Stages Of Tectonic Evolution Research Articles

Geochemical and chronological evidence for collision of proto-Yap arc/Caroline plateau and rejuvenated plate subduction at Yap trench

The Yap Arc was considered to have derived from the proto-Yap-Izu Bonin-Mariana arc system. It is a rare example of subduction of an oceanic plateau with short arc–trench distance and consists mainly of metamorphic rocks, which are distinct from the Izu Bonin-Mariana arc system. However, it is not known on the origin and formation time of the basement rocks of the Yap Arc. For the first time, in this study we provide the results of radiometric age-dating and whole-rock major element, trace element and Sr–Nd–Pb–Hf isotope analyses for the metamorphic basement rocks (amphibolites) of the Yap Arc. These rock samples can be classified into three groups based on their major and trace element compositions. Group 1 samples have strong depletion of LREEs and a Dupal-type isotopic signature, and they represent forearc basalts (FABs) of the nascent Yap forearc. Group 2 samples have an alkali basalt-like geochemistry and oceanic island basalts (OIBs) type trace element patterns, and they represent the basalts of the Caroline Plateau. Group 3 samples have island-arc-type negative anomalies of Nb–Ta–Zr–Hf, and they may represent the volcanic rocks of the proto-Yap Arc. These amphibolites were formed at 21 Ma according to 40Ar/39Ar amphibole dating and in situ SIMS UPb titanite dating, and they record the timing of the collisional event between the Caroline Plateau and the proto-Yap Arc. We propose that the Yap arc has been evolving distinctly from the Izu-Bonin-Mariana Arc since this collision time. These rocks were metamorphosed and brought onto the present Yap Arc as a result of the collision between the proto-Yap Arc and the Caroline Plateau. Based on the new results of age-dating and geochemistry of this study, we propose three stages of tectonic evolution for the Yap Arc as a result of collision from the Caroline plateau: an early stage (proto-Yap Arc) of subduction of the Caroline Plate, collision of the proto-Yap Arc with the in-coming young Caroline Plateau, and rejuvenated plate subduction at the Yap Trench with limited volcanism.

Age and Geodynamic Conditions of Formation for the Neoproterozoic Gold-Bearing Granitoids in the Eastern Sayan

The paper discusses the results of petrogeochemical and geochronological studies of the Tainsky granitoid stock containing the Tainsky gold deposit in the East Sayan. The Tainsky granitoid stock intrudes through ultrabasites of the Ospa-Kitoi ultrabasitic massif. Granitoids are the part of the ophiolite cover which overlap Archean basement rocks of the Tuva-Mongolian microcontinent of the Archean foundation. Consistent isotopic age values in the range of 850–860 Ma obtained by three independent methods (U–Pb, Re–Os, 40Ar/39Ar) are evidence of the Neoproterozoic age of granitoid magmatism and its genetic relationship with gold–(±copper)–porphyry mineralization. The geological setting, geochemical characteristics, and age of the Tainsky granitoid stock allow us to attribute these rocks to the Neoproterozoic Dunzhugur island arc sequences. Isotopic age values obtained by Rb–Sr and 40Ar/39Ar methods characterized by lower closure temperatures of isotopic systems make it possible to distinguish several tectonothermal events at 650, 435, 339–333, and 280–223 Ma, reflecting difference stages of tectonic evolution of the Eastern Sayan segment of the Central Asian folding belt.

Insights into post-orogenic extension and opening of the Palaeo-Tethys Ocean recorded by an Early Devonian core complex in South China

