Regional Tectonic Evolution Research Articles

Neoproterozoic Tectonics of the Arabian-Nubian Shield: Insights from U–Pb Zircon Geochronology, Sr–Nd–Hf Isotopes, and Geochemistry of the Deki Amhare Complex Granitoids, Central Eritrea

The Deki Amhare complex is located in central Eritrea, within the Arabian–Nubian Shield (ANS). It consists of an inner core of monzogranite porphyry and diorite enclaves (MMEs), surrounded outwardly by granodiorite and quartz diorite. The zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Hf isotopic compositions of the Deki Amhare complex granitoids were used to discuss the Neoproterozoic tectonics of the ANS. The Late Tonian granodiorite and quartz diorite are metaluminous and calc-alkaline to slightly high-K calc-alkaline I-type plutons, with ages of 811.2 ± 4.8 Ma and 811.6 ± 5.7 Ma, respectively. They exhibit positive εHf(t) (7.6–9.5) and εNd(t) (3.9–4.7) values and relatively low (87Sr/86Sr)i ratios (0.70374–0.70463), indicating that they derived from the partial melting of a metasomatized mantle wedge during intra-oceanic subduction. The Ediacaran monzogranite porphyry and MMEs are subalkaline to alkaline A2-type granitoids with ages of 620.0 ± 4.3 Ma and 614.8 ± 3.9 Ma. These display positive εHf(t) (5.3–8.7) and εNd(t) (4.2–4.7) values, as well as low (87Sr/86Sr)i ratios (0.70310–0.70480), implying that they formed through crust–mantle magma mixing related to post-collisional slab break-off. Based on these data, three stages of regional tectonic evolution can be described: (1) from ~1200 Ma to ~875 Ma, the mafic oceanic crust was derived from depleted mantle during the opening of the Mozambique Ocean; (2) from ~875 Ma to ~630 Ma, intra-oceanic subduction and arc formation occurred with the development of I-type batholiths; and (3) from ~630 Ma to ~600 Ma, crustal and lithospheric reworking took place post-collision, leading to the formation of A2-type granitoids.

The Indosinian Granitoids of the Songpan–Garze–West Kunlun Orogenic Belt, China: Distribution, Petrochemistry, and Tectonic Insights

During the Indosinian orogeny, the Songpan–Garze–West Kunlun orogenic belt experienced significant tectonic and magmatic activity, leading to the widespread emplacement of granitoid bodies. This study provides a detailed petrochemical and geochemical analysis of these granitoids, offering new insights into their tectonic settings and magmatic evolution. The granitoids of this belt are systematically categorized into arc calc-alkaline and arc tholeiitic granitoids (ACG and ATG), cordierite peraluminous and muscovite peraluminous granitoids (CPG and MPG), potassium calc-alkaline granitoids (KCG), and peralkaline granitoids (PAG) suites. ACG and ATG types dominate early magmatism (230–190 Ma), reflecting a convergent tectonic setting, while KCG and MPG types magmatism, respectively, emerged 10–20 Myr and 15–25 Myr later, during post-collisional extensional phases. Geochemical analyses show that ACG and ATG granitoids follow calcic and calc-alkalic trends, while KCG and MPG display alkalic characteristics. These findings align with the region’s tectonic transition from the closure of the Paleo–Tethys Ocean to Late Triassic transpressional deformation. This study enhances the understanding of granitoid petrogenesis and provides valuable implications for regional tectonic evolution and mineral exploration.

Crustal structures and anisotropy in southeastern China: Continental collision and intraplate earthquakes

