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Detrital U-Pb zircon age dating and grain morphometrics were used for provenance and maximum deposition age determination for the Lower Permian Dwyka and Middle to Upper Permian Ecca groups of southern Namibia's Aranos and Karasburg basins. Thirteen sedimentary samples and one ash fall sample were analysed using laser ablation – single collector – inductively coupled plasma – mass spectrometry (LA-ICP-MS). The results reveal prominent Cambrian to Neoproterozoic (500–750 Ma), a Lower Neoproterozoic to Mesoproterozoic (950–1300 Ma), and Upper Palaeoproterozoic (1775–1950 Ma) detrital zircon age populations. Multiple evidence (e.g. roundness of investigated zircon grains and ƐHf values) suggest the zircon populations are part of a Gondwana-wide recycling system, where basins act as intermediate reservoirs and eventual dispersers. Classic source to sink dynamics do not apply. A Permian age population (ca. 260–296 Ma) consisting of typically euhedral zircon grains is assumed to be derived directly from protolith rocks. Because no felsic Permian rocks are exposed in the southern African region, these findings suggest a significant input by ash fall from an unknown source, which may be linked to the southern Gondwanan arc volcanism during Permian times. The results reveal a ca. 36 Ma duration of the evolution of the Karasburg Basin and a shorter ca. 30 Ma lasting evolution of the Aranos Basin. The stratigraphic oldest datable unit is an ash bed of the Ganigobis Shale Member of the Zwartbas Fm (Dwyka Group) which gave a maximum deposition age of ca. 296 Ma, whereas the Aussenkjer Fm represents the uppermost Namibian Karoo-aged strata with a maximum age of deposition of ca. 260 Ma. [ABSTRACT FROM AUTHOR]

Eight samples from Oligocene sedimentary rocks of the Marseille-Aubagne basins have been analysed for their detrital zircon age spectra. These age spectra provide information about the regional evolution, from Oligocene to Archaean times. The Carboniferous Variscan and the Late Cretaceous to Eocene Pyreneo-Provençal belts represent the latest main tectonic, magmatic, and volcanic events that formed the major zircon age populations found in studied sediments. The obtained detrital zircon age record of the Marseille-Aubagne basins comprises eleven detrital zircon age clusters. They reflect the long and complex geologic history of the sediments source areas and can be ascribed to the opening of the western Mediterranean, the Variscan, Cadomian and Pan-African belts, to an unknown Mesoproterozoic event, to the Eburnean orogeny of West Africa and to the different tectono-metamorphic events that took place in Archaean times. In general, the Palaeo- and Mesozoic events are ascribed to the dispersal of Western and Eastern Gondwana and the Pangaean supercontinent cycle. Thus, the successive recycling of zircon grains from older and the incorporation of them to younger belts lead to new geodynamical models for the northern Gondwana margin evolution. Significant amounts of Mesoproterozoic detrital zircon are at odds with previous hypotheses and re-open the question of the provenance of these zircon age populations. Therefore, this tiny tertiary basin is a natural archive which records the main geological events in SE France and its vicinity. [ABSTRACT FROM AUTHOR]

The basement of the Saxo-Thuringian Zone consists of Upper Neoproterozoic (c. 650-570 Ma) Cadomian arc sediments (Lusatian greywackes) and voluminous intrusions of Early Cambrian granitoids with ages of c. 540 Ma (Lausitz Block and Karkonosze-Izera Massif). The latter basement complexes comprise several c. 505 Ma granites, granodiorites, and gneisses emplaced during the change from a collisional tectonic setting to rift-related geotectonics. We present a new age for the Rumburk granite of 504 ± 3 Ma linking Late Cambrian plutonism at the northern margin of Gondwana with the initial phase of a Cambro-Ordovician rift event. Trace element analysis points to a linkage of the Rumburk granite with other Late Cambrian aged rocks of the Karkonosze-Izera Massif. Furthermore, geochemical data also provide evidence of a melting and recycling of Lusatian greywackes by the intrusion of the Rumburk granite. The youngest age peak of the Rumburk granite at c. 504 Ma is considered to be the age of emplacement. Older inherited age populations at c. 540 and c. 610 Ma are present and likely the result of a melting and recycling of Lusatian granitoids and greywackes. The appearance of Neoproterozoic inheritance and Lu-Hf similarities with the Rumburk granite strongly suggest the Lusatian greywackes as source rocks. There is a significant age gap of c. 35 Ma between Cambrian plutonic and volcanic rocks in Saxo-Thuringia. Hence, we consider two distinct pulses of magmatic activity during the transition from the Cadomian orogeny to the opening of the Rheic Ocean. [ABSTRACT FROM AUTHOR]

