Early Carbonate Research Articles

LP/HTmetamorphism as a temporal marker of change of deformation style within the Late Palaeozoic accretionary wedge of central Chile

AbstractA Late Palaeozoic accretionary prism, formed at the southwestern margin of Gondwana from Early Carboniferous to Late Triassic, comprises the Coastal Accretionary Complex of central Chile (34–41°S). This fossil accretionary system is made up of two parallel contemporaneous metamorphic belts: a high‐pressure/low temperature belt (HP/LT– Western Series) and a low pressure/high temperature belt (LP/HT– Eastern Series). However, the timing of deformation events associated with the growth of the accretionary prism (successive frontal accretion and basal underplating) and the development of theLP/HTmetamorphism in the shallower levels of the wedge are not continuously observed along this paired metamorphic belt, suggesting the former existence of local perturbations in the subduction regime. In the Pichilemu region, a well‐preserved segment of the paired metamorphic belt allows a first order correlation between the metamorphic and deformational evolution of the deep accreted slices of oceanic crust (blueschists andHPgreenschists from the Western Series) and deformation at the shallower levels of the wedge (the Eastern Series).LP/HTmineral assemblages grew in response to arc‐related granitic intrusions, and porphyroblasts constitute time markers recording the evolution of deformation within shallow wedge material. IntegratedP–T–t–danalysis reveals that theLP/HTbelt is formed between the stages of frontal accretion (D1) and basal underplating of basic rocks (D2) forming blueschists atc. 300 Ma. A timeline evolution relating the formation of blueschists and the formation and deformation ofLP/HTmineral assemblages at shallower levels, combined with published geochronological/thermobarometric/geochemistry data suggests a cause–effect relation between the basal accretion of basic rocks and the deformation of the shallowerLP/HTbelt. The S2foliation that formed during basal accretion initiated near the base of the accretionary wedge at ~30 km depth atc. 308 Ma. Later, the S2foliation developed atc. 300 Ma and ~15 km depth shortly after the emplacement of the granitoids and formation of the (LP/HT) peak metamorphic mineral assemblages. This shallow deformation may reflect a perturbation in the long‐term subduction dynamics (e.g. entrance of a seamount), which would in turn have contributed to the coeval exhumation of the nearby blueschists atc. 300 Ma. Finally,40Ar–39Ar cooling ages reveal that foliated LP/HT rocks were already at ~350 °C atc. 292 Ma, indicating a rapid cooling for this metamorphic system.

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Contrasting views exist on the stability of the Earth’s shield regions over the last 1 Ga that have major implications for reconstructing erosion patterns on shields and the supply of sediment to intra-cratonic and marginal basins. This paper explores Phanerozoic denudation rates and patterns on the northern part of the Fennoscandian Shield in the Kola Peninsula, Northwest Russia. This shield region was intruded by magmatic rocks of the Kola Alkaline Province (KAP) in the Devonian and Early Carboniferous. The KAP comprises a varied suite of alkali–ultramafic plutonic and hypabyssal intrusions, diatremes and dykes that was emplaced at various depths in the crust and allows assessment of depths and rates of erosion during and since the KAP magmatic episode. Further evidence of long-term denudation is provided by Mesoproterozoic and Neoproterozoic cover rocks found around the margins of the Kola Peninsula and in the White Sea. The burial and exhumation history is compared to available Apatite Fission Track (AFT) data for the Kola Peninsula and adjacent areas. Post-Devonian denudation rates on the shield rocks of the Kola Peninsula have varied in space and time. Around the periphery of the Kola Peninsula, low long-term denudation of shield rocks is indicated by the survival of Riphean cover rocks and Late Devonian lavas, kimberlite crater facies and near-surface emplacement of dykes. In contrast, in the main belts of KAP intrusions, 4–6 km of rock was removed in response to doming between 460 and 360 Ma. Deep denudation is indicated by the emplacement depths of alkaline intrusions and Phoscorite–Carbonatite pipes (PCPs). Erosion on the Kola Peninsula since 360 Ma has been far more limited. Extensive, shallow, late-stage magmatism associated with PCPs, dykes and the large alkaline intrusions in the KAP indicates that erosion depths nowhere exceeded 2 km. Post-Devonian denudation has removed <1 km of rock from the margins of the Kola Peninsula and from the backslope of the Saariselka–Karelia scarp in northern Finland. AFT data point to an important phase of erosion in the early Mesozoic but depths of unroofing of 3–5 km based on AFT cooling ages for this later phase are in conflict with the evidence of lesser erosion provided by the late-stage KAP intrusions and also require unrealistic depths of former Devonian to Triassic cover rocks. Mean denudation rates were greatest (up to 40 m/Myr) during the KAP magmatic phase. Post-Devonian rates across the Kola Peninsula and adjacent shield areas were much lower (<3–6 m/Myr) and are compatible with low long-term denudation rates for other cratons. Further resolution of longterm denudation patterns and rates on the Kola Peninsula requires the application of low-temperature thermochronometry, detailed examination of the regional geomorphology and firmer dating of ancient weathering episodes.

