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Direct dating of vertebrate fossils is difficult due to complex postburial diagenetic processes and the often low and heterogeneous concentration of radioisotopes (e.g., U) in fossilized bone material. Here, we demonstrate a novel approach to dating vertebrate fossils via laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating of early diagenetic calcite cements precipitated within bone cavities of a Jurassic sauropod from the Sichuan Basin, South China. Early diagenetic calcite yielded a U-Pb age of 165.3 ± 3.6/5.6 Ma, in agreement with a maximum depositional age of 165.8 ± 1.0 Ma from detrital zircon ages of the surrounding rocks, suggesting that diagenesis occurred shortly after the death of the sauropod. This new age demonstrates that the best-known Jurassic large sauropod faunas in South China are much older than those in North America and Africa, suggesting the geographical isolation of South China. Authigenic apatite U-Pb dating on the fibrolamellar bones from the same sauropod gave a distinctly younger age, indicating more complex U-Pb system behavior, possibly due to U uptake by residual organic matter and recrystallization of apatite after early diagenesis. Our findings demonstrate that U-Pb dating of calcite cements within bone cavities has significant potential for constraining the burial age of vertebrate fossils, which could aid in constructing a more robust temporal framework for the radiation and evolution of vertebrates. [ABSTRACT FROM AUTHOR]

The Koras Group is a bimodal volcanosedimentary group located in post-tectonic grabens in a foreland thrust complex in the Kaaien Terrane of the Mesoproterozoic Namaqua-Natal Province of southern Africa. It contains two sequences of mafic and felsic volcanic rocks with an unconformity between them, only the lower sequence being slightly folded. The Koras Group was long regarded as having formed at the end of the 1 210 to 1 000 Ma Namaqua Orogeny, because it lacks the severe deformation and metamorphism of the underlying rocks, with igneous minerals preserved in many samples. Following years of unsuccessful attempts to precisely date the volcanic rocks, the first two ion probe U-Pb zircon studies both reported ages of ~1 172 Ma for the Swartkopsleegte Formation felsic lava in the slightly folded lower sequence (based on relatively few dated zircons) and ~1 100 Ma for the Leeuwdraai Formation rhyolite in the undeformed upper sequence. Thus a major 70 m.y. hiatus seemed apparent between the lower and upper sequences despite their similar geochemistry and rift-related setting. This gave rise to models which envisaged the Kaaien Terrane being unaffected by the syn- to late-tectonic deformation, migmatisation and granite intrusions, documented between 1 200 and 1 150 Ma in the adjoining Namaqua-Natal terranes to the west. A high-pressure (10 kbar) metamorphic event, recognised in the Kaaien Terrane basement just south of hardlydeformed Koras Group exposures and dated at 1 150 Ma, is inconsistent with such models. A re-investigation and microbeam dating campaign on the Koras Group confirms the 1 101 ± 2 Ma (n = 6) age for felsic volcanic rocks of the upper sequence, but establishes a new reliable age of 1 114 ± 4 Ma for the lower one (n = 2). The 1 170 ages obtained in the earlier two studies were revisited and are now considered to reflect the age of zircon xenocrysts from the source rocks, which dominate the zircon population of some Swartkopsleegte Formation samples. Several criteria to distinguish autocrystic (magmatic) from antecrystic (age-overlappping xenocrystic) data points were investigated. One sample had high Th levels in only the younger zircons, but histograms of sufficiently precise 207Pb/206Pb ages provided the main criterion. Calculations of zircon crystallisation temperature intervals were not useful in predicting the abundance or proportions of magmatic and antecryst zircons. A multi-episode model of magmatic generation and crystallisation events is probably appropriate. In cases when felsic volcanic samples yield few zircons, care must be taken to avoid the problem exposed in this study. The Koras Group sediments have similar detrital zircon U/Pb age distributions to those of the Rehoboth Basement Inlier. This supports the concept that the Kaaien Terrane originated as the southern part of the Rehoboth Province. [ABSTRACT FROM AUTHOR]

Metamorphic rocks from the Diancang Shan (DCS) complex along the Ailao Shan-Red River belt between the South China plate and Simao-Indochina block are studied in this contribution to constrain the Proto- to Palaeo-Tethys tectonic evolution of the eastern Tethys domain. LA-ICP-MS zircon U-Pb geochronological dating is conducted in this study on the metasedimentary rocks (garnet-biotite-plagioclase gneisses, biotite-quartz schists and phyllonites) from different stratigraphical horizons (Proterozoic and Triassic) of the DCS complex. The analyses yielded three major age peaks at ca. 248 Ma, ca. 441 Ma, ca. 1000–900 Ma and one subordinate age peak at ca. 828 Ma. The youngest ages for the samples help to constrain the maximum ages of deposition of the complex at Early Carboniferous and Late Triassic, respectively. The existence of the diagnostic age peak at ca. 440 Ma and the euhedral-subhedral morphology of the detrital zircons in the Palaeozoic and Mesozoic strata may indicate that there were early Palaeozoic magmatic activities along the eastern margin of the Simao-Indochina block. At the meantime, the age peak at ca. 440 Ma was never reported in the early Palaeozoic strata from the western margin of the South China plate, which supports the existence of an early Palaeozoic rift zone, i.e., the Proto-Tethys Jinsha Jiang-Ailao Shan-Song Ma rift zone, being consistent with geochemical discriminations. Furthermore, we conclude, from the significant difference between detrital zircon age data of Silurian to Devonian sedimentary rocks from the Simao-Indochina block and South China plate, the opening of the Palaeo-Tethys ocean since Early Carboniferous, the absence of evidence for the Palaeozoic orogeny, and the successive sedimentation from the Cambrian to Triassic along the western margin of the South China plate, that the Proto-Tethys rifting and subsequent Palaeo-Tethys ocean evolution along the Jinsha Jiang-Ailao Shan-Song Ma zone formed actually a complete 'Wilson Cycle' from early Palaeozoic to the Late Triassic. [ABSTRACT FROM AUTHOR]

The Lushan Massif has been considered an extensional dome which represents a typical extensional structure in South China. However, the composition and structure of the Lushan Massif are still unclear. In this study, we identified the eastern detachment fault (EDF) for the first time. In addition, many sinistral strike-slip structures have also been recognized in the Lushan area, such as the Xingzi shear zone (XZSZ) and Lianhua shear zone (LHSZ). Detailed field observation and structural analysis revealed that the former sinistral faults are tectonic boundaries of the later Lushan extensional dome (LSED). The tectonic evolution sequence was established after the structural analysis combined with zircon U-Pb dating and mica 40Ar-39Ar dating of metamorphic rocks, veins, and intrusive rocks from the strike-slip fault and detachment fault. The Lushan Massif has undergone sinistral ductile shearing within 162–150 Ma. The LSED was then formed in an extensional tectonic setting from 140 to 114 Ma. Together with the regional geological setting, we believe that the sinistral strike-slip structures, represented by the XZSZ and LHSZ, are coeval with the Tanlu fault system and could be controlled by a transpressional stress field resulting from the subduction of the Pacific Plate. The LSED was formed in a back-arc extension setting resulting from the rollback of a subducted slab. The tectonic transition from compression to extension in the South China Block took place at 150–140 Ma. [ABSTRACT FROM AUTHOR]

The chronostratigraphy of the Bushmanland Ore District and the Namaqua-Natal Province has long been debated, but recent microbeam dating has resolved several issues. An important aspect is the precise age of the sedimentaryexhalative ores and their tectonostratigraphic context. Published constraints on the maximum age of the ores from detrital zircon dating are 1 285 ± 14 Ma (n=4, Gamsberg ore), 1 215 ± 18 Ma (n=6, Wortel Formation) and a tentative 1 118 ± 33 Ma (n=3, Hotson Formation at Black Mountain). The ore is older than the 1 130 ± 35 Ma Koeris Formation metabasalt which unconformably overlies it. Aplite dykes, which intrude the ore of the Black Mountain deposit, provide another potential minimum age constraint on the ore. A sample was dated at 1 175 ± 15 Ma by ion probe U-Pb zircon dating. This shows that the aplite dykes belong to the late-collisional Springputs Suite of granitoids which includes the 1 163 ± 11 Ma Achab and 1 149 ± 15 Ma Hoogoor Gneisses, for which the field relationship with the ores had not been established. The regional M2 metamorphism was recorded in aplite zircon rims at 1 027 ± 9 Ma and at 1 030 ± 6 Ma in monazite and xenotime in the Hotson Formation host rock schists. Detrital zircons, dated by Laser Ablation ICPMS in a host rock schist sample, reflect a dominant Palaeoproterozoic provenance with major age group at 2 003 ± 17 Ma and minor groups at 1 847 and 2 105 Ma. Only 16 analyses were made, which probably accounts for the absence of minor Mesoproterozoic provenance components found in other published datasets. The age of the Black Mountain ore is now constrained between 1 215 ± 18 Ma and 1 175 ± 15 Ma. The tentative 1 118 ± 33 Ma detrital zircon maximum age is shown to be unreliable in view of two younger magmatic rocks with older dates (1 175 and 1 130 Ma). The SEDEX ores thus formed during or just before the ~1 210 Ma assembly of Namaqua terranes and before the ~1 150 Ma syntectonic Springputs Suite granitoid magmatism. [ABSTRACT FROM AUTHOR]