Zircon grains extracted from S-type granites of the Mêda-Escalhão-Penedono Massif (Central Iberian Zone, Variscan Orogen) constrain the timing of emplacement and provide information about potential magma sources. Simple and composite zircon grains from three samples of S-type granite were analyzed by LA-ICP-MS. New U-Pb data indicate that granites crystallized in the Bashkirian (318.7 ± 4.8 Ma) overlapping the proposed age range of ca. 321-317 Ma of the nearby S-type granitic rocks of the Carrazeda de Anciães, Lamego and Ucanha-Vilar massifs. The timing of emplacement of such S-type granites seems to coincide with the waning stages of activity of a D extensional shear zone (i.e. Pinhel shear zone) developed in metamorphic conditions that reached partial melting and anatexis (ca. 321-317 Ma). Dykes of two-mica granites (resembling diatexite migmatite) are concordant and discordant to the compositional layering and S (main) foliation of the high-grade metamorphic rocks of the Pinhel shear zone. Much of the planar fabric in these dykes was formed during magmatic crystallization and subsequent solid-state deformation. Field relationships suggest contemporaneity between the ca. 319-317 Ma old magmatism of the study area and the switch from late D extensional deformation to early D contractional deformation. Inherited zircon cores are well preserved in these late D-early D S-type granite plutons. U-Pb ages of inherited zircon cores range from ca. 2576 to ca. 421 Ma. The spectra of inherited cores overlap closely the range of detrital and magmatic zircon grains displayed by the Ediacaran to Silurian metasedimentary and metaigneous rocks of the Iberian autochthonous and parautochthonous domains. This is evidence of a genetic relationship between S-type granites and the host metamorphic rocks. There is no substantial evidence for the addition of mantle-derived material in the genesis of these late D-early D S-type granitic rocks. The εNd arrays of heterogeneous crustal anatectic melts may be just inherited from the source, probably reflecting mixing of a range of crustal materials with different ages and primary isotopic signatures. The generation of the Bashkirian S-type granites has been dominated by continental crust recycling, rather than the addition of new material from mantle sources. [ABSTRACT FROM AUTHOR]

Ediacaran and Early Cambrian sedimentary rocks from NW Iberia have been investigated for detrital zircon U-Pb ages. A total of 1,161 concordant U-Pb ages were obtained in zircons separated from four Ediacaran samples (3 from the Cantabrian Zone and one from the Central Iberian zone) and two Lower Cambrian samples (one from the Cantabrian Zone and one from the Central Iberian Zone). Major and trace elements including REE and Sm-Nd isotopes were also analyzed on the same set of samples. The stratigraphically older Ediacaran sequence in the Cantabrian Zone has a maximum sedimentation age of ca. 600 Ma based on detrital zircon content and is intruded by ca. 590-580 Ma granitoids constraining the deposition of this part of the sequence between ca. 600 and 580 Ma. The stratigraphically younger Ediacaran sequence in the Cantabrian Zone has a maximum sedimentation age of ca. 553 Ma. The Ediacaran sample from the Central Iberian Zone has an identical within error maximum sedimentation age of ca. 555 Ma. The detrital zircon U-Pb age patterns are very similar in all the Ediacaran samples from both zones including the main age groups ca. 0.55-0.75 Ga, ca. 0.85-1.15 Ga and minor Paleoproterozoic (ca. 1.9-2.1 Ga) and Archean (ca. 2.4-2.6 Ga) populations. Kolmogorov-Smirnov statistical tests performed on this set of samples indicate that they all were derived from the same parent population (i.e., same source area). The same can be said on the basis of Nd isotopes, REE patterns and trace element concentrations. The two Cambrian samples, however, show contrasting signatures: The sample from the Cantabrian Zone lacks the ca. 0.85-1.15 Ga population and has a high proportion of Paleoproterozoic and Archean zircons (>60 %) and