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The Tongbai complex plays an important role in the understanding of the tectonic evolution of the Tongbai‐Dabie orogenic belt. By detailed structural analysis, new zircon U–Pb dating, zircon Lu–Hf analysis and whole‐rock elements for the rocks in the Tongbai complex and the wrapped shear zones, we suggested that the Tongbai complex was derived from the partial melting of the basement of Yangtze Block and experienced a uniform orogen‐parallel extension with a top‐to‐NW shearing at 142–133 Ma. The migmatites yield a migmatization age of 116 ± 2 Ma and are identical to the metamorphic age of 115–111 Ma from the L and LS tectonites in the Tongbai complex. The late Early Cretaceous migmatization may give rise to the severance of the uniform top‐to‐NW shear zone and lead to an antiform folding of the Tongbai complex. The similar deformation and migmatization of the complexes in both the Tongbai and Dabie orogenic belts suggest that the Tongbai‐Dabie orogenic belt is likely to have a similar tectonic transformation from orogen‐parallel to orogen‐perpendicular extension in the Early Cretaceous, namely a uniform orogen‐parallel extension of the ductile lithosphere during the early Early Cretaceous and a widespread migmatization during the late Early Cretaceous. [ABSTRACT FROM AUTHOR]

The Hesar pluton in the northern Urumieh–Dokhtar magmatic arc hosts numerous mafic‐microgranular enclaves (MMEs). Whole rock geochemistry, mineral chemistry, zircon U‐Pb and Sr‐Nd isotopes were measured. It is suggested that the rocks are metaluminous (A/CNK = 1.32–1.45), subduction‐related I‐type calc‐alkaline gabbro to diorite with similar mineral assemblages and geochemical signatures. The host rocks yielded an U‐Pb crystallization age of 37.3 ± 0.4 Ma for gabbro‐diorite. MMEs have relatively low SiO2 contents (52.9–56.6 wt%) and high Mg# (49.8–58.7), probably reflecting a mantle‐derived origin. Chondrite‐ and mantle‐normalized trace element patterns are characterized by LREE and LILE enrichment, HREE and HFSE depletion with slight negative Eu anomalies (Eu/Eu* = 0.86–1.03). The host rocks yield (87Sr/86Sr)i ratios of 0.70492–0.70510, positive εNd(t) values of +1.55–+2.06 and TDM2 of 707–736 Ma, which is consistent with the associated mafic microgranular enclaves ((87Sr/86Sr)i = 0.705014, εNd(t) = +1.75, TDM2 = 729 Ma). All data suggest magma‐mixing for enclave and host rock formation, showing a complete equilibration between mixed‐mafic and felsic magmas, followed by rapid diffusion. The TDM1(Nd) and TDM2(Nd) model ages and U‐Pb dating indicate that the host pluton was produced by partial melting of the lower continental crust and subsequent mixing with injected lithospheric mantle‐derived magmas in a pre‐collisional setting of Arabian–Eurasian plates. Clinopyroxene composition indicates a crystallization temperature of ∼1000°C and a depth of ∼9 km. [ABSTRACT FROM AUTHOR]

[Objective] The Prydz Bay belt in East Antarctica recorded two significant tectono-thermal events, the Grenvillian event and the Pan-African event, which are considered to be closely related to the evolution of the Rodinia and Gondwana supercontinents. However, the geological history and the tectonic nature of the two events remain controversial. [Methods] Mineralogical and petrological analyses, phase equilibria modelling and zircon geochronology are combined to investigate the spinel-cordierite granulite from the Mirror Peninsula in order to better understand the tectono-thermal history of the Prydz Bay belt. [Results] The spinel-cordierite granulite contains different stages of mineral assemblages. The major stage of mineral assemblage involves cordierite, spinel, biotite, sillimanite, K-feldspar and minor garnet and ilmenite. The later stage of mineral assemblage is indicated by the emergence of magnetite as the increasing volumes of biotite and cordierite. Minor garnet and corundum are locally preserved, implying the mineral reaction 'g+cor→sp+sill' and more garnet and corundum in the peak stage. The garnet grains consist of 70%-72% almandine, 20%-22% pyrope, -4% grossularite and -4% spessartine. The XFe (Fe2+/(Fe2++Mg2+)) of representative garnet grains ranges from 0.77 to 0.80. The spinel exhibits an XFe range from 0.80 to 0.86. Different cordierite grains have similar compositions with Al of 3.89-3.93 a.p.f.u (atoms per formula unit) and XFe of 0.32-0.36. Biotite has high TiO2 (4.13%-5.23%) and Ti (0.23-0.30 a.p.f.u). K-feldspar grains consist of 78%-85% orthoclase, 15%-23% albite and -1% anorthite. Based on the mineral compositions and phase equilibrium modelling, the pressure-temperature (P-T) conditions of the major stage of mineral assemblage are constrained to 870-910 °C and 0.64-0.69 GPa, followed by later retrogression to 810-820°C and 0.49-0.53 GPa. A peak stage with higher P-T conditions (T>910 °C, P>0.69 GPa) can be inferred based on the relict peak minerals and characteristic mineral compositions (e.g. Ti in biotite). Zircon grains commonly show core-mantle-rim structures in cathodoluminescence (CL) images. The LA-ICP-MS zircon U-Pb dating analyses reveal a wide age range from 613±7 Ma to 877±9 Ma (except a maximum of 916±11 Ma) for the cores. The zircon bright rims yield a weighted mean age of 526±8 Ma with a wide range of Th/U (0.06-1.23), mostly higher than 0.1. [Conclusion] Based on the results, a few conclusions can be drawn: (1) The spinel-cordierite granulite recorded medium-low pressure/high-ultrahigh temperature metamorphism with a clockwise P-T evolution path and high dT/dP. (2) The results of zircon geochronological analysis show that zircon cores mainly record U-Pb ages in the range of 800--600 Ma, younger than typical ages of Grenvillian events, which may reflect younger inherited zircon cores or significant isotopic resetting. (3) The age of -530 Ma of zircon rims is interpreted to represent the post-peak cooling stage of the Pan-African tectono-thermal event. [Significance] This study examined the P-T conditions and the zircon ages of the spinel-cordierite granulite in the Mirror Peninsula. In combination with previous results, the P-T-t path constructed for the spinel-cordierite granulite provides new constraints on the evolution of the Prydz Bay belt during the Pan-African period. [ABSTRACT FROM AUTHOR]

In recent decades, blue and fancy-colour sapphires have been gathered from secondary deposits derived from Tertiary basalts in the Muling area of north-eastern China. In this article, zircon inclusions in the blue sapphires were studied to characterise their morphology and structure, as well as to obtain the age of the host sapphires. The zircon inclusions in the studied samples were euhedral and transparent, and their dominant morphology was similar to that of typical zircon inclusions in sapphires associated with alkali basalts. Raman spectroscopy of the zircons showed only slight radiation damage, and cathodoluminescence images revealed two distinctive zoning patterns (in their cores and rims). LA-ICP-MS analyses of the zircon rims showed typical magmatic Th/U ratios. In situ U-Pb dating of the zircon rims yielded ages of 9 to 8 Ma--which is the inferred upper limit of the formation age of the host sapphires--while cores had much older ages that exceeded 110 Ma (i.e. an inherited age component). The 9-8 Ma sapphire age coincides with Late Miocene basaltic eruptions in the Dunhua-Mishan graben. Age dating of zircon inclusions in the Muling sapphires helps elucidate their geological origin and provides useful information for the provenance determination of gem corundum. [ABSTRACT FROM AUTHOR]

The Jiamusi Block is a crucial geological unit joining multiple tectonic regimes, including the Late Palaeozoic Palaeo‐Asian Ocean and the superposition of the Early Mesozoic Palaeo‐Pacific tectonic domain. However, the duration of the Palaeo‐Pacific Plate subduction beneath the Jiamusi Block has long been controversial. In this paper, we focus on clastic rocks from the Nanshuangyashan and Yunshan formations on the east margin of the Jiamusi Block and use the modal analysis of sandstones and detrital zircon U–Pb dating to trace the subduction history of the Palaeo‐Pacific Plate. Our analysis results suggest that the two groups of samples are characterized by a high content of monocrystalline quartz and a low content of lithic and feldspar, indicating that the sedimentary provenances were stable continental blocks and magmatic arcs. The detrital zircon ages of the Nanshuangyashan Formation have a major peak at ca. 245 Ma and two secondary peaks at ca. 470 and 228 Ma, respectively. The Yunshan Formation has a major peak at ca. 494 Ma and a secondary peak at ca. 265 Ma. The provenances of the Nanshuangyashan Formation were attributed to the Jiamusi Block, Khanka Block, and a Late Triassic magmatic arc. Similarly, the provenances of the Yunshan Formation were attributed to the Jiamusi and Khanka blocks. Detrital zircon analysis results show that the eastern margin of the Jiamusi Block was in the same back‐arc basin settings in the Late Triassic and the Late Jurassic. Thus, we propose that the eastern margin of the Jiamusi Block had been affected by the Palaeo‐Pacific Plate subduction in the Late Triassic and had continued to the Late Jurassic. [ABSTRACT FROM AUTHOR]

Two episodes of late Neoarchean-early Paleoproterozoic and late Paleoproterozoic garnet-bearing leucogranite, named the Baotou and Jining–Liangcheng garnet-bearing leucogranite are recognized from the Khondalite Belt in the North China Craton. Geochemical studies show that garnet-bearing leucogranite has high Al2O3 content and FeOT/MgO ratio, with a large variation in the CaO content and K2O/Na2O ratio. Additionally, the garnet-bearing leucogranite is enriched in light rare earth elements and large ion lithophile elements and depleted in Nb, Ta, P, and Ti. However, there are some variations in Eu anomalies, as indicated by the Eu-enriched and Eu-depleted patterns. The sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb dating of the Baotou garnet-bearing leucogranite and Jining–Liangcheng garnet-bearing leucogranite show that their anatectic ages were 2.35–2.43 Ga and 1.90–1.92 Ga, respectively, with zircon εHf (t) values of −0.01–3.93 and −4.36–1.99, and two-stage model ages (TDM2) of 2.76–3.02 Ga and 2.57–2.83 Ga, respectively. U-Th-Pb SHRIMP analyses on zircon reveal ages of ca. 2.35–2.47 Ga for the Baotou metapelite gneiss and ca. 1.90–1.91 Ga for the Jining–Liangcheng metapelite gneiss, which represent the ages of tectonic metamorphic events related to the anatexis. Our results, combined with geological and petrographical observations, geochemistry, and geochronology, suggest that (1) Garnet-bearing leucogranites formed as a result of anatexis of metapelite gneisses; (2) They are mixtures of leucosomes, residual minerals and mantle-derived materials; (3) Two episodes of garnet-bearing leucogranites have been identified; (4) Both two episodes of garnet-bearing leucogranites corresponded to late Neoarchean-early Paleoproterozoic and late Palaeoproterozoic tectonothermal events, respectively. [ABSTRACT FROM AUTHOR]