The Tianshui-Sunjiaxia area is located in the connection zone of West Qinling Orogen and North Qilian Orogen, which could provide great insights into the amalgamation processes between the northern and southern blocks of China. Three subduction- and rift-related rocks gneissic granite from North Qilian arc-interarc belt (NQAI) granite and metabasalt from North Qinling back-arc basin (NQBA) are distinguished across the connection zone. The gneissic granite was generated by melts from older crustal materials of Longshan Group with the addition of a relatively juvenile basaltic source from the lower crust during the collision process. The Liwanxincun metabasalt reflects the mixing of the partial melting of the shallow asthenospheric mantle and the metasomatized mantle in a back-arc extension setting. The LA-ICP-MS zircon U-Pb dating of gneissic granite (068, 069) yields crystallization ages of 457.0 ± 1.6 Ma and 445.9 ± 2.1 Ma. The study area is divided into six tectonic units in Early Paleozoic time involving NQAI (Yanjiadian-Xinjie) continental arc, interarc rift basin (Maojiamo-Xiwali), continental arc (Chenjiahe-Wangjiacha); NQBA back-arc rift basin (Huluhe-Hongtubao), island arc and ophiolitic melange belt (North Qinling-Shangdan). A tectonic model is proposed in which the NQAI continental arc (Yanjiadian-Xinjie) might represent the early period of subduction of North Qilian Ocean (NQO) and the interarc rift is the product of the extension triggered by southward subduction of NQO. The ongoing subduction of NQO then leads to the formation of Chenjiahe-Wangjiacha continental arc, as well as the Hongtubao back-arc spreading ridge in NQBA back-arc basin (Huluhe). The tectonic evolution of the connection zone is closely associated with the closure of the North Qilian Ocean and North Qinling-Shangdan Ocean in the context of the convergence process of micro-continental blocks, including North China block, Longshan group and North Qinling Terrane. [ABSTRACT FROM AUTHOR]

Previous U-Pb dating of fossils has had only limited success because of low uranium content and abundance of common Pb as well as element mobility during late diagenesis. We report the first accurate U-Pb dating of fossilized soft tissue from a Pliocene phosphatized bivalve mold using laser ablation-inductively coupled mass spectrometry (LA-ICPMS). The fossilized soft tissue yields a diagenetic U-Pb age of 3.16 ± 0.08 Ma, which is consistent with its late Pliocene stratigraphy and similar to the oldest U-Pb age measured on accompanying shark teeth. Phosphate extraclasts give a distinctly older age of 5.1 ± 1.7 Ma, indicating that they are likely detrital and may have furnished P, promoting phosphatization of the mold. The U-Pb ages reported here along with stratigraphic constraints suggest that diagenesis occurred shortly after the death of the bivalve and that the U-Pb system in the bivalve mold remained closed until the present. Shark teeth collected from the same horizon show variable resetting due to late diagenesis. Data were acquired as line scans in order to exploit the maximum Pb/U variation and were regressed as counts, rather than ratios, in three-dimensional space using a Bayesian statistical method. [ABSTRACT FROM AUTHOR]

The Bengge biotite aegirine‐augite syenite (BAS) is located in the southern part of Yidun Arc, eastern margin of the Tibetan Plateau area. It is an integral part of the Bengge ultrapotassic rocks (UPR), an alkalic complex mainly consisting of BAS, biotite pyroxene syenite (BPS), and biotite syenite (BS). Geochronological studies including zircon LA‐ICPMS U–Pb dating and biotite 40Ar/39Ar dating have been conducted on the Bengge BAS to constrain its emplacement age. The zircon U–Pb dating yields a wide range of ages from 209 ± 2 Ma to 239 ± 2 Ma, with the concordia 206Pb/238U age being 228 ± 8.9 Ma (MSWD = 0.13). Meanwhile, the biotite 40Ar/39Ar dating yields a plateau age of 205.7 ± 1.5 Ma. The whole‐rock Zr‐saturation temperature (Tzir‐sat) of the Bengge BAS has shown to be very low (86 ± 13°C to 634 ± 13°C), which is much lower than Ti‐in‐zircon temperature (>758°C) of the zircons used for U–Pb dating. This indicates that the zircons in the Bengge BAS are inherited, and they were already present in the BAS melts before the melts became Zr‐saturated. Similarly, the Tzir‐sat of the Bengge BPS and BS are 346 ± 14°C ~ 549 ± 13°C and 281 ± 14°C ~ 525 ± 13°C, respectively, which is also too low for magmatic zircon crystallization in the melts. The inherited zircons of Bengge BAS have typical features of magmatic zircon, with high (Sm/La)N ratios (2.54–819), Ce/Ce* ratios (4.77–304) and low La concentration. Low εHf (T) values (−5.0 to 0.42) and high U/Yb (0.67–12.6) values imply that the inherited zircons (209–239 Ma) in the Benge BAS are derived from an early arc‐magma system of the Yidun Arc. The biotite 40Ar/39Ar dating constrains the Bengge BAS emplacement age at 205.7 ± 1.5 Ma, the time when the arc‐magma activity had ceased, and a regional geodynamic transition in the Yidun Arc from convergence to back‐arc spreading had started. [ABSTRACT FROM AUTHOR]

The Bangong–Nujiang suture zone (BNSZ) is the remnants of the Meso-Tethyan main oceanic basin in the Tibetan plateau. It is noted that several microcontinents, e.g., Amdo and Jiayuqiao, occur within the Meso-Tethyan ocean basin. These microcontinents were strongly reworked associated with the subduction and closure of this ancient ocean, thus they play a key role in understanding the evolution of this ocean. In this contribution, we report newly documented Early Jurassic gabbros (ca. 182–175 Ma) from the Amdo microcontinent in the middle segment of the BNSZ. The gabbros can be subdivided into two groups, i.e., OIB (ocean island basalt) and MORB (mid-ocean ridge basalt) groups. The OIB-group gabbros are characterized by highly enriched Nd Hf isotopic characteristics (zircon ε Hf (t) = −11.7 to −8.9; whole-rock ε Nd (t) = −11.0 to −10.1). They are geochemically similar to OIB and are interpreted to be products of the partial melting of a relatively deep mantle source (> 85 km) and subsequent continental crustal inputting. The MORB-group gabbros belong to the tholeiitic series and have similar compositions to those of MORB. They were most likely derived from a depleted mantle source (zircon ε Hf (t) = +3.7 to +16.5; whole-rock ε Nd (t) = +4.9 to +8.1) in a relatively shallow depth (< 85 km). Integrating previous studies with the data presented in this contribution, we suggest that the generation of coeval OIB- and MORB-like gabbros are related to lithospheric delamination after the Qiangtang-Amdo collision and the closure of the Bangong-Nujiang ocean basin. This result will give new constraint on the evolution of the Meso-Tethyan Ocean. • Early Jurassic gabbroic dikes were newly documented in the Amdo microcontinent, central Tibet. • Gabbroic rocks display different geochemical compositions with OIB and MORB features. • Zircon U-Pb dating on gabbroic rocks yielded nearly uniformed ages of 182–175 Ma. • Gabbroic rocks were formed by the lithospheric delamination after the Qiangtang-Amdo collision. [ABSTRACT FROM AUTHOR]