The Palaeo-Tethys Ocean formed during the Devonian as a consequence of blocks separating from northern Gondwana. The record of the Palaeo-Tethys Ocean stretches across Eurasia from the European Alps eastward to the southwestern South China block (SCB). Tectonic domes of the SCB record the contraction, extension, decompression, and partial melting of deep crust that occurred as a result of detachment faulting and tectonic evolution of the Palaeo-Tethys Ocean. This study investigates post-orogenic (Kwangsian) extension and opening of the Palaeo-Tethys Ocean as recorded by the Motianling core complex in the southwestern SCB, based on structural analysis and 40Ar/39Ar geochronology. The Motianling core complex in the southernmost part of the Jiangnan fold belt comprises the Sanfang gneissic granite surrounded by low-grade metasedimentary rocks. The core complex records at least three deformation (D) events: pre-D1, D1, and D2. The pre-D1 event produced large-scale NE-striking folds with axial surface cleavages and was coeval with emplacement of the Sanfang batholith. D1 deformation is represented by a top-to-the-NW ductile–brittle normal faulting system with mylonitic foliation and was coincident with greenschist-facies metamorphism, indicating that the core complex formed during NW–SE extension. D2 deformation is dominated by Cenozoic NW–SE-trending normal faults. The timing of D1 deformation and subsequent cooling was constrained by 40Ar/39Ar geochronology. Syn-kinematic muscovite yields an 40Ar/39Ar age of 417 ± 2.3 Ma (1σ) and suggests that the dome was initially developed in the Early Devonian through ductile shear zones. Magmatic biotite from the granitic mylonite yields a weighted mean 40Ar/39Ar age of 363.0 ± 3.1 Ma. Therefore, the Motianling core complex records at least two major stages of tectonic evolution: (1) Kwangsian (Caledonian) orogenic collapse and subsequent first-stage cooling at ∼417 to 363 Ma; and (2) Cenozoic regional extension and final cooling at ca. 45 Ma, as inferred from published apatite fission track data. The present results, combined with previous studies, indicate that the D1 deformation event resulted in the formation and exhumation of the Motianling core complex in a continental rifted margin during the opening of the Palaeo-Tethys Ocean.

АДАПТАЦІЯ МЕТОДИКИ СТРУКТУРНО-МОРФОМЕТРИЧНОГО АНАЛІЗУ ДО СЕРЕДОВИЩА ГІС ДЛЯ ПАЛЕОГЕОМОРФОЛОГІЧНИХ ДОСЛІДЖЕНЬ КАНІВСЬКОГО ПРИДНІПРОВ'Я

Kaniv Dnieper area is a unique region that has evolved through the Neogene-Quaternary phase. The application of geological and geomorphological methods, remote sensing data and GIS made it possible to identify the genetic relationship between the processes of geomorphogenesis and tectogenesis within the Kaniv Dnieper region, to build a number of geological and geomorphological models. The methodology of structural-morphometric analysis is adapted to the GIS and the process of cartometric constructions is automated. An algorithm for creating order maps of valleys and basal surfaces has been developed. Basal surfaces are complex surfaces that combine local erosion bases and express the total movements of the earth's crust over various time intervals. A study of the morphogenesis and tectogenesis of the territory of the Kaniv Dnieper region showed that the neotectonic movements within this region had a differentiated character. Five stages of tectonic evolution were determined during the Neogene-Quaternary stage of its development. Hypsometry of basic surfaces of five orders was investigated, and a detailed comparison of the morphology of single-order surfaces has been made. On the basis of the obtained data on the nature of the surfaces, absolute and relative elevations, the nature of the isobasite pattern, the geomorphological structure of each stage has been analyzed in detail. The conducted studies revealed a regular relationship between the relief and tectonics.

Subduction and closing evolutionary mode in western Xar Moron suture zone

The Xar Moron suture zone is located on the suture of North China Craton and Siberian Craton, which is one of the research hotspots in the Geoscience. In this paper, the western section of the Xar Moron suture zone is taken as the research object. Based on geological and geodynamic analysis, the tectonic and evolution stages of the study area were divided, the evolution model of the subduction and closure of the Paleo-Asian Ocean in the study area, the collision of plates and plates is established. The results show that Xar Moron fault is a suture, and there are obvious differences between the crustal structures on both sides of the fault, outcrop volcanic rocks are distinguished by high potassium calcium alkaline series and their magmatic source is a mixture of crust source and mantle source. The study area is divided into four tectonic evolution stages, C2-P2, P2-P3, P3-T3 and After T3 stage. It is estimated that in the late Permian to early Triassic, Paleo-Asian Ocean has experienced the post-arc dilation, the arc-continent collision and the pre-arc accretion stage. It established the subduction and closing evolutionary mode of the Paleo-Asian Ocean in the Xar Moron suture zone, which provide a reference for the study of the dynamic mechanism of the formation of the fault zone.

