Eastern Paleo-Tethys Research Articles

Response of Permian sediment provenance conversion in Hainan Island to the closure of the Eastern Paleo-Tethys Ocean

From the late Permian to Early Triassic, the eastern part of the Paleo-Tethys Ocean was closed, and the Jinshajiang–Ailaoshan–Songma suture belt formed between the Yangtze Craton and the Indochina Block. The structural belt extends eastward to Hainan Island as the Changjiang–Qionghai fault, which controls the closure of the southern and northern parts of Hainan Island and the transformation of the sedimentary environment. This study focuses on the late Permian Nanlong Formation in Nanlong village, Dongfang County, western Hainan Island. Detrital zircon U–Pb ages from the Permian strata in southern and northern Hainan Island are used to discuss the provenance and sedimentary environment during the early and late Permian. The detrital zircon U–Pb ages from the upper Permian Nanlong Formation are 2800–900, 700–500, 500–400 and 400–320 Ma, with the majority falling into the 500–400 Ma range. The sedimentary environment on Hainan Island transitioned from early Permian semi-deep to deep-sea to late Permian coastal and shallow sea. The sediment provenance changed from a recycled orogen belt during the early Permian to a combination of recycled and arc orogen belt (Devonian–Carboniferous) during the late Permian. This reflects the closure of the east Paleo-Tethys Ocean during the late Permian that resulted in the collision and assembly of south and north Hainan Island and its relative uplift in the central part, which controlled the transition in sedimentary provenance and environment during the late Permian on Hainan Island.

Evidence of detrital spinel geochemistry for depositional response to the Paleo-Tethyan closure recorded in the Songpan-Ganzi Terrane, eastern Tibetan Plateau

The Late Triassic evolution of the Songpan-Ganzi Terrane in the eastern Tibetan Plateau is crucial for understanding the closure of the eastern Paleo-Tethys Ocean. However, the strong thickening and deformation of sedimentary cover make the Songpan-Ganzi geological records complicated and even obscured, impeding the reconstruction of regional tectonic evolution. In this study, we provide new geochemical data of detrital spinels from the Upper Triassic strata in the eastern Songpan-Ganzi Terrane to reveal the provenance and the regional tectonic events involved in the eastern Paleo-Tethyan closure. Results show that detrital spinels from the Upper Triassic Xinduqiao, Zhuwo, and Zagunao formations have variable concentrations of Cr2O3 (24.36–68.56 wt%), Al2O3 (0.13–39.17 wt%), MgO (0.20–21.25 wt%), FeOT (11.15–48.49 wt%), and TiO2 (0.00–4.66 wt%). They are geochemically similar to spinels from both ophiolites and stratiform intrusions, and affinitive to the counterparts from island-arc, supra-subduction zone, or mid-ocean ridge settings. Based on comparison with the spinel compositions from adjacent tectonic zones and in combination with previously published evidence from paleogeography, paleocurrent orientation, and geochronology, we propose the detrital spinels from the Upper Triassic sequence in the eastern Songpan-Ganzi Terrane were mainly recycled from the Lower–Middle Triassic strata in the West Qinling Terrane, with minor concentrations derived from the A’nyemaqen ophiolites. This provenance inference presents a new insight into the closure time of the eastern Paleo-Tethys Ocean.

Geochronological constraints on the Hangenberg Event of the latest Devonian in South China

The Hangenberg Event was one of the most significant mass extinctions accompanied by large-scale climate changes at the end of the Devonian period. Lack of precise and accurate geochronological constraints in the eastern Paleotethys has hindered a high-resolution global correlation of the Hangenberg Event. Here, we report the U–Pb dates of zircons from the bentonite samples intercalated with strata recording the Hangenberg Event in the Muhua region, Guizhou, South China, using both sensitive high-resolution ion microprobe (SHRIMP) and chemical abrasion - isotope dilution - thermal ionization mass spectrometry (CA-ID-TIMS) methods. A bentonite within the Hangenberg Event strata in the Muhua area was dated at 360.47 ± 0.68 Ma by CA-ID-TIMS, which is more precise than the results obtained by SHRIMP methods (361.5 ± 2.9 Ma and 359.8 ± 1.5 Ma). Thus, we propose that the Hangenberg Event took place at 360.47 ± 0.68 Ma in South China, based on the first precise CA-ID-TIMS zircon age from the Daposhang section. The age obtained from South China for the Devonian–Carboniferous boundary overlaps with that in Geologic Time Scale 2020, within the total uncertainties.