Abstract The provenance of sediments in western Taiwan has been the subject of debate in recent years. Previous investigators, solely based on the U-Pb zircon geochronology for the detrital grains, all advocated the important roles, but with varying emphasis, of drainage systems in the South China Block. Influence of the Changjiang (Yangtze) River from the far-source Yangtze block versus nearby systems like Zhujiang, Minjiang and Jiulongjiang Rivers in the Cathaysia block has been the main issue. However, the fundamental question of whether the provenance is really the South China Block has never been evaluated. Here we report both the U-Pb zircon and Electron MicroProbe (EMP) monazite age data for seven sediment samples from two sides of the Taiwan Strait and synthesize the published data for all these rivers and sedimentary strata in western Taiwan to tackle this problem. The lack of, or insufficient, ~1.8 Ga monazites in the sediments of river mouths for all drainage systems in the South China Block makes them unlikely to be the source of Miocene sediments in western Taiwan where ~1.8 Ga monazite grains occupy 14.5–33.3% of the total age population. With reference to the tectonic evolution of the coastal southeast China-Taiwan region during Early Cretaceous to recent time, we propose a new explanation that invokes a now-concealed microcontinent along the Manila Trench. This microcontinent, probably related to a Paleoproterozoic orogen in Gondwana, eventually collided with the South China Block causing uplift of the easternmost structural element—the Pingtan-Dongshan Metamorphic Belt (PDMB) at ca. 130–120 Ma. It then drifted away sometime after 100 Ma and split into two parts with one becoming today's Palawan-Mindoro terrain of the Philippines. As indicated by the geophysical data near southern Taiwan, the remainder of this split microcontinent had subducted underneath the Philippine Sea plate along Manila Trench as a result of the opening of the South China Sea at ~33 Ma. Both the Peikang and Kuanyin basement highs in the offshore western Taiwan represent the unsubducted remnants of this microcontinent and also the major suppliers of Late Oligocene-Miocene sediments in western Taiwan. On the other hand, the Eocene-Early Oligocene strata of the Hsuehshan Range in central Taiwan show both zircon and monazite age patterns resembling the Eocene-Early Oligocene and recent sediments of the Zhujiang drainage system, indicating the southwestern origin of the protolith Taiwan. This scenario also matches the recent proposition that part of the Central Range belongs to the deep-level accretionary prism of a Miocene subduction system. Highlights • Disputes over the provenance of western Taiwan sediments are reassessed using EMP monazite ages. • Drainage systems in the South China Block are unlikely the major contributors. • A now-concealed microcontinent related to a Paleoproterozoic orogen is the alternative. • Protolith Taiwan was originated from South China carrying pre-Miocene Zhujiang sediments. • Younger sediments were derived from this microcontinent with adjacent basement highs as remnants. [ABSTRACT FROM AUTHOR]

U-Pb geochronology requires knowledge of a precise and accurate value for the 238 U/ 235 U ratio of any mineral or material being dated by this method. It is now well established that the long-accepted value of 137.88 is not representative of most terrestrial materials and that the ratio is variant both between and within samples. As most samples used for chronology have insufficient amounts of U to determine a precise isotopic composition, the U-Pb geochronology community has informally adopted the recommended value of 137.818 ± 0.045 based on a single data set of 44 zircons by Hiess et al. (2012). To evaluate the robustness of this value and the true range of U isotopic compositions in U-bearing minerals, we have measured the U isotopic composition of 28 bulk zircon samples as well as several co-existing accessory minerals from rocks with a wide range of ages and geographical distributions. The 238 U/ 235 U ratio of 137.817 ± 0.031 represents the mid-point value of our data with an uncertainty that includes all 28 zircon populations analyzed and their respective uncertainties. This value is indistinguishable from the previously recommended value but with a smaller uncertainty that may reflect the refined analytical methods employed in our study. This result provides confidence to the U-Pb geochronology community that the value recommended by Hiess et al. (2012) is appropriate and that their stated uncertainty appears to be conservative. We find variability in the 238 U/ 235 U ratio of coexisting phases within single samples of up to 2.9 ε-units (parts per 10,000). In addition, our range of U isotopic compositions for zircon is heavier than that reported for bulk continental crust in general and most granitoid intrusive rocks specifically. We attribute these observations to differences in the coordination environment of U in zircon and other U-bearing phases. With the amount of zircon formed in magmatic systems limited by the abundance of Zr, we estimate that the majority of U in granitoid rocks must reside in other phases with a bulk isotopic composition that represents a lighter complement to that of zircon. [ABSTRACT FROM AUTHOR]

Previous studies have shown that radiometric dating of fossils can be complicated by post-fossilisation alteration. A key challenge to obtaining geologically meaningful fossilisation dates in bioapatite is identifying regions that have remained relatively undisturbed since the time of fossilisation. In order to determine whether a geochemical indicator can be used to identify least-disturbed regions, we combine in situ trace element analysis and U-Pb geochronology of fossil teeth from the Arroyo Chijuillita Member, New Mexico, and the Dinosaur Park Formation, Alberta. The reliability of these U-Pb dates is supported by good agreement between the isotope dilution thermal ionization mass spectrometry (61.5 ± 1.6 Ma) and laser ablation ICP-MS (64.2 ± 2.4 Ma) dates for a targeted tooth region. Of fourteen teeth analyzed from these units, two record dates within uncertainty of the depositional age: one has a “diffusion” concave upward cross-sectional yttrium profile, the other a concave downward profile reflective of trace element loss. It was found for teeth from both units that smaller yttrium concentration ranges are correlated with younger U-Pb dates, likely the result of post-fossilisation alteration. A yttrium screen based on this relationship is proposed, and is found to be a better indicator of post-fossilisation open system behaviour in the samples analyzed than other geochemical features thought to be produced during fossilisation. This screen provides a new tool for identifying fossil material least disturbed since fossilisation, facilitating the use of bioapatite to date the time of diagenesis. [ABSTRACT FROM AUTHOR]

U–Pb calcite dating is a powerful tool for the analysis of geological processes as calcite cements are ubiquitous and sensitive markers of diagenesis, fluid-rock interaction, fluid-flow, and fracturing. This technique provides the possibility of constraining the timing and history of deformation in diverse tectonic scenarios. We analyze calcite cement from fossil-shells, rock-matrix, and tectonic veins emplaced in shortened Permian limestone layers of the Chicomuselo fold-thrust belt (CFTB) in southeastern Mexico. We report 99 in situ U–Pb calcite ages with high temporal and structural resolution from fold/fault-related veins and from complexly fractured rocks. Samples selected with structural criteria provide better constraints on specific deformational events, while complexly veined zones provide an inventory of accumulated deformation within small rock volumes. Calcite cement ages cluster in 6 intervals: 290-260 Ma, 255-225 Ma, 210-180 Ma, 170-120 Ma, 60-40 Ma, and 20-5 Ma, associated with (i) Permian carbonate deposition and diagenesis, (ii) CFTB shortening, (iii) Faulting related to the early breakup of Pangea, (iv) Gulf of Mexico rifting, drifting and the Pacific tectonic influence, (v) Paleogene Mexican orogeny, and (vi) Chiapanecan orogeny and Polochic Fault System activity, respectively. All of these are important events in the evolution of the southern margin of the North American plate. This study demonstrates that calcite is resilient and reliable for preserving the history of diverse brittle deformational events imprinted in limestone. [Display omitted] • In situ U–Pb calcite dating in fossils, host rock matrix and veins. • Dating the brittle deformation history of a fold and thrust belt. • Bracketing deformation dating fold/fault-related and randomly oriented veins. • Reactivated structures recorded by dating primary and secondary cements. • Recording deformation at the southern margin of the North American plate. [ABSTRACT FROM AUTHOR]

