| Full text | |
| Author(s): |
Zincone, Stefano A.
;
Oliveira, Elson P.
;
Laurent, Oscar
;
Zhang, Hong
;
Zhai, Mingguo
Total Authors: 5
|
| Document type: | Journal article |
| Source: | LITHOS; v. 266, p. 414-434, DEC 2016. |
| Web of Science Citations: | 5 |
| Abstract | |
High-silica rhyolites having U-Pb zircon ages of 3303 +/- 11 Ma occur along the eastern border of the Gaviao Block (Brazil) associated with the Contendas-Mirante and Mundo Novo supracrustal belts. Unlike many Archean greenstone sequences, they are not interlayered with mafic to intermediate units. Instead, they belong to an inter-related plutonic-volcanic system, together with granitic massifs having similar zircon crystallization ages of ca. 3293 +/- 3 Ma and 3328 +/- 3 Ma and plotting along the same geochemical trends as the rhyolites. The rhyolites show well-preserved primary volcanic features such as magma flow textures and euhedral phenocrysts. High emplacement temperatures are indicated by petrographic evidence (beta-quartz phenocrysts), zircon saturation temperatures (915-820 degrees C) and geochemical data, especially high SiO2 (74-79 wt.%) together with elevated Fe2O3(T) (similar to 3 wt.%), MgO (0.5-1.5 wt.%) and low Al2O3 (<11 wt.%). The rhyolites show homogeneous trace element ratios (La/Yb-N 4.8 +/- 1.8; EuN/Eu{*} similar to 0.55; Sr/Y similar to 0.7) and negative EHf(33 Ga) from 0 to -7, indicating derivation from a single crustal source for both occurrences. Specifically, the rhyolites would have derived from extraction and eruption of highly silicic residual liquid formed by crystallization of granitic magma in a relatively shallow (<10 km) reservoir, now represented by the granite massifs. The granite magma was formed by melting or differentiation of material similar to the diorite gneiss that occurs regionally. The 3.30 Ga volcanic plutonic systems formed after a period of crustal growth and stabilization of a thick continental lithosphere, represented by massive 3.40-3.33 Ga TTG and medium to high-K calk-alkaline magmatism in the Gaviao Block. The 3.30 Ga-old rhyolites and granites would therefore have formed in an intracontinental tectonic setting after the formation and stabilization of new continental crust, and accordingly would represent the first stages of rifting and continental break-up. Intraplate magmatism and intracrustal differentiation processes took place on Earth at 3.3 Ga and produced magmas that were distinct from Archean TTGs, questioning the reliability (or at least the uniqueness) of ``intraplate models{''} to explain the origin of the latter. (C) 2016 Elsevier B.V. All rights reserved. (AU) | |
| FAPESP's process: | 12/15824-6 - Evolution of archaean terranes of the São Francisco Craton and the Borborema Province, Brazil: global environmental and geodynamic implications |
| Grantee: | Elson Paiva de Oliveira |
| Support Opportunities: | Research Projects - Thematic Grants |