Zircon Age Distributions Research Articles

Oldest Basement (ca. 462 Ma) in Indonesian Borneo and its Implication for Early Paleozoic Tectonic Evolution of SE Asia

AbstractThe lack of preserved basement results in uncertain placements of many terranes in Southeast Asia. Here, we flag the first evidence of the oldest basement in Indonesian Borneo, which can help locate terranes in Borneo on the northern margin of Gondwana in the early Paleozoic and explain the regional tectonic setting of the island. Two schist samples from the Embuoi Complex in the Semitau Block, Northwest Kalimantan yielded zircon U‐Pb dates of 453.3 ± 1.9 Ma and 462.4 ± 2.6 Ma, respectively, representing the formation time of the protolith. Petrographic, internal structural and high Th/U ratios of zircons indicate that the protolith of schists is of magmatic origin. The zircons have εHf(t) values of –4.1 to +1.1 and Hf model ages of 1.37–1.69 Ga, indicating they were derived from a mixed source of juvenile crust with old components. By comparison of zircon age distribution, two‐stage Hf model ages and εHf(t) variations of the early Paleozoic igneous rocks from Semitau with those of South China, Tengchong–Baoshan, and Indochina, the Semitau Block was most likely a part of or placed next to the Indochina Block of northern Gondwana during the early Paleozoic. Such a similar tectono‐magmatic pattern on northern Gondwana formed a prolonged early Paleozoic arc‐related belt associated with subduction of the Proto‐Tethyan Ocean.

The Assabet barcode: Mesoproterozoic detrital zircons in Neoproterozoic strata from Mauritania, West Africa

Detrital zircon data are reported from Mesoproterozoic to Ordovician strata from two tectonic domains in Mauritania: 14 samples from the Taoudeni Basin of the West African Craton and 15 samples from the Mauritanide orogen. Taoudeni Basin samples show four sequential, distinctive detrital zircon age distributions, which we refer to as “barcodes”. From old to young these are the Char, Assabet, Téniagouri, and Oujeft barcodes, each named for a constituent stratigraphic unit. Zircon age maxima are as follows, with the dominant ones in italics. The Char barcode, from Mesoproterozoic (<i>ca.</i> 1100 Ma) strata including the Char Group, yielded zircon age maxima at 2941, 2871, 2703, <i>2447</i>, <i>2076</i>, and <i>2041</i> Ma, all potentially traceable to sources in the West African Craton. The Assabet barcode is from strata, including the eponymous Assabet el Hassiane Group, that were deposited between <i>ca</i>. 883 and <i>ca.</i> 570 Ma; it has age maxima at 2137, 2053, 1769, 1510, <i>1212</i>, 1021, and 936 Ma and a pronounced minimum during Geon 16 (1699–1600 Ma). The Assabet9s Mesoproterozoic to early Neoproterozoic zircons cannot have come from the West African Craton or any of its surrounding orogens. The Téniagouri barcode, which takes its name from the Téniagouri Group, was deposited at <i>ca.</i> 569 Ma; it has dominant maxima at 1983, 1872, <i>1522</i>, <i>1215</i>, 1109, 988, and 601 Ma and resembles the Assabet barcode but with the addition of the youngest population. The Oujeft barcode, named for the Oujeft Group, is from strata deposited between 541 or slightly earlier and 444 Ma or younger, has age maxima at 2124, 2053, 1197, <i>624</i> and <i>579</i> Ma. The Téniagouri and Oujeft barcodes record input from Pan-African orogens. In the Mauritanide orogen, most of the metasedimentary rock units that were sampled yielded detrital zircon age spectra that match one of the Taoudeni Basin barcodes. These results imply new depositional age constraints based on barcode correlation and suggest affinities between Mauritanide strata and the West African Craton. Detrital zircon age distributions that broadly resemble the Assabet barcode occur in the Neoproterozoic of Morocco, Ghana, Greece, Russia, Brazil, and, in the Appalachian orogen of Canada and the United States, Avalonia and Ganderia. The recent Rodinia reconstruction of Evans (2021) restores these far-flung localities to a more compact area, with Avalonia, Ganderia, and other peri-Gondwanan terranes occupying an oblong area between Amazonia, Laurentia, Baltica, and West Africa. Our preferred explanation is that most of these places received detritus via the same continent-scale fluvial system as the West African craton. Among the craton9s nearest Rodinia neighbors in the Evans (2021) reconstruction for 900 Ma, Amazonia has known igneous rocks corresponding to all of the major Assabet age populations, and also a lull, though not a complete magmatic gap, during Geon 16. This is consistent with overall north-directed paleocurrents in the Assabet El Hassiane Group and its correlatives on the West African Craton.

