Detrital Zircon Geochronology Research Articles

Genesis of the Island Gold Deposit, Ontario, Canada: Implications for Gold Mineralization in the Wawa Subprovince of the Superior Province

Abstract The Island Gold deposit represents an uncommon example of known economic mineralization in the Wawa subprovince, which has been tectonically correlated with the neighboring Abitibi subprovince that hosts worldclass orogenic gold deposits. The Island Gold deposit is hosted in dacite, gabbro, and tonalite-trondhjemite, and accompanied D2 deformation. The main ore zone dips steeply toward the south and consists of early shear-hosted laminated quartz veins and late extensional veinlets; both vein sets host gold mineralization. A set of shallowly dipping extensional quartz veins in the Goudreau zone located north of the main ore zones also host economic gold mineralization. Multiple sulfur isotope analysis of pyrite associated with gold-bearing alteration envelopes in the main ore zone indicates no involvement of sulfur affected by mass-independent fractionation, which rules out sulfur (± gold) sourced from nearby banded iron formation or metasedimentary material. However, a single analysis of pyrite from an auriferous Goudreau zone vein indicates the involvement of sulfur that underwent mass-independent fractionation, which suggests a different fluid source. Zircon U-Pb geochronology of pre- and postmineralization rock samples at Island Gold restricts the timing of mineralization to between ca. 2724 and 2672 Ma. Including previous results of detrital zircon geochronology, gold mineralization occurred between ca. 2680 and 2672 Ma. This age range is similar to the timing of gold mineralization at the Hemlo deposit in the Wawa subprovince but is slightly older than the bulk of orogenic gold mineralization in the neighboring southern part of the Abitibi subprovince. Multiple sulfur isotopes indicate that gold mineralization at Island Gold results from fluids of igneous affinity associated with second-generation transpressional deformation. The ore-controlling structures were developed in bends in regional shear zones focused around relatively competent premineralization plutons.

Geochronology and sediment provenance of the Precipice Sandstone and Evergreen Formation in the Surat Basin, Australia: Implications for the palaeogeography of eastern Gondwana

A new view of the palaeogeography and tectonic evolution of eastern Gondwana during the late Mesozoic is emerging, driven largely by the detrital zircon record of sedimentary basins comprising the Great Australian Superbasin (GAS). The updated model suggests that a long-lived magmatic arc was present on the eastern margin of Australia, which is in stark contrast to some previous views that eastern Australia was situated well-inland of a plate boundary. However, the active magmatic arc model is derived from Late Jurassic-Cretaceous strata, with tectonic processes and sediment pathways operating in the Early Jurassic still poorly understood. The Lower Jurassic Precipice Sandstone in the Surat Basin – an important stratigraphic component of the GAS – affords an opportunity to fill such a knowledge gap. The Precipice Sandstone is also economically important due to its aquifer capacity and prospectivity for CO2 sequestration. Previous work has hypothesized that the formation contains deposits sourced from multiple terranes, yet this has not been rigorously tested. In this study, we used detrital zircon geochronology, CA-TIMS dating, petrography, and palaeocurrent analysis to characterise the sedimentary provenance of the Precipice Sandstone and the overlying Evergreen Formation. Our analysis revealed mixed provenance with multiple source terranes within the Tasmanides. The bulk of sediment was derived from the Thomson Orogen, with a lesser contribution from the New England Orogen. We found no evidence for sediment derived from the Lachlan Orogen, despite a distinct northward palaeocurrent component. Syn-depositional volcanic material within the interval corroborates the notion of continued arc magmatism along the eastern Gondwana margin, which contributed sediment to the GAS throughout the Early Jurassic. Radiometric ages place the Precipice-Evergreen succession in the Sinemurian-Toarcian which falls within the broader Hettangian-Aalenian age range suggested by recent palynostratigraphic data and suggest diachronous deposition across the basin. Despite pronounced variations in formation thickness, the Precipice Sandstone shows relatively uniform provenance across the basin, showing little evidence for multiple depocenters.

