Search

The Permian to Triassic period represents a pivotal phase in the evolution of the Paleo-Asian Ocean, marked by significant tectonic transitions from subduction, collision, and post-orogenic extension. The timing of closure of the Paleo-Asian Ocean in northeastern China has always been controversial. In this contribution, the petrology, zircon U-Pb geochronology and geochemistry are conducted on granite found in well HFD1, Songliao Basin, eastern part of Central Asian orogenic belt. Zircon U-Pb dating indicates that granite crystallized at 258.9 ± 2.2 Ma, as the product of magmatism occurred in the early Late Permian. The rocks have high SiO2, Al2O3, Na2O content, negative Eu anomaly, light enrichment of rare-earth elements, depletion of heavy rare-earth elements, high Sr (448.29–533.11 ppm, average 499.68 ppm), low Yb (0.49–0.59 ppm, average 0.54 ppm), Y (4.23–5.19 ppm, average 4.49 ppm), and high Sr/Y ratios (98–125, average 112) and can be classified as O-type adakite. This is the first discovery of late Paleozoic adakite in the Songliao Basin and the neighboring areas. The geochemistry of adakite indicates derivation by partial melting of MORB-type subducted oceanic crust, indicating that the subduction of the Paleo-Asian Oceanic lithosphere lasted until at least 258.9 Ma. [ABSTRACT FROM AUTHOR]

The West Bogda Mountains separate the two largest petroliferous sedimentary basins in Northwest (NW) China and may record the evolution history of the Central Asian Orogenic Belt (CAOB). The timing of the initial uplift of the West Bogda Mountains is debated, which may provide the robust constraint on the CAOB evolution. Here we present an integrated study of sedimentology, geochemistry, and detrital zircon geochronology to constrain the timing of the initial uplift of the West Bogda Mountains. The late Lower Permian Lucaogou Formation in the West Bogda Mountains is dominated by organic-rich laminated shale, gravity flow deposits and dolomite without shallow-water sedimentary structures, suggesting a deep-water lacustrine depositional environment. The Middle Permian Quanzijie Formation is mainly composed of poorly sorted and sub-rounded conglomerate, which indicates that the depositional environment changed to an alluvial fan. The depositional environment changed to a meandering river system in the early Upper Permian Wutonggou Formation, with evidence from the widely developed cross-bedding in its sandstone and the typical 'dual structure'. The compositions of immobile elements and detrital zircon U-Pb geochronology reveal changes in sediment sources from the early to late Permian. The sediments of the late Lower Permian Lucaogou Formation were mainly sourced from the North Tianshan, while the sediments in the Middle Permian were mostly locally derived. Combining these evidences, we infer that the initial uplift of the West Bogda Mountains likely occurred in the period from the late Lower to Middle Permian (~289.8 Ma to ~265.7 Ma), and was probably caused by the intracontinental collision between Junggar Block in the north and the Tarim Block in the south. [ABSTRACT FROM AUTHOR]

The Carboniferous–Triassic period was an important stage of global sea–land transformation, with coal formation in the Carboniferous, biological extinction at the end of the Permian, and global drought in the Triassic. The MS-1 well in the Mosuowan High of the Junggar Basin is the deepest well drilled in Northwestern China. In this paper, we investigate the sedimentary environment and climate evolution of the Mosuowan area in the central Junggar Basin during the Late Carboniferous–Early Permian by the petrothermal, lipid biomarker, and isotopic composition of mud shale core samples, and explore the tectonic–climatic events and Central Asian orogenic belt evolution driving the sedimentary environment. The study shows that the organic matter from the Upper Carboniferous to the Lower Permian is at a mature stage, but biomarkers maintained the primary information although the organic matter was subjected to thermal evolution. In the late Carboniferous period (Tamugan Formation), the study area was a closed remnant sea with a relatively humid climate, triggering lush terrestrial vegetation and high organic carbon content in the sediments, which had the potential to evolve into natural gas. During the Xiazijie Formation of the Middle Permian, tectonic activity shifted to the subsidence period, and the salinity of the water decreased after a large input of fresh water. The lake basin area expanded, and the content of aquatic organisms continued to increase. As the Lower Permian stratigraphy is missing, this sea–land transition seems to jump. The low and upper Urho Formations of the Middle–Upper Permian are a deltaic foreland deposit, and geochemical indicators show an overall lake retreat process with a continuous increase in organic matter content of terrestrial origin. The lithologic assemblage of the Triassic Baikouquan Formation is braided river deltaic sedimentation with migration of deposition centers of the lake basin. In conclusion, the Late Carboniferous–Early Permian period was influenced by global changes, Paleo-Asian Ocean subduction, and continental splicing, which resulted in a continuous increase in terrestrial organic matter, water desalination, and oxidation-rich sediments in the Mosuowan region, but the P–T biological mass extinction event was not recorded. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcic minerals in skarns constrain distinct mineralizing stages and fluid evolution. • Garnet zoning in skarns reflects fluid dynamics, chemistry, temperature, and redox conditions, while the REE features result from surface adsorption and crystal chemistry substitutions. • Garnet U-Pb age and associated mineral assemblages source constraints as well as the distribution of skarn minerals and correlations between metal elements and andradite have exploration implications. The Mount Garnet Zinc deposit in NE Queensland, Australia, is located in the region of voluminous magmatism associated with the formation of Palaeozoic continental arcs of Gondwana. Ore-forming events of this deposit are related to the intrusion of the Kennedy Igneous Association (KIA) – a large suite of igneous rocks spanning Late Carboniferous to Early Permian in age – into the Silurian limestone (Chillagoe Formation) in the Hodgkinson Province (Mossman Orogen). Petrographic observations and in situ major and trace element analysis reveal the sequence of garnet growth and fluid-rock interaction during skarn formation. Three types of garnets are identified, Grt I (including IA and IB) and Grt II. Grt IB is related to Zn-Pb mineralization. All garnets have elevated Sn and W and the highest levels of W and Sn are observed in Grt II. Garnet U-Pb ages of Grt IB provide the first direct geochronological result of hydrothermal minerals in the Mount Garnet region. New data argues that the base metal mineralization may take place during early Permian period and be sourced from the Claret Creek Supersuite. Sn-W mineralization may be associated with the O'Briens Creek Supersuite. [ABSTRACT FROM AUTHOR]

The tuffs from Upper Permian Wujiaping Formation in Chaotian section of Guangyuan area, Sichuan are located above Wangpo claystone beds at the top of Maokou Formation, the origin of tuffs may provide a good chance to constrain the age of Emeishan large igneous province volcanism. Mineral contents, whole-rock geochemical characteristics and zircon U-Pb age, trace element and Hf isotopic composition for two tuff samples from Wujiaping Formation in Chaotian section were analyzed to discuss the sources and its geological significance for the age of Emeishan large igneous province volcanism. The results show that the tuffs from Upper Permian Wujiaping Formation in Chaotian section of Guangyuan area with zircon U-Pb age of(260.1±2.8)Ma, are dominated by clay minerals, and have high Al2O3/TiO2 ratios(37.90 and 31.49), strong negative Eu anomalies(Eu/Eu* ratios are 0.13 and 0.06), and no negative Nb and Ta anomalies; zircons from the tuffs have high εHf(t)(7.8-11.4)and low Th/Nb ratios(5.4-14.9); the geochemical characteristics are similar to the lower tuffs from Upper Permian in Shangsi section and the acid ignimbrites of Emeishan volcanic sequence in Binchuan section, but different from the εHf(t)and Th/Nb ratios of Wangpo claystone beds in Qingyinge. In general, the tuffs from Upper Permian Wujiaping Formation in Chaotian section of Guangyuan area, Sichuan are related to the acid volcanism of Emeishan large igneous province, and the age of Emeishan large igneous province volcanism may extend to the early period of Late Permian. [ABSTRACT FROM AUTHOR]

Earth's transition from an icehouse to hothouse during the Late Paleozoic was characterized by a series of high paleolatitude glacial-interglacial events. However, the exact timing of these events remains unresolved. Here, we report on fifty-five calcitic shells of brachiopods and bivalves screened to obtain reliable 87Sr/86Sr ratios for Cisuralian (298.9-272.95 Ma) and Guadalupian (272.95-259.1 Ma) seawater. Specifically, we used well-preserved shells to build a 87Sr/86Sr seawater curve for the Sydney Basin, and then with the marine Look-up Table of the Permian calculated numerical ages of the stratigraphic succession. This allowed us to match seawater changes to the coeval P1 – P3 glacial-interglacial cycles recorded in the sedimentary successions of the Sydney Basin. Evaluation of the 87Sr/86Sr results revealed that onsets of the P2 and P3 glaciations in the Sydney Basin should be assigned to the early Artinskian and late Wordian, respectively. The range of 87Sr/86Sr values recorded by brachiopods from the Wandrawandian Siltstone coupled with recent geochronological dating of the Broughton Formation suggest that glacial phase P3 lasted about 2 Myr and was confined to the late Wordian – early Capitanian. Dating obtained using the Sr-isotope proxy from brachiopods agrees with the geochronologic ages, and they suggest that the glacial phases P1 to P3 became progressively shorter in duration and less intense. Conversely, the corresponding interglacials became progressively longer, and thus, documenting the gradual transition of the Permian icehouse to an ice-free greenhouse world. Our study confirms that strontium isotopes measured in screened brachiopod shell archives are sufficiently robust to date Paleozoic marine sedimentary successions, and are most valuable in sedimentary successions that otherwise lack geo-chronological dating. • Strontium isotope stratigraphy applied to dating late Paleozoic marine sediments. • Geochemistry of brachiopod low magnesium shells. • Multiple-screening approach to the study of carbonate diagenesis. • Numerical dating of glacial-interglacial cycles characterizing the Lower and Middle Permian in the southern paleo-latitudes. [ABSTRACT FROM AUTHOR]