Genesis of the Early Indosinian Darongshan Granitoid in South China: Response to the Subduction of the Eastern Paleo-Tethys Ocean

The Bangxi–Chenxing suture zone is an essential area from which information about the closure history of the eastern Paleo-Tethys Ocean can be obtained. The Darongshan granitoid, which is adjacent to this suture, lies among the widely distributed granitic rocks and few basic rocks in the southern Guangxi Province. Herein, we report the petrogeochemistry, zircon U–Pb ages, and zircon Hf isotopic data of the Darongshan pluton in this region. The LA-ICP-MS U–Pb zircon analysis indicates that the Darongshan pluton had formed at 249.9±2.6 Ma. The Darongshan granites are silica-rich (SiO2=65.68–72.91 wt%, mean=69.89 wt%) with high Na2O contents (Na2O=0.46–6.58 wt%, mean=3.49), relatively high Mg (Mg#=35.12–73.31, mean=57.73), and an average Fe2O3T+TiO2+MnO+MgO of 4.96. These features are similar to those of the Mg-andesitic/dioritic rock- (MA-) like tonalite–trondhjemite–granodiorites (TTGs). Chemical analyses show that all rocks are enriched in large-ion lithophile elements (Rb, Th, and U) and light rare earth elements, with weak negative Eu anomalies (Eu/Eu∗=0.27–0.67), and Ta, Nb, and Ti depletion, with typical arc-like affinity. The zircon Hf isotopic results show zircon ƐHft values ranging from -18.2 to -7.4 and the TDM2 model ages 1.74–2.41 Ga. The petrogeochemistry and zircon Hf isotopic signatures indicate the magma generation of the Darongshan granitoid with fluid/melt released from the subducted slab and the fluid/melt assimilated and mixed with the mantle peridotite during ascent. Combining previous extant information on Permo–Triassic subduction/collision-related magmatism in the Bangxi–Chenxing with that of the Jinshajiang–Ailaoshan–Song Ma suture zones, the Darongshan granitoid is interpreted as a magmatic formation that was generated in an active continental margin arc environment during the subduction of the Early Indosinian eastern Paleo-Tethys Ocean and the South China Block, further supporting the idea that closure occurred during the Middle–Late Triassic.

Timeframe of eastern Paleo-Tethys closure: Constraint on the Songpan-Ganzi Complex by big data-based multiproxy provenance analysis

The Songpan-Ganzi Complex (SGC) is one of the largest turbidite complexes on Earth. The source-to-sink processes of the SGC are closely linked to the closure of the Paleo-Jinsha Ocean in the eastern Paleo-Tethys realm, so the spatiotemporal transitions in SGC provenance provide the potential to constrain the closure time. A comprehensive multiproxy provenance investigation, integrating detrital zircon UPb geochronology, whole-rock SmNd isotope data, and paleocurrent analysis, shed light on the origin of the Triassic SGC turbidites. In this study, it was determined that a significant proportion (exceeding 70%) of the detrital material comprising the SGC turbidites was sourced from the northwestern margin of the Yangtze Craton and the Qinling Orogen. A comprehensive and quantitative provenance study revealed that the Songpan-Ganzi turbidites primarily originated from collisional orogenic belts at convergent continental plate margins and secondarily from magmatic arcs and other tectonic units surrounding the basin. In this study, it was demonstrated that the SGC contains important information on the convergence of Eurasia and the tectonic evolution of surrounding terranes. (1) The South Qinling Orogen experienced significant rapid exhumation during the Ladinian to early Carnian. (2) The closure of the Paleo-Jinsha Ocean most likely occurred during the transition period between the upper and lower members of the Zhuwo Formation (ca. 231 Ma, middle Carnian). (3) During the Late Triassic, the crust of the Yidun Terrane underwent significant vertical accretion, resulting in a topography exceeding that of the Jomda-Weixi arc by the late Norian.