On the Statherian–Calymmian palaeogeography of northwestern Laurentia

The c. 1.75 to 1.27 Ga Hornby Bay intracontinental basin, exposed in northwestern Canada, NE of Great Bear Lake, includes the Big Bear, Mountain Lake and Dismal Lakes groups. The Big Bear group comprises mainly immature clastic rocks deposited by high-energy rivers in restricted fault-bounded basins formed during the late-stage assembly of supercontinent Nuna. Detrital zircon analysis of the Big Bear group suggests provenance from a combination of local sources including recycling of sedimentary rocks, which were originally derived from sources further east, such as the Thelon orogen. The overlying Mountain Lake group was deposited by westerly flowing rivers over a much broader region, with less evidence for syndepositional faulting, suggesting thermal subsidence. It displays provenance via recycling of strata from the proximal Coronation Supergroup and the more distal and correlative Goulburn Supergroup of Kilohigok Basin. Following tectonic uplift and erosion, basal clastic rocks of the Dismal Lakes Group were deposited in fluvial and then shallow-marine to paralic environments. Detrital zircon from these strata displays prominent late Archean peaks demonstrating provenance from adjacent rocks of the Slave craton and recycling of the Mountain Lake group. Detrital zircon geochronology of sandstones from the Hornby Bay Basin supports stratigraphic correlation with the Wernecke Supergroup in the Wernecke Mountains and the Muskwa assemblage, located further southward along the ancient western margin of Laurentia. Our data, along with Nd and C isotopes from corresponding shale and carbonate units, provide robust evidence for a palaeogeographical model whereby these successions represent the terrestrial and marine components of a west-facing, passive-margin clastic wedge, considered the westward extension of an Amazon-scale, braided fluvial system that originated in the foreland of the Trans-Hudson orogen, to the east. Elements of this system have been identified from inliers in northeastern Australia, which was attached to northwestern Laurentia prior to the break-up of supercontinent Nuna. Supplementary material: U–Pb and Hf results, and Hf isotopic compositions of reference zircons are available at https://doi.org/10.6084/m9.figshare.c.5980940

Back-arc basin closure at the East Asian margin during Permo-Triassic boundary: Evidence from geochemistry and U-Pb zircon data of sedimentary breccia from Maizuru Terrane, Southwest Japan

The paleo Maizuru back-arc basin, which was located at the East Asian continental margin opened in Early Permian times and closed during the Permo-Triassic (P-T) boundary. The back-arc basin sediments are exposed in the present-day Maizuru Terrane located in Southwest Japan and hold the key to understand the tectonic evolution of both this back-arc basin and that of the East Asian continental margin. The opening of the Maizuru back-arc basin was accompanied by the deposition of a massive black mudstone-dominated formation, presently recognized as the Maizuru Group. The closure of the back-arc basin which was accompanied by the deposition of coarse-grained materials such as the Tonoshiki breccia made up of differently-sized extremely angular clasts implies that the P-T boundary was a tectonically active period in the Maizuru Terrane. Petrographical and geochemical studies revealed that Tonoshiki breccia can be divided into two main types, a first type mainly made up of mafic to intermediate rock clast fragments (Type I) and a second type mostly consisting of felsic rock clast materials (Type II). Both types commonly contain massive black mudstone clasts that were derived from the underlying Maizuru Group. The U-Pb detrital zircon geochronology of those two types of breccia suggests that they were deposited during two phases of the tectonic activity-induced debris flow that occurred at ca. 259 Ma and ca. 251 Ma for the first and second type, respectively. Type I was sourced from the Southern zone, whereas Type II was sourced mostly from the Northern zone of the Maizuru Terrane. This switch of provenance testifies to the intense tectonic activity that reigned during the P-T boundary. The closure of the Maizuru back-arc basin was induced by the subduction of the basement crust of the basin under the East-Asian continent during the P-T boundary.

Provenance of the Late Cretaceous Pab Formation, Sulaiman fold‐thrust belt, Pakistan: Insight from the detrital zircon U–Pb geochronology and sandstone petrography

This study provides an insight to the provenance of the Late Cretaceous Pab Formation exposed in the Sulaiman fold‐thrust belt, Pakistan. The methodology adopted consisted of sandstone petrography and U–Pb detrital zircon geochronology. The sandstone petrography indicates craton interior and recycled orogenic provenances that points to an Indian provenance. The observed basaltic lithics were possibly derived from Rajmahal traps instead of Deccan traps, supported by younger detrital age. The detrital zircon ages exhibit a resemblance to the central and southern Indian provenances, while some detritus also matches the age spectrum of Tethyan Himalayas (~400–800 Ma). Combining sandstone petrography and U–Pb geochronology results, it is suggested that in the Late Cretaceous time, the sediments were mainly fed by the southern and central sources of the Indian Craton. This provenace is possible, as during the Cretaceous time, thermal doming of Indian Plate in the southern part occurred when it was passing over a mantle hotspot. This movement over the hotspot uplifted the southeastern region and increased sediment supply from southern and central Indian provenances and deposited along the western margin as the Pab Formation.