• The alkaline pluton of Balda, located at the boundary of the geological domains of Northwestern Cameroon and Mayo-Kébbi, underwent tectonic deformation subsequent to its emplacement. • The pluton was emplaced at 732.7 ± 7.5 Ma in a syn -orogenic extensional context of a back-arc basin. • The deformation is related to the continental collision of the NW Cameroon and Mayo-Kébbi domains and resulted from a sinistral simple shear-dominated transpressive tectonic regime, dated to around 680 Ma. Located on the border between the NW Cameroon and Mayo-Kebbi domains in northern Cameroon, the Balda pluton is a deformed alkaline granite. Due to its unique location and geological features, it holds crucial information for understanding the evolution of the Central African Orogenic Belt (CAOB), which remains poorly understood. This multidisciplinary study combines field data, microscopic observations, Anisotropy of Magnetic Susceptibility (AMS), and U-Pb zircon dating to constrain the geodynamic evolution of the CAOB. The Balda pluton is a NNE-SSW elongated pluton consists mainly of aegirine-riebeckite granite and leucogranite. It displays diverse magnetic susceptibility values (Km) spanning from 0.19 x 10-3 to 21.98 x 10-3. Notably, 93 % of the Km values exceed 5 × 10-4SI, indicating a prevalence of mixed paramagnetic and ferromagnetic mineralogy (such as magnetite-rich). This observation is supported by microscopic examinations and K-T curves. An analysis of AMS unveils high P% values (2.8 to 58.7 %, with a mean of 15 %) and prevalent oblate magnetic fabrics (68 %). The magnetic foliation generally aligns with the field foliation and has steep dips ranging from NNE to NE or from SSW to SW and magnetic lineations exhibit shallow plunges (<35°) from SSW to SW. Microscopic analysis reveals high-temperature, solid-state deformation microstructures, indicating post-emplacement deformation processes and the presence of kinematic markers consistent with sinistral shear. Zircon grain analysis reveals two distinct types: "bright" and "dark." These types differ in both their appearance under cathodoluminescence and their chemical composition. Bright zircons yield a U-Pb age of 732.7 ± 7.5 Ma, interpreted as the pluton emplacement age. Dark zircons are younger (ca. 680 Ma), suggesting a later tectono-metamorphic or alteration event. The integration of these results in a larger geodynamic context suggests that the Balda pluton formed within a syn -orogenic extensional back-arc basin. This emplacement was followed by significant post-emplacement deformation characterized by sinistral simple shear-dominated transpression likely related to the continental collision (ca. 680 Ma) of the NW Cameroon and Mayo-Kébbi domains. [ABSTRACT FROM AUTHOR]

Tandem in situ and isotope dilution U-Pb analysis of zircons from pyroclastic volcanic rocks and both glacial and non-glacial sedimentary strata of the Pocatello Formation (Idaho, northwestern USA) provides new age constraints on Cryogenian glaciation in the North American Cordillera. Two dacitic tuffs sampled within glacigenic strata of the lower diamictite interval of the Scout Mountain Member yield high-precision chemical abrasion isotope dilution U-Pb zircon eruption and depositional ages of 696.43 ± 0.21 and 695.17 ± 0.20 Ma. When supplemented by a new high-precision detrital zircon maximum depositional age of ≤670 Ma for shoreface and offshore sandstones unconformably overlying the lower diamictite, these data are consistent with correlation of the lower diamictite to the early Cryogenian (ca. 717-660 Ma) Sturtian glaciation. These 670-675 Ma zircons persist in beds above the upper diamictite and cap dolostone units, up to and including a purported "reworked fallout tuff," which we instead conclude provides only a maximum depositional age of ≤673 Ma from epiclastic volcanic detritus. Rare detrital zircons as young as 658 Ma provide a maximum depositional age for the upper diamictite and overlying cap dolostone units. This new geochronological framework supports litho- and chemostratigraphic correlations of the lower and upper diamictite intervals of the Scout Mountain Member of the Pocatello Formation with the Sturtian (716-660 Ma) and Marinoan (≤650-635 Ma) low- latitude glaciations, respectively. The Pocatello Formation thus contains a more complete record of Cryogenian glaciations than previously postulated. [ABSTRACT FROM AUTHOR]

• A "porphyroclast" system occurred in the Tuwu area in the late Early Permian. • The dextral shear event within the Kangguer Shear Zone was initiated at ca. 278 Ma. • The event provides constraints to the intracontinental convergence of the East Tianshan. The Kangguer Shear Zone, located in the East Tianshan, is one of the key faults for understanding the final amalgamation processes of the southwestern margin of the Central Asian Orogenic Belt. Magmatism was active in the Tuwu area of the Kangguer Shear Zone during the late Early Permian. LA–ICP–MS U–Pb dating analyses of the magmatic zircons from three monzogranite plutons, a felsic dyke, and a diorite dyke show ages of 286.9±0.78, 282.8±0.62, 281.7±0.89, 278.0±0.61, and 278.1±1.2 Ma, respectively. Detailed field and microscopic observations reveal that these intrusions form a "porphyroclast" system, and this area has undergone ductile dextral strike-slip deformation, with foliations dipping steeply to the south and subhorizontal stretching lineations trending to the east. Further structural analysis indicates that the three monzogranite plutons intruded into the Kangguer Shear Zone and cooled into rigid bodies before regional dextral strike-slip deformation, which limited the deformation that occurred after 282 Ma. The felsic dykes exhibit synkinematic characteristics, and the diorite dyke may have intruded before or at the same time as dextral strike-slip deformation, implying that regional dextral shear was initiated at ca. 278 Ma. These data, combined with previous studies, suggest that the initiation of dextral shear in the Kangguer Shear Zone occurred after the closure of the Kangguer Ocean and was the result of regional nearly N–S compression caused by the convergence of the Tarim Craton and plates north of the Kangguer Shear Zone. [ABSTRACT FROM AUTHOR]

As one of the widest terranes exposed in icy Antarctica, the Larsemann Hills in the Prydz Bay belt preserves diverse rock types with a complex metamorphic history and thus is critical to the tectono-metamorphic evolution of East Antarctica. Garnet-sillimanite-spinel-cordierite–bearing and garnet-orthopyroxene–bearing granulites are typical rocks in the region. Phase equilibrium modelling and mineral thermometry based on detailed petrological and mineralogical analyses indicate that the granulites underwent extreme metamorphism with peak conditions to ultrahigh temperatures (UHTs). The high-UHT metamorphism is characterised by extremely high dT/dP values (>1000°C/GPa) along a clockwise path with evident decompression at high temperatures and subsequent near isobaric cooling. Textural relationships, in situ NanoSIMS zircon U–Pb analysis, and LA-ICP-MS zircon and monazite dating and trace element analysis indicate protracted tectono-thermal evolution from the latest Neoproterozoic to early Palaeozoic (c. 570–500 Ma), with a prograde stage likely from c. 570 to c. 550 Ma, a peak stage from c. 550 to c. 540 Ma, and a retrograde stage from c. 540 to c. 500 Ma. During the retrograde stage, major decompression should have occurred before c. 530 Ma, as indicated by the age of zircon included in spinel, and then near isobaric cooling followed and persisted from c. 530 to c. 500 Ma. The geochronological data contribute to the establishment of the thermal–temporal framework of the late Neoproterozoic to early Palaeozoic Prydz tectonic event. The results also indicate that the assemblage of the investigated granulites basically resulted from the late Neoproterozoic to the early Palaeozoic tectono-thermal event, and the high-UHT conditions revealed by the granulites in the Larsemann Hills imply a much wider distribution of high heat flow and potential UHT metamorphism in the Prydz Bay region. Both the Larsemann Hills and the Rauer Group may have been in a similar and interrelated tectono-thermal setting from the late Neoproterozoic to the early Palaeozoic during the assembly of the Gondwana supercontinent. [ABSTRACT FROM AUTHOR]

Felsic tuff as a direct fallout deposit is known from one small area in the Kyrenia Range, north Cyprus, within deep-sea terrigenous turbidites. Nearby tuffaceous siltstones contain compositionally similar felsic volcanic rocks (c. 5–10%), mixed with terrigenous material. Sedimentary evidence indicates that the fallout tuff was variable reworked locally, whereas the tuffaceous siltstones are interpreted as turbidites mixed with terrigenous material derived from Anatolia. U–Pb dating of zircons that were extracted from a sample of relatively homogeneous tuff yielded a dominant age of 16.64 ± 0.12 Ma (Burdigalian). Zircon trace-element analysis indicates predominant derivation from within-plate-type felsic magma. Whole-rock chemical analysis of the tuffaceous sediments as a whole is compatible with a felsic arc source, similar to the post-collisional magmatism within Anatolia. Regional comparisons suggest that the nearest volcanism of similar age and composition is located c. 500 km away, within the Kırka area (Eskişehir region) of the Western Anatolia Volcanic Province. Evidence of tephra dispersal in the western Mediterranean region and climatic modelling suggests E-wards prevailing winds and therefore tephra transport over southern Anatolia and adjacent areas during early Miocene time. The north Cyprus tuffs could represent powerful Minoan (Plinian)-type eruptions in western Anatolia, coupled with SE-wards tephra transport during and soon after the onset of post-collisional magmatism. [ABSTRACT FROM AUTHOR]

