Early Carbonate Research Articles

Early carboniferous rifting of the Harlik arc in the Eastern Tianshan (NW China): Response to rollback in the southern Altaids?

Field, geochronological, geochemical and Sr-Nd isotopic analyses are applied to late Paleozoic gabbro-diorites and monzogranites in the Hulugou-Miaoergou regions, Harlik arc, in order to provide constraints on the tectonic evolution of the Eastern Tianshan orogen in the late Paleozoic. LA-ICP-MS zircon U-Pb ages show that the first pulse of gabbroic magmatism occurred at 348 ± 4 Ma, accompanied by simultaneous dioritic (342 ± 3 Ma) and monzogranitic (343 ± 5 Ma) magmatism, and the second pulse of gabbroic magmatism was at 334 ± 3 Ma. Most of the gabbros are medium- to high- K calc-alkaline in composition, and show enrichments in light rare earth elements (LREE) and large ion lithophile elements (LILE), but depletions in high field strength elements (HFSE, especially Nb and Ta). In combination with their juvenile isotopic signature (initial ⁸⁷Sr/⁸⁶Sr = 0.70345–0.70380, εNd(t) = 4.5–6), the geochemical features suggest that both pulses of gabbroic magmatism were likely derived from partial melting of asthenosphere facilitated by a flux from a subducting slab. The diorites also display the arc-related geochemical characteristics and juvenile isotopic signature (initial ⁸⁷Sr/⁸⁶Sr = 0.70355–0.70358, εNd(t) = 4.3–4.7), coupled with their intimate relationship with the gabbros indicate that they formed by fractional crystallization of clinopyroxene, plagioclase and amphibole from the first pulse of gabbroic magmatism. The monzogranites have relatively high A/CNK values (1.04–1.1) and are weakly to moderately peraluminous. Considering the presence of zircon xenocrysts dated at 510 to 450 Ma in the monzogranites, and their moderate molar Al₂O₃/(MgO+FeO^T) and molar CaO/(MgO+FeO^T) ratios, partial melting of supracrustal rocks of probable late Ordovician age was most likely the cause of their genesis and heterogeneity. These three different magmas (gabbroic, dioritic and monzogranitic) were probably extracted from a deep crustal hot zone. The primitive basaltic magmas continuously intruded the deep crust where they solidified, fractionated, assimilated, and heated the crust, generating in turn the peraluminous and A-type granitoids, similar to the magmas in the Lachlan orogen that intruded during progressive slab rollback. Based on all available evidence, we propose that southward slab rollback of the subducting Paleo-Asian Ocean in the early Carboniferous was responsible for the progressive emplacement of these different magmas, which eventually resulted in rifting of the Harlik arc.

A New Radiolarian Genus Nestelliana gen. nov. and New Species from the Late Devonian of the Polar Urals and the Early Carboniferous of the Volga–Ural Basin of Russia

A New Radiolarian Genus Nestelliana gen. nov. and New Species from the Late Devonian of the Polar Urals and the Early Carboniferous of the Volga–Ural Basin of Russia

Ordovician-Devonian lichen canopies before evolution of woody trees

Devonian evolution of woodlands has been envisaged as a protracted increase in size of vascular plants, which can be reconstructed from fossil stumps and trunks. However, Late Silurian and Early Devonian nematophytes such as Prototaxites would have towered over land plants, including vascular plant trees, in the same fossil plant assemblage, until finally overtaken by vascular land plants during the Early Carboniferous. Nematophytes lack tissues of vascular plants, and some have spherical photobionts encircled and indented by hyphae, as in lichens. Nematophytes were not monolithic poles, but branched, and trunk spacing in paleosols is evidence that they formed closed canopies. Depths of root and hyphal bioturbation and pedogenic calcite precipitation in paleosols though time increase with greater height of trees. In addition to large non-vascular trunks and early land plants in Ordovician to Devonian paleosols, there also were extensive, nutrient-gathering, networks of glomeromycotan mycorrhizae. An Ordovician-Silurian “age of lichens”, when nematophytes were the tallest elements of terrestrial vegetation and soils were riddled with mycorrhizae, may have nurtured and sheltered Ordovician-Silurian land plants and then Devonian woody plants. Fungi preceded and facilitated the evolution of early land plants.

