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Mafic rocks are the most common type of igneous rocks on Earth, however, constraining the crystallization age of mafic rocks can be challenging. Apatite is a common accessory phase in mafic rocks and is amenable to dating using the U–Pb system. However, the U–Pb system in apatite has a relatively low closure temperature (∼350°-550 °C) and is therefore prone to resetting by later thermal and metasomatic events. Here, a recently developed Lu Hf dating method using laser ablation reaction-cell mass spectrometry is applied to apatite from mafic rocks. The Lu Hf system in apatite has a higher closure temperature (∼650°-750 °C) compared to U–Pb, increasing the chances of obtaining primary crystallization ages. Furthermore, the laser-ablation method allows rapid data collection compared to traditional solution-based Lu Hf dating techniques. Four study areas were selected to compare the Lu Hf vs U–Pb systematics of apatite in mafic igneous rocks: the Paleoproterozoic Sudbury Igneous Complex (Canada), the Neoproterozoic Borborema Province (NE Brazil), the Paleoproterozoic Fennoscandian Shield (Finland), the Archean Yilgarn Craton and adjacent Mesoproterozoic Albany Fraser Orogen (Western Australia). For all analyzed samples that have apatite trace element compositions typical of an undisturbed primary mafic igneous lithology, the Lu Hf system retains primary igneous apatite crystallization ages, whereas the U–Pb system in the same grains often records isotopic disturbance or a cooling age. In few cases, the Lu Hf system has also been disturbed in response to recrystallization, however, such disturbance is readily detected with trace element data. Hence, this study demonstrates the potential of laser ablation apatite Lu Hf dating to obtain primary crystallization ages for otherwise difficult to date mafic rocks. • First study on Lu-Hf systematics for apatite from mafic rocks • U U-Pb system in apatite readily resets by thermal and metasomatic events • Lu Lu-Hf system is robust to volume diffusion < ∼660–730 °C, retaining primary crystallization ages. • Deformation leading to recrystallization 'resets' both U U-Pb and Lu Lu-Hf systems in apatite. • Apatite trace element data to differentiate isotopic disturbances related to recrystallisation versus volume diffusion [ABSTRACT FROM AUTHOR]

The Juiz de Fora Complex (JFC) in the Araçuaí-Ribeira orogenic system, southeastern Brazil, is a basement unit displaying a variety of rock types that is tectonically imbricated with the supracrustal rocks of the Raposos Group in the Upper Thrust System of the Occidental Terrane, Ribeira Belt. Here we report new petrological, geochemical, and zircon U–Pb and Lu–Hf isotopic data on mafic garnet-granulites from the JFC with a view to evaluate the timing and P-T conditions of the collisional event as well as protolith formation. This work presents the most comprehensive metamorphic study on the Juiz de Fora Complex rocks to date. Metamorphic P-T estimates for the metamorphic peak conditions of 800–900 °C and 8–9 kbar in basic garnet-bearing granulites were obtained for the JFC, indicating that metamorphism took place at deeper crustal levels. Geochemical, zircon U–Pb geochronology, whole-rock Sm–Nd, Rb–Sr isotopes, and Lu–Hf isotopic data of mafic granulites yielded U–Pb ages of ca. 2201 Ma, and moderately juvenile εNd(t) = −0.5 and were obtained from the JFC marking the timing of volcanic arc magmatism during the Rhyacian period. This arc-related stage was followed by the post-collisional period during the Early Paleoproterozoic with ca. 1.94 Ga E-MORB signature granulites that shows evidence of magma sourced from Neoarchean (∼2.8 Ga) crust with addition of juvenile components. The high-grade metamorphism is possibly related to the final collision of the Congo and São Francisco Cratons at 590–560 Ma, which placed the Neoproterozoic metasediments and the JFC rocks at the same level. The integrated information sheds light on two collisional episodes where the oldest is represented by arc-related granulites during the Rhyacian Orogeny and the youngest is the higher-pressure Neoproterozoic overprint during the Brasiliano Orogeny. • The garnet-bearing mafic granulites formed under 800–900 °C with pressures of 8–9 kbar. • Rhyacian and Brasiliano orogenic cycles imprinted the Juiz de Fora Complex rocks. • Zircon data and metamorphic textures indicate a complicated evolution over the two orogenic cycles. [ABSTRACT FROM AUTHOR]