• The Huangcheng basin has undergone three compression events since 100 Ma. • Slickenside analysis reveals north–south and east–west compression stresses. • Cretaceous sedimentary rocks in the area are sourced from the Qilian Shan-Nan Shan Block and Alashan Block. The sedimentary rocks in the Hexi Corridor, north-eastern Tibetan Plateau, contain information about crustal deformation during and after the closure of the Meso-Tethys Ocean and the growth of the Tibetan Plateau. This study examines the origin and deformation of Late Mesozoic sedimentary rocks in the Huangcheng basin where the source of Late Mesozoic sedimentary rocks and deformation styles of faults and folds remain controversial. Results from field mapping, fault kinematic analysis, and detrital zircon analysis suggest that the study region might have experienced three episodes of compression events since 100 Ma. The first episode is characterized by north–south compression, which could reflect the convergence between the Alashan and the Qilian Shan-Nan Shan. The second episode reflects the reactivation of the thrust faults related to the far-field effect resulting from the closure of the Neo-Tethys Ocean. The third episode is the regional east–west trending thrust due to the block extrusion. One set of slickensides indicates north–south compression while a second set implies nearly east–west compression, which could represent different stress orientations between the first two episodes and the third episode. Eleven detrital zircon samples from the Cretaceous to Neogene strata were collected for detrital zircon U-Pb dating and rare earth element analysis. Zircon U-Pb ages show major peaks around 265 Ma and 455 Ma with a notable lack of ages around 1.0 Ga. We infer that the source of the Neogene sedimentary rocks was the Qilian Shan while the sources of the Cretaceous sedimentary rocks were the Qilian Shan and Alashan. [ABSTRACT FROM AUTHOR]

The Paleozoic strata are widely distributed in the northwest of the Ordos Basin, and the provenance attributes of the basin sediments during this period are still controversial. In this paper, the detrital zircon LA-MC-ICPMS U-Pb age test was conducted on the drilling core samples of the Shanxi Formation of the Upper Paleozoic in the Otuokeqi area of the Ordos Basin, and the provenance age and the characteristic of the Shanxi formation in the Otuokeqi area in the northwest were discussed. The cathodoluminescence image shows that the detrital zircon has a clear core-edge structure, and most of the cores have clear oscillatory zonings, which suggests that they are magmatic in origin. Zircons have no oscillatory zoning structure that shows the cause of metamorphism. The age of detrital zircon is dominated by Paleoproterozoic and can be divided into four groups, which are 2500~2300 Ma, 2100~1600 Ma, 470~400 Ma, and 360~260 Ma. The first two groups are the specific manifestations of the Precambrian Fuping Movement (2.5 billion years) and the Luliang Movement (1.8 billion years) of the North China Craton. The third and fourth groups of detrital zircons mainly come from Paleozoic magmatic rocks formed by the subduction and collision of the Siberian plate and the North China plate. The ε Hf t value of zircon ranges from -18.36 to 4.33, and the age of the second-order Hf model T DM 2 ranges from 2491 to 1175 Ma. The source rock reflecting the provenance of the sediments comes from the material recycling of the Paleoproterozoic and Mesoproterozoic in the crust, combined with the Meso-Neoproterozoic detrital zircons discovered this time, indicating that the provenance area has experienced Greenwellian orogeny. [ABSTRACT FROM AUTHOR]

The South Altyn Block (SAB), located along the southern margin of the Altyn Tagh in Qaidam Basin, has a significant relationship with the tectonics of the Qaidam Basin basement. This study presents the petrological features, geochemical compositions, and zircon U–Pb and Hf isotope data of four granitic plutons from the eastern segment of the SAB to constrain the petrogenesis and tectonic setting of this region during the Palaeozoic. Basing on previous U–Pb dating results, the zircon U–Pb analysis in this study suggests that Palaeozoic magmatic events can be subdivided into four episodes: Late Cambrian (approximately 502 Ma), Late Ordovician (approximately 444 Ma), Early Devonian, and Middle Permian (approximately 271 Ma). The Palaeozoic granitoids were derived mainly from Neoproterozoic juvenile crustal components, with minor palaeoproterozoic ancient materials. The S‐ and I‐type granitoids in Late Cambrian indicate a compressional tectonic environment with respect to subduction, and A‐type granitoids suggest post‐collision regime. The Late Ordovician granodiorites of A‐type imply typical magmatism within a post‐collision extensional setting. Ascribing to the subduction of Palaeo‐Tethys Ocean during the Devonian, S‐type granites were emplaced in the Early Devonian accompanied with the crust thickening. The Middle Permian magmatic events include a series of S‐type granitoids, demonstrating the setting of oceanic subduction along with the closure of the Palaeo‐Tethys Ocean. [ABSTRACT FROM AUTHOR]

Although continental crust is characterized by the widespread occurrence of granitoids, the causal relationship between continental crust growth and granitic magmatism still remains enigmatic. While fractional crystallization of basaltic magmas (with or without crustal contamination) and partial melting of mafic lower crust are two feasible mechanisms for the production of granitoids in continental arc regions, the problem has been encountered in discriminating between the two mechanisms by whole-rock geochemistry. This can be resolved by an integrated study of zircon U-Pb ages and Hf-O isotopes together with whole-rock major-trace elements and Sr-Nd-Pb isotopes, which is illustrated for Mesozoic granitoids from the Gangdese orogen in southern Tibet. The results provide geochemical evidence for prompt reworking of the juvenile mafic arc crust in the newly accreted continental margin. The target granitoids exhibit high contents of SiO2 (65.76-70.75 wt%) and Na2O + K2O (6.38-8.15 wt%) but low contents of MgO (0.19-0.98 wt%), Fe2O3 (0.88-3.13 wt%), CaO (2.00-3.82 wt%), Ni (<5.8 ppm), and Cr (⩽10 ppm). They are enriched in large ion lithophile elements, Pb, and light rare earth elements but depleted in high field strength elements. The granitoids are relatively depleted in whole-rock Sr-Nd isotope compositions with low (87Sr/86Sr)i ratios of 0.7043-0.7048 and positive Nd(t) values of 0.5-2.6, and have relatively low 207Pb/204Pb and 208Pb/204Pb ratios at given 206Pb/204Pb ratios. Laser ablation-inductively coupled plasma-mass spectrometry and secondary ion mass spectrometry U-Pb dating on synmagmatic zircons yield ages of 77 ± 2-81 ± 1 Ma in the Late Cretaceous for their emplacement. Relict zircons have two groups of U-Pb ages in the late Mesozoic and the late Paleozoic, respectively. The whole-rock Sr-Nd isotopes in the granitoids are quite similar to those of Late Cretaceous mafic rocks in the Gangdese batholith. In addition, both synmagmatic zircons and relict zircons with Late Cretaceous U-Pb ages exhibit almost the same Hf-O isotope compositions to those of the slightly earlier mafic rocks. All these observations indicate that the granitoids were mainly derived from partial melting of the juvenile mafic arc crust. Therefore, reworking of the juvenile mafic arc crust is the mechanism for the origin of isotopically depleted granitoids in southern Tibet. It is this process that leads to differentiation of the juvenile mafic arc crust toward the felsic lithology in the continental arc. In this regard, the granitoids with depleted radiogenic isotope compositions do not necessarily contribute to the crustal growth at convergent plate boundaries. [ABSTRACT FROM AUTHOR]

• In the Ontario gneiss belt, Nd isotope boundaries can be identified in the field. • These isotope boundaries provide the best constraint on major crustal structures. • Spatial control from Nd isotope mapping complements age control from U-Pb dating. • Detrital zircon Hf model ages rather than U-Pb ages yield crustal extraction ages. With the increasing availability of U-Pb-Hf isotope analysis of zircon suites, does whole-rock Nd isotope analysis still have a role to play in mapping Precambrian gneiss terranes? I answer this question by examining the Ontario Gneiss Belt of the Grenville Province, and show that Nd isotope mapping still has a vital role to play in studies of Precambrian crustal evolution. Although U-Pb-Hf isotope analysis of detrital zircons can provide large suites of crystallization ages and epsilon Hf values, the poor spatial control of these data means that precise geographical control of crustal structure from Nd isotope mapping is still important. I demonstrate this for several regions of the Ontario Gneiss Belt, including northern Algonquin Park, western Lake Nipissing and Georgian Bay. In all these regions, mapping complex geographical patterns of crustal formation ages allows detailed documentation of large-scale crustal structure. Only with such an accurate understanding of crustal structure can accurate models of tectonic evolution be constructed in a complex, deeply exhumed orogenic belt such as the Grenville Province. [ABSTRACT FROM AUTHOR]

Neoproterozoic I-type granites could provide vital insights into the crust–mantle interaction and the crustal evolution along the western Yangtze Block, South China. This paper presents new zircon U–Pb ages, bulk-rock geochemistry, and in situ zircon Lu–Hf isotope on the Dalu I-type granites from the southwestern Yangtze Block. Zircon U–Pb dating show the crystallization ages of 781.1 ± 2.8 Ma for granodiorites and 779.8 ± 2.0 Ma for granites, respectively. The Dalu granodiorites are Na-rich, calc-alkaline, metaluminous to slightly peraluminous (A/CNK = 0.94–1.08). Zircons from granodiorite have positive εHf(t) values (+2.16 to +7.39) with crustal model ages of 1.21–1.54 Ga, indicating juvenile mafic lower crust source. The Dalu granites are high-K calc-alkaline, peraluminous rocks. They have variable zircon εHf(t) values (−4.65 to +5.80) with crustal model ages of 1.31–1.97 Ga, suggesting that they were derived from the mature metasediment-derived melts by the mixing of newly formed mafic lower crust-derived melts. The geochemical variations in Dalu pluton is dominated not only by the different source rocks but also by the different melting temperatures. Combining with the geochemistry and isotopic compositions of I-type granitoids and tectonic setting in the western Yangtze Block, we propose that the Dalu I-type granodiorites–granites associations are the magmatic response from different crustal levels, which were induced by the heat anomaly due to the asthenosphere upwelling in the subduction-related setting. [ABSTRACT FROM AUTHOR]