Constraints on Sandstone-Type Uranium Deposits by the Tectonic Uplift and Denudation Process in the Eastern Junggar Basin, Northwest China: Evidence from Apatite Fission Track and Detrital Zircon U-Pb Ages

The uplift and denudation history of the orogenic belt and the basin–mountain coupling process have directly or indirectly affected the generation, scale, and preservation of sandstone-type uranium deposits in the eastern Junggar Basin by controlling the uranium source, lithology, facies, hydrogeology, post-generation modification, and other mineralization conditions. Taking the eastern Junggar Basin as the research area, this study proposes the constraints on sandstone-type uranium deposits by the tectonic uplift and denudation history of the orogenic belt in the basin using the apatite fission track (AFT), detrital zircon geochronology, and other methods. The results of the AFT age test and thermal path simulation indicate that the orogenic belt in the eastern Junggar Basin underwent four rapid uplifts; (from approximately 300 Ma to approximately 250 Ma, from approximately 130 Ma to approximately 90 Ma, from approximately 65 Ma to approximately 30 Ma, and from approximately 20 Ma to 0 Ma). Moreover, the timing of the uplift has a spatial trend of gradually becoming younger from south to north. The detrital zircon U-Pb age test showed that the sediment source area of the basin is mainly distributed in three age intervals, i.e., 460–390, 360–270, and 190–170 Ma. The comprehensive evaluation of the clastic sediment composition, stratigraphic distribution of the erosion source area, and thermal history showed that a large amount of exposed Carboniferous–Permian granites in the Qinglidi and Karameri Mountain erosion source areas contributed dominant sediment material and uranium sources for the Triassic and Middle and Lower Jurassic strata in the basin. The Ordovician–Early Devonian granites only provided sediment sources for the Upper Triassic and Lower Jurassic strata in the basin. Altay Mountain contributed some sediment sources for the Middle and Upper Jurassic strata after the magmatic activity and rapid uplift occurred in the Middle Jurassic. Based on the comprehensive analysis of the influence of the tectonic uplift process of the orogenic belt and the transformation of material source areas on uranium mineralization, the granites in the erosion source areas are proposed to contribute both external and internal uranium sources for uranium mineralization. Uranium mineralization mainly occurred in the tectonic retreat period after the rapid uplifts of the Cretaceous and Paleogene. It was terminated by the intensive uplift-induced stratigraphic deformation in the Miocene.

A Classopollis “spike” in the Rugubivesiculites Zone of the Kayan Sandstone, western Sarawak, Borneo, suggests a Danian age for these deposits

The age of the Rugubivesiculites Zone of the lower Kayan Sandstone in western Sarawak, Borneo, is disputed. Detrital zircon (U–Pb) geochronology suggests a maximum depositional age (MDA) of ca. 72–71 Ma; however, palynology suggests a Paleocene age. The overlying Proxapertites Zone, for example, encompasses both the upper part of the Kayan Sandstone (non-marine) and the un-deformed Engkilili Formation (marine), which is known to post-date deformation of the Lubok Antu Mèlange ca. 60 Ma. Among the palynological concepts that led Muller to originally assign a Cretaceous age to the Rugubivesiculates Zone was the abundance of well-preserved, non-reworked Classopollis pollen, which was perceived at the time to have gone extinct prior to the end of the Cretaceous. Contemporary palynological perspectives recognize a “spike” or abundance anomaly in Classopollis pollen in Danian deposits in both the Northern and Southern Hemispheres. Therefore, Muller's original dataset are statistically reevaluated for evidence of a Classopollis spike. This study finds strong evidence for an increase in Classopollis pollen above background levels within the lower part of the Kayan Sandstone (p < .001–0.002), representing a highly significant, stratigraphically sharp increase in the proportion of these pollen (p < .00001), consistent with the interpretation that these deposits are Danian in age.

