Detrital Zircon Samples Research Articles

The birth of a forearc: The basal Great Valley Group, California, USA

AbstractThe Great Valley basin of California (USA) is an archetypal forearc basin, yet the timing, structural style, and location of basin development remain controversial. Eighteen of 20 detrital zircon samples (3711 new U-Pb ages) from basal strata of the Great Valley forearc basin contain Cretaceous grains, with nine samples yielding statistically robust Cretaceous maximum depositional ages (MDAs), two with MDAs that overlap the Jurassic-Cretaceous boundary, suggesting earliest Cretaceous deposition, and nine with Jurassic MDAs consistent with latest Jurassic deposition. In addition, the pre-Mesozoic age populations of our samples are consistent with central North America sources and do not require a southern provenance. We interpret that diachronous initiation of sedimentation reflects the growth of isolated depocenters, consistent with an extensional model for the early stages of forearc basin development.

Bayesian population correlation: A probabilistic approach to inferring and comparing population distributions for detrital zircon ages

Populations of detrital zircons are shaped by geologic factors such as sediment transport, erosion mechanisms, and the zircon fertility of source areas. Zircon U-Pb age datasets are influenced both by these geologic factors and by the statistical effects of sampling. Such statistical effects introduce significant uncertainty into the inference of parent population age distributions from detrital zircon samples. This uncertainty must be accounted for in order to understand which features of sample age distributions are attributable to earth processes and which are sampling effects. Sampling effects are likely to be significant at a range of common detrital zircon sample sizes (particularly when n < 300).In order to more accurately account for the uncertainty in estimating parent population age distributions, we introduce a new method to infer probability model ensembles (PMEs) from detrital zircon samples. Each PME represents a set of the potential parent populations that are likely to have produced a given zircon age sample. PMEs form the basis of a new metric of correspondence between two detrital zircon samples, Bayesian Population Correlation (BPC), which is shown in a suite of numerical experiments to be unbiased with respect to sample size. BPC uncertainties can be directly estimated for a specific sample comparison, and BPC results conform to analytical predictions when comparing populations with known proportions of shared ages. We implement all of these features in a set of MATLAB® scripts made freely available as open-source code and as a standalone application. The robust uncertainties, lack of sample size bias, and predictability of BPC are desirable features that differentiate it from existing detrital zircon correspondence metrics. Additionally, analysis of other sample limited datasets with complex probability distributions may also benefit from our approach.

Comment on “Detrital Zircons From the Nanaimo Basin, Vancouver Island, British Columbia: An Independent Test of Late Cretaceous to Cenozoic Northward Translation” by Matthews et al.

Key Point Errors in stratigraphic age assignment of Cretaceous detrital zircon samples result in incorrect understanding of ages of geologic units

Zircon provenance of the Carboniferous Mattson delta complex, western Laurentian margin, Canada: record of a Greenland-sourced pancontinental river system

New detrital zircon U–Pb dates for seven late Viséan to Bashkirian (Middle Mississippian to Lower Pennsylvanian) Mattson and Kindle formation sandstone samples from the Mattson delta complex in the Liard Basin of northeastern British Columbia, combined with two previously published detrital zircon samples from these units, indicate a dominant Greenland Caledonian clastic wedge and orogen source with a small contribution of Ellesmerian-aged material. This provenance remained consistent over time. The Labrador–Greenland high was the only paleogeographically viable source area during the time of deposition of the Mattson delta complex. Detritus deposited on the western margin of Laurentia in the Mattson delta complex was likely transported southwestward by a late Viséan to Bashkirian pancontinental river system. This conclusion contrasts with previous interpretations which proposed that these sediments were recycled from the Ellesmerian clastic wedge. Tectonic uplift and denudation of eastern Greenland provided detritus from the Silurian to Devonian Caledonian clastic wedge and orogen to the western margin of Laurentia and detritus from the Caledonian orogen to the Serpukhovian to middle Bashkirian (Namurian) conglomeratic successions of the Millstone Grits in England. Detrital zircon U–Pb dates for two samples from the unconformably overlying Cisuralian (lower Permian) Tika formation are similar to those of the Mattson delta complex samples, as are those from the Pennsylvanian Spray Lakes Group of the southern Prophet Trough, indicating they all probably shared the same dominant source areas. The Tika formation was mainly derived from recycling of the Mattson and other Caledonide-sourced sediments of northern Laurentia.

