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Although REE (lanthanides+Sc+Y) mineralization in alkaline silicate systems is commonly accompanied with Zr mineralization worldwide, our understanding of the relationship between Zr and REE mineralization is still incomplete. The Baerzhe deposit in Northeastern China is a reservoir of REE, Nb, Zr, and Be linked to the formation of an Early Cretaceous, silica-saturated, alkaline intrusive complex. In this study, we use in situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of zircon and monazite crystals to constrain the relationship between Zr and REE mineralization at Baerzhe. Three groups of zircon are identified and are differentiated based upon textural observations and compositional characteristics. Type Ia zircons display well-developed oscillatory zoning. Type Ib zircons are darker in cathodoluminescence images and have more irregular zoning and resorption features than type Ia zircons. In addition, type Ib zircons can locally occur as overgrowths on type Ia zircons. Type II zircons contain irregular but translucent cores and rims with oscillatory zoning that are murky brown in color and occur in aggregates. Textural features and compositional data suggest that types Ia and Ib zircon crystallized at the magmatic stage, with type Ia being least-altered and type Ib being strongly altered. Type II zircons, on the other hand, precipitated during the magmatic to magmatic-hydrothermal transition. Whereas the magnitude of the Eu anomaly is moderate in the barren alkaline granite, both magmatic and deuteric zircon exhibit pronounced negative anomalies. Such features are difficult to explain exclusively by feldspar fractionation and could indicate the presence of fluid induced modification of the rocks. Monazite crystals occur mostly through replacement of zircon and sodic amphibole; monazite clusters are also present. Textural and compositional evidence suggests that monazite at Baerzhe is hydrothermal. Types Ia and Ib magmatic zircon yield 207Pb-corrected 206Pb/238U ages of 127.2±1.3 and 125.4±0.7 Ma, respectively. Type II deuteric zircon precipitated at 124.9±0.6 Ma. The chronological data suggest that the magmatic stage of the highly evolved Baerzhe alkaline granite lasted less than two million years. Hydrothermal monazite records a REE mineralization event at 122.8±0.6 Ma, approximately 1 or 2 million years after Zr mineralization. We therefore propose a model in which parental magmas of the Baerzhe pluton underwent extensive magmatic differentiation while residual melts interacted with aqueous hydrothermal fluids. Deuteric zircon precipitated from a hydrosilicate liquid, and subsequent REE mineralization, exemplified by hydrothermal monazite, correlates with hydrothermal metasomatic alteration that postdated the hydrosilicate liquid event. Such interplay between magmatic and hydrothermal processes resulted in the formation of discrete Zr and REE mineralization at Baerzhe.

We present a statistical approach to data mining and quantitatively evaluating detrital age spectra for sedimentary provenance analyses and palaeogeographic reconstructions. Multidimensional scaling coupled with density-based clustering allows the objective identification of provenance end-member populations and sedimentary mixing processes for a composite crust. We compiled 58 601 detrital zircon U–Pb ages from 770 Precambrian to Lower Palaeozoic shelf sedimentary rocks from 160 publications and applied statistical provenance analysis for the Peri-Gondwanan crust north of Africa and the adjacent areas. We have filtered the dataset to reduce the age spectra to the provenance signal, and compared the signal with age patterns of potential source regions. In terms of provenance, our results reveal three distinct areas, namely the Avalonian, West African and East African–Arabian zircon provinces. Except for the Rheic Ocean separating the Avalonian Zircon Province from Gondwana, the statistical analysis provides no evidence for the existence of additional oceanic lithosphere. This implies a vast and contiguous Peri-Gondwanan shelf south of the Rheic Ocean that is supplied by two contrasting super-fan systems, reflected in the zircon provinces of West Africa and East Africa–Arabia.