Depositional and diagenetic processes in volcanic matrix‐rich sandstones from the Shanxi and Shihezi formations, Ordos Basin, China: Implication for volcano‐sedimentary systems

AbstractVolcanic eruptions can provide large amounts of sedimentary materials and expose fluvial valleys or lakes to catastrophic hyperpycnal flood events, but this process has not been documented in detail. The Ordos Basin Permian fluvio‐deltaic system reveals evidence for abundant volcanism linked to the tectonic evolution of orogenic belt around the basin and provides a ‘natural laboratory’ for investigating hyperpycnal flows associated with volcanic activity. This study analysed volcanic matrix‐rich sandstone (VMS) samples for petrology, mineralogy and geochemistry in order to address current and uncertain volcanogenic material provenance explanations and the lack of systematic investigations into the depositional and diagenetic processes of volcanic related sediments in the southwestern basin. By combining tectonic background surveys, detrital zircon geochronology and spatial distribution of volcanogenic materials, it was found that volcanogenic materials were not derived from the Yinshan‐Yanshan Orogenic Belt (YYOB) as previously thought, but instead evidence a southwestern origin from the North Qinling Orogenic Belt (NQOB). Volcanogenic materials retained in the provenance area during frequent volcanic eruptions were transported to the basin via fluvial systems shortly after the eruption. The associated sediments meet the criterion for hyperpycnites based on lithofacies associations, suggesting the occurrence of hyperpycnal flows during the deposition of VMS. During the subsequent burial stage, the VMS became three distinct types defined by their volcanic matrix content and have similar paragenetic sequences but different diagenetic intensities. The differing content of authigenic minerals in the three types was closely related to the sandstone pore structure characteristics and the evolution of volcanic‐matrix alteration materials. This article proposes a possible explanation for the previously unidentified tectonothermal events in the NQOB during the Permian, validating and reinforcing the theoretical work of hyperpycnal flow. This contribution provides new insights and understanding of the depositional and diagenetic processes of lacustrine basins with similar tectonic settings.

New age constraints support a K/Pg boundary interval on Vega Island, Antarctica: Implications for latest Cretaceous vertebrates and paleoenvironments

AbstractA second K/Pg boundary interval in the northern sector of the Antarctic Peninsula on Vega Island has been proposed, yet current temporal resolution of these strata prohibits direct testing of this hypothesis. To not only test for the existence of a K/Pg boundary on Vega Island but also provide increased age resolution for the associated vertebrate fauna (e.g., marine reptiles, non-avian dinosaurs, and avian dinosaurs), the Vega Island succession was intensively re-sampled. Stratigraphic investigation of the Cape Lamb Member of the Snow Hill Island Formation, and in particular, the overlying Sandwich Bluff Member of the López de Bertodano Formation, was conducted using biostratigraphy, strontium isotope stratigraphy, magnetostratigraphy, and detrital zircon geochronology. These data indicate a Late Campanian–early Maastrichtian age for the Cape Lamb Member and present three possible correlations to the global polarity time scale (GPTS) for the overlying Sandwich Bluff Member. The most plausible correlation, which is consistent with biostratigraphy, detrital zircon geochronology, sequence stratigraphy, and all but one of the Sr-isotope ages, correlates the base of the section to C31N and the top of the section with C29N, which indicates that the K/Pg boundary passes through the top of the unit. A second, less plausible option conflicts with the biostratigraphy and depends on a series of poorly defined magnetic reversals in the upper part of the stratigraphy that also correlates the section between C31N and C29R and again indicates an inclusive K/Pg boundary interval. The least likely correlation, which depends on favoring only a single Srisotope age at the top of the section over biostratigraphy, correlates the section between C31N and C30N and is inconsistent with an included K/Pg boundary interval. Although our preferred correlation is well supported, we failed to identify an Ir-anomaly, spherules/impact ejecta, or other direct evidence typically used to define the precise position of a K/Pg boundary on Vega Island. This study does, however, confirm that Vegavis, from the base of the Sandwich Bluff Member, is the oldest (69.2–68.4 Ma) phylogenetically placed representative of the avian crown clade, and that marine vertebrates and non-avian dinosaurs persisted in Antarctica up to the terminal Cretaceous.

