Neoproterozoic Zircons Research Articles

Provenance analysis of Nanyinger Group in the North Qilian Belt: constraints from zircon U–Pb geochronology

LA–ICP–MS U–Pb dating has been performed on detrital zircons from the Nanyinger Group in the eastern section of the north Qilian orogenic belt in Jingyuan County, Gansu Province. The results show five major age groups: 3.1–2.0, 1.8–1.4, 1.4–0.8, 0.6–0.4, and ~0.26 Ga. Archean to Neoproterozoic zircons were derived from the central Qilian belt. The early Paleozoic grains are considered to have been derived from the magmatic arc related to ocean closure. The youngest age may be derived from the recycling of sediments prior to the Nanyinger Group. The youngest detrital zircon age (262 ± 5 Ma) is close to the depositional age of the strata, suggesting rapid uplift of the Qilian Mountains. In the early Indosinian, the palaeo-Qilian Mountains uplifted rapidly and provided the main source for the Hexi Corridor basins. The North Qilian Belt is the southern boundary of the Hexi Corridor basins. From the Ordovician to the Triassic, the depocenter gradually moved to the Qilian Mountains and was very close to the Qilian Mountains in the Late Triassic. By comparing with previous research, we infer that the Hexi Corridor basin may not connect with the Ordos Basin in the Triassic.

Tracing magma sources of three different S-type peraluminous granitoid series by in situ U–Pb geochronology and Hf isotope zircon composition: The Variscan Montes de Toledo batholith (central Spain)

Three distinct S-type peraluminous granitoid types have been identified within the Variscan Montes de Toledo batholith, located in the Central Iberian Zone (SW European Variscides): type-1, extremely high peraluminous restite-rich granitoids; type-2, highly peraluminous restite-bearing granitoids; and type-3, moderately peraluminous granitoids with mafic microgranular enclaves. Type-1 and type-2 granitoids are restricted to the western part of the batholith, whereas type-3 granites are mostly restricted to the eastern segment. There is a sequential youngering of emplacement age from type-1 (late-tectonic) to type-2 and type-3 granitoids (post-tectonic), extending the timing of the batholith formation for about 19 Ma between 316 and 297 Ma. Although the degree of peraluminousity of the different series could be related to different partial melting conditions or to the variable entrainment of restitic components (including the peritectic mineral assemblage of the melting reactions), whole-rock geochemical signatures and isotope zircon composition of the peraluminous granitoid types suggest contribution of different crustal sources. There is no evidence for the direct mantle-derived material contribution in the genesis of these peraluminous melts. Type-1 and type-2 granitoids contain mostly Archean to Neoproterozoic inherited zircons, whereas type-3 granites show preferentially Neoproterozoic (up to late Cryogenian) and Ordovician inheritance. The wide range of initial Hf isotope composition, ranging to highly radiogenic values (ƐHf up to + 10), of Neoproterozoic zircon inheritances in type-1 and type-2 granitoids suggests derivation from heterogeneous Neoproterozoic metasedimentary sources composed of both juveline and recycled crustal materials, similar in composition to the host Schist–Greywacke Complex metasediments. Trace-element modelling clearly suggests the involvement of metasediments similar to those mentioned from the southern part of the Central Iberian Zone. Nevertheless, the highly negative initial Nd isotopic signature measured in some type-1 granitoids (ƐNd300 up to − 9.4) also suggests a contribution of more mature metasedimentary sequences, such as those described in the northern Central Iberian Zone. On the contrary, the high Ca, Na and Sr bulk-rock contents in type-3 granitoids, together with the presence of Ordovician magmatic inherited zircons, and the absence of inheritances older than Cryogenian ages, suggest the involvement of a metaigneous protolith. This conclusion is also supported by the similar mean whole-rock ƐNd300 isotopic values, TDM ages, ƐHf isotope zircon composition and trace-element modelling of type-3 granitoids when compared to data from outcropping augen orthogneisses from Central Spain. The estimated crystallisation temperatures for the granitoids from the Montes de Toledo batholith (750°–880 °C) suggest that the partial melting of the crustal protoliths could be induced by the own heat generated by the thickening of a highly radiogenic crust, such is that from central Spain. Our results not only indicate that the implication of metasedimentary and/or metaigneous sources contributes to enhance geochemical and isotopic differences in S-type peraluminous granitoid series in intracontinental orogenic settings, but also fractional crystallisation processes are responsible for the geochemical variability through the evolution of these felsic magmas.

Age and provenance of the Ergunahe Group and the Wubinaobao Formation, northeastern Inner Mongolia, NE China: implications for tectonic setting of the Erguna Massif

Here, we present the results of U–Pb dating of detrital zircons from the Ergunahe Group and the Wubinaobao Formation, within northeastern Inner Mongolia, NE China, with the aim of constraining the tectonic setting of the Erguna Massif. The majority of detrital zircons from five samples collected from the Ergunahe Group and the Wubinaobao Formation are magmatic, although some zircons have metamorphic growth rims. Zircons in two mica schists and in feldspar–quartz sandstone from the Ergunahe Group yield age populations that cluster around 738, 760, 792, 837, 890, 964, and 1050 Ma, whereas zircons from two quartz sandstones within the Wubinaobao Formation yield age populations that cluster at 466, 484, 515, 738, 795, 837, and 894 Ma. These data, combined with detrital zircon age populations (ca. 712 Ma) from the adjacent Xinghuadukou Group, and the fact that the Ergunahe Group intruded by Caledonian gabbros is overlain by upper Silurian units, indicate that the Ergunahe Group formed at 738–712 Ma (i.e. during the Neoproterozoic). In addition, the Wubinaobao Formation is subdivided into two units: a calcareous siltstone unit within the western part of the study area and a quartz sandstone within the eastern part. The calcareous siltstone formed at 712–795 Ma, similar to the Ergunahe Group, whereas the quartz sandstone formed between the 466 Ma and late Silurian. The age spectra of detrital zircons from the Ergunahe Group and the Wubinaobao Formation indicate that sediment in both of these units was derived from terranes that outcrop around the basin. The widespread occurrence of Neoproterozoic detrital zircons within both the Ergunahe Group and the Wubinaobao Formation suggests that Precambrian terranes are present within the Erguna Massif and that the massif has an affinity to the Siberian Craton.