The Linxia Basin is an important region for understanding the tectonism and uplift history in the northeast Tibetan Plateau, and also contains rich mammalian faunas of evolutionary significance. In this paper, we conduct a provenance study of Cenozoic sediments, relying primarily on U-Pb dating of detrital zircons, to investigate the exhumation history of surrounding terranes and to gain a better understanding of the relationship between tectonism, basin development and paleoenvironment. Samples were collected from the Maogou section in the central Linxia Basin, which has been recently dated by magnetostratigraphy. Detrital zircon populations show five U Pb age groups of 65–350 Ma, 350–600 Ma, 600–1600 Ma, 1600–2200 Ma and 2200–2600 Ma; however, U Pb age patterns varied up-section, indicating different sources at different times. Sediments from the lower part of the section (>27.8 Ma) were sourced from multiple regions, including the distal East Kunlun Shan, Qilian Shan, and Songpan–Ganzi terranes, and as well as the proximal West Qinling region. Contributions from the Songpan–Ganzi terrane increased considerably during the late Oligocene (27.8–23 Ma), as a result of strong tectonic movements of the northeastern Tibetan Plateau. During the early Miocene (23–17.2 Ma), the northern sources of the Laji Shan–Maxian Shan region supplied more sediments to the basin, indicating the uplift and exhumation of these mountain ranges. Until the middle Miocene (17.2–12.8 Ma), the Songpan-Ganzi terrane and the northern sources dominated the basin sediments, while the northern sources and the Jishi Shan region became increasingly important sources at around 11.6 Ma. This study explores the tectonosedimentary evolution of the Linxia Basin in the northeastern Tibetan Plateau, providing a reference for further research of the paleoclimate and mammalian evolution in this critical region. • Detrital zircon provenance study on sediments in the Linxia Basin. • Sediment sources supplied the central basin at the early stage. • The Songpan–Ganzi direction source largely increased in the late Oligocene. • The north source became an important early to middle Miocene source for the basin. • The Jishi Shan did not influence the Maogou section until around 11.6 Ma. [ABSTRACT FROM AUTHOR]

In this contribution, we carry out an integrated study of petrology, whole-rock geochemistry, as well as zircon morphology, trace element, U–Pb and Lu–Hf isotopes for granitic gneisses and leucogranites from the Yudongzi complex, a poorly studied Archean outcrop in the northwestern Yangtze Block. The granitic gneisses have the TTG affinity characterized by relatively high Na 2 O/K 2 O and Sr/Y ratios, and fractionated REE pattern with relatively high LREE but low HREE concentrations. Zircon grains in the granitic gneisses show magmatic cores and metamorphic rims. U–Pb dating on zircon core of four granitic gneiss samples yielded their formation ages as 2660–2632 Ma with a weighted average of 2650 ± 21 Ma (MSWD = 1.6; n = 4). Their average ε Hf (t) values range from −0.6 to 0.5 and two-stage model ages from 3.20 to 3.10 Ga, suggesting that the granitic gneisses were likely generated by remelting of thickened Mesoarchean proto-mafic crust. The metamorphic zircon rims have relatively high Th/U ratios and identical Hf isotope compositions to their corresponding cores, indicating that the rims were formed via solid-state recrystallization process. The metamorphic zircons recorded a metamorphic event at ca. 2.5 Ga. U-Pb dating and Lu-Hf isotopes on magmatic zircons from a leucogranite sample revealed a magmatic event at 2477 ± 18 Ma. The recognization of the 2.65 Ga TTG magmatism and the 2.48 Ga intercrustal remelting event in the Yudongzi complex demonstrates the widespread Neoarchean magmatism in the Yangtze Block. Combined with the age spectra of previous detrital zircons, we show that the Yangtze Block has experienced a major tectonothermal event in the late Archean. The Yudongzi complex has a distinct crustal evolution history compare with the Paleoarchean continent nucleus in the eastern part of the Yangtze Block, suggesting that the continent nucleus might have subjected to lateral growth by accretion processes. [ABSTRACT FROM AUTHOR]

Abstract: The Marrakech High Atlas contains some of the best exposures of the Triassic early‐rift strata related to Atlantic opening in NW Africa. We present the first detrital zircon U–Pb data of five Triassic redbed samples from the Tizi n'Test basin to quantify sediment provenance, transport and dispersal patterns during early rifting. These U–Pb ages document dominant sediment sourcing from the south, the Anti‐Atlas domain, with very limited to absent input from the Variscan Meseta domain to the north. This combined with stratigraphic and thermochronologic information points to a highly asymmetric palaeogeography during Triassic rifting. Furthermore, the occurrence of Archaean detrital zircon grains in Triassic sandstone, likely recycled from the Reguibat shield, suggests the presence of a fully developed regional drainage system with rivers and catchments reaching hundreds of kilometres into the hinterland of the rift flank. [ABSTRACT FROM AUTHOR]

The Saveh magmatic complex is a composite intrusion of diorite to tonalite. It is part of the Urumieh-Dokhtar magmatic arc in central Iran. Zircon U Pb dating indicates that emplacement and cooling occurred 37–40 Ma ago in late Eocene (Bartonian) time. Saveh igneous rocks define a continuous mafic-felsic continuum in terms of SiO 2 (55.4–70.8 wt%), Al 2 O 3 (14.2–19.8 wt%) and CaO (6.4–17.1 wt%) contents. The initial values of 87 Sr/ 86 Sr and ɛ Nd (t) are 0.7048 to 0.7062 and + 2.6 to +3.4 (Mean = +2.9). Nd model ages (T DM  = 555 to 616 Ma) are consistent with derivation from Iranian continental crust and subcontinental lithospheric mantle of Cadomian age (500–600 Ma). Saveh igneous rocks are enriched in K, Cs and Pb and depleted in P, Nb and Ta, indicating that the magma source was moderately affected by slab-derived fluids, as expected for the Eocene tectonic environment. The continuum of rock types from diorite to graphic eutectic tonalite indicates that magmatic evolution was controlled by the F (FeO + MgO + MnO)-Anorthite (An)-Orthoclase (Or) cotectic with minor contamination by supra-crustal components. Similar initial ratios of 87 Sr/ 86 Sr and 143 Nd/ 144 Nd for all of the rocks and the slightly younger age of tonalitic rocks (2–3 Ma younger) further indicate that the crystallization of quartz and plagioclase with graphic texture occurred in the final stage of magmatic differentiation. Saveh magmas reflected partial melting of Iranian subcontinental lithospheric mantle due to extension above the Neo-Tethys subduction zone. [ABSTRACT FROM AUTHOR]

The recognition of the Indosinian Orogeny in the South China block has been controversial and difficult because of strong weathering and thick cover. High temperature (HT) and high pressure (HP) metamorphic rocks related to this orogeny were considered to be absent from this orogenic belt until the recent discovery of eclogite and granulite facies meta–igneous rocks, occurring as lenses within the meta–sedimentary rocks of the Badu Complex. However, metamorphic state of these meta–sedimentary rocks is still not clear. Besides, there have been no geochronological data of HT pelitic granulites previously reported from the Badu Complex. This paper presents petrographic characteristics and zircon geochronological results on the newly discovered kyanite garnet gneiss, pyroxene garnet gneiss and the HT pelitic granulites (sillimanite garnet gneiss). Mineral assemblages are garnet + sillimanite + ternary feldspar + plagioclase + quartz + biotite for the HT pelitic granulite, kyanite + ternary feldspar + garnet + sillimanite + plagioclase + quartz + biotite for the kyanite garnet gneiss, and garnet + biotite + pyroxene + plagioclase + ternary feldspar + quartz for the pyroxene garnet gneiss, respectively. Decompressional coronas around garnet grains can be observed in all these pelitic rocks. Typical granulite facies mineral assemblages and reaction textures suggest that these rocks experienced HP granulite facies metamorphism and overprinted decompression along a clockwise P–T loop. Results from integrated U–Pb dating and REE analysis indicate the growth of metamorphic zircons from depleted heavy REE sources (100–50 chondrite) compared with detrital zircons derived from granitic sources (typically > 1000 chondrite). Metamorphic zircons in HP granulite exhibit no or subdued negative Eu anomalies, which perhaps indicate zircon overgrowth under eclogite facies conditions. The zircon overgrowth ages range from 250 to 235 Ma, suggesting that HP granulite (eclogite) to granulite facies metamorphism of these supracrustal rocks occurred in the Early–Middle Triassic. Based on the presence of HP granulite facies pelitic rocks, it is inferred that significant underthrusting was involved during the Indosinian Orogeny which introduced these supracrustal rocks to lower crustal levels. [ABSTRACT FROM AUTHOR]

U-Pb dating of zircon from amphibole latite of the central stock of the Nikolka shield volcano in Kamchatka provided the first data on its age. The end of activity falls to about 0.73 Ma (10 analyses). The local U-Pb analyses were carried out at the Isotope Research Center, Schmidt Joint Institute of Physics of the Earth (St. Petersburg) (VSEGEI) using SIMS SHRIMP II. Here, brief information about the geological structure, petrography, and chemistry of the rocks of the volcano are presented. A unique feature of the volcano is the occurrence of a gabbro-anorthosite sheet intrusion with derivates of monzonite and syenite composition in its central part. The correlation of the age obtained with the paleomagnetic data, indicating the formation of the volcano during the magnetic age of Matuyama, is also discussed. The date refers to the period of the change in epochs from the Brunhes to the Matuyama. The obtained age allows dating of the Pliocene volcanic stage in Kamchatka, when large shield volcanoes and plateaus formed. [ABSTRACT FROM AUTHOR]

Abstract: The development of fast and reliable instrumental methods for U‐Pb dating and Lu‐Hf isotope analysis of zircon has caused detrital zircon to become a popular provenance indicator for clastic sediments and an important tool in basin analysis. In parallel with the increasing ease of access to data, advanced methods of data interpretation have been developed. The downside of some techniques for visualization and comparison of detrital zircon distribution patterns is that the results are difficult to relate to what the zircon grains really record: The age and nature of geological processes in a protosource terrane. Some simple methods of data presentation and inter‐sample comparison that preserve a direct and intuitively understandable relationship between the data and the age of zircon‐forming processes in the protosource are proposed here: Comparison of confidence intervals around empirical, cumulative distribution curves combined with the use of a plot of upper vs. lower quartile values of cumulative zircon U‐Pb age or Lu‐Hf model age distributions. This approach allows a robust and transparent separation to be made between samples whose detrital zircon distributions are indistinguishable from each other, and those that are more or less similar. Furthermore, it allows simple comparison between detrital zircon distributions and the geological age record of potential protosource terranes, or the detrital zircon distributions of possible sedimentary precursors. [ABSTRACT FROM AUTHOR]