During the existence of Proto-Tethys Ocean (550–430 Ma), microcontinents in northern East Gondwana merged with the northern margin of India-Australia, completing the assembly of Gondwana. Ongoing controversy surrounds the disappearance of the Proto-Tethys Ocean, the dynamic mechanisms of suturing and the palaeogeographic relationships among microcontinents in northern East Gondwana, contributing to the uncertainty about the tectonic evolution of the region. This paper concerns the lower Silurian Zusailing Formation in the Hainan Island and focuses on the affinity between Hainan Island and various microcontinents in northern East Gondwana during the early Silurian. We use detrital zircon geochronology to reconstruct the closure process of the Proto-Tethys Ocean and show that the detrital zircon U–Pb age groups of the lower Silurian Zusailing Formation are 2800–2200, 2100–1350, 1250–950, 600–480 and 480–430 Ma, with a significant age peak of ca. 449 Ma. Furthermore, the analysis of detrital zircon geochemistry and europium anomalies shows that the Hainan Island crust continued to thicken during 600–434 Ma. Comparing the age spectrum of early Palaeozoic detrital zircons from Hainan Island and various microcontinents in northern East Gondwana, as well as the affinity among them during the Silurian, we conclude that the closure of the eastern Proto-Tethys Ocean evolved from unidirectional subduction (600–480 Ma) to bidirectional subduction (480–430 Ma).

Ash fall layers and vitroclastic-carrying sediments distributed throughout the entire Permian stratigraphic range of the Parana Basin (Brazil and Uruguay) occur in the Tubarao Supergroup (Rio Bonito Formation) and the Passa Dois Group (Irati, Estrada Nova/Teresina, Corumbatai, and Rio do Rasto Formations), which constitute the Gondwana 1 Supersequence. U-Pb zircon ages, acquired by SHRIMP and isotope-dissolution thermal ionization mass spectrometer (ID-TIMS) from tuffs within the Mangrullo and Yaguari Formations of Uruguay, are compatible with a correlation with the Irati and parts of the Teresina and Rio do Rasto Formations, respectively, of Brazil. U-Pb zircon ages suggest maximum depositional ages for the samples: (1) Rio Bonito Formation: ages ranging from 295.8±3.1 to 304.0±5.6 Ma (Asselian, lowermost Permian), consistent with the age range of the Protohaploxypinus goraiensis subzone; (2) Irati Formation: ages ranging from 279.9±4.8 to 280.0±3.0 Ma (Artinskian, Middle Permian), consistent with the occurrence of species of the Lueckisporites virkkiae zone; (3) Rio do Rasto Formation: ages ranging from 266.7±5.4 to 274.6±6.3 Ma (Wordian to Roadian, Middle Permian). All the SHRIMP U-Pb zircon ages are consistent with their superimposition order in the stratigraphy, the latest revisions to the Permian timescale (International Commission of Stratigraphy, 2018 version), and the most recent appraisals of biostratigraphic data. The ID-TIMS U-Pb zircon ages from the Corumbatai Formation suggest that U-Pb ages may be >10% younger than interpreted biostratigraphic ages.

The continental crust is the archive of the geological history of the Earth. Only 7% of the crust is older than 2.5 Ga, and yet significantly more crust was generated before 2.5 Ga than subsequently. Zircons offer robust records of the magmatic and crust-forming events preserved in the continental crust. They yield marked peaks of ages of crystallization and of crust formation. The latter might reflect periods of high rates of crust generation, and as such be due to magmatism associated with deep-seated mantle plumes. Alternatively the peaks are artefacts of preservation, they mark the times of supercontinent formation, and magmas generated in some tectonic settings may be preferentially preserved. There is increasing evidence that depletion of the upper mantle was in response to early planetary differentiation events. Arguments in favour of large volumes of continental crust before the end of the Archaean, and the thickness of felsic and mafic crust, therefore rely on thermal models for the progressively cooling Earth. They are consistent with recent estimates that the rates of crust generation and destruction along modern subduction zones are strikingly similar. The implication is that the present volume of continental crust was established 2-3 Ga ago.

