Pb Ages Of Detrital Zircons Research Articles

Tectonic evolution of the Triassic Songpan‐Ganzi basin as constrained by a synthesis of multi‐proxy provenance data

AbstractThe triangular Songpan‐Ganzi flysch terrane exposes a Triassic turbidite sequence with an average thickness of ca. 8 km. The sediments may have been accumulated in a remnant Paleo‐Tethyan ocean bounded by the converging North China, South China, and the Qiangtang terrane from three sides, or a back‐arc basin with an oceanic basement created during the Triassic closure of the Paleo‐Tethyan ocean. To differentiate the two competing models, we systematically reviewed the available provenance data that include U–Pb detrital zircon ages at the basin scale, paleocurrent directions, sandstone petrography, and heavy‐mineral assemblages from the Triassic Songpan‐Ganzi basin samples. We use the Kolmogorov–Smirnov tests to differentiate competing hypotheses for detrital‐zircon provenance interpretations and DZmix modelling to quantify relative contributions of detrital zircon from all potential source areas for the Triassic Songpan‐Ganzi deposits. The most important result of this work is that the Songpan‐Ganzi basin had a stable and locally derived source system: the western, central and eastern sub‐basins were mainly sourced from the north whereas the easternmost and southeastern sub‐basins were mainly sourced from westernmost South China (i.e., the Longmen Shan area) and the Qiangtang terrane. The stability of the source areas around the Songpan‐Ganzi basin throughout the Triassic is most compatible with the remnant ocean model that predicts a long‐lived marine basin with a pre‐Triassic oceanic/continental basement trapped between converging continental blocks during the Triassic.

Late Precambrian “Pre-Glacial” Sedimentation Stage in the Southern Siberian Platform

Abstract —We present new data on the chemical composition of the late Precambrian rocks in the upper part of the regional Balaganakh stratigraphic horizon (the Nugan Formation at the Baikal segment of the Sayan–Baikal–Patom belt (SBPB) and the Bugarikhta Formation of the Balaganakh Group at the Patom segment of the SBPB) and the U–Pb (LA-ICP-MS) age of detrital zircons from the Bugarikhta Formation. It has been established that the rocks of the Nugan and Bugarikhta formations resulted from the destruction of igneous and metamorphic rocks. The contents and ratios of trace and rare-earth elements in the rocks of the Nugan and Bugarikhta formations indicate a predominance of felsic igneous rocks in the provenance and the presence of rocks of mafic and intermediate compositions at the source of the terrigenous rocks of the Nugan Formation. The U–Pb age of detrital zircons from all rocks of the upper part of the regional Balaganakh Horizon is close to the age of the rocks in the basement of the southern margin of the Siberian Platform, which suggests that this basement was the main source of clastic material in the sedimentation basins. It is argued that the “pre-glacial” (pre-Marinoan) terrigenous deposits of the Nugan and Bugarikhta formations, as well as the deposits of the Ipsit Formation at the Sayan segment of the SBPB, accumulated in the Late Riphean (ca. 720–640 Ma), probably in postrift basins that formed immediately after the separation of Siberia from Laurentia at the early stages of the opening of the Paleoasian Ocean.

Jurassic tectonics of northeastern Gondwana: evidence from the detrital zircon record of the Nambour Basin

The Nambour Basin provides the easternmost record of Jurassic sedimentation for Australia. U–Pb detrital zircon age spectra constrain basin infill as Early–Middle Jurassic ( c. 195–163 Ma). Early Jurassic samples are dominated by 650–500 Ma detrital zircon sourced from the Lachlan Orogen of southeastern Australia. Distal Jurassic upland associated with this orogen was generated by epeiric uplift. Sediment sourced from it was transported northwards and eastwards into the Nambour Basin as corroborated by basinal paleocurrent data. In contrast, Devonian to Triassic detrital zircon from the New England Orogen, which abuts the Nambour Basin margin, are scarce. Topographic relief across this orogen generated by the Permo-Triassic ( c. 260–230 Ma) Hunter Bowen Orogeny, had been largely eliminated by the Early Jurassic. Dominant Jurassic detrital zircon for one sample of this age, combined with related paleocurrent data and the absence of a Jurassic zircon source in eastern Australia, reflects an easterly Jurassic igneous assemblage now located on submerged northern Zealandia. The detrital zircon data presented herein constrains tectonic interpretations proposed for Jurassic east Gondwana, continental margin sedimentary assemblages in New Caledonia and New Zealand. Documentation of continental epeiric uplift from detrital zircon age data obtained from basin fill has potential yet to be explored. Supplementary material: Tables S1 and S2 are available at https://doi.org/10.6084/m9.figshare.c.5988017