Prospects of search for diamondiferous kimberlites in the northeastern Siberian Platform

The objects of study are Triassic hypabyssal diamondiferous kimberlites with an age of 220-245 Ma, containing macrocrysts of unaltered olivine. The latter are close in the time of formation to the main stage of intrusion of the Siberian Trap Province (252 Ma), which lasted less than 1 Myr. A comparative high-precision analytical study of the Ti, Ca, Cr, and Al impurity patterns in about 1000 olivine macrocryst samples with a forsterite content Fo = (100Mg/(Mg + Fe)) of 78 to 93 has demonstrated the effect of traps on the lithospheric composition. A comprehensive comparative study of diamonds from northern placers and Triassic kimberlites, including determination of their carbon isotope composition, was performed. Chromatography-mass-spectroscopic analysis of submicron fluid inclusions in diamonds from northern placers and kimberlites has shown predominant hydrocarbons of a wide range of compositions and subordinate contents of N2, H2O, and CO2. These findings, together with the results of previous studies of subcalcic Cr-pyropes and diamonds found in the Lower Carboniferous gritstones of the Kyutyungde graben, lead to the conclusion that the Toluopka kimberlite field is promising for Paleozoic kimberlites. The results of comprehensive studies of diamonds and indicator minerals and U/Pb isotope dating of numerous detrital zircon samples from the basal horizon of the Carnian Stage (Upper Triassic) of the Bulkur site in the lower reaches of the Lena River suggest the presence of diamondiferous kimberlites within the northeastern Siberian Platform. The age of the probable primary diamond sources in the study area can be evaluated by an integrated U/Pb isotope dating of zircons, perovskites, and rutiles from the developed diamond placers and the basal horizon of the Carnian Stage.

Neoproterozoic tectonic geography of the south-east Congo Craton in Zambia as deduced from the age and composition of detrital zircons

The Southern Irumide Belt (SIB) is an orogenic belt consisting of a number of lithologically varied Mesoproterozoic and Neoproterozoic terranes that were thrust upon each other. The belt lies along the southwest margin of the Archaean to Proterozoic Congo Craton, and bears a Neoproterozoic tectono-thermal overprint relating to the Neoproterozoic–Cambrian collision between the Congo and Kalahari cratons. It preserves a record of about 500 million years of plate interaction along this part of the Congo margin. Detrital zircon samples from the SIB were analysed for U–Pb and Lu–Hf isotopes, as well as trace element compositions. These data are used to constrain sediment-source relationships between SIB terranes and other Gondwanan terranes such as the local Congo Craton and Irumide belt and wider afield to Madagascar (Azania) and India. These correlations are then used to interpret the Mesoproterozoic to Neoproterozoic affinity of the rocks and evolution of the region. Detrital zircon samples from the Chewore–Rufunsa and Kacholola (previously referred to as Luangwa–Nyimba) terranes of the SIB yield zircon U–Pb age populations and evolved εHf(t) values that are similar to the Muva Supergroup found throughout eastern Zambia, primarily correlating with Ubendian–Usagaran (ca. 2.05–1.80 Ga) phase magmatism and a cryptic basement terrane that has been suggested to underlie the Bangweulu Block and Irumide Belt. These data suggest that the SIB was depositionally connected to the Congo Craton throughout the Mesoproterozoic. The more eastern Nyimba–Sinda terrane of the SIB (previously referred to as Petauke–Sinda terrane) records detrital zircon ages and εHf(t) values that correlate with ca. 1.1–1.0 Ga magmatism exposed elsewhere in the SIB and Irumide Belt. We ascribe this difference in age populations to the polyphase development of the province, where the sedimentary and volcanic rocks of the Nyimba–Sinda terrane accumulated in extensional basins that developed in the Neoproterozoic. Such deposition would have occurred following late-Mesoproterozoic magmatism that is widespread throughout both the Irumide and Southern Irumide Belts, presently considered to have occurred in response to collision between a possible microcontinental mass and the Irumide Belt. This interpretation implies a multi-staged evolution of the ocean south of the Congo Craton during the mid-Mesoproterozoic to late-Neoproterozoic, which ultimately closed during collision between the Congo and Kalahari cratons.

