Tectonic Belt Research Articles

Tectonic and metallogenic implications of W-Sn related granitoid rocks in the Kawthaung-Bankachon area, southernmost part of Myanmar: Constraints from petrology, geochemistry, and U-Pb zircon geochronology

Granitoid rocks are widely distributed along the N-S trending tectonic belts encompassing Myanmar, Thailand, Peninsular Malaysia, and Indonesia and these granitoid rocks are host to the world's largest deposits of tin-tungsten, in terms of both production and reserves. The investigated study area belongs to the southernmost part of the Central Cretaceous-Eocene granitoid belt of SE Asia in the border region of Myanmar and Thailand within the Sibumasu or Shan-Thai Terrane. The granitoid units in the area are biotite granite, muscovite-biotite granite, porphyritic biotite granite, and diorite which occur locally as dykes. All granitic rocks in the area fall are recognized in High-K calc-alkaline series and show a high abundance of Cs, Rb, U, Th, K, Pb, Nd, Zr, and Sn. Based on the major oxide composition and tectonic discrimination diagram, all granitoid rocks in the area fall in the peraluminous, S-type granite category and have formed within the Post-Orogenic Granite and Post-Collisional Granite fields. Radiometric dating by LA ICP-MS U-Pb zircon method yielded the ages of 78.97 ± 0.63 Ma (biotite granite), 79.59 ± 0.76 Ma (muscovite-biotite granite), and 79.14 ± 0.91 Ma (porphyritic biotite granite) and 49.48 ± 0.83 Ma for the biotite granite from the Yadanabon W-Sn deposit. According to the zircon U-Pb ages, the timing of the granitoid intrusions of the Kawthaung-Bankachon area is the Campanian (Late Cretaceous) to Eocene. The magmatism and W-Sn mineralization in the area is attributable to Indian Ocean subduction and collision between the west Myanmar Terrane and the Sibumasu Terrane.

Nature of early Mesoproterozoic magmatism in the Qilian-North Qaidam tectonic belt, NW China: Implications for prolonged extension processes and transition from Columbia to Rodinia

Precambrian basement rocks exposed in uplift zones and orogenic belts provide accessible opportunities for paleogeographic reconstruction, especially for microcontinents and cratons with thick covers. Here we report early Mesoproterozoic rifting-related mafic and granitic metaigneous rocks preserved in the Qilian-North Qaidam tectonic belt, NE Tibetan Plateau. Mafic rocks include garnet amphibolite emplaced at 1.40 Ga and metagabbro that were emplaced at 1.39 Ga, exposed in the North Wulan area. They are derived from low-degree (<7 %) partial melting of slab-modified lithospheric mantle lherzolites with Sp:Grt ranging from 90:10 to 60:40. The calculated low P-T conditions of mantle melting (Tpmax < 1472–1451 °C at P = 2.0 Ga) are also consistent with a thermal normal lithospheric mantle upwelling event. Granitic rocks comprise ca. 1.44 Ga garnet-bearing and ca. 1.41 Ga two-mica granites that were emplaced in the North Wulan and Central Qilian areas, respectively. They are S-type granites derived from crustal reworking of psammitic-rich and/or clay-rich metasedimentary rocks. In addition, the two-mica granites represent the oldest basement rocks yet identified in Central Qilian and indicate the existence of ancient basement rocks older than ca. 1.41 Ga. All the mafic and granitic rocks belong to a part of intense Mesoproterozoic rift-related magmatism in the composite Qilian-Quanji block (QQB), and subsequently underwent 1.18–0.9 Ga metamorphic modifications. The composite QQB in the NE Tibetan Plateau was involved in the long-term processes including crustal reworking and mantle upwelling (1.5–1.35 Ga) correspond to the breakup of Columbia followed by oceanic subduction (1.2–1.0 Ga) and subsequent collision and exhumation (0.9–0.8 Ga) at the periphery of Rodinia. Our results improve the understanding of the Mesoproterozoic tectonic evolution for the whole QQB and provide important constrains on the transition from Columbia to Rodinia.

