Source Of Zircons Research Articles

The mid-Cretaceous bauxites of SE France: Geochemistry, U-Pb zircon dating and their implications for the paleogeography at the junction between Alpine Tethys and Pyrenean Rift

Karst bauxites mark episodic exhumation of carbonate platforms, thus providing key information for basin analysis and paleoclimate processes at the regional to continental scale. Most karst bauxite deposits of SE France lie between Jurassic platform carbonates in the footwall and Upper Cretaceous marine to continental sediments in the hanging wall. These deposits delineate a stratigraphic gap coeval with the Durance extensional tectonics, which led to the separation of the Vocontian and South Provence Basins, and shaped the junction between the Alpine Tethys and the Pyrenean Rift.Our new mineralogical and geochemical data show that SE France karst bauxites were affected by in-situ weathering and alteration in conjunction to sedimentary reworking. Statistical analysis of geochemical data indicates that bauxite deposits have a similar chemical footprint, likely pointing to a common and long-lasting bauxitization process. New U-Pb zircon data from the Provence deposits confirm that the source material for the SE France bauxites is to be primarily found in the Hercynian basement. The data suggest the presence of an additional exotic zircon source deriving either from Avalonia and/or Baltica. The comparison of the new U-Pb zircon data with those on coeval bauxites evidences a marked difference between the SE France and the Sardinian deposits. This difference indicates diversification in the detritus provenance of the two areas since the Lower Cretaceous, setting the bauxites of SE France and Sardinia in lateral continuity with the bauxites occurring on the two opposite margins of the Pyrenean Rift, and supporting the development of these deposits on the shoulders of the rift-related basin formed at the eastern termination of the Pyrenean Rift.

Geographic bias effects on interpretations of secular trends of Hf isotope times series in zircons

The analysis of εHf(t) time series data from zircon reveals notable discrepancies based on sample type (igneous versus detrital), statistical weighting methodology, and geographic sampling bias. These differences warrant caution when interpreting data in the context of tectonic settings and the history of supercontinents. In terms of tectonic setting, accretionary orogens dominate in both sedimentary basins that host detrital zircons and in igneous zircon sources. Because of differences between the various time series, emphasis in this study is on peaks, valleys and secular trends and not on absolute εHf(t) values. Specifically, the igneous time series for εHf(t) in zircons shows more peaks and valleys than corresponding detrital time series for both weighted and unweighted data (weighting corrects for disproportionate geographic sampling). Also, sample-based (each sample considered separately) and site-based (samples grouped by geographic location and age) results align closely to the igneous time series, whereas the site-based detrital series displays more negative εHf(t) values. Regardless of the type of time series, the failure to compensate for disproportionate geographic sampling increases the prospects of producing an unrepresentative time-series. Nine zircon age peaks (both detrital and igneous) have corresponding εHf(t) peaks (3200, 2700, 2500, 2150, 1500, 1100, 750 Ma) and two have corresponding age valleys (1800–2000, 550 Ma). With exception of a geographically widespread 1500 Ma peak, most of the εHf(t) peaks and valleys are controlled by specific geographic regions and are likely not be global in extent.Two distinct periods (200–0 and 1800–1600 Ma) display εHf(t) signatures that rise steadily for 100–200 Myr, coinciding with the final stages of supercontinent assembly and the transition to the retreat of exterior orogens. An εHf(t) peak at 750 Ma and a high at 1400–1100 Ma partly overlap with supercontinent breakup and valleys at 550 Ma and 900 Ma with supercontinent assembly. A large εHf(t) valley at 2000–1800 Ma corresponds with the onset of craton collisions that led to the final assembly of Columbia at 1800–1600 Ma. The steep rise in εHf(t) in the last 200 Myr in both igneous and detrital zircons is controlled by sites in Circum-Pacific orogens in North and South America and Southwest Asia, and it parallels the breakup of Pangea. The general increase in zircon εHf(t) in the last 500 Myr in both detrital and igneous data reflects an increase in the proportion of isotopically juvenile components in accretionary orogens.

