Orosirian-Stenian evolution of the Bolivian Precambrian Shield, SW Amazonian Craton, constrained by U–Pb geochronology and Nd–Hf isotopic parameters

We present new and compiled U–Pb zircon ages and Hf zircon and Nd constraints for rocks of the Bolivian Precambrian Shield southwestern fringe of the Amazonian Craton. The database and updated geologic information provide new insights into the Orosirian-Early Stenian evolution. This shield can be subdivided into the San Diablo and Paraguá domains considering their particular geologic histories and lithostratigraphic units: i) the southern San Diablo Domain consists mainly of amphibolite facies gneissic rocks with documented ages as old as 1940 Ma, intruded by the Correreca, Santo Corazón, Tauca, and Santa Terezita plutons with documented ages between 1874 and 1849 Ma; ii) the Paraguá Domain comprises the Lomas Maneches Granulite Complex (1820 Ma), the Chiquitania meta igneous-sedimentary complex (1750-1690 Ma), and the roughly coeval San Ignacio Schist Group (1690 Ma). Locally, the country rocks are crosscut by the Yarituses Suite (1683-1610 Ma), which is contemporary with the Lomas Maneches Granitoid Suite (1690-1660 Ma). The Pensamiento Granitoid Complex (1440-1270 Ma), constituted by syn-to late-kinematic and late-to post-kinematic granites, collectively known as San Ignacio Granitoids, is widespread in the studied region. Six zircon U–Pb datings and 76 compiled data determine that the continental crust experienced a long-lived tectonic-magmatic history, distinguished by three accretionary events: 1941–1849 Ma, 1690-1610 Ma, and 1430-1340 Ma. These events have relationships with the Proterozoic growth of Amazonia enclosing the distal Rio Apa Terrane. Later, the southern portion of the Bolivian Precambrian Shield experienced crustal shortening, magmatism, and overprints due to the Sunsás/Greenville (1200-1000 Ma) orogeny that marks the Amazonia-eastern Laurentia collage in Rodinia times. From a petrogenetic perspective, the country rocks of the San Diablo Domain yield documented Sm–Nd TDM ages and εNdT values of ca. 1.69 to 2.29 Ga and −5.7 to +1.8 respectively, suggestive of the derivation of short-lived protoliths. The Correreca intrusion (1874–1862 Ma) gives published zircon Hf model ages of 2.68 Ga and 2.29 Ga and coupled εHfT values of −4.6 to +2.8. The bulk isotopic signature for the San Diablo rocks is consistent with magma genesis in a moderately juvenile-like accretionary arc, where the calc-alkaline types show a subduction-related signature. In contrast, the country rocks in the adjoining Paraguá Domain show published Sm–Nd TDM model ages of ca. 1.55 to 2.48 Ga and εNdT values of −4.9 to +5.2, pointing to distinct protoliths in the magma genesis. The Yarituses Suite includes the following granites: La Cruz (1673 ± 21 Ma), Refugio (1673 ± 25 Ma; 1641 ± 4 Ma), San Pablo (1609 ± 17 Ma), San Miguel (1681 ± 13 Ma), and Rosario (1678 ± 21 Ma). These granites yield variable Sm–Nd TDM model ages of ca. 1.67 to 2.48 Ga and εNdT of +4.1 to −3. 8 (Ta ble 1), suggesti ng the derivation of distinct crustal components. The new and compiled data demonstrate first time that the Lomas Maneches and Yarituses suites, in conjunction with the Chiquitania complex and the newly dated Ambaybo rhyolite (1691 ± 8 Ma) of the San Ignacio Schist Group, belong to a distinct tectonic-magmatic episode akin to an active continental margin. The Pensamiento Granitoid Complex (1440-1270 Ma) shows documented Sm–Nd TDM model ages between ca. 1.55 and 2.42 Ga and predominantly crustal-like isotopic signatures as low as −4.6 typical of a continental arc setting. On a broader scale, the San Ignacio Granitoids are products of the Alto Guaporé orogeny, previously established in the Brazilian counterpart, characterized by an accretionary phase (ca. 1440 Ma) and a collisional one (ca. 1330 Ma) against the active margin of proto-Amazonia at the Ectasian. The regional structural framework of those plutons in the Bolivian counterpart suggests that the San Ramón and Coronación granodiorites (1429-1423 Ma) are pre-to syn-kinematic to the collisional phase. In contrast, the La Junta (1380 ± 17 Ma) and San Martin (1409 ± 17 Ma) granites are syn-to-late kinematic. The Diamantina granite (1357 ± 19 Ma) is coeval with the Alto Guaporé collisional phase, while the San Andrés granite (1289-1275 Ma) is a post-kinematic pluton. The εNdT of the Pensamiento Granitoid Complex varies from +5.2 to −4.6. The onset of the Sunsás orogeny, characterized by an allochthonous collisional-type belt (1.2–1.0 Ga) ends the polycyclic evolution of the Bolivian Precambrian Shield, leading to tectonic stability of the Amazonian Craton.