We studied the feasibility of using laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) for U-Pb dating of vertebrate and invertebrate apatite fossils. Two specimens of Carcharodon Carcharias from Pleistocene (2.58–0.01 Ma) sediments in Baja California peninsula, Mexico, give Gelasian ages of 2.0 ± 0.4 Ma and 2.0 ± 0.6 Ma which are consistent with the palaeontologic record reported for this species suggesting that the U-Pb system in the shark teeth remained closed until the present. Dentine data from an Oligocene (33.9–23.0 Ma) shark tooth, Otodus angustidens , from El Cien Formation, Mexico, give an anomalously young age of 19 ± 0.2 Ma with a low 207Pb/206Pb value of 0.65. This age is largely controlled by a sub-population of anomalously radiogenic data with low concentrations of U and Pb suggesting remobilization of Pb from high to low U domains. Regressing relatively non-radiogenic data from high U and Pb domains using a fixed average crustal value for initial common 207Pb/206Pb gives an age of 28.6 ± 0.2 Ma, which agrees with U-Pb zircon ages from tuff horizons in the sequence. Enamel from the same shark tooth is much lower in U and Pb and shows evidence for substantial mixing with radiogenic Pb from the dentine. Apatite shells from a brachiopod specimen, Lingula cobourgensis, and conodont fossils contain high U concentrations and significant proportions of radiogenic Pb. Some conodont specimens show high Th/U ratios combined with evidence of significant excess 206Pb. The amount of excess 206Pb requires a minimum Th partition coefficient of about 16,000 and likely much higher suggesting enrichment by ion exchange rather than recrystallization. In some cases conodonts with low Th/U can be precisely dated. A specimen of I. simulator gives an age of 302 ± 4 Ma which is consistent with its well constrained Gzhelian range (303.7–298.9 Ma). We conclude that processing LA–ICPMS data at the single cycle level allows more precise absolute dating of fossils. In some cases, separate regression of totally reset and partially reset domains can resolve ages of early and late diagenesis. [ABSTRACT FROM AUTHOR]

Paleoproterozoic metasedimentary successions of the northwestern Canadian Shield provide records of tectonic events, but the definition of depositional ages has proved elusive. Although previously poorly understood, the Montresor belt of western Nunavut yields new insight into the 2.2-1.8 Ga time window. On the basis of U-Pb analyses of detrital zircon in sedimentary rocks and igneous zircon in sills, we conclude that arenite of the lower Montresor group was deposited between 2.194 and 2.045 Ga, and arkose of the upper Montresor group after 1.924 Ga, adding constraints on the Rae cover sequence. The lower Montresor arenite yielded an older group (3.05-2.58 Ga) and a younger, more tightly constrained group (2.194 ± 0.014 Ga). Four of six zircon grains analyzed from a gabbro sill within the lower Montresor have discordant 207Pb/206Pb ages (2.71, 2.66, 2.53, and 2.39 Ga) and are considered to be inherited, whereas two grains provide an age of 2045 ± 13 Ma, interpreted to date crystallization and providing a minimum age for the lower Montresor package. Upper Montresor arkose contains detrital zircon with probability density peaks at 2.55-2.25 and 2.1-1.92 Ga, together with scattered older grains (3.8-2.65 Ga). The youngest grain yields an age of 1924 ± 6 Ma, establishing a maximum age for sandstone deposition. Provenance is inferred to have been from the west, where igneous sources of 2.5-2.3 Ga (Queen Maud block) and 2.03-1.89 Ga (Thelon orogen) are known. Collectively, the new ages suggest a minimum 120 million year gap between deposition of the pre-2045 ± 13 Ma lower and post-1924 ± 6 Ma upper parts of the Montresor group. Similar age constraints may apply to other parts of the Rae cover sequence. [ABSTRACT FROM AUTHOR]

Liaoning Province in China is an area known for the occurrence of numerous copper and/or molybdenum deposits of variable size. However, the age of mineralization and tectonic setting in this region are still a subject of debate. In this study we describe the geology of these deposits and apply zircon U–Pb and molybdenite Re–Os isotopic dating to constrain their ages and define the metallogenic epochs of this province. The Huatong Cu–Mo deposit yields molybdenite Re–Os model ages of 127.6–126.3 Ma and an isochron age of 127.4 ± 0.7 Ma. The Dongbeigou Mo deposit yields molybdenite Re–Os model ages of 132.6–127.1 Ma, an isochron age of 128.1 ± 5.1 Ma, and a zircon U–Pb age of 129.4 ± 0.3 Ma for the associated monzogranite. The granodiorite associated with the Wanbaoyuan Cu–Mo deposit yields a zircon U–Pb age of 128.4 ± 1.1 Ma; the plagiogranite associated with the Yaojiagou Mo deposit yields an age of 167.5 ± 0.9 Ma; and the biotite–plagioclase gneiss from the Shujigou Cu deposit yields an age of 2549.4 ± 5.6 Ma. These results, together with previous geochronology data, show that intense Cu–Mo porphyry and skarn mineralization were coeval with Early–Middle Jurassic and Early Cretaceous granitic magmatism. The former was associated with the orogeny that followed the collision of the Siberian and North China plates and the resulting closure of the palaeo-Asian Ocean, and the latter with rifting that followed the subduction of the palaeo-Pacific Plate and associated lithospheric thinning. Volcanogenic massive sulfide Cu deposit. mineralization took place much earlier, in the late Archaean, and was related to continent–continent collision, palaeo-ocean closure, the formation of a united continental landmass, bimodal volcanism, magma emplacement, and subsequent metamorphism and deformation of syn-collisional granites. [ABSTRACT FROM PUBLISHER]

The Wuliangshan Group occurs to the east of the Lancang giant igneous zone in SW Yunnan, and is mainly composed of low-grade metamorphosed sedimentary rocks. The group has been considered as the syn-orogenic product of the Baoshan with Simao-Indochina blocks. However, its depositional time and provenance remain to be poorly constrained. This paper presents zircon U-Pb dating and Lu-Hf-isotopic data for five representative sandstone samples from the Wuliangshan Group. The detrital grains yield a major age-peak at ∼259 Ma, and four subordinary age-peaks at ∼1 859, ∼941, ∼788, and ∼447 Ma, respectively. Our results suggest that the Wuliangshan metasedimentary sequence was deposited after Middle Triassic rather than previously-thought Cambrian. The detrital zircon age spectrum, along with in-situ Lu-Hf isotopic data suggest that the Wuliangshan Group might be a syncollisional sedimentary product related to the collision of Baoshan with Simao-Indochina blocks. It is inferred that the provenance of the Wuliangshan Group is mainly from the Simao/Yangtze blocks to the east rather than the Baoshan Block or Lancang igneous zone to the west. [ABSTRACT FROM AUTHOR]

The Nan-Uttaradit suture is marked by a narrow N-S trending and discontinuous ophiolite belt in northern Thailand. This suture zone is a mélange composed of gabbro, tholeiitic metabasalt, andesite and radiolarian chert. Samples of gabbro and meta-basalt in the Nan-Uttaradit suture yield zircon U-Pb ages of 311±10 and 316±3 Ma, respectively, interpreted as the crystallization ages of the rocks, suggesting the Nan-Uttaradit Ocean existed in the Late Carboniferous. Our results indicate that the Nan-Uttaradit Ocean co-existed with the Ailaoshan-Jinshajiang Ocean to the north and was probably an along-strike extension of the latter. [ABSTRACT FROM AUTHOR]

It is shown that the granitoids of the Main Kolyma Batholith Belt do not penetrate into the Upper Jurassic deposits of the Yana-Kolyma mesozoids. The applicability of U-Pb SHRIMP zirconometry to the Mesozoic period of geological history is subject to critical analysis. It is concluded that analytical limitations preclude the solution of the concordance-discordance alternative of the obtained datings in the Mesozoic U-Pb isotopic systems by computational approaches. The U-Pb isotopic system is established as highly sensitive to the superimposed processes. Based on the reconciliation of the U-Pb, Rb-Sr, Ar-Ar, and K-Ar geochronometric data, the granitoids of the Kolyma Main Batholith Belt intruded 170-160 Ma ago, while their isotopic systems were transformed 150-140, 135-125, and 100-80 Ma ago. The local SHRIMP zirconometry combined with other isotopic methods can be applied to date igneous rocks by the relic dates, to set the time of intrusion into their isotopic systems, and to predict thermal events not identified yet. The U-Pb SHRIMP zirconometry should not be considered as arbitrary. [ABSTRACT FROM AUTHOR]

The U-Pb geochronological data on detrital zircons from placers confined to Neoproterozoic quartzite-schist sequences, which are widespread in the Kokchetav massif of northern Kazakhstan, are discussed. Detrital zircons (332 grains in total) originate from the ore occurrences in the central, northern, and western parts of the massif. The concordant ages of detrital zircons from all the examined occurrences largely correspond to intervals of 1017-1528, 1628-1946, and 2653-2739 Ma. The obtained data imply that material of quartzite-schist sequences of the Kokchetav massif was provided by Mesoproterozoic, Paleoproterozoic, and Neoarchean rock complexes. The lower age limit determined for these sequences is approximately 1.06 Ga. The dates obtained for detrital zircons are most consistent with events that took place in Laurentia. They correspond to the formation and breakup of the Columbia/Nuna supercontinent (approximately 1650-1580 and 1450-1380 Ma ago, respectively) and formation of the Rodinia supercontinent in the period of 1300-900 Ma ago. [ABSTRACT FROM AUTHOR]

