American Plate Research Articles

Precise Relocation and Source Characterization of Two Earthquake Sequences in Yellow Sea Using Regional Lg-Wave Observations

ABSTRACT Two significant earthquakes of magnitude ML 4.6 and 4.5 occurred on 18 January and 3 December 2021 in the central region of the Yellow Sea, respectively. The earthquakes occurred beneath the Gunsan sedimentary basin at about 10 km depth with a strike-slip faulting mechanism on nodal planes striking northwest–southeast (NW–SE) and north-northeast–south-southwest (NNE–SSW). Despite a lack of close-by seismographic stations, we successfully utilized regional Lg-wave observations on both coasts of the sea—the Korean peninsula on the east and eastern China on the west. For nine earthquakes in two event sequences, the Lg-wave differential travel times of the nearby event pairs at the common station are carefully measured using the waveform cross-correlation technique. The double-difference earthquake relocation method is employed to obtain precise relative epicentral locations using the Lg correlation measurements. Relocated epicenters align along the NW–SE direction, indicating that the nodal plane striking the same direction is the likely fault plane on which both sequences occurred. This is the first case reported in the literature in which the causative fault plane has been identified for earthquakes in the central Yellow Sea region. It has an important implication for current regional tectonics; it favors neither old tectonic features trending NE–SW (Qianliyan uplift) nor the north–south alignment of significant earthquakes in the region along the Amur plate boundary. The Lg waves from the earthquake sequences are dominant seismic signals on all three-component records at stations in 160–550 km and allowed us to analyze source properties of the two largest earthquakes using the empirical Green’s function approach. Azimuthal variations of the source corner frequencies suggest that earthquake rupture likely propagated toward southeast (125°) along the fault plane, supporting the aftershock relocation results.

Upper mantle structure beneath the Mongolian region from multimode surface waves: Implications for the western margin of Amurian plate

Multimode phase speeds of surface waves are used to build a new radially anisotropic S wave model in the eastern Eurasian and Mongolian regions. Our dataset includes seismic waveforms of over 1655 teleseismic events (Mw≥5.8) from 2009 to 2021, recorded at permanent and temporary stations in and around Mongolia. The multimode dispersion curves of Love and Rayleigh waves were extracted using the nonlinear waveform fitting method for individual seismograms. Then, we retrieved phase speed maps for each mode and frequency, incorporating finite-frequency effects. Finally, localized multimode dispersion curves extracted from the phase speed maps were inverted for local 1-D SV and SH wave profiles, which are combined into a radially anisotropic 3-D shear wave model. Our new model exhibits significant lateral variations of S wave speeds at 70–100 km depth beneath Mongolia, i.e., slow anomalies in the tectonically active western Mongolia in contrast to fast anomalies in stable eastern Mongolia. In the radial anisotropy model, SH waves are faster than SV waves in most areas of the Mongolian lithosphere above 100 km depth, except for the northeast of the Altay Mountains. The Hangay Dome region is characterized by significantly slower velocities that may relate to its uplifting. A large-scale low velocity beneath the northeast of the Hangay Dome with a slower SV wave speed than SH may indicate the existence of partially molten layers. This study also reveals distinct lateral variations of S wave speeds across the boundary between the Amurian and Eurasian plates, characterized by the fast anomaly in eastern Mongolia, corresponding to the lithosphere in the western Amurian plate.

Wave velocities and anisotropy of rocks: Implication for origin of low velocity zone of the Qinling Orogenic Belt, China

Structure and composition of Earth is of fundamental importance in exploring the dynamic evolution of the crust and mantle. The Qinling Orogenic Belt (QOB) is located between the North China plate and the South China Plate, and is one of the main orogenic belts in China. To explore the composition and origin of anisotropy and the low wave velocity zone of the QOB, ten rock samples (gneiss and schist) were collected from the five sites of the QOB and the P- and S-wave velocities of these samples were measured under 0.6 to 2.0 GPa and 100 to 550 °C. The wave velocities increase with increasing pressure and decreasing temperature. The VP and VS of the schist and gneiss match the velocity of the middle and lower crust of the QOB, indicating that schist and gneiss are important component of the QOB. All the schist and gneiss samples exhibit obvious seismic anisotropy with 1.64%–17.42% for VS and 2.93%–14.78% for VP under conditions of crust and upper mantle. The CPO/LPO and layering distribution of mica in rock samples are the main reasons for this anisotropy. The VS structures below the five sampled sites from seismic ambient noise tomography were built to explore the effect of schist and gneiss on the composition and structure of the QOB. The results indicate that orientation-arranged gneiss and schist driven by the tectonic stresses might be a new origin of the character of VP/VS, seismic anisotropy, and the low velocity zone in the QOB.