Stratigraphy and Zircon Provenance of a Late Paleoproterozoic Terrestrial Sequence underlying the Xiong'er Volcanics in the Southern North China Craton

AbstractThe late Paleoproterozoic Dagushi Formation comprises a fluvial‐lacustrine succession and represents the initial fill of the Xiong'er Basin in the southern North China Craton. Employing integrated outcrop surveys and detrital zircon U‐Pb‐Hf dating, this study examines the provenance and depositional setting of the Dagushi Formation. Five major depositional facies, including braided channel, distributary channel, subaqueous stream/mouth bar, pro‐delta and shallow lake, were identified, based on lithofacies and associations. They were interpreted as representing a braided river delta‐lacustrine system. The ages of the last metamorphic event of the basement, covering volcanics and the youngest zircon together constrain a depositional age of ca. 1.79 Ga for the Dagushi Formation. Zircon age distributions reveal a provenance change from ca. 2.7–2.5 Ga rocks in the lower part, to ca. 2.3–1.9 Ga sources in the middle‐upper part of the Dagushi Formation. Considering the vertical sedimentology, this provenance change could be induced by the rising water‐level caused by a tectonic subsidence. The ca. 2.7–2.5 Ga zircons are suggested to be locally sourced from the late Neoarchean–Paleoproterozoic metamorphic basement. The northeast Zhongtiao Mts area (current co‐ordinates) is supposed to have appeared as a paleo‐uplift and served as a source area for the Paleoproterozoic grains. The Dagushi Formation records an early ‘underfilled’ stage of the Xiong'er Rift.

Peculiarities of the present structure of the Bug granulite complex developed within the Middle Bug area and its partitioning into series and suits

The Gaivoron-Zavalie site and the Golovanevsk suture zone (GSZ) of the Bug mining region (BMR) in the Middle Bug region have been a «testing ground» for studying the structure and stratigraphy of the Early Precambrian complexes of the USh for many years. In the article, using their example, the Early Precambrian part of the Correlation Chronostratigraphic Scheme of the USh (CCS USh) and the issues arising around its discussion and the need for changes have been considered here. The main problem is to find out series, formations and rock strata in the CCS of USh, which is quite debatable. It has been shown that some rock strata (leucogranulite formation and Zelenolevadov rock strata, a significant part of the Koshar-Alexandrov suite) refer to the formation-genetic series of quartz-feldspar metasomatites, in particular, to the structural-formation association of metasomatites of zones of regional faults and they are not stratigenic. According to isotope-geochronological data, the bereznin rock strata is not Archean and therefore does not belong to the Dniester-Bug series. The layering, banding and gneissovity of the enderbite-gneiss complex of the Gaivoron-Zavalie section are associated with its intersection of a dense network of fault zones and therefore this area refers to the area of development of highly dispersed metamorphic tectonites, rather than the stratigene rock strata, which some researchers try to call the «Salkovska Formation». The association of the iron-ore strata of the Bug mining region into the Pavlov rock strata of the Archean Dniester-Bug series is not correct, because the present overlapped section of such rock strata has been studied in the Moldovian structure in the GSZ structure, and it refers to the Bug series. However, the genesis of iron-ore rocks is disputable, so the authors consider it undesirable to include them in the CCS of the Ukrainian shield. The genesis of graphitic gneisses and quartzites of the Khaschevato-Zavaliev suite is also disputable, which leads to the conclusion that it should be excluded from the CCS of the Ukrainian shield. With the exclusion of the Zelenolevadov, Bereznin, and Pavlov strata from the Dniester-Bug Series, only the strata of hyperstene and dipyroxene plagiogneisses and crystalline schists, called as Tyvrovka, remains in it. Its stratotype becomes the stratotype of the entire series, so the stratum “Tyvrov rock strata” can also be removed from the series. The authors conclude that the division of the Bug granulite complex into suites and rock strata is impractible. When considering the division of the Bug granulite complex into series, it is shown that the concept “series” as set forth in the Stratigraphic Code of Ukraine, although it does not take into account the features of formation of the Archean series, however does not contradict them. Therefore, separation of the Dniester-Bug and Bug series of different composition and age is quite natural. Contrary to the opinions of some researchers on the continuous process of accumulation of sedimentary-volcanogenic rocks of the Middle Bug area, it is shown that the anomalies in the age distribution of clastogenic zircons from the rocks of the Gaivoron-Zavalie and GSZ correspond to the global one and reflect a worldwide process of crustal formation, in which relatively quiet tectonic regimes alternated with periods of tectonic activation. During such periods, both magmatic and metasomatic processes and sedimentary-volcanogenic processes were activated. Materials of the study of the hafnium isotope composition from the zircons of the Dniester-Bug and Bug series rocks indicate a possible difference in the age of their formation of 600—700 Ma. The questions of the origin and rearrangement of the Bug granulite complex developed in the study area are also considered here.