Abstract Geochemical analysis on sandstones from clastic sediments was carried out to understand the tectonic setting and subsequent post-depositional change in the Karoo basinal fill of the fluvial deposits of the Balfour Formation during the Late Permian to Early Triassic period. The major and trace element analysis reveal a relatively homogeneous provenance for the sandstones. The geochemical analysis shows that these rocks are first order mature sediments, derived from igneous and/or meta-igneous rocks of a felsic composition. The results show that the sandstone consists of SiO 2 (71.58 wt. %), followed by Al 2 O 3 (14.48 wt. %), but with low contents of Fe 2 O 3 +MgO (4.09 wt. %) and TiO 2 (0.47 wt. %). These sandstones are classified as litharenites and arkoses based on the elements constituent ratio of various schemed adopted. The sandstone in the provenance discrimination diagram plots in the dissected and transitional arc fields suggesting an active margin and continental island arc provenance, preserving the signature of a recycled provenance. The Chemical Index of Alteration (CIA) ranging from 63.56 to 67.10% suggests recycling processes, and that the source area has undergone a moderate degree of chemical weathering. The geochemical characteristics of the sediment suggest the source area of uplifted terrane of folded and faulted strata with detritus of sedimentary and metasedimentary origin. Highlights • The paper summaries the results of geochemical analysis of Balfour Formation. • Major elements and trace elements were analyzed to classify the sandstone. • The provenance and tectonic setting along with weathering conditions in the source are deduced based on the geochemical analysis. • The sediments are found to be chemically immature. • The study concludes that sediments were derived from igneous, metamorphic and older sedimentary rocks with only minor mafic rocks. [ABSTRACT FROM AUTHOR]

Calc–alkaline lamprophyres are known from several localities in the Malá Fatra Mountains. They form dykes (0.5–3 m) of varying degree of alteration that have intruded the surrounding granitoid rocks which are often incorporated xenoliths. Clinopyroxenes (diopside to augite), amphiboles (kaersutitic), biotites (annite) and plagioclases are major primary minerals of the dykes, accessory minerals include apatite, ilmenite, rutile, pyrite, chalcopyrite, and pyrrhotite. Apatite has a relatively low F, but increased Cl content compared to typical apatite from lamprophyres or magmatic apatite from granitic rocks in the Western Carpathians. The chemical composition of the lamprophyres indicates their calc–alkaline character, but affinity to alkaline lamprophyres is suggested by the Ti enrichment in clinopyroxene, amphibole and biotite. According to modal classification of the minerals, the studied rocks correspond to spessartite. The differences in the chemical composition of the rocks (including Sr and Nd isotopes) probably result from the contamination of primary magma by crustal material during magma ascent. The age of the lamprophyres, based on U/Pb dating in apatite, is 263.4 ± 2.6 Ma. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the Central Asian Orogenic Belt (CAOB) is related to the subduction and closure of the Paleo-Asian Ocean (PAO). Considerable controversy still surrounds whether, when and how the PAO subducted underneath the northern margin of the North China Craton (NCC). This study carries out whole rock geochemical and zircon U-Pb-Hf isotopic investigations on Paleozoic intrusive rocks in both the Bainaimiao arc and the northern margin of the NCC. Zircon U Pb dating of gabbroic diorite and diorite in the Bainaimiao arc and the granite and diorite at the northern margin of the NCC yielded crystallization ages of 458 ± 2 Ma, 428 ± 2 Ma, 326 ± 2 Ma, and 258 ± 2 Ma respectively. In the Bainaimiao arc, the middle Silurian diorite as the main body of the arc-related intrusive rocks there show geochemical characteristics of continental margin arc magma with negartive ƐHf(t) values and old Hf model ages. On the other hand, the middle Ordovician gabbroic diorite mainly shows typical calc-alkaline continental arc geochemical characteristics with positive ƐHf(t) values and relative young Hf model ages, indicative of the southward-propagating reworking and arc-accretion processes. Thus, we interpret these rocks as a consequence of southward subduction of the PAO beneath the Bainaimiao arc, here termed as Bainaimiao Arc terrane, BAT. The early Carboniferous granite and late Permian diorite at the northern margin of the NCC show geochemical characteristics similar to post-collisional adakites and typical continental arc rocks, respectively. Combined with previous work, the early Carboniferous post-collisional adakite shows limited distribution and corresponds to the subsequent effect of the amalgamation between the BAT and the NCC. Whereas most of the Carboniferous-Permian magmatic rocks (ca. 342–258 Ma) at the northern margin of the NCC are arc-related and resulted from the continued effect of the southward subduction of the PAO. Moreover, the southward subduction in the early Paleozoic was transformed from relative high angle subduction beneath the BAT to shallow subduction beneath the unity of the NCC and the BAT in the late Paleozoic, which lasted until the late Permian (ca. 258 Ma). [ABSTRACT FROM AUTHOR]

We performed geochronological and geochemical analyses of the A‐type granite in the Hongol area, central Inner Mongolia, to determine its age, petrogenesis and tectonic setting, which are significant for clarifying the Late Paleozoic tectonic evolution of the Xing'an Mongolian Orogenic Belt (XMOB). The rock type of the A‐type granite in the Hongol area is alkali‐feldspar granite, and it constitutes a western part of the Baiyinwula–Dongujimqin A‐type granite belt. Zircon U–Pb geochronology yields 206Pb/238U ages ranging from 293 to 286 Ma for the alkali‐feldspar granite, indicating this granitic pluton formed in the Early Permian. The alkali‐feldspar granite is high in silica (SiO2=75.13wt%–80.17wt%), aluminum (Al2O3=10.59wt%–13.17wt%) and alkali (Na2O+K2O=7.33wt%–9.11wt%), and low in MgO (0.08wt%–0.39wt%) and CaO (0.19wt%–0.70wt%). It is obviously enriched in LILEs such as Rb, Th and K, depleted in HFSEs such as Nb, Ti, La and Ce, with pronounced negative anomalies of Nb, Ti, P, Eu, Sr and Ba. Its Sr–Nd–Pb isotopic compositions show positive εNd(t) (+0.72–+3.08), low TDM2 (805–997 Ma), and high radioactive Pb with (206Pb/204Pb)i of 18.710–19.304, (207Pb/204Pb)i of 15.557–15.604 and (208Pb/204Pb)i of 37.887–38.330. Petrological characteristics and geochemical data suggest that the alkali‐feldspar granite in the Hongol area belongs to aluminous A‐type granite. This A‐type granite formed in a post‐collisional extensional setting and was generated by the partial melting of felsic rocks in the middle‐lower crust resulting from post‐collisional slab breakoff. It is suggested that the Paleo‐Asian Ocean was closed before the Permian in central Inner Mongolia. [ABSTRACT FROM AUTHOR]

The role of the mantle in generating ultrahigh-temperature metamorphism and peraluminous S-type granites, and the extent of crust−mantle interaction are topics fundamental to our understanding of the Earth's evolution. In this study we present geochronological, geochemical, and Sr–Nd–Hf isotopic data for dolerites and mafic volcanic rocks from the Darongshan granite complex belt in western Cathaysia, South China. LA–ICP–MS U–Pb zircon analyses yielded magma crystallization ages of ca. 250–248 Ma for the dolerites, which are coeval with eruption of the mafic volcanic rocks, ultrahigh-temperature metamorphism, and emplacement of S-type granites in the Darongshan granite complex belt. The mafic volcanic rocks are high-K calc-alkaline or shoshonitic, enriched in Th, U, and light rare earth elements, and depleted in Nb, Ta and Ti. The dolerites are characterized by high Fe 2 O 3 tot (11.61–20.39 wt%) and TiO 2 (1.62–3.17 wt%), and low MgO (1.73–4.38 wt%), Cr (2.8–10.8 ppm) and Ni (2.5–11.4 ppm). Isotopically, the mafic volcanic rocks have negative whole-rock ε Nd (t) values (−6.7 to −9.0) and high I Sr values (0.71232 to 0.71767), which are slightly depleted compared with the dolerite samples (ε Nd (t) = −10.3 to −10.4 and I Sr  = 0.71796 to 0.71923). Zircons in the dolerites have ε Hf (t) values of −7.6 to −10.9. The mafic volcanic rocks are interpreted to have resulted from the partial melting of an enriched lithospheric mantle source with minor crustal contamination during ascent, whereas the dolerites formed by late-stage crystallization of enriched lithospheric mantle-derived magmas after fractionation of olivine and pyroxene. The formation of these mantle-derived mafic rocks may be attributed to transtension along a NE-trending strike-slip fault zone that was related to oblique subduction of the Paleo-Pacific plate beneath South China. Such underplated mafic magmas would provide sufficient heat for the generation of ultrahigh-temperature metamorphism and S-type granites, and act as a mafic end-member for S-type granite genesis. [ABSTRACT FROM AUTHOR]

A transition from widespread humid to more drought tolerant floras characterized tropical terrestrial ecosystems during the Permian (Cisuralian). Tregiovo (Southern Alps, N-Italy) is one of the very few well dated Kungurian (late Cisuralian) plant localities in Euramerica. It was located in eastern palaeoequatorial Pangea. Two units bearing fossil plant assemblages occur in finely laminated sediments deposited in a playa-lake environment. In this paper, the sedimentology of the Tregiovo Basin is reviewed, and new palaeobotanical, palynological and stable isotopic data are presented, in order to reconstruct the palaeoclimatic and palaeoenvironmental conditions of the Kungurian in the Southern Alps. Both fossil plant assemblages are dominated by conifers ( Hermitia , Feysia , Quadrocladus , Dolomitia ), together with sphenophytes ( Annularia ), ginkgophytes ( Sphenobaiera ), pteridosperms ( Peltaspermum ), taeniopterids and sphenopterids. These taxa, which occur with different abundances in the two plant assemblages, both indicate semi-arid conditions. Associated palynoflora, dominated by bisaccate pollen, and extremely rare spore occurrences, is consistent with the xerophytic character of the macroflora, and suggests that the fossil plant record was not affected by collection or preservation bias. Stable isotopic analyses of two stratigraphic sections reveal an upward trend of increasingly negative δ 13 C org (VPDB), which may correlate with roughly coeval records from marine and continental successions such as in North China and South Africa. This isotopic shift may be attributed to a global perturbation of atmospheric δ 13 C, although the influence of local environmental factors cannot be excluded. [ABSTRACT FROM AUTHOR]