Organofacies and paleoenvironment of lower Carboniferous mudstones (Dishuiquan Formation) in Eastern Junggar, NW China

The sedimentary rocks of the Dishuiquan Formation represent an important potential source for volcanic rock reservoirs and record the transition of the depositional environment from marine to terrestrial during paleo-Junggar oceanic subduction. The source rock potential and paleoenvironment of mudstones from Dishuiquan Formation in Eastern Junggar, were determined by organic petrography, Rock-Eval, molecular and stable carbon (δ13C) analyses. TOC, S2, and hydrogen index (HI) values suggest a fair to good organic richness in mudstone samples from the C-2 well. Moreover, an early mature to mature state for all the samples is inferred based on the Rock-Eval and biomarker parameters. The maceral composition, molecular geochemistry and carbon isotopic results for kerogen reveal that all the mudstone samples are characterized by a mixed organic matter assemblage (Types II–III) with relatively high percentages of terrigenous organic matter. The low to intermediate values of Pr/Ph and the high abundances of β-carotene and gammacerane indicate the presence of a dysoxic, reducing, high-salinity sedimentary environment during the deposition of the Dishuiquan Formation. Numerous parameters derived from the organic geochemical analyses indicate that the terrigenous organic matter increased with decreasing salinity and oxidation in the sedimentary environment. This study concludes that a warm, wet climate provided a continuous fluvial input of terrigenous plant debris and fresh water. The organic geochemical data, combined with the tectonic setting, reveal a restricted, semi-closed marine depositional environment during the deposition of the Dishuiquan Formation in the early Carboniferous.

Famennian glaciation in the eastern side of Parnaíba Basin, Brazil: evidence of advance and retreat of glacier in Cabeças Formation

ABSTRACTGlaciotectonic features studied in the siliciclastic deposits of Cabeças Formation, Upper Devonian, represent the first evidence of Famennian glaciation in Southeastern Parnaíba Basin, Brazil. Outcrop-based stratigraphic and facies analyses combined with geometric-structural studies of these deposits allowed defining three facies association (FA). They represent the advance-retreat cycle of a glacier. There are: delta front facies association (FA1) composed of massive mudstone, sigmoidal, medium-grained sandstone with cross-bedding and massive conglomerate organized in coarsening- and thickening-upward cycles; subglacial facies association (FA2) with massive, pebbly diamictite (sandstone, mudstone and volcanic pebbles) and deformational features, such as intraformational breccia, clastic dikes and sills of diamictite, folds, thrust and normal faults, sandstone pods and detachment surface; and melt-out delta front facies associations (FA3), which include massive or bedded (sigmoidal cross-bedding or parallel bedding) sandstones. Three depositional phases can be indicated to Cabeças Formation: installation of a delta system (FA1) supplied by uplifted areas in the Southeastern border of the basin; coastal glacier advance causing tangential substrate shearing and erosion (FA1) in the subglacial zone (FA2), thus developing detachment surface, disruption and rotation of sand beds or pods immersed in a diamicton; and retreat of glaciers accompanied by relative sea level-rise, installation of a high-energy melt-out delta (FA3) and unloading due to ice retreat that generates normal faults, mass landslide, folding and injection dykes and sills. The continuous sea-level rise led to the deposition of fine-grained strata of Longá Formation in the offshore/shoreface transition in the Early Carboniferous.