a more negative ε and higher T values than the Ediacaran samples. The Early Cambrian sample from the Central Iberian Zone has the same U-Pb detrital zircon age distribution (based on KS tests) as all the Ediacaran samples but has a significantly more negative ε value. These data suggest apparently continuous sedimentation in the NW Iberian realm of northern Gondwana between ca. 600 and 550 Ma and changes in the detrital influx around the Ediacaran-Cambrian boundary. The nature and origin of these changes cannot be determined with available data, but they must involve tectonic activity on the margin as evidenced by the angular unconformity separating the Ediacaran and Lower Cambrian strata in the Cantabrian Zone. The absence of this unconformity and the apparent continuity of detrital zircon age distribution between Ediacaran and Cambrian rocks in the Central Iberian Zone suggest that the margin became segmented with significant transport and sedimentation flux changes in relatively short distances. As to the paleoposition of NW Iberia in Ediacaran-Early Cambrian times, comparison of the data presented herein with a wealth of relevant data from the literature both on the European peri-Gondwanan terranes and on the terranes of northern Africa suggests that NW Iberia may have lain closer to the present-day Egypt-Israel-Jordan area and that the potential source of the hitherto enigmatic Tonian-Stenian zircons could be traced to exposed segments of arc terranes such as that described in the Sinai Peninsula (Be'eri-Shlevin et al. in Geology 40:403-406, ). [ABSTRACT FROM AUTHOR]

Abstract: U–Pb geochronology of detrital zircon from Late Ediacaran (Beiras Group greywackes) and Early Ordovician (Sarnelhas arkosic quartzites and Armorican quartzites of Penacova) sedimentary rocks of the southwest Central Iberian Zone (SW CIZ) constrain the evolution of northern Gondwana active-passive margin transition. The LA-ICP-MS U–Pb data set (375 detrital zircons with 90–110% concordant ages) is dominated by Neoproterozoic ages (75% for the greywakes and 60% for the quartzites), among which the main age cluster (more significant for Beiras Group greywackes) is Cryogenian (c.840–750Ma), while a few Mesoproterozoic and Tonian ages are also present (percentages <8%). These two features, and the predominance of Cryogenian ages over Ediacaran ages, distinguish the Beiras Group greywackes (SW CIZ) from the time-equivalent Serie Negra (Ossa-Morena Zone – OMZ), with which they are in inferred contact. The age spectra of the Beiras Group greywackes also reveal three major episodes of zircon crystallisation in the source area during the Neoproterozoic that are probably associated with a long-lived system of magmatism that developed either along or in the vicinity of the northern Gondwana margin at: (1) c. 850–700Ma – Pan-African suture (not well represented in OMZ); (2) c. 700–635Ma – early Cadomian arc; and (3) c. 635–545Ma – late Cadomian arc. Comparison of Neoproterozoic ages and those of the Paleoproterozoic (c. 2–1.8Ga) and Archean (mainly Neoarchean – 2.8–2.6Ga, but also older) in the Beiras Group greywackes with U–Pb ages of Cadomian correlatives shows that: (1) SW CIZ, OMZ, Saxo-Thuringian Zone, North Armorican Cadomian Belt and Anti-Atlas) evolved together during the formation of back-arc basins on the northern Gondwana active margin and (2) all recorded synorogenic basins that were filled during the Ediacaran by detritus resulting from erosion of the West African craton, the Pan-African suture and a long-lived Cadomian magmatic arc. Differences in detrital zircon age populations in the greywackes of the Beiras Group (SW CIZ Cadomian basement) and the Serie Negra (OMZ Cadomian basement) are also observed in their respective overlying Early Ordovician quartzites. Since both these SW Iberia Cadomian basements evolved together along the active margin of Gondwana (but sufficiently separated to account for the differences in their detrital zircon content), this continuation of differing zircon populations into the Early Ordovician suggests that the inferred contact presently juxtaposing the Beiras Group and the Serie Negra is not pre-Early Ordovician and so is unlikely to demonstrate a Cadomian suture. [Copyright &y& Elsevier]