Geochemistry of the Cretaceous Kaskanak Batholith and genesis of the Pebble porphyry Cu-Au-Mo deposit, Southwest Alaska

The key magmatic processes that lead to the formation of large magmatic-hydrothermal porphyry copper mineral deposits remain uncertain, and a particular question is why a few of these deposits, such as the Pebble porphyry Cu-Au-Mo deposit, are strongly enriched in both gold and molybdenum. This study investigated the igneous rocks of the Pebble district and obtained major and trace element compositions, Sr and Nd isotopic compositions, and zircon age and trace element data to model the origin of the ore-forming magmas. The Pebble porphyry Cu-Au-Mo deposit, one of the world’s largest Cu-Au resources, formed during the final stages of regional Late Cretaceous arc magmatism (101–88 Ma) in the Southwest Alaska Range. Local pre-mineral intrusions (99–95 Ma) are dominated by alkaline compositions including monzodiorite stocks, shoshonite dikes, and monzonite porphyries, but also include lesser volumes of high-K calc-alkaline diorite and granodiorite sills. The occurrence of early alkaline magmas has been noted at other gold-rich porphyry systems, including Bingham and Kerr-Sulfurets-Mitchell. Mineralization at Pebble is associated with granodiorite to granite porphyry dikes related to the >165 km 2 high-K calc-alkaline Kaskanak granodiorite batholith (91–89 Ma). Over a period of 10 m.y., Late Cretaceous melts evolved from high temperatures (930–730 °C) and modestly hydrous and oxidized conditions to relatively low temperatures (760–680 °C) and very hydrous and oxidized conditions. Collectively, all Late Cretaceous igneous rocks at Pebble contain magnetite and little or no ilmenite, are metaluminous to weakly peraluminous, and have typical arc trace element enrichments and depletions. They have moderate Sr/Y ratios (20–55) and gently sloped REE profiles (La/Yb = 5–20) that are not adakitic, which supports a source area lacking garnet that is consistent with a thin crust in southwest Alaska. Radiogenic isotopes for Late Cretaceous intrusions at Pebble have a restricted range of primitive Sr and Nd isotopic compositions ( 87 Sr/ 86 Sr i = 0.70329–0.70424; ɛNd i = 4.9–6.1), which overlap with volcanic and plutonic basement rocks of the Jurassic Talkeetna Arc along the Alaska Peninsula. The Kaskanak batholith intrudes the Late Jurassic–Early Cretaceous Kahiltna flysch, and mixing models using Sr and Nd isotopes indicate that the Kaskanak batholith assimilated ≤10 wt% Kahiltna flysch in amounts that did not likely affect magma fertility. Xenocrystic zircon samples are abundant in Cretaceous pre-mineral intrusions and have U-Pb ages similar to detrital zircon samples in the Kahiltna flysch. These data support some assimilation of upper crustal Kahiltna flysch, but the dominance of Devonian–Mississippian xenocrystic zircon populations in some intrusions suggests derivation from unexposed older basement. The extraordinary endowment of Cu and Au at Pebble is inferred to result from primitive calc-alkaline and alkaline arc magmas and the hydrous and strongly oxidized conditions that suppressed the formation and fractionation of Cu- and Au-enriched sulfide melts. Furthermore, differentiation to silicic compositions was a product of extensive crystal fractionation of parental melts accompanied by minor crustal assimilation. The trace element content of the intermediate composition intrusions indicates that both hornblende and titanite fractionation processes in the mid- to shallow-crust were both required to produce the more evolved granodiorite and granite porphyry compositions. Despite the apparent lack of Mo-enriched continental crust in the region, primitive hydrous melts were produced by protracted arc magmatism and were modified by minor crustal assimilation including early alkaline magmatism, periodic recharge of mafic hydrous basalts and hybrid andesites, and fractional crystallization, which was apparently sufficient to enrich Mo in late stage felsic melts.