The geochemical characteristics of Cretaceous volcanics in southern Hainan Island and implications for tectonic evolution in the South China Sea

The southeastern Eurasian plate, where the South China Sea (SCS) is located, lies in a complex tectonic setting between the Pacific and Tethys tectonic belts. It is widely accepted that the tectonics of the SCS area were influenced by subduction in the late Mesozoic, but there is still controversy over whether it was paleo-Pacific subduction or Tethyan subduction. Volcanic activity in the south of Hainan Island was intense during the Cretaceous, and geochemical analysis of the collected basaltic andesite, andesite and rhyolite samples in this study indicate those intermediate-acid series igneous rocks are high-K calc-alkaline or calc-alkaline. Some andesites have high MgO contents and Mg# values (2.04–5.34 wt% and 36.83–55.29; Mg# = 100× Mg2+/(Mg2+ + TFe2+). Light rare earth elements (LREEs) and large ion lithophile elements (LILEs) are enriched in all the samples, but high field strength elements (HFSEs) are depleted. The negative Eu anomalies are more obvious in the rhyolites than andesites. The geochemical characteristics of the volcanic arc igneous rocks show that the mid-Cretaceous tectonic setting of Hainan Island can be classified as an Andean active continental margin. During the mid-Cretaceous, intermediate volcanism occurred in Hainan Island and its adjacent areas. The zircon-saturation temperatures of the acid volcanic rocks in study area exhibit relatively low values (ranging from 746°C–790°C). Unlike igneous rocks forming in the coastal area east of the South China Block at the same time, no A-type granitoids with alkaline dark minerals appear in Hainan Island. During the late Mesozoic, the western SCS, where Hainan Island was located, may not have been affected by the subduction of the paleo-Pacific Plate, but rather Neotethyan subduction which dominated the Cretaceous magmatic and tectonic activities along the western margin of the SCS. This finding helps to understand the late Mesozoic tectonic evolution of the southeastern edge of the Eurasian plate.

Two stages of Late Cretaceous to Neogene deformation of the Huayingshan tectonic belt, eastern Sichuan Basin, SW China

Two stages of Late Cretaceous to Neogene deformation of the Huayingshan tectonic belt, eastern Sichuan Basin, SW China

Geological conditions and controls on accumulation of tight sandstone gas, deep part of the Shengbei sub-sag, Turpan-Hami basin, NW China

With the further exploration of the Jurassic strata in the Turpan-Hami Basin, the targets for hydrocarbon exploration have been gradually shifted from the tectonic belts around sags to the proximal lithological zones of deep sags. Based on the systematic coring of the first exploration well (well Qintan-1) in the center Shengbei sub-sag, this study conducted experiments of organic carbon, pyrolysis, gas chromatography (GC), nuclear magnetic resonance (NMR), and low-temperature nitrogen adsorption. Then, this study systematically analyzed the geological conditions and major controlling factors for the accumulation of tight sandstone gas in the deep part of the Shengbei sub-sag. The results show that: (1) Multiple sets of coal-measure source rocks have developed in the Jurassic strata in the center Shengbei sub-sag, providing plenty of gas sources for multilayered hydrocarbon accumulation; (2) Tight sandstones have poor physical properties and complex pore structures. However, high-permeability zones and anomalous zones of nano-scale pores have developed in the deep part, providing favorable spaces for the accumulation and preservation of tight oil and gas in the deep part; (3) Compaction and late carbonate cementation are key factors in reservoir densification. The microscopic storage space and connectivity of the tight sandstone reservoirs in the Shengbei sub-sag were improved due to the dissolution of fluids in coal measure strata. The occurrence of high-quality reservoirs in the Shengbei sub-sag is significantly controlled by source rocks, and both the former and the latter are characterized by adjacent sources and reservoirs and short-distance migration and accumulation. Furthermore, the special geological phenomena of chert cementation, abnormally high homogenization temperatures of fluid inclusions, and abnormal pyrolysis parameters confirm the presence of low-temperature hydrothermal activity in the deep part of the target strata. Therefore, the center Shengbei sub-sag has geological conditions for the large-scale accumulation of primary gas and, thus, is a key area for future hydrocarbon exploration.