Permian-Triassic Magmatism in the Qin-Fang Tectonic Belt, SW China: New Insights into Tectonic Evolution of the Eastern Paleo-Tethys

Permian-Triassic Magmatism in the Qin-Fang Tectonic Belt, SW China: New Insights into Tectonic Evolution of the Eastern Paleo-Tethys

Geology, geochronology, geochemistry and Hf-Sr-Nd isotopes of the ‘green-bean rocks’ (felsic tuffs) in the western Yangtze Block, China: Implications for genesis and enrichment mechanism of Li

The widespread ‘green-bean rocks’ (GBRs) in the western Yangtze Block (YZB) are traditionally considered to be originally felsic volcanic tuff. These greenish or yellowish green GBRs are characterized by the presence of bean-like grains. Although the GBRs are enriched in Li in addition to K, the enrichment mechanism of Li during the formation process of GBRs remains controversial. Detailed petrography, scanning electron microscopy, X-ray diffraction, whole-rock geochemistry, U-Pb dating and Hf-Sr-Nd isotopes have been conducted on the GBRs from the Longmendong section in the western YZB to shed light on the genesis of GBRs, Li enrichment mechanism, and further exploration.The zircon and apatite from Longmendong GBRs yielded U-Pb ages of 247.2 ± 0.6 Ma and 247.0 ± 11.0 Ma, respectively. Longmendong GBRs show bull-rock (87Sr/86Sr)i ratios ranging from 0.72602 to 0.72948 and εNd(t) values between −9.8 and −10.4. Zircons have low εHf(t) values and old two-stage Hf model ages (TDM2) ranging from −16.1 to −7.4 and 1741 to 2285 Ma, respectively. Apatite grains display high (87Sr/86Sr)i ratios and low εNd(t) values in the range of 0.72225–0.72461 and −9.93–−11.18, respectively. The combined evidence from textures, mineral compositions, whole-rock geochemistry and Sr-Nd-Hf isotopic compositions indicates that the GBRs originated from felsic volcanic ashes that erupted along the Sanjiang Orogen. The magma of volcanic ashes was sourced from the remelting of ancient crust in response to the initial collision of Indochina-Yangtze Blocks during the closure of the eastern Paleo-Tethys Ocean. The apatite grains separated from GBRs show significantly low Sr and Eu contents (136–223 ppm and 4.23–6.53 ppm, respectively) and low (La/Sm)N (0.97–1.11) and (Sm/Yb)N (3.49–4.56) ratios, indicating that apatite crystallized earlier than the plagioclase and the original magma are highly evolved. The magma of GBRs originated from ancient crust with significant differentiation, facilitating the initial enrichment of Li during the magma evolution. On the other hand, the GBRs have elevated levels of K2O, MgO and clay minerals (e.g., illite and illite/smectite mixed layer minerals), which are proportional to the Li concentrations. This suggests that Li in the GBRs is adsorbed by clay minerals in ionic form and experience additional enrichment during the transformation from volcanic ashes into clay minerals. Furthermore, the GBRs in the northeastern Sichuan basin under a limited sedimentary environment have relatively higher Li concentrations, suggesting that continuous evaporation also positively contributed to Li enrichment in GBRs. Geographically, GBRs in the Sichuan basin are closely related to underground Li-rich brines hosted within the adjacent strata. Therefore, the widespread Li-rich GBRs in the western YZB not only hold promise as a potential Li resource, but also serve as a marker layer for the prospecting Li brines in the Sichuan basin.

Linking environmental changes and organic matter enrichment in the middle part of the Yanchang Formation (Ordos Basin, China) to the rollback of an oceanic slab in the eastern Paleo-Tethys

The Yanchang Formation, which records the whole evolutionary history of the Middle–Late Triassic lacustrine basin in the western part of the North China Block, provides an opportunity to understand the relationship between the tectono-sedimentary evolution and massive organic matter burial in lacustrine systems. The present study investigates the changes in the lithofacies association, provenance, regional tectonism, depositional environment, and organic matter accumulation in the lower-middle part of the Yanchang Formation, aiming to unravel their links. As a result of the rapid deepening of the southern Ordos Basin, the deposits in the depocenter of the basin shifted dramatically from shallow lacustrine sandstones of the lower part of the Yanchang Formation (i.e., Chang 8 Member) to deep lacustrine shales and gravity flow deposits of the middle part of the Yanchang Formation (i.e., Chang 7 Member). The provenance of the overlying Chang 7 Member is distinct from that of the underlying Chang 8 Member. It is proposed that crustal extension caused by the southwestward rollback of an oceanic slab in the eastern Paleo-Tethys may have triggered the rapid extensional subsidence in the southern Ordos Basin during the early Ladinian. In response to this deep geodynamic process, the depositional environment of the contemporaneous Ordos Basin changed significantly, as reflected by improved primary productivity, enhanced bottom-water anoxia, as well as reduced terrigenous clastic supply in the Ordos Lake. The coupling of these processes further led to the enrichment of organic matter in the Chang 7 Member.