Provenance of the Paleozoic to Mesozoic Siliciclastic Rocks of the Istanbul Zone Constrains the Timing of the Rheic Ocean Closure in the Eastern Mediterranean Region

AbstractThe Intra‐Pontide Suture between the Istanbul and Sakarya zones was regarded debatably either as a Neotethyan Suture or a trace of the Rheic Suture in Turkey. Here, we present U‐Pb ages and Lu‐Hf isotopic compositions of detrital zircons from the Silurian to Triassic sandstones of the Istanbul Zone. Upper Silurian‐Lower Devonian sandstone is dominated by Mesoproterozoic zircons (1950–900 Ma), with subordinate peaks at the latest Neoproterozoic to Silurian (750–420 Ma) and mid‐Archean (2850–2750 Ma) confirming their Avalonian affinity. Detrital zircon ages from Carboniferous‐Triassic sandstones show major peaks at Carboniferous‐Early Permian (360–270 Ma) and Late Neoproterozoic–Cambrian (750–480 Ma) while Mesoproterozoic zircons are insignificant. The εHf(t) values of the detrital zircons exhibit a wide range from −21.3 to +11.7, and over 62% of zircon grains have negative values, largely coinciding with those of the Paleozoic igneous rocks in the Sakarya Zone. The Istanbul Zone is devoid of Carboniferous igneous and/or metamorphic rocks. Therefore, abundant Carboniferous zircons and the disappearance of the Mesoproterozoic zircons in the Carboniferous‐Triassic sandstones of the Istanbul Zone require juxtaposition with a continental domain similar to the Sakarya and Strandja zones, which are characterized by widespread Carboniferous magmatism. We suggest that the Intra‐Pontide Suture represents the trace of the Rheic Suture in Turkey, along which Avalonia and Armorica collided during the Early Carboniferous.

Ages and tectonic attributes of Late Palaeozoic stratigraphic units in the Tarbagatay, West Junggar (NW China): revisited

ABSTRACT As the youngest single age of detrital zircons is used as the maximum depositional age, the ages and tectonic attributes of the Late Palaeozoic stratigraphic units in the Tarbagatay area, West Junggar, NW China, become very confusing. An improved statistical approach indicates that 5, 6 and 7 concordant zircons are required for the maximum depositional age at 95% confidence level when the quantity of total concordant zircon in a sample does not exceed 50, 140 and 432, respectively, but the defined maximum depositional age is valid only when it is compatible with geological facts. Otherwise, it is still uncertain if the age is valid. This approach is applied to resolve a chronological chaos in the Late Palaeozoic stratigraphic units in the Tarbagatay area. As a result, the maximum depositional ages obtained from the detrital zircon samples in literature and this study are at 95% confidence level, most of which are well compatible with the fossils in the units, intrusive relationships of plutons to country rocks and ages of interbedded volcanic rocks. The valid maximum depositional ages and other geological facts definitely show the presence of the Devonian, Early Carboniferous and Early Permian stratigraphic units in the Tarbagatay area. The Late Devonian-Early Carboniferous marine-dominated units occurred in the Zharma-Saur arc and its transition to a back-arc basin to the south during the southward subduction of the Irtysh-Zaisan Ocean, whereas the Permian terrestrial unit was formed in a post-collisional setting after the closure of the Irtysh-Zaisan Ocean in the Late Carboniferous.

Revisiting Phanerozoic evolution of the Qinling Orogen (East Tethys) with perspectives of detrital zircon

This paper presents 5383 detrital zircon U–Pb and 2079 Lu–Hf isotopic data, shedding new light on the Phanerozoic tectonic evolution of the Qinling Orogen. The Silurian rocks are characterized by negative εHf(t) values of early Paleozoic and Neoproterozoic zircon, which in the Devonian to Carboniferous samples show both positive and negative εHf(t) values. Late Paleozoic zircon peak with negative εHf(t) values occurs in the upper Carboniferous to Cretaceous strata. The Permian to Cretaceous strata show peaks at 1.9 Ga and 2.5 Ga. Early Paleozoic and Neoproterozoic peaks are back in Upper Triassic to Cretaceous rocks. A Mesozoic peak with negative εHf(t) values occurs in Cretaceous rocks. In terms of the sources of detrital zircon, the South Qinling Belt and Yangtze Block are major contributors for Silurian strata; South Qinling and North Qinling belts are major sources for Lower Devonian to upper Carboniferous rocks; early Carboniferous detrital zircon related to subduction of Mianlue oceanic slab emerges in upper Carboniferous rocks; North China Block is an important source for Lower Permian to Upper Triassic rocks; Lower Cretaceous strata exhibit diverse provenance, including North Qinling Belt, North China Block, and South Qinling Belt. Provenance changes suggest that the initial spreading of the Mianlue Ocean occurred in the Early Silurian during which the South Qinling Terrane and Yangtze Block had not completely separated. The Mianlue Ocean evolved into a mature stage of spreading in the Early Devonian. Meanwhile, the closure of the Shangdan Ocean took place. The Mianlue Ocean started to subduct in the early Carboniferous. Its final closure occurred in the Late Triassic, leading to uplift and exhumation of Qinling Orogen and cutting off detritus transport from North China Block in the Jurassic. The Qinling Orogen underwent collapse in the late Early Cretaceous.

