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It is well-established that lanthanide rare earth elements (REEs) have the potential to record the nature and source characteristics of their host magmas, in both whole-rock and their minerals. Accessory minerals that concentrate REEs are especially useful in crustal evolution studies, both for their elemental and isotopic information; the classic and unrivalled example being zircon. Approaches using a single radiogenic isotopic system, or one radiogenic and one stable isotope system (e.g., Hf and O) in one REE-bearing mineral (usually zircon) are common, but those involving multiple isotopes in several minerals remain scarce despite offering many advantages. Importantly, the latter approaches also allow comparing different techniques and provide evidence on whether isotopic systems were disturbed by secondary processes. This contribution documents several isotopic systems within the abundant accessory mineral of Caledonian high Ba-Sr granitoids from Northwest Scotland. We present a multi-isotope study of titanite, zircon and apatite from two localities (Strontian and Rogart), which were selected for their contrasting whole-rock isotopic signatures - the former deriving from a depleted mantle source, whereas the latter derived from a strongly enriched mantle source. New in-situ Sm-Nd in titanite and apatite and Hf in zircon isotope data are discussed and compared with in-situ oxygen isotope data previously published for the same samples. An internal consistency is observed for Nd isotopes in apatite and titanite. Nd isotopes values for both minerals strongly correlate with Hf isotopes in zircon. Isotopic data at the mineral scale confirm the Strontian and Rogart source characteristics previously defined from whole-rock isotope data, with the Rogart having a more enriched signature than the Strontian source along the "Caledonian Parental Magma Array"(CPMA). In contrast, a significant discrepancy exists between whole-rock and REE-mineral oxygen isotope data as the latter can be affected by post emplacement alteration and hence can be misinterpreted. Importantly, the contribution of sediments in the CPMA source(s) can be estimated from a diagram combining Sm-Nd isotopic signatures and (La/Sm) N in apatite and titanite. Overall, we demonstrate that detailed petrogenetic records are not only available in zircons but also in magmatic titanite and apatite, and we suggest that integrated multi-mineral approaches have potential to maximise constraints from in-situ mineral isotope geochemistry. [ABSTRACT FROM AUTHOR]

Voluminous rhyolitic lavas and ignimbrites (c. 34 000 km3) were formed in the NE German Basin in a post-collisional setting at c. 295 Ma. Trace elements, ϵHf and δ18O have been measured in dated magmatic and inherited rhyolitic zircons from three drill cores across the basin. Magmatic zircons crystallized in two stages: the first stage in less differentiated and isotopically heterogeneous magmas and the second stage in more differentiated and isotopically homogeneous magmas. The first and second stages can be related to the crystallization of zircons within a heterogeneous pluton and in an evolved, silicic magma that was later erupted. Some zircons crystallized entirely during the evolved magma stage and provide good resolution for identifying and characterizing processes happening shortly before eruption. The isotopic compositions of the magmatic zircons constrain the proportions of juvenile and reworked materials involved in the formation of voluminous silicic magmas in a post-collisional tectonic setting. The advantage of studying the volcanic rocks from the NE German Basin is that their petrogenesis involved a relatively simple, two-source interaction during magma production, which permits quantitative estimation of the amount of each source component. AFC modelling shows that the first stage zircons crystallized from magmas containing 5–80% of the juvenile component, whereas the final rhyolitic magmas contained 30–40% of this material. The inherited zircons have Hf model ages of 1·9–2·2 Ga, suggesting that much of the local basement was initially derived from the mantle at that time and that it was subsequently reworked at around 1·5 Ga. Similar model ages are a feature of Baltica-derived sediments and the implication is that such sediments underlie large areas of the NE German Basin. The lack of any record of Avalonian basement in the NE German Basin may indicate that both the sedimentary cover and the underlying basement are part of Baltica. [ABSTRACT FROM AUTHOR]