The U–Pb dating system has been widely used in geochronology because the system contains two independent parent/daughter pairs yielding three ages (i.e., 238U/206Pb, 235U/207Pb and 207Pb/206Pb ages) to internally check self-consistency. Among numerous U-bearing minerals, zircon has been recognized as the best mineral for U–Pb geochronology owing to its moderate U content, negligible initial unradiogenic Pb (or common Pb) and occurrence in a wide range of rock types. With the development of Secondary Ion Mass Spectrometry (SIMS) and in situ dating methods, the 238U/206Pb zircon age uncertainty could be achieved at an ∼1% level. However, the 207Pb/206Pb age uncertainty of Phanerozoic zircon is always very poor, when single-collector SIMS is used. The low level precision often hampers effective examination of concordance of young zircon between U–Pb and Pb/Pb ages, which is crucial to the data quality evaluation and chronological interpretations. In this study, we developed a hybrid “dynamic multi-collector U–Pb dating technique”. It takes advantage of both the static multi-collector mode and peak-hopping mono-collector mode. The technique is able to simultaneously measure with high-precision the 207Pb/206Pb ratio as in the static multi-collector mode without trade off in the analytical precision of the 238U/206Pb ratio of the conventional peak-hopping mono-collector mode. Four zircon reference materials (91500, M257, Temora and Plešovice) were measured to demonstrate that this new analytical protocol is able to achieve a higher precision for the 207Pb/206Pb age by a factor of two than the conventional mono-collector mode within the same working time. It is possible to simultaneously obtain the 207Pb/206Pb age and 238U/206Pb age with comparable quality to effectively evaluate the concordance of the U–Pb system for Phanerozoic samples. [ABSTRACT FROM AUTHOR]

U–Pb zircon ages of igneous and metaigneous rocks in orogenic belts provide important information concerning the occurrence and duration of magmatic and metamorphic events whereas detrital zircon ages of metasedimentary sequences place constrains on the sources and deposition ages of supracrustal rocks. With these data, it is possible to compare and establish correlations between different provinces or between domains of the same province. A sufficiently large dataset of U–Pb ages is now available from the Borborema Province, northeastern Brazil, allowing the use of statistical methods to identify age peaks. 210 U–Pb crystallization ages from magmatic rocks and ca. 2300 U–Pb zircon ages of detrital grains from metasedimentary rocks were compiled. The igneous age spectrum shows two large age clusters. The first spans about 300 Ma, from 2.25 Ga to 1.97 Ga. Orthogneissic complexes in the Rio Grande do Norte Domain have ages mainly between 2.22 and 2.15 Ga whereas in the remainder of the province they more commonly range from 2.18 to 2.0 Ga. The long duration of this magmatism is comparable to that of Neoproterozoic and Phanerozoic accretionary/collisional orogens and is inferred to have resulted from amalgamation of preexisting crustal blocks and juvenile material to the active margin of the Rio Grande do Norte Domain. The other large cluster of ages is much narrower, from 650 Ma to 550 Ma, which is more consistent with the duration of orogenesis in collisional belts. Orogenic granitoids older than 600 Ma were not yet identified in the Rio Grande do Norte Domain, perhaps reflecting a thicker lithosphere that delayed initiation of the Brasiliano Orogeny. In contrast with the igneous rock-zircon record, the detrital zircon record requires sources with ages that span almost the whole Proterozoic eon. The presence of zircons ages in the 1.5–1.0 Ga and 0.85–0.65 Ga intervals, which contrasts with their absence, in the first case, or rarity, in the second case, amongst the igneous rocks, may be explained by derivation from igneous sources as yet undiscovered or removed by erosion, and/or by provenance from distal sources. The occurrence of 2.15–2.05 Ga-old detrital zircons in the Rio Grande do Norte Domain and of Tonian zircons in this domain and in the Ceará Central and Médio Coreaú domains imply the inexistence of physical barriers separating the northern and southern domains of the Borborema Province during the Neoproterozoic. The results are consistent with deposition in an intracratonic setting that became the site of lithospheric extension in response to far-field stresses. The ages of the youngest detrital zircons (650–630 Ma) indicate that deposition ended just before or at the beginning of the Brasiliano Orogeny. [ABSTRACT FROM AUTHOR]

Dating the timing of motion on crustal shear zones is of tremendous importance for understanding the assembly of orogenic terranes. This objective is achieved in this paper by combining petrological and structural observations with novel developments in in situ U-Th-Pb geochronology of allanite. A greenschist facies shear zone within the Mont Blanc Massif is documented. Allanite is synkinematic and belongs to the mylonitic assemblage. LA- ICP- MS U-Th-Pb isotope analyses of allanite reveal high contents and highly radiogenic isotopic compositions of the common-Pb component. The use of measured Pb-isotope compositions of associated minerals (feldspars and chlorite) is critical for accurate common-Pb correction, and provides a powerful mechanism for linking allanite growth to the metamorphic assemblage. A mean 208Pb/232Th age of 29.44 ± 0.95 Ma is accordingly taken for synkinematic allanite crystallisation under greenschist facies conditions. This age reflects the timing of the Mont Blanc underthrusting below the Penninic Front and highlights the potential of directly dating deformation with allanite. [ABSTRACT FROM AUTHOR]

The article discusses a study which presents the first uranium-lead (U-Pb) isotope results of detrital zircons from the Riphean Stratotype of the Southern Urals. It tackles detrital zircon age dating which aims to investigate the age data of strata and deposits. The data gathered shows that at first approximation, zircons can be divided into three populations. It adds that the age spectra difference in zircons show that the Bashkir Meganticlinorium formed due to terrigenous material.

The end-Triassic extinction is characterized by major losses in both terrestrial and marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and flood basalt volcanism, existing geochronologic dates have insufficient resolution to confirm eruptive rates required to induce major climate perturbations. Here, we present new zircon uranium-lead (U-Pb) geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over about 600,000 years, indicating expansive volcanism even as the biologic recovery was under way. [ABSTRACT FROM AUTHOR]

The article estimates the age of the rocks of Solzan granitoid massif of the Khamar-Daban Province in Baikal, Russia using uranium-lead dating method. It analyzes the composition of the massif in the eastern which include granodiorite-gneiss and granite with amphibole, biotite, or garnet in dependence on the composition of host gneiss. It examines the accessory zircons that were extracted from samples representing biotite and garnet-biotite biotite leucogranites of layered bodies from the eastern part of the massif. It cites the uranium-lead dating of zircons which showed that magmatic zircons from granite melts in the Solzan massif started to crystallize 516-515 million years ago.

The build-up of large magmatic complexes can proceed piecemeal over periods of several million years through sequences of complex processes of magma production, differentiation, assimilation, final crystallization and subsequent metasomatic modification. All these stages can produce or modify minerals used as geochronometers, such as zircon, monazite and titanite. The present study exemplifies such complex relationships, also demonstrating how a systematic approach with comprehensive sampling and careful high-resolution U–Pb analyses can yield a coherent picture of the entire magmatic process. The study was conducted on the Pavia pluton, an elongated Variscan intrusion in the Ossa–Morena Zone of Portugal. The geochronological data show that the Pavia pluton was emplaced by the amalgamation of multiple magma pulses into the crust, over a period of c. 11 Myr. An early event at ∼340 Ma, revealed by xenocrystic zircon, preceded the magmatic activity at the exposed level of the pluton, but is recognized as the main magmatic event elsewhere in the Ossa–Morena Zone. A second event at 328 Ma formed tonalite, trondhjemite and granodiorite, and subordinate differentiates in the central domains of the pluton (units I and II). A third event at c. 324 Ma emplaced granodiorite in the flanking domains III–V and the contemporaneous and widespread two-mica granite in domain VI, together with late rhyodacite porphyries, microgranodiorites, aplite–pegmatite and pegmatite dikes. A fourth event at 319–317 Ma was characterized by the emplacement of some microgranites and pegmatite dikes. These two last magmatic events also had an effect on the previously emplaced rocks, causing local overgrowths and isotopic resetting of minerals. The occurrence of a fifth magmatic event at depth at 313 Ma is the inferred cause of the hydrothermal activity responsible for local zircon, monazite and titanite resorption and/or recrystallization and for some of the textures exhibited by the main rock-forming minerals. The magmatic episodes were interspersed with periods of quiescence; this cyclicity presumably reflects an external control by the transtensional tectonic regime of the Ossa–Morena Zone. [ABSTRACT FROM AUTHOR]