Early-stage intracontinental rifting in the Neoproterozoic Centralian Superbasin: Systematic U–Pb and Lu–Hf isotopes in detrital and inherited zircons from the Yeneena Basin, northwest Australia

Detrital zircons from different lithostratigraphic units of Supersequence 1 across the Neoproterozoic northwest Officer and Yeneena basins were investigated using LA-ICPMS U−Pb and Lu − Hf isotope analyses to understand the source of detritus and potential links to regional tectono-magmatic events, as well as the crustal evolution of the sedimentary sources terranes. All data show that Proterozoic detritus dominate the age spectra of samples from the Yeneena Basin and northwest Officer Basin, with signatures varying in the heights of peaks rather than the presence or absence of age groups in different formations. The Archean and Proterozoic ages overlap with known magmatic events in the Pilbara Craton, Fortescue Basin, Rudall Province, Capricorn Orogen, Musgrave Province, Madura Province, and the Coompana Province suggesting these terranes are possible sources of the detritus. The detrital zircon population of the samples have main age peaks in the range 1300 to 1000 Ma, suggesting magmatic rocks of the Rudall and Musgrave provinces are the main sources of detrital zircons, which can be differentiated by Hf signature. The distal Musgrave Province persistently dominates the provenance of detritus in the northwestern Officer and Yeneena basins, while detritus from the proximal Rudall Province contributes to a lesser extent. This suggests that the distal Musgrave Province remained emergent during the evolution of the northwestern Officer Basin and the Yeneena Basin, whereas the proximal Rudall Province potentially became buried by the accumulating sedimentary rocks and contributed less detrital zircons. The 833.6 ± 1.4 Ma maximum depositional age obtained in this study for the sedimentary rocks of the northwestern Officer and Yeneena basins point to the approximate time of the start of basins development. The extensional event in this age period is related to emplacement and extrusion of the ca. 830 Ma Willouran Large Igneous Province (LIP). The Duke gabbro sills observed in the Yeneena Basin are part of this LIP, which extends from the Adelaide Rift Complex, through the Musgrave Province, central–northwest Officer Basin and into the Yeneena Basin. The sediment source terranes suggest a southeast–northwest oriented depositional system between central and Western Australia, possibly because of intracontinental rifting related to widespread mafic–ultramafic magmatic events that could include the earlier Ngaanyatjarra Rift formed by the 1090–1040 Ma Warakurna LIP as well as the ca. 830 Ma Willouran LIP, synchronous with the breakup of Rodinia in the mid-Neoproterozoic.

Lithology, U[sbnd]Pb zircon geochronology, and geochemistry of the Austroalpine Sieggraben Complex: Pre-Alpine vs. Alpine history

The Sieggraben Complex (SC) in Eastern Austria provides comprehensive information on the pre-Permian, Permian, and Alpine (Cretaceous) evolutional stages of the crustal and mantle sections included into the Austroalpine basement HP/UHP belt. The SC in the Sieggraben–Schwarzenbach area consists of three, top-to-bottom tectono-stratigraphic units: (1) the Paragneiss unit, (2) the Marble–Eclogite unit, which contains MORB and OIB types of mafic rocks, and (3) the Micaschist–Calcschist unit. The N-MORB type mafic rocks yield a UPb age of 369.7 ± 2.0 Ma, have εNd(370) = +8.5 to +7.4 and TDM(2st) of 0.42–0.50 Ga, while the E-MORB types (UPb ages around 400 Ma) show εNd(400) = +9.4 to +5.6 and TDM(2st) of 0.37–0.67 Ga, both indicating rather juvenile mantle sources during the formation of the inferred oceanic Devonian basin. The rocks of these units revealed Cambrian, Proterozoic, and Archean zircon sources. The ages of 285.8 ± 9.2 and 265.7 ± 2.1 Ma from eclogite and amphibolite, respectively, and 265.5 ± 1.4 Ma from paragneiss indicate an important Permian metamorphic overprint. Permian granitic dykes dated from ∼265 to 260 Ma, exceptionally at 273 and 253 Ma, crosscut the lithological units. A clinopyroxenite dyke, which crosscuts harzburgite of the underlying mantle fragment, yielded a magmatic age of 253.3 ± 2.9 Ma. Overall, these ages suggest a strong Permian extension, overheating, and melting of the crustal and mantle rocks. The eclogite ages from ∼100 Ma, but mainly between 92 and 90 Ma, constrain the Late Cretaceous metamorphic event terminated by an 88.4 ± 0.8 Ma pegmatite intrusion in the Paragneiss unit. The Permian and Cretaceous metamorphic events often caused resetting of the relatively older zircon ages, together with a decrease of zircon εHf(t) values, and an increase of whole-rock 87Sr/86Sr values. A Carboniferous metamorphic age of ∼340 Ma was rarely detected. The SC finally represents a part of an early Late Cretaceous intra-continental subduction zone, which formed within a strongly-thinned crystalline basement due to the Devonian and Permian extensions. A similar Cretaceous suture zone with HP amphibolite, dated at ∼130–100 Ma by white mica ArAr ages (100–90 Ma exhumation), has been described around the Lubeník line between the Gemeric and Veporic tectonic units of the Inner Western Carpathians in the framework of the Cenozoic AL–CA–PA (Alpine–Carpathian–Pannonian) microplate.