The Central Asian Orogenic Belt is the world’s largest accretionary orogenic belt, associated with the closure of the Paleo-Asian Ocean (PAO). However, the final closure timing of the eastern PAO remains contentious. The Permian-Triassic sedimentary sequences in the Wangqing area along the Changchun-Yanji suture zone offer important clues into this final closure. New data on petrology, whole-rock geochemistry, zircon U-Pb geochronology and zircon Hf isotopes of sedimentary rocks from the Miaoling Formation and Kedao Group in Wangqing area provide new insights into the final closure of the eastern end of the PAO. The maximum deposition ages of the Miaoling Formation and Kedao Group have been constrained to the Late Permian (ca. 253 Ma) and early Middle Triassic (ca. 243 Ma), respectively. These sedimentary rocks exhibit similar geochemical characteristics, showing low textural and compositional maturities, implying short sediment transport, with all detrital zircons suggesting their origins from felsic igneous rocks. The εHf(t) values of the Miaoling Formation range from −6.09 to 12.43 and from −2.20 to 7.59 for the Kedao Group, implying these rocks originated from NE China. Considering our new data along with previously published data, we propose that a reduced remnant ocean remained along the Changchun-Yanji suture zone in the early Middle Triassic (ca. 243 Ma), suggesting the final closure of the eastern PAO likely occurred between the latest Middle Triassic and early Late Triassic.

Raman spectroscopy provides information on the residual strain state of host-inclusion systems that, coupled with the elastic geobarometry theory, can be used to retrieve the P-T conditions of inclusion entrapment. In situ Raman measurements of zircon and coesite inclusions in garnet from the ultrahigh-pressure Dora Maira Massif show that rounded inclusions exhibit constant Raman shifts throughout their entire volume. In contrast, we demonstrate that Raman shifts can vary from the center to the edges and corners of faceted inclusions. Step-by-step polishing of the garnet host shows that the strain in both rounded and prismatic inclusions is gradually released as the inclusion approaches the free surface of the host. More importantly, our experimental results coupled with selected numerical simulations demonstrate that the magnitude and the rate of the strain release also depend on the contrast in elastic properties between the host and the inclusion and on the inclusion crystallographic orientation with respect to the external surface. These results allowed us to give new methodological guidelines for determining the residual strain in host inclusion systems.

A comprehensive study based on U–Pb and Hf isotope analyses of zircons from gneisses has been conducted along the western part (Babina area) of the E–W-trending Bundelkhand Tectonic Zone in the central part of the Archaean Bundelkhand Craton. 207Pb–206Pb zircon ages and Hf isotopic data indicate the existence of a felsic crust at ~ 3.59 Ga, followed by a second tectonothermal event at ~ 3.44 Ga, leading to calc-alkaline magmatism and subsequent crustal growth. The study hence suggests that crust formation in the Bundelkhand Craton occurred in a similar time-frame to that recorded from the Singhbhum and Bastar cratons of the North Indian Shield.

Zircon is a ubiquitous accessory mineral in silicic igneous rocks. We have carried out new zircon dissolution experiments to refine our understanding of Zr diffusion and zircon solubility in several rhyolitic melts. Zr diffusivity depends strongly on temperature and H2O content, and weakly on pressure and anhydrous melt composition. The diffusion data for each individual melt follows the Arrhenius relation. The dependence of Zr diffusivity on temperature, pressure, and melt composition (including H2O content) is modeled for different rhyolitic melts in this study and for the combined literature and our data. Our data on Zr concentration at zircon saturation in silicic melts show strong dependence on temperature and weak dependence on pressure and melt composition, and are somewhat off the trend based on existing zircon solubility models. The dissolution or growth rate of a freely falling zircon crystal in a specific hydrous rhyolitic melt is modeled. The controlling factors are mostly the temperature and Zr concentration in the melt. Typical zircon growth rate in wet rhyolitic melt is 0.01 to 1.0 µm/yr. The size of zircon crystals can be used to place limit on the cooling rate of its hosting magma. The presence of large indigenous zircon crystals in Bishop Tuff requires slow cooling of the Bishop Tuff magma chamber.