The Lower Permian Hasan-Robat syenogranite occurs as a single pluton and intruded the Upper Carboniferous-Lower Permian sandstones and dolomitic limestones in the central part of the Sanandaj-Sirjan zone. This syenogranitic intrusion shows A-type granitic affinity and is a good representative of Early Permian igneous activity in Iran. SIMS U-Pb zircon analyses indicate a crystallization age of 294.2 ± 2.5 Ma for the Hasan-Robat A-type granite. In-situ Lu-Hf and oxygen isotope analyses of magmatic zircons were carried out to infer the magma sources and evolution of the Hasan-Robat A-type syenogranite. The Hf-O zircon isotopic compositions are relatively homogeneous, with nearly chondritic εHf values of −0.8 to +2.4 corresponding to two-stage zircon Hf model ages of 1.15-1.36 Ga. The δO values of zircon range from +7.6 to +8.6‰. The Hf model ages of the Hasan-Robat zircons is within the range of those reported from the Cadomian granitoids in Iran. The isotopic features of the Hasan-Robat syenogranite are in good agreement with Hf isotopic values and Hf and Nd model ages reported from the Cadomian arc magmatic suites in Iran. Thus, partial melting of these Cadomian igneous rocks would be the favorite source for the Hasan-Robat syenogranitic magma during the opening of the Neotethys Ocean and separation of Iranian terranes from the northern margin of Gondwana. [ABSTRACT FROM AUTHOR]

The Terreneuvian Series of the early Cambrian records the first major diversification phase of the canonical Cambrian explosion. However, a paucity of precise radio-isotopic ages for key stratigraphic horizons has resulted in a poor temporal calibration of fossil lowest occurrences (LO) and corresponding rates of evolution throughout the Terreneuvian. Here we present integrated SIMS and CA-ID-TIMS U-Pb analyses on zircons from the basal Shuijingtuo Formation in the Yangtze Gorges area, South China. The dating results provide a depositional age of 526.43 ± 0.54 Ma for the basal Shuijingtuo Formation, and compiled detrital zircon U-Pb dates from the Ediacaran-Cambrian transitional strata in the Yangtze Gorges area indicate their local provenances. The new high-precision date provides a minimum age constraint on the ZHUCE (Zhujiaqing positive carbon isotope excursion) and LOs of Watsonella crosbyi and Aldanella attleborensis in South China, and allows correlation of ZHUCE with either 5.5p or 5p/I′ in Siberia and Morocco. We construct two models of the Ediacaran-Cambrian transitional timescale based on the two alternative correlations of the ZHUCE. The first model correlates the ZHUCE with 5.5p and yields significantly diachronous LOs of W. crosbyi and A. attleborensis between the Siberian Platform and South China. In contrast, the second and our preferred model equates ZHUCE with 5p/I′ and implies relatively synchronous LOs of W. crosbyi and A. attleborensis between the Siberian Platform and South China. In the preferred model, the couplet of ZHUCE/5p/I′ and LOs of W. crosbyi and A. attleborensis serves as a reliable combination to bracket the base of Cambrian Stage 2. • The basal Shuijingtuo ash bed at Yanjiahe section is dated at 526.43 ± 0.54 Ma. • The ZHUCE is correlated to either 5.5p or 5p/I′ in Siberia and Morocco. • Potential markers for the Cambrian Stage 2 are evaluated based on the new date. [ABSTRACT FROM AUTHOR]

We have targeted the southern side of the Dronning Maud Land (DML) mountains in search of moraine material that might reveal the geology in the ice-covered region of the East Antarctic polar plateau. Nine samples of unconsolidated moraine material, carried by the northward flowing East Antarctic ice sheet to the southern side of the DML escarpment, were collected and processed for U-Pb zircon analyses. The analyses resulted in ca. 1100 new U-Pb zircon spot ages between ca. 2000 and 500 Ma. The oldest, Palaeoproterozoic rocks come from the easternmost localities with a probable source region between the Sør Rondane Mountains and Dome Fuji. The samples have major Stenian and early Tonian age peaks. Early Tonian rocks are well known from the SW Terrane in the Sør Rondane Mountains and characterise the major Tonian Oceanic Arc Super Terrane (TOAST). Stenian ages are far less common in the outcropping region. Although Stenian ages are common in both the Maud Province of western-central DML as well as in the Rayner Complex, our samples differ with respect to composition and/or isotope geochemistry; they are juvenile, subduction-related and resemble an early phase of oceanic arcs that was so far unknown in this region. In the westernmost sample, the oldest age peak is ca. 800–720 Ma with possible counterparts in the Schirmacher Oasis. All samples show a protracted Late Neoproterozoic/Early Palaeozoic metamorphic overprint, accompanied by igneous addition, most likely related to the East African-Antarctic Orogen. This overprint appears most intense in clasts collected from the westernmost locality, lasted for ca. 150 Ma and an eastward younging of metamorphic ages is observed. The new moraine samples together with previous outcrop studies reveal that this region has undergone two major phases of oceanic arc/terrane accretion; the first one from ca. 1100 to 900 Ma is probably related to accretion tectonics outboard of Rodinia, the second one from ca. 850 to 580 Ma occurred as a result of ocean closure and finally Gondwana amalgamation. No significant old components are found, but the high proportion of Late Neoproterozoic/Early Palaeozoic ages confirms that the East African-Antarctic Orogen transects DML and East Antarctica. [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]

U-Pb geochronology and trace element chemistry of zircons in a microscale analysis were applied to the Ishizuchi caldera in the Outer Zone of Southwest Japan in order to estimate the timescale of the magma process, in particular, the magma differentiation. This caldera is composed mainly of ring fault complexes, major pyroclastic flow deposits, and felsic intrusion including central plutons. Using SHRIMP-IIe, our new U-Pb zircon ages obtained from the major pyroclastic flow deposits (Tengudake pyroclastic flow deposits), granitic rocks from central plutons (Soushikei granodiorite and Teppoishigawa quartz monzonite), and rhyolite from the outer ring dike (Tenchuseki rhyolite) and the inner ring dike (Bansyodani rhyolite) are 14.80 ±0.11 Ma, 14.56 ±0.10 Ma, 14.53 ±0.12 Ma, 14.55 ±0.11 Ma and 14.21 ±0.19 Ma, respectively. Based on the U-Pb ages, the Hf contents and the REE patterns of the zircons, three stages are recognized in the evolutionary history of the magma chamber beneath the Ishizuchi caldera: (i) climactic Tengudake pyroclastic flow eruption; (ii) Tenchuseki rhyolite intrusion into the outer ring dike and central pluton intrusion; and (iii) Bansyodani rhyolite intrusion in the inner ring dike. These results indicate a magma evolution history of the Ishizuchi caldera system which took at least ca 600 kyr from the climatic caldera-forming eruption to the post-caldera intrusions. Our new geochronological data suggest that the Ishizuchi caldera formed as part of the voluminous and episodic magmatism that occurred in the wide zone along the Miocene forearc basin of Southwest Japan during the inception of the young Philippine Sea Plate subduction. [ABSTRACT FROM AUTHOR]

• Correlation of profiles of the Volyn LIP using zircon CA-ID-TIMS analysis. • Discovery of younger than 567 Ma felsic phase of Volyn volcanism. • Constraining ages of glaciations older and younger than basalt flows. • Constraining ages of Redkino-Kotlin boundary and Podillya Ediacaran biota. • Correlating Podillya Ediacaran with the felsic phase of Volyn volcanism. Combined single zircon crystal CA-ID-TIMS U-Pb dating, micropaleontological study, and quantitative XRD analysis were used to correlate sections of the Podillya-Moldova Ediacaran succession with sections of the Volyn Large Igneous Province (Volyn LIP). Five U-Pb zircon ages were obtained from Volyn LIP rocks, and four from three distinct Podillya bentonite horizons. Biostratigraphic determinations were made for one section in Volyn, and two sections in Podillya. It was concluded that Volyn LIP activity had two phases. A first phase of mafic and felsic magmatism was characterized by eruption of numerous basalt lava flows, and lasted from c. 580 to 567 Ma; a second phase of pyroclastic felsic magmatism, with no lavas, lasted from 567 to c. 545 Ma. The two phases can be distinguished in the quantitative mineral composition of rocks from the Kobryn 1K borehole in western Belarus. In the central area of the Volyn LIP, near Brest, rocks of the felsic phase were removed by erosion before deposition of the Kotlin subgroup. The Podillya Ediacaran succession, from the top of the Hrushka formation to the top of the Kalyus beds, (i.e. the Mohyliv-Podilsky group), hosts soft-bodied organisms. This succession corresponds to the felsic phase of the Volyn LIP. The age of the Redkino-Kotlin subgroup biostratigraphic boundary, at the base of the Nagoryany formation, is constrained at 555–545 Ma, close to the end of the Volyn LIP activity. The newly discovered glaciation in Volyn is dated as c. 567 Ma. The period of development of kaolinitic paleosols on top of the Volyn LIP effusive rocks is dated at c. 570–550 Ma. [ABSTRACT FROM AUTHOR]

The Sumdo complex is a Permian–Triassic eclogitic metamorphic belt in south-east Tibet, which marks the location of a suture zone that separates the northern and southern Lhasa terranes. An integrated geochronological and petrological study of a mafic eclogite from the complex has constrained its tectonometamorphic history and provides a case study of zircon growth in eclogite as a product of prograde dissolution–precipitation. In situ U–Pb geochronology indicates that the eclogite contains a single population of zircon with a crystallisation age of 273.6 ± 2.8 Ma. The morphology and chemistry of the zircon grains are consistent with growth by dissolution–precipitation of protolith magmatic zircon. The presence of zircon grains as inclusions in the cores of peak phases indicates that zircon dissolution–precipitation occurred during prograde metamorphism, and calculated pressure and temperature conditions over which mineral inclusions in zircon are stable suggest that the zircon most likely precipitated at ~15.5–16.5 kbar and 500–560 °C. Subsequent peak metamorphism is calculated to have reached pressure–temperature conditions of 27 ± 1 kbar and 670 ± 50 °C. Previous studies, which have documented a range of peak metamorphic conditions from high- to ultrahigh-pressure at c. 266–230 Ma, indicate that the Sumdo complex is a composite belt that experienced protracted eclogite exhumation. The results of this study are consistent with this interpretation, and extend the age range of high-pressure metamorphism in the complex to over 40 Myr. Analysis of published pressure–temperature–time data indicates two systematic behaviours within this spread. First, peak metamorphic temperatures declined over time. Second, eclogite exhumation occurred in two discrete intervals: soon after formation, and during the demise of the subduction zone. The latter behaviour serves as a reminder that eclogite exhumation is the exception rather than the rule. [ABSTRACT FROM AUTHOR]