Zircon U-Pb geochronology, major, trace elemental, and Sr-Nd-Pb isotopic geochemistry: constraints on the age and magmatic origin of Mesozoic mafic dykes in the Guangxi Zhuang Autonomous Region, South China

ABSTRACT As a direct product of lithospheric extension, the mafic dyke group have become an ideal object for studying the formation, evolution and dynamics of both the crust and continental orogenic belts. Given the scientific significance of mafic dykes and their utility in addressing outstanding questions concerning the origin and development mafic dyke swarms Mesozoic age with-in the South China Plate, in this study, 54 representative mafic dykes within the Guangxi Zhuang Autonomous Region, South China, were examined. Research methods include laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb age-dating, whole rock geochemistry, and the Sr-Nd-Pb isotope geochemistry of the studied mafic dykes. The results indicate that these rocks formed between 139 Ma and 113 Ma and have typical doleritic and lamellar textures. They fall into the alkaline and shoshonitic series, are characterized by enrichment of light rare earth elements, some large ion lithophile elements (Rb, Ba, and Sr), Th, U, and Pb, and have depleted Nb, Ta, Hf, and Ti. Moreover, the mafic dykes studied have high initial87Sr/86Sr ratios (0.7055–0.7057), negative εNd(t) values (from −15.2 to −11.4), and relatively constant initial Pb isotopic ratios (that are Enriched Mantle-1 (EM I)-like; 206Pb/204Pb = 16.765–16.816, 207Pb/204Pb = 15.429–15.476, and208Pb/204Pb = 36.882–37.144). The above results indicate that the group of dolerites and lamprophyres studied herein were likely derived from magma generated via low-degree partial melting (1.0%–10%) of an EM1-like garnet-lherzolite mantle source. The parental magmas to these fractionated olivine-, clinopyroxene-, plagioclase, and Ti-bearing phases, with negligible crustal contamination during ascent and dyke emplacement. On the basis of existing research and evidence from this study, we propose a reasonable model for the origin of the mafic dykes: the ancient Pacific Plate subducting below the South China plate led to extension of the lithosphere, an upsurge of the asthenosphere, which triggered partial melting of the lower mantle lithosphere in the Early Cretaceous, and the formation of the parent magma to the Mesozoic mafic dykes in the Guangxi Zhuang Autonomous Region study area. The involvement of slab-derived fluids from the subduction of the ancient Pacific Plate was responsible for metasomatism of the mantle source to these mafic magmas.

Discovery of Eclogite Facies Kyanite Quartzite in Central Jilin Province:Evidence of Ultra-high-pressure Metamorphism