Detrital zircon U–Pb dating and Hf isotope study of late Palaeozoic sedimentary rocks in central–eastern Jilin Province, NE China: Constraints for tectonic evolution of the eastern segment of the Paleo‐Asian Ocean

This paper reports in situ U–Pb ages and Hf isotopic data on detrital zircons from Palaeozoic strata in central‐eastern Jilin Province, NE China, with the aim of constraining the timing of final closure of the Paleo‐Asian Ocean and the tectonic evolution of the eastern segment of the Central Asian Orogenic Belt (CAOB). Zircons from Middle to Late Permian Fanjiatun and Yangjiagou formations in central Jilin Province are characterized by four major groups of age populations (2.5–2.3 Ga, 1.9–1.7 Ga, 1.3–1.0 Ga, and Late Palaeozoic ages). The Paleo‐Mesoproterozoic and Cambrian zircons have positive εHf(t) values, suggesting that the source was mainly locally derived from the CAOB, whereas a lesser amount of Archean zircons with positive εHf(t) values, indicating that source from the North China Craton (NCC). The Phanerozoic zircons have both positive and negative εHf(t) values indicates that material from bidirectional provenances in the CAOB and the NCC. However, Late Permian Kaishantun Formation in eastern Jilin Province contain a single group of Phanerozoic zircons with positive εHf(t) values, distinct from known igneous zircons in the NCC, suggesting a local source. These observations, along with the results of previous studies on Middle–Late Permian igneous rocks in Jilin Province, indicate that the eastern segment of the Paleo‐Asian Ocean underwent the initial closure in central Jilin Province during the Middle Permian and the final closure in eastern Jilin Province in the Late Permian–Early Triassic. The detrital zircon geochronological data clearly record two stages of tectonic evolution and the scissor‐like closure model of the Paleo‐Asian Ocean in the eastern segment of the CAOB.

From Kenorland to modern continents: tectonics and metallogeny

There are three stages in tectonic evolution of the Earth: (1) nucleation — from origin of protocratons to their assembly into Supercontinent Kenorland (2.7–2.5 Ga); (2) cratonization — from breakup of Kenorland (2.45 Ga) to the assembly of Columbia (1.85 Ga) and its reorganization into Rodinia (1.0–0.72 Ga); (3) modern plate tectonics — from breakup of Rodinia at 720 Ma until present. Analysis of time-space reorganizations of Archean granulite-gneiss terranes, which correspond to continental lithospheric keels, reveals five groups of protocratons (Nena, Ur, Congo-Sahara, NAsia and Atlantica) that remained almost intact during long time intervals.
 After the breakup of Kenorland, the continental crust rotated counter-clockwise. NAsia and Atlantica the least rotated and drifted relative to Nena, however the latter was rotated by 180°. Congo-Sahara, Ur and Kalahari were the most rotated. The assembly and breakup of the supercontinents clearly correlates with secular changes in dominant types of base, precious and ferrous metal deposits, as well as formation and emplacement of diamonds.

From Kenorland to Modern Continents: Tectonics and Metallogeny

There are three stages in tectonic evolution of the Earth: (1) nucleation, from the origin of protocratons to their assembly into the Kenorland supercontinent (2.7–2.5 Ga); (2) cratonization, from the breakup of Kenorland (2.45 Ga) to the assembly of Columbia (1.85 Ga) and its reorganization into Rodinia (1.0–0.72 Ga); and (3) modern plate tectonics, from the breakup of Rodinia 720 Ma until the present. Analysis of the time-space reorganizations of Archean granulite–gneiss terranes, which correspond to continental lithospheric keels, reveals five groups of protocratons (Nena, Ur, Congo–Sahara, NAsia and Atlantica) that remained almost intact during long time intervals. After the breakup of Kenorland, the continental crust rotated counterclockwise. NAsia and Atlantica rotated the least and drifted relative to Nena; however, the latter rotated by 180○. Congo‒Sahara, Ur, and Kalahari rotated the most. The assembly and breakup of the supercontinents clearly correlates with secular changes in dominant types of base, precious, and ferrous metal deposits, as well as the formation and emplacement of diamonds.