U/Pb age and sources of detrital zircon from Upper Riphaean sandstones of the Nemskaya Upland (South Timan)

U/Pb age and sources of detrital zircon from Upper Riphaean sandstones of the Nemskaya Upland (South Timan)

BOUNDARY BETWEEN THE TIMANIAN AND URALIAN TECTONIC CYCLES: RESULTS OF DATING OF DETRITAL ZIRCONS FROM BASAL HORIZONS OF THE LOWER PALEOZOIC SYNRIFT COMPLEX OF THE POLAR URALS, AND IGNEOUS ROCK AGE DATA REPORT

The Upper Cambrian-Lower Ordovician terrigenous strata, unconformably overlying the Upper Riphean-Vendian rocks of the Timanide orogen in the north of the Urals, and contemporaneous bimodal volcanics and intrusive rocks are considered complexes marking the beginning of rifting which led to the opening of the Paleo-Ural Ocean later on. The article presents the results of U-Pb (LA-ICP-MS) dating of detrital zircons from sandstones lying at the base of the section of the rift complex in the Malaya Usa River basin in the Polar Urals. It was found that the clastic sequence (identified as the Khoydyshor formation) began to accumulate no earlier than the Cambrian–Ordovician transition. Zircon ages fall within the continuous Vendian to Early Ordovician (575–478 Ma) interval with peak at 512 Ma. This age range overlaps with the age of rhyolites interlayered conformably with sandstones and rhyolite porphyry dikes intruding the Khoydyshor formation, thus indicating a possible admixture of products of synsedimentary volcanism. A narrow zircon age pattern allows us to conclude that the main sources of detrital zircons in sandstones were the Early-Middle Cambrian igneous rocks formed at the stage of pre-rift uplift, and, to a lesser extent, the Late Cambrian-Early Ordovician riftogenic magmatic complexes, marking the beginning of the Uralian tectonic cycle, as well as the Late Vendian igneous rocks of the underlying Timanide orogen. Judging by the Th/U ratio, most of the detrital zircons within the sandstones were derived from the Early Paleozoic silicic volcanic and hypabyssal rocks and the Vendian granitoids and diorites. The almost complete absence of older grains, which are typical of coeval sandstones of the northern part of the Urals, may indicate the accumulation of the considered sandstones in a local trough with local clastic material sources. Probability density estimation of U-Pb ages for zircon from igneous and metamorphic rocks of the Polar Urals indicates that there were no gaps in the Late Riphean to Early Ordovician endogenous activity in this region. The main peaks occur at 552, 521 and 500 Ma, and an additional peak – at 665 Ma. The results of dating of detrital zircons from sandstones of the Khoydyshor formation together with the database of U-Pb isotope ages of igneous and metamorphic rocks of the Polar Urals (119 items), compiled by the authors, indicate that the change in geodynamic regime from collisional orogenesis in the Late Vendian to the Early-Middle Cambrian pre-rift uplift and following Late Cambrian rifting was not accompanied by a longterm discontinuity in magmatic activity.

Revisiting the Geochemical Classification of Zircon Source Rocks Using a Machine Learning Approach

Trace element fingerprints preserved in zircons offer clues to their origin and crystallization conditions. Numerous geochemical indicators have been established to evaluate the source rock characteristics from a geochemical perspective; however, multivariate trace element data have not been sufficiently investigated statistically. As substantial amounts of zircon data from a wide range of rock types have become accessible over the past few decades, it is now essential to reassess the utility of trace elements in discriminating source rock types. We employed a new zircon trace element dataset and established classification models to distinguish eight types of source rocks: igneous (acidic, intermediate, basic, kimberlite, carbonatite, and nepheline syenite), metamorphic, and hydrothermal. Whereas a conventional decision tree analysis was unable to correctly classify the new dataset, the random forest and support vector machine algorithms achieved high-precision classifications (> 80% precision, recall, and F1 score). This work confirms that trace element composition is a helpful tool for province studies and mineral exploration using detrital zircons. However, the compiled dataset with many missing values leaves room for improving the models. Trace elements, such as P and Sc, which cannot be measured by quadrupole inductively coupled plasma mass spectrometry, are vital for more accurate classification.