The present-day 238U/235U ratio has fundamental implications for uranium-lead geochronology and cosmochronology. A value of 137.88 has previously been considered invariant and has been used without uncertainty to calculate terrestrial mineral ages. We report high-precision 238U/235U measurements for a suite of uranium-bearing minerals from 58 samples representing a diverse range of lithologies. This data set exhibits a range in 238U/235U values of >5 per mil, with no clear relation to any petrogenetic, secular, or regional, trends. Variation between comagmatic minerals suggests that 238U/235U fractionation processes operate at magmatic temperatures. A mean 238U/235U value of 137.818 ± 0.045 (2δ) in zircon samples reflects the average uranium isotopic composition and variability of terrestrial zircon. This distribution is broadly representative of the average crustal and "bulk Earth" 238U/235U composition. [ABSTRACT FROM AUTHOR]

The article presents a study which discusses uranium (U)-lead (Pb) geochronological dating of Paleozoic era granitoide rock formation of the Kiviliyskii complex in the Bureya Terrane in Russia. It says that porphyroblastic granites and rare quartz diorites from the Kiviliyskii massif were used as samples, in which accessory zircon crystals were selected and were subjected to multiple removal of surface contamination with ethanol, acetone, and nitric acid (HNO3). It says that Krogh's modified procedure was used for the chemical decomposition of zircon and U and Pb separation and isotope analyses were performed with the use of the MAT 261 multicollector mass spectrometer from Finnigan Corp. Results show that the granitoides in the site have an early Paleozoic era age.

Abstract: In-situ SIMS zircon U–Pb dating and O isotope analysis as well as LA-(MC)-ICPMS zircon U–Pb dating and Lu–Hf isotope analysis were carried out for postcollisional mafic–ultramafic rocks in the Dabie orogen, China. The zircon U–Pb dating gave consistent ages of 126±1 to 131±1Ma for magma crystallization. Survival of residual zircon cores is identified by CL imaging and U–Pb dating, yielding ages of 697±10 and 770±11Ma that agree with protolith U–Pb ages of UHP metaigneous rocks in the Dabie orogen. The zircon Hf–O isotope compositions show systematic variations that can be categorized into three groups. Group I has the lowest δ18O values of 2.0 to 2.9‰ but the highest εHf(t) values of −3.5 to −1.0 with the youngest Hf model ages of 1.2 to 1.4Ga. Group II displays intermediate δ18O values of 4.0 to 5.1‰ and εHf(t) values of −22.5 to −13.2 with Hf model ages of 2.0 to 2.6Ga. Group III exhibits the highest δ18O values of 5.2 to 7.3‰ but the lowest εHf(t) values of −29.1 to −18.6 with the oldest Hf model ages of 2.4 to 3.0Ga. The three groups of Hf–O isotope compositions correspond to a three-layer Hf–O isotope structure in the subducted continental crust, suggesting their involvement in the mantle source. Along with existing data for whole-rock Sr–Nd isotopes and trace elements, it appears that the mantle source for the postcollisional mafic–ultramafic rocks is characterized by fertile lithochemistry, the arc-like signature of trace elements, the heterogeneous enrichment of radiogenic isotopes, the differential incorporation of supracrustal materials, and the variable concentrations of water. Clearly, such a source is neither the asthenospheric mantle nor the refractory subcontinental lithospheric mantle (SCLM). It is a kind of the orogenic SCLM that would be generated by reaction of the overlying SCLM-wedge peridotite with hydrous silicate melts derived from different layers of the subducted continental crust. Therefore, the postcollisional mafic–ultramafic rocks provide a petrological record of crust–mantle interaction during the continental deep subduction. [Copyright &y& Elsevier]

U-Pb dating of zircons (SHRIMP-II) has been performed for the first time for granites, granodiorites, and synplutonic granodiorite and melanodiorite bodies of the Shartash and Shabry massifs in the Middle Urals. The time of the formation of the massifs is 300-306 Ma, which is 25 Ma younger than the previous estimates. The age data obtained are in line with the time of the formation of the adamellite-granite series of the Verkhisetsk Batholite (the master sample of tonalite-granodiorite-granite magmatism in the Middle Urals), the series of which is petrochemically close to the rocks of the massifs. [ABSTRACT FROM AUTHOR]

The article presents a study to determine the geologic age of early caledonides formation in Olkhon Island, Russia. It says that the region possesses unique geological characteristics where different levels of the Earth's crust are exposed and separated by three main lithoplates created by collisional-shear zone deformations. The lithoplates are the Chernorud zone, composed of granulite facies metamorphism, the Anga-Sakhyurty zone, composed of amphibolite facies metamorphism, and the Anga zone, composed of epidote-amphibolite metamorphism. It says the study used Uranium-Lead (U-Pb) isotope dating of zircons performed on the SHRIMP-II ion microprobe and confirmed through the Triton X-100 mass spectrometer. The results show that Birkhin gabbroic massif age is at 500 million years (Ma).

Abstract: The geological evolution in the southwestern Chinese Tianshan orogen in NW China is poorly understood because of controversial geochronological results of the low-temperature eclogites. It is likely due to Sm–Nd and Rb–Sr isotopic disequilibrium in different mineral fractions, excess 40Ar in the high-pressure K-bearing minerals, and multi-stage growths of zircon in U–Pb system. Rutile, as a typical eclogite-facies mineral with high U/Pb ratio, is a feasible candidate to constrain the eclogite-facies metamorphic event. In this study, we measured U–Pb rutile age data using SIMS (Cameca IMS 1280) for low-temperature eclogites from southwestern Chinese Tianshan orogen, NW China. We demonstrate that SIMS is a powerful technique for in-situ U–Pb dating of rutile with U content as low as 1ppm. SIMS U–Pb rutile dating yielded an age of 318±7Ma, which may record the time when the rocks cooled down to the closure temperature of Pb in rutile (ca. 500°C), but should be very close to the time of eclogite-facies metamorphism in terms of common fast exhumation of coesite-bearing eclogite. This new proof strongly suggests a late Carboniferous collision between Kazakhstan–Yili block and Central Tianshan microcontinent. [ABSTRACT FROM AUTHOR]

Abstract: U–Pb zircon geochronology of two Permo-Triassic granites (samples OT-52 and OT-272 with ages of 229±8Ma and 256±2Ma, respectively) in the Unazuki area, Hida Metamorphic Belt, southwest Japan, revealed the presence of Eoarchean to Paleoproterozoic inheritance. Inheritance is consistent with both samples showing low zircon saturation temperatures for their bulk compositions. In OT-52, dark in CL, low Th/U zircon domains have a mean 207Pb/206Pb age of 1940±17Ma, which is consistent with an age of 1937±6Ma for anatexis in the Precambrian Busan gneiss complex in Korea. Eoarchaean inherited zircons with 207Pb/206Pb ages from ca. 3750 to 3550Ma are common in OT-272 but are few in OT-52, suggesting a source from rocks with affinities to those in the Anshan area in the northeast China part of the North China Craton. On the other hand, a Hida Metamorphic Belt metasedimentary gneiss into which the granites were intruded contains ca. 1840, 1130, 580, 360, 285 and 250Ma zircons (). These ages suggest that the Unazuki Mesozoic granites did not originate from proximal Hida Metamorphic Complex rocks, but instead from unrelated rocks obscured at depth. The predominance of Eoarchean to Paleoproterozoic age components, and the marked lack of 900–700Ma components suggest that the source was the (extended?) fringe of the North China Craton, rather than from Yangtze Craton crust. The Mesozoic evolution of Japan and its linkages to northeast Asia are discussed in the context of these results. [ABSTRACT FROM AUTHOR]