Detrital zircon geochronology and provenance of the Neoproterozoic Hammamat Group (Igla Basin), Egypt and the Thalbah Group, NW Saudi Arabia: Implications for regional collision tectonics

Detrital zircon U–Pb SIMS dating is used to evaluate the provenance of two correlative basins in the Arabian-Nubian Shield (ANS). The Wadi Igla Formation in the Central Eastern Desert (CED) of Egypt and the Thalbah Group in the Midyan Terrane (MT) of NW Saudi Arabia are considered to be post-amalgamation terrestrial basins, developed during closure of the Mozambique Ocean and amalgamation of the ANS in Cryogenian-early Ediacaran time. The analytical results indicate that the upper-part of the Wadi Igla Formation has a maximum depositional age of 628±6Ma, contains 98% Neoproterozoic zircon with ages between 815 and 628Ma, and has two distinct peaks at 690Ma and 652Ma. A rhyolite clast from the upper-part of the Wadi Igla Formation gives a U–Pb age of 700±6Ma. This age significantly pre-dates Dokhan volcanism, indicating that the dominant rhyolitic clasts within the Wadi Igla Formation are not from the Dokhan Volcanics, as previously believed. Analytical results from the Thalbah Group suggest multiphase basin formation and development. The lower part of the Thalbah Group is intruded by monzogranites of the Liban complex, has a minimum depositional age of 635±5Ma, resembling that of the Wadi Igla Formation. Its middle part has a maximum age of 612±7Ma and is comprised of 90% Neoproterozoic zircon with ages ranging from 820 to 612Ma. The upper part of the Thalbah Group has a maximum age of 596±10Ma and contains a wider range of Neoproterozoic detritus with ages between 985 and 596Ma. The basement of the Thalbah Group is represented by metasediments and metavolcanics of the Zaam Group. The sample collected from the uppermost part of the Zaam Group (Um Ashsh Formation) contains zircon of mostly Cryogenian age (ca. 812–697Ma) and has a maximum age of 700±4Ma, suggesting that the Zaam Group might be correlative with the subduction-related metavolcanic and metasedimentary rocks that are overlain unconformably by the Wadi Igla Formation in the CED.The Wadi Igla basin and the lower and middle parts of the Thalbah basin have similar provenance, record a Cryogenian-early Ediacaran age, and represent syn-subduction (rather than post-amalgamation) basins. The upper part of the Thalbah Group, in contrast, has a distinct provenance representing an Ediacaran syn-collisional basin. The narrow age range of the Wadi Igla Formation and the lower and middle parts of the Thalbah Group indicates a restricted source from the CED and MT island arc basement, whereas the wide age range for the upper part of the Thalbah Group indicates a contribution from other parts of the ANS. The sediment sources and the age patterns of detrital zircons change abruptly at ca. 596Ma. This may coincide with the onset of collision of the CED and MT basements with the older Hijaz-Gebeit terrane (850–680Ma) to the south along the Yanbu-Onib-Sol Hamed-Gerf-Allaqi-Heiani (YOSHGAH) suture in the ANS during the East African Orogeny.

Detrital zircon provenance of early Palaeozoic sediments at the southwestern margin of the Siberian Craton: Insights from U–Pb geochronology

Detrital zircons from the Ordovician and Devonian sedimentary cover of the Siberian Craton were analyzed for U/Pb geochronology to understand their sediment provenances. Five main age-peaks were identified in the zircon U/Pb age-spectra: (1) Neoarchaean – early Palaeoproterozoic (2.7–2.4Ga); (2) late Palaeoproterozoic (2.0–1.65Ga); (3) minor early Neoproterozoic (1.0–0.75Ga); (4) Ediacaran (0.65–0.60Ga) and (5) Cambrian – Early Ordovician (0.54–0.47Ga), reflecting the main magmatic events in the sediment source regions. The oldest zircons (groups 1 and 2) are derived from the Siberian Craton which amalgamated during the Neoarchean – Palaeoproterozoic. The Neoproterozoic zircons (groups 3 and 4) likely sourced from southwestern basement uplifts and Neoproterozoic belts of the Siberian margin such as the Yenisey Ridge and Baikal-Muya region. The provenance of the youngest zircons (group 5) can be traced to the Altai–Sayan fold-belt, where peri-Gondwanan microcontinents and island-arcs accreted to Siberia during late Neoproterozoic – early Palaeozoic progressive consumption of the Palaeo-Asian Ocean.