Сравнительная характеристика региональных сейсмогенерирующих структур Европейско-Африканского сквозного тектонического пояса

Based on new data on seismicity and materials from surveys of active faults, information was obtained on regional seismogenic structures of the European-African through tectonic belt. The kinematic characteristics of the faults that make up the through tectonic belt and earthquakes that occurred within these structures are given. An analysis of gravity anomalies based on satellite data suggests that the seismogenic structures of the European -African through tectonic belt have an ultra-deep penetration into the mantle, which determines their high seismic potential. This potential was manifested by catastrophic earthquakes in the Mediterranean-Caspian region on February 6, 2023. Afterthe earthquakes onFebruary 6, 2023,themigration ofseismic activity inthe northeast direction, inthe area ofthe Caucasus fold structure and the East European platform, was noted.

Mesozoic–Cenozoic cooling, exhumation and tectonic implications of Chaqiabeishan–Shaliuquan Li[sbnd]Be ore district in the northeastern Qinghai–Tibet Plateau

The Mesozoic-Cenozoic exhumation and deformation of the northeastern Qinghai–Tibetan Plateau generated extensive regional rugged mountains. We aimed to explore the prolonged kinematic evolutionary history since the Mesozoic. We collected Mesozoic magmatic rock samples from the Chaqiabeishan-Shaliuquan lithium‑beryllium ore district in the Northern Qaidam tectonic belt (NQTB) to constrain the cooling exhumation history using apatite fission track (AFT) thermochronology. Twenty samples yielded AFT ages from 111 to 11 Ma, including four age groups:111–103, 89–75, 71–47, and 30–11 Ma, with mean track lengths of 12.5–11.2 μm. Four thermal history phases of 120–90, 90–50, 50–20, and 20–0 Ma were established based on the inverse thermal model and isostatic adjustment of the lithosphere. Additionally, the average cooling rates of the four phases were 1.67 ± 0.17, 1.25 ± 0.13, 0.33, and 1.75 ± 0.5 °C/Myr, with a corresponding exhumation amount of 1.15 ± 0.07 km, 0.98 ± 0.06 km, 0.86 ± 0.05 km, and 1.09 ± 0.06 km respectively, and the maximum exhumation was 6.021–6.787 km since 120 Ma. In the first phase, the far-field effects of Mid-Tethys Ocean subduction and closure drove the rapid exhumation of the research area. The closure of the Neo-Tethys Oceans and the continuing collision of the India-Asia plate disturbed the northeastern plateau, inducing regional backlash fault events in the NQTB, demonstrated in the second phase of thermal history. The third phase of the stable tectonic setting is consistent with previous research results, suggesting a similar cooling history for the NQTB and Qilian Mountains, evidenced by the widespread absence of Eocene to Miocene cooling signals. The rapid exhumation and reactivation of the NQTB and Qilian thrust fault system since 20 Ma represents the final stage of growth and expansion of the northeastern Qinghai–Tibet Plateau.

Origin and tectonic setting of Cretaceous ophiolites in the Gaoligong tectonic belt, SW China: Implications for the tectonic evolution of the Bangonghu–Nujiang Meso–Tethys

