Leucogranitos intrusivos no Grupo Araxá: registro de um evento magmático durante colisão neoproterozóica na Porção Meridional da Faixa Brasília
14
Citation
24
Reference
12
Related Paper
Citation Trend
Abstract:
This study presents the geological characteristics of granitic magmatism associated with the Araxa Group in its type-area in the southern segment of the Neoproterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a regional fold, the Araxa Synform, overlying two other thrust sheets comprising the Ibia and Canastra Groups. The Araxa Group comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic and psammitic metasedimentary rocks. All rocks were metamorphosed in the amphibolite facies at ca. 640 Ma and were intruded by leucocratic granites with collisional mineralogical-geochemical signatures at ca. 637 Ma ago. The intrusions were linked to the evolution of gently depping shear zones. These granites represent an important magmatic event in a collisional environment during the final collage of West Gondwanaland. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust.This study reviews the geological characteristics and puts forward a new evolution model for the Araxa Group in its type-area, the southern segment of the Neoproterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a synformal regional fold, the Araxa Synform, overlying two other thrust sheets made of the Ibia and Canastra Groups. The Araxa Group is described as a tectonostratigraphic terrane in the sense of Howell (1993). It comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic metasedimentary rocks, and subordinate psanmites. All rocks were metamorphosed to amphibolite facies at ca. 630 Ma ago and were intruded by collisional granites. The amphibolites represent original basaltic and gabbroic rocks, with minor ultramafics (serpentinite/ amphibole-talc schist). The basalts are similar to high FeO tholeiites, with REE signatures that resemble E-MORB and a Nd(t) =+ 1.1. The metasedimentary rocks are interpreted as the result of a marine deep-water sedimentation. They have Sm-Nd model ages of 1,9 Ga, and a Nd(t) = -10.21. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust. The data presented here differ significantly from the original definition of Barbosa et al. (1970) who describe the Araxa Group as a pelitic/psanmitic sequence and the collisional granites as a basement complex.
Pelite
Cite
Citations (33)
Phyllite
Geochronology
Protolith
Diamictite
Cite
Citations (70)
Orogeny
Back-arc basin
Continental arc
Island arc
Continental Margin
Cite
Citations (129)
Abstract The Brasília Belt comprises terranes and thrust-sheets that were tectonically transported towards the western passive margin of the São Francisco–Congo palaeocontinent during an orogenic episode resulting from collision of the Paranapanema and Goiás blocks and the Goiás magmatic arc against São Francisco–Congo at 0.64–0.61 Ga. The tectonic zones of the belt are, from east to west: a foreland zone with Archaean–Palaeoproterozoic granite–greenstone basement covered by Neoproterozoic anchimetamorphic sedimentary rocks (Bambuí Group); a low metamorphic grade thrust-fold belt of proximal shelf successions, mostly siliciclastic, containing rare basement slivers; metamorphic nappes in upper greenschist to granulite facies of distal shelf and slope metasediments and subordinate tholeiitic metabasalts; the Goiás massif, possibly a microcontinent; and the Goiás magmatic arc. The accretion of these terranes against the western margin of the São Francisco–Congo palaeocontinent took place during an early phase of Gondwana supercontinent amalgamation, when terranes accreted around São Francisco–Congo to create a proto-West Gondwana landmass, around which subsequent collisional and accretionary events followed, such as those in the Borborema–Trans-Saharan province ( c. 0.62–0.60 Ga); in the Ribeira–Araçuaí belt ( c. 0.58 Ga); along the Araguaia and Paraguay belts (collision of Amazonia, c. 0.54–0.52 Ga); and the accretion of Cabo Frio terrane in the Ribeira Belt ( c. 0.53–0.50 Ga).
Cite
Citations (129)
Felsic
Geochronology
Cite
Citations (72)
Geochronology
Rodinia
Orogeny
Supercontinent
Passive margin
Cite
Citations (173)
This paper focuses the tectonic evolution of the southern Brasilia belt, with emphasis on the Furnas segment, along the 21°S parallel. The uppermost structural unit (Passes Nappe - PN) comprises a highly deformed metasedimentary succession interpreted as a fragment of the Neoproterozoic passive margin of western Sao Francisco craton. An inverted metamorphic gradient ranging from greenschist to lower granulite facies of medium to high-pressure regime characterizes the PN as relict of a subduction zone. The External Domain displays a complex imbrication of basement rocks (Archean Piumhi greenstones, a turbiditic graywacke succession and a calc-alkaline granitoid suite) with undated siliciclastic low-grade metasedimentary rocks. The Sap Francisco Craton (SFC) comprises pre-1.8 Ga basement rocks covered by anchimetamorphic Neoproterozoic carbonatic shallow marine platform deposits of the Bambui group. The Brasiliano thrust stacking generated a coarse clastic influx of molassic character on the foreland zone of Sao Francisco Craton, coeval with the exhumation of the External Domainthrust sheets. New K-Ar determinations on mineral separates are presented and interpreted among previous data. The SFC basement rocks display Paleo- to Mesoproterozoic cooling ages. The allochthonous units, in contrast, display K-Ar ages within the 560-675 Ma range. Brasiliano thrust stacking is therefore interpreted to have taken place onto a cold Sao Francisco craton foreland, in a thin-skinned style, as basement rocks were not heated enough to have their K-Ar systems reset during the allochthony.
Basement
Imbrication
Greenschist
Orogeny
Diachronous
Cite
Citations (31)
Rodinia
Back-arc basin
Geochronology
Cite
Citations (172)
Back-arc basin
Cite
Citations (157)
Passive margin
Continental Margin
Cite
Citations (108)