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.

U–Pb age constraints on the protolith, cooling and exhumation of a Variscan middle crust migmatite complex from the Central Iberian Zone: insights into the Variscan metamorphic evolution and Ediacaran palaeogeographic implications

The Figueira de Castelo Rodrigo–Lumbrales Anatectic Complex (FCR-LAC) located in the Central Iberian Zone of the European Variscan Belt is delimited by two shear zones, which have been interpreted as constraining its exhumation. New U–Pb zircon and apatite ages for the migmatites allowed us to obtain a peak metamorphic age of the anatectic complex (316.8 ± 2.0 Ma), and to estimate fast cooling (7–54°C Ma –1 ) and fast exhumation (0.2–1.3 mm a −1 ) after a vertical displacement of c. 6–9 km. Our results show a similar zircon age distribution between migmatites and the Excomungada Formation from the host Ediacaran–Cambrian Douro–Beiras Supergroup. Although the existence of an inherited zircon population lasting c. 500 Ma, absent in the metasedimentary units, suggests the contribution of Ollo de Sapo magmatic rocks during the Lower–Middle Pennsylvanian melting events. Detrital zircon ages of the Pinhão Formation (Douro Group) have contrasting sources to units from the Beiras Group, which may indicate the presence of a barrier that prevented older detrital components from reaching the Douro basin. However, at odds with what has been postulated before, such a barrier must have been placed farther south of the FRC-LAC, and thus not coincident with the Juzbado–Penalva do Castelo shear zone. Supplementary material: A full description of the stratigraphy and lithologies (Supplementary 1 and 2, respectively); the analytical conditons of the LA-ICP-MS analyses (Supplementary Material 3); the U–Pb zircon and apatite data of the FCR-LAC migmatites and the U–Pb detrital zircon data of the DBSG (Supplementary Material 4) are available at https://doi.org/10.6084/m9.figshare.c.6002006

Geochemical and detrital zircon age constraints on Meso- to Neoproterozoic sedimentary basins in the southern Yangtze Block: Implications on Proterozoic geodynamics of South China and Rodinia configuration

The late Mesoproterozoic to early Neoproterozoic sedimentary sequences in the southwestern Yangtze Block, represented by the Julin, Huili, and Kunyang groups, provide vital evidence for deciphering the tectonic evolution of the Yangtze Block that have implications on the reconstruction of the Rodinia supercontinent. Zircon geochronological data reveal that the Julin and Huili groups were deposited at 1167–982 Ma and 1176–958 Ma, respectively. The Haizishao Formation, the conventionally thought the upper most of the Julin Group, was deposited after 982 Ma. The stratigraphicphic position of the Haizishao Formation basal conglomerate and diversity in its detritus source, and tectonic setting, suggest that the Haizishao Formation may not be a part of the Julin Group but represents an independent sedimentary event. Geochemical tectonic discrimination characteristics based on major elements, Th-Sc-Zr/10, Ti/Zr-La/Sc, La/Th-Hf and Sc/Th-La/Sc plots, in combination with detrital zircon age distribution pattern and bimodal magmatism, point toward a transition from continental rift to passive continental margin setting followed by an active continental margin setting for Julin and Huili groups. However, the Huili Group is significantly different from both the Julin and Kunyang groups in terms of lithological composition, depositional environment, detrital zircon age distribution, and tectonic setting, implying that the Julin and Huili basins may have been located in different microcontinents during the late Mesoproterozoic - early Neoproterozoic times.Detrital zircon U-Pb ages and Lu-Hf isotopic characteristics of Julin and Huili groups indicate detritus sourced from the continental interior and exotic terranes, such as the Yudongzi, Douling, and Kongling complexes and magmatic rocks at the southwestern margin of Yangtze Block, the Gawler Craton in Australia, the Transantarctic Mountains in East Antarctica, and the Ongole domain in the Eastern Dharwar Craton of India. Combining provenance analyses and comparison of detrital zircon data, the Yangtze Block was paleogeographically placed in the external position to the Rodinia supercontinent, close to north-central India, Australia, and East Antarctica during the late Mesoproterozoic to early Neoproterozoic.