The Lüliang Complex is located at the western margin of the middle segment of the Trans-North China Orogen, along which the Western and Eastern Blocks collided to form the North China Craton. The complex mainly consists of metamorphosed granitic plutons and supracrustal rocks, of which the latter are subdivided into the Jiehekou, Lüliang, Yejishan, Lanhe and Heichashan Groups. The Lanhe Group is composed of meta-conglomerates, quartzites, and phyllites with minor meta-basalts, whereas the Heichashan Group consists of molasse-like meta-conglomerates and coarse-grained quartzites. Geochemistry of the Yejishan meta-sedimentary rocks indicates weak source weathering and dominantly chemical immature features, whereas the Lanhe and Heichashan samples display opposite features. U–Pb ages of detrital zircons from the Lanhe Groups yield four age peaks at ~ 2180 Ma, ~ 2370 Ma, ~ 2520 Ma and ~ 2700 Ma. The former three peaks coincide with ages of the Chijianling–Guandishan TTG gneisses (2199–2151 Ma) and meta-volcanic rocks from the Lüliang and Yejishan Groups (2213–2156 Ma), age of the Gaijiazhuang porphyritic gneisses (2375–2364 Ma) and age of the Yunzhongshan TTG gneisses (2499 Ma) respectively, whereas detrital zircons forming the oldest age peak were most likely derived from the early Neoarchean crust of the Eastern Block. For the Heichashan Group, the dominant 2.2–2.0 Ga detrital zircons were probably recycled from the underlying Jiehekou Group and the minority is directly derived from the early Paleoproterozoic granitoids in the Lüliang Complex. The youngest detrital zircon age peaks of ~ 2.17 Ga and ~ 1.82 Ga place maximum depositional ages on the Lanhe and Heichashan Groups respectively, whereas the local 1.81–1.79 Ga massive granites place constraint on their minimum depositional ages. Taking into account the lithostratigraphic features, provenance and formation ages, we suggest that the Lanhe Group formed in a shrinked remnant back-arc basin and the Heichashan Group was deposited in a foreland basin. Conversion of the tectonic basin from the middle Paleoproterozoic back-arc basin to the late Paleoproterozoic foreland basin is well consistent with the model that the single collision to form the basement of the North China Craton happened at ~ 1.85 Ga. [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 Penglaitan section, as the Global Stratotype Section for the Guadalupian-Lopingian boundary (GLB), displays continuous deposition with a complete succession of pelagic conodont zones across the GLB. However, there is no reliable radiometric age from the Penglaitan section itself to constrain the GLB. Here, we report SIMS zircon U-Pb ages from two bentonite layers (Bed 7c) in the Penglaitan Global Stratotype Section near the GLB. The sample PL-62-1 yields a weighted mean 238U/206Pb age of 257.1 ± 2.2 Ma, and the sample PL-62-2 yields a weighted mean 206Pb/238U age of 257.0 ± 4.2 Ma. Therefore, we consider 257.0-257.1Ma as the age of deposition of Bed 7c (the end of the C. postbitteri postbitteri conodont Zone, ca. 86 cm above the GLB), and, considering the depositional rate of chert, we suggest 258.6Ma as the age of the GLB. [ABSTRACT FROM AUTHOR]

The Attic-Cycladic Crystalline Belt in the central Aegean region represents a major tectono-stratigraphic unit of the Hellenides. The essential geological, magmatic and tectono-metamorphic features are well documented. Unresolved questions concern the time of sediment accumulation and litho- and/or tectono-stratigraphic relationships across the study area. In order to address this issue we have studied siliciclastic metasedimentary rocks from Andros Island, northern Cyclades. The sampling strategy aimed at covering the complete age range recorded by the Andros metamorphic succession. Detrital zircon U-Pb dating of nine samples indicates maximum depositional ages of c. 260 Ma for the topmost part of the metamorphic succession and of c. 160-140 Ma for rock sequences below a prominent serpentinite belt that is interpreted to outline a major tectonic contact. These age constraints are in accordance with interpretations suggesting that the metamorphic rocks of Andros represent different tectonic subunits (Makrotantalon Unit and Lower Unit) that are separated by a thrust fault. Modification of the internal structure of the Lower Unit by tectonic stacking can currently not be ascertained. The new data for the Lower Unit corroborate the importance of Late Jurassic-Early Cretaceous sediment accumulation for the larger study area. In contrast to some of the neighbouring islands, no evidence for transfer of Late Cretaceous ( c. 80 Ma) material into the Andros sedimentary environment was found. The most striking feature of the zircon populations of the Lower Unit is a remarkable age cluster at 250-200 Ma that documents the importance of Triassic igneous sediment sources. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

During LA-ICP-MS analysis,the key factor influencing data accuracy of sample analysis is whether the sample can be uniformly delivered from the laser sample chamber to the torch of the ICP-MS.An external container between LA and ICP-MS and a multi-channel rotary sampling cell,which can effectively eliminate the sample position effect during the laser ablation was designed for the study reported in this paper.The pattern of aerosol delivered to ICP-MS is approximately continuous and at the same time,this can greatly improve the stability.Under optimal conditions,using 91500 as external standard,the standard zircons GJ-1,Ple ovice,TEMROA and QH yield U-Pb ages of 604±3 Ma(2δ,MSWD=1.2),337±1 Ma(2δ,MSWD=1.18),419±3 Ma(2δ,MSWD=0.15) and 161±1 Ma(2δ,MSWD=0.6),respectively,which agree well with the previously reported ID-TIMS and SHRIMP ages.For the same conditions,using NIST610 as external standard,most trace element results of the glass standards NIST612 and BHVO-2G fall within 10% range of the reference values.The 207Pb/206Pb weighted mean age of zircons from the Tianshan Orogen of Xinjiang is consistent with the previous SHRIMP U-Pb age within uncertainty.This method can effectively reduce the elemental fractionation effects and improve the reliability of the analytical data. [ABSTRACT FROM AUTHOR]

The East Kunlun Orogen in the Northern Qinghai–Tibet Plateau is an ideal region to investigate the geodynamic processes of magmatism related to the closure of the Paleo-Tethys Ocean. Here, we report petrology, zircon U–Pb geochronology, whole-rock geochemistry and multiple isotope data from granodiorites and the associated dioritic enclaves in a dominant Nan'getan granitoid in the East Kunlun Orogen. Zircon U–Pb ages indicate that the host granodiorites and dioritic enclaves were synchronously emplaced at ~ 243 Ma. The granodiorites are medium- to high-K calc-alkaline, metaluminous (A/CNK = 0.93–0.98), with high Al 2 O 3 content (15.28%–16.10%), Mg # (47–49), very low Sr/Y ratios (127–217), high abundances of incompatible elements (Y = 3.87–8.36 ppm, Nb = 3.04–5.71 ppm, Th = 3.04–5.71 ppm), low ( 87 Sr/ 86 Sr) i (0.7050–0.7079), negative whole-rock ε Nd (t) (− 8.2 to − 5.8), ( 206 Pb/ 204 Pb) 243Ma of 18.520 to 18.772, ( 207 Pb/ 204 Pb) 243Ma of 15.611 to 15.650, ( 208 Pb/ 204 Pb) 243Ma of 38.227 to 38.528, δ 18 O SMOW = 6.8‰–9.1‰, ε Hf (t) of − 1.2 to + 2.4. The dioritic enclaves (SiO 2 = 51.08%–56.29%) have Mg # values of 48–51, with negative Eu anomalies (δEu = 0.59–0.79), low ( 87 Sr/ 86 Sr) i (0.7058–0.7080), negative whole-rock ε Nd (t) (− 8.2 to − 5.8), ( 206 Pb/ 204 Pb) 243Ma of 18.376 to 18.809, ( 207 Pb/ 204 Pb) 243Ma of 15.606 to 15.661, ( 208 Pb/ 204 Pb) 243Ma of 38.244 to 38.540, δ 18 O SMOW = 5.6‰–10.0‰, ε Hf (t) of − 3.5 to + 1.7. These isotopic features of arc-type rocks from the East Kunlun suggest that the parental magmas of the Nan'getan granodiorites and the dioritic enclaves originated from an enriched lithospheric mantle. The Nan'getan granitoids might have recorded the northward subduction of the Paleo-Tethys ocean lithosphere following the initial collision of the Bayan Har–Songpan Ganzi–East Kunlun terrane and the closure of the Paleo-Tethys Ocean at ~ 243 Ma. [ABSTRACT FROM AUTHOR]