Vestiges of Saxothuringian crust in the Central Sudetes, Bohemian Massif: Zircon evidence of a recycled subducted slab provenance

Four detrital zircon concentrates from the metasediments and metavolcanics of the Central Sudetes, Bohemian Massif, have been dated using SHRIMP II. The Wyszki paragneiss yielded Precambrian age spectra similar to those characteristic of the Cadomian terranes: (1) Archaean and Palaeoproterozoic zircons are scattered between 2830 and 1867Ma, and (2) there are abundant Neoproterozoic zircons dated at 803–577Ma. The estimated maximum sedimentation age for this rock is 566±4Ma. The Kłodzko Fortress pyroclastic metarhyodacite gave an igneous emplacement age of 536±2Ma. The magmatic precursor to the subvolcanic Gniewoszów metarhyolite was dated at 501±3Ma. Finally, the Ścinawica subvolcanic rhyolite yielded an igneous emplacement age of 338±3Ma and a large population of inherited zircons dated at: Palaeoproterozoic, Neoproterozoic, Cambro-Ordovician and Late Devonian–early Carboniferous.The dated samples come from two adjacent suspect terranes —the Orlica–Śnieżnik dome and the Kłodzko massif in the Central Sudetes that are characterised by contrasting timing of metamorphism and exhumation. Despite this difference, the results obtained show, in conjunction with earlier data, a similar provenance of the studied units and their common affinity to the Saxo-Thuringian terrane. Since the Central Sudetes are separated from Saxo-Thuringia by a collisional suture, the pre-Variscan rocks must represent the deformed and metamorphosed, allochthonous equivalents to Saxo-Thuringian lithologies. They were probably subducted together with the Saxo-Thuringian passive margin during a Variscan collision and then exhumed within an accretionary wedge in front of Brunia/East Avalonia. The Central Sudetic suspected terranes must have been derived from a dismembered single accretionary complex and were then juxtaposed by strike–slip faults.

Geochemistry, zircon U–Pb ages and Lu–Hf isotopes of early Paleozoic plutons in the northwestern Chinese Tianshan: Petrogenesis and geological implications

The northwestern Chinese Tianshan is a key part of the southern Central Asian Orogenic Belt. Voluminous arc-related igneous rocks in this region have recorded the opening and closure of several oceanic basins that may represent southern branches of the Paleo-Asian Ocean. We have conducted geochemical, geochronological and Hf-in-zircon isotopic studies on mafic and felsic intrusive rocks in the northwestern Chinese Tianshan to provide important clues for the evolution of the Junggar Ocean and to understand the early Paleozoic crustal growth in the Central Asian Orogenic Belt. The mafic plutons are composed of metagabbro (453.8±2.0Ma) and fine-grained diorite (461.1±2.0Ma). These rocks are mostly sub-alkaline in composition and belong to calc-alkaline series. The mafic rocks are enriched in LILE (such as Rb, Sr, Ba, Pb) with pronounced negative Nb–Ta–Ti anomalies. Depleted εHf (t) (−0.03–+8.32), high Ba/Th (>79) and Ba/La (>11) as well as low Th and Th/Yb suggest that these mafic rocks were likely generated by partial melting of slab fluid-metasomatized mantle peridotite. The felsic plutons consist of quartz diorite (463.1±2.0Ma, 462.4±2.0Ma), granodiorite (460.2±3.0Ma) and muscovite-bearing granite (448.9±6.0Ma) and show characteristics of calc-alkaline igneous rocks. These felsic rocks are also enriched in LILE and display HFSE depletion with obvious Nb–Ta–Ti troughs, showing typical geochemical features of arc-related magmas. The quartz diorite is characterized by slightly depleted juvenile εHf (t) values (−0.69–+4.52) and relatively young Hf crustal model ages (TDMC: 1.16–1.49Ga), indicating a relatively juvenile magmatic source. The occurrence of Neoproterozoic zircon xenocrysts suggests that the quartz diorite was produced, at least in part, by partial melting of Precambrian basement rocks with limited involvement of a juvenile mantle component. The granodiorite and muscovite-bearing granite both exhibit enriched εHf (t) values (−3.88–+0.11), relatively old TDMC ages (1.44–1.69Ga) and contain numerous early Paleozoic to Meoproterozoic inherited zircons (493–1012Ma). Their εHf (t) values plot on the evolution trend of the Neo- to Mesoproterozoic basement rocks and demonstrate an origin through partial melting of the Precambrian basement. Therefore, the petrogenesis of the mafic and felsic rocks unravels an arc-related tectonic setting in the early Paleozoic. The ages of these intrusive rocks suggest that the onset of a southward subduction of the Junggar Ocean beneath the Yili block predates the middle Ordovician. The subduction process produced extensive arc-related granitoid complexes and triggered the involvement of juvenile mantle components in producing new continental crust and probably played an important role in vertical crustal growth in the CAOB during the early Paleozoic. In combination with new data from adjacent regions, the Middle Ordovician arc-related magmatism in the northwestern Chinese Tianshan and Cambrian to early Ordovician arc-derived magmas in the southern West Junggar was likely produced by bidirectional subduction of the Junggar Ocean.

Early evolution of the Paleoasian ocean: LA-ICP-MS dating of detrital zircon from Late Precambrian sequences of the southern margin of the Siberian craton

We present U–Pb (LA-ICP-MS) data on detrital zircon from the Late Precambrian terrigenous rocks of the Baikal Group and Ushakovka Formation, western Cisbaikalia (southern flank of the Siberian craton). The sources of clastic material for the studied sediments are interpreted. The youngest group of detrital zircon grains from the upper Baikal Group and Ushakovka Formation permits assigning these sediments to the Vendian. The lack of Mesoproterozoic detrital zircon in most of the analyzed samples confirms the hypothesis of a global (~1 Gyr) break in endogenic activity within the southern flank of the Siberian craton through the Precambrian. The abundance of Neoproterozoic zircon in sandstones from the upper horizons of the Baikal Group and the Ushakovka Formation might be due to the shrinkage of the ocean basin as a result of the convergence of the craton with the microcontinents and island arcs within the Paleoasian ocean.