Middle Visean (Mississippian) conodonts from shallow-water deposits in the Yashui section, Guizhou, South China, and their stratigraphic significance

AbstractThe typical Mississippian shallow-water deposits of the Jiusi and Shangsi formations are well exposed in the Yashui section in southern Guizhou, South China. The strata are composed mainly of platform limestones intercalated with shales and sandstones. Conodonts obtained from the limestones are dominated by two assemblages of cavusgnathids: the Cavusgnathus aff. Cav. unicornis and Clydagnathus windsorensis assemblage from the upper Jiusi Formation and the Cavusgnathus unicornis assemblage from the lowest Shangsi Formation. Vogelgnathus campbelli (Rexroad, 1957) is reported for the first time in Eastern Paleotethys and is characterized by small lateral denticles. The evolutionary first occurrence of Cavusgnathus unicornis Youngquist and Miller, 1949 is recognized as a marker for the regional Shangsian stage. This biostratigraphic datum is interpreted to be correlative with other shallow-water conodont zones marked by Cavusgnathus unicornis s.l. and similar species from North America and Europe.

Formation of the Middle Permian Danzhou monzogranite in northern Hainan Island (South China): Insight into the evolution of the eastern Paleo-Tethys

Formation of the Middle Permian Danzhou monzogranite in northern Hainan Island (South China): Insight into the evolution of the eastern Paleo-Tethys

Depositional and metamorphic events recorded in voluminous metasedimentary rocks from northwestern Vietnam: Tectonic implications for eastern Paleo-Tethys evolution, Tibetan Plateau

Metasedimentary rocks in the Son La area of northwestern Vietnam provide unique geochronological and metamorphic evidence for constraining Paleo-Tethys evolution. In this study, detrital zircons from the metasedimentary rocks in the Nam Co Complex were dated and yield ages between 2787 and 618 Ma. Their maximum depositional ages are constrained to ca. 870 Ma and ca. 835 Ma for the lower and upper formations, respectively. Similarly, the ages of detrital zircons from metasedimentary rocks in the Ta Khoa antiform cluster from 3280 to 749 Ma. The depositional ages of the metasandstone and gneisses are constrained at ca. 800 Ma and ca. 760 Ma, respectively. The age patterns and Hf isotope compositions of the Nam Co Complex and the Ta Khoa antiform are similar to those of the western Yangtze Block, suggesting that the metasedimentary rocks in northwestern Vietnam represent the southeastern extent of the western Yangtze Block.Metamorphic zircon and monazite from metasedimentary rocks in northwestern Vietnam constrain Triassic tectonic events at 247–240 Ma. The P-T conditions of the metasedimentary rocks from the Ta Khoa antiform were defined at P = ca. 7.0–7.5 kbar and T = ca. 685 °C. Additionally, mineral chemical analyses indicate that phengites occur in Grt-Ph schists from the Nam Co Complex. The phengites have high Si contents (up to 3.542p.f.u.), indicating that the Grt-Ph schist experienced a high-pressure metamorphic event. Previous studies have also reported that eclogites and granulites in the Jinshajiang, Ailaoshan, and Song Ma zones record Triassic high-pressure metamorphism with a clockwise P-T-t path. These results suggest that the Jinshajiang-Ailaoshan-Song Ma suture zone (JASSZ) is a Paleo-Tethyan ocean-continent subduction-collision orogenic belt. The spatial distribution and tectonic evolution of the metasedimentary rocks in the Son La area support the hypothesis of west-dipping subduction of the Yangtze Block beneath the Indochina Block along the JASSZ.