Inherited zircons in Early Cretaceous dyke: Implication of growth and reworking of continental crust in the Jiaodong Peninsula

Inherited zircons from Early Cretaceous dykes across the Jiaodong Peninsula provide a means of exploring magmatic episodes. Negative Eu anomalies, high Th and U contents, and high U/Yb ratios confirmed a zircon source of ancient continental crust. Differences in mineralogy, chronology, geochemistry, and Hf isotopes showed that these inherited zircons were not brought in by the Triassic Yangtze Craton collision. Zircons within 2938–2800 Ma confirmed that the ancient crust in the Jiaobei Terrane originated from the Mesoarchean crustal growth. This crustal growth continued until the Early Paleoproterozoic and was accompanied by crustal transformation activities in the later period. After the collision of the Jiao–Liao–Ji Belt, the Jiaodong Peninsula entered a typical craton period until it was reactivated at the end of the Neoproterozoic, which was characterised by the Archean crustal transformation. During the Palaeozoic, smooth crustal thickness change with limited addition of oceanic crust material indicated the Qinling–Dabie–Sulu Orogenic Belt as a distal island arc system that slowed the impact of Paleo-Tethys subduction. There was no record of positive-εHf(t) zircons in the Jiaodong Peninsula during the Mesozoic, but the crust thickened rapidly. This confirmed that the Paleo-Pacific Plate may have directly subducted beneath the lithospheric mantle and had little contact with the lower crust. This subduction pattern released little hydrous fluid but much heat, which prompted the remodelling of the lower crust in the Mesozoic. Furthermore, the large-scale lithospheric thinning event around 120 Ma was identified as a result of the delamination of the lithospheric mantle together with lower crust.

A combined methodology for reconstructing source-to-sink basin evolution, exemplified by the Triassic Songpan–Ganzi basin, central China

Source-to-sink evolution of a basin is a key to understand sedimentary processes, especially in a complex regional orogenic setting. Detrital zircon populations can be traced from their primary sources to their depositional settings. The resulting interpretations are enhanced by calculation of the adjacent orogen's paleoaltimetry, which provides additional insights into paleogeography. In this study, we present a combined methodology which aims to reconstruct source-to-sink evolution by the analysis of detrital zircon age distribution in sandstones, together with the calculation of paleo-elevation of surrounding orogens based on the chemical compositions of coeval magmatic rocks. We test the method using detrital zircon U–Pb geochronological data sets from the Triassic Songpan–Ganzi basin in central China, combined with whole-rock geochemical data from intermediate-composition magmatic rocks in adjacent crustal blocks. Application of the combined methodology supports a syn-collisional basin model for the formation of the Triassic Songpan-Ganzi basin in preference to a continental back-arc basin. The clastic sediments, mainly deep-marine turbidites, accumulated in a remnant Paleotethyan Ocean that was surrounded by the converging North China Block, South China Block, East Kunlun Orogenic Belt and the Qiangtang Block. The North China Block and the North Qaidam Block were major proto-sources of detrital zircons to the basin, contributing on average 12 % and 15 %, respectively. Triassic magmatic rocks in the East Kunlun and Qiangtang regions were major sources of igneous zircons, up to 68 % for the former and up to 56 % for the latter. Despite being located at a calculated elevation of ca. 4000 m, the Qinling Orogenic Belt contributed only ca. <10 % of the zircons, mostly restricted to the eastern depocenter of the basin. In contrast, supply from the North Qiangtang Block, despite its calculated lower elevation (1000–3000 m), accounts for 2–10 % of the detrital zircons in the basin, suggesting high erosion rates of this block. The minimal supply of zircons from the South China Block, restricted to 3–6 % in the central and western depocenters, is inconsistent with the zircon abundances predicted in the alternative back-arc basin model of the Songpan–Ganzi basin.

PROVENANCE OF THE PERMIAN-TRIASSIC RED BEDS FROM THE EASTERN PART OF THE MOSCOW BASIN, EAST EUROPEAN PLATFORM: U-Pb LA-ICP-MS AND RAMAN SPECTROSCOPY DETRITAL ZIRCON DATA

We present the first systematic results of U-Pb LA-ICP-MS dating of detrital zircons from 12 samples representing different stratigraphic levels of 5 sections of the Permian-Triassic rocks, located within the eastern part of the Moscow basin (syneclise) – Zhukov ravine, Astashikha, Nedubrovo, Balebikha and Klykovo. It is shown that the accumulation of the Upper Permian and Lower Triassic terrigenous complexes occurred under the influence of competing sources with two contrasting provenance signals with Neoproterozoic (Vendian)-Paleozoic and Paleo-Mesoproterozoic ages. The identified provenance signal patterns were used to detail the correlation and stratigraphic subdivision of the Permian-Triassic terrigenous complex of the Moscow basin. Raman spectroscopy of detrital zircon, first applied to the Permian-Triassic rocks of the East European platform, made it possible to identify sedimentary complexes of a relatively older terrigenous basin as a separate source of zircons, which experienced superimposed thermal impact in the VendianCambrian time (~500–600 Ma).