Detrital zircon U–Pb geochronology and Hf isotopes of Mesozoic through Cenozoic sandstones from the southern Junggar Basin, NW China: Implications for the provenances and uranium source

Junggar Basin is an important exploration zone for sandstone‐hosted uranium deposits in north‐west China. However, neither the provenance of the host sandstone nor the uranium supply capacity of the potential source rocks have been well evaluated. To determine the provenances of the Mesozoic to Cenozoic sandstone grains and to evaluate relationships between the uranium source and the detritus provenances, a field investigation was performed at the Honggou section in the southern Junggar Basin. U–Pb geochronology and Hf isotopes were obtained from populations of detrital zircons from Jurassic through Palaeogene sandstones. The detrital zircon U–Pb ages display three main groups: 145–190 Ma, 250–360 Ma, and 360–460 Ma. The detrital zircon age distributions and the Hf isotopic characteristics of the sandstones correspond to different igneous rock units within the North and Central Tianshan Mountains. Therefore, the changes in the relative proportions of the zircon age populations indicate that there were major shifts of the provenance areas for the sandstones throughout the Early Jurassic to Palaeogene interval. The majority (92%) of Hf isotope εHf(t) values are positive and in the range of +0.7 to +15.5, which indicates that the majority of the zircons had crystallized in igneous rocks that were mainly derived from juvenile crust or depleted mantle. The majority (93%) of the two‐stage model ages (TDM2) are less than 1.8 Ga, thereby indicating the source of the majority of the igneous rocks was from the melting of ancient Meso‐Proterozoic juvenile crust. Carboniferous–Permian intermediate‐felsic igneous rocks in the Tianshan Mountains may be the primary source of released mobilized uranium and uranium‐enriched siliciclastics into the southern Junggar Basin. This study will assist in future uranium prospecting in this region.

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 &amp;gt; 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), &amp;gt; 45 million years (m.y.) older than these strata. Additionally, Paleozoic grains are extremely uncommon (&amp;lt; 0.1%; n = 2,927 grains).

Age and origin of the H9 member from the Bayan Obo Group: Implications for the genesis of the giant Bayan Obo Fe-Nb-REE deposit, China

The Bayan Obo deposit hosted in a set of metamorphic sedimentary strata contains the world’s largest rare earth reserve. However, the genesis of its ore-bearing dolomites remains controversial. The temporal and spatial relationships and compositions of the surrounding strata could provide indirect genetic indications for ore-bearing dolomites, particularly the overlying H9 member. Our data suggest that the compositions of H9 member are complex, consisting of quartz sandstone, biotite shist, metamorphic volcanic rocks and alkaline rocks. The origin and genesis of different lithologies in the H9 member are different. Based on the age distribution of detrital zircons, the basement rocks from the Bayan Obo region are presumed to be the material sources for the quartz sandstone in the H9 member. The biotite schist is the alteration products of wall rocks reacting with the fluids extracted from the ore-bearing dolomite. Metamorphic volcanic rocks and alkaline rocks are also distinguished in the H9 member. Th-Pb dating of zircons from the H9 volcanic rocks indicates its formation age is around 1.4 Ga, which is earlier than the mineralization age of the ore body, and the H9 member is also affected by the Caledonian tectonic compression recorded by the age of 427 Ma. According to the temporal and spatial distribution of H9 member and ore-bearing dolomites, the dolomites are considered to be magmatic origin. H9 member acts as the caprocks of the ore-bearing dolomite, and the contribution of its material composition and entrapment play an important role in the formation of the Bayan Obo deposit.