Yenisei–Khatanga Composite Tectono-Sedimentary Element, northern east Siberia

Abstract The Yenisei–Khatanga Composite Tectono-Sedimentary Element (CTSE) is located between the Siberian Craton and the Taimyr–Severnaya Zemlya Fold and Thrust Belt. The total thickness of the Mesoproterozoic–Cenozoic sediments of the Yenisei–Khatanga CTSE reaches 20–25 km, and they are divided into four tectono-sedimentary elements (TSEs): (i) Mesoproterozoic–early Carboniferous Siberian Craton continental margin; (ii) middle Carboniferous–Permian synorogenic Taimyr foreland basin; (iii) late Permian–Early Triassic synrift; and (iv) Triassic–Early Paleocene post-rift. The last one is the most important in terms of its petroleum potential and is the most drilled part of the CTSE. Its thickness accounts for half of the total thickness of the Yenisei–Khatanga CTSE. The margins of the post-rift TSE and the inner system of inversion swells and adjacent troughs and depressions were shaped by three tectonic events: (i) Middle Triassic uplift of South Taimyr; (ii) the Late Jurassic–Early Cretaceous Verkhoyansk Orogeny; and (iii) Late Cenozoic uplift. These processes led to more intense migration of hydrocarbons, the trap formation and their infill with hydrocarbons. Triassic, Jurassic and Lower Cretaceous source rocks are mostly gas-prone; and of the 20 discovered fields in Jurassic and Cretaceous plays, 17 are gas or mixed-type fields.

An orocline in the eastern Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) is the largest accretionary orogen in the world with considerable Phanerozoic juvenile crustal growth. The eastern segment of the CAOB is occupied by NE China and its adjacent areas, which locates in a triangle area surrounded by Siberian Craton to the northwest, North China Craton (NCC) to the south and Pacific oceanic plate to the east. Therefore, the NE China is a key area to study the geological evolution of multiple tectonic systems and overprinting, which has become a hot research topic. In the past five decades, especially the last two decades, there have been many detailed geological investigations carried out and a lot of new data reported in NE China. A progress has been achieved in tectonic evolution, however, there are still many open questions and arguments dealing with the tectonic models, correlation of tectonic units, amalgamation of different blocks and their tectonic affinity. In this study, we did a detailed review of the tectonic evolution of NE China and regional comparison and correlation of the different tectonic units in the eastern segment of CAOB. We re-subdivided NE China into two old blocks of Erguna block (EB) and Jiamusi block (JB) with Precambrian basement and three accretionary terranes of Xing'an accretionary terrane (XAT), Songliao accretionary terrane (SAT) and Zhangguangcai accretionary terrane (ZGCAT), which are separated from each other by the Xinlin-Xiguitu suture (XXS), Hegenshan-Heihe suture (HHS), Longfengshan suture (LFS) and Mudanjiang-Yilan suture (MYS), respectively. The ZGCAT is dominantly composed of early Paleozoic magmatic arc materials and minor late Paleozoic igneous rocks with an old Yichun mini-block, while the SAT consists dominantly of the late Paleozoic magmatic rocks with two small old blocks of the Xilinhot and Longjiang mini-blocks. According to the tectonic correlation and comparation of different tectonic units, we established a new orocline tectonic model for the eastern CAOB: 1) the XAT and ZGCAT accreted to the southern (present position) margin of Ereendavaa-Erguna-Mamyn block (EEMB) and Bureya-Jiamusi-Khanka block (BJKB) with the closure of Xinlin-Xiguitu-Heilongjiang ocean during the early Paleozoic; 2) Subsequently, the SAT accreted to the southern (present position) margin of integrated XAT-ZGCAT terrane with the closure of Hegenshan-Nenjiang-Longfengshan ocean during the late Paleozoic. These initially W-E linear shaped accretionary orogenic belts were ultimately bent southward through Paleozoic time and constituted a huge Paleozoic orocline, NE China Orocline, which collided with NCC by a scissor-like style closure of Paleo-Asian Ocean (PAO) from west to east along the Solonker-Xar Moron-Changchun-Yanji suture (SXCYS) during the late Permian-middle Triassic. The NE China Orocline, together with Tuva-Mongol Orocline and Kazakhstan Orocline in the western CAOB, constituted a huge multiple orocline tectonic system in the CAOB during the Paleozoic era. Our study will contribute to the understanding on tectonic evolutions of CAOB and the NE Asian, and suggests that the orocline should be a common tectonic model for accretionary orogeny. • NE China consists of two Precambrian blocks and three Paleozoic accreted terranes. • A new orocline tectonic model is established for first time in NE China. • Blocks in NE China had been integrated in later Early Carboniferous.