The work area is located in the convergence domain of the Siberian plate and North China plate. The Jilin Province of the Soren-Xilamnlun river-Changchun-Heilog jiang plate collision zone. Before 2000, there was no empirical evidence of high-ultrahigh pressure transformation in the middle Jilin section. For this reason, the Changchun-Panshi-Jiaohe area was selected as the primary geological survey area. After comprehensively analysing the previous regional geological and mineral exploration data, we drew on the experience and achievements of studying the collision between the Suiu-dabie plate. Jiaohe blueschist origin was concerned. After fine field investigation, collecting fresh and representative samples, conducting microscopic identification, electron probe analysis and other work, the key identification and measurement results were obtained. Comprehensive results proved that the geological body producing kyanite undergoes high-pressure kyanite-quartzite was a metamorphic rock of gernet pgroxenite facies. This discovery is of fundamental importance for the establishment of the Jihei high pressure human ultra-high-pressure collision subduction zone. The discovery was briefly reported in 2000 and is now being published in detail. The garnet-phase blueschist quartzite is massive, laminated, ienticular, and rootless hook like bodies occur in within the luoguangou Dashihu narrow ductile shear zone. The rock being sheared is late paleozoic Early perntian Daheshan formation and late variscan Granite Porphyry, which were deformed and metamorphosed to form. blueschist dolomite quartz schist and dolomitic blueschist quartzite. The Peak mineral combination is Ky2+Qz2+Ms2 (Phn2) +Zt+Rt+Miss, without Sili and Pl, which basically meets the constraining charactenstics of eciogite facies. The peak metamorphic temperature reaches 700-750℃, indicating the Si (pfu) =3. 440-3. 535 of phengite, and indicated metamorphic pressure reaches p=2. 75-3. 30GPa, which shows that the rock has undergone ultra-high pressure metamorphic process, and its temperature and pressure conditions have been comparable to those formed by coesite. The temperature of secondary peak period of is about 550℃-600℃ and the pressure is about 1. 6-1. 7GPa. The multi-phase nature of the blueschist, muscovite and quartz indicates that the rock is subjected to prosess of subduction exhumation, and exhumation suffering from strong progressional and retrograde metamorphism. The temperature and pressure numbers of the metamorphism indicate that the paths are successively hornblende and green schist phases, with temperatures of about 500℃-450℃ and pressures of about 0. 5-0. 7GPa, and temperatures of about 300℃-350℃ and pressures of about 0. 3-0. 4GPa, respectively.

Geochemistry and Zircon LA–ICP–MS U–Pb Geochronology of the Shuangwang Au Deposit, Shaanxi Province: Implications for Tectonic Evolution and Metallogenic Age

The Shuangwang Au deposit (with a gold resource of approximately 70 t Au), is located in the Fenxian-Taibai fore-arc basin in the West Qinling Orogen of central China. Igneous intrusions in the region include the Xiba granitic pluton and granite porphyry and lamprophyre dykes. The Xiba pluton is composed of granodiorite and monzonite granite. The granodiorite is typical I-type granite, and it yields a crystallization age of 221.1 ± 1.2 Ma and a two-stage Hf model age of 1432–1634 Ma. The monzonite granite shows a transitional characteristic between I-type and A-type granite, and it yields a crystallization age of 214.8 ± 1.2 Ma and a two-stage Hf model age of 1443–1549 Ma. The granitoid was derived mainly from a crust–mantle mixed source. The ages indicate that the granodiorite and monzonite granite formed during two different stages. The REE distribution patterns of the Xiba granitoid exhibit significant fractionation between LREE and HREE, showing right-dipping curves, with an enrichment of LREE and a deficit of HREE. The granodiorite displays a light negative Eu anomaly, while the monzonite granite displays an obvious negative Eu anomaly. The granite porphyry dikes are distributed in the No. I breccia and Jiupinggou granite porphyry, and they yield crystallization ages of 219.9 ± 1.5 Ma and 213.1 ± 0.89 Ma, respectively, and two-stage Hf model ages of 1382–1501 Ma and 1373–1522 Ma, respectively. The lamprophyre dikes in the deposit yield a crystallization age of 214.4 ± 2.7 Ma. After the collision event between the Yangtze and the North China Plates along the Qinling orogenic belt, at approximately 220 Ma in the Late Triassic, the detachment of the slab produced the upwelling of the asthenosphere material. Under conditions of mantle heat and tectonic stress, widespread partial melting of the subducted continental crust and the upper lithosphere mantle occurred, forming granitoids with various degrees of adakite characteristics.

A new fossil species of Callipteris (Callipteridae) in the Early Permian from the Xishan Area in Beijing, North China

A new early Permian Medullosa (Pteridospermatophyta) is described based on a moderately well-preserved sample from Xishan Area in Beijing, North China. Callipteris seshufenensis Chen sp. nov. represents the first record of genus Callipteris in the early Permian period in Beijing region. Callipteris seshufenensis has a remarkable morphology characterized by a narrow midvein with distinct transverse stripes, small pinnules with 2–3 lateral branches directly connected with pinna-rachis except for the rounded-obtuse apex of pinnule and costule divided more than three times (sometimes more than five times). Together with coeval callipterid fossils recorded from the North China plate and the Siberian plate, the present discovery suggests that the migration route of callipterids in China extended from West China to Northeast China.