Provenance of early Permian Li-rich claystone from Central Yunnan, South China: Constrained by Sr-Nd-Pb isotopes, geochemistry, and zircon U–Pb ages

A new lithium-rich claystone from the Lower Permian has been detected in Central Yunnan, Southwestern China that could be great potential for Lithium (Li) exploration, yet the origin of the claystone is still being debated. To study it further, new geochronological, geochemical, and Sr–Nd–Pb isotopic analyses were systematically conducted on the Daoshitou Formation (P1d) claystone, as well as on the underlying strata. Through detrital zircon U–Pb dating of the claystone in the Daoshitou Formation, three major age peaks were revealed, at ∼960 Ma, ∼790 Ma, ∼550 Ma, respectively, along with three minor peaks of ∼2500 Ma, ∼1500 Ma, and ∼1200 Ma. Detrital zircons in the claystone have age spectra that closely match those of the Lower Ordovician sedimentary rocks in Central Yunnan, indicating these rocks are the major contributor of detrital zircons. However, the rock source determined by geochemical features decouples with the zircon source determined by detrital zircon data. The A–CN–K ternary diagram obviously reveals analogous predicted weathering trends between the Weining Formation (C2w) and Daoshitou Formation, suggesting a potential provenance link. Furthermore, the weathering trends of samples from three drill cores indicate that the transformation of clay mineral (smectite–illite–chlorite/kaolinite) may facilitate Li enrichment. Smectite, as the precursor mineral for Li enrichment, typically forms and preserves in a slightly alkaline environment, which suggests that the Li-rich claystone is likely to formed in this environment. Low Na/Li and K/Li ratios indicate low cation exchange selectivity in sedimentary environments, which promote the proliferation of adsorption sites for Li on smectite. The weathering products from the Weining Formation, composed of impure carbonates, could provide a slightly alkaline environment with low ion strength for the adsorption of Li. In addition, Sr–Nd–Pb isotopic compositions also reveal the significant similarity between the Daoshitou Formation and Weining Formation. Therefore, we suggest that the weathering of the Weining Formation provided the primary material to Daoshitou Formation claystone.

GEOCHEMISTRY OF HIGH-PHOSPHORUS ZIRCON FROM THE UPPER RIPHEAN METASANDSTONES OF THE SOUTHERN TIMAN

A detailed mineralogical and geochemical study (using the EPMA and SIMS methods) of zircon from metasandstones of the Dzhezhim Formation in the South Timan made it possible to establish an anomalously high content of phosphorus in it (up to 10.27 wt % P2O5 according to EPMA data), which correlates with an increased content of other non-formula admixture elements, the main of which are Y, REE, Ca, Fe, Al, Ti, Sr, Ba, Th, U. Of particular note is the significant amount of volatile components in zircon (up to 0.49 wt % water and up to 0.26 wt.% fluorine, determined by the method SIMS). The total content of non-formula admixture elements can exceed 20 wt %, which is a characteristic feature of the composition of zircon exposed to fluid or formed as a result of hydrothermal-metasomatic processes. The main mechanism for the incorporation of admixture elements into the composition of zircon was xenotime-type heterovalent isomorphism, when the presence of quinquevalent phosphorus is compensated by the participation of trivalent Y and REE. Of subordinate importance was the isomorphism scheme, which ensures the entry of hydrogen (water). The areas of zircon enriched in phosphorus and other adulterants are confined to the edge of the grains, or to systems of scissures and fluid-permeable areas. Granitoids served as a possible source of zircon, and the process of transformation of its composition (recrystallization and enrichment of local areas, less often whole grains) probably occurred already in the sandstone sequence, during metamorphism and/or hydrothermal process.

