Explore the vast range of titles available.

Recent high‐precision geochronological studies have delineated three main pulses of basaltic magmatism between ca. 130‐80 Ma in the Cretaceous High Arctic Large Igneous Province (HALIP) in northern Canada. Here we report new U‐Pb TIMS baddeleyite and zircon dates for samples from Axel Heiberg and Ellesmere Islands, which further support the duration and pulsed nature of the magmatism previously documented. We add new LA‐ICPMS U‐Pb zircon dates on samples analyzed in a previous study to help resolve age heterogeneity observed in some samples. We also report the first LA‐ICPMS zircon Lu‐Hf results from HALIP intrusives to better constrain the HALIP mantle source composition. Initial εHf zircon results for five HALIP basalts with minimal evidence for continental crustal contamination from the Canadian Arctic Islands range from +9.0 to +14.7, and indicate extraction from a depleted mantle source similar to plume‐derived oceanic plateaux such as Kerguelen. Plain Language Summary The High Arctic Large Igneous Province (HALIP) is primarily a suite of mafic intrusions with lesser basaltic volcanic rocks that occur on the continental margins surrounding the submarine basins of the Arctic Ocean. In a plate tectonic reconstruction for the geological time that they were emplaced, they surround a seafloor region with a distinctive geophysical character called the High Arctic Magnetic High (HAMH). Previous research indicated that the HAMH domain was the magmatic center of HALIP, analogous to oceanic LIPs. Here, we characterize the Hf isotope composition of the magmas that intruded the Canadian portion of the continental margin and find that they match oceanic plateaux in general, consistent with a melt source in the mantle below the HAMH from which the magmas spread laterally into and through the crust of the continental margin. Key Points First published laser ablation zircon Lu‐Hf isotopes from the High Arctic Large Igneous Province on 5 mafic samples New single zircon and baddeleyite U‐Pb TIMS dates Least contaminated samples indicate a mantle source most consistent with oceanic rather than continental LIPs

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).

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.

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.

Granulite facies rocks frequently show a large spread in their zircon ages, the interpretation of which raises questions: Has the isotopic system been disturbed? By what process(es) and conditions did the alteration occur? Can the dates be regarded as real ages, reflecting several growth episodes? Furthermore, under some circumstances of (ultra-)high-temperature metamorphism, decoupling of zircon U–Pb dates from their trace element geochemistry has been reported. Understanding these processes is crucial to help interpret such dates in the context of the P–T history. Our study presents evidence for decoupling in zircon from the highest grade metapelites (> 850 °C) taken along a continuous high-temperature metamorphic field gradient in the Ivrea Zone (NW Italy). These rocks represent a well-characterised segment of Permian lower continental crust with a protracted high-temperature history. Cathodoluminescence images reveal that zircons in the mid-amphibolite facies preserve mainly detrital cores with narrow overgrowths. In the upper amphibolite and granulite facies, preserved detrital cores decrease and metamorphic zircon increases in quantity. Across all samples we document a sequence of four rim generations based on textures. U–Pb dates, Th/U ratios and Ti-in-zircon concentrations show an essentially continuous evolution with increasing metamorphic grade, except in the samples from the granulite facies, which display significant scatter in age and chemistry. We associate the observed decoupling of zircon systematics in high-grade non-metamict zircon with disturbance processes related to differences in behaviour of non-formula elements (i.e. Pb, Th, U, Ti) at high-temperature conditions, notably differences in compatibility within the crystal structure.

A detrital zircon U–Pb laser ablation–inductively coupled plasma–quadrupole mass spectrometry (LA-ICP-QMS) provenance study was undertaken on samples selected from the Lower Gondwana successions preserved in the fault-bounded Bokaro and Jharia basins in India to investigate the provenance of the sediment and determine whether the strata were deposited in isolated syn-depositional graben basins or formed part of a wider regional depositional system. A total of 730 concordant U–Pb detrital zircon ages revealed six distinct age fractions: (i) a latest Neoproterozoic to earliest Cambrian age fraction (530 to 510 Ma), which tails down in some samples to older Neoproterozoic ages (650 to 630 Ma); (ii) a major age fraction with an age peak of earliest Neoproterozoic (950 Ma), accompanied in some samples by a twin Mesoproterozoic peak (1000 Ma); (iii) a middle Mesoproterozoic age fraction (1330 to 1300 Ma); (iv) a prominent earliest Mesoproterozoic zircon age fraction (1600 Ma); (v) a less well-defined late Palaeoproterozoic zircon age fraction (2100 to 1700 Ma, or 1600 Ma); and (vi) an Archaean zircon age fraction that typically comprises two zircon age fractions, namely zircons with early Neoarchaean ages (2800 to 2750 Ma) coupled with zircons with ages older than 3100 Ma. Comparison of these newly obtained age fractions with detrital zircon age data presented by Veevers & Saeed (2009) shows similarities with the Gondwana strata of the Mahanadi and Pranhita–Godavari basins, implying that strata preserved in the fault-bounded Gondwana basins in central east India formed part of a much wider regional depositional system and that they were not deposited in isolated half-graben or graben basins. Potential source regions to the Gondwana strata of the Bokaro and Jharia basins include the Eastern Ghats Mobile Belt and rock units in Antarctica.