Whether the ophiolites in the southeast margin of the Gaoligong tectonic belt are related to subduction or rift is hotly debated. The aim of this paper is to present the geological and geochemical data of these ophiolitic blocks in order to understand the significance of these in the tectonic evolution of the Meso–Tethys. The peridotites in the ophiolites are dominantly harzburgites with high Mg# (88.7–92.2) and low Al2O3 (<0.8 wt.%) and CaO (<0.5 wt.%) contents, and display U-shape chondrite-normalized rare-earth element patterns. However, they show two different groups of mineral chemistries and occurrences. Group I are with olivine Fo 90.6–92.3, orthopyroxene Mg# 91.0–92.6, clinopyroxene Mg# 91.1–93.3, and spinel Cr# 42.1–67.4 and Mg# 62.8–71.6. They exhumed adiabatically and were intruded by mafic dikes from the melts through low-degree melting of asthenospheric mantles and by orthopyroxenites in the Early Jurassic. Group II are with olivine Fo 89.8–95.3, orthopyroxene Mg# 91.3–94.6, and spinel Cr# 62.4–94.1 and Mg# 19.5–51.0. They underwent brittle deformation and medium- to low-temperature fluid replacement. The two group’s peridotites have experienced the similar partial melting degrees and are the fragments of subcontinental lithospheric mantles. Extensive continental affinity tholeiites erupted in the Middle Jurassic, coeval with the primary spreading time of the Bangonghu–Nujiang Ocean in the central Tibet. The peridotites, mafic rocks, and marine-facies sediments represent the opening products of the Meso–Tethys in the Jurassic as ophiolites in a continental margin.

Geochemical characterization of the metasedimentary rocks of the Yaounde Group within the southernmost North Equatorial tectonic belt: insights into geodynamic evolution

Geochemical characterization of the metasedimentary rocks of the Yaounde Group within the southernmost North Equatorial tectonic belt: insights into geodynamic evolution

The Mid-Cretaceous Tectonothermal Evolution of the Zhangbaling Tectonic Belt, East China: Evidence from Zircon (U–Th)/He and Detrital Zircon U–Pb Dating

The Zhangbaling tectonic belt (ZTB), one of the most representative tectonic belts in East China, has experienced uplift since the Early Cretaceous and is, thus, an excellent object for understanding the tectonic uplift and topographical evolution of East China and the whole of East Asia. On the basis of field observations, in this contribution to the literature, we carried out detrital zircon LA-ICP-MS U–Pb dating for the Upper Cretaceous sediments in the basins adjacent to the ZTB and zircon (U–Th)/He dating for the Early Cretaceous plutons along the western flank of this belt. Detailed field observation showed that the orthogneiss of the Feidong Complex experienced sinistral strike–slip activities, while the marbles underwent thrusting; thrust faults were developed in the Early Cretaceous plutons and volcanic rocks, and normal faults were superimposed on thrust or strike–slip faults. The detrital zircon dating results showed that the Upper Cretaceous sediments are characterized by an Early Cretaceous major cluster with just a minor cluster from the middle Neoproterozoic ages, indicating that the Zhangbaling Group and the Feidong Complex of the ZTB are not their main provenance. Zircon (U–Th)/He dating results showed that the ZTB experienced rapid uplifting during the mid-Cretaceous and recorded another rapid uplifting after 30 Ma. Combining existing research with our new data, it can be concluded that the ZTB was characterized by thrust activity in the mid-Cretaceous, which occurred under regional compression setting and was the basis of the formation of a watershed after 30 Ma.

LA–ICP–MS U–Pb geochronology and geological significance of two types of monazite in the Xinjiazui gold deposit, northwestern margin of Yangtze Block, China

The newly discovered Xinjiazui gold deposit situates on the northwestern margin of the Yangtze Block, China. Previously, the absolute age of gold metallogenesis in this area has yet to be well defined due to the lack of suitable dating minerals, significantly hindering the study of ore genesis and metallogenesis of gold deposits. This study presents high precision in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) U–Pb ages of monazite to address this issue. Two types of monazite have been found in this deposit, with Type 1 developed in the sedimentary diagenetic stage and Type 2 formed in the ore-forming stage. Type 1 monazite collected from carbonaceous slate is symbiotic with framboidal pyrite in a skeletal texture. It exhibits a high total amount of rare earth elements (REE) and low Y, Th, and U contents, indicating a low-grade metamorphic origin. In contrast, Type 2 monazite from the auriferous quartz vein is intergrown with hydrothermal mineral assemblages including free gold, Au-bearing pyrite and arsenopyrite, ankerite and sericite, suggesting a hydrothermal origin. The monazite (Type 1) LA–ICP–MS 206Pb/238U age is 460.8 ± 7.0 Ma, representing the sedimentary age of the host rock. A combination of lithologic associations and geochemical characteristics indicates that the Ordovician strata (O2ch) are important surrounding rocks in the Xinjiazui gold deposit. Additionally, the forming ages of monazite symbiotic with free gold in the auriferous quartz–sulfide veins range from 206.4 to 207.4 Ma, representing the gold mineralization age of the Xinjiazui deposit. Field geological observation shows that the vertical vein wall of columnar quartz crystals grows inward in the auriferous quartz–sulfide vein geodes and the euhedral granular sulfides develop in geodes. Therefore, this study proposes that the tectonic system changed from compression to extension in the late orogenic period with the closure of Paleo-Tethys and gold mineralization occurred in the Back-Longmenshan tectonic belt.