The Tournaisian (Early Carboniferous) of the Kahanag section (central Alborz; northern Iran); biostratigraphy with calcareous algae and foraminifers; palaeobiogeographic implications

The Tournaisian beds of the Kahanag section in central Alborz (northern Iran) are described. This Tournaisian is probably complete and continuous from MFZ1 to MFZ8 biozones; nevertheless, (1) the base is only lithostratigraphically characterized, (2) the biozones MFZ1 to MFZ5 cannot be differentiated, and (3) in topmost beds, Eoparastaffella simplex indicative of the basal Viséan have not yet found. This Tournaisian is subdivided into a local lower Tourmaisian (MFZ1-MFZ5) showing a poor assemblage of monolocular and bilocular foraminifers, and a local upper Tournaisian where the biozones MFZ 6 and 7 are precisely defined. In Kahanag, MFZ 6 is characterized by the FO of Eotextularia diversa; MFZ 7 is the range-zone of Darjella monilis; and the base of MFZ8 is marked by the appearance of Eoparastaffellina. The biozone MFZ 8 is particularly developed in Kahanag, and represents almost one third of the field-section; therefore, a local subdivision is proposed, especially in order to characterize an upper MFZ8 subbiozone. Additionally, some algae of the section are accurately described; especially a trio which might be characteristic of the latest Tournaisian in Iran, (1) the unilayered “Koninckopora” mentioned for the first time in Iran; (2) a new genus of dasycladaleans Kahanagella n. gen.; and (3) a new genus of palaeoberesellaceans, Oblikamaena n. gen. More classical Algospongia (incertae sedis algae) are briefly mentioned Issinella, Crassikamaena, Kamaena, Palaeoberesella, Exvotarisella, Pseudostacheoides, Sinustacheoides and Stacheoides. Regionally, the new genus Kahanagella might be an important palaeobiogeographic marker because it was also discovered in the Tabas Block, while it seems absent in the adjacent, well-known areas (Taurus, southern Urals, Kazakhstan). Perhaps, Kahanagella might permit to reconstruct the initial geography of the latest Tournaisian Iranian platforms. Oblikamaena elbursica n. gen. n. sp. is an endemic taxon for the moment but might become also palaeobiogeographically interesting. Finally, the whole foraminiferal and algal Tournaisian assemblage permits to propose a reconstruction of the initial palaeoposition of the Iranian terranes prior to the progressive assemby of the Cimmerian terranes.

Late Paleozoic subduction–accretion along the southern margin of the North Qinling terrane, central China: Evidence from zircon U-Pb dating and geochemistry of the Wuguan Complex

The Qinling Orogen separating the North China plate from the Yangtze plate is a key area for understanding the timing and process of aggregation between the two plates. Two competing and highly contrasting tectonic models currently exist to explain the timing and nature of collision; one advocates a Devonian continental collision while the other favors a Triassic collision. The Wuguan Complex, between the early Paleozoic North Qinling and the Mesozoic South Qinling terranes, can provide important constraints on the late Paleozoic evolutionary processes of the Qinling Orogen. Metamorphosed sedimentary rock of the Wuguan Complex have a detrital zircon age spectrum with two major peaks at 453Ma and 800Ma, several minor age populations of 350–430Ma and 1000–2868Ma, and a youngest weighted mean age of 358±3Ma, indicating a mixed source from the North Qinling terrane. The recrystallized zircons yield a weighted mean age of 333±2Ma, representing the metamorphic age. Geochemical analyses imply that the sedimentary rocks were originally deposited in an active continental margin dominated by an acidic-arc source with a subordinate mafic-ultramafic source. The youngest population of detrital zircons (358Ma) suggests that the Wuguan Complex developed as forearc basin along the southern accreted margin of the North Qinling terrane during the early Carboniferous, whereas the ca. 520–460Ma mafic rocks with E-MORB, N-MORB, OIB or island arc basalt signatures probably derived from the Danfeng Group. In combination with regional data, we suggest that the depositional age of the Wuguan Complex is ca. 389–330Ma, but it was subsequently incorporated into tectonic mélange by the northward subduction of the Paleo-Qinling Ocean. A long-lived southward-facing subduction-accretionary system in front of the North Qinling terrane probably lasted until at least the early Carboniferous.

A Diverse Tetrapod Fauna at the Base of 'Romer's Gap'