The Namuskluft and Dreigratberg sections in southern Namibia (Kalahari Craton, Gariep Belt): a geological history of Neoproterozoic rifting and recycling of cratonic crust during the dispersal of Rodinia until the amalgamation of Gondwana

This paper presents combined U/Pb, Th/U and Hf isotope analyses on detrital and magmatic zircon grains together with whole-rock geochemical analyses of two basement and eight sedimentary rock samples from the Namuskluft and the Dreigratberg in southern Namibia (Gariep Belt). The sedimentary sections evolved during the Cryogenian on the SW part of the Kalahari Craton and where therefore deposited in an active rift setting during the break-up of Rodinia. Due to insufficient palaeomagnetic data, the position of the Kalahari Craton within Rodinia is still under discussion. There are possibilities to locate Kalahari along the western side of Australia/Mawsonland (Pisarevski et al. in Proterozoic East Gondwana: supercontinent assembly and break-up, Geological Society, London, 2003; Evans in Ancient Orogens and modern analogues. Geological Society, London, 2009; and others) or together with the Congo-Sao Francisco and Rio de la Plata Cratons (Li et al. in Prec Res 45: 203–2014, 2008; Frimmel et al. in Int J Earth Sci (Geol Rundsch) 100: 323–354, 2011; and others). It is sill unclear which craton rifted away from the Kalahari Craton during the Cryogenian. Although Middle to Upper Cryogenian magmatic activity is known for the SE Kalahari Craton (our working area) (Richtersveld Suite, Rosh Pinah Fm), all the presented samples show no U/Pb zircon ages younger than ca. 1.0 Ga and non-older than 2.06 Ga. The obtained U/Pb ages fit very well to the exposed basement of the Kalahari Craton (1.0–1.4 Ga Namaqua Province, 1.7–2.0 Ga Vioolsdrif Granite Suite and Orange River Group) and allow no correlation with a foreign craton such as the Rio de la Plata or Australia/Mawsonland. Lu–Hf isotopic signatures of detrital zircon point to the recycling of mainly Palaeoproterozoic and to a smaller amount of Archean crust in the source areas. eHf(t) signatures range between −24 and +14.8, which relate to TDM model ages between 1.05 and 3.1 Ga. Only few detrital zircon grains derived from magmas generated from Mesoproterozoic crustal material show more juvenile eHf(t) signatures of +14, +8 to +4 with TDM model ages of 1.05–1.6 Ga. During Neoproterozoic deposition, only old cratonic crust with an inherited continental arc signature was available in the source area clearly demonstrated by Hf isotope composition of detrital zircon and geochemical bulk analysis of sedimentary rocks. The granodiorites of the Palaeoproterozoic basement underlying Namuskluft section are ca. 1.9 Ga old and show eHf(t) signatures of −3 to −5.5 with TDM model ages of 2.4–2.7 Ga. These basement rocks demonstrate the extreme uplift and deep erosion of the underlying Kalahari Craton at its western margin before general subsidence during Cryogenian and Ediacaran time. The sedimentary sequence of the two examined sections (Namuskluft and Dreigratberg) proposes the presence of a basin and an increasing subsidence at the SW part of the Kalahari Craton during the Cryogenian. Therefore, we propose the initial formation of an intra-cratonic sag basin during the Lower Cryogenian that evolved later to a rift basin at the cratonic margin due to increasing crustal tension and rifting together with the opening of the Adamastor Ocean. As the zircons of the sedimentary rocks filling this basin show neither rift-related U/Pb ages nor an exotic craton as a possible source area, the only plausible sedimentary transport direction providing the found U/Pb ages would be from the E or the SE, directly from the heart of the Kalahari Craton. Due to subsidence and ongoing sedimentation from E/SE directions, the rift-related magmatic rocks were simply covered by the input of old intra-cratonic material that explains the absence of Neoproterozoic zircon grains in our samples. The geochemical analyses show the erosion of a continental arc and related sedimentary rocks with an overall felsic provenance. The source area was a deeply eroded and incised magmatic arc that evolved on continental crust, without any evidence for a passive margin. All of this can be explained by the erosion of rocks related to the Namaqua Belt, which represents one of the two major peaks of zircon U–Pb ages in all analysed samples. Therefore, the Namaqua Belt was well exposed during the Cryogenian, available to erosion and apart from the also well-exposed Palaeoproterozoic basement of the Kalahari Craton one potential source area for the sedimentary rocks in the investigated areas.

Hf isotopic composition of single zircons from Neoproterozoic arc volcanics and post-collision granites, Eastern Desert of Egypt: Implications for crustal growth and recycling in the Arabian-Nubian Shield

Zircon Hf isotopic compositions for Neoproterozoic igneous rocks in the Central Eastern Desert of Egypt are presented and interpreted. The Humr Akarim (633±7 and 603±9Ma)–Humrat Mukbid (625±8 and 619±8Ma) plutons are Early Ediacaran post-collsional subsolvus granites. Their zircon ages range from 0.57 to 0.71Ga, with high positive ɛHf(T) values of +4.0 to +11.9. Hf model ages (Hf-TDMc) of 0.81–1.3Ga, are close to the U–Pb crystallization ages. These isotopic characteristics, along with published whole-rock Nd isotopic data, indicate that the protoliths were juvenile. The Wadi Kareim and Wadi El-Dabbah metavolcano-sedimentary rocks are Cryogenian (∼750Ma) arc-related metabasalts, meta-andesites and meta-tuffs. Their U–Pb zircon age populations range between 0.7–0.9, 0.9–1.5Ga and 2.0–3.0Ga. The youngest group represents magmatic zircons in the metavolcanics or reworked Neoproterozoic rocks in the metasediments. The 0.9–1.5Ga and 2.0–3.0Ga age groups are similar to those in pre-Neoproterozoic rocks that surround the Arabian-Nubian Shield and represent inherited or older detrital grains. The highly variable ɛHf(T) values (+23.5 to −35.0) and Hf-TDMc ages (0.78–3.8Ga) of Neoproterozoic zircons indicate that at least some of these magmas interacted with a pre-Neoproterozoic crustal source.