The Lower to Middle Permian terrestrial successions in the southern Junggar and Turpan basins provide a wealth of information regarding the paleoclimatic and paleogeographic evolution of mid-latitude NE Pangea. Two sections, namely the Xiaolongkou section in the southern Junggar Basin and the southwest (SW) Tarlong section in the Turpan Basin, were systematically studied using detrital zircon geochronology and whole-rock geochemical analysis. Stratigraphic studies suggest that, in both sections, the Lucaogou and Hongyanchi formations are dominated by lacustrine deposits, while the Quanzijie Formation represents mixed fluvial-lacustrine and loess environments. The Lucaogou Formation displays low CIA (Chemical Index of Alteration) values and Th/U ratios, suggesting semiarid to arid conditions in both sections. The Hongyanchi Formation shows low to intermittently moderate CIA values and Th/U ratios, indicating variably semiarid-arid conditions alternating with subhumid-semiarid episodes. The lower part of the Quanzijie Formation reflects subhumid-semiarid to semiarid-arid conditions, while the upper part of the Quanzijie Formation mainly records semiarid-arid and shifts into subhumid conditions toward the top. Detrital zircon and element data indicate that, within each section, all three formations display similar zircon age distributions and geochemical characteristics, suggesting no significant changes in provenance during deposition. However, the provenance characteristics of the two sections differ from each other; the Xiaolongkou section is rich in felsic material, with two detrital zircon age peaks, while the SW Tarlong section contains more mafic components, with a single peak in detrital zircon age spectrum. This suggests that the greater Junggar-Turpan Basin was highly partitioned with several independent provenance systems active during the Early-Middle Permian. The abrupt change in depositional environments in both sections may have resulted from uplift of the North Tian Shan, which induced rapid regression of the lakeshore and uplift of sediment source and catchment areas. [ABSTRACT FROM AUTHOR]

Detailed sedimentological and geochemical records across the Permian-Triassic boundary (PTB) in five offshore wells of the central Persian Gulf served to interpret the end-Permian sea-level change in this region. A decrease in sea level at the PTB was established by petrographical and geochemical study of the boundary. Thin sections showed that Upper Permian strata are composed of dolomite with minor anhydrite, changing into limestone in Lower Triassic sediments. Brine dilution toward the boundary supports sea-level fall in the Permian-Triassic transition, reflected by a decrease in anhydrite content and a shallowing-upward trend from lagoonal to peritidal facies. Isotopic changes at the boundary are in favor of sea-level fall. Changes in both carbon (from about 4 to -1‰) and oxygen (from 2 to -5‰) stable isotopes show negative excursions. The shift in carbon isotope values is a global phenomenon and is interpreted as resulting from carbonate sediment interaction with 12C-rich waters at the end-Permian sea-level fall. However, the oxygen isotope shift is attributed to the effect of meteoric waters with negative oxygen isotope values. The increase in strontium isotope ratios is also consistent with the high rate of terrestrial input at the boundary. The effect of meteoric conditions during diagenesis is evident from vuggy and moldic porosities below the PTB. The following transgression at the base of the Triassic is evident from the presence of reworked fossils and intraclasts resulting from deposition from agitated water. [ABSTRACT FROM AUTHOR]

The petrogenesis of the Permian magmatic rocks in the Shalazhashan Belt is helpful for us to understand the tectonic evolution of the Central Asian Orogenic Belt (CAOB) in the northern margin of the Alxa Block. The Permian volcanic rocks in the Shalazhashan Belt include basalts, trachyandesites and trachydacites. Our study shows that two basalt samples have negative ε Nd (t) values (–5.4 to −1.5) and higher radiogenic Pb values, which are relevant to the ancient subcontinental lithospheric mantle. One basalt sample has positive ε Nd (t) value (+10) representing mafic juvenile crust and is derived from depleted asthenosphere. The trachyandesites are dated at 284 ± 3 Ma with ε Nd (t) = +2.7 to +8.0; I Sr  = 0.7052 to 0.7057, and they are generated by different degrees of mixing between mafic magmas and crustal melts. The trachydacites have high ε Nd (t) values and slightly higher I Sr contents, suggesting the derivation from juvenile sources with crustal contamination. The isotopic comparisons of the Permian magmatic rocks of the Shalazhashan Belt, the Nuru-Langshan Belt (representing the northern margin of the Alxa Block), the Solonker Belt (Mandula area) and the northern margin of the North China Craton (Bayan Obo area) indicate that the radiogenic isotopic compositions have an increasingly evolved trend from the south (the northern margins of the Alxa Block and the North China Craton) to the north (the Shalazhashan Belt and the Solonker Belt). Three end-member components are involved to generate the Permian magmatic rocks: the ancient subcontinental lithospheric mantle, the mafic juvenile crust or newly underplated mafic rocks that were originated from depleted asthenosphere, and the ancient crust. The rocks correlative with the mafic juvenile crust or newly underplated mafic rocks are predominantly distributed along the Shalazhashan Belt and the Solonker Belt, and the rocks derived from ancient, enriched subcontinental lithospheric mantle are mainly distributed along the northern margins of the Alxa Block and the North China Craton. The magmatic rock types, isotopic features and their temporal, spatial distributions suggest an extensional regime probably related to rifting. [ABSTRACT FROM AUTHOR]

We present geochemical and Sr–Nd–Pb–Hf isotope data as well as the results of single grain U–Pb zircon dating for ten granitoid and alkaline intrusions of the Alai segment of Kyrgyz South Tien Shan (STS). The intrusions comprise four geochemically contrasting series or suites, including (1) I-type and (2) shoshonitic granitoids, (3) peraluminous granitoids including S-type leucogranites and (4) alkaline rocks and carbonatites, closely associated in space. New geochronological data indicate that these diverse magmatic series of the Alai segment formed in a post-collisional setting. Five single grain U-Pb zircon ages in the range 287–281 Ma, in combination with published ages, define the main post-collisional magmatic pulse at 290–280 Ma, which is similar to ages of post-collisional intrusions elsewhere in the STS. An age of 287 ± 4 Ma, obtained for peraluminous graniodiorite of the Liayliak massif, emplaced in amphibolite-facies metamorphic rocks of the Zeravshan-Alai block, is indistinguishable from ca. 290 Ma age of peraluminous granitoids emplaced coevally with Barrovian-type metamorphism in the Garm block, located ca. 40 km south-west of the research area. The Sr-Nd-Pb-Hf isotopic compositions of the studied intrusions are consistent with the reworking of crustal material with 1.6–1.1 Ga average crustal residence times, indicating the formation of the Alai segment on a continental basement with Mesoproterozoic or older crust. The pattern of post-collisional magmatism in the Alai segment, characterized by emplacement of I-type and shoshoninitic granitoids in combination with coeval Barrovian-type metamorphism, is markedly different from the pattern of post-collisional magmatism in the adjacent Kokshaal segment of the STS with predominant A-type granitoids that formed on a former passive margin of the Tarim Craton. We suggest that during the middle-late Carboniferous the Alai segment probably comprised a microcontinent with Precambrian basement located between the Turkestan Ocean to the north and an inferred oceanic basin to the south, where the evidence of supra-subduction magmatism was largely destroyed by subsequent tectonic processes. In this scenario, after collision, the position of the Alai microcontinent between two major sutures enabled delamination of its lithospheric mantle, which resulted in production of diverse post-collisional magmatic series by interaction of ascending asthenospheric material with lithospheric mantle and various crustal protoliths. [ABSTRACT FROM AUTHOR]

The Western Tianshan in NW China is one of the most important gold provinces in the Central Asian Orogenic Belt (CAOB). The recently discovered Kuruer Cu-Au deposit has been interpreted to represent a transition from high-sulfidation epithermal to porphyry mineralization system. In this study, we present new LA-ICP-MS zircon U-Pb ages for the many magmatic rock types at Kuruer, including the Dahalajunshan Formation andesitic tuff (333.2 ± 1.6 Ma), diorite porphyry (269.7 ± 2.0 Ma), slightly-altered (264.4 ± 2.6 Ma) and intensively-altered (270.5 ± 2.5 Ma) albite porphyry. These ages reveal two distinct magmatic episodes: The Early Carboniferous Dahalajunshan Formation (wall rocks) andesitic tuff samples contain narrow ranges of SiO 2 (60.29–61.28 wt.%), TiO 2 (0.96–0.98 wt.%), Al 2 O 3 (16.55–16.57 wt.%) and Fe 2 O 3 T (5.36–5.57 wt.%). The tuff is characterized by LREE enrichment and HFSE depletion, as well as LREE/HREE enrichment ((La/Yb) N = 8.31–8.76) and negative Eu anomalies (δEu = 0.64–0.76). Zircon ε Hf (t) values are 5.4–8.2, and two-stage Hf model ages ( T DM2 ) are 821–1016 Ma, indicating partial melting of a moderately depleted mantle wedge with Precambrian continental crustal input. The ore-forming Middle Permian diorite porphyry and (quartz) albite porphyry have variable major oxide compositions (e.g., SiO 2 = 53.09–53.12 wt.% for the diorite porphyry, 70.84–78.03 wt.% for the albite porphyry, and 74.07–75.03 wt.% for the quartz albite porphyry) but similar chondrite-normalized REE and primitive mantle-normalized multi-element patterns. These porphyries display LREE enrichment and HFSE depletion, as well as elevated LREE/HREE enrichment and negative Eu anomalies. The positive zircon ε Hf (t) values (11.7–15.9 for the diorite porphyry, 8.9–14.9 for the albite porphyry) and young two-stage Hf model ages ( T DM2 ) (282–542 Ma for the diorite porphyry, 337–717 Ma for the albite porphyry) indicate a major juvenile continental crustal involvement. We propose that the Carboniferous and Middle Permian magmatism was formed in a continental arc and post-collisional settings, respectively, with the latter episode responsible for the Cu-Au mineralization. [ABSTRACT FROM AUTHOR]