Evolution of Contact Metamorphic Rocks in the Zhoukoudian Area: Evidence from Phase Equilibrium Modelling

The Yanshan intraplate tectonic belt is a tectonic-active area in the central part of the North China Craton that has undergone long-term orogenic evolution. Detailed studies on magmatic activity and metamorphism of this belt are significant for restoring its orogenic thermal evolution process. The Fangshan pluton in the Zhoukoudian area within this tectonic belt is a product of the late Mesozoic Yanshan event. However, there is a lack of detailed research on the metamorphic evolution history of the ancient terrane surrounding the Fangshan pluton subjected to contact thermal metamorphism. To further constrain the metamorphic P–T evolution of contact metamorphism associated with the Fangshan pluton, we collected rock samples in the andalusite–biotite contact metamorphic zone of the Fangshan pluton, and conducted petrographic investigations, geochemical and mineral composition analysis, and phase equilibrium modeling. The phase equilibrium modeling in the MnO–Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O system indicates that the peak mineral assemblages of andalusite–biotite schists are pl + q + mu + bi + and ± kfs + ilm + mt, formed at 550 to 610 °C, 1 to 3.5 kbar, and the peak mineral assemblage of garnet–andalusite–cordierite–biotite schists is gt + pl + q + bi + and + cord + ilm + mt, formed at 580 to 620 °C, 1.5 to 2.1 kbar. Therefore, we believe that the rocks in the andalusite biotite contact metamorphic zone of the Fangshan pluton underwent low pressure and medium temperature metamorphism, with the peak metamorphic conditions of about 550–610 °C, &lt;3.5 kbar. The results show that the rocks in contact with the thermal metamorphic zone were rapidly heated by the heat released by the Fangshan pluton, and after reaching the peak metamorphic temperature, they were cooled down simultaneously with the cooling of the rock mass, defined in a nearly isobaric P–T trajectory.

Distribution, evolution and structural properties of Wushenqi paleo-uplift in Ordos Basin, NW China

This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny (Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55–94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170–196 m and 11 298 kmbrespectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle–Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma4 Member–pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.

Characteristics and genetic mechanism of the Mesoproterozoic rift system, Ordos Basin, China

The Mesoproterozoic rifts are developed in the Ordos Basin located in the western margin of the North China Plate. Based on the latest 3D seismic data and previous research results, this study intends to discuss the zonal differential deformation characteristics and genetic mechanism of the Mesoproterozoic rifts in the Ordos Basin. NE-trending rifts are developed in the Mesoproterozoic in the south-central Ordos Basin, the main part of which are located near the western margin of the North China Plate. NNW-trending rifts are developed in the north of the basin, while NW-NNW rifts in the Mesoproterozoic in Hangjinqi area. The genetic mechanism of the Mesoproterozoic rifts is related to regional extensional stress field, plate boundary conditions and internal preexisting structures. The main extensional stress direction strikes NWW-SSE (120°) in the western margin of the North China Plate, based on the forward rift trend of the northern Mesoproterozoic. In Hangjinqi area, the reactivation of the existing NW-trending Wulansu fault and NW-NW-trending Daolao fault, results in dextral shear stress field. The boundary between the western margin of the North China Plate and its adjacent plates forms a nearly NS-trending preexisting basement tectonic belt, which intersects with the NWW-SSE (120°) extensional stress at an acute angle of 60°. Therefore, the western margin of the North China Plate is formed by oblique normal faults under oblique extension. Due to the long time span of Columbia Supercontinent breakup (1.8–1.6 Ga), the oblique rift in the south-central Ordos Basin is formed under the continuous oblique extension at the western margin of the North China Plate.