Abstract: The palaeogeographic position of South China in relation to India in the Neoproterozoic is controversial. Resolution of this controversy constrains the reconstruction of Rodinia during its breakup and contributes to our understanding of Snowball Earth. This work compares the Neoproterozoic histories of the Lesser Himalaya in northern India and the Yangtze block in southern China. We present U–Pb LA-ICP-MS ages of detrital zircon grains from six Indian and three Chinese siliciclastic sedimentary rocks, such as sandstones or diamictites/tillites. In total, 1148 grains were analysed from which 833 measurements gave ages with a degree of concordance between 90 and 110%. The correlation of the Indian and the Chinese sections is possible using the tillites of both areas purportedly deposited during the Snowball Earth time interval: the Blaini tillite from India and the Nantuo tillite from China. The U–Pb ages confirm the Marinoan age of the Chinese Liantuo tillite. Although the youngest zircon age for the Indian Blaini tillite is about 678Ma, the Marinoan age is indicated by the presence of a typical Marinoan white to bright yellowish overlying cap carbonate. In addition to the tillites, representative detrital zircon ages from over- and underlying clastic rocks were determined. The Chinese samples are dominated by zircons with Neoproterozoic ages with a main peak between ca. 750Ma and ca. 950Ma and are characterised by the absence of Archaean ages. The Indian samples contain abundant Neoproterozoic zircon grains, but also contain Mesoproterozoic to Archaean zircons. For all samples, a local source area that provided the Neoproterozoic zircons is likely. A synchronous Neoproterozoic magmatic event in both cratons probably reflects the breakup of the supercontinent Rodinia and therefore the same tectono-magmatic event. Our results indicate a similar history for India and South China which both underwent at least one synchronous episode of crustal growth during the Neoproterozoic. In addition, our data set shows that both passive margin clastic sequences had the same source area for all zircons older than Neoproterozoic. Therefore we infer that India and South China were close to each other and along the same passive margin during the breakup of Rodinia in the Late Neoproterozoic. [Copyright &y& Elsevier]

The Variscan granites from the Western Erzgebirge were repeatedly dated by various methods, but no consensus has been reached about their exact intrusion ages. This study presents a multi-dating approach for the four largest intrusions from the Western Erzgebirge (Aue-Schwarzenberg, Bergen, Eibenstock, Kirchberg). We analysed several samples from each pluton/suite with zircon U–Pb CA-ID-TIMS (chemical abrasion-isotope dilution-thermal ionization mass spectrometry) to obtain robust temporal information on their age and tempo of intrusion. These data enable us for the first time to define three intrusive episodes of 1–2 Ma each, separated by quiet periods of several Ma. The Aue-Schwarzenberg suite represents the oldest granites that intruded at ~323–322 Ma followed by the granites from Bergen and Kirchberg 2–4 Ma later. The highly evolved ore-bearing granites from the Eibenstock pluton intruded after a time lag of ~5 Ma at ~315–314 Ma. The new data show that there is a resolvable age difference between the two known granite groups. Granite group 2 (also assigned as younger igneous complex, represented by the Eibenstock pluton) is ≥5 Ma younger than granite group 1 (assigned as older igneous complex, represented by granites from Aue-Schwarzenberg, Bergen and Kirchberg). Protracted magmatism and late-/post-magmatic fluid flow partly reset the U–Pb system of these granites to variable degrees, making a precise and accurate dating of their intrusion ages challenging. Pb loss in zircons is often combined with high common Pb (Pb c). SHRIMP/SIMS (sensitive high mass resolution ion microprobe/secondary ion mass spectrometry) and LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) on non-CA zircons document that Pb loss and high Pb c is quite variable within zircon grains and may be located in micro-fractures. We demonstrate that chemical abrasion (CA) clearly minimizes or removes both Pb loss and Pb c. Results from prior LA-ICP-MS and SHRIMP dating on non-CA zircons from the same samples considerably helped the interpretation of the CA-ID-TIMS data when Pb loss was not completely erased by CA. In such cases we often had to choose the oldest analyses for mean age calculation in contrast to the common practice of the CA-ID-TIMS community to choose the youngest dates. Rb–Sr and Ar–Ar dating systems revealed age differences between the older group and the younger