Impacts may have been important mechanisms of crustal redistribution and differentiation, particularly during intense postaccretionary bombardment between 4.5 Ga and 3.9 Ga ago. Evidence of crustal processes during this period is largely provided by detrital zircons from the Yilgarn craton, Australia. Trace element compositions, crystallization temperatures, and inclusion populations of these ancient zircons have been taken as evidence for predominantly granitic source magmas, implying widespread felsic continental crust on the early Earth. However, there is little knowledge of zircons formed in impact melt sheets, a potential source for the Hadean zircons. Here we present Ti thermometry, trace elements, and inclusion populations of zircons from the 1.85 Ga Sudbury impact melt sheet (Ontario, Canada). Our results demonstrate that large variations in zircon crystallization temperature and composition will be an inevitable consequence of the evolution of such magmatic systems. We also show that zircons in mafi c rocks crystallize in residual liquids of granitic composition, producing inclusion assemblages that are remarkably similar to those reported for the ancient Yilgarn grains. Thus, we conclude that the trace element compositions and inclusion populations of the Hadean zircons are consistent with crystallization from more mafi c melts than previously recognized, although high crystallization temperature distributions of Sudbury zircons indicate that impact melt sheets were not a dominant source for the grains older than 3.9 Ga. [ABSTRACT FROM AUTHOR]

The ϵHf and δ18O values in detrital zircons from the Slave craton, Canada, indicate three episodes of crust formation between ca. 4.5 and 2.8 Ga, namely at ca. 4.4-4.5 Ga, ca. 3.8 Ga, and ca. 3.4 Ga. Most of the juvenile crust appears to have been mafic in composition, and there is no clear evidence for initial granitic protocrust in the Hadean of the Slave craton. The range of initial ϵHf values in zircons increases from 3.9 to 2.8 Ga, indicating that both extraction of new material from mantle and reworking of the older crust are important for the secular evolution of the continental crust. A preliminary review of available Hf data in zircons suggests that the three episodes of crust generation may have been of global importance. The mafic crust formed in the Archean and the Hadean was then reworked for at least ~0.5-1.5 b.y., as indicated by data from the Slave craton, Gondwana, and the Limpopo Belt of Africa. [ABSTRACT FROM AUTHOR]

Detrital zircon grains are employed to decipher sediment provenances and crustal evolution, and they provide unique evidence of Hadean crust-mantle differentiation processes. We demonstrate that mineral inclusions in zircon provide valuable information on the conditions under which zircon crystallized. Zircon grains from selected plutonic rocks from Dronning Maud Land, Antarctica, contain inclusions of apatite, biotite, amphibole, and pyroxenes that accurately reflect the chemical compositions of the equivalent phases in the host-rock matrix, and the compositions of the whole rocks. High concentrations of Y and low concentrations of Sr in apatite inclusions in zircon are diagnostic of evolved, felsic granitoid host rocks. In contrast, the relative abundances and compositions of plagio clase and alkali feldspar inclusions in zircon are decoupled from the composition of the whole rock, and they are generally indicative of granitic melts regardless of the bulk rock. This is best explained by the late crystallization of zircon relative to the bulk of the feldspars. We conclude that inclusions of apatite and mafic phases in zircon constrain the potential source rocks of detrital zircon, whereas feldspar inclusions do not. [ABSTRACT FROM AUTHOR]

Abstract: The in situ Lu–Hf isotope analysis of zircon by laser ablation has emerged as a high-calibre tool for tackling magmatic and crustal evolution. The strength of the approach lies with the ability to target specific zircon growth domains identified by imaging, and thus to unravel polyphase crystallisation histories. However, due to the volume of material being sampled during analysis there remains the possibility of ablation-induced mixing between Hf from domains of different age. Inaccurate Hf isotope ratios and spurious geological interpretations could result. One approach to this problem involves dating the same volume of material analysed for Hf isotopes by concurrently measuring 207Pb/206Pb ratios during ablation [Woodhead, J.D., Hergt, J.M., Shelley, M., Eggins, S., Kemp, R. 2004. Zircon Hf-isotope analysis with an excimer laser, depth profiling, ablation of complex geometries, and concomitant age estimation. Chemical Geology 209, 121–135.]. This paper explores the viability of this dual analysis by investigating complex zircons from three different geological contexts, detrital zircons in sedimentary rocks, inherited zircons in granites, and zircons in metamorphosed Eo-Archaean TTG gneisses from Greenland. The implications of the Greenland data for Archaean crustal evolution are discussed in the light of published solution zircon Hf isotope datasets from these gneisses. A case study of detrital zircons from modern river sands in the Himalayas highlights the potential of the technique for providing a rapid, cost-effective picture of crustal evolution that should complement regional bulk rock studies. [Copyright &y& Elsevier]