The lack of fossil tetrapod bearing deposits in the earliest Carboniferous (‘Romer’s Gap’) has provoked some recent discussions regarding the proximal cause, with three explanations being offered: environmental, taphonomic, and collection failure. One of the few, and earliest, windows into this time is the locality of Blue Beach exposed in the Tournaisian deposits at Horton Bluff lying along the Avon River near Hantsport, Nova Scotia, Canada. This locality has long been known but, because the fossils were deposited in high energy settings they are almost always disarticulated, so the fauna has not been described in detail. Recent intensive collection has revealed a diverse assemblage of material, including for the first time associated elements, which permits an evaluation of the faunal constituents at the locality. Although not diagnosable to a fine taxonomic level, sufficient apomorphies are present to identify representatives from numerous clades known from more complete specimens elsewhere. The evidence suggests a diverse fauna was present, including whatcheeriids and embolomeres. A single humerus previously had been attributed to a colosteid, but there is some uncertainty with this identification. Additional elements suggest the presence of taxa otherwise only known from the late Devonian. Depositional biases at the locality favor tetrapod fossils from larger individuals, but indirect evidence from trackways and tantalizing isolated bones evidences the presence of small taxa that remain to be discovered. The fossils from Blue Beach demonstrate that when windows into the fauna of ‘Romer’s Gap’ are found a rich diversity of tetrapods will be shown to be present, contra arguments that suggested this hiatus in the fossil record was due to extrinsic factors such as atmospheric oxygen levels. They also show that the early tetrapod fauna is not easily divisible into Devonian and Carboniferous faunas, suggesting that some tetrapods passed through the end Devonian extinction event unaffected.

Lithologic mapping test for gravity and magnetic anomalies: A case study of gravity–magnetic anomaly profile in the eastern segment of the China–Mongolia border

An inversion calculation is usually needed to map lithologies with gravity–magnetic anomalies. A lithological-physical property correspondence can be established by combining data of regional rock density and magnetic susceptibility to build topological equations. In this study, topological calculations were performed using inversion data and combined with physical property data to interpret and map lithologies. Gravity–magnetic profiles from the eastern segment of the China–Mongolia border were used (Jining–Bainaimiao–Ha'ernaode geological–composite geophysical profile) in this paper. Based on gravity–magnetic anomaly inversion, the rock density and magnetic susceptibility data of Bainaimiao and Jining were adopted for lithological inversion. Distribution characteristics of four major types of magmatic rocks within 50km of the lower half space were obtained, and results of lithologic mapping and tectonic framework were analyzed. The position of convergence between the North China Plate and Siberian Plate was confirmed. Two tectonic stages were identified, namely, interplate squeezing and intraplate deformation. Regional gravity–magnetic field properties were analyzed to discuss the orientation and date of andesites and diorites in the northern part of the survey line. We believe that they have a northeast–southwest orientation similar to gravity–magnetic anomalies of Erenhot–Xilinhot. They resemble the igneous rock near Erenhot because they both indicate magmatic intrusion during the early Carboniferous.

The multistage crystallization of zircon in calc-alkaline granitoids: U–Pb age constraints on the timing of Variscan tectonic activity in SW Iberia

CL imaging and U–Th–Pb data for a population of zircons from two of the Evora Massif granitoids (Ossa-Morena Zone, SW Iberia) show that both calc-alkaline granitoids have zircon populations dominated by grains with cores and rims either showing or not showing differences in Th/U ratio, and having ages in the range ca. 350–335 Ma (Early Carboniferous). Multistage crystallization of zircon is revealed in two main growth stages (ca. 344–342 Ma and ca. 336–335 Ma), well represented by morphologically complex zircons with cores and rims with different ages and different Th/U ratios that can be explained by: (1) crystallization from melts with different compositions (felsic peraluminous to felsic-intermediate metaluminous; 0.001 837 °C; granulite facies) and/or because they were derived from inheritance-poor felsic and mafic rocks from a previous cycle, as suggested by the internal structures of zircon cores. These Variscan magmatic rocks with crystallization ages estimated at ca. 336–335 Ma are spatially and temporally related to high-temperature metamorphism, anatexis, processes of interaction between crustal- and mantle-derived magmas and intra-orogenic extension that acted in SW Iberia during the Early Carboniferous.

English

Posidonomya is common in the Kubang Pasu and Singa Formations in northwest Peninsular Malaysia. It was discovered from the red mudstone layers (redbeds) in many localities in Langkawi Islands, Perlis and Kedah. Previous studies suggested that the age of Posidonomya ranged from Middle Devonian to Carboniferous. Posidonomya beds in Kedah and Perlis are located above the Tournaisian radiolarian chert layers. The age of Posidonomya from Peninsular Malaysia is comparable to those of Europe, Morocco, Turkey and South China which range from Tournaisian to Serpukhovian, Early Carboniferous. The fossil specimens exhibit morphological features closely related to Posidonomya becheri Bronn. Two taxa were identified namely Posidonomya becheri Bronn and Posidonomya cf. kochi (von Koenen). The occurrence of Posidonomya indicates that the age of the lower part of the Kubang Pasu and Singa Formations is Early Carboniferous. Its geographic distribution formed a wide paleobiogeographic province in the Paleo-Tethys. The province was located in the warm tropical-subtropical climatic zone. Therefore, Posidonomya can be a good indicator for warm climate. Its wide distribution and short stratigraphic range make it a good index fossil for the Early Carboniferous.