Detrital zircon record of Neoproterozoic active-margin sedimentation in the eastern Jiangnan Orogen, South China

Precambrian sedimentary sequences in the eastern Jiangnan Orogen, South China, include the Neoproterozoic Shuangqiaoshan and Xikou Groups and the overlying Nanhua Sequence. U–Pb ages of detrital zircons provide tight constraints on the deposition of the Shuangqiaoshan and Xikou Groups at 831–815Ma and 833–817Ma, respectively. Rocks from the lower parts of these strata contain dominantly Neoproterozoic detritus with a pronounced age peak at 830–850Ma, interpreted to be derived from a magmatic arc that has been mostly eroded. This magmatic arc was associated with sedimentation characterized by compositionally immature sediments with dominant early-Neoproterozoic (∼860–810Ma) zircons that have variable ɛHf(t) values of −21.5 to 14.8. The upper parts of these strata, uncomfortably underlain by the low units, are molasse-type assemblages with additional input of pre-Neoproterozoic detritus, representing sediments accumulated in a retro-arc foreland basin associated with the Jiangnan Orogen.Combining four samples from the Nanhua Sequence, three major magmatic activities at 2.50–2.35Ga, 2.10–1.90Ga and 980–810Ma in the source areas are identified. The older two events are characterized by reworking of pre-existing continental crust. Grenville magmatism and juvenile crust were insignificant in the eastern Jiangnan Orogen. Neoproterozoic zircons reflect generation of juvenile crust at 980–860Ma, involvement of both juvenile and recycled materials at 860–810Ma and reworking of pre-existing crust at 805–750Ma, corresponding to island arc, continental magmatic arc and post-collisional rifting stages in the eastern Jiangnan Orogen.

Zircon ages of metamorphic and magmatic rocks within peridotite-bearing mélanges: Crucial time constraints on early Carboniferous extensional tectonics in the Chinese Tianshan

We dated and geochemically characterized peridotite-bearing mélanges in the Chinese South Tianshan and within the Main Tianshan Shear Zone. The Yushugou-Tonghuashan mélange in the Chinese South Tianshan exposes a tectonic juxtaposition of a diapirically emplaced metaperidotite (predominantly lherzolite) massif with a high-grade metamorphic terrane (ca. 10km long; protolith age≥ca. 445–466Ma). Metamorphic zircons of a mafic granulite (εNd(t)=5.0) yielded a weighted mean 206Pb/238U age of 341±8Ma that we interpret as the time of granulite-facies metamorphism. The youngest zircon rims of an intermediate granulite (εNd(t)=−4.3) have a mean age of 332±13Ma that records a retrogressive metamorphic event. These ages determine the timing (ca. 341–332Ma) of mantle diapirism through continental crust. A dolerite dike (εNd(t)=2.3) emplaced into metaperidote has a crystallization age of 335±5Ma, that, on the basis of geochemistry, we interpret as representing E-MORB-OIB magmatism that accompanied mantle diapirism. An undeformed pink granite (εNd(t)=−3.6) intrudes the mélange matrix and has an emplacement age of 324±5Ma, thus providing an upper time limit for a tectonic movement that led to mélange formation. The older time limit of deformation (ca. 362–352Ma) is constrained by the youngest ages of thermo-tectonically modified zircons in a mylonitized metagabbro and a foliated meta-andesite. Magmatic zircons in the meta-andesite (εNd(t)=−3.3) and a dacite (εNd(t)=−5.6) have eruption ages of 433±4Ma and 435±3Ma that date formation of the mélange matrix. A microgabbro dike (εNd(t)=10.0) cutting metasediments (i.e. mélange matrix) has an emplacement age of 279±3Ma and contains abundant zircon xenocrysts ranging in age from Archean to late Paleozoic. Similarly, a dolerite dike, a meta-andesite, an intermediate granulite, and a metagabbro all contain inherited Precambrian to Paleozoic zircons. We accordingly conclude that the mélange was formed by mantle diapirism in the early Carboniferous and was subsequently affected by an early Permian volumetrically minor mafic episode. Two foliated garnet granites (εNd(t)=−7.0 and −6.9), in direct contact with metaperidotite within the Main Tianshan Shear Zone have emplacement ages of 341±2Ma and 329±4Ma that reflect an early Carboniferous episode of crustal anatexis. They also contain Neoproterozoic zircon xenocrysts. Also within the Main Tianshan Shear Zone, a gabbro (εNd(t)=8.7) has an emplacement age of 297±3Ma and contains abundant Neoproterozoic to late Paleozoic zircon xenocrysts. Based on the regional geological relationships, we associate early Carboniferous mantle diapirism and crustal anatexis with lower crustal delamination-induced asthenospheric upwelling. The numerous Precambrian zircon xenocrysts support a Chinese Tianshan–Tarim connection. The early Permian mafic episode coincided in time with the development of an early Permian unconformity in the Chinese North Tianshan.