Stratigraphic architectures and associated unconformities of Pearl River Mouth basin during rifting and lithospheric breakup of the South China Sea

The lithosphere breakup processes from initial rifting of the crust to the complete rupture of the lithosphere underwent several tectonic evolution stages and resulted in the formation of a distinct stratigraphic architecture and associated unconformities. In this study, a dense grid of seismic profiles tied to industrial borehole data are used to investigate the stratigraphic architecture and unconformity interfaces in the Pearl River Mouth basin of the northern South China Sea margin. The Pearl River Mouth typed rifted margin evolved from stretching, thinning, to finally seafloor spreading. Our results indicate that a distinct stratigraphic architecture with well defined unconformities are formed in the proximal to distal zone of the margin. The syn-rift strata have been constrained by the top of basement unconformity and the lithosphere breakup unconformity. Polyphase rift strata during lithospheric rupture process are mainly controlled by two fault patterns, high-angle normal faults and low-angle detachment faults. In the proximal domain, multiple episodes of syn-rift strata are characterized by vertical superimposed half-graben or graben type stratigraphic patterns separated by crack-related unconformity. However, in the more distal zones, syn-rift strata composed two distinct intervals separated by detachment-related unconformity, including small-scaled dispersed half-graben or graben at the lower part and large-scaled wide syn-detachment depression at the upper part. Based on these observations we provide an effective method for the correlation of sedimentary strata from the proximal to distal domains of the passive rifted margins during the lithospheric rupture process.

The Cenozoic tectonic evolution of the faulted basins in the northern margin of the Eastern Qinling Mountains, Central China: Constraints from fault kinematic analysis

A series of NE and NW-trending Cenozoic faulted basins, located at the north margin of the Eastern Qinling Mountains, document Cenozoic intracontinental extension process in Central China. Based on fault kinematic analysis of the faulted basins, coupling with the stratigraphic sequence, we rebuilt a tectonic stress sequence of the faulted basins since the Cenozoic era. Combined with the previous chronological data, we define the Cenozoic faulted basin formation process including two stages of tectonic evolution. The first stage largely presents the NW-SE extensional rifting in a long period from the Paleocene to the Middle-Late Miocene due to northwestward subduction of the Pacific plate. It is marked by the basin occurrence along the north margin of the Eastern Qinling Mountains (e.g., the Sanmenxia, Lushi, Shangluo, and Weihe Basins) in the Paleocene to the Early-Middle Miocene in accordance with a NW-SE extension, and regional basin inversion in the Middle Miocene as the result of a NW-SE compression. The second stage is featured by the three-episode extension since the Middle-Late Miocene, which is probably affected by the combination of the northeastward growth of the Tibetan Plateau and the northwestward subduction of the Pacific Plate. The earliest episode of NW-SE extension caused by regional NE-SW compression in the Late Miocene to Early Pleistocene, which leads to the formation of the Yuncheng Basin. A gentle NE-SW extension subsequently dominated here in the Late Pleistocene, as represented by the widespread appearance of paleo-lakes in the basins. Then the youngest tectonic regime controlled this region, characteristic of a tectonic transpression (ENE-SWS compression and NNW-SSE extension), causing evidently strike-slip activities on the primary faults in the basins.