Early Carboniferous high-silica granites in the Kalejun Mountains, Chinese western Tianshan: Petrogenesis, tectonic setting and geodynamic implications for the South Tianshan Ocean

ABSTRACT Early Carboniferous granitoids, distributed in the Yining and Central Tianshan blocks, Chinese western Tianshan, are important for deciphering their tectonic contexts and evolutionary history of the South Tianshan Ocean. Here we present LA-ICP-MS zircon U-Pb ages, in situ Hf isotopic data, and whole-rock geochemical data of the monzogranites and syenogranites from the Kalejun Mountains, southern part of the Yining Block, aiming to constrain their petrogenesis and geodynamic background. The results reveal that these monzogranites and syenogranites were emplaced at 356 Ma and 344 Ma, respectively. Geochemically, they are characterized by high SiO2 (68.74–75.76 wt.%) and K2O (4.58–6.18 wt%), low MgO (0.14–0.76 wt.%) and P2O5 (0.04–0.24 wt.%) contents. In addition, they are depleted in Ba, Sr, Eu, Ti, Nb, and Zr, and enriched in Rb, Cs, Th, and U. These features indicate that the Kalejun granites are high-silica I-type granites. The low positive εHf(t) values (+1.1 to +8.2) and old model ages (1294 to 827 Ma) of the studied zircons imply that the parental magma of these granites were derived from the reworking of Proterozoic basement with minor involvement of juvenile materials. Combined with the Late Devonian to Early Carboniferous magmatic activities in the Yining and Central Tianshan blocks (e.g. the discovery of A-type bubble rhyolites and high-Mg andesites), it is suggested that the Kalejun granites were likely related to the roll-back of the South Tianshan oceanic slab. Finally, we argue that the subduction of South Tianshan Ocean probably terminated at the end of the Early Carboniferous.

DEVONIAN-CARBONIFEROUS MAGMATISM AND METALLOGENY IN THE SOUTH URAL ACCRETIONARY-COLLISIONAL SYSTEM

The oceanic stage in the history of the South Urals completed in the Ordovician – Early Silurian. The Ordovician through Devonian events in the region included the formation of an island arc in the East Ural zone from the Middle Ordovician to Silurian; westward motion of the subduction zone in the Late Silurian – Early Devonian and the origin of a trench along the Main Ural Fault and the Uraltau Uplift; volcanic eruptions and intrusions in the Magnitogorsk island arc system in the Devonian. The Middle-Late Paleozoic geodynamic evolution of uralides and altaides consisted in successive alternation of subduction and collisional settings at the continent-ocean transition. The greatest portion of volcanism in the major Magnitogorsk zone was associated with subduction and correlated in age and patterns of massive sulfide mineralization (VMS) with Early – Middle Devonian ore-forming events in Rudny Altai. Within-plate volcanism at the onset of volcanic cycles records the Early (D1e2) and Middle (D2ef2) Devonian slab break off. The volcanic cycles produced, respectively, the Buribay and Upper Tanalyk complexes with VMS mineralization in the Late Emsian; the Karamalytash complex and its age equivalents in the Late Eifelian – Early Givetian, as well as the lower Ulutau Formation in the Givetian. Slab break off in the Late Devonian – Early Carboniferous obstructed the Magnitogorsk island arc and supported asthenospheric diapirism. A new subduction zone dipping westward and the Aleksandrovka island arc formed in the Late Devonian – Early Carboniferous. The Early Carboniferous collision and another event of obstructed subduction led to a transform margin setting corresponding to postcollisional relative sliding of plates that produced another slab tear. Postcollisional magmatism appears as alkaline gabbro-granitic intrusives with related rich Ti-magnetite mineralization (C1). Transform faulting persisted in the Middle Carboniferous through Permian, when the continent of Eurasia completed its consolidation. The respective metallogenic events included formation of Cu-Ni picritic dolerites (C2–3), as well as large-scale gold and Mo-W deposits in granites (P1–2).

Mg and Sr isotopic evidence for basin wide alteration of early diagenetic dolomite in the Williston Basin by ascending crustal fluids