Carboniferous arc magmatism in the Qiangtang area, northern Tibet: Zircon U–Pb ages, geochemical and Lu–Hf isotopic characteristics, and tectonic implications

The Longmu Co–Shuanghu suture zone (LSSZ), which lies between the southern Qiangtang–Baoshan block and northern Qiangtang–Qamdo block on the Tibetan Plateau, represents remnants of the Paleo-Tethys Ocean. Previous investigations have focused on the ophiolite, high-pressure zone, and metamorphic belt in this zone, whereas few studies have considered the arc magmatism. The present study examines a suite of Carboniferous arc-magmatic rocks in the western region of the LSSZ that consist of acidic to basic volcanic rocks, including rhyolite, dacite, andesite, basaltic andesite, basalt, and pyroclastics. Zircon U–Pb dating of three samples (two andesites and one dacite) by laser ablation–inductively coupled plasma–mass spectrometry demonstrates that these rocks were emplaced at ca. 351–346 Ma. The basalts have low Cr and Ni abundances, indicating that they were generated by varying degrees of partial melting of an enriched lithospheric mantle that was metasomatized by subduction-derived components. Zircons in the felsic rocks have positive εHf(t) values of 0.8–14.8, indicating an origin by varying degrees of partial melting of juvenile basaltic lower crust, consisting mainly of underplated magmas with similar compositions to the basalts. Geochemical data show that the volcanic rocks are enriched in light rare earth elements and large ion lithophile elements (e.g., Th, U, and Pb) but are strongly depleted in high field strength elements (e.g., Nb, Ta, and Ti), have high Al2O3 and low Zr concentrations, and are calc-alkaline. These magmas are therefore subduction-related volcanic arc rocks, indicating that Paleo-Tethys subduction began in the early Carboniferous.

Early Carboniferous Nautiloids from the Ruddell Shale Member in Arkansas, Midcontinent North America

Abstract. An early Chesterian (early Carboniferous; Late Mississippian) nautiloid fauna is described from the Ruddell Shale Member of the Moorefield Formation in Arkansas, Midcontinent North America. It consists of the three orthocerids, Euloxoceras buffalowallowense sp. nov., Mitorthoceras perfilosum Gordon and Moorefieldoceras yochelsoni gen. et sp. nov., and the two nautilids, Tylonautilus sp. and Peripetoceras milleri sp. nov. Reexamination of M. perfilosum, the type species of the genus, provides grounds for emendation of the generic concept emphasizing the supracentral position of the siphuncle. Moorefieldoceras is differentiated from comparable genera by its relatively rapid shell expansion, prominent annulations with a distinct ventral sinus, and relatively large siphuncle diameter with a central to subcentral position.

Origin, characteristics and distribution of fault‐related and fracture‐related dolomitization: Insights from Mississippian carbonates, Isle of Man

AbstractViséan limestones on the Isle of Man host numerous examples of fault‐controlled and fracture‐controlled dolomitization, which have been investigated to determine their macro‐scale to micro‐scale characteristics, geofluid origin, timing and relation to basin evolution. Geobodies composed of fabric destructive, ferroan, non‐planar dolomite range from several centimetres to &gt;300 m wide and tens to hundreds of metres long parallel to faults and/or fractures; they have sharply defined margins, cross‐cut stratigraphy and locally finger out along beds or bed boundaries for tens of metres. Larger geobodies accompany NNE–SSW extensional faults with substantial breccia zones. One of these bodies hosts a sphalerite‐rich breccia deposit cemented by dolomite. Saddle dolomite lines or fills vugs and fractures within dolomite geobodies, and is a minor late diagenetic phase in undolomitized limestones. Replacive dolomite has low matrix porosity owing to non‐planar texture and associated cementation, and there is no evidence for subsequent leaching. Three dolomite stages are discriminated by texture, cathodoluminescence petrography and electron microscopy. Disseminated ‘Dolomite 1’ is substantially replaced and may be residual early diagenetic dolomite. Pervasive ‘Dolomite 2’ and ‘Dolomite 3’ have overlapping carbon–oxygen–strontium isotopic and fluid‐inclusion characteristics that indicate precipitation from allochthonous, high‐temperature (98 to 223°C) and high‐salinity (15 to 24 wt% NaCl eq.) brines. These variably equilibrated with host limestones and mixed with resident pore fluids. Overlying mudrocks formed a seal for ascending fluids. Integration of data from the mineral deposit suggests that fault‐fracture systems tapped different deep‐seated fluid reservoirs at different temperatures, and implies fluid interactions with both metamorphic basement and sedimentary cover in large‐scale circulation systems. This phenomenon probably took place during Mesozoic rifting, although an earlier event at the end of the Early Carboniferous cannot be discounted. In either case, a transient heat flow anomaly, previously unrecognized in the Irish Sea region, may be required to account for the hottest fluids.