Back-arc suture zone along the north margin of the eastern Cimmerian continent

The Cimmerian continent is the north piece of the Gondwana super-continent collaged to the south edge of the Laurasia super-continent during the closure of the Paleo-Tehyan Ocean. Researchers recently have identified the Rushan-Pshart-Longmu Co-Shuanghu-Bitu-Changning-Menglian-Inthanon suture zone as the northern boundary of the eastern Cimmerian continent. However, a detailed correlation of this complicated tectonic zone from Pamir to Sumatra remains unclear. For example, while a back-arc suture is developed in southeast Tibet and Southeast Asia, no evidence of the same suture has been reported in eastern and central Tibet. In this study, we investigate an ophiolite mélange suite exposed in the Deqin back-arc suture of this tectonic zone in eastern Tibet, and interpret it as the northward extension of the Jinghong-Nan River back-arc suture. The mélange includes serpentinites, gabbros, basalts, and minor abysmal radiolarian-bearing cherts, and these rocks appear as isolated blocks in fault contact with Permian strata. Geochemical data of the serpentinites from the Deqin suture and Bitu suture indicate that they are MOR-type and SSZ-type sutures, respectively. Zircon UPb dating of the gabbro and diorite from the Deqin suture yields crystallization ages ranging from ca. 246 Ma to ca. 276 Ma, and a zircon UPb age of ca. 285 Ma is obtained from the Bitu suture. Geochemical analysis shows that the rocks from the Deqin suture have OIB or MORB characteristics, suggesting southwest subduction of the oceanic lithosphere beneath the North Lancangjiang tectonic belt since the Middle Permian. Two Meso-Tethyan magmatic rock samples from the Bitu and the Deqin sutures crystalized at 114 Ma and 111 Ma, respectively, and their geochemical data indicate OIB-type signature. We conclude that the Bangong Co-Nujiang Ocean lithosphere subducted northeastward beneath the Qamdo terrane at a low angle. Based on the correlation between the Rushan-Pshart suture and the Longmu Co-Shuanghu suture, our pre-Cenozoic plate reconstruction suggests that the Karakorum fault right-laterally offset the northern boundary of the Cimmerian continent by 140 ± 10 km. The offset further implies that the Cenozoic deformation of the Tibetan plateau is accommodated mainly by distributed structures rather than by several discrete fault systems.

Metamorphic P–T conditions, in‐situ LA–ICP–MS biotite–muscovite Rb–Sr geochronology and tectonic implications of two‐mica–quartz schist from the Kuanping Group in the North Qinling Orogenic Belt

The Kuanping Group is an important lithotectonic unit in the North Qinling Tectonic Belt, which has experienced metamorphism from greenschist to high amphibolite facies and is of great significance in defining the orogenic process of the Qinling Orogenic Belt. This study presents the results of petrology, geothermobarometry, phase equilibrium modelling, in‐situ laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) biotite–muscovite Rb–Sr analysis, for the two‐mica–quartz schist of the Kuanping Group in the Hongtuling and Heihe areas. These results are employed to better understand their metamorphic P–T conditions and ages, as well as geological implications. Garnet‐bearing two‐mica–quartz schist in the Hongtuling area records a clockwise P–T trajectory on the basis of phase equilibrium modelling, with peak P–T conditions of ~600°C and ~0.85 GPa. In addition, the Ti‐in‐biotite thermometry yielded metamorphic temperature conditions of ~578°C–580°C and ~590°C–596°C for the garnet‐bearing two‐mica–quartz schist from the Hongtuling area and the two‐mica–quartz schist from the Heihe area, respectively. These results indicate that metamorphic temperature conditions in both areas are higher than the closure temperature of the Rb–Sr isotopic system of muscovite and biotite. In‐situ LA–ICP–MS biotite and muscovite Rb–Sr analyses yielded three groups of isochron age, i.e., ca. 410 Ma, ca. 360 Ma and ca. 320–300 Ma. On the basis of previously published data and the data in this study, the Kuanping Group underwent ca. 440 Ma regional metamorphism in the NQB, retrograde cooling at ca. 410–360 Ma due to exhumation and ca. 320–300 Ma tectonothermal overprinting.