Introduction: The ~31-km-wide Hiawatha structure, located beneath Hiawatha Glacier in northwestern Greenland, has been proposed as an impact structure that may have formed after the Pleistocene inception of the Greenland Ice Sheet [1]. However, available age constraints for the Hiawatha structure have only been tentative. The bedrock under the structure is likely a continuation of the highly metamorphosed 1.95-1.75 Ga [2] bedrock exposed immediately adjacent to Hiawatha Glacier, providing a maximum constraint on the structure's age [1]. Further age estimates have been based on indirect constraints, such as estimates of erosion rates and the structure's relationship to the Greenland Ice Sheet [1]. Here we dated the structure using detrital materials sampled immediately downstream thereof. We report 40Ar/39Ar analyses of impact-related glaciofluvial sand collected in 2016 and U-Pb analyses of shocked zircon from pebble-sized glaciofluvial clasts of impact melt rock collected in 2019. Results: Of the 50 grains that underwent 40Ar/39Ar step-heating analysis, 29 developed 'U'- or 'saddle'-shaped age spectra, with 23 giving minimum apparent ages in the Paleocene. Two mini-plateaus gave Late Paleocene ages of 58.5 ± 0.3 Ma and 60.2 ± 0.5 Ma, respectively. The 62 U-Pb analysis performed on 43 zircon grains using secondary ion mass spectrometry (SIMS) defined a discordant array in concordia space, spreading between an upper intercept of ~1915 Ma and a Late Paleocene lower intercept. The ~1915 Ma age for the majority of unshocked zircon grains from the impact melt rocks agrees with known geological events and zircon ages from the bedrock adjacent to Hiawatha Glacier [2], supporting a local origin for the samples. Of the 45 analyses performed on shocked zircon grains, the youngest nine data points are statistically indistinguishable, giving a robust concordia age and a weighted mean 206Pb/238U age of 57.99 ± 0.54 Ma (MSWD = 1.18; probability = 0.30; n = 9). We consider this to be the most robust estimate for the age of the impact structure [3]. Discussion: Impact melt rocks collected less than 10 km downstream from the edge of the Hiawatha structure contain unshocked zircon with ages matching that of the bedrock adjacent to Hiawatha Glacier. Shocked zircon in these samples gives a ~58 Ma U-Pb age, which agrees with the younger of two 40Ar/39Ar mini-plateau ages from the sand sample. The samples were thus derived from a Late Paleocene impact structure somewhere upstream but sufficiently proximal that the target geology is indistinguishable geochronologically from that exposed where the samples were recovered. Given existing geomorphic evidence for an eroded complex impact structure beneath Hiawatha Glacier, we suggest this is the source of the samples and thus that the Hiawatha structure is a relatively large impact structure that formed in the Late Paleocene. The new age indicates that the Hiawatha impact structure significantly predates Pleistocene glaciation and is unrelated to either the Paleocene-Eocene Thermal Maximum or flood basalt volcanism in east Greenland. The impact was contemporaneous with the Paleocene Carbon Isotope Maximum, although the impact's exact paleoenvironmental and climatic significance await further investigation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Collapsed breccia zone associated with normal faulting is found in the Taihang Shan. • Allochthons in the Taihang Shan were formed by basal detachment in NW-SE extension. • Upper-crustal extensional deformation occurred in the Taihang Shan at ∼134 Ma. • The Taihang Shan experienced crustal extension like the Eastern Block during NCC destruction. Whilst geophysical exploration and petrological analyses imply that the Early Cretaceous North China Craton (NCC) destruction may have impacted the Taihang Shan in the central NCC, associated evidence indicative of contemporary upper-crustal extension is lacking. We herein investigate the formation mechanism and timing of the allochthons that consist of Mesoproterozoic to Mesozoic sedimentary rocks within the Paleoproterozoic Fuping complex in the middle Taihang Shan, based on field investigation and zircon U-Pb analysis. Our results indicate that the western boundary of the selected allochthon features wide collapsed breccias filled with synchronous Early Cretaceous (∼134 Ma) pyroclastics. These allochthons likely formed under extension along with the basement doming of the Fuping complex in response to crustal stretching in Early Cretaceous. Our results provide explicit evidence of upper-crustal extension in the Taihang Shan associated with the Early Cretaceous NCC destruction. [ABSTRACT FROM AUTHOR]

The morphology, REE geochemistry and U-Pb geochronology of zircons from quartz monzodiorite in the Sunzhuang area, Fanshi County, Shanxi Province are presented in this study. The zircon crystals can be classified into four main types as: AB, L, S and P, and 24 subtypes such as AB4, AB5, L5, and S3. The maximum crystallization temperature of zircon was estimated as 850°C, with the minimum of 550°C. The peak temperatures of the zircon crystallization range from 650°C to 700°C. The abundances of Th and U in the zircon grains show large variation with the Th/U values > 0.4. The Th and U values also show a positive correlation in most zircons. The REE abundance of zircon in the quartz monzodiorite ranges from 280.4 ppm to 2143 ppm with an average of 856.4 ppm. The chondrite normalized zircon REE patterns show two types, one is characterized by HREE enrichment and LREE depletion with positive Ce-anomaly and negative Eu-anomaly whereas the other is HREE enriched and LREE depleted with negative Eu-anomaly but without positive Ce-anomaly, and relatively flat patterns. The LA-ICP-MS U-Pb geochronology on the zircons yields a mean age of 133±0.87 Ma. Our data on zircon morphology, composition and U-Pb geochronology reveal that the parent magma of the quartz monzodiorite which was emplaced during late Yanshanian had a mixed crust-mantle source, with crustal components dominating. The magma is inferred to have been water rich and alkaline with initial high oxygen fugacity. Post-magmatic hydrothermal activity occurred under relatively reducing conditions which was conductive for gold precipitation in the Yixingzhai gold deposit. [ABSTRACT FROM AUTHOR]

Investigation of the petrogenesis and the origin of zircons from the volcanic rocks of the Liujiaping Group of the back-Longmenshan tectonic belt in the northwest margin of the Yangtze Block is conducted by analysis of U-Pb geochronology and geochemistry. Results show that selected zircons are characterized by internal oscillatory zonings and high Th/U ratios (0.43-1.18), indicating an igneous origin. Geochronological results of LA-ICP-MS U-Pb dating of the Liujiaping Group zircons yield an age of 809 ± 11 Ma (MSWD = 2.2), implying that the volcanic rocks were formed in the Late Neoproterozoic. Geochemical analysis shows that the rocks are calc-alkaline, supersaturated in Al, and metaluminous to weakly peraluminous. Rare-earth elements are present at high concentrations (96.04-265.48 ppm) and show a rightward incline and a moderately negative Eu anomaly, similar to that of continental rift rhyolite. Trace element geochemistry is characterized by evident negative anomalies of Nb, Ta, P, Th, Ti, inter alia, and strong negative anomalies of K, Rb, Sr, et al. We conclude that the Liujiaping Group volcanic rocks resulted from typical continental crust source petrogenesis and were formed in a continental margin setting, which had no relation to subduction, and thus, were the products of partial melting of the lower crust due to crustal thickening caused by active continental margin subduction and arc-continent collision orogeny in the northwestern Yangtze Block and were triggered by the breakup of the Rodinia supercontinent during the Neoproterozoic. [ABSTRACT FROM AUTHOR]

This study investigates the behaviour of the geochronometers zircon, monazite, rutile and titanite in polyphase lower crustal rocks of the Kalak Nappe Complex, northern Norway. A pressure-temperature-time-deformation path is constructed by combining microstructural observations with P-T conditions derived from phase equilibrium modelling and U-Pb dating. The following tectonometamorphic evolution is deduced: A subvertical S1 fabric formed at ~730-775 °C and ~6.3-9.8 kbar, above the wet solidus in the sillimanite and kyanite stability fields. The event is dated at 702 ± 5 Ma by high-U zircon in a leucosome. Monazite grains that grew in the S1 fabric show surprisingly little variation in chemical composition compared to a large spread in (concordant) U-Pb dates from c. 800 to 600 Ma. This age spread could either represent protracted growth of monazite during high-grade metamorphism, or represent partially reset ages due to high- T diffusion. Both cases imply that elevated temperatures of >600 °C persisted for over c. 200 Ma, indicating relatively static conditions at lower crustal levels for most of the Neoproterozoic. The S1 fabric was overprinted by a subhorizontal S2 fabric, which formed at ~600-660 °C and ~10-12 kbar. Rutile that originally grew during the S1-forming event lost its Zr-in-rutile and U-Pb signatures during the S2-forming event. It records Zr-in-rutile temperatures of 550-660 °C and Caledonian ages of 440-420 Ma. Titanite grew at the expense of rutile at slightly lower temperatures of ~550 °C during ongoing S2 deformation; U-Pb ages of c. 440-430 Ma date its crystallization, giving a minimum estimate for the age of Caledonian metamorphism and the duration of Caledonian shearing. This study shows that (i) monazite can have a large spread in U-Pb dates despite a homogeneous composition; (ii) rutile may lose its Zr-in-rutile and U-Pb signature during an amphibolite facies overprint; and (iii) titanite may record crystallization ages during retrograde shearing. Therefore, in order to correctly interpret U-Pb ages from different geochronometers in a polyphase deformation and reaction history, they are ideally combined with microstructural observations and phase equilibrium modelling to derive a complete P-T-t-d path. [ABSTRACT FROM AUTHOR]

The Upper Proterozoic sequence in the southern part of the East Anabar Basin, as throughout the entire framing of the Anabar uplift, has a two-unit terrigenous-carbonate structure. The results of the U-Pb dating of detrital zircons show that there is a difference in stratigraphy of Riphean strata in the north and south of the Anabar Uplift. In the north, deposits of the entire sequence are regarded as Early Riphean; in the south, the thickness of these deposits is reduced to 70 m. The overlying stratum is regarded as Upper Riphean-Vendian. As the strata in the southern part of the East Anabar Basin strata are of younger (Late Riphean-Vendian) age, they cannot be assigned to the Mukun and Billyakh groups. The Riphean-Vendian deposits accumulated mainly through erosion of crystalline rocks of the Anabar Uplift. In the upper part of the sequence, the Vendian magmatic complexes located probably within the Taimyr Orogen played a significant role as provenance areas. [ABSTRACT FROM AUTHOR]

A large number of Paleoproterozoic borate deposits are hosted by the lower units of a volcanic-sedimentary sequence in Liaoning Province, northeastern China, and are a major source of boron in China. The ore-bearing wall rocks in the deposits are serpentinized ultrabasic rocks and carbonates, with layered leptynites, leptites, amphibolites, and migmatites adjacent to the ore. Both the borate ores and country rocks contain tourmaline, although the country rocks have much lower abundances of the mineral. Based on in situ boron isotope measurements using laser ablation–multi-collector–inductively coupled plasma–mass spectrometry (LA–MC–ICP–MS), boron isotope data show that: (1) δ 11 B values of borate ores range from + 6.8‰ to + 13.9‰ (mean + 10.8‰); (2) tourmalines from the borate ores have δ 11 B values from + 9.5‰ to + 12.7‰; and (3) the wall rocks within the borate ores yield slightly lower δ 11 B values ranging from + 5.7‰ to + 7.6‰, and those outside the deposits from − 9.9‰ to − 5.9‰. Positive δ 11 B values in borates as well as in tourmalines inside the mining area indicate that boron in these Paleoproterozoic borate deposits was derived from marine evaporites. δ 34 S V-CDT (where V-CDT is Vienna Canyon Diablo Troilite) values of borate ores, serpentinized marbles, and anhydrites range from + 16.1‰ to + 24.7‰, whereas δ 13 C V-PDB (where V-PDB is Vienna Pee Dee Belemnite) values of marbles range from + 3.2‰ to + 5.9‰. These isotopic characteristics are interpreted to reflect formation in a marine evaporative environment. LA–MC–ICP–MS zircon weighted 207 Pb/ 206 Pb ages of leptite and serpentinized olivine basalt from the hanging wall of the borate deposits are 2139 ± 13 Ma and 2130 ± 19 Ma, respectively. Therefore, the (~ 2.2 Ga) borate deposits may have originated from marine evaporative boron-bearing sediments, which were interbedded within bimodal volcanic rocks during the early stages of development of the Liaoji rift. [ABSTRACT FROM AUTHOR]