Provenance of pre- and Carboniferous sequences of the Esquel-Arroyo Pescado-Tepuel regions (Argentine Patagonia): A combined U–Pb and Hf isotope study of detrital zircon and constraints on depositional setting

Provenance and stratigraphic age of pre-Carboniferous or pre-glacial (Esquel and Arroyo Pescado formations) and Carboniferous glacial (Valle Chico Formation) metasedimentary units exposed in the southwestern sector of the North Patagonian Argentine region are analyzed by sedimentary petrology and combined U–Pb and Lu–Hf isotope on detrital zircons. Additionally, a sample of the Jaramillo Formation (Tepuel Group) allowed comparison and correlation to the Carboniferous deposits in the type area of the Tepuel-Genoa basin.Despite differences, samples of all units studied indicate deposition linked to an arc tectonic environment using ternary petrological diagrams. U–Pb detrital zircon age distribution of the Esquel Formation show a dominance of Famatinian, Pampean-Brazilian and Mesoproterozoic ages, whereas the Arroyo Pescado Formation displays a predominant Mesoproterozoic data cluster. On the other hand, the Valle Chico Formation records a main input of post-Famatinian or Chanic (Devonian) ages and minor Gondwanic (Carboniferous) ages. The Jaramillo Formation is unique due to the remarkable unimodal concentration of Gondwanic ages (Carboniferous) and the scarcity of older than Famatinian detrital zircon ages. The maximum sedimentation age is Lochkovian (Lower Devonian) for the Esquel Formation and, Tournaisian and Tournaisian-Visean (lower Carboniferous) for the Valle Chico and Jaramillo formations, respectively; the youngest records for the Arroyo Pescado Formation indicate a middle Cambrian to Middle Ordovician age. Most Mesoproterozoic zircon grains show a remarkable juvenile Hf isotopic character and a slight age difference between U–Pb and Hf TDM data. These records are equivalent to those identified in different units of the Paleozoic of the Patagonian region and the Malvinas/Falkland Islands, where the Mesoproterozoic detrital zircons with positive εHf (t) values indicative of a juvenile character are present. The conspicuous participation of Mesoproterozic zircons ages within the pre-Carboniferous units supports the probable existence of an unexposed Mesoproterozoic crust in the North Patagonian region, as mentioned by previous authors.The allochthonous or autochthonous character of South Patagonia is tested using combined U–Pb ages and initial Hf-isotope compositions of single zircons. The allochthonous alternative of South Patagonia in the pre-Carboniferous stage, favours contributions from eastern Antarctica, South Africa, Malvinas/Falkland Islands and local sources such as the Deseado Massif and the suspected Chaitenia terrane. An autochthonous scenario suggests that the North Patagonian, Deseado Massifs, Malvinas/Falkland Islands and local areas (Chaitenia terrane) were the main source for the pre-Glacial and Glacial studied units, with minor influence from distant regions of South America.

Provenance of Devonian–Carboniferous strata of Colorado: The influence of the Cambrian and the Proterozoic

ABSTRACTWe report new LA-ICP-MS U–Pb detrital zircon ages and sedimentary petrology of silty to sandy limestones and dolostones, as well as calcareous to dolomitic sandstones of the Devonian–Carboniferous (Mississippian) Chaffee Group. We also report new detrital zircon ages from the late Cambrian Sawatch Quartzite, and a U–Pb zircon crystallization age on a late Mesoproterozoic (1087.9 ± 13.5 Ma) granitoid of underlying basement from the Eagle Basin of northwest Colorado. Grain populations in the Chaffee Group are mostly bimodal. More than 84% of zircons centered around a Paleoproterozoic (ca. 1.78 Ga) mode typical of the Yavapai province that forms much of the basement of Colorado and an early Mesoproterozoic (ca. 1.42 Ga) mode typical of A-type granites that intrude this region. A notable late Mesoproterozoic (ca. 1.08 Ga) mode exists in some Chaffee samples, giving those samples a trimodal detrital zircon age distribution. These bipartite or tripartite detrital zircon age modes exist in Cambrian, Devonian, and Carboniferous strata from paleogeographically adjacent successions, but the correlation between the Chaffee zircons is highest with the region’s basal Cambrian sandstones of the Sawatch Quartzite, Flathead Sandstone, and Ignacio Quartzite, which have similar (ca. 1.08 Ga, 1.43 Ga, 1.70 Ga, respectively) zircon populations, and a paucity of > 1.8 Ga grains. This similarity suggests that most grains in the Chaffee Group derive from recycling of these basal sandstones, and that little sediment was derived directly from thenexposed Precambrian basement highs, from the Wyoming craton to the north, or from Paleoproterozoic arcs and orogens to the west and northeast. Minor Mesoarchean to early Paleoproterozoic (ca. 3.00 to 2.40 Ga) grains exist in the Chaffee Group, an attribute shared by the Late Ordovician Harding Sandstone of Colorado’s Front Range, but that is absent from the region’s underlying Cambrian sandstones—suggesting some recycled mixture of Cambrian and Ordovician sedimentary rocks. No near-depositional age grains are present in the Chaffee Group. The youngest grain is Early Devonian (~417 Ma), > 45 million years (m.y.) older than these strata. Additionally, Paleozoic grains are extremely uncommon (< 0.1%; n = 2,927 grains).