Evaluating the Age Distribution of Exposed Crust in the Acasta Gneiss Complex Using Detrital Zircons in Pleistocene Eskers

AbstractThe Acasta Gneiss Complex (AGC) is a ∼2,400 km2 Hadean‐Mesoarchean terrane that contains the oldest known zircon‐bearing rocks on Earth. Despite its importance for early Earth geology, only a small fraction (∼50 km2) of the AGC has been mapped in detail. We use detrital zircon grains from late Pleistocene eskers that transect the Complex to approximate the lateral extent and relative proportions of diverse‐aged ancient rock units within the vast, little‐studied parts of the AGC. The esker sediment was derived from glacially eroded bedrock and therefore zircon grains can serve as a proxy for the ages of exposed bedrock in the study area. U‐Pb dates on ∼2400 detrital zircons from coarse and fine grain‐size fractions along the esker transect yield age distributions that coincide with ages of regionally mapped AGC bedrock, the adjacent Wopmay Orogen, and granitoids of the Slave craton. Based on detrital zircon age distributions and new reconnaissance‐scale mapping, we infer that 3.37 Ga granitoids are a volumetrically significant component of the unmapped AGC. Esker zircons older than 3.7 Ga are present in most esker samples but at low abundance, which suggests that Eoarchean and Hadean rocks are a volumetrically subordinate component of the AGC. However, the data also suggest that unmapped rocks at least as old as 3.95 Ga are present toward the inferred eastern limit of the AGC, a location where Eoarchean rocks have not been recognized previously.

Precambrian tectonic affinity of the Beishan Orogenic Belt: Constraints from Proterozoic metasedimentary rocks

The Precambrian metasedimentary rocks that are extensively distributed in the Beishan Orogenic Belt (BOB) can provide crucial geological information to constrain its tectonic affinity and geological evolution. Field investigation, zircon U–Pb dating and Lu–Hf isotopic analyses were conducted in combination for investigating them. Detrital zircon U–Pb dating shows that a quartzite sample of the Beishan Complex yields the youngest age at ca. 1710 Ma, with a major age peak at 1828–1778 Ma. Five quartzite samples from the Gudongjing Group and Pingtoushan Formation exhibit similar detrital zircon age distributions mainly from the late Paleoproterozoic to Mesoproterozoic, with the youngest ages at ca. 953 Ma, ca. 1000 Ma, ca. 978 Ma, ca. 960 Ma and ca. 985 Ma. Considering the 1.4 Ga granitoids and age peak of the early Neoproterozoic metasedimentary rocks, the supracrustal rocks within the Beishan Complex were probably deposited during the late Paleoproterozoic to early Mesoproterozoic (ca. 1.7–1.4 Ga). Moreover, owing to the presence of ca. 933–871 Ma granitoids, the deposition ages of the Gudongjing Group and Pingtoushan Formation can be constrained during the early Neoproterozoic (ca. 953–933 Ma). The metasedimentary rocks, the same as the Meso-Neoproterozoic granitic magmatism, support the existence of a Precambrian microcontinent in the BOB. The early Neoproterozoic metasedimentary rocks have continuous detrital zircon ages during the Mesoproterozoic, mainly with positive εHf(t) values. Integrated with the magmatic records of ca. 0.9 Ga and ca. 1.4 Ga, we believe that the Precambrian basement of the BOB could be a fragment drifted from the Fennoscandia of the Baltica Craton. Field investigation revealed that carbonate rocks, mature sandstones and siltstones primarily comprise the protoliths of the early Neoproterozoic metasedimentary rocks, implying the sedimentation in a passive continental margin. However, an almost contemporaneous granitic magmatism was formed in a continental arc setting associated with the assembly of Rodinia. Therefore, it can be inferred that the BOB could be located in the periphery of the Rodinia supercontinent, where the sedimentation of the passive continental margin occurred at its outboard position.

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.