The isotope ratios of Sr are useful tracers for studying parent material sources, weathering processes, and biogeochemical cycling. Mineralogical and geochemical investigations of two lateritic weathering covers, in an area close to the Tropic of Cancer (Guangxi Province, southern China), were undertaken to study the regional weathering processes and Sr isotopic sources. We found that weathering and decomposition of Rb- and Sr-bearing minerals change the Sr isotopic composition in weathering products (lateritic soils). Weathering of illite lowered the 87Sr/86Sr ratio whereas dissolving and leaching of carbonate minerals increased the 87Sr/86Sr ratio. An Fe nodular horizon is widely developed on the top of the weathering covers in the studied area and it differs from the lateritic soil horizon in mineral composition, construction, and elemental concentration. Furthermore, both Fe2O3 and P2O5 (concentrations) are negatively correlated with the 87Sr/86Sr ratios, suggesting fixation of apatite by Fe oxides is a controlling factor of the Sr isotopic composition in the Fe nodular horizon. The 87Sr/86Sr and Nb/Sr ratios imply the contents and proportions of Fe nodules and clay are critical in controlling the changes of Sr isotopic composition in the Fe nodular horizon. The two stages of the weathering process of carbonate rocks are revealed by the87Sr/86Sr versus Nb/Sr diagram. The 87Sr/86Sr and Rb/Sr ratios suggest that Sr isotopes in the weathering covers within the studied area are derived mainly from parent rock weathering and that the contributions from allothogenic Sr isotopes are limited. A comparison of Sr isotopic composition signatures in the weathering covers of the studied area and Guizhou Province provided insight into the Sr isotopic source and paleogeographic evolution of southern China. From the Permian to the Triassic, the continental fragment sources of the South China sedimentary basin changed significantly. In the Permian, Southern China presented the paleogeographic pattern that the north was higher (in elevation) than the south. [ABSTRACT FROM AUTHOR]

Shales in the Middle Permian Lucaogou Formation have been considered as one of the most important unconventional reservoirs in NW China, due to their excellent shale oil and tight oil potential. Based on the data of previous organic geochemical studies, the overall evolution of the ecosystem in the lake, water conditions and organic matter sources have been outlined. Here we present the results of the mineralogical and organic-petrological examinations and the Rock-Eval pyrolysis, on samples of a fine-grained, mixed carbonate-clastic sedimentary succession from the Santanghu Basin, providing new detailed insights into paleoenvironmental evolution and lake level changes. In addition, shale oil potential was further evaluated on this oil-prone shale. Analytical results from a total of 196 shale samples from the second member of the Lucaogou Formation, collected from one newly drilled core, indicate algal/microbial sources of organic matter, classified by Rock-Eval pyrolysis as type I kerogen. Samples characterized by lower hydrogen index (HI) values (type II kerogen) contain increased contributions of terrigenous organic matter, evidenced by enhanced inertinite and vitrinite contents. Vertical variations in mineralogical and bulk geochemical composition reflect an evolution from a saline, anoxic to a deep, freshwater lake. Two environmental changes subdivided the sequence into three units. The boundary between the lower Unit I and the middle Unit II is characterized by the drastic decrease of smectite and K-feldspar contents and a sharp increase in total organic carbon (TOC) content. The upper Unit III is distinguished by high TOC/S ratios. Based on variations in petrography and carbon isotopes of hopanes, the middle Unit II can be further subdivided into two parts reflecting changes in water level of the lake. All the periods of high-water level are characterized by higher lamalginite contents (> 40 vol%) and higher HI values than those obtained from sediments deposited during periods of shallower water levels. Deposition in a shallow lake is evidenced by increased dolomite and decreased lamaginite contents. Lake level fluctuations, indicated by mineralogical and geochemical parameters, are associated with changes in organic matter sources, leading to the great variability in mineral content, organic petrography and hydrocarbon generation potential. High TOC and brittle minerals contents, micro-nanopores system and large thickness of the shale show that the Lucaogou Formation holds a significant shale oil potential in areas where oil window maturity is reached. [ABSTRACT FROM AUTHOR]

New high-resolution geochemical and sedimentological data from Fiskegrav, East Greenland, reveal fluctuations in marine redox conditions associated with the final disappearance of bioturbating organisms during the latest Permian mass extinction (LPME). Sedimentological observations imply a transgressive episode, and associated geochemical evidence for decreasing oxygen availability and the establishment of persistently ferruginous (Fe 2 + -rich) conditions implies the shoreward migration of oxygen deficient waters. The long-term decline in dissolved oxygen (DO) availability could have been exacerbated by increasing water temperatures, reducing the solubility of oxygen and promoting thermal stratification. Mixing of the water column could have been further inhibited by freshwater influxes that could have generated salinity contrasts that reinforced thermal stratification. Enhanced runoff could also have increased the delivery of nutrients to the marine shelf, stimulating biological oxygen demand (BOD). During the transition to persistently ferruginous conditions we identify intervals of intermittent benthic meiofaunal recolonization, events that we attribute to small transient increases in DO availability. The mechanism controlling these fluctuations remains speculative, but given the possible centennial- to millennial-scale frequency of these changes, we hypothesise that the mid-latitude setting of Fiskegrav during the Late Permian was sensitive to changes in atmospheric circulation patterns, which may have influenced local precipitation and intermittently modulated some of the processes promoting anoxia. [ABSTRACT FROM AUTHOR]

Here, the Lower Permian, post-glacial fossiliferous Lontras black shales from the Paraná Basin (southern Brazil) are studied using integrated palynological, geochemical and petrographic methods for the first time in order to decipher the prevalent palaeoenvironmental conditions during their sedimentation. These black shales were deposited in a restricted marine environment. Inorganic geochemical data (U/Th ratios, authigenic uranium, molybdenum), organic geochemical data (total organic carbon, biomarkers) and framboid pyrite size distributions point to predominantly anoxic/euxinic bottom-water conditions. Moreover, the presence of aryl isoprenoids and maleimide biomarkers indicates that euxinia in the water column was intermittently present in the photic zone. The onset of anoxic conditions was caused by elevated productivity in the basin, which was related to deglaciation, marine transgression and the increased delivery of terrestrial nutrients. The presence of a positive organic carbon isotope excursion indicates that the black shale deposition resulted from increased productivity and the expansion of anoxic and nitrogen- and phosphate-enriched waters into the shallow photic zone. The high values of δ 15 N (exceeding 9‰) may be related to the deglaciation-driven sea-level rise and advection of denitrified water mass from the Panthalassic Ocean to the intracratonic Paraná Basin. Prolonged periods of sea-floor anoxia/euxinia excluded potential scavengers and bioturbators, thus enhancing the preservation of numerous fossil taxa, including fish, sponges, insects and their larval cases, and conodont apparatuses. The intermittent photic zone euxinia may also have contributed to the mass mortality of fish populations, the fossils of which are very well-preserved in these black shales. [ABSTRACT FROM AUTHOR]

Late Permian mafic flows and dikes are prominent features in and around the Western Guangxi region in southern China. Based on petrographic, geochemical and Sr-Nd isotopic data, the western Guangxi mafic rocks are geochemically akin to the Emeishan large igneous province (ELIP) high-Ti basalts, except that they possess extremely elevated Ti/Y ratios (750–2000). The Dy/Yb and Ti/Y vs. Dy/Dy ∗ covariations of the mafic rocks indicate a garnet-controlled magmatic differentiation of a mafic melt at relatively great depth. The limited ε Nd(t) range from +0.41 to +1.81 also suggests minimal crustal contamination of such a melt. Geochemical modeling using TiO 2 /Yb vs. Nb/Yb and Zr/Y vs. Nb/Y projections indicate that the parental melts of the western Guangxi mafic rocks formed at a low degree (<5%) of partial melting at or over 3.5 GPa, consistent with a deep mantle plume source under a thick continental lithosphere. Thus, the Guangxi extremely high Ti/Y mafic rocks most likely represent a part of outer zone of the ELIP plume magmatism. Results of this study reinforce the previously proposed temporal and spatial distribution of the ELIP. [ABSTRACT FROM AUTHOR]

Bulk-rock major and trace elements and zircon U-Pb data are reported for Permian metamafic rocks from Guoganjianan, in the western part of Longmuco-Shuanghu-Lancang suture zone. These results offer new insights into mantle source characteristics and geodynamic setting of Permian ophiolitic fragments. U-Pb isotopic dating using SHRIMP II method reveals that the metamafic rocks were formed at 274.7±3.9 and 279.8±3.6 Ma. The metamafic rocks mostly show N-MORB-typed rare earth element patterns and are enrichment in large-ion lithophile elements, indicating that they are probably derived from partial melting of a depleted mantle in a back-arc basin. Our new data, together with recent studied results on Paleozoic ophiolitic fragments suggest the Paleo-Tethys Ocean in Central Qiangtang opened at Cambrian and widened between Ordovician and Devonian. Northward subduction started in the Late Devonian-Early Carboniferous and a back-arc basin developed during Permian. [ABSTRACT FROM AUTHOR]

A detailed study of a relatively well-exposed fragment of the Barabash Formation in the southern part of the Voznesenka terrane is carried out to specify the geodynamic settings of the Permian volcanogenic and volcanogenic-sedimentary complexes in South Primorye. It is established that the basaltic flows juxtaposed in the studied sequence originated from sharply different sources. The geochemical characteristics indicate that the basalts from the sequence base were presumably derived by melting of oceanic lithospheric mantle or asthenosphere, while the source of the overlying basalts was lithospheric mantle reworked by a subduction process. The basalts are subsequently overlain by tuffaceous-terrigenous and terrigenous rocks and limestones with remains of Capitanian (Middle Permian) fauna. Accessory zircons extracted from the tuffaceous-terrigenous rocks yield an U-Pb concordant age of 233.3 ± 3.3 Ma (Middle Triassic Ladinian Stage) for the youngest zircon population. The obtained data lead us to conclude that the Barabash Formation is a tectonostratigraphic rather than stratigraphic unit and may be a fragment of the Triassic accretionary wedge. The obtained data cast doubt on the accepted assignment of this unit to the Voznesenka terrane. It is more logical to include it in the Laoelin-Grodekov terrane, which represents a fragment of the Late Paleozoic active continental margin. This suggests that the boundary between these blocks should be specified and the timing of the final stage of amalgamation of the Laoelin-Grodekov terrane with the terranes of the Bureya-Khanka orogenic belt should be revised. [ABSTRACT FROM AUTHOR]