This study investigates the role of crustal structures and anisotropy in southeastern China regarding intraplate earthquakes within the context of concentrated and perturbed tectonic stresses. The region is characterized by a complex multiphase tectonic history,including the ongoing collision between the Philippine Plate and the South China Sea margin. Utilizing the teleseismic receiver function method, we offer a comprehensive depiction of the crustal structures and layered anisotropy in Guangdong and Fujian, two earthquake-prone areas. Our results reveal that the crustal anisotropy is stratified into two layers, with a slow axis perpendicular to the orogenic belt in the upper-middle crust, whereas the fast axis aligns perpendicularly at lower crust levels. The lateral heterogeneity and anisotropy of the crustal structure emphasize both the boundary delineation and differential movement between continental blocks. The observed increase in density and intensity of intraplate earthquakes across this boundary supports our conclusion regarding a connection between decoupled crustal deformation and seismicity. Specifically, the foliation of metamorphic rocks during the Mesozoic collision generated orogen-parallel fabrics in the upper-middle crust, while ductile shearing resulted in orogen-perpendicular fast directions at lower crust levels. In contrast, mismatch evolution between continental blocks reactivated by present collision provides stress conditions conducive to earthquake occurrence in southeastern China. Our findings provide valuable insights into mechanisms behind intraplate earthquakes as well as tectonic evolution within continental collision zones.Plain Language SummaryThe mechanism of intraplate earthquakes is a topic of great interest in the study of continental collision and regional tectonic evolution. The controlling factors behind these earthquakes are highly complex and uncertain. In this study, we aim to investigate the role of crustal structures and anisotropy in southeastern China within the context of intraplate seismic activity. This region, which is currently experiencing a collision between the Philippine Plate and the South China Sea Margin, has a multiphase tectonic history that includes remnants of paleo-Pacific subduction. By utilizing the receiver function method, we provide a detailed picture of crustal structures and layered anisotropy in Guangdong and Fujian, two earthquake-prone regions in southeastern China. Our findings reveal that anisotropy in the crust can be stratified into two layers: an upper-middle crust and a lower crust with a slow axis and a fast axis, both perpendicular to the orogeny, respectively. The lateral heterogeneity and anisotropy of the crustal structure highlight the boundary and differential movement between the continental blocks. The enhanced density and intensity of the intraplate earthquakes across this boundary provide evidence for a connection between decoupled crustal deformation and seismicity. Specifically, our observations suggest that (1) the Mesozoic continental collision induced metamorphic foliation in the upper-middle crust, (2) ductile shearing is characteristic of the lower crust, and (3) ongoing collision has led to mismatch evolution between continental blocks, which creates stress conditions favorable for earthquake occurrence.

Detrital zircon provenance record of the northern shelf in the Rakhine Basin, Bay of Bengal

The Cenozoic strata in the Rakhine Basin play a crucial role in hydrocarbon exploration; however, the provenance of these sedimentary rocks remains poorly investigated. In this study, we employed detrital zircon geochronology and geochemistry in the northern Rakhine shelf to investigate the provenance of sedimentary rocks and, combined with the previous studies, to identify their spatial and temporal variations and to elucidate the provenance evolution since the middle Miocene. The geochemical results of the zircons indicate that the primary source rocks of the sedimentary rocks are magmatic and metasedimentary rocks, particularly those of continental arc and post-collision granites. The origin of these rocks can be attributed to the Gangdese arc magmatic belt in the north, as well as the Indo-Burma Ranges in the east. The sedimentary rocks in the northern Rakhine yield zircon U-Pb age peaks primarily at 0-150 Ma, 400-600 Ma, 600-1000 Ma, and 1600-2100 Ma, with minor populations at 150-400 Ma and >2100 Ma. The detrital zircon provenance study shows that the zircons in the Miocene sedimentary rocks were primarily derived from the paleo-Brahmaputra River, with contributions ranging from 68.7% to 77.0%. During the Pliocene, the paleo-Brahmaputra River and the Chittagong-Tripura Fold Belt were the most significant sediment suppliers. Since the early Pleistocene, the northern Rakhine coastal region has played a significant role in their composition. The Brahmaputra River was the predominant contributor to upper Pleistocene rocks, and the Rakhine coastal region’s contribution to the shelf intensified throughout the Pleistocene. In conjunction with regional tectonic evolution, our study underscores the importance of the Indian Plate subduction as a pivotal factor influencing the provenance transitions in the northeastern Bay of Bengal.

In situ geochemistry of apatite: Petrogenetic and tectonic interpretations of Jurassic felsic magmatism in the Yanbian area, NE China