Uncoupled O and Hf isotopic systems in zircon from the contrasting granite suites of the New England Orogen, eastern Australia: Implications for studies of Phanerozoic magma genesis

The Permo-Triassic granites of the New England Orogen, eastern Australia, were emplaced into a volcanic arc complex accreted to the eastern Gondwana margin in the Late Devonian or Early Carboniferous. Zircon U–Pb dating shows that the S-type Hillgrove (∼297Ma) and Bundarra (∼287Ma) Supersuites predated intrusion of the I-type Moonbi Supersuite (∼250Ma) by up to 50Ma. The high δ18Ozrn of the S-type granites (10.0–11.5‰), and range of U–Pb ages (∼370–300Ma) and δ18Ozrn (∼5–10‰) of their inherited zircon cores, show that their source rocks were predominantly weathered Carboniferous volcaniclastics, the youngest deposited<25Ma before the granites were emplaced. In contrast, the lower δ18Ozrn (6.9–7.8‰) and lack of inheritance in the I-type granites is consistent with a zircon poor, more juvenile source, probably a mafic igneous underplate mixed with a small amount of volcanogenic and/or oceanic sediment. Despite the differences in source materials, the εHf(t) values of all granites, both S- and I-type, are similar (+5.0±0.5 cf. +5.9±0.5), consistent with both the mafic and sedimentary components in the granite sources being relatively young and similar in Hf isotopic composition at the time of granite genesis. In young, isotopically juvenile orogens, the O isotopic composition of well-dated igneous and inherited zircon can be a much more sensitive indicator of petrogenetic processes than the zircon Hf isotopic compositions alone.

Early Carboniferous adakitic rocks in the area of the Tuwu deposit, eastern Tianshan, NW China: Slab melting and implications for porphyry copper mineralization

Existing geochronological and geochemical data for the Early Carboniferous magmatic rocks in the eastern Tianshan, Xinjiang, have been interpreted in a variety of theories regarding petrogenesis and geodynamic setting. The proposed settings include rift, back-arc basin, passive continental margin, island arc, ridge subduction, and post-collisional environment. To evaluate these possibilities, we present new SHRIMP zircon U–Pb geochronology and geochemical data, whole-rock geochemical, Hf isotope, and S isotope data for tonalitic rocks and ores associated with the Tuwu porphyry copper deposit located in the center of the late Paleozoic Dananhu–Tousuquan arc, eastern Tianshan. SHRIMP zircon U–Pb dating indicates that the magmatic activity and thus associated copper mineralization occurred ca.332Ma. The tonalitic rocks are calc-alkaline granites with A/CNK values ranging from 1.16 to 1.58; are enriched in K, Rb, Sr, and Ba; and are markedly depleted in Nb, Ta, Ti, and Th. They show geochemical affinities similar to adakites, with high Sr, Al2O3, and Na2O contents and La/Yb ratios; low Y and Yb contents; and slight positive Eu anomalies. In situ Hf isotopic analyses of zircons yielded positive initial εHf(t) values ranging from 6.9 to 17.2. The δ34S values of the ore sulfides range from −3.0‰ to +1.7‰, reflecting a deep sulfur source. Our results indicate that the paleo-Tianshan oceanic slab was being simultaneously subducted northward beneath the Dananhu–Tousuquan arc, and southward beneath the Aqishan–Yamansu arc during the Early Carboniferous. The Tuwu adakitic tonalitic rocks were derived from the partial melting of the subducted paleo-Tianshan oceanic slab, which was subsequently hybridized by mantle wedge peridotites. The slab-derived magmas have considerably high copper contents and are highly oxidized, thus leading to porphyry copper mineralization. Such Early Carboniferous tonalitic rocks that are widespread in the eastern Tianshan define a province with high potential for copper mineralization.