Age assignment and geological significance of the “Budate Group” in the Hailar Basin

Age and nature of the Budate Group in the Hailar Basin are of great significance in studying the evolution of the Hailar Basin and the Xing’an-Mongolian Orogenic Belt (XMOB). Zircon U-Pb ages of eight volcanic rocks from the Budate Group and two basement granites in the Hailar Basin were reported in this study. The dating results indicated that the formation of these volcanic rocks was consistent with the emplacement of Late Paleozoic basement granite in age (356–290 Ma), i.e., Early Carboniferous to Early Permian rather than Early Mesozoic. Combined with regional geology, it was concluded that the Budate Group is the component of the basement of the Hailar Basin, and these volcanic rocks were formed at an active continental margin, which is related to the closure of the Hegen Mountains suture zone. The captured Neoproterozoic zircons (814–873 Ma) were probably derived from the Neoproterozoic basement materials in the Ergun Block, implying the close genetic relationships between the Ergun Block (including the Hailar Basin) and the Siberian Block.

The provenance of the southeastern Yellow Sea sediments constrained by detrital zircon U–Pb age

Abstract U–Pb ages of detrital zircon grains collected from sandy sediments in the southeastern Yellow Sea were analyzed to infer their provenance. The zircon age spectra show E–W direction differences with a wide age range from Early Cenozoic to Late Archean; the western samples were dominated by Paleozoic to Neoproterozoic zircons, whereas the eastern samples by Paleoproterozoic zircons. This age distribution suggests diversity of age populations in the source terranes and changes in sediment supply to the sample locations. Comparison of these results with the basement rock geology and detrital zircon ages of river sediments in the surrounding land areas indicates that the eastern and western parts of the southeastern Yellow Sea sandy sediments were mainly supplied from the Korean Peninsula and southern China along with now-submerged shelf bedrocks, respectively, with a mixing zone in the middle. Differences in zircon age populations resulted from the change of proportions in sediment supply from two dominant provenances due to sea-level rising and associated reworking during the Holocene transgression.

Detrital zircon geochronology and polycyclic sediment sources, Upper Jurassic – Lower Cretaceous of the Scotian Basin, southeastern Canada 1This article is one of a series of papers published in this CJES Special Issue on the theme of Mesozoic–Cenozoic geology of the Scotian Basin.

Sources of Tithonian–Albian sediment in the Scotian Basin are interpreted from detrital zircon geochronology to test previous hypotheses about the sources and pathways of sediment to thick deltaic successions that are important hydrocarbon reservoirs. Sediment provenance influences reservoir quality, but also provides information on tectonism during rifting of the North Atlantic Ocean. More than 760 zircons were dated by laser ablation U–Pb methods from nine offshore wells and one borehole on land and were characterized by external morphology, internal zoning, and Th/U ratio. A Meguma terrane source to the LaHave Platform was confirmed by peaks in detrital zircon abundance at 550–650 Ma, 1.0–1.2 Ga, and ∼2.1 Ga. Samples from the Sable Subbasin show a large peak in detrital zircon abundance at ∼1050 Ma, with lower peaks from 400–650, ∼1480, ∼1650, ∼1860 Ma and 2.7 Ga, characteristic of inboard Appalachian terranes of Laurentide affinity. Many late Paleozoic to Neoproterozoic zircons are euhedral or subhedral, and apparently first cycle, as are a few older zircons that indicate transport from the rising rift shoulder in southern Labrador as far north as the Makkovik Province (∼1860 Ma). About half the zircons are rounded and polycyclic. Samples from the Abenaki Subbasin are similar, but late Paleozoic to Neoproterozoic zircons are rare and ∼40% of the Mesoproterozoic zircons are subhedral, implying a different Laurentide source through the Humber valley. Euhedral–subhedral unzoned zircons yielded two groups of Cretaceous dates: ∼105 Ma from the Cree Member, and ∼120 Ma from the Missisauga Formation.

U–Pb LA-ICP-MS detrital zircon ages from the Cambrian of Al Qarqaf Arch, central-western Libya: Provenance of the West Gondwanan sand sea at the dawn of the early Palaeozoic

Detrital zircons from various stratigraphic levels of the sandstone-dominated Cambrian Hasawnah Formation of the Al Qarqaf Arch type area (central-western Libya, Saharan Metacraton area) were geochronologically investigated for the first time by LA-ICP-MS techniques for U, Th, and Pb isotopes. Of 720 analyzed grains, 329 were concordant. Of the total, about 60% of the U–Pb zircon ages are Neoproterozoic and earliest Cambrian and cluster at c. 700–680, 670–650, 615–610, 590, 570–560, and c. 540–525Ma. These zircon populations are interpreted as detrital material derived from the Pan-African and possibly to a smaller proportion from the Cadomian orogen situated marginal to northwestern Gondwana. A few slightly older Neoproterozoic ages (c. 950–750Ma) point to rifting events related to the dispersal of the Rodinia supercontinent. A minority of zircons became formed during the configuration of Rodinia and cluster around the Mesoproterozoic–Neoproterozoic boundary (1039±11, 1006±12 and 993±13Ma). Further, some early Mesoproterozoic zircon ages had been found (1592±39 and 1475±20Ma). The potential source area for the Mesoproterozoic zircons is interpreted to have been far distant from the Al Qarqaf Arch, probably concealed within the Arabian–Nubian Shield or situated in Chad, or in the Congo and Tanzania cratons. There is still no evidence for the existence of massive Mesoproterozoic crust in the Saharan Metacraton area. A considerable proportion (28%) of zircons represents Palaeoproterozoic populations at c. 2.4–2.3Ga, and c. 2.2–1.6Ga. Less than 5% of all zircons are Archaean in age (c. 3.4–3.25Ga, c. 2.95–2.7Ga, c. 2.6–2.5Ga). A potential source area for Palaeoproterozoic and Archaean zircon grains is the West African Craton and the western part of the Saharan Metacraton. The best candidates for the main source region for the sandstones of the Hasawnah Formation in the Al Qarqaf Arch type area are the Neoproterozoic–early Cambrian orogens of the Pan-African cycle in the Trans-Saharan Belt (Pharussian and Dahomeyean belts) and of the peri-Gondwanan terranes (Cadomia). This conclusion is in accordance with published data from the Hoggar (Tassilis, Algeria) and from southwestern (eastern Murzuq Basin) and southeastern Libya (Al Kufrah Basin). In comparison to the strong input of Neoproterozoic zircon grains, input from the Palaeoproterozoic and Archaean sources of the cratonic basement (Saharan Metacraton and West African craton) is relatively limited. The exact source of the exotic Mesoproterozoic zircons remains problematic. The presented data lead to the conclusion that the centre of early Palaeozoic thermal subsidence in central-northern Africa has to be located in the region of the Saharan Metacraton. The distinct unconformity at the base of the Cambrian Hasawnah Formation indicates major uplift and considerable denudation in the latest Neoproterozoic to early Cambrian time interval. Because of the conspicuous maturity of the Hasawnah Formation siliciclastic deposits, a coeval intense chemical weathering under warm to humid climatic conditions in low to moderate southern latitudes and the formation of a Gondwanan peneplain is indicated.

