Geochemistry of Jamari complex, central-eastern Rondônia: Andean-type magmatic arc and Paleoproterozoic crustal growth of the southwestern Amazonian Craton, Brazil

摘要: Abstract The Jamari complex (gabbro-diorite-tonalite/enderbite-granodiorite/charnoenderbite) represents a Paleoproterozoic (ca. 1.76–1.74 Ga) magmatic arc emplaced along the southwestern Amazonian Craton in central-eastern Rondonia, Brazil. Comprising metaplutonic and metasedimentary rocks, constitutes polydeformed basement of Rondonia state. Together with regional data from Rondonia-Juruena Province, our findings suggest that border was site evolution at least ca. 1.78 to 1.63 Ga. Elemental geochemical show intermediate/acid orthogneisses are metaluminous mildly peraluminous, have medium high-K, calc-alkaline signature, suggesting they were formed an immature Andean-type arc. Gabbros signatures similar tholeiites active continental margin diorites characteristics compatible rocks tholeiite/calc-alkaline volcanic chemical felsic plutonic general trends increasing contents incompatible elements (K 2 O, Rb, Nb, Th, La, Ba Sr) decreasing (Ni, V, Sc, MgO, Fe O 3 , Al CaO TiO ) SiO . Although these variations consistent closed system fractional crystallization processes, wide variation Rb/Zr, La/Sm, K/Rb, Nb/Y, Th/Y Th/Yb may indicate random crustal contamination during rocks. Normalized trace element patterns enrichment LILEs (Rb, Ba, K, Th Ce) relative HFSEs (Nb, Zr, P Ti) very subduction-related orogenic belts. western extension (Juruena Complex, Mato Grosso), occurring some 500 km Madeirinha orogen (1.78–1.63 Ga). During this event metamorphosed under upper amphibolite granulite facies conditions only disturbed their igneous characteristics. Zircon U–Pb ages (ID-TIMS, SHRIMP LA-ICP-MS) set acretional phase between 1.76 1.74 Ga. Metamorphic mineral paragenesis textural features combined geochronologic data, metamorphic study area reached ( T  = ca. 750–800 °C,  = 7 8 kbar) tectonothermal collisional occurred 1.67 region subsequently reworked Rondonian-San Ignacio Orogeny (1.50–1.30 Ga), tectonic episode characterized by crytical assemblages anatexis, upper-amphibolite-facies metamorphism. youngest recognized is associated reactivation, deformation, thermal overprint, magmatism related Sunsas (1.30–0.95 Ga). Its effects represented extensive development shear zones (Ji-Parana system), mylonitic belts, rifts sedimentary deposits, post-collisional A-type intrusions. Nd isotopic high-grade range e values (−1.5 to +5.6) spectrum DM model-ages, 1.79 2.2 Ga. These demonstrate generation processes involved juvenile mantle sources variable proportions older recycled crust.