Time to reconsider the enigmatic tail of eastern Paleo-Tethys: New insights from Borneo

The rise of Tibet and growth of Asia resulted from successive accretion of Gondwana-derived continental fragments at the expense of Tethyan oceans, yet how and where the eastern Paleo-Tethys closed in SE Asia remain controversial. Here we report new and synthesized detrital zircon data from Borneo and relevant regions revealing that West and SW Borneo show consistent Precambrian age profiles resembling that of Northern Australia (Kimberley to Pine Creek), but contrasting with those of NW/NE Australia, Bird's Head, and Cathaysia/Indochina. Considering the questionable suture between West and SW Borneo, we suggest a united Borneo basement that originated from Northern Australia, with a position between Sumatra and Timor. Surprisingly, Borneo lacks NE Australia-sourced ca. 1700–1400 and 400–280 Ma zircons that prevail in Triassic-Jurassic strata of Timor, Babar, and Tanimbar offshore Northern Australia, which may be best explained by pre-Triassic rifting of the Borneo basement from Northern Australia. Combining with recent investigations, we propose a new tectonic scenario involving a Permian separation of Borneo (probably together with Sumatra) from northern Gondwana through opening of the Meso-Tethys Ocean followed by a Triassic docking with Eurasia that closed the eastern Paleo-Tethys. Thus, assembly of Sundaland (continental core of SE Asia) completed in the Late Triassic, rather than Cretaceous as previously thought, and the tail (or the southeasternmost section) of eastern Paleo-Tethys lies within the Kuching zone of Borneo. Our new reconstruction challenges current understanding of Gondwana dispersion and Asian accretion, shedding new light on Asian climate change and biogeographic diversity.

Triassic amphibolite-facies metamorphism in northeastern Hainan Island, South China

The Permian-Triassic tectonic evolution of Southeast Asia has long been a subject of considerable debate. Hainan Island in China is located at the junction of the South China and Indochina blocks adjacent to the Pacific (Philippine) Plate. Studies of metamorphic complexes in Hainan Island may shed lights on the Permian-Triassic tectono-thermal events of the eastern Paleo-Tethys. Among these complexes, the newly recognized Mulantou Metamorphic Complex is sporadically exposed in northeastern Hainan Island provides evidence for above-mentioned issues. In this paper, we present the result of a combined petrological and geochronological study of paragneisses in this complex. The paragneisses consist mainly of biotite, plagioclase, quartz, and rutile/ilmenite, with or without garnet, sillimanite, and muscovite. Textural relationships, mineral compositions, and thermobarometric calculations show that these paragneisses record peak metamorphic P − T conditions of 720–770 ℃ and 4.4–5.8 kbar. Zircon and monazite U − Pb dating by laser ablation–inductively coupled plasma–mass spectrometry indicates that metamorphism occurred at 250–235 Ma. Integrating published geochronological, geochemical, and structural data of Hainan Island and along the Jinshajiang − Ailaoshan − Song Ma suture zone, we infer that the Triassic amphibolite-facies metamorphism of the Mulantou Metamorphic Complex resulted from collision between the South China and Indochina blocks after closure of the Paleo-Tethys.

Metamorphic Evolution and Orogenic Process Related to the Eastern Paleo-Tethyan Warm Subduction and Indochina–South China Collision

Abstract The eastern Paleo-Tethyan Jinshajiang–Ailaoshan–Song Ma orogenic belt in the Southeast Tibetan Plateau represents the tectonic boundary between the Indochina and South China blocks. Regional Cenozoic lithospheric strike-slip movements caused by the India–Asia collision have modified many of the pristine geological records associated with the Indosinian orogeny. The lack of reliable petrological evidences, particularly of high-pressure (HP) metamorphism, has hindered the tracing of the evolutionary history of the Paleo-Tethyan orogenic belt. We report the mineralogy, geochemistry, geochronology and thermodynamic modelling of eclogite lenses/blocks and their host garnet–phengite schists from the Song Ma Suture Zone of Northwest Vietnam and reveal their protolith origins and metamorphic evolution. The eclogites are geochemically similar to mid-ocean ridge basalt, showing weak depletions in high field-strength elements, positive to slightly negative whole-rock ɛNd(t) ratios (−1.69 to +5.15) and slightly high 87Sr/86Sr(t) ratios (0.70466–0.70834). The igneous protolith of the eclogites formed in the late Silurian (425.4 ± 3.6 Ma; igneous zircon dating, 638–459 Ma TDM dating), which makes them the oldest known mid-ocean ridge mafic rocks in an ancient Paleo-Tethyan Ocean. Various eclogites preserve similar peak mineral assemblages (garnet + omphacite + phengite + rutile + quartz ± epidote/clinozoisite ± kyanite ± winchite) under indistinguishable peak conditions. Their prograde P–T trajectories show a uniform pattern of progressive heating and weak compression along a geothermal gradient of 8°C–10°C/km, indicating a warm subduction setting at a low angle that contrasts with the cold oceanic subduction recorded in the adjacent Paleo-Tethyan suture zones. Combined with detrital U–Pb ages from previous studies, our geochronological data indicate that the host schists originated from continental crust within the South China Block and underwent a pervasive Triassic HP metamorphism related to the Indosinian orogeny. The eclogites and host schists yielded HP metamorphic ages of 239–234 Ma and retrogressive amphibolite-facies metamorphic ages of 231–229 Ma, suggesting rapid cooling (14.0°C–21.6°C/Myr) and exhumation (6.4 km/Myr) from the mantle to the crust. The Song Ma eclogites and their host schists formed when the final ocean closure transitioned to the initial Indochina–South China collision. The Song Ma eclogites and their host schists provide essential information on the opening and closure of the eastern Paleo-Tethys and the subsequent amalgamation of Southeast Asian continental fragments.