Detrital zircon geochronology of the Permian Lower Shihezi Formation, northern Ordos Basin, China: time constraints for closing of the Palaeo-Asian Ocean

AbstractTemporal constraints on the closure of the eastern segment of the Palaeo-Asian Ocean along the northern margin of the North China Craton (NCC) remain unclear. As a part of the NCC, the sedimentation and tectonic evolution of the Late Palaeozoic Ordos Basin were closely related to the opening and closing of the Palaeo-Asian Ocean. We use petrology, quantitative mineralogical analysis, U–Pb geochronology and trace element signatures of detrital zircons of the Lower Shihezi Formation from two sections in the eastern north Ordos Basin and two sections in the western north Ordos Basin to reconstruct the sedimentary provenance and tectonic background of the northern Ordos Basin. The results show that the sediments of the western sections were mainly derived from the Yinshan orogenic belt and Alxa block, and that those in the eastern sections only came from the Yinshan orogenic belt. The trace element ratios in detrital zircons from the Late Palaeozoic sandstones indicate that the source areas were mainly subduction-related continental arcs, closely related to the continued subduction of the Palaeo-Asian Ocean in the Late Palaeozoic. Since the main Late Palaeozoic magmatic periods vary on the east and west sides of the northern margin of the Ordos Basin, two main collisions related to Palaeo-Asian Ocean closure are recorded. The collision on the west side occurred significantly earlier than that in the east. This study implies that the Palaeo-Asian Ocean began to subduct beneath the NCC in the Carboniferous and gradually closed from west to east thereafter.

Detrital zircon geochronology of middle Paleozoic to lower Mesozoic strata from Hainan: implications for sedimentary provenance and tectonic evolution of Hainan

Detrital zircon geochronology of middle Paleozoic to lower Mesozoic strata from Hainan: implications for sedimentary provenance and tectonic evolution of Hainan

Tracing the continental margins of the Southern Ribeira belt, Brazil: Provenance and connections of post-Rodinia fragments

The reconstruction of ancient continental margins encompassed in continent–continent collision is a complex task. The continental blocks generally record a multiphase evolution with interaction of tectonic settings, plate polarities, basins and their depositional architecture.The Ribeira belt (Southeast-Southern Brazil) resulted from the juxtaposition of several crustal blocks during the Brasiliano/Pan-African tectonic events (800–490 Ma) leading to the amalgamation of Western Gondwana. In this context, a series of pre-Brasiliano blocks underwent variable rates of tectonic reworking, including fragments derived from Rodinia.Some of the metasedimentary strata of the Southern Ribeira belt are representative of Late Meso- to Neoproterozoic basins which bordered these pre-Brasiliano continental fragments, such as the Capiru Group.The Capiru Group (Late Meso- to Neoproterozoic) is a low-grade metasedimentary unit that crops out on the Curitiba microplate and records passive to active continental margin stages.In this work we show new provenance data (U-Pb geochronology of detrital zircon) of the Capiru Group and compare them to the other chrono-correlative continental margin units of the region (Lajeado and lower Itaiacoca groups).Through the evolution of Capiru, Lajeado, and Itaiacoca groups we show that the post-Rodinia continental margins of the Southern Ribeira belt show similar Paleoproterozoic contributions (2,000 – 2,185 Ma) and slightly different Mesoproterozoic populations, suggesting distinct paleogeographic contexts: the Capiru Group was deposited on the Northern margin of the Curitiba-Angola block, with Mesoproterozoic “exotic” contribution (1,508 – 1,100 Ma). On the other hand, the Lajeado and Itaiacoca groups were deposited on the East-Southeastern margin of the Paranapanema continental block.

U–Pb detrital zircon geochronology and source provenance in the Moroccan Meseta (Variscan belt): A perspective from the Rehamna massif