Confirmation of the southwest continuation of the Cat Square terrane, southern Appalachian Inner Piedmont, with implications for middle Paleozoic collisional orogenesis

Detailed geologic mapping, U-Pb zircon geochronology and whole-rock geochemical analyses were conducted to test the hypothesis that the southwestern extent of the Cat Square terrane continues from the northern Inner Piedmont (western Carolinas) into central Georgia. Geologic mapping revealed the Jackson Lake fault, a ∼15 m-thick, steeply dipping sillimanite-grade fault zone that truncates lithologically distinct granitoids and metasedimentary units, and roughly corresponds with a prominent aeromagnetic lineament hypothesized to represent the southern continuation of the terrane-bounding Brindle Creek fault. Results of U-Pb SHRIMP geochronology indicate Late Ordovician to Silurian granitoids (444–439 Ma) occur exclusively northwest of the fault, whereas Devonian (404–371 Ma) granitoids only occur southeast of the fault. The relatively undeformed Indian Springs granodiorite (three individual bodies dated 317–298 Ma) crosscuts the fault and occurs on both sides, which indicates the Jackson Lake fault is a pre-Alleghanian structure. However, detrital zircon signatures from samples southeast of the Jackson Lake fault reveal dominant Grenville provenance, in contrast to Cat Square terrane detrital zircon samples from the northern Inner Piedmont, which include peri-Gondwanan (600–500 Ma) and a prominent Ordovician-Silurian (∼430 Ma) signature. We interpret the rocks southeast of the Jackson Lake fault to represent the southwestern extension of the Cat Square terrane primarily based on the partitioning of granitoid ages and lithologic distinctions similar to the northern Inner Piedmont. Data suggest Cat Square terrane metasedimentary rocks were initially deposited in a remnant ocean basin setting and developed into an accretionary prism in front of the approaching Carolina superterrane, ultimately overridden by it in Late Devonian to Early Mississippian time. Burial to >20 km resulted in migmatization of lower plate rocks, forming an infrastructure beneath the Carolina superterrane suprastructure. Provenance patterns support ∼250 km of Devonian dextral translation of the composite Inner Piedmont, which places the northern portion of the Inner Piedmont adjacent to a suite of ∼430 Ma plutons in the Virginia Blue Ridge during deposition. The megascopic thrust-nappe structural style of the northern Inner Piedmont, combined with southwest-directed lateral extrusion at mid-crustal depths, may reconcile differences in timing of metamorphism between the Carolina and central Georgia Inner Piedmont and structural contrasts between the Brindle Creek and Jackson Lake faults.

Late Jurassic-Cretaceous fluvial evolution of central Africa: Insights from the Kasai-Congo Basin, Democratic Republic Congo

The Congo Basin in central Africa is one of the largest intracratonic sedimentary basins in the world. The geological knowledge of Congo Basin is mainly based on studies from the central part of the basin (“Cuvette Centrale”). We present the results of sedimentary provenance investigations of the Jurassic–Cretaceous strata from the southwestern part of the basin, called the Kasai region. This study combines sandstone petrography with U-Pb and Lu-Hf analyses of detrital zircons to assess the stratigraphy, sedimentary provenance and drainage history of the Upper Jurassic-Cretaceous strata in the Kasai region. The stratigraphy is subdivided into a single Upper Jurassic unit (J1) and four Cretaceous units (C1–C4). Petrographically, sandstones from all units except the conglomeratic C3 are texturally and compositionally mature, dominated by quartzarenite and subarkosic compositions. These characteristics can be attributed to considerable recycling of older sedimentary strata and crustal sources, along with long distance fluvial and aeolian processes. The analyses of fifteen detrital zircon samples from the Upper Jurassic–Cretaceous strata yielded mainly Archean and Proterozoic zircons. This result suggests that sandstones are likely sourced from the underlying Archean-Paleoproterozoic Congo–Kasai Craton and from nearby Proterozoic mobile belts, particularly the Irumide and Lufilian Belts to the south of the basin. The dominance of Archean and Proterozoic detrital zircons in Upper Jurassic–Cretaceous strata suggests that the Kasai portion of the Congo Basin experienced exhumation and erosion, which is possibly associated with far-field reactivation of Archean and Proterozoic structures during and following Gondwana rifting in the late Mesozoic. A large fluvial drainage network sourced from the south of the basin, is interpreted to have developed across central Africa during the Late Jurassic–Cretaceous. This fluvial system is believed to have flowed northward across the Congo Basin and ultimately drained into a wrench fault system called the Central African Shear Zone, which extends in an ENE direction from the Gulf of Guinea through Cameroon into Sudan and Kenya.