Triassic provenance shifts and tectonic evolution of southeast Ordos Basin, Central China

Tectonic evolution of the North China Craton underwent a complicated process during the early Mesozoic owing to almost simultaneous closures of the Mianlue Ocean to the south and the Palaeo-Asian Ocean to the north. The tectonic setting of the Triassic sedimentary basin in the southern North China Craton remains a subject of debate. The conventional view is that early Mesozoic basins resulted from plate collision and crustal shortening, whereas new petrological evidence of crustal extension has been identified in the southern North China Craton. In this study, we used petrology, sedimentology, subsidence and geochronology to trace basin provenance and reconstruct source-to-sink around the southeast Ordos Basin. The petrographic modal compositions showed that the provenance changed from recycled orogenic to a mixture of recycled orogenic and arc magmatic materials. Tectonic subsidence of the southeast Ordos Basin revealed two episodes of rapid subsidence, the second of which lasted ~10 Ma and caused the depocenter of the basin to move southward. Early Triassic detrital zircons with distinguishing ages of 1100–700 Ma were derived from the Central China Orogenic Belt and North China Craton; then, they were sourced from the Inner Mongolia Palaeo-uplift, based on zircon ages clustered at ~400–250 Ma. The petrographic modal composition, tectonic subsidence and zircon age distribution imply a provenance shift from short and rapid uplift (North Qinling Orogenic Belt) to remote continuous uplift (Inner Mongolia Palaeo-uplift); this is also supported by the palaeo-current direction. This shift defined a change in the Qinling Orogenic Belt from collision and uplift to extension, which caused the depositional centre of the Ordos Basin to move southward. This integrated tectono-sedimentary environment study provides new insight into the closure process of the Mianlue Ocean during the Triassic and its impact on the tectonic environment of the southern North China Craton.

Petrology and zircon U–Pb geochronology of pelitic gneisses and granitoids from the Dai Loc Complex in the Truong Son Belt, Vietnam: Implication for the Silurian magmatic-metamorphic event

The Dai Loc Complex, located in the southern Truong Son Belt, is separated from the northern Kontum Massif by the early Paleozoic Tam Ky–Phuoc Son suture zone. This study presents new zircon U–Pb ages and petrographic observations of the migmatitic pelitic gneisses and mylonitized granite intrusions from the Dai Loc Complex in order to constrain the Early Paleozoic thermal history of the eastern Indochina Block. The identification of metamorphic zircon with sillimanite inclusions, euhedral cordierite, and garnet in the migmatitic pelitic gneisses indicates high temperature metamorphic conditions at ca. 430–440 Ma. The metamorphism was followed by an isobaric cooling stage defined by the replacing of cordierite by kyanite–staurolite–quartz symplectite. The Dai Loc granite likely intruded the metapelites at ca. 430 Ma and was subsequently mylonitized. The thermal event in the Dai Loc Complex may be correlated with Ordovician–Silurian low pressure/high temperature metamorphism caused by subduction related arc magmatism in the Kannack and Ngoc Linh Complexes of the Kontum Massif. However, the frequency distribution of detrital zircon ages suggests the metasedimentary rocks from Dai Loc Complex have a unique provenance that was distinct from those of the neighboring A Vuong Formation and South China Block.

History of crustal growth in Africa and the Americas from detrital zircon and Nd isotopes in glacial diamictites