Metasandstones from early Cambrian to early Carboniferous stratigraphic successions were sampled in the Rehamna massif of the Western Meseta in Morocco. The early Cambrian sample shows a single Paleoproterozoic population at ca. 2 Ga suggesting a local basement source. The Ordovician sample is largely dominated by a Cryogenian-Ediacaran population and minor Paleoproterozoic peaks. The Devonian sample reveals age populations similar to North-West African Cambrian to Devonian age spectra indicating that the southern-derived West Gondwana source essentially pertained up to the Devonian. The two early Carboniferous samples show more heterogeneous zircon age spectra with a marked Ediacaran peak accompanied by Paleoproterozoic and Mesoproterozoic sub-peaks indicating important re-organization of the drainage systems. One sample also shows presence of Upper Devonian to early Carboniferous zircon grains, which suggests local magmatic sources associated to the formation of intracontinental extensional basins. The comparison of detrital zircon spectra with paleogeographic reconstructions indicate that the early Carboniferous change in detrital zircon sources can be interpreted in the framework of the opening of the Paleotethys ocean with coeval erosion of orogenic topographies linked to the emplacement of a Mid-Variscan Allochthon, and/or collision of an Avalonian indenter to the north.

Mesoarchean diamonds formed in thickened lithosphere, caused by slab-stacking

When and how Earth's ancient crust – the cratons – became underpinned by cool, thick lithospheric mantle roots capable of hosting diamonds are among the most controversial aspects of Archean geology. Alluvial diamonds in cratonic sedimentary cover rocks, whose minimum age is determined by detrital-zircon geochronology, provide a unique perspective on this topic. A new discovery of a diamond-bearing quartz-pebble conglomerate from the northern Slave craton, Canada contains detrital zircon with a restricted U-Pb age distribution that has a dominant peak at ∼2.94 Ga and depositional age of ∼2.83 Ga. Pressure-temperature constraints derived from an olivine-diamond host pair lie on a conductive Mesoarchean geotherm of ∼36–38 mW/m2, comparable to the coolest modern lithospheric geotherms. This result is at odds with a hotter geothermal gradient related to nearby Mesoarchean komatiites. We propose a model whereby early building blocks for cratons were small but with deep cool roots that formed by slab-stacking, and were subsequently juxtaposed with regions of thinner, hotter lithosphere. This heterogeneous initial architecture later amalgamated and thickened through lateral accretion forming the more uniformly thick cratonic lithosphere observed today. Thermal modelling indicates that stacking/thickening of cool initial lithosphere into a lithospheric keel thick enough to stabilise diamonds is the most likely way of generating the observed geotherm by Mesoarchean times.

Palaeogeography and provenance transition of Precambrian–Cambrian unconformity at the southern margin of the North China Craton

The Precambrian–Cambrian unconformity boundary is ubiquitous and globally documented, which is of great significance to studying major global scientific issues such as environmental transition, positions of the supercontinent, Cambrian explosion, and global geochemical cycle. However, few studies have been on the palaeogeographic features and provenance changes of the Precambrian–Cambrian unconformity boundary at the southern margin of North China Craton (NCC). This uncertainty hampers us from further understanding the early climate change and plate evolutionary history of the NCC. To improve the knowledge of the palaeogeographic features and provenance changes of the Precambrian–Cambrian unconformity boundary on the southern margin of the NCC, the Luoquan and Xinji formations at the southern margin of the NCC were selected as the research object integrated with sedimentary petrology, trace elements, and detrital zircon geochronology investigation. The results suggest a depositional gap between the Luoquan and Xinji formations. The former is glacial to deglaciation deposits, while the latter is shallow to coastal sediments. Compared with the sedimentary stratum of the South China Craton, the Luoquan Formation lacks at least one transgression and regression cycle. The Xinji Formation has detrital zircon age peaks of 1200, 1100, and 950 Ma, unavailable in the Luoquan Formation. The provenance areas of the Luoquan and Xinji formations have changed, indicating that the provenances of the Luoquan Formation belong to the NCC and part of the provenances of the Xinji Formation belong to the North Qinling Terrane (NQT). The trace element data indicate that the tectonic setting of the Luoquan and Xinji formations has changed from a continental island arc to a passive continental margin. It is suggested that the NCC be involved in the evolution of Rodinia supercontinent, which leads to the change of the provenance and tectonic setting. This research provides an explanation for the Precambrian–Cambrian tectonic history, basin development, stratigraphic correlation, and palaeogeographic reconstruction of NCC.