Absolute dating of sedimentary rocks and fossils from the Mesozoic are still rare, mainly due to the difficulties arising from diagenetic changes. Diagenesis promotes changes in the primary structure and chemical composition of biomineralization, which should remain unchanged from the time of deposition and fossilization. Three bioapatite teeth extracted from a jaw fragment of Cladocyclus gardneri from the Romualdo Formation, Araripe Basin, Northeastern Brazil were dated by the U/Pb method in order to obtain an absolute age. The rocks that contain this fossil are dated to Aptian by biostratigraphy of palynomorphs (Sergipea variverrucata biozone, Petrobras P-270), ostracods (Damonella grandiensis biozone, Petrobras) and from the international biozoning of planktonic foraminifera Microhedbergella miniglobularis. The teeth were mounted in 25 mm epoxy resin rounds, imaged by optical microscope and SEM and dated with a Nu Instruments AttoM single-collector ICP-MS coupled to an NWR193nm UC (Ultra Compact) ArF excimer laser system. A Discordia U–Pb date obtained from three separate Cladocyclus gardneri dentine is 110.5 ± 7.4 Ma (2s, MSWD = 2.6), consistent with the biostratigraphic age. This date was based on 155 integrations of line scan analyses (spot size of 30 μm, scan moved at 2 μm per second/100 μm in total length). 238U/206Pb ratios that differed from the mean value by more than 2SD for each tooth were excluded based on the likelihood they reflect U-redistribution during fossilization/post-fossilization fluid alteration. Remaining variations in 238U/206Pb and 207Pb/206Pb ratios along the Discordia reflect variable contributions from common Pb, both within and between the three teeth. They reflect primary U/Pb compositions given that they date the expected age of fossilization. • Direct dating on fossils is still a challenge to be overcome in Geochronology. • Biomineralized parts are more likely to be preserved in the fossilization. • First absolute dating result for the Romualdo Formation, Araripe Basin. • The U–Pb dating corroborates biostratigraphy data. [ABSTRACT FROM AUTHOR]

Abstract: The Sergipano Belt is the outcome of collision between the Pernambuco–Alagoas Massif and the São Francisco Craton during Neoproterozoic assembly of West Gondwana. Field relationships and U–Pb geochronology of granites intruded in garnet micaschists of the Macururé Domain are used to constrain the main collisional event (D2) in the belt. The granites are divided into two groups, the pre-collisional granites (pre- to early-D2) and the syn-collisional granites (syn- to tardi-D2), the latter were emplaced as sheets along the S2 axial plane foliation or they were collected at the hinge zones of F2 folds. A U–Pb SHRIMP zircon age of 628±12 Ma was obtained for the pre-collisional Camará tonalite. Two U–Pb TIMS titanite ages were obtained for the syn-collisional granites, 584±10 Ma for the Angico granite and 571±9 Ma for the Pedra Furada granite, and these ages are close to the garnet-whole rock Sm–Nd isochron of 570 Ma found for the peak of metamorphism in the Sergipano Belt. The ages of the Camará tonalite (628 Ma) and the Pedra Furada granite (571 Ma) mark respectively the maximum age for beginning of the D2 event and minimum age for the end in the Macururé Domain. Using these ages, the main Neoproterozoic D2 collisional event has been in operation in the Sergipano Belt for at least 57 million years. Correlation with coeval granitoids farther north in the Borborema Province indicate that while in the Sergipano Belt the syn-D2 granites (ca. 590–570 Ma) were emplaced under compression, in the Borborema Province they emplaced under extensional conditions related to regional strike-slip shear zones. These contrasting emplacement settings for contemporaneous Neoproterozoic granitoids are explained by a combination of continent–continent collision and extrusion tectonics. [Copyright &y& Elsevier]

• Archean and Paleoproterozoic rocks emerge within the Neoproterozoic Araguaia Belt-AB. • Northern AB exhibits Mesoarchean (2.93–2.87 Ga) and 1.86 Ga granitic gneisses. • Southern AB shows Rhyacian orthogneisses (2.06 Ga) and 1.87 Ga deformed granite. • Northern and southern basement already formed a single crustal segment by the Orosirian. • This Archean/Paleoproterozoic basement integrated the Amazonian Craton. Archean and Paleoproterozoic basement rocks are exposed in the Araguaia Belt, a Neoproterozoic orogen bordering the eastern portion of the Amazonian Craton. Zircon LA-MC-ICPMS U-Pb and Lu-Hf isotopic systematics allowed a more accurate dating of the basement rocks and investigating the evolution of this large Archean/Paleoproterozoic crustal segment and discuss the relationship with the southeastern Amazonian Craton. Archean TTG orthogneisses (2.93 to 2.87 Ga) prevail in the northern belt while distinct magmatic events generated their protoliths in approximately 60 Ma. Zircon Hf model ages (~3.0 to 3.4 Ga) and Ɛ Hf(2.87-2.93) from −4.3 to +5.3 suggest crustal reworking of Mesoarchean juvenile sources, with the subordinated contribution of older crust. A Mesoarchean source is also indicated by the Hf model ages (2.93–3.25 Ga) and Ɛ Hf(−1.86 Ga) from −4.8 to −1.6 of a 1.86 Ga granitic gneiss intrusive in the Archean TTG. An orthogneiss and an intrusive granitoid from southern segment of the belt were dated 2.06 Ga and 1.87 Ga, respectively. The Hf model ages (2.65–2.86 Ga) determined for these rocks, the Ɛ Hf(-2.06 Ga) (−4.8 to −1.6) for the orthogneiss and the Ɛ Hf(1.87 Ga) (−15.8 to −9.7) found for the granitoid reveal a dominant crustal source for the southern basement rocks. The Archean and Paleoproterozoic basement constituted a single crustal segment by the Orosirian, since both segments present intrusive granites of this geological period. The Archean orthogneisses of the Araguaia Belt and the granitoids of the Carajás Province Mesoarchean domains in southeastern Amazonian Craton share some similarities, such as the TTG affinity magmatism formed in a relatively similar time interval, the Orosirian intrusive granites, and the Mesoarchean juvenile source. Therefore, the basement rocks cropping out in the northern segment of the Araguaia Belt may represent portions of the adjacent Amazonian Craton. [ABSTRACT FROM AUTHOR]