ore-bearing granites albeit with diverging absolute ages. Most Ar–Ar ages are identical with CA-ID-TIMS ages and would imply rapid cooling. However, samples from the older group have excess Ar that could have led to too old ages. In contrast, Rb–Sr ages for the older granites are 0–7 Ma younger than their intrusions. Fluid induced alteration led to the formation of Li-mica, fluorite and cassiterite (greisenization). For the youngest granite (Eibenstock), Li-mica was used to date the first greisenization. Samples without visible hydrothermal overprint yielded identical Ar–Ar and Rb–Sr ages as severely greisenized samples. This implies re-equilibration due to the hydrothermal overprint for all Ar–Ar and Rb–Sr ages from the Eibenstock pluton. According to Ar–Ar dating, the first ore formation (~315 Ma) is coeval with the CA-ID-TIMS intrusion age of the Eibenstock granite while it is delayed by ~6 (±3) Ma according to Rb–Sr dating (308 ± 3 Ma). [ABSTRACT FROM AUTHOR]

• Ages of detrital zircons on two formations belonging to the Kibaran belt provide more younger ages (1180 and 1120 Ma) than previously expected. • This younger part of the Kibaran belt could be considered as a precursor of the modern Rift branch. The Kibaran Belt is one of the major Mesoproterozoic orogens formed between 1.4 and 1.0 Ga during the Rodinia assembly. Despite several decades of geologic investigations, correlations, evolution, and geodynamic models are still under debate. Modern studies distinguish the north-eastern Karagwe-Angkole Belt (KAB) and the southern Kibaran Belt (KIB). A further distinction of the KAB and the poorly studied northwestern Kivu Belt (KVB) has to be suggested. Latest researches in the KAB agree with a separation between a lower unit formed prior to 1375 Ma, and late tectono-magmatic events around 1250 Ma. The KIB model considers a continental collision starting at ∼1.25 Ga with latest tectonic events at ca. 1.00 Ga. A more precise correlation was achieved by U-Pb age determinations on detrital zircon from six samples of the metasedimentary Nya-Ngezie and Bugarama groups. Both of them occur along the Congo, Rwanda and Burundi borders and have frequently been used for interregional correlations despite their unknown age. Detrital zircon grains indicate Archaean to Mesoproterozoic inheritance for the Upper Nya-Ngezie Group (ca. 2800 to ca. 1120 Ma) and a similar age range for the lower Bugarama Group (ca. 2850 to ca. 1207 Ma). Accordingly, the two latest Kibaran-Burundian events of sedimentary deposition and tectonic overprint are younger than ca. 1207 and ca. 1120 Ma. This is inconsistent with prior age estimates for the bulk of formations in the vicinity. Thus, the time frame for the deposition of the numerous formations that have previously been correlated to the Nya-Ngezie and Bugarama groups has to be re-examined. New radiometric data indicate two formations in the western KVB that are younger than in the eastern KAB. Additionally, the detrital zircon record indicates significantly changing source rocks of the Nya-Ngezie deposits through time. Resulting correlations with the belts of the Kibaran-Burundian Orogen, suggest four geological "units", seven tectonic events, five tectono-sedimentary cycles and two different geodynamic "models". Additionally, three early, middle and late Kibaran belts are proposed. This allows proposing a reconciling model including a plate tectonic model to the West (KVB and KIB) and a coeval extensive model in the early stage of this orogen (KAB). Finally, the relationships between the N-S elongated structures belonging to the late Kibaran, late pan-African and modern rifting events in the same area are discussed. [ABSTRACT FROM AUTHOR]

Laser ablation ICP-MS U–Pb analyses were conducted on detrital zircons of Triassic sandstone and conglomerate from the Lusitanian basin in order to: i) document the age spectra of detrital zircon; ii) compare U–Pb detrital zircon ages with previous published data obtained from Upper Carboniferous, Ordovician, Cambrian and Ediacaran sedimentary rocks of the pre-Mesozoic basement of western Iberia; iii) discuss potential sources; and iv) test the hypothesis of sedimentary recycling. U–Pb dating of zircons established a maximum depositional age for this deposit as Permian (ca. 296 Ma), which is about sixty million years older compared to the fossil content recognized in previous studies (Upper Triassic). The distribution of detrital zircon ages obtained points to common source