The U–Th–Pb Age of Detrital Zircons from Oolitic Limestones of the UK Formation: Traces of the Grenville Provenance Areas in the Late Riphean of the Southern Urals

The U–Th–Pb Age of Detrital Zircons from Oolitic Limestones of the UK Formation: Traces of the Grenville Provenance Areas in the Late Riphean of the Southern Urals

Age, provenance and geological significance of (meta)–sedimentary rocks in the Yitong–Gongzhuling area, NE China: Constraints from zircon U–Pb geochronology

The Permo–Triassic was a crucial interval for the Changchun–Yanji suture zone in NE China since it witnessed the late–stage tectonic evolution of the Paleo–Asian Ocean (PAO). Thus, provenance analysis of Triassic sedimentary rocks in this region can shed light on the eventual closure process of the PAO. In this study, we carried out petrological, geochemical, and detrital zircon U–Pb geochronological research on two (meta)–sedimentary rocks from the Yitong–Gongzhuling area located in the westernmost section of the Changchun–Yanji suture zone. LA–ICP–MS U–Pb ages of detrital zircons from the two samples indicate a middle Triassic maximum depositional age (~ 240 Ma). The two samples present a most significant Permo–Triassic (299–240 Ma) detrital zircon population that corresponds to the multi–phase subduction and collision–related magmatism along the Changchun–Yanji suture zone. In addition, a late Silurian–early Devonian (429–390 Ma) detrital zircon population is also present and presumably fed from a pre–existing accreted arc terrane along the northern margin of the North China Craton (NCC). In contrast to some previously reported Permo–Triassic sedimentary rocks in adjacent areas, our new results show an absence of ~ 2.5 and ~ 1.8 Ga ages characteristic of NCC magmatism or metamorphism. The results imply that the Yitong–Gongzhuling area probably has a higher relief than the adjacent area during the middle Triassic, preventing the deposition of materials from the NCC to the south. This is further evidenced by the proximal orogenic source, short–distance transportation, and rapid accumulation for the studied samples as indicated by the subhedral to anhedral and poor roundness morphology of detrital zircons. The inferred regional uplift was hypothesized to be caused by the continued transpression during the PAO final closure based on the widely distribute early–middle Triassic syn–collisional granitic rocks along the Changchun–Yanji suture zone.

Origin and evolution of the Paleo‐Kuril arc inferred from detrital zircon U–Pb chronology in eastern Hokkaido, NE Asia

AbstractThe Nemuro and Saroma Groups and Yusenkyo Formation occur in eastern Hokkaido and are considered to be forearc or intra‐arc basin sediments of the Paleo‐Kuril arc (PKA) deposited during the Late Cretaceous to middle Eocene. To further clarify the origin of the PKA, we examined the U–Pb ages of detrital zircons within these sandstones and acidic tuff beds; based on our results, we drew the following conclusions. (1) The PKA originated from an oceanic island arc on the oceanic Izanagi Plate around 85 Ma, to which the Nikoro Group greenstone complex was accreted between 81–80 Ma; the Lowest Unit of the Saroma Group covered the surface of the Nikoro accretional greenstone complex. (2) The PKA then first collided with NE Asia around the beginning of the deposition of the Hamanaka Formation (~70 Ma) and transitioned to a continental arc adjacent to NE Asia. This collision generated giant slump beds during deposition of the Akkeshi Formation. During deposition of the Kiritappu Formation, the entire Nemuro Peninsula was uplifted, supplying large volumes of clastic sediments. (3) Although we do not have data directly bearing on why the North American Plate was established in the edge of NE Asia, we speculate that it separated from the Eurasian continent around ~70 Ma when NE Asia first collided with the PKA. Subsequently, the PKA has behaved as part of the North American Plate. The Paleo‐Japan arc (or East Sikhote–Alin arc) and the PKA became joined via the Hidaka Belt. Around 40 Ma, during the deposition of coarse conglomerate beds of the Urahoro Group, the PKA was uplifted and bent clockwise due to a second collision with NE Asia. (4) The modern Kuril arc was established around 36 Ma (late Eocene–early Oligocene), and the Kuril backarc basin opened into the present tectonic setting in the late Oligocene–early Miocene.