The thermal evolution of magmatic systems of the Altenberg‐Teplice and Tharandter Wald calderas, which erupted during the terminal post‐collisional phase of the Variscan orogeny in the Bohemian Massif, was investigated. The zircon saturation temperatures and Ti‐in‐zircon thermometer indicate that the intrusive and extrusive units of the two calderas were sourced from medium‐ to high‐temperature (∼770–930°C) felsic lower crustal magma. Using an integrated rock‐magnetic and paleomagnetic approach through thermal demagnetization and stepwise thermomagnetic curves, it was estimated that intracaldera ignimbrites reached temperatures of 550–600°C. The low‐temperature component (350–450°C) likely corresponds to the alteration of magnetic minerals during cooling or late‐stage magmatic/hydrothermal events. Placing these findings in the broader context of Variscan post‐collisional magmatism might suggest a trend of decreasing magma temperatures from 330 Ma to 302 Ma within the two lower‐to mid‐crustal (Moldanubian) and upper‐crustal (Saxothuringian) units of the Bohemian Massif, possibly reflecting the cooling of the hot collisional orogen. Lastly, we suggest that a combination of zircon temperature estimates with the rock‐magnetic methods may provide a comprehensive framework for further research on the thermal evolution of felsic magmatic systems. Key Points The magmatic systems of the Altenberg‐Teplice and Tharandter Wald calderas were fed by relatively hot (∼770–930°C) felsic lower‐crustal magma Saxothuringian crust in the Bohemian Massif experienced a heat flow similar to the Moldanubian crust during the post‐collisional Variscan phase Intra‐caldera ignimbrites of the Tharandter Wald Caldera were deposited at relatively high temperatures of ∼550–600°C

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.

Metabasic rocks (eclogites and amphibolites) from four Betic ophiolite outcrops (Lugros, Almirez, Cóbdar, and Algarrobo), comprising Ol-Px gabbros, dolerites, and MORB-affinity basalts, were studied. U-Pb SHRIMP zircon dating yielded Early to Middle Jurassic ages (187–174 Ma). At Cóbdar and Algarrobo, several magmatic levels were identified (187 ± 1.7 to 174 ± 1.8 Ma, and 184 ± 1.8 to 180 ± 1.6 Ma, respectively). In Lugros, two gabbros were dated to 187 ± 2.5 and 184 ± 1.4 Ma, while a dolerite dyke intruding serpentinites in Almirez gave 184 ± 1.6 Ma. Algarrobo xenocrystic zircons, predominantly Precambrian, resemble those from the MAR (13° N–15° N) in age and chemistry, suggesting a similar tectonic setting. δ18O values (4.2–6.2‰) of Betic ophiolite zircons (gabbros, basalts, dolerites) match those of MAR and SWIR samples, reflecting also oceanic alteration. Some zircons preserve δ18O variations linked to Jurassic (~150 Ma) oceanic metamorphism and later orogenic overprints. REE patterns show depletions in HREE and Y, with localized enrichments in LREE and Hf, which are more marked in metamorphically recrystallized zones. Xenocrystic zircons may derive from Precambrian protoliths assimilated during Jurassic magma ascent near transform faults. This integrated geochronological and geochemical evidence provides the key constraints for a revised geodynamic framework, confirming the existence of a Betic Jurassic ocean basin, which is a crucial precursor to the Alpine orogenic events that shaped the region.

The essential sources and processes required for the formation of Cu–(Au)-porphyry deposits have been part of a long-standing debate. In this study we investigate one of the youngest and best-preserved world-class Cu–(Au)-porphyry systems in order to learn more about melt sources and what geochemical tracers in zircon and apatite might be useful to identify ore-forming intrusions within porphyry systems. Combined, in-situ Hf, O, and Nd isotope analyses in zircon and apatite imply that the Tampakan magmas were derived from depleted mantle sources. Hence, we suggest that older crustal components or metasomatized mantle are not required for the production of metallogenically fertile magmas in island arc settings. Based on the compositions of apatite and zircon, we confirm that previously established fertility-indicator signatures of these minerals are useful to identify fertile porphyry systems. Our data show that intrusions directly associated with mineralization events contain apatite with elevated Cl and S concentrations compared to pre- and post- mineralization igneous events.