Record of orogenic cyclicity in the Alberta foreland basin, Canadian Cordillera

Jurassic–Cretaceous sedimentary rocks of the Alberta foreland basin are a key record of the evolution of the Canadian Cordillera. We test a recent model for cyclical development of Cordilleran orogenic systems using detrital zircon analysis of the major sandstone units deposited between 145 and 80 Ma exposed in the Rocky Mountain Foothills near Grande Cache, Alberta. The basin history is well constrained by decades of study, and the stratigraphy has been previously subdivided into tectonostratigraphic wedges. U-Pb data from 14 detrital zircon samples are included in this study. All the major magmatic provinces of North America are represented in each sample, with the relative proportions varying between samples. The samples are assigned to five groups with the aid of multidimensional scaling. Groups 1–3 are interpreted to record recycling from specific passive-margin units of western North America with varying input from the Cordilleran magmatic arc. Group 4 is interpreted to record recycling from sedimentary strata in the United States and dispersal by basin-axial fluvial systems. Group 5 is dominated by Mesozoic zircon grains interpreted to have originated in the Cordilleran magmatic arc. Detrital zircon age spectra do not form groups based on the tectonostratigraphic wedges from which they were sampled; rather, within each tectonostratigraphic wedge, they exhibit evolution from diverse age spectra to a less-diverse distribution of detrital zircon ages.

U-Pb age and Hf-O isotopes of detrital zircons from Hainan Island: Implications for Mesozoic subduction models

A compilation of magmatic ages from the Mesozoic South China Block suggests a number of “magmatic quiescence” periods at ca. 205–195Ma, ca. 150–140Ma and ca. 125–115Ma, casting doubt on tectonic models that suggest ongoing Andean-type subduction along the South China continental margin. However, SIMS U-Pb analyses on two detrital zircon samples from the Cretaceous Lumuwan Formation on Hainan Island, southeast China, reveal three major age peaks at ca. 120Ma, ca. 155Ma and ca. 235Ma. Zircons of these ages are mostly euhedral and show typical magmatic oscillatory zoning, suggesting short-distance transport from nearby magmatic sources. The extremely rare occurrence of ca. 120Ma magmatic records onshore suggests that detrital zircons of this age population may be derived from a source proximal to Hainan Island but presently missing. Therefore, our data provide new evidence for ongoing magmatic activity in late Mesozoic South China.In situ Hf and O isotope analyses of the Mesozoic detrital zircons reveal large variations in both εHf(t) (−21.2 to 10.5) and δ18O (4.4‰ to 13.6‰) values. A general negative correlation between them suggests the reworking of old supracrustal materials (average crustal residence age of ca. 2.0Ga) by juvenile mantle-derived magmas. The progression of increasing εHf(t) and decreasing δ18O values of zircons from the Triassic to the Cretaceous suggests progressive crustal growth during the Mesozoic. The results are consistent with hybridization at an active continental margin. We briefly review tectonic models for the Indosinian orogeny and suggest that the petrologic evidence indicates that Mesozoic magmatism was part of the circum-Pacific accretionary orogens that formed along the continental margin of East Asia no later than ca. 250Ma and continued at least to the late Cretaceous.