Organic matter accumulation in response to tectonism: New data from the Upper Permian Dalong Formation black shales in the Western Hubei Basin, South China and its implications for the end-Permian mass extinction

Redox conditions and primary productivity are proposed to be the major controls of organic matter accumulation in sediments. Studies of the impacts of tectonic processes on organic matter accumulation are still limited. We took the Late Permian-Early Triassic Western Hubei Basin, located in the north of South China, as an example. In black shales in the Dalong Formation, bottom-water redox conditions and surface-water productivity are constrained as shown by the analysis of total organic carbon (TOC) as well as geochemical (enrichment of Mo, U, Ni, Cd and Zn) and mineralogical characteristics. The highest productivity is present in the lower Dalong Formation, and the most intensively anoxic and restricted conditions are found in the middle Dalong Formation. The correlation of the sedimentary successions on the two sides of the basin's boundary fault indicates a subsidence of the basement during the deposition of the lower-middle Dalong Formation, followed by an uplift during the deposition of the upper Dalong Formation. When looked at in conjunction with the tectonic background of the basin, the new data in the present study support that: (1) the collision of the South and North China plates controlled the paleoceanographic and hydrographic evolution of the Western Hubei Basin, as well as organic matter accumulation in sediments; (2) upwelling-induced high productivity and good preservation in an anoxic environment jointly contributed to organic matter enrichment in the lower Dalong Formation, while good preservation in an anoxic environment was the major cause of organic matter enrichment in the middle-upper Dalong Formation. This study indicates that tectonism can act as the ultimate drive mechanism for organic matter accumulation in black shales. Our data also suggest that plate tectonism in related to the assembly of East Asian blocks with the main body of Pangea can also be treated as one of the ultimate drive mechanisms of the end-Permian mass extinction as it created the restricted, anoxic Paleo-Tethys Ocean, which greatly disturbed- global seawater circulation.

SEISMICITY of YAKUTIA in 2018–2019

According to the information received from 20 stationary digital seismic stations of the Yakutia Branch of Geophysical Survey of the Russian Academy of Sciences, two-year (2018–2019) seismic monitoring of the territory of the Republic of Sakha (Yakutia) was carried out. During this time interval, more than 730 earthquakes with an energy class of KR≥7.2 (magnitude M≥1.8) were registered. During the previous two years, their number was 801. Manifestations of seismicity fixed the spatial position of the contact zones and their constituent blocks of known lithospheric plates: the Eurasian and North American plates in the northeastern and arctic regions, as well as the Eurasian and Amur plates – in the southern areas of Yakutia. The epicentral fields traced individual relief lineaments and identified active boundary structures combined into two large-scale seismic belts – BaikalStanovoy and Arctic-Asian. Their outlines are seen as bands of earthquake epicenters, elongated from the Olekma River to the Sea of Okhotsk in the south and as ensembles of separate groups and chains of earthquakes between the Laptev and Okhotsk Seas in the northeast and in the Arctic. Significant seismic activity has been detected in the northeast of the region – in the Olekminsk region and the Aldan Highlands (South Yakutia), as well as in the Yano-Oymyakon Highlands, the Chersky Ridge and the Laptev Sea. A map of epicenters was constructed for the entire territory of the region, where 12 districts were identified and an analysis of the seismotectonic situation in each of them was given. The map of Arctic earthquakes in the Lena River delta is considered separately. It is compiled according to the processing of digital seismograms obtained at 25 autonomous field stations installed in accordance with the Russian-German project "Seismicity and Neotectonics of the Laptev Sea Region" (SIOLA). In this area during 2016–2019 more than 2 thousand shocks of small energy classes KR≥7.2–10.7 (M≥1.8–3.7) were recorded within the depth interval of 1–36 km of the Earth's crust. The characteristics of the most seismically active local tectonic structures developed in this region are given.