Abstract: New U–Pb SHRIMP zircon ages and Sm–Nd isotopic results identify early Mesoarchean (∼3150Ma) granitic crust cropping out in the eastern Gawler Craton, southern Australia. These rocks are more than 500 million years older than the oldest previously dated rocks from the Gawler Craton, and challenge the view that pre-3.0Ga crust in Australia is restricted to the Yilgarn and Pilbara Cratons of Western Australia. We interpret these new data to indicate the presence of ∼3150Ma crust at or near the surface throughout a wedge-shaped region covering an area of at least ∼1500km2. The region is characterised by high surface heat flow, and contains Paleo- and Mesoproterozoic intrusive rocks with evolved Nd isotopic compositions and high radiogenic heat production values. The newly identified Mesoarchean rocks provide an obvious source for the evolved Nd signatures, and are themselves relatively enriched in heat producing elements, particularly considering their age. We speculate that the presence of relatively radiogenic Mesoarchean crust underlies much of the area covered by the South Australian Heat Flow Anomaly. Identification of Mesoarchean crust near the eastern margin of the Gawler Craton prompts consideration of links with other Australian Cratonic elements. As far as we are aware, no direct age equivalents of these rocks have been identified elsewhere in Australia, although we note that some recent models for Australian Proterozoic geodynamic evolution may be used to predict the presence of equivalent aged crust in the North Australian Craton. [Copyright &y& Elsevier]

We describe the geological, geochronological, geomorphological, and faunal context of the Malapa site and the fossils of Australopithecus sediba. The hominins occur with a macrofauna assemblage that existed in Africa between 2.36 and 1.50 million years ago (Ma). The fossils are encased in water-laid, clastic sediments that were deposited along the lower parts of what is now a deeply eroded cave system, immediately above a flowstone layer with a U-Pb date of 2.026 ± 0.021 Ma. The flowstone has a reversed paleomagnetic signature and the overlying hominin-bearing sediments are of normal polarity, indicating deposition during the 1.95- to 1.78-Ma Olduvai Subchron. The two hominin specimens were buried together in a single debris flow that lithified soon after deposition in a phreatic environment inaccessible to scavengers. [ABSTRACT FROM AUTHOR]

Abstract: The northern border of the Variscan Moroccan Meseta is characterized by the presence of Cambrian rocks affected by pre-Variscan deformation (the Sehoul block) thrust to the south onto Ordovician, Silurian and Devonian sediments and volcanics of the Bou Regreg corridor. A correct appraisal of the significance of this tectonic contact in the framework of the Variscan orogen needs new data on the age, geochemical features and field relationships of granitoids cropping out in the Sehoul block (Rabat granitoids) and the Bou Regreg corridor (Tiflet granitoids). Accordingly, we provide here with new geochemical data and accurate U–Pb geochronology of these granitoids, which lead us to conclude that: (i) the Rabat granitoids are Late Devonian in age (367Ma); (ii) the Tiflet granitoids are Late Proterozoic in age (605–609Ma) and display Andean-arc features, thus being genetically linked to the Cadomian/Pan-African subduction and forming part of the Variscan basement during the Palaeozoic; (iii) the previously accepted 430Ma Rb–Sr age, common for the Rabat and Tiflet granitoids, which would imply a trivial Carboniferous displacement of the Sehoul thrust, must be rejected; and (iv) the Sehoul thrust might be a major Variscan boundary, perhaps hiding the Rheic Ocean suture. [Copyright &y& Elsevier]

The article discusses the study on the mineralogy, geochemistry and age peculiarities of zircon distribution on gneissose leucocratic miaskites of the Ilmenogorsk massif deposit at the southern region of Ural Mountains in Russia. Researchers conducted recrystallization of the zircon samples from amphibole miaskites that yielded formation of emulsion structures, crushing and corrosion, and new growth. From the authors' findings, ages of miaskite crystallization, 434 plus 15 minus 10 million years (Ma), and metamorphism, 239 plus 40 minus 45 Ma, were determined by standard uranium-lead (U-Pb) dating method.

The article offers information on the results of the dating of alkaline granitoids of the Ulug-Tanzek Massif deposit in Tuva, Russia through uranium-lead (U-Pb) method for zircon and Argon-Argon (Ar-Ar) method. A sample from polylithionite-bearing ribeckite granite was studied for Ar-Ar geochronological investigations, in which, results revealed that approximately 85% of Ar that has clearly formed reflected three-step plateau with an age of 296 plus-minus two million years (Ma). In U-Pb dating, a sample of muscovite quartz-albite-microline granite with a netlike texture was used, in which, the determined age of 301 plus-minus three Ma, is similar within the error limits of the age estimation for the first sample using Ar-Ar method.

Abstract: The Kokchetav Massif of northern Kazakhstan is the best-known metamorphic diamond locality among numerous ultrahigh-pressure (UHP) terranes in the world. At the Kumdy-Kol deposit, diamondiferous rocks are interbedded with granitic gneisses, and biotite gneisses; some have been migmatized. Some granite gneisses and migmatites were formed by partial melting of diamondiferous rocks. To verify such suggestion, sensitive high resolution ion microprobe (SHRIMP) U–Pb dating of zoned zircons from migmatites at the Kumdy-Kol region was performed to constrain the age of partial melting of the Kokchetav UHP metamorphic rocks. Most age data from core and rim domains of zircon separates are concordant. The apparent 206Pb/238U ages for core and rim domains of zirconsare nearly identical within analytical error. All SHRIMP analyses of zircons from four samples fall in the range 508–538 Ma with the weighted mean age for all zircon domains at 526±2.1 (MSWD=1.7). Our data show that migmatization of UHP pelites occurred later than the peak metamorphism (537±9 Ma) and the decompression partial melting took place during exhumation of diamondiferous rocks from mantle depths to amphibolite-facies conditions at mid-crustal levels (507±8 Ma). [Copyright &y& Elsevier]

The Maizuru terrane, distributed in the Inner Zone of southwest Japan, is divided into three subzones (Northern, Central and Southern), each with distinct lithological associations. In clear contrast with the Southern zone consisting of the Yakuno ophiolite, the Northern zone is subdivided into the western and eastern bodies by a high-angle fault, recognized mainly by the presence of deformed granitic rocks and pelitic gneiss. This association suggests an affinity with a mature continental block; this is supported by the mode of occurrence, and petrological and isotopic data. Newly obtained sensitive high mass-resolution ion microprobe (SHRIMP) zircon U–Pb ages reveal the intrusion ages of 424 ± 16 and 405 ± 18 Ma (Siluro–Devonian) for the granites from the western body, and 249 ± 10 and 243 ± 19 Ma (Permo–Triassic) for the granodiorites from the eastern body. The granites in the western body also show inherited zircon ages of around 580 and 765 Ma. In addition, electron probe microanalysis (EPMA) monazite U–Th–total Pb dating gives around 475–460 Ma. The age of intrusion, inherited ages, mode of occurrence, and geological setting of the Siluro–Devonian granites of the Northern zone all show similarities with those of the Khanka Massif, southern Primoye, Russia, and the Hikami granitic rocks of the South Kitakami terrane, Northeast Japan. We propose that both the Siluro–Devonian and Permo–Triassic granitic rocks of the Northern zone are likely to have been juxtaposed through the Triassic–Late Jurassic dextral strike-slip movement, and to have originated from the Khanka Massif and the Hida terrane, respectively. This study strongly supports the importance of the strike-slip movement as a mechanism causing the structural rearrangement of the Paleozoic–Mesozoic terranes in the Japanese Islands, as well as in East Asia. [ABSTRACT FROM AUTHOR]

• Tectonometamorphic evolution of the Southern Ethiopian Shield. • The U-Pb zircon dating of high-grade rocks and intrusives (Hammar Domain) • Geodynamic evolution of the East-African Orogen. Based on new U–Pb zircon data, field structural analysis and a detailed petrological study of the plutonic and high-grade metamorphic rocks of the Hammar Domain (Southern Ethiopian Shield) overall geodynamic scenario was inferred, bringing broad implications for the East-African Orogeny. The structural evolution of the Hammar Domain can be summarized into four phases, D 1 to D 4 , resulting in (a) relict compositional banding (S 1), (b) flat-lying migmatite foliation (S 2) defining the primary contacts of granulites and migmatites, (c) superimposed steeply dipping N–S trending compressional foliation (S 3) due to regional ~E–W oriented compression and (d) later ~NW–SE trending left-lateral transpressive fabric (S 4). New geochronological data point to long-lasting orogenic convergence forming the East-African Orogeny which resulted in two main geodynamic events: (a) Late Tonian to late Cryogenian episode (ca. 770 to 650 Ma) where large volcanic arc construction as the source of rock photoliths (dated at ca. 770 Ma) was followed by crustal accretion and flat-lying fabrics origin (D 2 stage), intense migmatization and HT-MP metamorphism (T: 700–850 °C and P: 0.7–0.9 GPa) at depths of ~25–35 km (dated at ca. 720 and 715 Ma). (b) Late Cryogenian to early Ediacaran episode (ca. 650 to 620 Ma) as the key era of continental collision leading to the Greater Gondwana assembly. An early ~E–W oriented compression (D 3 stage) resulted in ~N–S trending fabrics that have been continuously changed to the left-lateral transpression (D 4 stage) forming ~NW–SE oriented foliations. The time-scale of D 3 and D 4 events is inferred by syn -tectonic granitoid intrusions yielded at ca. 648 Ma and ca. 630 Ma respectively. Furthermore, the syn- to post-tectonic leucogranite dike, dated at ca. 630 Ma, marks the upper limit for the ductile or brittle-ductile deformation and regional metamorphic events. [ABSTRACT FROM AUTHOR]