Detrital zircon record of Neogene exhumation of the central Alaska Range: A far-field upper plate response to flat-slab subduction

Far-field deformation in the upper plate of many ancient and modern convergent margins is commonly attributed to flat-slab subduction processes. Recent studies have suggested that the high topography of the central Alaska Range (Alaska, USA), for example, is the far-field deformational response to Neogene shallow subduction processes in southern Alaska. In this study, we analyze six stratigraphically controlled detrital zircon samples from Miocene–Pliocene sandstone of the Tanana foreland basin to evaluate the temporal and spatial links between exhumation of the central Alaska Range and shallow subduction. The Tanana basin, located north of the central Alaska Range, contains ∼2 km of Neogene strata. Lower Miocene strata from the basin have detrital zircon ages with dominant Precambrian populations. These grain ages are attributed to sediment derivation from the Yukon composite terrane source area located at the northern edge and north of the Alaska Range. During the early–middle Miocene the provenance of the Tanana basin switched to a distinctly Mesozoic source signal. These Mesozoic-age grains are attributed to sediment derived from source areas within and south of the Alaska Range. The early–middle Miocene change in provenance from predominantly Precambrian to Mesozoic sediment sources, in the context of previously published basin analysis studies, is interpreted to represent the onset of Neogene uplift of the central Alaska Range. The timing of exhumation of the central Alaska Range is important not only for understanding the tectonics of the highest mountain range in North America, but additionally because recent modeling studies predict that this range is one of the first expected products of Neogene flat-slab subduction along the southern Alaska convergent plate boundary. Results of our study provide a needed chronologic framework to fully evaluate the temporal and spatial upper plate responses to shallow subduction processes.

Detrital mineral age, radiogenic isotopic stratigraphy and tectonic significance of the Cuddapah Basin, India

The Cuddapah Basin is one of a series of Proterozoic basins that overlie the cratons of India that, due to limited geochronological and provenance constraints, have remained subject to speculation as to their time of deposition, sediment source locations, and tectonic/geodynamic significance.Here we present 21 new, stratigraphically constrained, U–Pb detrital zircon samples from all the main depositional units within the Cuddapah Basin. These data are supported by Hf isotopic data from 12 of these samples, that also encompass the stratigraphic range, and detrital muscovite 40Ar/39Ar data from a sample of the Srisailam Formation. Taken together, the data demonstrate that the Papaghni and lower Chitravati Groups were sourced from the Dharwar Craton, in what is interpreted to be a rift basin that evolved into a passive margin. The Nallamalai Group is here constrained to be deposited between 1659±22Ma and ~1590Ma. It was sourced from the coeval Krishna Orogen to the east, and was deposited in its foreland basin. Nallamalai Group detrital zircon U–Pb and Hf isotope values directly overlap with similar data from the Ongole Domain metasedimentary rocks. Depositional age constraints on the Srisailam Formation are permissive with it being coeval with the Nallamalai Group and it was possibly deposited within the same basin. The Kurnool Group saw a return to Dharwar Craton derived provenance and is constrained to being Neoproterozoic. It may represent deposition in a long-wavelength basin forelandward of the Tonian Eastern Ghats Orogeny. Detrital zircons from the Gandikota Formation, which is traditionally considered a part of the Chitravati Group, constrain it to being deposited after 1181±29Ma, more than 700Ma after the lower Chitravati Group. It is possible that the Gandikota Formation is correlative with the Kurnool Group.The new data suggest that the Nallamalai Group correlates temporally and tectonically with the Somanpalli Group of the Pranhita–Godavari Valley Basin, which is tightly constrained to being deposited at ~1620Ma. These syn-orogenic foreland basin deposits firmly link the SE India Proterozoic basins to their orogenic hinterland with their discovery filling a ‘missing-link’ in the tectonic development of the region.