Proficiency testing for drug susceptibility testing of Mycobacterium tuberculosis complex using commercial broth microdilution plate in China in 2021

The characteristic and performance of Broth microdilution (BMD) plates for drug susceptibility of Mycobacterium tuberculosis have not been systematically evaluated in China. This study was designed to review the key information and assess the performance of BMD plates by analysis of proficiency testing results. We retrospectively analysed the proficiency testing results of phenotypic drug susceptibility testing (PT-DST) of 45 laboratories using BMD plates in China in 2021. Critical information, such as drug layout, concentration range of each drug, plate storage conditions and duration, operating procedures, and interpretation criteria for binary results were compared. The performance was also analysed. Eight types of BMD plates produced by four manufactures were reported. The drug layout, number of drugs on plates, and concentration range varied a lot between different plates. The total sensitivity and specificity of BMD plates for drug susceptibility of Mycobacterium tuberculosis to ten drugs (isoniazid (INH), rifampin (RIF), kanamycin (KAM), amikacin (AM), levofloxacin (LFX), moxifloxacin (MFX), bedaquiline (BDQ), linezolid (LZD), clofazimine (CFZ), and delamanid (DLM)) were 93.9% (95% CI 92.-94.9) and 99.1% (95% CI 98.8-99.3), respectively. The lowest sensitivity was 84.8% (95% CI 80.3-88.4) for LFX and 86.4% (95% CI 82.5-89.6) for MFX, or 87.5% (95% CI 84.2-90.2) for Y1 plate and 87.9% (95% CI 83.5-91.1) for T plate. The lowest specificity was 94.4% (95% CI 91.4-96.4) for DLM, or 97.9% (95% CI 96.8-98.7) for B3 plate. Commercial BMD plates in China showed varied drug layouts and operational procedures, indicating the urgency of standardization. The lower performance for some drugs showed the low quality of the plates utilized or lack of proficiency of lab staffs in operating and interpreting results.

Metamorphic P-T-t path of Triassic eclogite from the Rongcheng region, eastern China: implications for the tectonic evolution of Sulu orogenic belt

ABSTRACT Interpretation and inversion of P-T (Pressure-Temperature) paths of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks are critical to understanding the subduction and exhumation histories of an orogen. The Sulu orogen constitutes the eastern part of the Dabie-Sulu orogen, in which, HP metamorphic rocks are relatively poorly as studied compared to the well-documented UHP metamorphic rocks. This study presents the P-T paths of HP eclogites constructed by petrography, mineral chemistry, and pseudosection modelling by using the GeoPS software within the MnNCFMASKHTO (Mn-CaO-FeO-MgO-Al2O3-SiO2-K2O-H2O-TiO2-O2) system. Sample 19LR70–1 mainly consists of omphacite, garnet, quartz, minor rutile, ilmenite, and amphibole. Sample 19LR71–1 is mainly composed of omphacite, garnet, kyanite, and accessory minerals of rutile and amphibole. These two eclogite samples recorded clockwise P-T paths with peak P-T conditions of P ≥ 21.3 kbar, T ≥ 755°C and P ≥ 23.0 kbar, T ≥ 871°C, respectively. Well-correlated U-Pb ages and trace element data show that the protoliths of eclogites were 655–699 Ma and 676–754 Ma, the metamorphic ages were 212–232 Ma, and the time of partial melting were 221–225 Ma. Combined with regional geological data, we conjectured that before 240 Ma, the South China plate was subducted to the North China craton; subsequently, at 240–220 Ma, HP eclogite facies metamorphism occurred at a depth of 60–70 km. This was followed by the exhumation of these HP metamorphic rocks, coupled with concurrent partial melting, around 220–200 Ma.

New data on Silurian (Llandovery) sinacanthids from Wuhan, South China and their biostratigraphic and paleobiogeographic implications

Sinacanthids are a group of Silurian spine-based mysterious taxa, probably representing a lineage of stem chondrichthyans. New sinacanthid fossils attributed to Sinacanthus wuchangensis, S. triangulatus, Sinacanthus sp., Neosinacanthus planispinatus, Tarimacanthus bachuensis, Eosinacanthus shanmenensis, and fin spine morphology 1, 2 and 3 are identified from the upper member of the Qingshui Formation and the Fentou Formation (Telychian, Llandovery) of Wuhan, South China. These sinacanthid fin spines are similar to those from the Rongxi Formation in northwestern Hunan and the Ymogantau Formation in the northwestern Tarim. This study provides further evidence for the presence of diverse sinacanthid faunas from the South China plate. As the part of the Zhangjiajie Vertebrate Fauna of China, they have great significance in the paleogeographic division of vertebrates and the regional stratigraphic division and correlation. The Silurian sinacanthids from China were mainly grouped into three assemblages, i.e., the Wentang/Tataertag assemblage (early Telychian), the Fentou/Ymogantau assemblage (middle Telychian), and the Maoshan assemblage (middle to late Telychian). In addition, the sinacanthids from the South China plate, Tarim plate, and Qiongzhong block belong to the Zhangjiajie Vertebrate Fauna and there was certain extent of migration of sinacanthids among these areas during the Telychian, Silurian.