Dolomite is a predominantly diagenetic mineral that forms by replacing marine calcite and aragonite during burial. Dolomitization requires subsurface fluid flow to deliver Mg and remove product Ca, and only forms abiotically in laboratory experiments at temperatures above ~100°C, equivalent to burial depths of 3 km or greater. Limited sources of Mg at these depths would appear to restrict most dolomite formation to shallow burial depths using seawater as a source of reactive Mg, despite the kinetic limitation imposed by lower temperatures. The Williston Basin is replete with evaporites and dolomites that appear to have formed using Mg from evaporatively concentrated seawater at near surface temperatures. However, two dolomite bodies examined in this study record basin wide gradients in 87Sr/86Sr ratios and δ26Mg values that are inconsistent with dolomitization by seawater. We evaluate the processes that may have created these gradients. We propose a model whereby seepage reflux created early diagenetic protodolomite that was later altered during deep burial by 87Sr and Mg-enriched fluids ascending from the deep structural center of the basin with the degree of alteration decreasing towards the edges. The ascending fluid flow event is tentatively linked to anomalous heating in the Late Devonian / Early Carboniferous. Vertical faults are hypothesized to have behaved as conduits for channeling 87Sr and Mg-enriched crustal fluids upwards into the bottom of the Williston Basin, pressurizing the basal aquifer system and commencing up-dip directed fluid flow through confined aquifers. Clumped isotope and fluid inclusion thermometry indicate that the ascending fluids were hydrothermal with an estimated δ26Mg value of –0.65 ±0.20‰, which is much lower than estimates of early Paleozoic seawater δ26Mg values of +0.09 to +0.23‰. Two sources of crustal Mg are consistent with the low inferred δ26Mg values of the ascending fluid: (1) chlorite, which preferentially releases isotopically light Mg, with literature values in the range of –0.78‰ to –1.8‰, and (2) magnesite, which forms during carbonation of serpentinite with literature values in the range –0.7‰ to –1.1‰. Ultramafic rocks belonging to the Thompson Nickel Belt pass beneath the center of the Williston Basin in North Dakota, indicating that dissolution of both chlorite and magnesite may have contributed reactive Mg to the Williston Basin during the ascending fluid flow event. As dolomite is a mineral that is easily altered during burial, our findings warrant caution in choosing dolomites for reconstructing the 26Mg history of seawater.

Environment and Age of the Upper Devonian–Carboniferous Zhulumute and Hongguleleng Formations, Junggar Basin, NW China: Ichnological and Palynological Aspects

AbstractTwo Upper Devonian to Lower Carboniferous sections, namely the Bulongguoer and Haer (Gennaren area) in the Junggar Basin, Central Asian Orogenic Belt, in northwestern China were examined with regard to ichnology and palynology. The deposits of the Hongguleleng Formation and Namu Member of the Heishantou Formation, respectively, are mostly unbioturbated or poorly bioturbated, with poorly diversified trace fossils, which indicate unfavourable conditions for the burrowing benthic community during the Late Devonian and Early Carboniferous. The main factor governing the growth of the bioturbating population was the rapid sedimentation of fine‐grained, volcanic material documented as tempestites, which buried the benthic fauna. In the Bulongguoer section, the presence of miospores Teichertospora torquata and Grandispora gracilis enabled identification of the broad Teichertospora torquata‐Grandispora gracilis Miospore Zone from the transitional Frasnian/Famennian interval. More accurate identification of palynostratigraphical levels (DE and CZ Miospore zones) is only tentative. On the basis of palynofacies analysis, samples from the lower Bulongguoer section indicate deposition in more proximal conditions, whereas samples from the top of the section indicate deposition in a more distal environment. In the Haer section, only a general biostratigraphic indication for the Tournaisian was possible, owing to poor preservation of organic matter.

Paleomagnetism of the Ordovician and Early Carboniferous Geological Complexes of Tuva

Paleomagnetism of the Ordovician and Early Carboniferous Geological Complexes of Tuva

The Truong Son, Loei-Phetchabun, and Kontum Terranes in Indochina: Provenance, Rifting, and Collisions

The three main regions of Indochina are defined as the Truong Son, Loei-Phetchabun, and Kontum terranes. The aim of this review is to integrate numerous petrological studies with sedimentary, palaeontological, and provenance studies in order to construct a preliminary tectonic model which shows the terranes docked in the earliest Carboniferous (Truong Son with Loei-Phetchabun) and in the Permian (Kontum). The Kontum Terrane is characterized by Proterozoic magmatism, mid-Ordovician to Early Devonian granites, and Permian charnockites. Major carbonate platforms developed in the Givetian to earliest Tournaisian on Truong Son and from the Visean to mid-Permian across Truong Son and Loei-Phetchabun terranes. The Truong Son has Silurian granites and a Late Ordovician to Silurian magmatic arc along its southern and western borders caused by subduction of oceanic lithosphere, the remnants of which are now partially preserved in the Loei and Tamky sutures. A region to the east of the Loei Suture in the Loei Foldbelt has a similar-age volcanic arc extending northwards into Laos and is included in Truong Son. A platform-margin coral-stromatoporoid reef developed on Truong Son in the Frasnian and was coincident with a gap in magmatism until the Pennsylvanian with granite magmatism became widespread until the Late Triassic. In the Loei-Phetchabun Terrane, Devonian siliciclastics, volcanics are overlain by Givetian limestones and patch reefs and in turn overlain by Late Devonian to earliest Tournaisian radiolarian cherts and siliciclastics. Tournaisian to early Visean siliciclastic turbidites were coincidental with initial uplift and deformation and were replaced by Visean terrestrial evaporites and coal and marine limestones. Arc magmatism along the Loei-Phetchabun Terrane indicates intermittent eastward subduction from mid-Devonian to mid-Triassic. Carboniferous-Triassic volcanism extends eastward along the northern margin of Cambodia and is probably an extension of Loei-Phetchabun. Ordovician within-plate basalts in Kontum and the transition from shallow marine Ordovician siliciclastics to Silurian deep-marine sediments and a volcanic arc in Truong Son suggest rifting of both terranes from Gondwana in the Late Ordovician. Initial docking of Truong Son with South China was probably in the late Silurian to Early Devonian and docking of Loei-Phetchabun and Truong Son was in the late Tournaisian to early Visean.