Zircon U–Pb ages, geochemical data and Sr–Nd isotopic data are presented for volcanic rocks from the lower Permian Dashizhai Formation. These rocks are widely distributed in the south-eastern Central Asian Orogenic Belt in central Inner Mongolia, China. The volcanic rocks mainly consist of basaltic andesite and rhyolite, subordinate dacite and local andesite, and exhibit bimodal geochemical features. The results of zircon U–Pb dating indicate that the volcanic rocks formed during the early Permian (292–279 Ma). The mafic volcanic rocks belong to low-K tholeiitic to medium-K calc-alkaline series. These mafic volcanic rocks are also characterised by moderately enriched light rare earth element (LREE) patterns; high abundances of Th, U, Zr and Hf; negative Nb, Ta and Ti anomalies; initial 87 Sr/ 86 Sr ratios of 0.70514–0.70623; and positive ε Nd (t) values (+1.9 to +3.8). These features indicate that the mafic volcanic rocks were likely derived from the high-percentage partial melting of subduction-related metasomatised asthenospheric mantle. The felsic rocks show an A-type affinity, with enrichments in alkalis, Th, U and LREEs. The felsic rocks are depleted in Ba, Sr, Nb, Ta and Ti and exhibit moderately LREE-enriched patterns (La N /Yb N = 2.09–6.45) and strongly negative Eu anomalies (Eu/Eu ∗ = 0.04–0.25). These features, along with the positive ε Nd ( t ) values (+2.6 to +7.7) and young T DM2 ages (T DM2 = 435–916 Ma), indicate that the felsic rocks were likely derived from a juvenile crustal source that mainly consisted of juvenile mid-ocean ridge basalt -related rocks. The volcanic association in this study and in previously published work widely distributed in central Inner Mongolia. The observations in this study suggest that the lower Permian volcanic rocks formed in an identical tectonic environment. The regional geological data indicate that the bimodal volcanic rocks from the lower Permian Dashizhai Formation in the study area formed in an extensional setting that was likely related to post-collisional delamination. [ABSTRACT FROM AUTHOR]

Organic-rich siliceous rocks of Late Permian age from western Hubei Province, China are markedly high in trace elements including V (2031 μg/g), Cr (856 μg/g), Mo (245 μg/g), and U (39.2 μg/g). The mineralogy and geochemistry of these siliceous rocks were investigated using various petrological, mineralogical, and geochemical methods. The results show that the siliceous rocks are high in total organic carbon (TOC), which range from 3.88 to 46.99%, with a weighted average of 17.83%. TOC is dominated by amorphous organic debris, resulting from intense degradation, and lesser amounts of marine microfossils (e.g. foraminifera , algae, and poriferan ). The minerals mainly consist of quartz, mixed layer illite/smectite (I/S), and small proportions of calcite, dolomite, K-feldspar, albite, pyrite, gypsum, apatite, marcasite, jarosite, kaolinite, and bassanite. Trace amounts of xenotime-(Y) ((Y,REE)PO 4 ), rhabdophane-(Nd) ((Nd, Ce, La,)PO 4 ·H 2 O), chalcopyrite, and sphalerite were observed using SEM-EDX. The SEM-EDX results indicate that V and Cr are mainly within the organic matter and mixed layer I/S; Mo is closely associated with organic matter and sulfides (e.g., pyrite, sphalerite, and chalcopyrite); U is only detected in P-bearing minerals, especially in xenotime-(Y) and rhabdophane-(Nd). The sampled interval was deposited in a transitional marine basin between a continental margin and open-ocean pelagic setting, where the anoxic environment was attributed to intense organic matter degradation and restricted water mass renewal. The enriched elements V, Cr, Mo, and U were mainly derived from submarine hydrothermal activities. [ABSTRACT FROM AUTHOR]

This paper presents zircon U-Pb ages, whole-rock major and trace element data, and Hf isotope data for the metagabbros from the Zhushan pluton and gabbros from the Taiping pluton along the boundary area of Jiamusi and Songnen-Zhangguangcai Range massifs and adjacent regions, which will not only place important constraints on the rock-forming ages, source characteristics and tectonic setting of these gabbros, but will also provide insights into understanding the Permian tectonic evolution between the Jiamusi Massif and the Songnen-Zhangguangcai Range Massif. Zircon U-Pb dating, determined using laser ablation-inductively coupled plasma-mass spectrometry and secondary-ion mass spectrometry, indicates that the magmatic zircons from the Zhushan and Taiping plutons yield 206 Pb/ 238 U ages of 256 ± 2 Ma and 259 ± 3 Ma, respectively, interpreted as the emplacement ages of the intrusions. The metagabbros from the Zhushan pluton display the geochemical characteristics of calc-alkaline series rocks, and are enriched in light rare earth and large ion lithophile elements, and depleted in Nb, Ta, P, Zr and Hf. The ε Hf (t) values of magmatic zircons in these metagabbros vary from − 5.47 to + 0.74. All these geochemical features indicate that the primary magma of the Zhushan pluton was derived from an enriched lithospheric mantle source that was metasomatized by subducted slab-derived fluids. The gabbros from the Taiping pluton are also enriched in large ion lithophile elements (e.g., Rb, Ba and U) relative to high field strength elements, and have negative Nb-Ta-P anomalies, with ε Hf (t) values of − 4.02 to − 1.70. It is inferred that they also formed from a primary magma generated by the partial melting of enriched lithospheric mantle that was metasomatized by subducted slab-derived fluids. The rocks from the Zhushan and Taiping plutons have similar petrogenetic processes, but their primary magmas are likely to be derived from two distinct magma sources based on geochemical and isotopic compositions. According to zircon U-Pb ages, geochemical data, Hf isotope data and regional geological investigations, we conclude that the generation of the metagabbros in the Zhushan pluton was most likely related to westward subduction of the Mudanjiang oceanic plate beneath the Songnen-Zhangguangcai Range Massif, and the gabbros from the Taiping pluton were the result of eastward subduction of the Mudanjiang oceanic plate beneath the Jiamusi Massif. Hence, we suggest that the Jiamusi Massif and Songnen-Zhangguangcai Range Massif were not amalgamated before the Late Permian. [ABSTRACT FROM AUTHOR]

Rare metals in coal deposits have attracted much attention in recent years because of their potential economic significance. This paper reports the abundance and enrichment origin of rare metals in the Late Permian coals (K1 and K2 Coals) of the Moxinpo Coalfield, Chongqing, southwestern China. The K1 Coal is characterized by highly-elevated concentrations of U-Re-V-Cr-Se and Nb(Ta)-Zr(Hf)-REE assemblages; the latter assemblage is also enriched in the K2 Coal. The high temperature ash (815 °C) of the K1 Coal is enriched in V, Cr, Se, Re, U and REE; the ash of the K2 Coal, and also the floor strata of each seam, are enriched in REE, potentially making all of the units economically viable sources for these elements. The minerals in the K1 Coal are mainly represented by kaolinite, illite and mixed-layer illite/smectite, and pyrite, while the minerals in the K2 Coal consist mainly of kaolinite and tobelite [(NH 4 ,K)Al 2 (AlSi 3 O 10 )(OH) 2 ]. Authigenic roscoelite [K(V 3 + ,Al) 2 (AlSi 3 O 10 )(OH) 2 ] is commonly observed in the K1 Coal under the SEM, and was probably formed by interaction of kaolinite with V derived from permeating U-Re-V-Cr-Se-rich solutions during early diagenesis. The tobelite enriched in the K2 Coal was formed by reaction between kaolinite already present in the coal and NH 4 + derived from decomposition of the organic matter during hydrothermal alteration at a relatively high temperature. The mafic tuffs directly underlying the K1 Coal and containing limestone residual breccias not only served as the substrate for coal accumulation but also as the source of sediment from the uplifted areas around the coal basin. The latter is indicated by low Al 2 O 3 /TiO 2 ratios (from 10.09 to 14.24), positive Eu anomalies enrichment of medium rare earths (relative to upper continental crust), and detrital calcite of terrigenous origin. The highly-elevated concentrations of U-Re-V-Cr-Se assemblages in the coal were derived from exfiltrational hydrothermal solutions and were then deposited in a euxinic environment. The terrigenous materials in the K2 Coal, however, were derived from felsic-intermediate rocks at the top of the Kangdian Upland, although the elevated concentrations of Nb(Ta)-Zr(Hf)-REE assemblages are attributed to the input of hydrothermal solutions. [ABSTRACT FROM AUTHOR]

Abstract The paper "Enrichment of Bi-Be-Mo-Cd-Pb-Nb-Ga, REEs and Y in the Permian coals of the Huainan Coalfield, Anhui, China" by Munir et al. (2018) provides new data on the geochemical compositions of the late Paleozoic coals from five different mines in the Huainan Coalfield, China, as well as proximate analyses, vitrinite reflectance measurements, maceral contents, and mineralogical constituents. A critical examination, however, suggests that a large proportion of the reported data are questionable, and also that references cited at a number of points are either improper or incomplete. [ABSTRACT FROM AUTHOR]

The Huainan coalfield situated in the southern margin of North China Plate contains coal deposits of Carboniferous–Permian age. The 1 and 3 seams of the Early Permian Shanxi Formation and seams 4-1, 4-2, 5-1, 7-2 and 8 of the Late Early Permian Lower Shihezi Formation were analyzed for coal petrography, mineralogy and geochemical parameters. Collected data were designed to offer basic information on the assessment of coal quality and further to reveal possible factors controlling on coal quality. The shift of basin subsidence center from Huaibei coal-bearing basin to Huainan coal accumulation region caused the change of coal-forming environment (groundwater table, detrital matters and swamp style) which may further cause the differences in coal quality. The average vitrinite contents, ash yields and mineral matters are higher in the Lower Shihezi Formation coals than in the Shanxi Formation coals. The contents of vitrinite sharply decrease upward within coal seam 4, whereas the inertinite contents, ash yields and mineral matters show opposite trend which may be attributed to the relatively high-accommodation settings produce coals usually in the form of an upward high-to-low vitrinite succession. Two groups of elements are classified among coal seams. According to the vertical variation of elements contents among coal seams, most of elements in Group 1 are depleted in coal seam 4-2 except for Be, B, Sc, Fe, Mg, Ca, Li, Sn while almost all the elements in Group 2 are enriched in coal seam 4-2. [ABSTRACT FROM AUTHOR]

