Combined U-Pb and Lu-Hf isotope analyses by laser ablation MC-ICP-MS: methodology and applications

the lutetium-hafnium isotopic system represents one of the most innovative and powerful tools for geochronology and isotopic studies. combined u-pb and lu-hf in situ analyses on zircon by la-mc-icp-ms permit to characterize isotopically the host magma from which it crystallized furnishing significant information for sediment provenance and crustal evolution studies. in this paper e describe the lu-hf systematic by la-mc-icp-ms developed in the laboratory of geochronology of the university of brasilia and report the results obtained by repeated analyses of 176hf/177hf isotopic ratio of three zircon standards: gj-1 = 0.282022 ± 11 (n=56), temora 2 = 0.282693 ± 14 (n=25) and uqz = 0.282127 ± 33 (n=11). the 176hf/177hf ratio (0.282352 ± 22, n=14) of gem quality zircon used as in-house standard have been also characterized. as a geological application, we analyzed two complex zircons selected from a migmatitic rocks from the borborema province, ne brazil. on the basis of u-pb and lu-hf data, two main crystallization events have been identified in both studied zircons. an older event at ca. 2.05 ga recognized in the inherited cores represents a well-characterized paleoproterozoic magmatic event that affected the whole borborema province. a second crystallization event at ~ 575 ma, recognized at the rims, represents a neoproterozoic (brazilian) high grade metamorphic-magmatic event.