Geochemical analyses of individual minerals provide more detailed insights into the petrogenesis of igneous rocks than whole-rock analyses. This study conducted in situ geochemical and Nd isotope analyses of apatites from 10 Jurassic granitic plutons in the Yanbian area, NE China, to establish the petrogenesis and regional tectonic evolution. The results indicate that the apatite geochemistry of Jurassic granitoids in the Yanbian area was controlled primarily by the composition of parental melt. Post-magmatic alteration may lead to geochemical decoupling between apatite and parental melt, while Nd isotopes exhibit some resilience to such alterations. Apatites from Early Jurassic granitoids display characteristics that are consistent with an I-type origin, whereas those from Middle and Late Jurassic granitoids exhibit an adakitic affinity. Variations in apatite compositions indicate the fractional crystallization of other rare earth element (REE)-bearing minerals during magma evolution. The early crystallization of plagioclase and allanite led to decreases in Sr and Th contents in apatite, respectively, resulting in a negative Eu anomaly and light REE depletion. The fractional crystallization of titanite and hornblende resulted in the depletion of middle REE in apatite. Hornblende is regarded as the main residual phase in the magma source of Middle and Late Jurassic adakitic granitoids in the Yanbian area. Apatite Nd isotopic compositions suggest that the Jurassic granitoids in the Yanbian area originated from two crustal sources: the Central Asian Orogenic Belt and the North China Craton. Additionally, increasing trends in apatite Sr/Y and (La/Yb)N ratios from the Early to Late Jurassic suggest a gradual thickening of the regional crust, which is likely driven by the continentward migration of the subduction zone associated with the Paleo-Pacific Plate.

Tectonic evolution of the South Tazin Lake shear zone; a major Arrowsmith-age (ca. 2.36 Ga) structure in the SW Rae craton, Laurentia

The Rae Province records the effects of multiple, staggered orogenies along both margins, leaving a complex record of tectonism within major crustal-scale shear zones. While the recently recognized 2.5–2.3 Ga Arrowsmith orogeny is now known to have affected a large tract of the western Rae, few related structures have been described. In this paper, we present the first detailed investigation of such a structure, the ‘South Tazin Lake shear zone’, localized along the Nolan-Zemlak lithotectonic domain boundary in the SW Rae. Multi-scale structural analysis undertaken herein documents the lithostructural zonation and strain progression across this structure and evaluates its context in the regional tectonic evolution. Strain intensity increases dramatically from north to south, with onset of thick, continuous intervals of protomylonite to ultramylonite toward and into a 3–5 km wide corridor that straddles the Nolan-Zemlak domain boundary and constitutes the core of the shear zone. New U-Pb zircon igneous crystallization ages are consistent with previous results for units across the Nolan-Zemlak domain boundary while 40Ar-39Ar thermochronology of hornblende and biotite provides temporal constraints on deformation and a more detailed thermal evolution than previous studies. An 40Ar-39Ar date of 2361 ± 12 Ma for hornblende overgrowing the sheared and recrystallized matrix in blastomylonitic rocks places a minimum age on D2 mylonitization. This, together with similar ages in the core of the shear zone from foliation-parallel hornblende, definitively links ductile shearing and the related S2 fabric along the South Tazin Lake shear zone with Arrowsmith orogenesis. Cooling rates suggest an initial accelerated phase (∼2360–2350 Ma) of post-Arrowsmith exhumation, but the absence of extensional shear-sense indicators implies control by structures outside of the immediate area; or masking by younger (Taltson-age) structures. This was likely followed by a much slower erosion-related (≤2.35 Ga) phase. All-told, the South Tazin Lake shear zone represents a significant Arrowsmith-age tectonic front that was reactivated only along its southern margin under ductile–brittle conditions during the ca. 1.93 Ga Taltson orogeny. These dual fronts were later transposed to the northeast in concert with deformation along the Black Bay fault during the ca. 1.90 Ga Snowbird orogeny.

Mesozoic to Cenozoic tectonic evolution in the central Bohai Bay Basin, East China