The petrology, geochronology, and geochemistry of the early Permian volcanic rocks from Houtoumiao area, south Xiwuqi County in central Inner Mongolia of China, are studied to elucidate the early Permian tectonic setting of the region. The volcanic rocks, which are interbedded with sandstone, feature both mafic and felsic compositions and show a bimodal nature. Zircon U–Pb dating reveals that the volcanic rocks formed at 274–278 Ma, similar to the ages of bimodal magmatism in neighbouring areas. The mafic rocks are composed of tholeiitic basalt, basaltic andesite, basaltic trachyandesite, and trachyandesite. They are rich in Th, U, and LILEs, depleted in HFSEs Nb, Ta, and Ti, and have positive εNd(t) values (+3.6 to +7.9). Geochemical analyses indicate that the mafic rocks originated from metasomatized lithospheric mantle. The felsic volcanic rocks are mainly rhyolite, with minor trachyte and dacite. They have different evolutionary tendencies of major elements, chondrite-normalized REE patterns, and isotopic compositions from the mafic volcanic rocks, which preclude formation by fractional crystallization of mafic melts. The εNd(t) values of the felsic rocks are similar to those of the Carboniferous Baolidao arc rocks in the region. It is suggested that Permian felsic melts originated from the partial melting of Carboniferous juvenile arc-related rocks. By comparison with typical Cenozoic bimodal volcanism associated with several tectonic settings, including rift, post-collisional setting, back-arc basin, and the Basin and Range, USA, the bimodal volcanic rocks in central Inner Mongolia display similar petrological and geochemical characteristics to the rocks from back-arc basin and the Basin and Range, USA. Based on the analysis of regional geological data, it is inferred that the early Permian bimodal volcanic rocks in the study area formed on an extensional continental margin of the Siberian palaeoplate after late Carboniferous subduction–accretion. [ABSTRACT FROM AUTHOR]

The end-Permian mass extinction reflects the most severe life crisis during the Phanerozoic and was associated with major global environmental changes. However, the consistency of the time and pattern of the terrestrial and marine extinctions remains controversial. In this paper, we presented detailed analyses of the high-resolution biostratigraphical and geochemical data from terrestrial sections in South China. Our analyses show that the transitional Kayitou Formation actually recorded the process of terrestrial mass extinction as evidenced by the mass disappearance of the Gigantopteris megaflora in the lower part, the dramatic reduction in abundance of palynomorphs in the middle, and the last occurrences of plant remains and abundant charcoal fossils in the uppermost part. It is associated with a distinct negative shift of δ 13 C org , beginning in the middle part of the formation, which is correlative with that in the top of Bed 26 at the marine Meishan section. In addition, the Kayitou Formation is characterized by a distinct shift of lithofacies of fresh lake-swamp or river flat environment from olive/grey/black mudstone, siltstone, fine to coarse sandstone in the lower part to gradually increasing maroon rocks, to purely maroon mudrocks with poorly-sorted breccia, calcic palaeosols and calcareous nodules in the lowest part of the Dongchuan Formation, which indicates a dramatic collapse of soil system associated with rapid deforestation and climatic warming and drying. In the coastal area, the Kayitou Formation contains marine beds with the typical Permian–Triassic mixed faunas and floras which are correlative with the latest Changhsingian marine mixed fauna 1 at Meishan. The Kayitou Formation also recorded a distinct transgression that began in the latest Changhsingian. All above phenomena suggest that the Kayitou Formation is actually the witness of the terrestrial end-Permian mass extinction; and it is mostly or entirely of latest Changhsingian (Permian), rather than Triassic age. [ABSTRACT FROM AUTHOR]

The alternating marine-terrigenous shale facies of the Lower Permian Taiyuan (P 1 t) formation and the Lower Permian Shanxi (P 1 s) formation in the north margin of the southern North China basin (SNCB) are characterized by their high TOC values (1.76–5.09%), types II and III organic matter, and high Ro values (> 3.0%). Geochemical parameters of 12 gas samples from the Lower Permian shale formations from well Weican-1 were analyzed in this study. The gases are dominated by methane, with small amounts of ethane, without propane and butane. Wetness of the gas is only 0.25–0.58% reflecting extremely high maturity of the source rock. The δ 13 C 1 values range from − 31.6 ‰ to − 26.8 ‰ and the δ 13 C 2 values range from − 35.9 ‰ to − 33.2 ‰, the δ 2 H CH4 values range from − 221.1 ‰ to − 187 ‰. Furthermore, carbon isotopic compositions of the alkane gases from the Lower Permian shale are characterized by δ 13 C 1 > δ 13 C 2 , this indicates that the gases released from Permian shale are of thermogenic origin and mostly sourced from the continental shale and coal measures, with minor contribution from oil cracked gas from marine mudstones. Geochemical fractionation during the adsorption/desorption process of the shale system may play a significant part in influencing δ 13 C 1 values of shale gas. The results show that the δ 13 C 1 becomes heavier with increasing degree of gas desorption. Based on isotope fractionation during desorption of gas in shales, an equation was established to estimate the proportion of free and adsorbed gas in shales using δ 13 C 1 of shale gas. In comparison with other equations, this equation is based on the direct data of gas desorption experiment to avoid the adsorbed gas content often exhibit maxima from excess sorption isotherms experiment. This method provides efficient way to understand the gas storage behavior in shales and broaden the application of gas isotope. [ABSTRACT FROM AUTHOR]

Silicic eruptive units can constitute a substantive component in flood-basalts-dominated large igneous provinces, but usually constitute only a small proportion of the preserved volume due to poor preservation. Thus, their environmental impact can be underestimated or ignored. Establishing the original volume and potential climate-sensitive gas emissions of silicic eruptions is generally lacking for most large igneous provinces. We present a case study for the ∼260 Ma Emeishan province, where silicic volcanic rocks are a very minor component of the preserved rock archive due to extensive erosion during the Late Permian. Modal and geochemical data from Late Permian sandstones derived from the province suggest that silicic volcanic rocks constituted some ∼30% by volume of the total eroded Emeishan volcanic source rocks. This volume corresponds to > 3 × 10 4 km 3 on the basis of two independent estimate methods. Detrital zircon trace element and Hf isotopic data require the silicic source rocks to be formed mainly by fractional crystallization from associated basaltic magmas. Based on experimental and theoretical calculations, these basalt-derived ∼10 4 km 3 silicic eruptions released ∼10 17 g sulfur gases into the higher atmosphere and contribute to the contemporaneous climate cooling at the Capitanian–Wuchiapingian transition (∼260 Ma). This study highlights the potentially important impact on climate of silicic eruptions associated with large igneous province volcanism. [ABSTRACT FROM AUTHOR]

This paper reports the mineralogy and geochemistry of the Early Permian No. 5 coal from the Chuancaogedan Mine, Junger Coalfield, China, using optical microscopy, scanning electron microscopy (SEM), Low-temperature ashing X-ray diffraction (LTA-XRD) in combination with Siroquant software, X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS). The minerals in the No. 5 coal from the Chuancaogedan Mine dominantly consist of kaolinite, with minor amounts of quartz, pyrite, magnetite, gypsum, calcite, jarosite and mixed-layer illite/smectite (I/S). The most abundant species within high-temperature plasma-derived coals were SiO2 (averaging 16.90%), Al2O3 (13.87%), TiO2 (0.55%) and P2O5 (0.05%). Notable minor and trace elements of the coal include Zr (245.89 mg/kg), Li (78.54 mg/kg), Hg (65.42 mg/kg), Pb (38.95 mg/kg), U (7.85 mg/kg) and Se (6.69 mg/kg). The coal has an ultra-low sulfur content (0.40%). Lithium, Ga, Se, Zr and Hf present strongly positive correlation with ash yield, Si and Al, suggesting they are associated with aluminosilicate minerals in the No. 5 coal. Arsenic is only weakly associated with mineral matter and Ge in the No. 5 coals might be of organic and/or sulfide affinity. [ABSTRACT FROM AUTHOR]

To constrain the Permian–Early Mesozoic tectonic evolution of the eastern segment of the Paleo-Asian Ocean, we conducted zircon U–Pb dating and whole-rock geochemical analyses on six middle Permian–Middle Triassic intrusive plutons in central–eastern Jilin Province, NE China. Zircons from the six plutons display distinct oscillatory zoning and striped absorption in cathodoluminescence (CL) images, and Th/U ratios of 0.11–1.41, indicating a magmatic origin. Zircon U–Pb dating indicates that the intrusive rocks formed in the middle Permian (ca. 260 Ma) to Middle Triassic (ca. 245 Ma). In central–eastern Jilin Province, the middle Permian and Middle Triassic plutons are composed mainly of strongly deformed monzogranites with affinities to adakitic rocks, which are formed from partial melting of thickened mafic lower crust. In contrast, the late Permian–the Early Triassic plutons in central–eastern Jilin Province consist of a bimodal association (including gabbros and granitoids) and deformed monzonites, which typically form in extensional settings. These observations, along with the results of previous studies on early–middle Permian granitoids in western Jilin Province, indicate that the eastern segment of the Paleo-Asian Ocean underwent the initial closure in central–western Jilin Province during the middle Permian and the final closure in eastern Jilin Province in the Middle Triassic. [ABSTRACT FROM AUTHOR]

The limestone of the Ruteh Formation of Upper Permian age in the Kanigorgeh district (northeast of Bukan, NW Iran) contains several layers and lenses of bauxitic ores. Mineralogical data show that this limestone consists of calcite and quartz as major and plagioclase, kaolinite, and hematite as minor mineral phases. Geochemical analyses reveal that the proportions of ΣREEs (La-Lu) in this limestone vary from 35.28 to 160.78 ppm. The values of Eu and Ce anomalies (normalized to PAAS) of the limestone have ranges of 1.11-1.68 and 0.89-1.16, respectively. The high values of ΣREEs; low values of Y/Ho; strong and positive correlations between ΣREEs and elements such as Si, Al, Ti, V, Co, Ni, Rb, Cu, and Nb; and negative correlations between CaO and ΣREEs suggest that the observed variations in values of ΣREEs in the limestone were controlled principally by the quantity of detrital materials. Geochemical data also illustrate that the observed positive Eu anomalies in the limestone may be due to the presence of plagioclase and also a function of diagenetic processes. Furthermore, the variations in Ce anomalies may be due to the detrital input. The distribution of REEs (normalized to chondrite) illustrates different patterns in both rocks (the limestone and the bauxitic ores) in light of differentiation degree of LREEs from HREEs and values of conservative indexes such as Eu anomaly. Considering these pronounced discrepancies, it appears that the limestone, despite having relatively high concentration of ΣREEs, did not play a significant role in supplying lanthanides for the bauxitic ores. [ABSTRACT FROM AUTHOR]