Correlation among the Ailaoshan–Song Ma–Song Chay orogenic belts and implications for the evolution of the eastern Paleo-Tethys Ocean

The timing and mechanism of the combination between the South China Block (SCB) and the Indochina Block (IB) are controversial. Three ophiolitic mélange zones (Ailaoshan, Song Ma, and Song Chay) have been proposed as suture zones within this collisional orogen. However, the relationships among the three corresponding tectonic belts are unclear. In this study, we present detailed structural data for the three tectonic belts. The bulk architectures of the Ailaoshan, Song Ma, and Song Chay belts correlate well with one another. This similarity is also revealed by our new zircon UPb geochronological results from the Song Ma and Song Chay ophiolites. The regional deformation age is constrained to between 250 and 240 Ma by our new muscovite 40Ar/39Ar ages, and the medium-low temperature conditions are revealed by the quartz c-axis fabric. Considering the transformation effect of the Cenozoic large-scale sinistral strike-slip of the RRF and DBF, the Early Mesozoic Ailaoshan, Song Ma, and Song Chay suture zones should represent different segments of the same belt. Based on this hypothesis, we compiled the ages of the magmatism in this region, which allows us to propose an evolutional model as follows: i) ∼380–310 Ma continental rifting and subsequent Ailaoshan–Song Ma–Song Chay ocean spreading as a branch of the Paleo-Tethys, ii) ∼310–250 Ma oceanic subduction coeval with continental-arc magmatism, iii) ∼250–240 Ma continental collision, iv) ∼240–220 Ma post-collisional extension.

Geochronology and geochemistry of lithium-rich tuffs in the Sichuan basin, western Yangtze: Implication for the magmatic origin and final closure of eastern Paleo-Tethys

The felsic volcanogenic tuffs named “green-bean rocks” (GBRs), characterized by a green or yellowish green color, are widely distributed in the western Yangtze platform and have a high lithium content (286–957 ppm). This paper studies the ages, origin and tectonic setting of the GBRs in the Sichuan basin on the western margin of the Yangtze platform through the whole-rock geochemistry and zircon trace elements by using U–Pb dating and Hf–O isotopes. The GBR samples from the Quxian and Beibei sections yielded zircon U–Pb ages of 245.5 ± 1.8 Ma and 244.8 ± 2.2 Ma. These samples can be used as the isochronous stratigraphic marker of the Early–Middle Triassic boundary (EMTB) for regional correlation. The whole-rock and zircon geochemistry, and zircon Hf–O isotopes exhibited S-type geochemical affinities with high positive δ18O values (9.28‰–11.98‰), low negative εHf(t) values (−13.87 to − 6.79), and TDM2 ages of 2150–1703 Ma, indicating that the lithium-rich GBRs were generated by the remelting of the pre-existing ancient Paleoproterozoic layer without mantle source contamination in the arc-related/orogenic tectonic setting. The results of this study demonstrate that the lithium-rich GBRs in the western Yangtze platform were derived from arc volcanic eruptions along the Sanjiang orogen, triggered by the closure of the eastern Paleo-Tethys Ocean and the syn-collision between the continental Indochina and Yangtze blocks at ca. 247 Ma. This was marked by a major shift from I-type magmas with intermediate εHf(t) values to S-type magmas with low negative εHf(t) values. Collectively, our results provide new insights into the origin of the GBRs and decodes the closure of the eastern Paleo-Tethys.