Zircon Chemistry and Oxidation State of Magmas for the Duobaoshan-Tongshan Ore-Bearing Intrusions in the Northeastern Central Asian Orogenic Belt, NE China

The Duobaoshan (DBS)-Tongshan (TS) porphyry Cu–(Mo) deposit (4.4 Mt Cu, 0.15 Mt Mo) is located in the northeastern part of the central Asian orogenic belt (CAOB) in northeastern China. It is hosted by early Ordovician dioritic to granodioritic intrusions which are characterized by the subduction-related geochemical signatures including high concentrations of large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and low concentrations of heavy REEs (HREEs) and high-field -strength elements (HFSEs), such as Nb, Ta, Zr and Ti in bulk rock compositions. Furthermore, they show adakitic geochemical signatures of high Sr/Y ratios (29~55) due to high Sr (290~750 ppm) and low Y (<18 ppm). Zircon trace element abundances and published Sr-Nd-Hf isotope data of these rocks suggest that the parental magmas for these ore-bearing intrusions were rich in H2O and formed by partial melting of a juvenile lower crust/lithospheric mantle or metasomatized mantle wedge during the northwestward subduction of the Paleo-Asian Ocean before the collision of the Songnen block with the Erguna-Xing’an amalgamated block in the early Carboniferous. Values of Ce4+/Ce3+ and Ce/Nd in zircons are 307~461 and 14.1~20.3 for mineralized granodiorites, and 231~350 and 12.4~18.2 for variably altered diorite and granodiorites in DBS, whereas those for DBS-TS microgabbros are 174~357 and 7.4~22, and 45.9~62.6 and 5.0~5.8 for the early Mosozoic Qz-monzonites, respectively. Zircon Eu/Eu* values are high and similar among mineralized granodiorites (~0.6), altered diorite and granodiorites (~0.6) and the Mesozoic Qz-monzonites (~0.8), whereas the values are low and variable for the DBS-TS microgabbros (0.3~0.6). The magma oxidation state calculated from zircon chemistry and whole rock compositions are FMQ +1.0 to +1.5 in mineralized samples, and FMQ +2.4 to +4.2 in altered samples. The values are comparable to those for the fertile intrusions hosting porphyry Cu-Mo-(Au) deposits in the central and western CAOB and elsewhere in the world. Elevated oxidation state is also observed in the TS microgabbros, FMQ +1.4 to +1.9, and the early Mesozoic Qz-monzonites, FMQ +2.4 to +2.5. Comparison of zircon geochemistry data from porphyry deposists elsewhere suggests that positive Ce anomalies are generally associated with fertile intrusions, but not all igneous rocks with high Ce anomalies are Cu fertile. The findings in this study are useful in exploration work and evaluating oxidation state of magmas for porphyry Cu-(Mo) deposits in the region and elsewhere.

Locomotory behaviour of early tetrapods from Blue Beach, Nova Scotia, revealed by novel microanatomical analysis.

Evidence for terrestriality in early tetrapods is fundamentally contradictory. Fossil trackways attributed to early terrestrial tetrapods long predate the first body fossils from the Late Devonian. However, the Devonian body fossils demonstrate an obligatorily aquatic lifestyle. Complicating our understanding of the transition from water to land is a pronounced gap in the fossil record between the aquatic Devonian taxa and presumably terrestrial tetrapods from the later Early Carboniferous. Recent work suggests that an obligatorily aquatic habit persists much higher in the tetrapod tree than previously recognized. Here, we present independent microanatomical data of locomotor capability from the earliest Carboniferous of Blue Beach, Nova Scotia. The site preserves limb bones from taxa representative of Late Devonian to mid-Carboniferous faunas as well as a rich trackway record. Given that bone remodels in response to functional stresses including gravity and ground reaction forces, we analysed both the midshaft compactness profiles and trabecular anisotropy, the latter using a new whole bone approach. Our findings suggest that early tetrapods retained an aquatic lifestyle despite varied limb morphologies, prior to their emergence onto land. These results suggest that trackways attributed to early tetrapods be closely scrutinized for additional information regarding their creation conditions, and demand an expansion of sampling to better identify the first terrestrial tetrapods.