The Mesozoic and Cenozoic tectonic evolutionary history of the East Asian continental margin has been the focus of many researchers because of the overprinting of multiple tectonic domains. Previous studies have suggested that the westward subduction of the Paleo-Pacific Plate and the Pacific Plate resulted in the deconstruction of the North China Craton and controlled the formation of the related basins on the continental margin of East Asia. However, controversy remains regarding the tectonic transition processes and mechanisms that occurred from the Mesozoic to the Cenozoic. Since the Mesozoic, the Bohai Bay Basin on the eastern margin of the North China Craton of East China has been influenced by multiple tectonic domains of the Paleo-Tethys, Paleo-Pacific, and Pacific oceans, and there are complete records of these tectonic transition processes. The Bozhong Depression is a subbasin in the Bohai Bay Basin, which is a crucial area for researching the tectonic evolution of the Bohai Bay Basin throughout the Mesozoic−Cenozoic and the regional tectonic evolution of the eastern continental margin of China. Based on 3-D seismic data, logging core data, and a balanced cross section in the Bozhong area, combined with data from the apatite fission-track inversion model, we reconstructed the tectonic evolutionary history of central Bohai Bay Basin and established a three-cycle and eight-stage tectonic model of the central Bohai Bay Basin during the Mesozoic−Cenozoic. The three cycles are the Indosinian, the Yanshinian, and the Himalayan. (1) The Indosinian was marked by two stages. During the early Indosinian, NW-trending thrust faults were formed due to the collision and northward subduction of the South China Block underneath the North China Block. In the late Indosinian, the tectonic stress in the central Bohai Bay Basin shifted from compression to extension. Consequently, the thrust faults reversed, leading to the deposition of Early−Middle Jurassic strata. (2) The Yanshanian cycle comprises three main phases. Early Yanshanian transpressional shearing led to the formation of a NE/NNE-trending, left-lateral strike-slip fault due to NWW-directed subduction of the Paleo-Pacific Plate. Middle Yanshanian transtensional shearing was driven by Paleo-Pacific Plate rollback and resulted in regional extension and the negative inversion of previous compressive faults. Late Yanshanian compression gave rise to the basin reversion, which resulted from an increased subduction speed of the Paleo-Pacific Plate and a transition from a high angle to a low angle. (3) The Himalayan cycle was marked by three phases. During the early Paleogene, the region was characterized mainly by extension, and NE-trending, right-lateral strike-slip normal faults began to form. This coincided with a decrease in the Pacific Plate’s subduction speed. In the late Paleogene, the subduction rate of the Pacific Plate increased, resulting in the change of the central Bohai Bay Basin from an extensional environment to one marked by regional differential compression. In the Neogene, regional thermal subsidence and depression sedimentation occurred, which were probably induced by the increasing subduction speed and rollback of the Pacific Plate. The Bozhong Depression has experienced multiple stages of tectonic evolution, which indicates the concurrent and superimposed effects and transition of multiple tectonic domains.

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.

Mesozoic–Cenozoic tectonic–palaeogeographical evolution of Bayingobi Basin: response to subduction and collision of the Mongol–Okhotsk Ocean plate

The structures, sedimentary fill and magmatic rocks of sedimentary basins are the products of regional tectonic evolution and are crucial to studying the basin's tectonic–palaeogeographical environment and regional tectonic evolution. The present study discusses the zircon U–Pb dating of volcanic rock samples, in situ Hf isotope and whole-rock geochemistry analysis, and the palaeogeographical, sedimentary filling and tectonic background of the Bayingobi basin through outcrop and core descriptions of Meso-Cenozoic strata, stratigraphic correlation and lithofacies analysis. The U–Pb age of the volcanic rocks is 132–102 Ma, and the in situ Hf isotopic values range from −20.99 to +29.48. The 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic ratios of the volcanic rocks are 0.707049–0.879761 and 0.511846–0.512540, respectively, and the Nd isotopic values range from −0.62 to −6.83. The volcanic rocks in the basin have the characteristics of continental margin island arc volcanic rocks (CAA) with loss of Nb and Ta and enrichment of Pb, originating mainly from dehydration melting of the subducting plate. The lower Cretaceous Bayingobi, Suhongtu and Yingen Formations developed specifically delta–lacustrine deposits. The lower and upper member of the Bayingobi Formation was deposited in the Berriasian to Valanginian and Valanginian to late Aptian, respectively. The Suhongtu Formation was deposited during the late Aptian to early Albian and was controlled by the strike of the Engeer Us fault. The Yingen Formation was deposited in the late faulted depression stage in the late Albian. Because of the subduction of the Mongol–Okhotsk Ocean plate in the Early Cretaceous, several depressions (sags) were formed in the Bayingobi basin, accompanied by the eruption of continental plate margin island arc magmas. With the closure of the Mongol–Okhotsk Ocean in the late Early Cretaceous, the basin was uplifted as a whole and the Upper Cretaceous Ulansuhai Formation was deposited. Supplementary material : Supplementary figures and tables are available at https://doi.org/10.6084/m9.figshare.c.7105807

Geochronology, geochemistry, and Hf isotope of quartz monzonite and diorite in dachaigou, the East Kunlun orogenic belt, China, and their geological significance