Sedimentary evolution and sea-level fluctuation of a Paleo-Tethyan Permian carbonate-dominated succession from central China

The Paleo-Tethys experienced major geographic, tectonic, climatologic, and environmental changes during the Permian. A newly documented and complete Permian carbonate-dominated succession (>3 km) in the Xikou section, Zhen'an, Shaanxi, central China provides a unique opportunity to record its depositional environment evolution, sea-level fluctuation, and associated paleogeographic and paleoclimatic perturbation of the eastern Paleo-Tethys. Field observation and petrographic analysis document eighteen facies and indicate evolutional facies of a carbonate ramp within the Xikou section. The vertical distribution of those facies in the Xikou section indicates a fluctuated sea-level during the Permian, which reflected the global climatic changes and was associated with eastern Paleo-Tethys evolution. The relatively low sea-level accompanied by high-frequency fluctuations during the Asselian to Artinskian may be related to the expansion of glaciation (P1 and P2), while the followed significant rising at Kungurian may reflect the major deglaciation of the Late Paleozoic Ice Age (LPIA). The abrupt falling of sea-level at the end of the Capitanian was globally synchronous and may be relevant to mid-ocean ridge spreading and superimposed with global cooling (P4), which was in accord with the skeletal grain replacement of the fusulinaceans and dasyclads by small foraminifers and Gymnocodium, and was considered as a major reason for Middle Permian Extinction. The early Wuchiapingian characterized by densely mixed sequences of carbonate and siliciclastic intervals had a highly frequent fluctuating sea-level, which may be influenced by high frequent short-term climatic variations. The sea-level falling after it reached its highest stand during the middle Wuchiapingian, was suggested as a far-field response to the expansion of the Permian glaciation episode P4, or as a result of a regional tectonic transition from extension to compression relevant to the eastern Paleo-Tethys evolution. In addition, the overall rising trend of the sea-level and the thick succession in the Xikou area suggest that the South Qinling belt was primarily under an extensional setting during the Late Carboniferous to Early Triassic, in response to Tethys rifting, which may imply the subduction of Mianlue Ocean was possibly beyond the Permian.

Low-latitude climate change linked to high-latitude glaciation during the late paleozoic ice age: Evidence from terrigenous detrital kaolinite

The Late Paleozoic Ice Age (LPIA; ca. 335–260 million years ago) was one of the most significant glacial events in Earth’s history. It records cycles of ice advance and retreat in southern high-latitude Gondwana and provides a deep-time perspective for climate–glaciation coevolution. However, climate records using clay mineral proxies from the LIPA are poorly developed in low latitudes, particularly in the North China Plate (NCP) on the eastern Paleo-Tethys. We address this through a detailed mineralogical study of the marine–continental sedimentary succession in the Yuzhou Coalfield from the southern NCP. We apply biostratigraphy and high-resolution clay mineral composition to reconstruct the latest Carboniferous to early Permian chronostratigraphy and climate change. The Benxi, Taiyuan, and Shanxi formations in the study area are assigned to the Gzhelian, Asselian–Artinskian, and Kungurian-Roadian stages, respectively, and the Carboniferous and Permian lithostratigraphic units across the NCP recognized as widely diachronous. Under scanning electron microscopy, the detrital micromorphology of kaolinite is mostly found as irregular fragments with sizes of 1–5 μm. Illite crystallization varies from 0.22 to 1.88 ∆°/2θ (x̄ = 0.49 ∆°/2θ) and indicates changes in kaolinite content to be a robust proxy for paleoclimate reconstruction. Kaolinite data show alternating warm-humid and cool-humid climate conditions that are roughly consistent with the calibrated glaciations and nonglacial interval successions recognized in high-latitude Gondwana. These include the Asselian-early Sakmarian and late Sakmarian-early Artinskian glacials and the climatic transition to glacial P3 during the Roadian. Our results indicate a comparatively cool-humid and warm-humid climate mode in low-latitude NCP during glacial and nonglacial periods, respectively. This is a significant step toward connecting climate change in low-latitude to high-latitude glaciation during the LPIA in eastern Paleo-Tethys.