Huge sedimentary hiatus in the southern margin of the North China Craton from mid-Mesoproterozoic to Neoproterozoic

ABSTRACT The Meso- to Neoproterozoic Eras were characterized by environmental, evolutionary, and lithospheric stability in the North China Craton (NCC). It is controversial that huge uplift(s) occurred in the North China Craton during this period. The southern NCC developed early terrestrial deposition in the late-Paleoproterozoic and glacial sequence in the late Neoproterozoic record integrated geological history of the NCC in the intervening interval. Geochemistry compositions of mid-Mesoproterozoic carbonaceous slates (ca. 1330 Ma) show similar provenances to the underlying Mesoproterozoic sedimentary rocks in the southern NCC. Detrital zircons from the mid-Mesoproterozoic strata yield U–Pb ages from ca. 2450 to 1850 Ma with minor ages of 2950 and 2750 Ma. U–Pb ages of detrital zircons from the Neoproterozoic strata yield from ca. 1700 to 1000 Ma besides peak ages of 2600, 2400, and 1950 Ma. The early Paleozoic sedimentary rocks also display peak ages between ca. 1850 and 1000 Ma along with peaks at ca. 2500 and 2300 Ma. These detrital zircon ages are quite different from those of the Mesoproterozoic sedimentary rocks in the NCC. According to paleogeography study, the late-Paleoproterozoic to the early Mesoproterozoic clastic sequences are controlled by Xiong’er volcanic event in the southern NCC and carbonate platform developed later. The Mesoproterozoic sequences are overlain disconformably by the Neoproterozoic strata. In combination with compiled magmatic and detrital zircon ages, a sedimentary gap spanned at least 300 Ma from mid-Mesoproterozoic to Neoproterozoic in the southern NCC. Thus, the disconformity between the Mesoproterozoic and Neoproterozoic sedimentary sequences in the southern NCC should represent a huge sedimentary hiatus. Both the variable provenances and huge sedimentary hiatus between the Mesoproterozoic and Neoproterozoic sedimentary sequences support that the NCC might not split from relict landmass of Columbia Supercontinent before Neoproterozoic. The relict landmass was involved in aggregation of the Rodinia supercontinent.

U–Pb age and Hf isotopic characteristics of detrital zircon from the Nanhua System in Longsheng, northern Guangxi Province, and their geological significance

U–Pb dating and Hf isotopes of detrital zircons from the Nanhua System in Longsheng, northern Guangxi, were investigated to determine the depositional age and provenance of the Nanhua System and the early crustal evolution stages of the South China. U–Pb ages of detrital zircons from the Chang'an Formation of the Nanhua System in Longsheng, northern Guangxi, are mainly 0.66 ~ 0.72 Ga and 0.72 ~ 0.90 Ga, with εHf(t) ranging from −17.05 to 12.79. The dominant provenance is composed of Neoproterozoic magmatic rock from the southeastern margin of the Yangtze Block and the Nanhua period detrital material from Cathaysia Block. U–Pb ages of detrital zircons from the Fulu Formation can be divided into four major groups, that is, 0.64 ~ 0.72 Ga, 0.72 ~ 0.90 Ga, 1.80 ~ 2.20 Ga, and 2.30 ~ 2.80 Ga, with εHf(t) ranging from −27.66 to 11.68. The main provenance is Neoproterozoic magmatic rock from the southeastern margin of Yangtze Block, followed by the Nanhua period detrital material from the Cathaysia Block and geological body equivalent to the assembly of the Columbia Supercontinent. U–Pb age of detrital zircons from Lijiapo Formation is concentrated in 0.72 ~ 0.90 Ga, with εHf(t) ranging from −16.02 to 11.87, and the main provenance comes from Neoproterozoic magmatic rock in the south‐east margin of Yangtze Block. The second‐stage Hf model age (TDM2) of the Nanhua System is 0.84 ~ 4.51 Ga, with two obvious peak intervals of 0.90 ~ 1.30 Ga and 1.40 ~ 2.10 Ga, and two secondary peak intervals of 2.40 ~ 3.00 Ga and 3.10 ~ 3.60 Ga, which can be interpreted that the research area has experienced four stages of crustal growth: 3.10 ~ 3.60 Ga, 2.40 ~ 3.00 Ga, 1.40 ~ 2.10 Ga, and 0.90 ~ 1.30 Ga. The detrital zircon age spectra indicate that the Chang'an Formation and Fulu Formation of the Nanhua System contain more detrital zircons which is contemporaneous with strata due to the Xuefeng orogeny, while the Lijiapo Formation contains a very small amount of detrital zircon which is contemporaneous with strata, suggesting that the tectonic setting has shifted to a passive continental margin or pull‐apart basin during the period of the Lijiapo Formation.