The depositional environment of the Upper Permian quartzose sandstone (Kuishan sandstone in Shihezi Formation of Upper Permian) in the North China epicontinental basin is controversial. In order to test the previous hypotheses, we analyzed sedimentological characteristics of the Kuishan sandstones in outcrops and boreholes, and carried out trace element geochemical analysis by electron probe microanalyzer. Three lithofacies were recognized, including normal-graded conglomerate (Cng), trough and planar cross-bedded coarse sandstone (CStpc), and planar cross-bedded medium sandstone (MSpc). Normal-graded conglomerate (Cng) formed in the meandering river or deltaic distributary channels. Trough and planar cross-bedded coarse sandstone (CStpc) formed in meandering river or distributary channels of near-source deltaic plain. Planar cross-bedded medium sandstone (MSpc) formed in the siliciclastic beach with high- to moderate-energy conditions. By the petrology and trace elements analysis, three relatively large-scale transgressions were revealed. Each transgression was reflected by the lower content of Ba and ratios of Fe/Mn, and the high content of B and ratios of B/Ga. The ratios of Ni/Co of all samples are all lower than 2, suggesting oxygen-enriched shallower water environment during deposition of the Kuishan sandstones. [ABSTRACT FROM AUTHOR]

Located between the Tarim, Kazakhstan, and Siberian plates, the West Junggar terrane is a key component of the Paleozoic Central Asian Orogenic Belt (CAOB) with widespread late Paleozoic igneous rocks. In this paper, we report petrological, geochronological, and geochemical data for selected granitoids from the West Junggar. Based on geochronology, the I-type and A-type granites were formed predominantly at 347.9-319.0 Ma and at 321.4-290 Ma respectively. The early-stage I-type granites are characterized by low SiO2, Na2O, and K2O contents with Na2O/K2O ratios > 1 and are metaluminous to weakly-peraluminous. They are enriched in large ion lithophile elements (LILE) and in Sr but depleted in high field strength elements (HFSE), with (87Sr/86Sr)i ratios of 0.7028-0.7044 and εNd(t) values varying from + 5.74 to + 7.76. The late-stage I-type granites are characterized by low contents of Si2O and K2O and relatively high contents of FeO, MgO, and Na2O with Na2O/K2O ratios > 1, and are metaluminous to weakly-peraluminous. They are also enriched in LILE and depleted in HFSE with Eu anomalies, (87Sr/86Sr)i ratios of 0.703-0.704, and εNd(t) values varying from + 5.20 to + 8.00. The A-type granites have high SiO2 contents, high K calc-alkaline-shoshonitic affinities, positive εNd(t) values (5.76-7.77), and low initial 87Sr/86Sr ratios (0.7017-0.7045). Along with reported Sr-Nd isotopic data and regional geologic evidence the Early Carboniferous I-type granites are interpreted as products of partial melting of trapped oceanic crust triggered by underplated mantle wedge-derived basaltic magma; the Late Carboniferous-Early Permian I-type granites as derivatives of partially melted trapped oceanic crust; and the A-type granites as resulting from partial melting of trapped juvenile oceanic crust in an extensional regime. The A-type granitoids with high positive εNd(t) values and high Zr-saturation temperatures could be genetically related to a mantle plume or a regional-scale mantle upwelling in the CAOB. [ABSTRACT FROM AUTHOR]

Zircon U-Pb dating and Hf isotopic compositions, whole-rock and mineral geochemistry, as well as field and petrographic observations, are reported for the Permian gabbroic intrusions in the southern margin of the Altai orogenic belt. Similar zircon ages (~ 280 Ma) of these intrusions to that of the Permian Tarim mantle plume suggest a possible link to the Tarim plume. Olivine grains from the intrusions have Fo contents ranging from 69 to 81 and NiO from 0.05 to 0.21 wt.%, indicating the crystallization from evolved mafic magmas. Clinopyroxene grains from the intrusions have 0.3 to 1.5 wt.% TiO2 and display a rift- to arc-like affinity. The intrusions are tholeiitic and have slightly LREE-depleted to LREE-enriched chondrite-normalized rare earth element (REE) patterns. Zircons from the intrusions have εHf(t) values higher than + 8.0, whereas the whole-rock εNd(t) values range from + 2.7 to + 7.0. Rocks from the intrusions have Nb/La of 0.2 to 0.8, consistent with the derivation from a depleted sub-lithospheric mantle with variable degrees of crustal contamination. The presence of primary hornblende and/or biotite in the rocks indicates metasomatism by slab-derived fluids/melts in the mantle source. We propose that upwelling of asthenospheric mantle in the Permian Tarim mantle plume along the Irtish suture zone, resulted in partial melting of the sub-continental lithospheric mantle. Based on a comparison between the Ni-Cu sulfide-bearing Kalatongke complex and un-mineralized intrusions, we suggest that Ni-Cu sulfide mineralized intrusions in the Altai orogenic belt are characterized by the enrichments of LREEs and LILEs and by the presence of primary water-bearing minerals. [ABSTRACT FROM AUTHOR]

Abstract: Permian mafic and felsic intrusions occur along the Kangguer Shear Zone (KSZ) in the Jueluotage area, Eastern Tianshan, northwest China. This study focuses on the Permian felsic intrusions (288–276.2Ma). Systematic geological and geochemical investigations show that granite plutons in the western KSZ (Dikan, Guandao and Hongshi) have lower Al and higher alkali contents than those in the eastern KSZ (Longdong, Huangshan and Baishandong). The western granite plutons experienced higher degrees of crystal fractionation than the eastern granite plutons. Both of the western and eastern Permian granite intrusions along KSZ were derived from juvenile crust, the Nd–Pb isotopic characteristics of which exhibit mixed compositions of DM and EMII type mantles. Both of the western and eastern Permian granites along KSZ were formed within post-collision background. The Dikan, Guandao and Hongshi plutons in the west KSZ sector were formed in an extensional tectonic setting, whereas the Longdong, Huangshan and Baishandong plutons in the east KSZ formed in a compressional tectonic setting. [Copyright &y& Elsevier]

Abstract: The Late Permian picritic porphyries are spatially and temporally associated with the Pingchuan iron oxide deposit in Emeishan Large Igneous Province (ELIP), southwestern China. The Pingchuan iron deposit carries an estimated ore reserve of 40Mt at ~60wt.% Fe. The iron oxide deposit is associated with an ancient volcanic edifice, which is located at the intersection of the NW- and NE-trending deep faults. The iron ore bodies are intimately associated with the intrusive masses of picritic porphyry, occurring mainly along the contact zone between the picritic porphyries and the Early Permian limestone. The most important ore types are massive and brecciated ores which together make up 90vol.% of the deposit. The massive type ores generally occur as dykes consisting predominantly of magnetite with minor calcite and apatite. The picritic porphyries are characterized by a marked range of SiO2 (37.12–47.39wt.%) and MgO (19.22–29.08wt.%), but show only a minor variation in Na2O+K2O (0.12–1.58wt.%) and TiO2 (0.64–1.44wt.%). The total concentration of rare earth elements (REE) is relatively low (21–83ppm), and shows moderate enrichment in light rare earth element (LREE; [La/Yb]N =3.01–3.63) compared to the HREE. The primitive-mantle-normalized patterns of the rocks are comparable to those of ocean island basalt, possibly indicating a plume source, which is considered to have generated the ELIP. Petrographic observation suggests that the Pingchuan picritic porphyries are virtually primary picritic magma with excess olivine. The primary magma possibly experienced fractional crystallization of Cr-spinel+olivine+clinopyroxene during the magma chamber process, but has not been significantly crustal contaminated. Moreover, the primitive magma was possibly produced by partial melting of the garnet-facies peridotite. In combination with the available information including field observation and geochemical studies, e.g. fluid inclusions and stable isotope data, we infer that the deposit is hydrothermal in origin and the ore-forming fluids are predominantly primary magma-derived fluids which had been released from the picritic porphyry during the emplacement at near the surface and mixed with fluids from country rocks. We envisage that the Pingchuan iron deposit was formed by the shallow emplacement, the aqueous chloride alteration and carbonate solutions and iron precipitation as a continuous process, and thus could be classified as a subvolcanic-hosted iron ore type. [Copyright &y& Elsevier]

Abstract: In the early Permian large volumes of volcanic rocks developed in the Eastern Tianshan of the southern Altaids. The Shaerhu alkaline complex, which occurs along a NW-trending transcurrent fault in the Dananhu arc, is composed of alkaline gabbro intrusions, granites and rhyolites; the gabbros and rhyolites have similar zircon crystallization ages of 286.5±2.1Ma and 286.7±2.1Ma, respectively. The granitic and rhyolitic rocks have typical A-type granite geochemical signatures, i.e. high oxide ratios (in wt.%): K2O+Na2O, (K2O+Na2O)/CaO, K2O/MgO, and SiO2, high trace element values: Zr, Nb, Ga, Ce, Y, and REE, and high Zr+Ce+Y, and 10,000∗Ga/Al ratios. However, spidergrams and REE patterns indicate major depletions in Ba, Sr, P, Ti and Eu. The presence of positive ε Nd(t) values of +7.0 to +11.2 and low (87Sr/86Sr)i (0.70148–0.70416) indicates that these alkaline rocks were derived from a depleted mantle, and not from old continental crust. The geochemical characters indicate that the rocks of the complex have the same source and that fractionation was important in their generation. A-type granitic rocks are the most highly fractionated of alkaline basic rocks. In summary, the Shaerhu complex is a product of mantle-derived alkaline magma fractionation, which is one of the main mechanisms of A-type granite genesis. The felsic rocks of the Shaerhu complex have the geochemical signature of an A2-type granite, and thus were not derived from a rift or mantle plume. In the early Permian, oblique subduction in the southern Altaids gave rise to strike-slip extensional faults, which controlled the emplacement of large volumes of mantle-derived melts. [Copyright &y& Elsevier]