Composition and Age of Sources of the Lower–Middle Cambrian (?) Terrigenous Rocks from The Ernichny Formation in the Argun Massif, Eastern Part of the Central Asian Fold Belt

The paper presents the results of the mineralogical and geochemical studies of sandstones and siltstones of the Ernichny formation of the Argun series in the Argun continental massif, and the results of U–Pb (LA‑ICP-MS) dating for the detrital zircons from these rocks. It is established that the youngest detrital zircons from sandstone of the Ernichny Formation have age of 549–570 Ma. A maximum on the relative probability curve of zircon age corresponds to 566 Ma. These data determine the lower age limit of their accumulation on the border of the Ediacaran and Paleozoic age. According to the results of U–Pb dating of detrital zircon, the majority of detrital zircons from sandstones of Ernichny Formation are characterized by Neo- and Paleoproterozoic ages. The sources of zircons were Neo- and Paleoproterozoic igneous and metamorphic rocks that were widely developed within the Argun continental massif. In turn, the geochemical features of the terrigenous rocks of the Ernichny Formation, together with the presence of the poorly sorted and rounded clastic material in the studied samples, as well as the presence of interlayers of gravelstones, enabled us to establish that they were formed in a subduction-related setting.

Detrital geochronology of the Cunningham Lake formation: an overlap succession linking Cache Creek terrane to Stikinia at ∼205 Ma

Detrital zircon from three coarse-grained marine siliciclastic rocks was analyzed for U–Pb, Lu–Hf, and trace element compositions to constrain the timing of deposition and sediment provenance of the Cunningham Lake formation (formerly siliciclastic unit of the Sitlika assemblage) in north-central British Columbia. This strategy tests previously proposed sedimentary linkages between the Cache Creek terrane and the westerly rocks of the Stikine terrane. All three samples indicate maximum depositional ages at ca. 205–202 Ma (Rhaetian). The samples contain a predominant ca. 225–215 Ma detrital population, sourced from proximal contemporaneous volcanic arcs, and minor Permian to Middle Triassic and Carboniferous arc-derived detrital populations. The absence of Precambrian grains is consistent with the strongly suprachondritic zircon compositions (εHf(t) = +7 to +20), and indicates exclusively juvenile sources for the Cunningham Lake formation. Late Triassic sources of zircon are not known in the Cache Creek terrane and, except within western Stikine terrane, are uncommon among the Intermontane terranes that amalgamated with the Cache Creek terrane during Late Triassic–Early Jurassic. The Stikine suite (ca. 230–214 Ma) and coeval volcanic rocks in western Stikinia are the most probable sources of Late Triassic detritus for the Cunningham Lake formation. Stikinia’s Paleozoic basement is the probable source of Carboniferous detrital zircon. Volcanic arc–backarc complexes in the Cache Creek terrane are the most likely sources of Permian to Middle Triassic detritus in the Intermontane terranes. Accordingly, the siliciclastic rocks of the Cunningham Lake formation represent an overlap sedimentary succession that links Stikinia to the Cache Creek terrane by the latest Triassic.

Zirconium and neodymium isotopes record intensive felsic volcanism in South China region during the Permian-Triassic boundary crisis

The Permian-Triassic mass extinction (PTME), the largest biocrisis in Earth's history, is regarded as having been triggered by volcanism, although the source and nature of this volcanic activity in the South China region remains in debate. In this regard, determining the geochemical composition of the volcanic and terrestrial source fluxes to marine depositional systems is crucial for differentiating material derived from the Siberian Traps Large Igneous Province versus regional volcanic arcs. Here, we report zirconium (Zr) isotopic compositions (δ94/90Zr) of Permian-Triassic boundary strata from a deep carbonate-ramp setting at Xiakou, South China, providing new insights regarding the provenance of volcanic ash layers and their host silicic mudstones. The δ94/90Zr composition of magmatically sourced materials is generally controlled by degree of melt crystallization and has the potential to discriminate between primitive and evolved igneous sources. At Xiakou, the pre-PTME Lower Unit contains volcanic ash layers with δ94/90Zr (+0.05 ± 0.03‰, 2SD) similar to that of upper continental crustal (UCC), recording dominantly detrital zircon sources. About 10 kyr before the mass extinction, a single ash layer (Bed 249) records a transient excursion to mantle-like values (∼0‰), followed by a protracted shift across the Permian-Triassic boundary (PTB) toward signatures characteristic of more evolved felsic sources (+0.19 ± 0.12‰) accompanied by a positive shift in Nd isotopes (εNd(t)). The high δ94/90Zr of volcanic ash layers from the Middle Unit (corresponding approximately to the interval between the PTME and PTB) indicates dominance of regional felsic volcanic sources. In this interval, volcanic ash δ94/90Zr values at Xiakou are distinctly higher than those at Meishan, suggesting that primary volcanic signatures are better preserved in deep-water facies (Xiakou) than in shallow-water facies (Meishan). In the Middle (excluding the Bed 249) and Upper (post-PTME) units, positive covariation of δ94/90Zr with Al2O3/TiO2, Zr/TiO2 and Zr/Sc ratios was the product of mixing of detrital and volcanic materials, with the latter having a dominantly felsic source. This study provides new insight into the sources of zircons in PTB sections of South China, and it demonstrates the general utility of sedimentary Zr isotopic compositions in determining magmatic provenance.