New Constraints on the Distributary Pattern of Clastics in Fore-arc and Tectonics in Paleogene SW Japan: U–Pb Ages of Detrital Zircons of the Domeki Formation in the Shimanto Belt, Western Shikoku

New Constraints on the Distributary Pattern of Clastics in Fore-arc and Tectonics in Paleogene SW Japan: U–Pb Ages of Detrital Zircons of the Domeki Formation in the Shimanto Belt, Western Shikoku

Provenance of sediments from Barra del Tordo and Tesoro beaches, Tamaulipas State, northwestern Gulf of Mexico

The mineralogy, bulk sediment geochemical composition, and U–Pb ages of detrital zircons retrieved from the Barra del Tordo (Tordo) and Tesoro beach sediments in the northwestern Gulf of Mexico were analyzed to determine their provenance. The beach sediments are mainly composed of quartz, ilmenite, magnetite, titanite, zircon, and anorthite. The weathering proxies such as the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), and Plagioclase Index of Alteration (PIA), reveal a moderate-to-high intensity of weathering in the source area. The chondrite-normalized rare earth element (REE) patterns are similar to felsic igneous rocks, with large negative europium anomaly (Eu/Eu* = ~ 0.47–0.80 and ~ 0.57–0.67 in the Tordo and Tesoro beach sediments, respectively).Three major zircon U–Pb age groups are identified in the Tordo and Tesoro beach sediments, i.e., Proterozoic (~ 2039–595 Ma), Mesozoic (~ 244–70.3 Ma), and Cenozoic (~ 65.9–1.2 Ma). The differences of the zircon age spectrum between the Tordo and Tesoro beach sediments are not significant. The comparison of zircon U–Pb ages in this study with ages of potential source terranes suggests that the Mesozoic and Cenozoic zircons of the studied Tordo and Tesoro beach sediments were derived from the Eastern Alkaline Province (EAP) and Mesa Central Province (MCP). Similarly, the likely sources for the Proterozoic zircons were the Sierra Madre Oriental (SMOr) and Oaxaquia in the northwestern Gulf of Mexico. The results of this study further indicate that the sediments delivered to the beaches by rivers and redistributed by longshore currents were crucial in determining the sediment provenance.

Crustal stabilization: Evidence from the geochemistry and U–Pb detrital zircon geochronology of quartzites from Simlipal Complex, Singhbhum Craton, India