Detrital zircon geochronology of Cordilleran retroarc foreland basin strata, western North America

AbstractWe present a compilation of 8717 U‐Pb analyses from 95 detrital zircon samples of Jurassic‐Eocene North American Cordillera foreland basin strata. Of these samples, 30 are new and previously unpublished. Variation in detrital zircon age spectra between samples records erosion or recycling of basement and cover rocks within the Cordilleran orogenic wedge. Each sample can be classified into one of six major provenance groups, whose age spectra suggest derivation from (1) Mesozoic eolianites of the western United States, (2) Paleozoic passive margin strata of the western United States, (3) Paleozoic passive margin strata of western Canada, (4) the Mogollon Highlands, (5) the Cordilleran magmatic arc, or (6) Yavapai‐Mazatzal Province crystalline basement rocks. Referencing these provenance interpretations to their location and stratigraphic deposition age produces a detailed spatial and temporal record of sediment dispersal within the foreland basin system. Late Jurassic provenance is dominated by recycling of Mesozoic eolianites from sources in the Sevier thrust belt. Cretaceous‐Eocene provenance is dominated by recycling of the passive margin, with increasing complexity upsection. We interpret that this provenance transition records a basin‐wide unroofing sequence. A composite age‐probability plot of 1539 young (&lt;250 Ma) detrital zircons reveals at least four age‐abundance peaks that we interpret to represent periodic high‐flux magmatism in the Cordilleran arc.

U‐Pb Detrital Zircon Analysis – Results of an Inter‐laboratory Comparison

Inter‐laboratory comparison of laser ablation ICP‐MS and SIMS U‐Pb dating of synthetic detrital zircon samples provides an insight into the state‐of‐the art of sedimentary provenance studies. Here, we report results obtained from ten laboratories that routinely perform this type of work. The achieved level of bias was mostly within ± 2% relative to the ID‐TIMS U‐Pb ages of zircons in the detrital sample, and the variation is likely to be attributed to variable Pb/U elemental fractionation due to zircon matrix differences between the samples and the reference materials used for standardisation. It has been determined that ~ 5% age difference between adjacent age peaks is currently at the limit of what can be routinely resolved by the in situ dating of detrital zircon samples. Precision of individual zircon age determination mostly reflects the data reduction and procedures of measurement uncertainty propagation, and it is largely independent of the instrumentation, analytical technique and reference samples used for standardisation. All laboratories showed a bias towards selection of larger zircon grains for analysis. The experiment confirms the previously published estimates of the minimum number of grains that have to be analysed in order to detect minor zircon age populations in detrital samples.

Fluctuations in Sedimentary Provenance of the Upper Cambrian Mount Simon Sandstone, Illinois Basin, United States

Abstract Understanding sedimentary provenance is essential when investigating clastic strata. The lack of compositional variability in mature sediments associated with Cambrian cratonic sequences in the United States makes traditional petrographic discrimination of sedimentary origin difficult. The upper Cambrian Mount Simon Sandstone of the Illinois Basin is a quartz arenite (Q93F5L2 and Qm85F5Lt10) with unconstrained sediment provenance and is also the reservoir for ongoing injection of a million tons of CO2. This study investigates whether fluctuations in sedimentary provenance caused changes in the composition and texture of the Mount Simon Sandstone reservoir through its deposition. Core descriptions, petrographic analyses of 35 thin sections, and LA-ICPMS analyses of five detrital zircon samples, collected from 878 feet of the Mount Simon Sandstone depositional interval in Stephenson County, Illinois, the only known core that includes the entire formation, yield new compositional data and U-Pb ages....

Detrital zircon U-Pb geochronology of Mesozoic sandstones from the Lower Yana River, northern Russia

The formation of the Amerasian Basin of the modern Arctic remains enigmatic in terms of both timing and method of formation. Most models used to describe its formation involve movement of the Arctic Alaska-Chukotka microplate across the basin’s current location. Detrital zircon U-Pb geochronology has been shown to be an inexpensive yet powerful method by which the tectonic correlation and proximity between multiple terranes over geologic time can be approximated. Five detrital zircon samples were collected from Late Jurassic sandstones from the Lower Yana River area and compared to previous results from detrital zircons collected from nearby Triassic strata. Jurassic samples had detrital zircon age populations of 147–210 Ma, 223–396 Ma, 1639–2183 Ma, and 2281–3116 Ma. Comparison of all detrital zircon ages from the Lower Yana River to those dated from Triassic and Jurassic sandstones of Chukotka, the Verkhoyansk fold-and-thrust belt, and the In’yali-Debin synclinorium supports the interpretation that Chukotka was separated from the Kular area during the Triassic. Jurassic detrital zircon age populations suggest that the Anyui Ocean had closed by the Tithonian, bringing Chukotka to a location where it could be fed by similar depositional systems as the Verkhoyansk fold-and-thrust belt and the Lower Yana River area. Sedimentological and detrital data presented here also suggest that the Yana fault does not represent a regional suture between the Kolyma-Omolon superterrane and the Siberian craton.