Eocene to present evolution of the Pearl River, China: A quantitative provenance interpretation on large detrital zircon U–Pb geochronological data

AbstractDrainage evolution of the Pearl River, one of the major rivers in the eastern margin of the Asian continent, has important implications for the tectonomorphic evolution of the northern margin of the South China Sea and the southeastern Tibetan Plateau. Previous reconstructions using different methods suggested discrepant timings for the formation of river, ranging from Early Oligocene to Middle Miocene. Here, we address this heavily debated topic using quantitative unmixing modelling of detrital zircon data from the Pearl River Mouth Basin in the northern margin of the South China Sea. In this study, we develop a novel approach for estimating the relative contributions of detrital zircon sources to their shared sink, and propose to use the correlation coefficients among zircon contribution models to evaluate the trade‐off among sources with similar age spectra, to avoid the potential overinterpretation of individual contributions. Our new method is applied to new (997) and published detrital zircon U–Pb data from offshore boreholes and modern Pearl River samples to quantitatively interpret and reconstruct the sediment provenance of the Pearl River Mouth Basin and the development of the Pearl River. Our findings reveal that the provenance change of the Pearl River Mouth Basin can be divided into three main stages. Eocene sediments were mainly sourced in the intra‐basinal highlands and the eastern coastal tributaries, indicating a local drainage system. Early Oligocene provenances extended westward, as shown by the increase in sediment contribution from the central and western parts of the Pearl River (28% in total). Since the Late Oligocene, the eastern, central and western parts of the modern Pearl River have contributed equal amounts of zircons to the Pearl River Mouth Basin, indicating the establishment and long‐term stability of the modern‐like drainage system, as highlighted by our new data acquired from the borehole Miocene strata. The Late Oligocene westward expansion of the Pearl River is consistent with the timing of the coeval breakup and spreading of the South China Sea and the intensified Asian monsoon precipitation, highlighting the importance of base level fall and climate in controlling the drainage evolution.

SOURCES OF THE LATE CENOZOIC DEPOSITS FROM THE AEOLIAN “SANDS” MASSIF IN THE CHARA BASIN OF THE BAIKAL RIFT ZONE: FIRST RESULTS OF U–TH–PB (LA-ICP-MS) GEOCHRONOLOGICAL STUDY OF DETRITAL ZIRCON

The results of U–Th–Pb (LA-ICP-MS) geochronological studies of detrital zircon (fraction more than 50 µm) from the Late Cenozoic deposits of the large aeolian “Sands” massif of the Chara Basin of the eastern flank of the Baikal Rift Zone show that they are dominated by detrital zircon with ages of 263–265 and 1861–1864 Ma. Archean ages have been obtained only for individual zircon grains. Quite possibly, this is due to the fact that zircon of this age is present in “small” fractions, the study of which is not possible due to the technological features of the method of geochronological studies used. Based on the geological situation, only granites of the Kodar complex can be considered as the only source of detrital zircon of the Early Proterozoic age. The source of detrital zircon with an age of 263–265 Ma remains a mystery. Granitoids of this age are not known on the territory of the Aldan Shield. They are widespread in its western frame.

Zealandia and Australia at Ordovician continental margins: reconciling their similar and differing detrital zircon provenances within Rodinia

ABSTRACT New detrital zircon ages from biostratigraphically well-controlled Ordovician sandstones in southeast Australia are compared with published counterparts in southern Zealandia. During Rodinia supercontinent assembly (RA), Australia and Zealandia age patterns are similar, everywhere with ubiquitous late Mesoproterozoic magmatic zircon sources. However, during earliest Gondwana supercontinent assembly (GA), the age patterns have different sediment sources: (1) those of late Neoproterozoic age are more strongly represented in Zealandia but of uncertain location, but (2) those of late Cambrian-Ordovician age are more prominent in eastern Australia, having probable origins in the Ross-Delamerian Orogen. In particular, a distinctive zircon component, ca. 600–650 Ma, is ubiquitous in Zealandia but rare in Australia. Early Paleoproterozoic and Archean (Nuna, NU) zircon sources (2000–3200 Ma) become important (and locally up to 25% total) in Zealandia but not in Australia. It is difficult to reconcile all these sediment source requirements within disparate and distant Australian-Antarctic Precambrian complexes. Instead, it is proposed that, through the early Palaeozoic, Zealandia had only local sediment sources in a discrete Rodinia basement continental block outcropping in South Zealandia that was formerly adjacent to South China.