Diamictites produced by continental glaciations were deposited in the Mesoarchean (∼2.9 Ga), Paleoproterozoic (∼2.4–2.2 Ga), Neoproterozoic (∼0.75–0.58 Ga), and Paleozoic (∼0.3 Ga), and, with the exception of the Mesoarchean, occur on multiple modern continents. We examine the provenance of a selection of these diamictites from all four time periods and three continents via detrital zircon U-Pb geochronology and Hf isotope and whole-rock Nd isotope analyses. Mesoarchean samples from South Africa contain mostly Mesoarchean zircon, with a much smaller number of Paleoarchean grains. Zircon Hf and whole-rock Nd point towards their derivation from reworked Paleoarchean crust. Paleoproterozoic samples from North America share a similar unimodal zircon age distribution, with a peak at 2.7 Ga and a narrow range in Hf isotopes that is slightly superchondritic. Coupled with whole-rock Nd results, these data point to their derivation from reworked juvenile Mesoarchean crust. By contrast, the Nd isotope data and existing published detrital zircon U-Pb data for Paleoproterozoic diamictites from South Africa indicate a mix of Neoarchean and Mesoarchean sources. Neoproterozoic samples from Namibia share a Paleoproterozoic detrital zircon population with variable but subchondritic Hf isotope compositions, indicating derivation from reworked Neoarchean crust. Most samples also have Mesoproterozoic and Neoproterozoic zircon with both positive and negative εHf(i), and all have Nd isotope compositions yielding Paleoproterozoic model ages. A Neoproterozoic sample from Canada contains mostly Neoproterozoic detrital zircon with variable Hf isotope compositions, indicating a mix of juvenile and reworked Mesoproterozoic crust. Samples from different parts of the Paleozoic Dwyka Group in South Africa show significantly different provenance, with a western locality containing only zircon older than 2.0 Ga and a Neoarchean Nd model age. By contrast, eastern samples have Paleoproterozoic model ages and published detrital zircon ages are largely Mesoproterozoic and younger. Paleozoic samples from Bolivia have a Paleoproterozoic Nd model age.Overall, the difference between zircon initial Hf isotope compositions and the depleted mantle is smallest for Archean zircons, indicating major episodes of crustal reworking followed shortly after crust formation (perhaps reflecting the last stage of cratonization). Hf and Nd data together record major episodes of juvenile crust formation at 3.2, 2.8–2.7, 2.0–1.7, and 1.3–0.9 Ga, consistent with previously documented global crust formation events. The diamictites provide no evidence for pre-3.6 Ga felsic crust in these regions.

Age and provenance of the Precambrian Middle Timan clastic succession: Constraints from detrital zircon and rutile studies

The Precambrian sedimentary succession of Middle Timan provides important information on the coeval history of Baltica prior to assembly of the Rodinia supercontinent. This study comprises a comprehensive integrated provenance study based on samples collected from Precambrian clastic rocks of the Chetlassky Kamen and Volsko-Vymskaya Ridge. The maximum depositional age of the studied succession is constrained as latest Mesoproterozoic – earliest Neoproterozoic based on the youngest detrital zircon and rutile ages. Metasandstone samples within the succession are arkose, sublitharenite and litharenite. The distributions of detrital zircon U-Pb ages from the studied metasedimentary rocks are very comparable, yielding approximately 50% Mesoproterozoic ages within the ranges 1470 – 1550 and 1170 – 1370 Ma, 45% Paleoproterozoic ages and 5% Archean ages, with predominant populations grouping at 2500–2700 and 1800–1900 Ma. Comparable detrital zircon age distributions within the coeval strata of northern Baltica suggest a common provenance area. Analysis of detrital rutile suggests the widespread distribution of latest Mesoproterozoic – earliest Neoproterozoic metamorphism within the provenance area. A comparison of detrital zircon age distributions from the coeval strata of Baltica and Laurentia also revealed a striking similarity. Therefore, we suggest that clasts were in fact predominantly sourced from the Grenvillian-Sveconorwegian Orogen, with possible reworking of older zircon grains from older sedimentary rocks involved in the deformation and uplift. Our data support the tectonic model invoking a continuation of the Grenvillian-Sveconorwegian Orogen further to the east across the Barents Sea from its closest modern outcrop in Scandinavia.

Tracing southern Gondwanan sedimentary paths: A case study of northern Namibian late Palaeozoic sedimentary rocks