Correlation of lithospheric “de‐rooting” of the Sulu‐Dabie Orogen to tectonic‐sedimentary process of the Hefei Basin: Constraints from Mesozoic coupling of basin and orogen

The lithospheric “de‐rooting” of the Sulu‐Dabie Orogen (SDO) is an important tectonic mechanism for post‐orogenic tectono‐magmatism, which influenced the sedimentation, evolution, and development of oil–gas accumulation in the Hefei Basin (HB). Combined with seismic, geological, and sedimentary data of the HB and the SDO, this paper studies the coupling of the HB and the SDO since the Late Mesozoic. While the North China Block (NCB) indented south‐eastwards under the Greater South China Block (GSCB) since the Mesozoic, the SDO underwent three intense tectonic stages, i.e., subduction, exhumation, and uplift. The upwelling of deep mantle material causes the exhumation of the ultrahigh‐pressure metamorphic (UHPM) rocks to the upper crust or surface, forming the UHPM. Influenced by the indentation of the NCB, the “de‐rooting” of the SDO lithosphere, caused the delamination and thinning of the lithosphere, accompanied by the continuous flexural subsidence in the HB. The basin underwent at least four stages of tectonic evolution, involving sequentially: the flexural basin, the foreland basin, the strike‐slip‐related basin, and the faulted graben development periods. The tectonic evolution of the HB was closely coupled with the SDO orogeny. The “de‐rooting” of the SDO lithosphere resulted in a strong uplift and erosion of the orogen, providing abundant source of material for the HB and causing the successively northwards migration of basin depocenters at its early stage. Finally, influenced by the subduction retreat of the (Palaeo‐) Pacific Plate and the strike‐slip movement of the Tanlu Fault, the depocenters migrated to the east.

Early-Middle Paleozoic volcanic rocks from the Ereendavaa terrane (Tsarigiin gol area, NE Mongolia) with implications for tectonic evolution of the Kherlen massif

We report our newly obtained geochronological and geochemical data of volcanic rocks in the Tsarigiin gol area, Ereendavaa terrane to better understand of the Early-Middle Paleozoic tectonic evolution of the Kherlen massif, NE Mongolia. LA-ICP-MS zircon U-Pb dating reveals two stages of magmatism in the southern part of the Ereendavaa terrane: one in Late Ordovician (∼462 to 455 Ma) and the other in Early Devonian (∼418 Ma). The Late Ordovician Tsarig volcanic rocks are medium to high-K calc-alkaline and intermediate to felsic in composition and characterized by relative enrichment of LREE and LILEs (e.g., Rb and U) and also by relative depletion of HFSEs (e.g. Nb, Ta, P and Ti), a typical feature of subduction-related magmas. These rocks have mostly positive whole-rock ƐNd(t) (+1.65 to +1.35) and zircon ƐHf(t) (+0.1 to +4.07) values with Mesoproterozoic Nd and Hf model ages of 1.59–1.09 Ga. They were likely generated in a continental arc setting, and their parental magmas were originated from a common source as the product of extensive fractional crystallization of mafic melts and their interaction with arc crust.The Early Devonian Chandmana volcanic rocks consist of rhyolite and minor trachybasalt, displaying a typical bimodal distribution. The trachybasaltic rocks are characterized by low Lan/Smn (2.08–2.60), Tbn/Ybn (1.42–1.50) and La/Yb (7.51–8.96) ratios and relatively flat MREE to HREE patterns with ƐNd(t) values being close to zero (−1.36 to +0.13). The rhyolites are high-K calc-alkaline and possess variably negative ƐHf(t) (−4.96 to −0.29) and ƐNd(t) (−2.14 to −0.57) values, exhibiting a strong affinity to A2-type granites. Considering the distinct compositional gap between the end-members and geochemical and isotopic signature of the bimodal suite, the felsic magma is interpreted to have derived from partial melting of a hybrid crustal source composed of both Pre-Neoproterozoic and juvenile crustal materials, while the mafic rocks were probably derived from a mantle source previously metasomatized by slab-derived melt.The two phases of magmatism in the southern part of the Ereendavaa terrane reflected two stages of tectonic evolution: Early-Middle Paleozoic subduction of the Paleo-Asian Ocean plate that gave rise to the Late Neoproterozoic-Early Cambrian Undur-Khaan island arc and Late Cambrian to Late Ordovician Ereendavaa active continental margin. Silurian amalgamation of the Ereendavaa and Idermeg terranes (Kherlen massif) caused the break-off of the subducted slab and the Early to Middle Devonian extension in the area.