Cratonic stabilization was a critical crustal process during the Hadean to Archean for the formation of cratons. The understanding of how and where this process took place is significant to evaluate the architecture of continents. The Singhbhum Craton of eastern India has well preserved Precambrian volcano-sedimentary sequences. The Simlipal volcano-sedimentary complex of Singhbhum Craton consists of circular bands of mafic volcanic rocks interlayered with quartzites/ shales/phyllites. In the present study, we report petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U–Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton. The quartzites are texturally mature with sub-angular to sub-rounded quartz grains followed by feldspars embedded in a silty matrix. Based on modal compositions and major element ratios, these quartzites are categorized as quartz arenite and sub-lithic arenites. Trace element abundances normalized to Archean Upper Continental Crust (AUCC) display positive anomalies at U, Zr, Hf and negative anomalies at Nb. REE patterns are characterized by negative Eu anomalies (Eu/Eu* = 0.47–0.97) and flat HREE suggesting felsic provenance. These quartzites show depletion of LILE, enrichment of HFSE and transition metals relative to AUCC. High weathering indices such as CIA, PIA, and ICV are suggestive of moderate to intense chemical weathering. Low trace element ratios such as Th/Cr, Th/Sc, La/Sc, La/Co and Th/Co indicate a predominantly felsic source for these rocks. The overall geochemical signatures indicate passive margin deposition for these quartzites. Detrital zircons from the Simlipal quartzites yield U–Pb ages 3156 ± 31 Ma suggesting Mesoarchean crustal heritage. The trace element geochemistry of detrital zircons suggests that the zircons are magmatic in origin and possibly derived from the 3.1 Ga anorogenic granite/granitoid provenance of Singhbhum Craton. These observations collectively indicate the Mayurbhanj Granite and Singhbhum Granite (SBG-III) provenance for these quartzites, thereby tracking the stabilization of the eastern Indian Shield/Singhbhum Craton back to Mesoarchean.

Traces of intra-oceanic arcs recorded in sandstones of eastern Kazakhstan: implications from U–Pb detrital zircon ages, geochemistry, and Nd–Hf isotopes

Traces of intra-oceanic arcs recorded in sandstones of eastern Kazakhstan: implications from U–Pb detrital zircon ages, geochemistry, and Nd–Hf isotopes

Was there an exchange of detritus between the northern and southern Black Sea terranes in the Mesozoic-early Cenozoic?

Resolving the time of rifting of the Black Sea basin is critical to reconstructing the tectonic evolution of the Pontides arc in northern Turkey. U–Pb geochronology of detrital zircons from Middle Jurassic, Upper Cretaceous, and lower Eocene formations in the Eastern Pontides (NE Turkey), as well as published data from circum-Black Sea terranes, reveals that sediments preserved along with the northern (East European Craton-Scythian Platform) and southern (Eastern and Central Pontides-southern flank of the Greater Caucasus-Transcaucasus) margins of the Eastern Black Sea basin display distinct detrital provenances. The U–Pb detrital zircon ages of the sedimentary samples from the Eastern Pontides have distinct populations with ages of ~650–540, ~200, ~170, ~80, and ~50 Ma. In contrast, the ages of the sedimentary samples from the northern Black Sea terranes are characterized by age peaks of ~1400 and ~1100 Ma compared to those of the Eastern Pontides. Only a few detrital zircons in the range of ~650–540 Ma and <200 Ma are identified in the sedimentary samples from the northern Black Sea terranes. This contrast in detrital zircon ages, together with modal analysis of the samples and published paleocurrent data, suggests that Middle Jurassic–lower Eocene sedimentary samples in the Eastern Pontides were locally sourced from Gondwana affinity crustal basement rocks and associated Mesozoic–Cenozoic igneous rocks. Furthermore, there was no exchange of detritus across the Eastern Black Sea basin during the Middle Jurassic–early Eocene. These inferences require the Eastern Black Sea basin to have rifted in a back-arc setting behind the Eastern Pontides arc by the Middle Jurassic or survived as a relict basin of the Paleotethys.

New South American record of the Cretaceous–Paleogene boundary interval (La Colonia Formation, Patagonia, Argentina)

The La Colonia Formation is an Upper Cretaceous to Paleogene shallow marine sedimentary unit in Chubut Province (Patagonia), Argentina that preserves important vertebrate and plant fossils. Despite good exposures and significant paleontological investigation, the precise age of the La Colonia Formation and its stratigraphic relationship to the Cretaceous–Paleogene (K–Pg) boundary are not well understood. The K-Pg boundary is associated with one of the largest mass extinctions in Earth's history yet there are few continental stratigraphic records of the boundary in South America, resulting in poor understanding of its effects there. This study combines magnetostratigraphy, detrital zircon uranium–lead (U–Pb) geochronology, and preliminary palynological results to constrain the age of the La Colonia Formation and its fossils more precisely and determine whether it preserves the K–Pg boundary. U–Pb ages of detrital zircons from the directly underlying Puntudo Chico Formation indicate that the base of the La Colonia Formation is younger than ~71.7 Ma. The studied palynological assemblage includes Quadraplanus brossus, which is restricted to the Maastrichtian in other southern hemisphere records. Paleomagnetic results show that the ~125 m Cerro Buitre Norte section of the La Colonia Formation and the overlying Cerro Bororó Formation has dominantly normal polarity except for a ~5 m zone of reversed polarity near the base that is interpreted to correlate to Chron C30R of the Geomagnetic Polarity Timescale (GPTS), and a ~13 m zone of reversed polarity near the top of the La Colonia Formation that is interpreted to correlate to Chron C29R. The presence of a magnetozone correlated to C29R in the La Colonia Formation suggests that it preserves the K–Pg boundary, making it an important target for continued paleontological collection to better understand the K–Pg extinction and recovery dynamics in South America.