Detection of Long‐ and Short‐Term Slow Slip Events Using a Network Inversion Filter and Dense Global Navigation Satellite System Network in Shikoku, Japan

AbstractThe study of slow slip events is essential to elucidating the slip mechanisms and frictional properties of plate interfaces. We imaged the aseismic slip at the plate interface between the subducting Philippine Sea Plate and overriding Amur Plate beneath Shikoku Island, Japan, by applying a network inversion filter to the position time series obtained from Global Navigation Satellite System data spanning January 2012 to April 2022. The results show long‐term slow slip events in the Bungo Channel, central Shikoku, and the Kii Channel, which started from 2018. We also identified 39 short‐term slow slip events associated with low‐frequency tremors. The estimated moment magnitudes of the Bungo Channel, central Shikoku, and Kii Channel slow slip events were Mw7.0, Mw6.4, and Mw6.3, respectively, with a rigidity of 30 GPa. The estimated moment magnitudes of the short‐term slow slip events ranged from Mw5.7 to Mw6.4. Most of the detected short‐term slow slip events are associated with low‐frequency tremor, and many showed propagation through the spatial domain. Events with magnitudes of ≥Mw6.30 typically consist of subevents. The slip rate of short‐term slow slip events ranges from 1 to 7 mm/day, which is considerably larger than the plate convergence rate. The short‐term slow slip events are 6 to 40 days, and follow the accepted scaling law between slip event duration and total magnitude. The short‐term slow slip event zone is consistent with a three‐segment hypothesis. The short‐term slow slip event in northwest Shikoku and long‐term slow slip event in central Shikoku may be correlated.

Mechanical properties and constitutive model of Q345GJ thick steel plate in China

The Q345GJ steel plate is a common Chinese product that has an increasingly wide usage in civil engineering. However, previous research on Q345GJ steel plates with thicknesses of no less than 60 mm is limited, especially the systematic cyclic loading tests, causing an inadequate understanding of the cyclic behaviour and corresponding constitutive parameters of thick steel plates. To further investigate the mechanical property of Q345GJ thick steel plates and fill the gap of test databases, layered specimens obtained from five different thickness positions of the 60-mm and 100-mm thick Q345GJ steel plates were tested under monotonic tension and five cyclic loading protocols. The mechanical properties of specimens in different thickness positions were compared and analysed. Moreover, parameters of the Chaboche cyclic constitutive model were calibrated and then validated by finite element analysis (FEA). Results indicated that the surface-layer specimens exhibited greater strength and lower ductility than the middle-layer specimens. Furthermore, the hysteretic curves of all the specimens were plump, where the energy dissipation of the surface-layer specimens was greater than that of the middle layer, particularly for the 100-mm thick plate. Based on the test results and calibrated parameters of the Chaboche constitutive model, significant isotropic softening characteristics were observed for all thickness positions. Following the tests and analysis, the cyclic constitutive model calibrated in this study was verified to support further numerical simulations.

Thermal Evolution, Hydrocarbon Generation, and Heat Accumulation of a High Geothermal Coalfield: A Case Study of Pingdingshan Coalfield, China.