This study focuses on quartz monzonite and diorite plutons in Dachaigou, East Kunlun, examining their formation, age, petrogenesis, magmatic source, and tectonic setting. Through comprehensive field observations, zircon geochronology, geochemistry, and Hf isotope analysis, new insights into the Paleozoic tectonic evolution of the proto-Tethys Ocean in the East Kunlun orogenic belt are provided. Zircon U–Pb dating reveals that quartz monzonite and diorite formed at 417.4 ± 2.1 and 404.6 ± 1.8 Ma, respectively. Geochemical analysis shows that the A/CNK value of quartz monzonite ranges from 0.98 to 1.07, with the Pb content proportional to SiO2, which aligns with the characteristics of I-type granite. The εHf(t) values for quartz monzonite and diorite are −0.84 to 2.2 and −13.22 to 2.04, respectively. Considering the formation age, geochemical characteristics, and regional tectonic evolution, it is concluded that quartz monzonite has a crust-derived origin, whereas diorite has a crust–mantle mixing origin. Both were formed in a post-collision extensional tectonic setting resulting from slab break-off, implying the Proto-Tethys Ocean East Kunlun entered a post-collisional extension stage in the Late Silurian–Early Devonian.

Petrogenesis and tectonic implications of late Permian andesites from Rongzharinian, northern Qiangtang, Tibet

At convergent margins, high-magnesian andesitic rocks (HMAs) can offer vital information about the formation of the continental crust and the interactions between the deep crust and mantle. This study focuses on new identified HMAs from the Rongzharinian area, northern Qiangtang Terrane (NQT). We report the major, trace elemental, Sr-Nd-Hf isotopic data, and zircon U-Pb age of volcanic rocks with the aim of understanding their petrogenesis and tectonic setting. A concordant age of 257.7 ± 1.5 Ma for the Rongzharinian high-Mg andesites is determined by zircon U-Pb dating using LA-ICP-MS techniques. The Rongzharinian HMAs have high MgO contents (5.88–7.39 wt%), Mg# values (63–68), and Cr (143–185 ppm) and Ni (48–66 ppm) concentrations, close to primitive HMAs. They underwent variable degrees of fractionation of amphibole and minor clinopyroxene and negligible crustal contamination during magma evolution. REE modeling results show that the Rongzharinian HMAs can be generated by 4 %–7% melting of hydrous spinel lherzolite at relatively shallow depths. Geochemical data indicate that the Rongzharinian HMAs were dominantly derived from the mixed mantle wedge source composed of N-MORB-like and E-MORB-like components. Based on the regional tectonic evolution, we propose that the Late Permian rollback of the Paleo-Tethyan slab may induce upwelling of the asthenosphere mantle, resulting in melting of the mantle source and the generation of the Rongzharinian high-Mg andesites.

Characteristics of geothermal field and tectono-thermal evolution in Baiyun Sag, Pearl River Mouth Basin, China

Baiyun Sag has become the primary focus of deepwater exploration in the Pearl River Mouth Basin. However, its complex and high-variate geothermal characteristics have severely constrained further oil and gas exploration and resource evaluation. In this study, the present-day geothermal field and tectono-thermal evolution histories of Baiyun Sag were systematically studied based on measured rock thermal conductivity and heat generation data, borehole temperatures, low-temperature thermochronometer analyses, and geodynamic methodologies. The thermal conductivity of 251 core samples ranges from 1.131 to 4.478 W/(m·K), with an average of 2.258 W/(m·K), while the heat generation rate of 106 samples ranges from 0.868 to 1.735 μW/m³, averaging 1.499 μW/m³. The thermal conductivity in Baiyun Sag exhibits a gradual decrease from the Wenchang Formation to the Hanjiang Formation, whereas the heat generation rate decreases with depth. The present-day heat flow in Baiyun Sag ranges from 66.6 to 139.1 mW/m2, with an average of 89.7 ± 14.7 mW/m2, showing a gradual increasing trend from northwest to southeast. Formation temperature at depths of 1–5 km increases proportionally with depth. Thermal inversion, as inferred from low-temperature thermochronological data of six basement samples, reveals distinct temperature paths for each tectonic unit in Baiyun Sag. These paths are primarily linked to regional tectonic uplift-subsidence and basement heat flow variation. Geodynamic simulations further indicate two extensional events in Baiyun Sag during the Eocene and Middle Miocene, leading to a rapid increase in basement heat flow. This study systematically elucidates the present-day geothermal field characteristics and tectono-thermal evolution history of Baiyun Sag, bearing significant implications for regional tectonic evolution and future deepwater oil and gas explorations.