Eogene to Neogene north‐eastward expansion of the arcuate tectonic belt in north‐east Tibetan Plateau: Constraints from detrital zircon geochronology and heavy minerals

The north‐eastward extrusion of the Tibetan Plateau has always been under debate. The arcuate tectonic belt is located at the north‐east margin of the Tibetan Plateau and bears crucial information about the tectonic and geomorphic evolution of north‐east Tibetan Plateau. Combined with sedimentary sequence, detrital zircon U–Pb geochronology, and heavy mineral combinations, significant provenance transformation can be determined both in the south‐west and north‐east of the arcuate tectonic belt during the Eocene to Miocene. The far‐field effect of north‐eastward extrusion of the Tibetan Plateau first arrived at the south‐west of the arcuate tectonic belt during the Miocene and resulted in the angular unconformity between the Eocene Qingshuiying period and Miocene Zhangenbao Formation. Then the regional exhumation spread from south‐west to north‐east across the arcuate tectonic belt, and sedimentary hiatus developed between the Miocene Zhangenbao period and Pliocene Ganhegou period. Therefore, tectonic uplift and mountain building of the arcuate tectonic belt expanded north‐eastward during the Eogene to Neogene. This research shed new insights on the north‐eastward extrusion of the Tibetan Plateau from the coupling relationship between basin and range.

Detrital zircon provenance and transport pathways of Pleistocene-Holocene eolian sediment in the Pampean Plains, Argentina

AbstractThe Pampas of Argentina contain a broad distribution of Pleistocene to Holocene loessic sediments and eolian dune deposits. Models describing the sediment provenance of this eolian system have, at times, conflicted. We address the provenance of these deposits through U-Pb detrital-zircon geochronology. Our results indicate broad similarity in age distributions between samples, with a dominant Permian-Triassic mode, and widespread but lesser Cenozoic, Devonian-Mississippian, Ediacaran-Cambrian, and Mesoproterozoic modes. These data are inconsistent with a large contribution of detritus from Patagonia as previously suggested. These data are consistent with very limited contribution of first cycle volcanogenic zircon to the Pampean eolian system, but abundances of older Neogene zircon indicate proto-sources in the Andes. The ríos Desaguadero, Colorado, and Negro contain populations that were likely within the dust production pathways of most of the loess, paleosol, and eolian dune deposits, but the derivation of the zircon ages in these sediments cannot be explained solely by these river systems. One statistical outlier, a loess sample from the Atlantic coast of the Pampa region, indicates quantitative similarity to the age spectra from the ríos Colorado and Negro, consistent with derivation from these subparallel rivers systems during subaerial exposure of the continental shelf under high global ice-volume. Another statistical outlier, a paleosol sample from the Río Paraná delta region, has zircon ages more closely associated with sediments in the Paraná region than in rivers south of the Pampa region. Collectively, these data point to the complexity of the Pampean eolian system and substantial spatial-temporal variation in this Pleistocene–Holocene eolian system.

Detrital zircon geochronology and stratigraphy of the Proterozoic strata in the Olongbuluke terrane of Northwest China: Implications for the Great Unconformity

The Great Unconformity that separates the early Cambrian sandstones from the Proterozoic metamorphosed sedimentary rocks has been recognized in many blocks on Earth. However, whether it represents a globally synchronous event or a composite of a series of diachronous events, and its formation mechanism remain largely unknown. In this study, we carry out detrital zircon U-Pb analyses for seven samples collected from the Paleoproterozoic Quanji Group and the overlying Neoproterozoic strata in the Olongbuluke terrane (OLT) of Northwest China. The results show that apart from age populations of ∼ 1.8–2.0 Ga and ∼ 2.2–2.5 Ga for all samples, additional ∼ 1.55–1.65 Ga age population occurs in sample from the Zhoujieshan Formation, and more scattered age populations ranging from ∼ 0.75 to ∼ 1.7 Ga are present in samples from the Heitupo and Hongtiegou formations. The ∼ 1.8–2.0 Ga and ∼ 2.2–2.5 Ga zircons correlate well with the magmatic and metamorphic events in the OLT basement, indicating their local provenances, while other zircons were possibly derived from the North China craton (NCC) or other adjacent blocks. Combined with published paleontological, stratigraphic, and geochronological data, the present study supports previous inference that the OLT had a close paleogeographic affinity to the NCC during late Paleoproterozoic to Neoproterozoic. New zircon U-Pb ages indicate that the Heitupo Formation was deposited later than ∼ 750 Ma, and the underlying Hongzaoshan Formation was deposited at ∼ 1.66 Ga, implying a huge break between them. Whereas the duration of the sedimentary break between the Heitupo Formation and the overlying Hongtiegou Formation is uncertain, biostratigraphic data suggest that a break of ∼ 30 Myr may exist between the late Ediacaran Zhoujieshan Formation and the overlying early Cambrian Xiaogaolu Group. The occurrences of these multiple unconformities in OLT are comparable to those in NCC, indicating that the Great Unconformity is represented by a series of lengthy denudations during the Proterozoic-early Cambrian in both the OLT and NCC, which may result from multiple tectonic activities in these two blocks.