Geochronology and geochemistry of ore-hosted zircon reveal the genesis of typical Sb-(Au-W) deposits in South China

The Xikuangshan and Woxi Sb-(Au-W) deposits are the most important Sb-related mineralization in the Xiangzhong metallogenic province, South China. In this study, trace element, U-Pb dating, and Hf isotopic results of zircon in typical ore samples from the Xikuangshan and Woxi deposits provide new insights into metal/fluid sources and mineralization processes. The zircons in different samples from the Xikuangshan deposit have a similar distribution of zircon U-Pb ages with two major groups: 400–500 Ma and 700–900 Ma, which are consistent with those from their host rocks (Devonian strata) and underlying basement rocks (Lengjiaxi and Banxi Groups). By comparison, the zircons from the Woxi deposit have younger U-Pb ages which are the same as contemporaneous magmatism in South China. The 176Hf/177Hf ratios, εHf(t), and TDM1 further proved an original relationship between the younger zircons (with ages < 500 Ma) and magmatism. The systematic trend in the size and roundness of zircons captured from basement rocks for Xikuangshan might be resulting from gravity separation in the sedimentary process which required a stable and long-lasting mineralization process. On the other hand, the homogenous size and roundness of zircons from the Woxi deposit, regardless of zircon ages and sampling locations, might have been caused by a relatively short and intense mineralization process. The differences in the mineralization process for the two deposits lead to different alteration degrees of zircons and are reflected by the variable concentrations of Y, Hf, Pb, and Th, as well as rare earth elements. In the deposit scale, some samples are considered to be altered at high grade and represent the main mineralization stages for the Xikuangshan and Woxi deposits, as their zircons have variable concentrations of trace and rare earth elements. Combined with previous studies, the sources of zircons and mineralizing material are distinct for the Xikuangshan and Woxi deposits: originated from basement rocks (Xikuangshan deposit) and magmatism (Woxi deposit). In addition, stable and long-lasting deep-circulated meteoric water is considered the mineralizing fluid for the Xikuangshan deposit, whereas the mineralizing fluid for the Woxi deposit might be related to magmatism. This research highlights the use of zircon geochronology and geochemistry in revealing the genesis of Sb deposits, making this method applicable worldwide to similar vein-type mineralization.

Multimethod provenance analysis using detrital zircon and rutile U-Pb geochronology across Devonian basin systems in the Tasmanides of eastern Australia

The Devonian represents a period of transition for the accretionary orogens of the Australian Tasmanides where the largest and inboard Thomson Orogen became stabilised and orogenic processes became focused in the outboard and newly developing New England Orogen. The end of tectonic activity in the Thomson and the adjacent Delamerian and Lachlan orogens culminated with the development of several overlying intracratonic sedimentary basins. We examine the two largest cover basins, the Adavale and Darling, using stratigraphic logging, sandstone petrography, detrital zircon and rutile U-Pb geochronology to fingerprint sediment sources to test whether the basins were once connected and part of a much larger cover basin system. Sediment provenance in the Adavale Basin is characterised by (i) continuous input from a basement-derived Ordovician (∼480 Ma) igneous zircon source, (ii) reworking of metasedimentary basement rocks with a ‘Pacific-Gondwana’ age signature (iii) reworking of detrital rutile from Cambro-Ordovician sedimentary rocks in the Thomson Orogen ultimately sourced from the Musgrave Block and (iv) an addition of syn-depositional volcanic zircon from contemporary volcanism between ∼380 and 360 Ma. Sediment provenance of the Darling Basin is dominated by reworking of (meta)sedimentary basement, evident from large proportions of rounded zircons exhibiting a ‘Pacific-Gondwana’ age signature and detrital rutile with Peterman Orogeny ages. A much less significant age population of syn-depositional volcanic detrital zircons suggests input from contemporary volcanic sources which were more distal and extra-basinal.The comparison of sandstone compositions and detrital age information indicate both basins record similar provenance signals in terms of reworking of their respective hinterlands and receiving contributions from relatively distal syn-depositional volcanism. However, the comparison of sediment provenance proxies, suggests that the Adavale and Darling basins were not connected during the Devonian and that the basins are intracratonic or cover basins, recording the stabilisation of the Thomson and Lachlan orogens, respectively.