Two pulsed activities of the Emeishan large igneous province in southwestern China inferred from dolomite U-Pb geochronology and significance

Abstract The Emeishan large igneous province (ELIP) was a major geological event that took place around the Middle–Late Permian boundary. The major episode of the ELIP is generally considered to have occurred at 260–259 Ma, although an increasing number of geological data have suggested that multiple episodes of magmatic activity might have occurred. Here we report a study of a Lower Permian dolomite whose formation was influenced by the ELIP in the Sichuan Basin of southwestern China. Results show two new pulsed activities at 273.2 ± 9.7 Ma to 269.1 ± 12.0 Ma (ELIP-I) and 263.2 ± 10.3 Ma to 258.7 ± 8.1 Ma (ELIP-II). The two stages of the ELIP magmatism and thermal activity controlled the regional tectonic, sedimentary, and diagenetic evolution and exerted a profound influence on the oil and gas reservoirs, source rocks, and lithofacies paleogeography. This study is the first to interpret the timing of the ELIP from analysis of hydrothermal dolomite and provides new clues and data for improving our understanding of the dynamic formation mechanism and Earth system of the ELIP.

Present-Day Geothermal Regime and Thermal Evolution of the Fukang Sag in the Junggar Basin, Northwest China

The Fukang Sag in the Junggar Basin is an important petroleum exploration and exploitation region. However, the geothermal regime and tectono-thermal evolution of the Fukang Sag, which control its hydrocarbon generation and conservation, are still controversial. This study involved a systematic analysis of the present-day geothermal gradient, heat flow, and thermal history of the Fukang Sag for better further exploration. According to the well log data and well-testing temperature data, we calculated that the geothermal gradient of the Fukang Sag ranges from 16.6 °C/km to 29.6 °C/km, with an average of 20.8 °C/km, and the heat flow ranges from 34.6 mWm−2 to 64.3 mWm−2, with an average of 44.6 mWm−2. Due to the basement relief, they decrease from northeast to southwest. The weight averages of the single-grain apatite (U-Th)/He ages of the core samples are 1.3–85.2 Ma, and their apatite fission track ages range from 50.9 Ma to 193.8 Ma. The thermal modeling results revealed that the Fukang Sag experienced late Permian, late Jurassic, and late Cretaceous cooling events (although the timing and magnitude of these events varied among the samples), which were related to the continuous compression of the Junggar Basin. In addition, basin modeling indicated that the heat flow of the Fukang Sag decreased from 80 mWm−2 in the Carboniferous to the current value of 44.6 mWm−2. The Fukang Sag’s edge exhibits prolific hydrocarbon generation in the Carboniferous–Permian source rocks, while the Jurassic source rocks within the sag also undergo abundant hydrocarbon generation. This study provides new insights into the present-day geothermal field and tectono-thermal evolutionary history of the Fukang Sag, which are significant in terms of regional tectonic evolution and oil and gas resource assessment.

A Pliocene lacustrine system in the Nellis basin, southern Nevada, USA: implications for the Colorado River drainage system

ABSTRACT Lacustrine basins and the sediments in them provide a critical component of regional tectonic development and climate history. Each sub-basin in the landscape records the interplay between active tectonism and shifting climate. Many of the basins in southern Nevada that contain deposits of the Muddy Creek Formation were closed fluvio-lacustrine systems during the latest Miocene and into the Pliocene. They were subsequently integrated into the regional Colorado River system. Lacustrine deposits of the Muddy Creek Formation are exposed along the trace of the Las Vegas Valley shear zone in the Nellis Dunes Recreation Area (NDRA), northeast of Las Vegas, Nevada. The Muddy Creek Formation in NDRA consists of approximately 130 m of mixed carbonates and clastics, and new tephrochronology suggests an early to late Pliocene age (∼ 4.7 to ∼ 2.6 Ma) for the lowermost lacustrine deposits and an unknown, but younger, age for the uppermost spring-fed lacustrine deposit. These sediments were deposited in an arid to semiarid lake (Lake Nellis) and alluvial floodplain system based on the interpretation of lithologies and facies associations. The stratigraphic succession coarsens upward and reflects establishment of a lacustrine carbonate system overlain by a clastic succession of peripheral lake sediments of alluvial and floodplain origin. The peripheral lake deposits consist of spring-fed and fluvial wetland mudflats of brown claystone and siltstone. This brown claystone is capped by a succession of yellow and red sandstones deposited by fluvial and minor eolian processes. The second, and youngest, freshwater limestone, likely disconformably, overlies the yellow and red sandstones, and is thought to be temporally and depositionally distinct from the underlying Muddy Creek deposits. The transition from the lower lacustrine carbonates to clastic fluvial channel and flood-plain deposits indicates desiccation of Lake Nellis and possibly occurs soon after ∼ 2.7 to ∼ 2.6 Ma based on the ages of tuffs occurring in the uppermost limestone and marl beds. This is consistent with an interpreted increase in regional aridity after ∼ 2.8 Ma (Smith et al. 1993). The second limestone deposit at the top of the section represents an even younger spring-fed lacustrine deposit of unknown age. Throughout the lower carbonate section, three tuffs were identified, and geochemically correlated, using a discriminant-function analysis, to the tuff of Napa (≤ 4.70 ± 0.03 Ma), the Putah Tuff (∼ 3.3 Ma), and the lower tuffs of the Badlands (∼ 2.7 to ∼ 2.6 Ma). The timing of deposition of Lake Nellis sediments postdates the integration of the three major lake systems in this region (Lake Grand Wash, Lake Hualapai, and Lake Las Vegas) into the Colorado River drainage (5.6–4.9 Ma), and also postdates the full integration of the river to sea level (4.8–4.63 Ma) (Howard et al. 2015; Crow et al. 2021). Lake Nellis represents an isolated lake basin that was one, and maybe the last, lacustrine system to be fully integrated into the Colorado River drainage in this region.