Major, trace and rare earth elements were measured in 27 samples of the Middle to Late Permian limestones from the Tieqiao section located on the marginal zone of an isolated platform (Laibin, South China). Shale-normalized REE+Y patterns of all samples show notably negative Ce anomalies (0.21-0.66, average 0.33), slightly positive Gd anomalies (1.08-1.30, average 1.20), and positive Y anomalies with superchondritic Y/Ho ratios (36-91, average 55), which are consistent with those of modern shallow seawater. Their relative LREEs enrichment with higher Nd/Yb ratios (0.58-1.80) than those of modern shallow seawater (0.21-0.50) suggests complicated sources of REEs for all samples. Compared with geochemical features of sediments influenced by terrigenous particles and hydrothermal fluids, it is concluded that ambient shallow seawater was the primary source of REEs in these limestones. Comparing the indicators of REE+Y elements (ΣREE, Nd/Yb, Ce/Ce*, Gd/Gd*, Eu/Eu* and Y/Ho) in limestones with those in bedded cherts from the Tieqiao section, we consider that limestone and bedded chert have similar sources of REE+Y elements: ambient shallow seawater with more or less hydrothermal fluids. In addition, there is a completely negative correlation between CaCO and SiO contents in limestones and bedded cherts. These results imply that precipitation of CaCO was inhibited by that of SiO which was derived mainly from hydrothermal fluid, especially in bedded cherts from the Tieqiao section. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Guichi Mn district is the important Mn metal producing area in eastern China. [•] The geochemical data of manganese deposits support a hydrothermal origin. [•] The Guichi Mn deposits were formed in high-salinity and oxidative environment. [•] The sources of manganese include volcanic, terrigenous and organic materials. [ABSTRACT FROM AUTHOR]

Abstract: The late Permian granitoids exposed in the Phan Si Pan zone of northwestern Vietnam consist mainly of the Ye Yen Sun metaluminous granites and the Nam Xe–Tam Duong peralkaline granites. Laser ablation inductively coupled plasma mass spectrometry U–Pb zircon analysis reveals that both the granite suites were emplaced from 253Ma to 251Ma. They have a distinctive A-type geochemistry of high 10,000×Ga/Al ratios of 3.0–5.7 and are also characterized by elevated contents of high field strength elements, A/CNK values of 0.85–1.58, negative Eu-anomalies. Magmatic zircons from the granitoids exhibit positive initial ɛ Hf values ranging from 6.4 to 15.9 and yield single-stage depleted mantle Hf model ages of 257–663Ma. This Hf isotopic feature implies significant contribution of juvenile mantle material to the magmas of the spatially and temporally associated Ye Yen Sun metaluminous and Nam Xe–Tam Duong peralkaline granites. [Copyright &y& Elsevier]

Abstract: The Dahuangshan oil shale, located in the northern Bogda Mountain, on the southern margin of the Junggar Basin, was deposited in a Late Permian lacustrine environment. A combined investigation of element and organic geochemistry was performed to define the source rock potential, the paleoenvironment, and source of the organic matter. Thick sequences of oil shales with an average thickness of 638m were deposited in Lucaogou Formation which mainly consists of oil shale, argillaceous dolomite, silty claystone, tuff, limestone, and dolomitic marl. A spot of plant stem fossils and abundance of pyrite crystals, fishtail and fish skeleton can also be found there. Analyzed oil shale samples from Dahuangshan area are characterized by high total organic carbon (TOC) contents (5.6–34.75%), S2 (22.65–199.25mgHC/g rock), hydrogen index (HI, 359–1068mgHC/g TOC), and oil yield (4.9–26.6%), indicating the oil shales have excellent source rock potential. T max values (433–453°C) show an early to medium maturation stage of organic matter, which is supported by organic geochemical maturation parameters. All of the obtained kerogen types are types II and I, with oil prone source rock potential. Dahuangshan oil shale samples are rich in SiO2 (68.59%), followed by Al2O3 (10.18%) and Fe2O3 (5.43%). Compared with average shale and North American Shale Composite (NASC), analyzed oil shale samples are obviously enriched in P (0.71%). There is a significant correlation between Al2O3 and Fe2O3, MgO, K2O, MnO, Cu, Ba, Co, and Ni for their association with clay minerals. Besides, the significant correlations between Fe2O3 and MnO, Co, and Ni are considered to result from their similarity on geochemical behavior. All selected oil shales are characterized by distinctly sloping light rare earth elements (LREE) trends (LaN/SmN =2.70–5.95) accompanied by flat heavy rare earth elements (HREE) trends, with distinct Eu negative anomalies (0.60–0.73). Two slightly different patterns of REEs in the oil shale samples are distinguished by the difference in Ce depletion and Nd anomaly. In addition, Dahuangshan oil shale samples are characterized by short- to middle-chain n-alkanes, low carbon preference index (CPI) values (0.93–1.24), single peak composed of nC20 or nC22, low Pr/Ph (0.41–0.91), relatively high Homohop index (0.061–0.99), and high concentrations of C27 sterane, indicating reducing, deep-water, and moderate saline environment with prevalent contribution of algae and microorganisms to organic matter accumulation. [Copyright &y& Elsevier]

We conducted bulk-rock geochemical and zircon U–Pb–Hf isotope analyses of gneissic granites from the northern Jiamusi Massif, in order to investigate their sources, petrogenesis, and geodynamic significance. Zircons contain fine-scale oscillatory zoning with high Th/U ratios (0.12–0.80), indicative of a magmatic origin. U–Pb dating indicates that they formed during the middle Permian (264 ± 4.2 Ma to 268.6 ± 0.81 Ma), and contain a 531 Ma inherited zircon core. The gneissic granites have high contents of K2O + Na2O and Al2O3, and low MgO and CaO. With A/CNK ratios of 1.01–1.11, they are classified as peraluminous calc-alkaline to alkaline S-type syn-collisional granites. Enriched in large ion lithophile elements such as K, Rb, Ba, and Th, they are depleted in high field strength elements such as Nb, Ta, and Ti. Bulk-rock geochemical analyses display moderately negative Eu anomalies (Eu/Eu*) of 0.36–0.52, and (La/Yb)Nratios of 13.24–29.51.In situHf analyses of zircon gave ϵHf(t) values of –0.1 to –3.2 and crustal average model ages () of 1.35–1.4 Ga. These data suggest that the gneissic granites formed by partial melting of Mesoproterozoic continental crust during a middle Permian collisional event. Hf isotopes indicate the substantial presence of Mesoproterozoic juvenile crust in the northern Jiamusi Massif, derived from depleted mantle that underwent crustal contamination at 1.4–1.35 Ga. The Jiamusi Massif provides a local record of the assimilation and subsequent rifting of the Rodinia–Gondwana supercontinent. [ABSTRACT FROM AUTHOR]

Abstract: The Palaeozoic and lowermost Mesozoic marine carbonate reservoirs of the Sichuan Basin in China contain variably sour and very dry gas. The source of the gas in the Carboniferous, Permian and Lower Triassic reservoirs is not known for certain and it has proved difficult to discriminate and differentiate the effects of thermal cracking- and TSR-related processes for these gases. Sixty-three gas samples were collected and analysed for their composition and carbon stable isotope values. The gases are all typically very dry (alkane gases being >97.5% methane), with low (<1%) nitrogen and highly variable H2S and CO2. Carboniferous gas is negligibly sour while the Lower Triassic gas tends to be most sour. The elevated H2S (up to 62%) is due to thermochemical sulphate reduction with the most sour Triassic and Permian reservoirs being deeper than 4800m. The non-TSR affected Carboniferous gas is a secondary gas that was derived from the cracking of sapropelic kerogen-derived oil and primary gas and is highly mature. Carboniferous (and non-sour Triassic and Permian) gas has unusual carbon isotopes with methane and propane being isotopically heavier than ethane (a reversal of typical low- to moderate-maturity patterns). The gas in the non-sour Triassic and Permian reservoirs has the same geochemical and isotopic characteristics (and therefore the same source) as the Carboniferous gas. TSR in the deepest Triassic reservoirs altered the gas composition reaching 100% dryness in the deepest, most sour reservoirs showing that ethane and propane react faster than methane during TSR. Ethane evolves to heavier carbon isotope values than methane during TSR leading to removal of the reversed alkane gas isotope trend found in the Carboniferous and non-sour Triassic and Permian reservoirs. However, methane was directly involved in TSR as shown by the progressive increase in its carbon isotope ratio as gas souring proceeded. CO2 increased in concentration as gas souring proceeded, but typical CO2 carbon isotope ratios in sour gases remained about −4‰ V-PDB showing that it was not solely derived from the oxidation of alkanes. Instead CO2 may partly result from reaction of sour gas with carbonate reservoir minerals, such as Fe-rich dolomite or calcite, resulting in pyrite growth as well as CO2-generation. [Copyright &y& Elsevier]

Abstract: The appinite–granite suite commonly occurs within post-subduction regimes during the final stage of an orogeny and thus holds the key to monitoring critical geodynamic and crustal evolutionary processes. The present zircon U–Pb dating and geochemical study documents the Late Permian appinite–granite complex from northwestern Liaoning, North China Craton. The hornblende-rich appinitic rocks have an SiO2 range from 41.8 to 53.4%, moderate to high alkali contents, enrichment in large ion lithophile elements and depletion in high field strength elements, with initial 87Sr/86Sr ratios of 0.7066 to 0.7128, εNd(t) of −8.3 to −13.3 and zircon εHf(t) from −10.1 to −18.7. These features suggest that their generation most likely involves metasomatism of mantle peridotites by sediment-derived liquids related to subduction and a later partial melting. The associated monzogranites range in SiO2 from 72.6 to 75.0% and exhibit a high-K calc-alkaline character, with high Sr–Ba abundances and elevated Sr/Y and La/Yb ratios. Such potassic adakitic signatures, plus their evolved isotopic compositions (87Sr/86Sri =0.7063 to 0.7066, εNd(t)=−15.6 to −16.3, zircon εHf(t)=−16.5 to −18.8), are consistent with partial melting of mixed protoliths including newly underplated enriched mafic lower crust and minor old lower crustal materials. Such a mafic and felsic magma association not only attests to a heterogeneously enriched sub-continental lithospheric mantle beneath the northern North China Craton, but also indicates reworking within a post-orogenic transcurrent regime of lithospheric delamination. The temporal coincidence of the present appinite–granite complex with regional transcurrent fault activity leads to the further suggestion that such mafic–felsic magmatic suites could provide spatial markers for monitoring important post-orogenic structural and geodynamic processes. [Copyright &y& Elsevier]