As an important energy base in central China, the Pingdingshan coalfield has abundant coal and geothermal resources. The cooperative exploration of coal and geothermal resources is significant for the comprehensive utilization of energy resources. This work collected coal-bearing samples from the Pingdingshan coalfield to investigate the tectono-thermal evolution of a high geothermal coalfield, especially the present geothermal field and hydrocarbon generation model. The geochemical results show that the Shanxi and Taiyuan source rocks have average R o values of 0.88 and 0.97%, respectively, with an average Rock-Eval T max value of 442 °C. Hydrocarbon generation of source rocks started at ∼205 Ma, with the highest rates at ∼170 Ma, reaching the maximum transformation ratio of 40-50% in the middle of the Early Cretaceous. The age and length of apatite fission tracks (AFTs) indicate that coal-bearing strata underwent significant post-depositional annealing after the Late Permian and suggest an abnormal thermal event that occurred in the Late Mesozoic. Meso-Cenozoic thermal event was mainly caused by the plutonic metamorphism of the Early Jurassic and magmatic thermal metamorphism of the Early Cretaceous, achieving a maximum paleotemperature of ∼140 °C. The magmatic thermal event resulted from the intensive post-orogenic extension of the Qinling-Dabie Orogenic Belt caused by the tectonic transition of the North and South China Plates. The present-day high geotemperature of Pingdingshan Coalfield is dominated by the horst structure caused by the regional extension of the basin-mountain system. The Cambrian limestone with a high thermal conductivity underlying coal measure collects deep heat, forming a heat accumulation center of this horst structure with a heat flow of 74 mW/m2 and a maximum temperature of ∼50 °C nowadays.

Continent‐Continent Collision Between the South and North China Plates Revealed by Seismic Refraction and Reflection at the Southern Segment of the Tanlu Fault Zone

AbstractThe Tanlu Fault Zone (TFZ) is considered as a suture of the intra‐continental collision between the South and North China plates, and it has attracted considerable geological, geochemistry, and geophysical investigations. However, its deep structures still lack clear delineation and the related tectonic processes are still debated without a clear consensus. To better characterize the TFZ as a plate boundary in east China, a 2‐D land seismic survey extending 87 km was conducted across its southern segment to investigate the underlying complex structures. Acoustic full‐waveform inversion (FWI) is applied to the early arrivals of the land seismic data to reconstruct the high‐resolution P‐wave velocity model of the upper crust (above ∼3.5 km). Structures of the crust and the uppermost mantle are further constrained through deep seismic profiling (DSP). The integrated geological interpretation from the FWI and DSP results suggests massive magma upwelling activities, characterized by the reflection‐free zone revealed by DSP and the high‐velocity anomaly recovered by FWI. The TFZ in the study area is found to be a deeply seated fault system with a positive flower structure at its shallow part, which suggests it has undergone a transpression regime. Also, the DSP result provides evidence for the subduction of the South China plate under the North China plate. Finally, a three‐stage model including the compression, transpression, and extension stages is proposed based on the new seismic results to better constrain the tectonic evolution of the southern segment of the TFZ.

Silurian phyllocarid crustaceans (Phyllocarida, Archaeostraca) from South China

In the Silurian, the suborder Caryocaridina of the phyllocarids was replaced by the suborder Ceratiocaridina as the dominant group. The latter did not achieve a global distribution until the late Silurian. In the early Silurian, ceratiocarids were a little-diversified group and palaeogeographically restricted mainly to Laurussia. Although previous studies have mentioned phyllocarid fossils from the Silurian of the South China plate, these have never been systematically described. This study describes three genera and four species (including one new genus, two new species, and two undetermined species), i.e. Cugocaris future gen. et sp. nov., Gonatocaris wuhanensis sp. nov., Gonatocaris sp. and Warneticaris sp., based on 38 phyllocarid specimens from the Fentou Formation in Wuhan. Cugocaris future gen. et sp. nov. is distinguished by an elliptic carapace ornamented by sinuous and anastomosing longitudinal striae, a styliform telson, and slender furcal rami. Gonatocaris wuhanensis sp. nov. is characterized by anastomosing longitudinal striae on the carapace, greatest carapace width in the centre of the carapace, and three different types of ornamentations on the surface of the abdominal segments. A phylogenetic analysis of 41 Palaeozoic phyllocarids reveals that Gonatocaris, Rolfecaris and Cugocaris gen. nov. form a monophyletic group. Thus, a new family, Gonatocarididae fam. nov., is proposed. This family is characterized by a carapace lacking median dorsal plate, rostral plate, a well-developed anterior carapace horn, and ornamented with prominent raised, wavy, anastomosing longitudinal striae. A palaeoecological analysis suggests that G. wuhanensis was a fairly active swimmer, while C. future was necto-benthic with relatively weak swimming abilities. This study not only extends the known morphological range of phyllocarids, but also has implications for the functional morphology, taxonomy, and evolution of archaeostracans as a whole. http://zoobank.org/urn:lsid:zoobank.org:pub:4B6B60B6-19F1-4A58-AC65-3B1AEE5D0939

Sedimentary Characteristics of the Permian Zhesi Formation in Eastern Inner Mongolia, China: Implications for Sedimentary Background and Shale Gas Resource Potential.

