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Título

PROTRACTED TECTONIC EVOLUTION OF AN ULTRA-HOT AND THIN MID-PROTEROZOIC CRUST: INSIGHTS FROM THE JURUENA PROVINCE IN THE AMAZON CRATON

Texto do resumo

The “Boring Billion” is the interval of Mid-Proterozoic between 1850-850 Ma characterized by a stability of climatic, biologic, and lithospheric records compared with other periods of the Earth's evolution. In concern of the geological record, this period exhibits metamorphic rocks with elevated thermobaric rates and an increase in A-type magmatism. In the present study, the Mid-Proterozic record of the Amazon Craton was investigated in the Juruena Geochronological Province. We integrated a P-T-t study in the metamorphic rocks of the Nova Monte Verde Complex and whole-rock trace element crustal thickness proxies to a large igneous geochemical dataset from the Alta Floresta region.
The rocks of the Nova Monte Verde Complex achieved peak conditions of ~950-1000ºC and 6-7 kbar and evolved in a quasi-isobaric cooling. Zircon petrochronology results indicate that in the period from 1870 to 1790 Ma the Nova Monte Verde Complex underwent a period of garnet consumption during the prograde heating, and melt was crystallized in close-peak conditions from 1790 to 1750 Ma. Geochemical proxies of the basement rocks (Cuiú-Cuiú Complex, 2050-1950 Ma) are consistent with magmas formed in a crust with ~60 km. The Matupá Intrusive Suite and contemporaneous magmatic rocks (1910-1880 Ma) have trace elements signatures that point to formation at 50-40 km, while the Juruena-Teles Pires Suite (1840-1750 Ma) at depths <30 km. These results suggest a progressive regional thinning of the continental crust during a period of 100 Ma, from 1850 to 1750 Ma, coeval with the ultra-high-T, low-P metamorphic evolution of the Nova Monte Verde Complex and the A-type magmatism of the Juruena-Teles Pires Suite. This crustal thinning could be related to mantle rise, a likely heat source for the UHT metamorphism. A mantle contribution is consistent with the primitive isotopic and geochemistry signatures of the A-type Juruena-Teles Pires Suite. Our results furnish important insights concerning the transition between the Paleoproterozoic to mid-Proterozoic geological record in the Amazon Craton and can be explored to understand geodynamic changes during this period.

Palavras Chave

Boring billion; zircon petrochonology; UHT metamorphism