Structural and geochronological constraints on the evolution of the eastern margin of the Tanzania Craton in the Mpwapwa area, central Tanzania

A study of the position, nature and geochronology of the eastern margin of the Tanzania Craton near Mpwapwa yields new constraints on Archaean to Neoproterozoic orogenesis of central Tanzania. The eastern part of the craton comprises typical Neoarchaean grey granodioritic orthogneisses dated with the LA-ICP-MS method by U–Pb zircon at ca. 2.7Ga. A gradual eastward increase in strain in these rocks culminates in a 1–2km wide, locally imbricated, north–south-trending, ductile thrust/shear zone with an oblique top-to-the-NW sense of movement. East of the craton-edge shear zone, high-grade supracrustal rocks are termed the “Mpwapwa Group” in view of uncertain regional correlations. There is an apparent lithological zonation of the Mpwapwa Group parallel to the craton margin shear zone. In the west, the group consists of typical “shelf facies” metasedimentary rocks (marbles, calc-silicates, quartzites, etc.). U–Pb dating of detrital zircons from two quartzites reveal only Archaean detritus, constraining their maximum depositional age to <ca. 2.6Ga. The shelf rocks pass eastwards into semi-pelitic gneisses interlayered with bimodal mafic-felsic gneisses, which may have volcanic protoliths and are intruded by multiple mafic sills. Dating of a felsic gneiss showed it to probably be a Neoarchaean rock which underwent Palaeoproterozoic metamorphism during the Usagaran event at ca. 1930Ma. This date likely represents initial juxtaposition of the (Archaean) Mpwapwa Group against the Tanzania Craton. Consequently the Group are not considered to be stratigraphic correlates of the Usagaran Konse Group or Isimani Suite seen further south, but rather form part of the Neoarchaean crust of the “Western Granulite” terrane of the East African Orogen. The Mpwapwa Group was intruded by weakly foliated biotite granite at 1873±31Ma. Zircons in the granite have metamorphic rims dated between 550 and 650Ma that grew during the East African orogenic event.Distinctive para- and orthogneisses, including charnockite dated at 2707±21Ma, outcrop in the southern part of the area. A sliver of southern tonalitic orthogneiss, entrained in the craton margin shear zone, is an igneous rock of probable early Palaeoproterozoic or Archaean age (>ca. 2300Ma) with a strong metamorphic overprint at ca. 1960Ma (zircon), confirmed by a metamorphic titanite age of ca. 1990Ma, again believed to date the initial phase of craton-margin shearing and juxtaposition of the Archaean crustal blocks. The role of the Neoproterozoic East African orogeny in the evolution of the craton margin is unclear, but the geometry of the shear zone, the presence of Neoproterozoic zircon rims in the Palaeoproterozoic granite and published studies from nearby, all suggest that the latest movements on the shear zone may be Neoproterozoic in age and that the structure may represent the local western front of the East African Orogeny.

U–Pb ages and trace elements of detrital zircons from Early Cretaceous sedimentary rocks in the Jiaolai Basin, north margin of the Sulu UHP terrane: Provenances and tectonic implications

The Dabie–Sulu orogen in east-central China is the largest UHP belt in the world. Many studies have dealt with detrital minerals from sedimentary basins surrounding the Dabie belt in order to constrain the tectonic unroofing of this terrane. On the other hand, still few are the works focused on detritals from the basins associated with the Sulu belt. The Jiaolai basin, adjacent to the Sulu belt, is made of Mesozoic sedimentary rocks. Two sandstone samples collected from the Early Cretaceous Laiyang Group in the northern and southern margins of the Jiaolai basin were selected for zircon U–Pb dating and trace element analysis. The zircons show main U–Pb age clusters at ca. 2500–2400, 2000–1700, 850–700, and 330–130Ma, with a minor peak at ca. 1100Ma and a few Archean ages. Most zircons show texture features reflecting a magmatic origin, whereas several late Paleoproterozoic and Triassic zircons show homogeneous CL images and low Th/U ratios, indicating a metamorphic origin. The Neoproterozoic ages are consistent with the protolith ages of the metamorphic rocks in the Sulu terrane, implying that the Sulu tarrane may be a major source for this component. Whereas most Neoproterozoic zircons are euhedral to subhedral or angular in shape and are not surrounded by overgrowths, this implies that low-grade metamorphic Neoproterozoic metaigneous rocks ocurring along the northern margin of the Sulu terrane or metasediments overlying the HP–UHP rocks in the Sulu terrane might provide source materials to these detrital zircons. The late and early Paleoproterozoic age peaks are consistent with the thermal events occurred in the Jiaobei terrane, slightly younger than those in the Yangtze Block. These suggest that the Jiaobei terrane was a potential source for the Paleoproterozoic to Archean detrital zircon components. Only two early Paleozoic zircon grains were found in the studied samples, indicating the early Paleozoic arc did not extend into the Sulu terrane. According to the distribution of different kinds of rock adjacent to the Sulu terrane, the Early Cretaceous detrital zircons may be potentially derived from Cretaceous plutons from the Sulu belt. Eight detrital zircons including six metamorphic grians and two metamorphic overgrowth rims yield the Triassic ages, which might be derived from HP–UHP rocks from the Sulu terrane. A metamorphic overgrowth rim yields a metamorphic age of 246±3Ma, probably recording the timing of the prograde metamorphism of the Sulu terrane. One metamorphic grain yields an age of 212±2Ma, which is interpreted to record a retrograde metamorphic event. Based on the REE patterns, the remaining six Triassic analyses can be subdivided into two groups. Four of them record a weighted mean age of 230±6Ma and show nearly flat HREE patterns and slight negative or positive Eu anomalies. The last two grains are enriched HREE; considering their ages and the REE patterns, it is suggested that they may originate from other diverse UHP rocks. The Triassic metamorphic zircons were detected in the Laiyang Group, indicating that the Sulu UHP rocks were exposed to the surface before the Early Cretaceous.