Long-lived stable shelf deposition along Gondwana's southern margin during the Ordovician-Silurian: Inferences from U[sbnd]Pb detrital zircon ages of the Table Mountain Group (South Africa) and correlatives in Argentina and the Falklands/Malvinas Islands

The Ordovician-Silurian siliciclastic units of the Table Mountain Group (TMG; Cape Supergroup) of the Cape Fold Belt (CFB) are classically considered to signify a period of long-lived sedimentation along the southern margin of southern Africa. Despite its vast, prominent outcrop, meaningful interpretations regarding the provenance of the TMG, based on a representative number of UPb detrital zircon age fractions, remains lacking. Within southern Gondwana, the TMG succession is considered broadly time-correlative to the Sierra del Volcan and Balcarce formations of the Sierras Tandilia and lowermost successions of the Ventana Group of the Sierras Australes in Argentina and the Port Stephens Formation of the West Falkland Group (WFG) in the Falkland/Malvinas Islands and Natal Group (South Africa). UPb detrital zircon ages have previously been reported for the Balcarce Formation and Ventana and West Falkland groups. However, their age fractions have not necessarily been compared to the broadly time –equivalent units of the TMG. In addition to the overall scarcity of detrital zircon age data on the TMG, the validity of using conventional, qualitative probability density diagrams to display and interpret such data sets have come into question, with some authors arguing for a quantitative approach for comparing detrital zircon age data sets. A total of 1521 concordant UPb detrital zircon ages and some 330 LuHf isotope analysis for the Peninsula- and Skurweberg formations (TMG) are therefore contributed, from samples obtained throughout the CFB, along with detrital zircon age fractions for the Balcarce, Providencia and Port Stephens formations. A qualitative as well as quantitative approach to compare the UPb detrital zircon age fractions measured for these units were adapted. Noticeable similarities among detrital zircon age fractions of the Peninsula- and Skurweberg formations throughout the western to south-eastern reaches of the CFB could be confirmed by quantitative pairwise comparisons. These point towards very little change in sediment source during the deposition of the lower to upper formations of the TMG during the Ordovician-Silurian. Pairwise comparisons of the TMG zircon age fractions to those of the Balcarce-, Providencia and Port Stephens formations revealed that they all have major late Neoproterozoic to Cambrian and a late Mesoproterozoic to early Neoproterozoic age fractions in common, with some minor contributions from Ordovician-Silurian sources. Due to the overlap in prevalent detrital zircon age fractions as well as Hf-isotope signature of these units, it is difficult to assign a specific provenance area for them with a fair amount of confidence, even if dominant palaeocurrent directions are considered. A quantitative pairwise comparison among data sets of the same or time-equivalent formation did not necessarily allow for age fractions from different source areas to be sufficiently distinguished from each other. In contrast to the classically inferred Namaqua-Natal Metamorphic Complex (NNMC) as source major proto-source for the TMG, it is argued that the sediment sources were located much further to the north such as the Damara and Mozambique belts, given that parts of the NNMC were likely denudated and covered by the sediments such as those of the Nama and Vanrhynsdorp Groups during the Ordovician-Silurian. Older sedimentary successions such as the Nama Group, were likely recycled during the deposition of the TMG: a scenario which also provides a feasible explanation for the noticeable lack of Archean ages among the detrital zircon age fractions. The ages of the youngest detrital zircon fraction conforms to the maximum age of deposition as proposed in literature, although the newly reported ages does not allow for more stringent cross-basin correlations. Regions within Patagonia, considered to have been in relatively close proximity to the relevant depositories, and possibly the Famatinian Belt (Argentina), are considered the source of the youngest Ordovician-Silurian detrital zircons.