Geological features and the first isotopic data of volcanic rocks in the Iset river basin, East-Urals megazone

Relevance of the work. The Iset river basin contains the most extensive outcrops of volcanogenic formations of the Beklenishchevsky complex of the East Ural megazone, the age of which is determined as Early Carboniferous by the ratio of volcanic rocks with faunistically characterized sedimentary deposits. Volcanics here compose flows of andesite-basaltic and andesitic lavas and lava breccias. There are no geochronological dates specifying the age of the rocks, which makes it difficult to assess their role in the formation of the megazone. Therefore, isotopic dating of these formations is very important. Methods. The U – Pb age and data on the geochemistry of zircons were obtained by laser ablation (LA – ICP – MS). Purpose of the research is to study the features of the geological structure, the material composition of volcanic rocks in the Iset river basin, the geochemistry of zircons from andesites and the determination of their isotopic age. Results of the work and the scope of their application. Lava flows of andesites and basaltic andesites with minor amounts of basalts and dacites have tectonic contact with sedimentary rocks of the Early Carboniferous age. The distribution of rare elements in volcanics is typical of supra-subduction formations. Zircons in andesites are represented by prismatic and isometric crystals. Prismatic differences in the nature of the distribution of REE and the content of Li, Ti, Sr, Th, U refer to zircons of magmatic genesis, isometric – to “hydrothermal”. According to the U / Yb – Y ratios, the former correspond to the zircons of the ocean floor, while the latter are related to the continental ones. Isotopic dating of zircons from andesites was carried out for the first time. Their age was 311 million years. The data can be used in geological mapping, as well as in the compilation of large-scale geodynamic maps and diagrams. Conclusions. Volcanic rocks in the Iset river basin were formed in supra-subduction continental-marginal geodynamic conditions that took place in the Urals in the Carboniferous. The obtained value of the age of zircons from andesites, possibly, fixes the stage of their transformation. Keywords: East-Ural megazone, volcanic rocks, zircon, isotopic age.

Petrography, geochemistry and tectonic setting of adakitic bodies in the Tighanab area and their relationship with iron skarn mineralization (southeast of Sarbisheh-east of Iran)

Petrography, geochemistry and tectonic setting of adakitic bodies in the Tighanab area and their relationship with iron skarn mineralization (southeast of Sarbisheh-east of Iran)

Syn-collisional detrital zircon source evolution in the northern Moroccan Variscides

U–Pb dating and Hf isotopic analyses of detrital zircon grains from Cambrian-Devonian strata in the Moroccan Mesetas were undertaken in order to constrain its Paleozoic paleogeographic evolution. In this work, we analyzed 12 Late Devonian-Late Carboniferous samples of syn-collisional detrital rocks from the Western and Eastern Moroccan Mesetas. All our samples present significant Ediacaran (ca. 620 Ma) and Rhyacian (ca. 2.1 Ga) detrital zircon populations, suggesting that the West African Craton remained the main source of sediments for northern Morocco at least until the Late Carboniferous. Locally, a Stenian-Tonian (ca. 1.0 Ga) detrital zircon population is also present, probably fed from intermittent and distant source areas located in NE Africa (e.g. Sahara Metacraton). The collisional evolution started with the approach of an Avalonian promontory to the northern Gondwana continental margin (latest Devonian - earliest Carboniferous), after the closure of the Rheic Ocean. This process entailed the former subduction of the Rheic oceanic lithosphere underneath the Avalonian continental terrane and the formation of a magmatic arc in the upper plate. In this scenario, the first syn-collisional sediments (Tournaisian; Tiflet and Debdou-Mekkam areas) are characterized by a Devonian detrital zircon population (ca. 370 Ma), presumably derived from the magmatic arc, and an increasing number of Mesoproterozoic dates, putatively also sourced from the continental crust of the Avalonian terrane. After the initial collision, only the Visean samples located in areas close to the exotic terrane (e.g. Ben Slimane area) displayed a minor Avalonian component. Finally, the Late Carboniferous samples from the Jerada area recorded an important Middle Carboniferous (ca. 330 Ma) detrital zircon population, probably sourced from Variscan granitoids emplaced in the Eastern Moroccan Meseta and attesting to crustal thickening and subsequent thermal maturation of the Gondwana continental crust in this area.