An improved chronology for the Arthur’s Seat volcano and Carboniferous magmatism of the Midland Valley of Scotland

Synopsis The Early Carboniferous Arthur’s Seat volcano in central Edinburgh is of geological significance and landscape value but lacks a precise chronology. New 40 Ar/ 39 Ar step-heating plateau analyses date the lowest Lava 1 of the eruptive sequence to 341.2 ± 0.8 Ma (Visean, Holkerian), with Lava 3a at 336.7 ± 4.7 Ma. Intrusive or lava-lake basalts within the Lion’s Haunch Vent are precisely dated at 338 ± 0.6 Ma at Dunsapie and 335.1 ± 0.6 Ma at Crow Hill (Visean, Asbian). Taken together with existing 40 Ar/ 39 Ar dates recalculated to recent decay constant and standard values, and U/Pb dates, a revised magmatic chronology consistent with biostratigraphy is presented for the Midland Valley of Scotland. The Garleton Hills Volcanic Formation is older than the Arthur’s Seat Volcanic Formation, whereas the Clyde Plateau and Arthur’s Seat volcanic formations are partly coeval, requiring minor re-adjustments to existing stratigraphy. Supplementary material: Excel spreadsheets with raw analytical data and recalculation of existing 40 Ar/ 39 Ar ages are available at www.geolsoc.org.uk/SUP18773 .

Taxonomy, Biostratigraphy and Palaeobiogeography of the Late Tournaisian rugose corals of north-western Turkey

This article provides the first taxonomic description of Ivorian (Late Tournaisian, Early Carboniferous) rugose coral associations from north-western Turkey (Zonguldak and Bartin). Eleven species belonging to ten genera are described, one species is new. Three biostratigraphic assemblages are recognized. The oldest assemblage includes Cyathaxonia cornu, Cyathoclisia uralensis, ‘Lophophyllum’ konincki and Uralinia multiplex. This corresponds to the RC3 Biozone (early Ivorian). The middle assemblage in characterised by Amplexus coralloides, Sychnoelasma hawbankense and Zaphriphyllum daleki sp. nov. and is correlated with the early late Ivorian RC4α Biozone. The youngest assemblage (RC4β1 Biozone, latest Ivorian) is composed of Corphalia fourmarieri, Corphalia sp. and Amydgalophyllum? sp. These three assemblages have a low specific and generic diversity compared to time-equivalent assemblages but contain genera with a wide distribution in the Palaeotethys Ocean, such as Cyathoclisia, Uralinia and—in a lesser extend—Zaphriphyllum, as well as typically European taxa such as Corphalia and Sychnoelasma. These latter two, identified for the first time outside of Europe, allow associating north-western Turkey with the European Coral Province.

Carboniferous–Permian tectonic framework and its later modifications to the area from eastern Kazakhstan to southern Altai: Insights from the Zaysan–Jimunai Basin evolution

The Zaysan–Jimunai Basin is located in the area from eastern Kazakhstan to southern Altai. The structural deformation and sedimentary filling succession of this basin are a response to amalgamation processes and the intracontinental evolution of the Zharma–Saur and Altai terranes. This paper focuses on the Carboniferous–Early Permian tectonostratigraphic evolution and the Mesozoic–Cenozoic structural patterns of the Zaysan–Jimunai Basin using 2D and 3D seismic reflection profiles and geochronological and geochemical data to reveal an integrated Carboniferous–Permian tectonic framework and its later modifications to the area from eastern Kazakhstan to southern Altai. The Jimunai Basin comprises Devonian–Lower Carboniferous, Upper Carboniferous, Lower Permian and Paleogene strata, while the Zaysan Basin preserves the Mesozoic, Carboniferous–Permian and Cenozoic strata. The possible Devonian–Lower Carboniferous strata exhibit oppositely oriented thrust imbricate structures. The Late Carboniferous–Lower Permian strata are characterized by a fan-shaped filling pattern. The Mesozoic and Paleogene strata are dominated by high-angle thrust faults across/along the tectonic belt. The Late Carboniferous strata from Well JC1 in the Jimunai Basin are composed of dark grey basalt, andesite, tuff and minor pyroclastic rocks. The basalt was dated using zircon SIMS U–Pb method, yielding an age of 313.2±2.1Ma. These basalts belong to the calc-alkaline series and are characterized by low TiO2 and Th contents, low initial 87Sr/86Sr, high whole rock εNd(t) and zircon εHf(t) values, enrichment in LREEs and depletion of Nb and Ta, suggesting that they are most likely derived from partial melting of a spinel Iherzolite and garnet-bearing peridotite mantle metasomatized by subduction-related fluids and slab melts in an island arc setting. The data presented here are combined with previous works to propose a double subduction model for the Irtysh–Zaysan Ocean in the area from eastern Kazakhstan to southern Altai. During the Carboniferous, the Saur terrane underwent tectonic transition from flat subduction (to slab rollback) to normal subduction compared to the continued normal subduction of the Altai area. The angular unconformity between the Upper Carboniferous and Lower Permian series most likely indicates the closure of the Irtysh–Zaysan Ocean. The high-angle thrust and growth strata in the basin suggest that area from eastern Kazakhstan to southern Altai experienced episodic modifications related to transpressional events from the Messozoic to the Paleogene.