Crustal structure of the southern Lower Yangtze region and its geological implications: a deep reflection seismic profile

Abstract The southern part of the Lower Yangtze Region, located in the area bounded by the Jiangnan and Dabie orogenic belts, is characterized by a complex fault structure and unique magmatism, and is one of the key areas in regional tectonic evolution and magmatism. In this study the authors used a 45-km-long deep reflection seismic profile to study the crustal structure of the southern Lower Yangtze Region. The results show that the crust in the study area is ∼31.5–33.6 km thick, with the Huaining Basin as the thinnest part. A detachment surface at a depth of around 12 km divides the crust into the upper and lower crust, act as a key tectonic decoupling layer. Two sets of thrust nappe faults with opposite tendencies have horizontally developed above the detachment surface, with the Huaining Basin as the centre. A typical wedge-shaped structure has developed below the Qianshan Basin, suggesting that two sets of thrust nappe faults may have formed in the same dynamic system. The reflection patterns of the lower crust on both sides of the profile exhibit a monoclinic feature with opposite tendencies, while the lower part of the Huaining Basin exhibits an arcuate upward-arch feature. A prominent ductile shear zone in the lower crust has developed on the west side of the Huaining Basin, which can provide a favourable channel for magma migration. The results of this study deepen our understanding of the deep structure of the Lower Yangtze Region, and provide important constraint data for research on dynamic mechanisms.

Permian tectonic evolution and continental accretion in the eastern Central Asian Orogenic Belt: A perspective from the intrusive rocks

The tectonic evolution and history of continental accretion of the eastern Central Asian Orogenic Belt (CAOB) are not yet fully understood. In this study, we investigate Permian intrusive rocks from the Jiamusi Block of the eastern CAOB to constrain the tectonic evolution and continental accretion of this region during the late-stage evolution of the Paleo-Asian Ocean. Our new data show that Early Permian gabbro-diorites were derived from the partial melting of depleted mantle metasomatized by oceanic-slab-released fluids. Middle Permian adakitic granites have low Na2O and MgO and high K2O contents, indicating a thickened-lower-crust source. Late Permian S-type granites were derived from the partial melting of continental crust. A compilation of the available geochronological data for Permian intrusive rocks (including adakitic and A-, S-, and I-type granites and mafic rocks) from the eastern CAOB reveals that the A-type granites formed mainly during the Early–Middle Permian, S-type and adakitic granites mostly during the Middle–Late Permian, and I-type granites and mantle-derived mafic rocks throughout the Permian. The A-type granites, which are proposed to have been sourced from thinned continental crust, indicate an extensional setting in the eastern CAOB during the Early Permian. The Middle–Late Permian adakitic granites imply a thickened continental crust, which indicates a compressional setting. Therefore, the eastern CAOB underwent a transition from extension to compression during the Middle Permian, which was probably triggered by the late-stage subduction of Paleo-Asian oceanic crust. Considering the petrogenesis of the intrusive rocks and inferred regional tectonic evolution of the eastern CAOB, we propose that vertical underplating of mantle- and oceanic-slab-derived magmas contributed the materials for continental crust accretion.