Newly discovered Early Carboniferous and Late Permian magmatic rocks in eastern Myanmar: Implications for the tectonic evolution of the eastern Paleo-Tethys

Eastern Myanmar is located at the junction of the Changning-Menglian and Chiang Rai-Chiang Mai zone and is a crucial region for constraining the evolution of the eastern Paleo-Tethys. This study presents new zircon U-Pb geochronological, mineral and whole-rock geochemical, and Sr-Nd-Hf-O isotopic data for magmatic rocks from the Sukhothai arc in eastern Myanmar. The rock suites analyzed include 360–355 Ma basaltic rocks and trondhjemitic dikes, and 257–254 Ma volcanic rocks and gabbroic cumulates. The basaltic rocks were derived from partial melting of mélange pair with peridotite and experienced assimilation and fractional crystallization (AFC). The trondhjemitic dikes were formed by partial melting of the basaltic rocks and experienced fractional crystallization at shallow depth. We suggest that andesite and dacite were derived from partial melting of depleted mantle wedge and underwent AFC process. The gabbroic cumulates are a crystallizing phase associated with the melts that produced the coeval volcanic rocks. We propose that eastern Myanmar, Central Tibet, SW Yunnan and Southeast Asia share a similar three-staged magmatic history, forming a ∼ 4000 km long magmatic belt. Stage I records the magmatic events related to subduction of the eastern Paleo-Tethys Ocean during the Early Carboniferous. A back-arc basin was opened during the Late Carboniferous, and extensive subduction-related magmatism was followed since the Permian. Stage II records the igneous rocks formed during the final amalgamation between the Indochina and Sibumasu Blocks during the Late Permian to Middle Triassic. Stage III is defined by the post-collisional magmatism distributed across the suture zone during the Late Triassic.

Geological and geochemical evaluation of phosphorite deposits in northwestern Saudi Arabia as a possible source of trace and rare-earth elements

The Sirhan-Turayf region in northwestern Saudi Arabia hosts one of the largest Paleogene phosphate-bearing deposits in the Middle East and forms part of the world’s largest accumulation of Neo-Tethys Oceanic phosphorite. The Hazm Al-Jalamid and Umm Wu’al areas in the north and northeastern parts of the Sirhan-Turayf region are the largest and most famous phosphorite deposits in Saudi Arabia. The studied phosphorite localities are essentially carbonaceous phosphorites with similar major constituents (P2O5 and CaO), but different trace element and REE compositions. Umm Wu’al phosphorites are highly enriched in trace and ∑REEs contents compared with Hazm Al-Jalamid phosphorites. In Hazm Al-Jalamid phosphorites, P2O5 as well as most trace elements and REE contents progressively increased from the coarse- to fine-size fractions (<1 mm). The negative correlation between the terrestrial components (SiO2 + Al2O3 + TiO2) and the authigenic components (P2O5 + CaO + Na2O), as well as the very low Th contents of the studied phosphorites indicate pristine formation from seawater rather than derivation from detrital input. The low to moderate ∑REEs contents and their distribution patterns, substantial negative Ce-anomaly, and characteristic redox indices of the studied phosphorites all are indicative of formation from oxygenated seawater under fairly oxic marine conditions during early diagenesis. Compositional characteristics of the studied phosphorites, in terms of trace and REE, are similar to those of the Eastern Mediterranean phosphorites, but clearly different from those of the North African phosphorites. The low to intermediate ∑REEs contents and other redox proxies in the studied phosphorites, along with the Eastern Mediterranean phosphorites, compared to those in the North African phosphorites, are attributed to the relatively shallow water depth of eastern paleo-Tethys and global warming and greater water depth in the western side of paleo-Tethys in the North African countriesduring the Paleocene – Eocene time. Based on the ∑REEs contents and considering the outlook coefficient (Koutl) of REE composition, and the percentage of critical elements in ∑REE (REEdef), an attempt has been made to evaluate the economic potentialof the studied phosphorites as a source for U and REE. Despite of the low to intermediate REE contents and considering the huge phosphorite resources, as well as the big Wa’ad Al-Shamal Phosphorite Project in northern Saudi Arabia, studied phosphorites can be considered as promising to highly promising REE ores representing a valuable and profitable alternative source for critical REE.