We present an improved U–Pb age dating method for zircon and monazite crystals using 193 nm excimer laser ablation and 200/266 nm femtosecond laser ablation (200/266FsLA) multiple-Faraday collector inductively coupled plasma-mass spectrometry (MFC-ICP-MS). Optimization of a 266 fs laser beam enabled an analysis of 207Pb/206Pb and 206Pb/238U ratios with an in-run precision of 1–2% from a crater of dimensions 50 μm × 10 μm (diameter × depth) at a repetition rate of 2 Hz for 30 s. The same in-run precision was obtained from a 30 μm × 20 μm crater using a 200 fs laser beam of 20 μm in diameter rastered along the circumference of a circle with a 7 μm radius at 25 Hz for 15 s. With an enhanced sensitivity ion interface, the sensitivity for the total amount of Pb was ∼2 mV ppm−1 or ∼125 000 cps ppm−1 using the above crater setup. The use of high gain amplifiers equipped with a 1012Ω register enabled the determination of the U–Pb age of zircon and monazite crystals with an internal and intermediate precision comparable to that obtained from sensitive high resolution ion microprobe (SHRMP) techniques. We analysed standard zircon crystals using a 91500 zircon crystal (1065.4 ± 0.6 Ma determined by isotope dilution thermal ionization mass spectrometry (ID-TIMS)) as a bracketing standard. Ages determined from TEMORA2, Prešovice, and OD-3 zircons compared very well with their reference ages determined by ID-TIMS and/or SHRIMP. Thompson Mine and Monangotory standard monazites, dated using a 44069 monazite crystal (424.9 ± 0.4 by ID-TIMS) as a standard, also reproduced the U–Pb ages determined by ID-TIMS/LA-MFC-ICP-MS, but at a sample volume four times smaller than that required for zircons. Zircon and monazite ages are accurate given the small offsets from ID-TIMS ages, 0.15–0.7% for zircons and 0.2–0.7% for monazite well within internal precision from the primary standard in the analytical session and competitive with an internal precision of 0.43–0.6% for zircon and 0.2–0.8% for monazite. More easily obtaining high resolution age data is useful for the precise determination of the U–Pb age. [ABSTRACT FROM AUTHOR]

Zircon SHRIMP dating of granites from Dulan, east segment of North Qaidam UHP belt shows that they are 406.6±3.5 Ma for Yematan-E, 407.3±4.3 and 397±6 Ma for Balijiehatan-W, 404.5±4.0 and 397.0±3.7 Ma for Shuiwenzhan-N, 380.5±5.0 Ma for Shuiwenzhan-S, 382.5±3.6 and 372.5±2.8 Ma for Chachagongma. These granites from Dulan represent the products of the third and fourth periods of Paleozoic magmatism in North Qaidam. Geochemically, the granitoids with metalumious to weak peratuminous are quartz diorite, granodiorite, and granite in composition and mainly belong to calc-alkaline series, a few samples to calc or alkali-calc series. The third period of granites is a rock association of granodiorite + granite, with initial Sr/Sr ratios from 0.7082 to 0.7110 and T model ages from 1.41-1.90 Ga; and the fourth period of granites is a rock association of quartz diorite+granodiorite+granite, with initial Sr/Sr ratios from 0.7072 to 0.7091 and T model ages from 1.07-1.38 Ga. Therefore, the third period of granites has higher initial Sr/Sr ratios and T model ages. On the contrary, the fourth period of granites has ɛ( t) values from 0.6 to −3.0, higher than that of the third granite with ɛ( t) values −3.2 to −9.3. Thus, the data comparison indicates that the third granites may derive from Paleo-proterzoic continental crust with mantle material whereas the fourth granites may derive from the Meso-proterzoic basalt crust with continental material. Combined with regional geology, we thought that the third granites were formed relative to plate exhumation and the fourth granites to delamination of the lithospheric mantle. [ABSTRACT FROM AUTHOR]

A table tuff interlayer at the bottom of Chang-7 Member of Yanchang Formation, the Ordos Basin, may serve as an indicator for stratigraphic division and correlation. In this study, zircon SHRIMP U-Pb dating was performed on the tuff at the bottom of Chang-7 Member using samples from wells Luo-36 and Zhuang-211 in the southwest of the basin, which yielded weighted average Pb/U ages of 241.3±2.4 and 239.7±1.7 Ma, respectively. The cathodoluminescence images and the U/Th element ratio of tuff indicate that the zircons are magmatogenic and their ages represent that of the sedimentation age of the tuff at the bottom of Chang-7, which is 239.7-241.3 Ma in age. This finding confirms presence of the Middle Triassic strata at the bottom of Yanchang Formation. Taking previous findings into account, we suggest restricing the Late Triassic Yanchang Formation sensu stricto to the interval from Chang-7 to Chang-1 and assigning the interval from Chang-10 to Chang-8 as the Tongchuan Formation. The tuff at the bottom of the Chang-7 Member of Yanchang Formation represents the sedimentary response to the Qinling orogenic event in the early Indosinian. This tectonic event resulted in major changes in paleogeomorphology and the sedimentary environment of the lake basin during deposition of the Yanchang Formation. During this period, extremely favourable conditions were present for subsequent hydrocarbon generation and pooling of lake basin. [ABSTRACT FROM AUTHOR]

The Delbar Metamorphic-Igneous Complex (DMIC) consists of the medium to high-grade metamorphic rocks and granites - leucogranites is located in the Biarjmand region, in Central Iran. U-Pb dating of the gneisses yielded the ages of 546±3.7-547±6.8Ma similar to the crystallization ages of leucogranites (541±4.7-547±11Ma) are consistent to the Late Ediacaran-Early Cambrian ages of Cadomian magmatic arc (~545Ma). The 206Pb/238U ages of the detrital zircons from the mica-schists sample are from 551±5.1-549±5.1Ma. The youngest ages of the meta-pelitic protolith have 10Ma age intervals compared to the granites emplacement age, which indicates rapid Late Precambrian crustal recycling involving erosion, burial, metamorphism to partial melting of the continental crust in less than ca. 10Ma. These rapid crustal evolutions were related to the final collision and amalgamation of Gondwana, the Rheic Ocean clouser and coeval paleotethys opening at the end of the Avalonian-Cadomian orogeny. The studied granites are similar to the volcanic arc granitoids and originated from the crustal source in an active continental margin based on the geochemical characteristics and Hf isotopes data. Exhumation of the DMIC Complex, is marked by deposition of Lower Jurassic conglomerates contains pebbles of basement rocks. These rocks were interrupted by mafic swarms dikes that have generated in a back arc extensional setting related to the Neotethys subduction under the Central Iran at the 152±35Ma (Middle-Late Jurassic) based on the U-Pb apatite dating. [ABSTRACT FROM AUTHOR]

• Abundant zircon xenocrysts were captured by the late Paleozoic (<342 Ma) Maping diamondiferous kimberlites. • Xenocrystic zircon peak ages at ∼2.9 Ga, ∼2.6 Ga and ∼2.0 Ga are older than the Neoproterozoic outcrops. • Highly evolved Archean basement may exist beneath the southern Yangtze Block. • The basement underwent complex crustal growth at 2.6–2.5 Ga and reworking at 3.0–2.6 Ga. • Newly identified ∼2.0 Ga metamorphic event was probably linked to the assembly of the Nuna/Columbia supercontinent. Crustal zircon xenocrysts from mantle-derived magmatic rocks have the potential to probe the deep crust. Here we present integrated U–Pb dating and Hf-isotope analyses of zircons from a Paleozoic diamondiferous kimberlite dike in the Maping area of Zhenyuan County (southeastern Guizhou Province), with implications for the tectonothermal evolution of unexposed continental crust beneath the southern Yangtze Block, South China. All zircons (n = 236) show a wide range of U–Pb ages between Mesoarchean and middle Carboniferous. Among them, 96 zircons with 90–110% concordance yield concordant ages from 2942 ± 8 Ma to 342 ± 2 Ma, and form major age peaks at ∼2.9 Ga, ∼2.6 Ga and ∼2.0 Ga. The overwhelming majority of zircons are dominated by Mesoarchean–Paleoproterozoic U–Pb ages regardless of their concordance degrees. The zircon populations mainly consist of magmatic zircons, with minor metamorphic grains (Th/U < 0.10). The youngest magmatic zircon (Th/U = 0.43) with a well concordant 206Pb/238U age of 342 ± 2 Ma (M1-16) is interpreted as the maximum emplacement age of the Maping diamondiferous kimberlites. Most zircons with pre-eruption ages are considered to be xenocrysts, and they may be derived from the deep-seated continental crust through which kimberlite host magmas have passed. Their U–Pb ages and Hf isotopic compositions suggest the possible existence of a highly evolved Archean basement beneath the southern Yangtze Block, South China, which is much older than its known surface rocks. A lot of magmatic zircon xenocrysts reveal complex Precambrian crustal evolution in the southern Yangtze Block. These processes involved the important growth of continental crust at 2.6–2.5 Ga, and in the meantime, crustal reworking could be intermittently proceeding at 3.0–2.6 Ga. In addition, a group of xenocrystic zircons are identified to be of metamorphic origin, indicating that the proposed Archean basement beneath the southern Yangtze Block likely experienced a metamorphic event around 2.0 Ga. This geologically significant episode is consistent with the well-developed coeval metamorphism in other places of the Yangtze Block (e.g., Kongling Terrane), which has been considered to link to the assembly of the Paleoproterozoic Nuna/Columbia supercontinent. Our zircon data implies that the unexposed Archean basement beneath the southern Yangtze Block was affected by multiple thermal activities. [ABSTRACT FROM AUTHOR]