Eastern Inner Mongolia of China is located between the Siberian plate, the North China plate, and the Pacific plate and has a complex history of tectonic and sedimentary evolution. The sedimentary strata of the Zhesi Formation in the Middle Permian recorded rich environmental, structural, and petroleum geological information, which has great significance to the Paleozoic geological research in Northeast China. Through field outcrop observation and profile measurement, combined with geochemistry, mineralogy, and the reservoir physical property test, the sedimentary environment, tectonic setting, and shale gas resource potential of the Middle Permian Zhesi Formation are analyzed. The sedimentary facies of the Zhesi Formation are distributed in strips in the northeast direction, mainly developing littoral, shallow marine, and bathyal sedimentary environments. Clastic rock deposits are mainly developed in the littoral facies, carbonate platform and tempestite deposits are mainly developed in the shallow marine facies, and mudstone mixed with turbidite deposits are mainly developed in the bathyal facies. The sedimentary environment and chronological characteristics show that the Paleo-Asian Ocean was not completely closed in the Middle Permian, and its complete closure time should be later. The characteristics of source rocks and the shale gas resource potential in the Solon area are discussed. Controlled by the sedimentary environment, the Solon area mainly deposited thick dark shale mixed with turbidite sandstone, the accumulated thickness of the dark shale is more than 200 m, with an average vitrinite reflectance (Ro) of 2.44%, and the average residual total organic carbon (TOC) content is 0.85%. The average content of brittle minerals is 60.2% and the shale foliation fracture is developed, which is easy to form natural fractures and induced fractures, so the shale has good hydrocarbon generation potential, and the generated shale gas can exist in shale in an adsorbed state and a free state. In addition, the shale gas generated in the shale can migrate to the lenticular turbidite sand body in a short distance to form free shale gas. Therefore, there is a certain shale gas resource potential in the Solon area, and finding a favorable area with high TOC is the key to future exploration of Upper Paleozoic shale gas.

Geochemical Characteristics of Graptolite Shale in the Pingliang Formation of the Ordos Basin, China: Implications for Organic Matter, Thermal Evolution, and Hydrocarbon Reservoir

Graptolite-rich shale is the main layer of shale gas resources in the southern marine sedimentary basin. Recently, shale gas resources were discovered in the Ordovician marine graptolite-rich strata in the Ordos Basin. The graptolite shale in the study area is different from the marine graptolite shale in the Yangtze plate in southern China, and further exploration is needed. This paper presents core samples of the graptolite-rich shale of the Pingliang Formation in the southwest Ordos Basin as research objects. The graptolite genus and graptolite shale characteristics were studied using core observation, electron microscopy, scanning electron microscopy, and geochemical analysis. We determined the role of the sedimentary environment and thermal maturation of graptolite shale in hydrocarbon formation and explored the possibility of hydrocarbon generation. Many graptolite epidermises provide buried organic matter. The quiet sea and low-energy marine environment create favorable conditions for preserving organic matter. The tectonic process resulted in the evolution stage in the oil generation window. Different types of pores formed the spaces of hydrocarbons. Therefore, the shale of the Pingliang Formation has shale oil exploration potential, which complements the shale gas in the northwestern margin of the basin, and provides new venues for shale oil and gas exploration in northern China.

Current Stress Pattern and Geodynamics of the Baikal Rift System

Abstract—The crustal stress field of the Baikal Rift System has been reconstructed by tectonophysical inversion of focal mechanisms from the catalog of earthquakes recorded by the regional seismological network. Cataclastic analysis of fault slip data developed at the Shmidt Institute of the Physics of the Earth (Moscow) revealed previously unknown features in the behavior of principal stresses. Namely, the maximum deviatoric stresses diverge off the rift axis while the normalized spherical and deviatoric stress tensor components reach high magnitudes in the crust of the Baikal Basin. The obtained stress pattern of the Baikal Rift System is consistent with the rift origin by a joint action of a vertical mantle flow (upwelling branch of convection) and a horizontal flow in the asthenosphere which drives the NW–SE motion of the Amur plate off Eurasia.