t paths demonstrate no overlap in the timing or spatial distribution of tectonic and metamorphic activity. The separate cooling histories indicate the presence of a major tectonic boundary between the polycyclic basement rocks and the metasedimentary belt. This structure marks the suturing of the Paragua craton in the late Mesoproterozoic and is evidence that the accretionary history of the present outline of the Amazon craton was completed during the final stages of the amalgamation of Rodinia.