Evolution and provenance of Neoproterozoic basement and Lower Paleozoic siliciclastic cover of the Menderes Massif (western Taurides): Coupled U–Pb–Hf zircon isotope geochemistry

In the Menderes Massif (western Taurides) a Neoproterozoic basement comprising metasediments and intrusive granites is imbricated between Paleozoic platform sediments. U–Pb–Hf zircon analyses of Menderes rock units were performed by us using LA-ICP-MS. The U–Pb detrital zircon signal of the Neoproterozoic metasediments is largely consistent with a NE African (Gondwana) provenance. The oldest unit, a paragneiss, contains significant amounts (~30%) of Archean-aged zircons and εHf (t) values of about a half of its Neoproterozoic zircons are negative suggesting contribution from Pan-African terranes dominated by reworking of an old crust. In the overlying, mineralogically-immature Core schist (which is still Neoproterozoic), the majority of the detrital zircons are Neoproterozoic, portraying positive εHf (t) values indicating derivation from a proximal juvenile source, resembling the Arabian–Nubian Shield.The period of sedimentation of the analyzed metasediments, is constrained between 570 and 550Ma (Late Ediacaran). The Core schist sediments, ~9km thick, accumulated in less than 20My implying a tectonic-controlled sedimentary basin evolved adjacent to the eroded juvenile terrane. Granites, now orthogneisses, intruded the basin fill at 550Ma, they exhibit ±0 εHf (t=550Ma) and TDM ages of 1.4Ga consistent with anatexis of various admixtures of juvenile Neoproterozoic and Late Archean detrital components. Granites in the northern Arabian–Nubian Shield are no younger than 580Ma and their εHf (t) are usually more positive. This implies that the Menderes does not represent a straightforward continuation of the Arabian–Nubian Shield.The lower part of the pre-Carboniferous silisiclastic cover of the Menderes basement, comprises a yellowish quartzite whose U–Pb–Hf detrital zircon signal resembles that of far-traveled Ordovician sandstones in Jordan (including 0.9–1.1Ga detrital zircons), supporting pre-Triassic paleorestorations placing the Tauride with Afro-Arabia. The detrital signal of the overlying carbonate-bearing quartzitic sequence indicates contribution from a different source: the majority of its detrital zircons yielded 550Ma and ±0 εHf (t=550Ma) values identical to that of the underlying granitic gneiss implying exposure of Menderes-like granites in the provenance.260–250Ma lead-loss and partial resetting of the U–Pb system of certain zircons in both basement and cover units was detected. It is interpreted as a consequence of a Permian–Early Triassic thermal event preceding known Triassic granitoid intrusions.

U–Pb and Lu–Hf isotopes in detrital zircon from Neoproterozoic sedimentary rocks in the northern Yangtze Block: Implications for Precambrian crustal evolution

A combined study of Lu–Hf isotopes and U–Pb ages for detrital zircons from sedimentary rocks can provide information on the crustal evolution of sedimentary provenances, and comparisons with potential source regions can constrain interpretations of paleogeographic settings. Detailed isotopic data on detrital zircons from Neoproterozoic sedimentary rocks in the northern part of the Yangtze Block suggest that these rocks have the maximum depositional ages of ~750Ma, and share a similar provenance. In their source area, units of late Archean (2.45 to 2.55Ga) to Paleoproterozoic (1.9 to 2.0Ga) U–Pb ages made up the basement, and were overlain or intruded by magmatic rocks of Neoproterozoic U–Pb ages (740 to 900Ma). Hf isotopic signatures of the detrital zircons indicate that a little juvenile crust formed in the Neoarchean; reworking of old crust dominates the magmatic activity during the Archean to Paleoproterozoic, while the most significant juvenile addition to the crust occurred in the Neoproterozoic. Only the Neoproterozoic zircon U–Pb ages can be matched with known magmatism in the northern Yangtze Block, while other age peaks cannot be correlated with known provenance areas. Similar zircon U–Pb ages have been obtained previously from sediments along the southeastern and western margins of the Yangtze Block. Thus, it is suggested that an unexposed old basement is widespread beneath the Yangtze Block and was the major contributor to the Neoproterozoic sediments. This basement had a magmatic activity at ~2.5Ga, similar to that in North China; but zircon Hf isotopes suggest significant differences in the overall evolutionary histories between the Yangtze and North China.