Detrital zircon age constraints for the Winton Formation, Queensland: Contextualizing Australia's Late Cretaceous dinosaur faunas

The Winton Formation provides an important snapshot of Australia's late Mesozoic terrestrial biota, boasting a vertebrate fauna that includes dinosaurs, crocodyliforms, aquatic squamates, turtles, lungfish and teleost fishes, and a flora that has previously been considered to include some of the world's earliest known flowering plants. Despite its significance, poor age control has thus far prevented precise regional and global correlations, limiting the depth of paleobiogeographic assessments. The goal of this study was to use U–Pb isotope dating of detrital zircons by laser ablation to refine the depositional age range of selected horizons within the Winton Formation. We applied this technique, with refined instrumental tuning protocols, to systematically investigate detrital zircon grain ages for five samples from different stratigraphic levels and vertebrate-bearing fossil locations throughout the Winton Formation. Seven different metrics for interpreting the maximum depositional age of each of the detrital zircon samples were compared and our results suggest that sedimentation of the Winton Formation commenced no earlier than latest Albian (~103.0–100.5Ma) and that deposition of the upper vertebrate fossil-rich portion of the section began roughly near or after the Cenomanian–Turonian boundary (93.9Ma), demonstrating that the formation and its important flora and fauna were deposited primarily during the Late Cretaceous. These results provide a significant advancement in understanding the age of the Winton Formation's flora and fauna, and will help to contextualize Australia's Late Cretaceous terrestrial biota within a broader Gondwanan framework.

U–Th/Pb geochronology of detrital zircon and monazite by single shot laser ablation inductively coupled plasma mass spectrometry (SS-LA-ICPMS)

A modified single-shot laser ablation inductively coupled plasma mass spectrometry (SS-LA-ICPMS) technique is presented that enables rapid acquisition of in-situ U–Th/Pb dates on accessory minerals from a single laser pulse. Advances over existing techniques include formulation of a semi-automated data reduction method and robust error propagation. The effects of pulse-to-pulse laser stability and analyte transport configurations on the precision and accuracy of the analyses are systematically assessed. The validity of the SS-LA-ICPMS approach is demonstrated by repeat analyses of multiple zircon and monazite reference materials, which consistently reproduce to within uncertainty of accepted reference values. Application of the method to detrital zircon and monazite samples with a wide range of ages and variable parent and daughter nuclide concentrations results in U–Th/Pb age spectra that are statistically indistinguishable from conventional laser ablation protocols that employ continuous laser pulsing. The SS-LA-ICPMS technique is minimally destructive, offers increased sample and grain throughput and enables rapid dating of large numbers of grains—enabling, e.g., to identify grains that are geologically significant yet rare.

Detrital zircon evidence for the linkage of the South China block with Gondwanaland in early Palaeozoic time

AbstractLA-ICP-MS U–Pb dating of Lower Devonian detrital zircon samples from three representative sections in the South China block yields dominant Grenvillian and Pan-African populations, similar to the age distribution of early Palaeozoic samples from Gondwana, the Tethyan Himalaya and West Australia, in particular. Hf isotopic compositions indicate the contributions of juvenile crust at 1.6 Ga and 2.5 Ga, and bear a resemblance to their counterparts from SE Australia and West Antarctica, revealing the mixed origin of the Pan-African and Grenvillian grains from juvenile magmas and melting of pre-existing crustal rocks. These results suggest that the South China block should be considered an integral part of East Gondwana in early Palaeozoic time, rather than a discrete continental block in the Palaeo-Pacific or a fragment of Laurentia.