Geochronology, pyrite trace elements, and sulfur isotope geochemical characteristics of the Saibagou gold deposit in the eastern part of the northern Qaidam Basin

Introduction: The Saibagou gold deposit, located in the eastern part of the tectonic belt of the northern Qaidam Basin in western China, has its gold ore bodies strictly controlled by the regional fault system. Despite this understanding, there remain controversies surrounding the deposit’s metallogenic epochs, sources of ore-forming materials, and properties of ore-forming fluids. To address these controversy, the metallogenic process of the Saibagou gold deposit can be further determined by analyzing the U-Pb ages of hydrothermal zircons in the gold-bearing quartz veins and investigating the trace element and sulfur isotope compositions of pyrite in the gold deposit.Methods: This study does not focus on the mineral characteristics susceptible to interference by the metallogenic condition in gold ore bodies. Instead, it offers a detailed discussion on stable associated minerals and their indicative markers formed in the process of gold mineralization.Results: The results of this study showed that the metallogenic process of the gold deposit can be categorized into the following stages: 1) quartz–pyrite veins, 2) milky-white quartz—pyrite—native gold veins, 3) hoary quartz—native gold—polymetallic sulfide veins. As indicated by the U-Pb ages of hydrothermal zircons in the gold-bearing quartz veins, the Saibagou gold deposit has two metallogenic ages, namely, 423.91 ± 4.5 Ma (the Silurian) and 470.18 ± 4.92 Ma (the Ordovician).Discussion: The Silurian metallogenic age, predominates and nearly aligns with the expansion of the regional NWW-trending brittle-ductile shear zone, followed by the Ordovician metallogenic age. Data on the trace elements and sulfur isotopes of pyrite, show that the Saibagou gold deposit has similar pyrite compositions in the three metallogenic stages. Gold in the deposit primarily occurs as native gold or minor petzite inclusions and has a very low lattice gold concentration. As indicated by the concentrations of elements such as Co, Ni, and as in the pyrite, as well as the variation range of δ34S values, the ore-forming fluids were derived from low-temperature arsenic-bearing acidic magmas. In addition, the primary ore-forming materials appear to encompass mantle-derived materials from the deep earth.

Crustal structure and geodynamics of the eastern Qilian orogenic belt, NE margin of the Qinghai-Tibet plateau, revealed by teleseismic receiver function

The eastern segment of the Qilian orogenic belt, comprising the Linxia block and Longzhong block, is at the Qinghai–Tibet Plateau’s northeastern margin. The area has experienced multiple tectonic events, including closure of the Qilian Ocean, convergence of the North China block and Qilian terrane, and collision of the Indian and Eurasian plates, forming a complex tectonic framework. To investigate the area’s geological evolution and the suture’s current location between the blocks, we used 3-year data recorded by 33 portable ChinArray II broadband stations (2013–2016). Using three teleseismic P-wave receiver function methods, H-κ stacking and common conversion point stacking (CCP), crustal structure, Poisson’s ratio, and Moho morphology were obtained at 33 stations. The results are described as follows: 1) The Maxianshan fault is an important boundary fault that divides the Linxia block and Longzhong block. The Linxia block’s layered crustal structure is obvious, and there is a low-velocity anomaly in the middle and lower crust, which may contain saline fluid and has Japanese-type island arc characteristics. 2) The layered structure of the Longzhong block’s upper crust is significant, while the middle and lower crust’s layered structure is weak with weak low-velocity characteristics and oceanic-island basaltic crust characteristics. The Longzhong block may have originally been formed by Mariana-type island arcs. 3) The Conrad interface and Moho lateral variation in the Ordos block’s southwestern margin are weak, showing stable craton characteristics. 4) Our results show that the Maxianshan fault cuts through the Earth’s crust and is a continuous west-dipping negative seismic phase in the Common Conversion Point section. The fault zone is the suture line between the Linxia block and Longzhong block. 5) The middle and upper crust of the Liupanshan tectonic belt is thrust upwards on the Ordos block’s southwestern margin, providing deep structural evidence of the Cenozoic uplift of the Liupanshan structural belt.