Geological characteristics and main controlling factors of the helium-rich gas reservoirs in Sozak Gas Field, Kazakhstan

Based on core data, physical properties, well logging, gas testing, composition, and helium distribution from 13 newly drilled wells, in combination with regional tectonic evolution, depositional background, and typical gas reservoir profiles, helium-rich gas reservoirs geology characteristics and main controlling factors have been explored. The results show that three gas reservoirs formed from bottom to top, i.e., granite and metamorphite fractured reservoir in the basement, tight sandstone structural reservoirs in the Devonian, and huge continuous carbonate reservoirs in the Lower Carboniferous. Fractures developed on structural points control high-production, and gas is prominently displayed in low structural areas. The dry gas exhibits richness in helium, with decreasing helium content from the basement to the Carboniferous. The pre-Devonian large-scale granite and metamorphite basement serve as the primary helium source, while the high-gamma sandstones of the Devonian and the Carboniferous act as secondary sources. Fractures play a dual role, being filled up and conducting in two ways: gas from the Carboniferous source rocks migrates downward, and helium migrate upward. Thick interbedded gypsum-tight limestone on top of the Lower Carboniferous act as the regional caprock, effectively preserving the helium-rich gas reservoirs.

The Effect of Magma Poor and Magma Rich Rifted Margins on Continental Collision Dynamics

AbstractThe transition between non‐rifted continental lithosphere and oceanic lithosphere in rifted margins can display a wide range of characteristics, depending on the regional tectonic evolution. The velocity and duration of the rifting process as well as the geodynamic setting influence the properties and geometry of the margins, which are often grouped into two main categories: magma‐poor and magma‐rich. We show how different types of rifted margins can influence the dynamics of continental collision, focusing on the time and depth of slab break‐off after collision and the fate of margin material. We find that rifted margins have a noticeable impact on subduction dynamics, as we observe large variability in slab break‐off times and depths. In particular, the presence of a rifted margin can delay slab break‐off to up to 60 Myr after the onset of collision. Our results show that a large portion of the weak crust of magma‐poor margins is likely to detach from the subducting plate and accrete to the upper plate, while the dense and strong mafic and ultramafic component of magma‐rich margins causes most of the margin to subduct and be lost into the mantle, leaving only a small fraction of transitional and oceanic crust at the surface. Therefore, the volume of accreted material is much larger when the margin is magma‐poor than magma‐rich, which is consistent with geological observations that fossil magma‐poor rifted margins are preserved in many mountain ranges, whereas remnants of magma‐rich rifted margins are scarce.

Unraveling the early Paleozoic tectonic history of the South Qinling Belt: Evidence from geochronology, geochemistry, and Sm-Nd isotopes of meta-sedimentary rocks

The determination of the petrogenesis and age of meta-sedimentary rocks plays a crucial role in enhancing our understanding of regional tectonic evolution. In this study, we conducted comprehensive geochemical, zircon U-Pb, and Sm-Nd isotope dating analyses of the biotite gneiss of the Changjiaoba group to investigate the tectonic evolution of the South Qinling belt. The age range of detrital zircons from the biotite gneiss was estimated to be 446–2798 Ma, with prominent peaks observed at approximately 454, 660, 790, 1998, and 2770 Ma. The earliest data indicate that the final sedimentary age of the Changjiaoba group corresponds to the late Ordovician. The protoliths of the biotite gneiss were argillaceous rocks, classified as parametamorphic rock. The chondrite-normalized rare earth element (REE) diagram exhibited right-inclined patterns with negative Eu anomalies. The upper continental crust (UCC)-normalized trace element patterns exhibited insignificant enrichment of Ba, Sr, and K; negative anomalies of Hf, Th, U, and Ti; and depletion of Cr and Ni. Geochemical indicators suggest that the precursor sediments are felsic rocks that have undergone moderate weathering. The εNd (t) values of the biotite gneiss (−10.2 to −3.4) suggest a mixture of a few juvenile crust components and abundant ancient material, indicating an arc-realted setting. Collectively, our findings suggest that the primary material sources of the Changjiaoba group were predominantly the North Qinling belt during the Paleozoic and the Yangtze block during the Neoproterozoic. The tectonic setting discrimination diagrams imply that the biotite gneiss were formed in an active continental margin environment, supporting the notion of the northward oceanic subduction during the early Paleozoic. In conclusion, our study provides valuable insights into the composition and deposition history of the Changjiaoba group in the South Qinling belt, contributing to our understanding of the regional geology.