Cenozoic tectonic evolution of the East China Sea Shelf Basin and its coupling relationships with the Pacific Plate subduction

The East China Sea Shelf Basin is one of the Mesozoic-Cenozoic basins located in the edge of eastern China continent whose formation and evolution are closely related to the subduction of the Pacific Plate. However, the underlying correlations between the tectonic evolution of the East China Sea Shelf Basin and the Pacific Plate subduction (65 Ma to present) remain poorly understood. In this paper, the basin is divided into western and eastern depression groups to further study its tectonic evolution. In combination with the characteristics of Pacific Plate subduction, this paper performs a coupling analysis of the basin evolution regarding its migration direction and evolution rate. The results of balanced section and deformation rate analyses reveal that the East China Sea Shelf Basin experienced different regional activities during the Cenozoic, which could be summarized as four geologic periods and three tectonic evolution stages. In this interpretation, it is recognized that tectonic activity occurred in the western depression group and then shifted to depocenters of the eastern group. In contrast, the Pacific Plate subducted westwards beneath the Eurasian Plate over the same geologic time span. Surprisingly, a slightly negative correlation between the intensity of the tectonic deformation of the East China Sea Shelf Basin and the subduction rate of the Pacific Plate is demonstrated when the subduction rate is no more than 75 mm/a. However, the basin deformation intensity increases with the plate subduction rate after 75 mm/a. The results of this work have implications for explaining the major role that the subduction of the Pacific Plate played in the formation and evolution of the eastern China basins.

Deciphering the origin of the Cenozoic intracontinental rifting and volcanism in eastern China using integrated evidence from the Jianghan Basin

Intracontinental rifting and low-volume volcanism are a globally common phenomenon, yet the underlying driving mechanisms and whether they can be explained through classic plate tectonic concepts, remain hotly debated. A prominent example is the Cenozoic rift and volcanic province in eastern China. Using an integration of geological, geophysical and geochemical data, we unravel the spatial and temporal variations of the rifting and volcanism in the Jianghan Basin. Both rifting and volcanism in the Jianghan Basin show two intense-to-weak cycles (65–50 Ma and 50–26 Ma, respectively) with significant enhancement in activity during the late rift phase. Moreover, rifting and depocentres progressively migrated eastward. The Jianghan basalts all share an asthenospheric origin while the source of the late phase basalts is slightly more enriched and heterogenous in Nd-Hf isotopes than that of the early phase basalts. The late phase basalts also display a smaller extent of partial melting even under a thinner lithosphere, likely indicating a significant decrease of volatile content in the mantle source. Based on regional tectonic correlations, the main stages of tectonic evolution of the Jianghan Basin and eastern China are not synchronous with changes in Pacific plate motion, while they are coincident with India-Asia collision processes. These observations lead us to propose that the asthenospheric flow driven by India-Asia collision rather than the rollback of the subducted Pacific slab has caused the widespread rifting and volcanism in eastern China. The variations of rifting and volcanism in the Jianghan Basin suggest a multiphase and eastward asthenospheric flow beneath eastern China driven by India-Asia collision, with an intense upwelling when passing through the North-South Gravity Lineament (NSGL). The much more intense rifting and volcanism during the late rift phase may indicate a much larger scale of volatile-poor asthenospheric flow than the early rift phase which could result in a more intense erosion of ancient enriched lithospheric mantle and the volatile content in the mantle source dropping sharply. This study provides an improved model based on our multidisciplinary observations for asthenospheric flow which may be an alternative driving mechanism for intracontinental rifting and low-volume volcanism in the regions where there are step changes in lithospheric thickness globally.