U–Pb detrital zircon ages in the Lajas Formation at Portada Covunco: Maximum depositional age and provenance implications for the Neuquén Basin, Argentina

The Lajas Formation of the Neuquén Basin (Argentina) was deposited mainly during the Middle Jurassic but with a highly diachronic pattern. The exact time elapsed in the deposition of this unit remains controversial and depends on the location within the basin. Particularly in the Portada Covunco locality, north of the Huincul High, the debate on the age of the Lajas Formation persists. The age of the unit has been assigned by sequence stratigraphy, palynological, and magnetostratigraphic studies. Moreover, previous studies suggest that the Lajas Formation in this locality is composed of two depositional sequences (Sq1 and Sq2) with a change in the composition of the sandstone, indicating different areas of sedimentary supply. The new U–Pb data (LA-ICP-MS) in the detrital zircons allows us to define a maximum depositional age of approximately 163 Ma for Sq1 and 162 Ma for Sq2, suggesting a Callovian age for the Lajas Formation in the studied area. Furthermore, we propose that the provenance pattern in Sq1 was dominated by U–Pb ages of detrital zircons from the Permian–Triassic (peak at 264, 244 and 215 Ma), indicating derivation predominantly from the North Patagonian Massif magmatic units; while Sq2 shows a provenance pattern of detrital zircons associated with the uplift and exhumation of units located to the southwest margin of the basin during the end of the Middle Jurassic. Interestingly, it is not possible to rule out that the Huincul High may be related to the change in the sedimentary supply area; the probable uplift of the Huincul High has resulted in an effective physical barrier that limited sediment input from the extreme southeast during the deposition of Sq2.

Use of detrital zircon U–Pb ages to assess the timing of deposition of Cretaceous trench-fill deposits in the active continental arc along the East Asian margin

Abstract The Cretaceous Shimanto accretionary complex in southwestern Japan consists mainly of trench-fill deposits and formed in an active continental margin setting along the East Asian margin. Here, we present U–Pb ages of detrital zircons from the complex and compare youngest detrital zircon ages obtained from trench-fill sandstones with true depositional ages inferred from radiolarian fossils to assess the accuracy of zircon ages for estimating the timing of deposition of the trench-fill sediments. Four different methods were used to calculate the youngest detrital zircon ages, giving four different measures: youngest single-grain age (YSG), weighted mean age of the youngest cluster overlapping in age at 1σ (YC1σ) or 2σ (YC2σ), and youngest cluster age estimated using the Mixture Models (auto) of the DensityPlotter program (YCM). The YSG and YC1σ show good agreement with true depositional ages for Albian–Cenomanian strata, which were deposited during weak magmatic activity, and we find no age gap between YC2σ and the true depositional age, but YCM is clearly older. For Turonian–Maastrichtian strata, which were deposited during a period of strong magmatism, YC2σ and YCM correspond to the true depositional ages, and there is no age gap between YC1σ and the true depositional age. However, YSG is clearly younger than the true depositional age for Turonian–Maastrichtian strata. These results indicate that YC1σ and YC2σ show the closest correspondence to the true depositional ages, which suggests that these two measures best represent the true depositional age of trench-fill deposits in an active continental margin.

Provenance of metasedimentary rocks of the western Dom Feliciano Belt in Uruguay: Insights from U–Pb detrital zircon geochronology, Hf and Nd model ages, and geochemical data

New isotopic and geochemical data for the Paleo- Meso- and Neoproterozoic metasedimentary cover of the southern Dom Feliciano Belt (Brasiliano/Pan-African) are presented and evaluated combined with published information. Whole-rock major and trace element geochemistry indicates that the dominant source for all the units had a composition similar to average upper continental crust. The geochemistry is similar even for late Ediacaran successions with a source component from slightly older Ediacaran granites, due to the crustal origin of these granites. Age constraints based on detrital zircon, fossil content, interbedded volcanic rocks and isotope geochemistry confirm Paleo-, Meso-, and Neoproterozoic successions, despite uncertainties remain in some cases. Detrital zircon data show the dominance of Archean (3.3–2.8 Ga) to Paleoproterozoic (2.2–1.9 Ga), and subordinated Mesoproterozoic (1.5–1.3 and 1.1 Ga) and Neoproterozoic (0.5–0.6 Ga) ages. Lu–Hf zircon and Sm–Nd whole-rock model ages confirm that the Archean and the Paleoproterozoic were the major crustal growth periods for the source areas. U–Pb detrital zircon age distributions and model ages demonstrate that the Nico Pérez Terrane and not the Río de la Plata Craton was the source for most metasedimentary rocks of the western Dom Feliciano Belt. Likewise, comparison of Archean, Paleo-, Meso- and Neoproterozoic events supports that the Nico Pérez Terrane could represent a fragment of the Congo Craton.