AbstractThe northern Namibian Karoo‐aged successions are part of a Gondwana‐wide sedimentary system emerging at the Carboniferous–Permian boundary and existing for more than 50 Ma. The Karoo Supergroup sedimentary successions are of importance in understanding the evolution of the Karoo rift system. This study presents new whole‐rock geochemical data combined with detrital zircon morphology as well as U−Pb ages and Lu−Hf composition of late Palaeozoic siliciclastic rocks of the Namibian Huab Basin and Kunene area (south‐west Africa). Inferred by youngest detrital zircon U−Pb ages the Verbrande Berg Formation (lower Ecca Group) yields a Sakmarian to Asselian maximum depositional age, whereas the overlying Tsarabis Formation yields an Artinskian maximum depositional age. These ages coincide with the end of the Dwyka ice age and an overall warming and a contemporaneous evolution of the Karoo I rift system across southern Gondwana. The zircon age distribution of the investigated samples yields clusters ranging between ca 500 to 650 Ma (Cambrian–late Neoproterozoic), ca 950 to 1200 Ma (early Neoproterozoic–Mesoproterozoic) and ca 1800 to 1900 Ma (Palaeoproterozoic). Their rounded shapes characterize the zircon grains of the Kunene area and the lower Huab Basin section, whereas upper Huab Basin strata yield mostly unrounded grains. The rounded nature of zircon grains with a diverse U−Pb age spectrum putatively points towards sediment homogenization and multiple recycling stages during the deposition of the sediments and large catchment areas of the depositing rivers. As suggested by zircon grains with a low roundness value and a single Palaeoproterozoic age cluster, the upper Huab Basin successions were probably deposited under drier climatic conditions, small catchment areas and limited sedimentary homogenization. Therefore, the southern Gondwana sedimentary transport and homogenization system may change over time and is dependent on the climate prevailing during deposition. This study shows that the laws of detrital zircon are very complex and are yet to be explored.

Provenance of metasedimentary rocks of the Kheis Terrane and Kakamas Domain: support for accretionary tectonics during the development of the western Namaqua-Natal metamorphic province

Abstract The ~1 200 to 1 000 Ma Namaqua-Natal Metamorphic Province (NNMP) is part of a major orogenic belt in the west-central parts of South Africa and most likely formed during the convergence of the Laurentia and Kalahari cratons during the assembly of Rodinia. Controversy exists regarding the mode of formation of the Namaqua sector of the NNMP, with some supporting the idea of accretion of different crustal fragments while others argue that it formed in a continental back-arc setting. Here we address this controversy and provide information regarding the provenance of two metasedimentary successions that are preserved to the east and west of the Trooilapspan shear zone, which represents the Eastern Namaqua Front. 207Pb/206Pb SHRIMP ages for detrital zircon grains sampled from the Keis supergroup, which is preserved in the Kheis Terrane and situated on the Kalahari Craton, support derivation from Archaean to Paleoproterozoic source areas on the Kaapvaal Craton. In contrast, SHRIMP ages from detrital zircon grains of the Korannaland Group, which forms the metamorphosed supracrustal sequence of the Kakamas Domain, show derivation from late-Paleoproterozoic to Mesoproterozoic source areas like the Bushmanland and Richtersveld domains as well as the gneissic basement of the Kakamas Domain. The zircon age distribution data show that the metasedimentary rocks of the Keis supergroup and Korannaland Group did not obtain detrital material from the same source areas during their deposition, and that the Keis supergroup never served as a source for the detrital material in the Korannaland Group. This indicates that these successions had different geological histories prior to the formation of the NNMP, which supports the accretionary model for the development of the Namaqua Sector of the NNMP.

FIRST DETRITAL ZIRCON GEOCHRONOLOGY DATA FOR CLASTIC ROCKS OF THE EAST SAKHALIN ACCRETIONARY TERRANE

First detrital zircon geochronology data and results of geochemical studies for clastic rocks of the Rymnik and Nabil zones of the East Sakhalin accretionary terrane, located within the region of the East Sakhalin Mountains, are presented. The studies have been carried out at the Center for Collective Use of Far Eastern Geological Institute of the Far East Branch of the Russian Academy of Sciences in Vladivostok. The established geochemical features suggest that the source of the clastic material of the zones was felsic rocks of the deeply eroded continental island arc or arcs. Although the geochemical characteristics are similar, there are sharp differences between the detrital zircons’ age distribution patterns of rocks of these zones. In the sandstone of the Nabil zone, 75 % of the zircon grains are of the middle Cretaceous age (94–108 Ma) with a peak of 96 Ma, 15 % are the middle Permian-Early Jurassic, and 10 % are the Precambrian (mainly Paleoproterozoic). The sandstone of the Rymnik zone has a more complex (polymodal) pattern of the detrital zircon age distribution, with a significant contribution of the Precambrian grains (37 %). Most of the grains belong to the Early Jurassic (peak 196 Ma) and the Early Cretaceous (peak 137 Ma), with 47 % of the Mesozoic grains. The likely provenances of the clastic material were the Middle Cretaceous volcanic arcs of the Asian eastern margin older complexes of the continent.