The Colíder Paleoproterozoic felsic volcanism:New insights into stratigraphy and petrogenesis in the southern Amazonian Craton

The eastern side of Alta Floresta Mineral Province(AFMP)(União do Norte region)comprises an effusive/-subvolcanic phase,explosive phase,and epiclastic rocks.The effusive/subvolcanic phase comprises massive porphyritic rhyolite with different degrees of crystallinity,porphyritic rhyolite with flow structure,and microcrystalline rhyolite.The explosive phase is characterized by welded lapilli tuff,lapilli tuff with flow structure,stratified lapilli tuff,and tuff with accretionary lapilli.Sandstones and siltstones characterize epiclastic rocks.There are porphyritic rhyolite dikes that cut the volcanic sequence.The rocks of the Colíder Group are rhyolites(>70%SiO2)with calcic-alkaline to alkaline-calcic affinity.A rhyolitic rock is predominantly ferroan and metaluminous,while a pyroclastic rock is predominantly magnesian to ferroan and meta-to peraluminous in composition.The rocks have a high LREE content,and slight fractionation of HREE suggests they have hybrid geochemical characteristics of high potassium calc-alkaline,shoshonitic,and suggestive affinities of A-type magmas,probably produced in a post-collisional orogenic environment.These rocks have a relatively high level of Ba and Rb and a negative anomaly for Sr,P,Nb,Ta,and Ti,suggesting an intra-plate mantle source with contributions from a metasomatized mantle edge.The rocks do not have adakitic characteristics nor fertility for Cu-Au(Sr/Y<1.9 and LaN/YbN<38.0)as in other regions of the AFMP.The welded lapilli tuff rocks show U-Pb age of 1838±17 Ma and 1817±2 Ma and are the older explosive phases.The effusive/subvolcanic phase has U-Pb ages of 1800±3 Ma and 1792±3 Ma obtained in the massive porphyritic rhyolite.The age interval of approximately 46 Ma(1838–1792 Ma)suggests the presence of two or more volcanic cycles or distinct volcanic events.Based on the interpretation of volcanic and epiclastic deposits and remote sensing products,the paleoenvironmental reconstruction includes subaerial with effusive/subvolcanic and explosive stages in a probable eroded volcanic caldera system with epiclastic rocks from a fluvial depositional system.This volcanic scenario provides more information about the Colíder–Teles Pires volcano-plutonic event,uniquely mapped in AFMP,and offers new insights into the tectonic frame of the Amazonian craton.