Azimuthal Anisotropy of Receiver Functions in the Central South China Block and its Tectonic Implications

By the H-к stacking of the receiver functions and the splitting of the Pms phases, using seismic data from the Regional Seismic Network and the Huanan Seismic Array, a high-resolution temporary seismic array deployed for 2 years in the study area. This study revealed the strong lateral heterogeneity in crustal structures in the central South China block. Crustal thickness reduces from northwest to southeast, with significant differences across the boundary of sub-blocks. The average crustal Vp/Vs ratio gradually increases from west to east, leading to high values in the coastal region, which suggests that the subduction of the Pacific plate has possibly caused the underplating of magma or the upwelling of upper mantle material. The crustal azimuthal anisotropy of the Dabie orogen and the Jiangnan orogen is generally consistent with the strike of the tectonic belt as well as with the orientation of the absolute plate movement. We suggest that the crustal azimuthal anisotropy of the orogen is related to the extension and deformation of the lithosphere. The anisotropy in the crust is close related to crustal deformation. The orientation in the crust and the upper mantle in the Cathaysia block are generally consistent with the orientation of the absolute plate motion, indicating that the azimuthal anisotropy of the Cathaysia block is related to lithospheric deformation and the under-invasion of upper mantle material.

Petrogenesis and Geodynamic Significance of the Early Triassic Nanpo Adakitic Pluton of the Luang Prabang-Loei Tectonic Belt (Northwestern Laos) in the East Tethys Domain: Constraints from Zircon U-Pb-Hf Isotope Analyses and Whole-Rock Geochemistry

Adakites are magmatic rocks with specific geochemical characteristics and specific dynamics that provide important clues to understanding the magmatic-tectonic evolution of orogenic belts. We studied the Early Triassic Nanpo adakitic pluton of the Luang Prabang-Loei tectonic belt in the Eastern Tethys domain (Laos Sarakan) using detailed petrological, zircon U-Pb chronological, whole-rock geochemical, and zircon Lu-Hf isotope studies to constrain their petrogenesis. The rocks are predominantly diorites and granodiorites with Early Triassic zircon U-Pb emplacement ages ranging from 247.9 ± 1.0 to 249.0 ± 2.4 Ma. Moderate SiO2 (56.26–65.95 wt%) and Na2O (3.24–5.00 wt%) contents, with Na2O/K2O values between 1.76 and 2.51 and A/CNK values between 0.81 and 0.94, indicate that the rocks belong to the metaluminous calc-alkaline rock series. The high Sr content (590–918 ppm), low Y (6.30–11.89 ppm) and Yb (1.99–3.44 ppm) contents, intermediate Mg# (42–50) values, and high Sr/Y and (La/Yb) N ratios (Sr/Y = 24–41, (La/Yb) N = 6.84–13.8) are typical for adakites. Zircon Hf isotope analysis shows a significant variation in the εHf(t) values (6.7–12.0), with a mean value of 9.4 and a TDM2 of 512–845 Ma. Geochemical evidence indicates that the Nanpo adakitic rock was formed by the partial melting of the thickened lower crust in the plate-breaking environment and has an important contribution to the underplated mantle-derived magma. We propose that the Early Triassic adakites in the Luang Prabang-Loei tectonic belt formed during the transition from subduction to a continental collision, and the mixing of crust- and mantle-derived magmas is the main mechanism for the growth of continental crust in the Paleo-Tethys orogenic belt of southeastern Asia.