The Segmented Zambezi Sedimentary System from Source to Sink: 2. Geochemistry, Clay Minerals, and Detrital Geochronology

Elemental geochemistry, Nd isotopes, clay minerals, and U-Pb zircon ages integrated by petrographic and heavy-mineral data offer a multiproxy panorama of mud and sand composition across the Zambezi sediment-routing system. Detrital zircon geochronology highlights the four major episodes of crustal growth in southern Africa: Irumide ages predominate over Pan-African, Eburnean, and Neoarchean ages. Smectite, dominant in mud generated from Karoo basalts or in the equatorial/winter-dry climate of the Mozambican lowlands, prevails over illite and kaolinite. Elemental geochemistry reflects quartz addition by recycling (Uppermost Zambezi), supply from Karoo basalts (Upper Zambezi), and first-cycle provenance from Precambrian basements (Lower Zambezi). Mildly negative for sediments derived from mafic granulites, gabbros, and basalts, εNd values are most negative for sand derived from cratonic gneisses. Intrasample variability among cohesive mud, very coarse silt, and sand is principally caused by the concentration of Nd-rich monazite in the fine tail of the size distribution. The settling-equivalence effect also explains deviations from the theoretical relationship between εNd and TNd,DM model ages, suggesting that monazite carries a more negative εNd signal than less dense and less durable heavy minerals. Elemental geochemistry and Nd isotopes reveal that the Mazowe-Luenha river system contributes most of the sediment reaching the Zambezi delta today, with minor supply from the Shire River. Sediment yields and erosion rates are much lower on the low-relief Kalahari Plateau than in rugged Precambrian terranes. On the plateau, mineralogical and geochemical indices testify to extensive breakdown of feldspars and garnet unjustified by the present dry climate. Detrital kaolinite is recycled by incision of Cretaceous–Cenozoic paleosols even in the wetter lower catchment, where inefficient hydrolysis is testified to by abundant fresh feldspars and undepleted Ca and Na. Mud geochemistry and surficial corrosion of ferromagnesian minerals indicate that, at present, weathering increases only slightly downstream the Zambezi River.

Evolution of the Continental Crust in the Northern Tibetan Plateau: Constraints From Geochronology and Hf Isotopes of Detrital Zircons

To investigate the evolution of the continental crust in the northern Tibetan Plateau, detrital zircon U–Pb geochronology and Hf isotopes analysis were performed on two fluvial sand samples from North Qaidam (the Yuka and Shaliu rivers). A total of 443 detrital zircon U–Pb ages and 244 Hf isotopic results were obtained and reveal that the South Qilian, North Qaidam, and East Kunlun terranes show affinity to the western Yangtze Block. Age distributions of detrital zircons from the Yuka River cluster mainly in two age intervals of 1,000–700 and 480–400 Ma. The corresponding εHf(t) values are mostly negative, with depleted two-stage Hf model ages (TDM2) of 2.1–1.6 Ga. In contrast, age data for the Shaliu River fall in the ranges of 1,000–700, 460–380, and 260–200 Ma, with TDM2 ages of 2.0–1.6 and 1.6–1.2 Ga. In addition, zircons with Neoproterozoic ages from both river samples possess common Paleoproterozoic TDM2 ages (2.0–1.6 Ga, with a peak of 1.8–1.7 Ga), indicating that the South Qilian, North Qaidam and East Kunlun terranes were probably part of the same Neoproterozoic continent. The East Kunlun and North Qaidam terranes are inferred to include Mesoproterozoic continental crust (1.6–1.0 Ga), suggesting differences in crustal evolution between the East Kunlun–North Qaidam and Qilian terranes. Phanerozoic magmatism in these three terranes was sourced mainly from the recycling of ancient continental crust with minor contributions from the juvenile crust.