Petrogenesis and geodynamic setting of the Late Carboniferous granodiorite porphyry in Miaoergou pluton, southern West Junggar

位于西准噶尔南部的庙尔沟岩体主体由碱长花岗岩和少量紫苏花岗岩组成。本文在前人工作基础上，以岩体东南边缘新发现的花岗闪长斑岩为研究对象，开展岩石学、年代学和Hf同位素以及全岩地球化学研究，确定花岗闪长斑岩形成时代、揭示岩石成因类型及源区属性、探讨其与碱长花岗岩和紫苏花岗岩岩浆演化成因联系及其形成的深部动力学过程。锆石U-Pb定年结果显示，花岗闪长斑岩形成于317.4±1.9Ma，为晚石炭世早期岩浆活动的产物，明显早于紫苏花岗岩（~307Ma）和碱长花岗岩（~303Ma）。岩石地球化学数据表明，花岗闪长斑岩具有较高硅、中等铝，贫钙、铁、镁，富集Rb、K、Th、U，强烈亏损Nb、Ta、Ti的特征，为钙碱性弱过铝质I型花岗岩；紫苏花岗岩更多的表现出钙碱性-高钾钙碱性镁质I型紫苏花岗岩特征；碱长花岗岩为碱性准铝质-弱过铝质A型花岗岩。锆石Hf同位素分析结果表明，花岗闪长斑岩、紫苏花岗岩和碱长花岗岩均具有高正的ε_Hf（t）值（+11.6~+15.8）和年轻的二阶段模式年龄（325~600Ma），表明其原始岩浆主要起源于亏损地幔新衍生的年轻地壳物质。综合分析认为，庙尔沟岩体花岗闪长斑岩形成于晚石炭世早期洋壳俯冲背景，由底侵的、受流体交代的幔源基性岩浆与其诱发的年轻下地壳酸性岩浆在深部混合而成。紫苏花岗岩和碱长花岗岩形成于弧后伸展背景，前者是伸展初期继续底侵于下地壳的幔源玄武质岩浆降温释放大量的水和热诱使早期侵位于下地壳的镁铁质岩石再次发生部分熔融的产物，后者是伸展后期大规模软流圈地幔上涌底垫加热年轻中下地壳使其部分熔融而成。;The Miaoergou pluton, located in southern West Junggar, is mainly composed of alkali-feldspar granites with small amount of charnockites. On the basis of previous researches, this paper mainly focuses on the newly discovered granodiorite porphyry in southwestern margin of the Miaoergou pluton. A comprehensive study of petrographical, zircon U-Pb geochronological and in-situ Hf isotopic, whole-rock geochemical analyses were carried out to determine its diagenetic age and reveal the petrogenesis, the nature and composition of the magma source of this porphyry, and furthermore, to discuss the genetic relationships among the granodiorite porphyries, alkali-feldspar granites and charnockites and their geodynamic processes. LA-ICP-MS zircon U-Pb dating for the granodiorite porphyry yielded crystallization age of 317.4±1.9Ma, defining an early Late Carboniferous magmatic event in southern West Junggar, which is significantly earlier than the ages of charnockites (~307Ma) and alkali-feldspar granites (~303Ma). The geochemical characteristics indicate that the studied granodiorite porphyries belong to cal-alkaline weakly peraluminous I-type granite, and are characterized by slightly high silicon, medium aluminum, but low ferrum, calcium and magnesium, and also enrichment in Rb, K, Th, U with pronounced negative Nb, Ta and Ti anomalies. The charnockites possess calc-alkaline to high-K calc-alkaline magnesian I-type charnockite affinities, which were previously considered A-type granites by some geologists, while alkali-feldspar granites belong to alkaline metaluminous to weakly peraluminous A-type granites. In-situ zircon Hf isotope analyses show that these granites have high positive ε_Hf(t) values (+11.6~+15.8) and very young two-stage Hf model ages of 325~600Ma, indicating that the magma was sourced from juvenile crust originated from depleted mantle during the Late Neoproterozoic to Early Carboniferous period. In association with previous analysis, it is proposed that the Miaoergou granodiorite porphyries were formed in an oceanic crust subduction setting during early Late Carboniferous. They are probably the products of the acidic magma formed by partial melting of the juvenile lower crust and mixed with the underplated basaltic magma derived from the fluid metasomatic mantle wedge in the deep crust to some extent. Both the charnockites and alkali-feldspar granites were formed in a back-arc extensional setting related to the northwestward subduction of the Junggar oceanic crust. The charnockites may be generated by re-melting of juvenile lower crust mafic rocks, probably triggered by addition of water and heat released from cooling of underplated depleted mantle-derived basaltic magma during the incipient rifting stage of the back-arc basin, and the alkali-feldspar granites may be generated by partial melting of the juvenile middle-lower crust induced by the large-scale upwelling of asthenosphere during the later stage of the back-arc extension.