A critical question in radiometric dating of metamorphic rocks is whether minerals used to define internal isochrons have achieved isotopic equilibrium during a given metamorphic event, followed by preservation of the equilibrium afterward. A garnet peridotite at Zhimafang in the Sulu terrane of eastern China shows incongruent U-Pb, Rb-Sr, and Sm-Nd ages. Zircon SHRIMP U-Pb dating yielded an isochron age of 224 ± 8 Ma, pointing to zircon growth during Triassic UHP metamorphism. Two mineral assemblages gave consistent Rb-Sr internal isochron ages of 201 ± 4 and 205 ± 4 Ma, but much older Sm-Nd internal isochron ages of 376 ± 16 and 378 ± 24 Ma. Apparently, the Sm-Nd radiometric system fails to reequilibrate among the dated minerals during the Triassic UHP metamorphic event for the garnet peridotite. This result is confirmed by the state of oxygen isotope equilibrium (or disequilibrium) among the constituent minerals in the garnet peridotite. In particular, garnet is not in oxygen isotope equilibrium with any other of the analyzed minerals. The degree of oxygen isotope disequilibria among the other minerals varies from pair to pair. Oxygen isotope equilibrium is observed only between orthopyroxene and olivine for both samples and between phlogopite and clinopyroxene for one sample. It appears that the U-Pb, Rb-Sr, Sm-Nd, and O isotope systems in minerals of the garnet peridotite are in partial equilibrium during UHP metamorphism, i.e., equilibrium with respect to some isotopes and minerals, but not all. Based on available experimental diffusion data, our study of the combined U-Pb, Rb-Sr, Sm-Nd, and O isotope systems in the garnet peridotite demonstrates that the time scale for the UHP metamorphism and subsequent HP eclogite-facies recrystallization is possibly in the range of about 12 to 26 Ma, which was not long enough for the reequilibration of the Sm-Nd and O isotope systems, but just long enough for the reequilibration of t... [ABSTRACT FROM AUTHOR]

Examines the chronology of deformation, metamorphism, and magmatism of the Karakoram Mountains in Northern Pakistan. Evolution of plate crust after collision of the Kohistan arc and the Indian plate; .

Two populations of kimberlitic zircon are present in the Timber Creek kimberlites, Northern Territory. Laser-ablation ICP-MS U–Pb dating yields an age of 1483 ± 15 (2σ) Ma for the main group and an age of 179 ± 2 Ma for the other group. This distinction of two age groups is strongly supported by Hf isotope data on the same zircons. Although the trace-element patterns of both populations are typical of mantle-derived zircons, the ‘young’ population has slightly higher concentrations of most trace elements, but has lower Hf, Nb, Ta and Pb contents. The distinct differences in trace-element contents and Hf isotopic composition of the two zircon populations indicate that they were derived from different magma sources. The dating results indicate that the emplacement age of the Timber Creek kimberlites cannot be older than the age of the ‘young’ zircon population (i.e. 179 ± 2 Ma). This clarifies the inconsistency between the previously reported SHRIMP age of the Timber Creek zircons (1462 ± 53 Ma) and the much younger age (1200 Ma) of the sediments of the Victoria River Basin into which these kimberlites have intruded. The Timber Creek kimberlites are a newly recognised extension of the widespread Jurassic kimberlite activity known in Western Australia and South Australia (Wandagee, Orroroo, Cleve and Eurelia kimberlites). [ABSTRACT FROM AUTHOR]

Examines crystal residence times using in situ uranium-lead (U-Pb) dating of zircons from the Bishop Tuff in east-central California. Maximum mean crystal residence time for zircon; Analysis of zircons from fallout and intercalated ash-flow deposits and unpolished rims; Storage of Bishop Tuff rhyolite prior to eruption.

The Mushgai Khudag complex consists of numerous silicate volcanic-plutonic rocks including melanephelinites, theralites, trachytes, shonkinites, and syenites and also hosts numerous dykes and stocks of magnetite-apatite-enriched rocks and carbonatites. It hosts the second largest REE–Fe–P–F–Sr–Ba deposit in Mongolia, with REE mineralization associated with magnetite-apatite-enriched rocks and carbonatites. The bulk rock REE content of these two rock types varies from 21,929 to 70,852 ppm, which is much higher than that of syenites (716 ± 241 ppm). Among these, the altered magnetite-apatite-enriched rocks are characterized by the greatest level of REE enrichment (58,036 ± 13,313 ppm). Magmatic apatite from magnetite-apatite-enriched rocks is commonly euhedral with purple luminescence, and altered apatite displays variable purple to blue luminescence and shows fissures and hollows with deposition of fine-grained monazite aggregates. Most magmatic apatite within syenite is prismatic and displays oscillatory zoning with variable purple to yellow luminescence. Both magmatic and altered apatite from magnetite-apatite-enriched rocks were dated using in situ U–Pb dating and found to have ages of 139.7 ± 2.6 and 138.0 ± 1.3 Ma, respectively, which supports the presence of late Mesozoic alkaline magmatism. In situ 87Sr/86Sr ratios obtained for all types of apatite and calcite within carbonatite show limited variation (0.70572–0.70648), which indicates derivation from a common mantle source. All apatite displays steeply fractionated chondrite-normalized REE trends with significant LREE enrichment (46,066 ± 71,391 ppm) and high (La/Yb)N ratios ranging from 72.7 to 256. REE contents and (La/Yb)N values are highly variable among different apatite groups, even within the same apatite grains. The variable REE contents and patterns recorded by magmatic apatite from the core to the rim can be explained by the occurrence of melt differentiation and accompanying fractional crystallization. The Y/Ho ratios of altered apatite deviate from the chondritic values, which reflects alteration by hydrothermal fluids. Altered apatite contains a high level of REE (63,912 ± 31,785 ppm), which are coupled with increased sulfur and/or silica contents, suggesting that sulfate contributes to the mobility and incorporation of REEs into apatite during alteration. Moreover, altered apatite is characterized by higher Zr/Hf, Nb/Ta, and (La/Yb)N ratios (179 ± 48, 19.4 ± 10.3, 241 ± 40, respectively) and a lack of negative Eu anomalies compared with magmatic apatite. The distinct chemical features combined with consistent Sr isotopes and ages for magmatic and altered apatite suggest that pervasive hydrothermal alterations at Mushgai Khudag are most probably being induced by carbonatite-evolved fluids almost simultaneously after the alkaline magmatism. [ABSTRACT FROM AUTHOR]

The article offers a study on zircon U-Pb dating of the rhyolitic tuff and rhyolite within the Manketouebo Formation in the southern Manzhouli area, with the aim to constrain the timing of the Manketouebo Formation. Topics discussed include Zircon U-Pb dating was performed using the Sensitive High-Resolution Ion Microprobe; and concludes that the rhyolitic tuff and rhyolite from the Manketouebo Formation was dated by the Sensitive high-resolution ion microprobe U-Pb method.

The article discusses significance of the uranium-lead (U-Pb) geochronological study of bastnaesite from the Karasug complex deposit at the Central Tuva in Russia. Bastnaesite is a typomorphic mineral that is usually found in siderite carbonatites. During the analytical method of the study, modified Krogh technique was employed to decompose bastnaesite and chemically separate Pb and U. According to the author, U-Pb dating of bastnaesite was taken through a supergene altered siderite carbonatite with hematite. In the process, the authors noted that there is a possibility of applying bastnaesite as a tool for U-Pb geochronological dating of endogenous ore processes.