areas: the Ossa–Morena and Central Iberian zones that outcrop in and close to the Porto–Tomar fault zone. The high degree of immaturity and evidence of little transport of the Triassic sediment suggests that granite may constitute primary crystalline sources. The Carboniferous age of ca. 330 Ma for the best estimate of crystallization for a granite pebble in a Triassic conglomerate and the Permian–Carboniferous ages (< ca. 315 Ma) found in detrital zircons provide evidence of the denudation of Variscan and Cimmerian granites during the infilling of continental rift basins in western Iberia. The zircon age spectra found in Triassic strata are also the result of recycling from the Upper Carboniferous Buçaco basin, which probably acted as an intermediate sediment repository. U–Pb data in this study suggest that the detritus from the Triassic sandstone and conglomerate of the Lusitanian basin is derived from local source areas with features typical of Gondwana, with no sediment from external sources from Laurussia or southwestern Iberia. [ABSTRACT FROM AUTHOR]

The Permo-Carboniferous glacial Dwyka Group deposits in Namibia provide the first evidence for high sedimentation rates caused by a Carboniferous/Permian extensional stress regime in southern Gondwana, which eventually led to the opening of the southern Atlantic Ocean in the Early Cretaceous. Besides palaeocurrent direction measurements, the use of U–Th–Pb data in combination with morphometrics of detrital and magmatic zircons is a not well studied approach to determine fluxes and reworking processes of glacial and marine clastic sediments. Roundness values of 7–8 for the investigated zircon grains are very common, suggesting long transport distances and/or multiple recycling. In addition, abundant scratches and collision marks indicate high energy environments during transport. Only one ash bed and one sandstone sample featured low roundness values and smooth zircon surfaces, indicating low transport energies. Zircon ages from all concordant analyses can be clustered into several groups: Cryogenian to early Cambrian (c. 0.7–0.5 Ga; 15%), major early Neoproterozoic to late Mesoproterozoic (c. 0.95–1.25 Ga; 46%), late (1.9–1.7 Ga; 8%) as well as a middle Palaeoproterozoic (2.1–1.9 Ga; 5%) and scarce Archaean (3%). The first age group may be confined to Pan-African magmatic events occurring around the Kalahari Craton margin, whereas the protosource of Mesoproterozoic ages may be the Namaqua Metamorphic Complex. Palaeoproterozoic structural units folded in the course of the Namaqua Orogeny as well as the late Palaeoproterozoic Rehoboth Belt, are possible source areas for the Palaeoproterozoic ages. The youngest zircons from an ash bed were dated at 296.2 ± 2.3 Ma and suggest an Asselian age for the upper Zwartbas Formation (DS II), pointing to a duration of 12 Ma for DS II-IV, assuming a duration of 3–6 Ma for the three uppermost glacio-eustatic cycles. The data suggests that the siliciclastic successions of the Dwyka Group mainly consist of reworked material, with minor input of freshly eroded material. An initial diamictite deposit, possibly induced by a southerly directed ice advance, occurring in the southern part of the Aranos Basin, recycled parts of the Nama Basin fill and covered the latter strata based on the difference in zircon age spectra. All subsequent deglaciation sequences indicate prevalent westward ice movement. A recycling of the detrital zircon grains over several generations is also implied by an increase in mean zircon width/length ratio and width as a function of age. The Permian evolution of southern Gondwana was confined by the occurrence of pre-Dwyka erosional plains and deep glacial scoured valleys reaching into its interior, which were successively covered by extensively recycled material of various protosources and consequently eroded by the Dwyka aged tillites. Image 1 The Aranos Basin is the result of numerous major recycling processes at the southern margin of Gondwana. The Gibeon Formation of the lower Dwyka Group of Namibia features two distinct ice advances and directions. The age of the upper Ganigobis Shale Member (uppermost Zwartbas Formation) is 296.2 ± 2.3 Ma. The three upper glacio-eustatic cycles of the Dwyka glaciation lasted between 3 and 6 Ma. Morphological features of detrital zircon grains are a feasible marker determining sediment transport intensities and are of great interest for further sediment recycling studies. [ABSTRACT FROM AUTHOR]