Estudo isotópico de U-Pb, Lu-Hf e Ti em rochas vulcânicas associadas aos sulfetos maciços da Faixa Piritosa Ibérica (Espanha)

Abstract

In this work, new U-Pb, Ti and Lu-Hf isotope data are presented from the study of representative samples of the felsic volcanic rocks associated with the massive sulfide bodies of different regions of the Iberian Pyrite Belt (IPB). The IPB is a giant volcanogenic massive sulfide province divided into two distinct units, the Northern Region and Southern Region.The two regions are characterized by large geological differences, such as massive sulfide formation, host rock, ages, temperatures and magmatic sources. The U-Pb and Ti isotopes studies were performed at SHRIMP, while Lu-Hf studies were performed at LA-MC- ICPMS.The NorthernRegion is subdivided into two different domains, the Central Sector and the Northern Belt. The U-Pb isotopes of the volcanic rocks of the Northern Region show this region is associated with Tournaisian volcanism, a later volcanic interval in comparison with the widely recognized Strunian volcanism in the Southern Region. The rocks of the Northern Belt had a range associated with the massive sulfide bodies between 354-347 Ma, while La Zarza in the Central Sector had a range of 357-355 Ma. In Rio Tinto, the geochronological study was more thorough and characterized a wide range of intermittent pulses between 358-339 Ma. The main interval is associated with the VMS formation and dated between 352-348 Ma. The rocks of the Southern Region showed U-Pb ages associated with massive sulfide bodies between 365-359 Ma. Other ages in the range of 352-348 Ma are also observed in the Southern Region in plutonic rocks and a barren volcanic rock in Las Cruces but these samples are barren and are also different from Strunian rocks in relation to the crystallization temperature. Tournaisian volcanic rocks associated with massive sulfide bodies have temperatures of 49 Ti below 760°C, while the temperatures of Strunian volcanic rocks that have been studied in this thesis and by other authors are above 800°C. These colder temperatures are unexpected and complement the scenario presented in the literature for the IPB massive sulfide deposits and the literature as a whole, which shows the massive sulfide bodies associated with higher temperature volcanic bodies (T> 800°C). The Rio Tinto is the largest deposit of IPB and presents temperatures below 730°C. The ƐHf signatures obtained from the Lu-Hf isotopes also show the differences between the different IPF sectors. In the Northern Belt of the Northern Region there is a large amount of mantle material contributed and the average value of ƐHf is ~ -0.2. The Central Sector still has a contribution of this mantle material and has an average Hf signature of ~ -3.2. The Southern Region has ƐHf ~ -5.2 in Spain, while the Portuguese portion has ƐHf ~ -7.97. The geochronology of the volcanic Felsic unit associated with the Rio Tinto deposit was studied in detail and showed three distinct periods: Felsic Unit I, at 358 Ma, which marks the onset of the Felsic Unit volcanism in the Rio Tinto region. The Felsic Unit II is the unit related to the massive sulfide bodies and ...

U-Pb zircon SHRIMP dating of a protracted magmatic setting and its volcanic emplacement: Insights from the felsic volcanic rocks hosting the sulphide ore of the giant Aljustrel deposit, Iberian Pyrite Belt

“…However, in general, no relationship can be seen between zircon age fractions and Th (zircon/rock)/ U (zircon/rock) (see also Siégel et al, 2018). Considering that temperatures obtained in the volcanic rocks of the IPB by Ti-in-zircon and quartz-hosted melt inclusions are in excess of 700-800 • C (Marques et al, 2020;Mello, 2020), and assuming this as a reference temperature for equilibrium between zircon and melt, the expected Th (zircon/rock)/ U (zircon/rock) ratio is ~0.6-0.4. For higher temperatures the ratio decreases (Kirkland et al, 2015).…”