Triassic limestone, turbidites and serpentinite–the Cimmeride orogeny in the Central Pontides

AbstractThe basement of the Central Pontides, and by implication that of Crimea, consists of pre-Permian low-grade metaclastic rocks intruded by latest Permian – Early Carboniferous (305–290 Ma) granitoids. Further up in the stratigraphic sequence are Triassic limestones, which are now preserved as olistoliths in the deformed Upper Triassic turbidites. New conodont and foraminifera data indicate an Anisian to Carnian (Middle to Late Triassic) age for these hemi-pelagic Hallstatt-type limestones. The siliciclastic turbidites surrounding the Triassic limestone contain the Norian (Late Triassic) bivalveMonotis salinaria; the same species is also found in the Tauric series in Crimea. The Upper Triassic flysch in the Central Pontides is locally underlain by basaltic pillow lavas and includes kilometre-size tectonic slices of serpentinite. Both the flysch and the serpentinite are cut by an undeformed acidic intrusion with an Ar–Ar biotite age of 162 ± 4 Ma (Callovian–Oxfordian). This indicates that the serpentinite was emplaced into the turbidites before Middle Jurassic time, most probably during latest Triassic or Early Jurassic time, and that the deformation of the Triassic sequence pre-dates the Middle Jurassic. Regional geological data from the circum-Black Sea region, including widespread Upper Triassic flysch, Upper Triassic eclogites and blueschists of oceanic crustal affinity, and apparent absence of a ‘Cimmerian continent’ between the Cretaceous and Triassic accretionary complexes indicate that the latest Triassic Cimmeride orogeny was accretionary rather than collisional and is probably related to the collision and accretion of an oceanic plateau to the southern active margin of Laurasia.

Re-Os Geochronology of the Hitachi Volcanogenic Massive Sulfide Deposit: The Oldest Ore Deposit in Japan

The Hitachi volcanogenic massive sulfide (VMS) deposit in the Hitachi belt is one of the largest Cu-Zn sulfide deposits in Japan. However, its primary formation age has not been precisely determined because regional and contact metamorphism have disturbed some radiometric isotope systems, e.g., K-Ar ages on wall rocks. Further metamorphism has greatly reduced the fossil record, which has limited the use of biostratigraphy. To establish the ore deposit age, we applied Re-Os isotope dating to samples from two representative sulfide deposits of the greater Hitachi VMS deposit: the Fudotaki and Fujimi deposits. Re-Os isotope data from the Fudotaki deposit yields a model 3 age of 533 ± 13 Ma, with an initial 187 Os/ 188 Os ratio of 0.35 ± 0.20. In contrast, Re-Os isotope data from the Fujimi sulfide ore did not exhibit a linear correlation, suggesting that the Re-Os isotope system there has been disturbed by regional metamorphism of higher grade than the Fudotaki deposit as well as contact metamorphism during intrusion of Cretaceous granitic rocks. Although the Fudotaki sulfide ores have been metamorphosed to lower epidote-amphibolite facies, the well-defined Re-Os isochron allowed us to interpret the timing of primary sulfide deposition on the paleoseafloor. Some orebodies of the greater Hitachi VMS deposit have been estimated to be Early Carboniferous based on the scarce fossil records and considered to be distributed in the Daioin Formation, but our results revealed that the Fudotaki deposit were formed during the Cambrian and occurs in the Upper Akazawa Formation, which strongly supports the idea that the Cambrian beds are widely distributed in the Hitachi belt and that a significant unconformity exists between the Cambrian and Early Carboniferous above the Fudotaki deposit. The Cambrian Re-Os date classifies the Hitachi VMS deposit as the oldest dated ore deposit in Japan, and in turn provides an insight to understand the geologic framework and genesis of the proto-Japanese islands and the East Asian region.