Multiple-phase tectonic superposition and reworking in the Junggar Basin of northwestern China—Implications for deep-seated petroleum exploration

The Junggar Basin is one of the major petroliferous basins in Northwest China, where deeper hydrocarbon exploration has become an inevitable trend for resource development. In this paper, the structural features and tectonic evolution of the Junggar Basin are discussed based on seismic profiles, drilling data, isochore maps, and additional balanced cross sections. Our results suggest that the basin has undergone five extension-to-compression stages of tectonic evolution since the Permian. The Junggar Basin initially developed from several isolated continental rifts in the early Permian. At the beginning of the middle Permian, the basin developed into a more integrated terrigenous lake basin with the deposition of fine-grained, organic-rich lacustrine sediments; the basin inverted during the late Permian compressional uplifting. Then the sedimentary basin was superimposed and reworked by episodic Mesozoic to Cenozoic tectonic events, giving rise to the uplift and erosion at the basin margins while folding or tilting within the basin. At present, the basin presents a wedge-shaped geometry, with thickest strata in the south and thinnest strata in the north. The presence of source rocks, reservoirs, regional seals, and traps is closely related to the multiphase, basin-scale, extension-to-compression tectonic cycles of the basin. Episodic tectonic movements are also responsible for the adjustment and destruction of earlier-formed hydrocarbon pools and the formation of secondary pools. The preferential accumulation sites for prospective deep-seated petroleum exploration are also proposed.

Deformation Mechanisms of Darreh Sary Metapelites, Sanandaj‒Sirjan Zone, Iran

The Darreh Sary metapelitic rocks are located in the northeast of Zagros orogenic belt and Sanandaj-Sirjan structural zone. The lithological composition of these rocks includes slate, phyllite, muscovitebiotite schist, garnet schist, staurolite-garnet schist and staurolite schist. The shale is the protolith of these metamorphic rocks, which was originated from the continental island arc tectonic setting and has been subjected to processes of Zagros orogeny. The deformation mechanisms in these rocks include bulging recrystallization (BLG), subgrain rotation recrystallization (SGR) and grain boundary migration recrystallization (GBM), which are considered as the key to estimate the deformation temperature of the rocks. The estimated ranges of deformation temperature and depth in these rocks show the temperatures of 275–375, 375–500, and >500°C and the depths of 10 to 17 km. The observed structures in these rocks such as faults, fractures and folds, often with the NW-SE direction coordinate with the structural trends of Zagros orogenic belt structures. The S-C mylonite fabrics is observed in these rocks with other microstructures such as mica fish, σ fabric and garnet deformation indicate the dextral shear deformation movements of study area. Based on the obtained results of this research, the stages of tectonic evolution of Darreh Sary area were developed.

Permo–Triassic granitoids of the Xing’an–Mongolia segment of the Central Asian Orogenic Belt, Northeast China: age, composition, and tectonic implications

ABSTRACTThe Xing’an–Mongolia orogenic belt is located in the southeastern segment of the Central Asian Orogenic Belt. Its tectonic evolution, especially during the Late Palaeozoic to Early Mesozoic, remains controversial. Here, we report new zircon U–Pb dates, whole-rock geochemistry, and Hf isotopes of representative samples from four plutons in the Linxi area of Northeast China to provide new constraints on this issue. Zircon U–Pb dating indicates that the intrusions were emplaced in two stages: (1) Late Permian to Early Triassic (the Banshifangzi and Xinangou plutons (252 ± 3)–(246.3 ± 3.3) Ma); and (2) Late Triassic (the Baoshan and Hada plutons (220.8 ± 2.7)–(211.4 ± 2.6) Ma). Their positive εHf(t) values (6.6–14.1), coupled with their geochemical characteristics, suggest that the provenance of investigated granitoids were most likely to be dominated by juvenile crustal materials. Based on these new data and previous studies, we propose three stages of tectonic evolution during the Late Palaeozoic–Early Mesozoic in the XMOB: (1) Late Carboniferous–Early Permian (330–270 Ma): double-sided subduction of the Palaeo-Asian Ocean; (2) Middle Permian–Middle Triassic (270–237 Ma): the closure of the Palaeo-Asian Ocean and subsequent continent–continent collision between the North China Craton and the South Mongolia Terrane; and (3) Late Triassic (237–211 Ma): post-collisional extension.

Response of unconfined turbidity current to relay‐ramp topography: insights from process‐based numerical modelling

AbstractThis natural‐scale experimental study combines structural modelling of soft‐linked normal‐fault relays with a CFD (computational fluid dynamics) numerical simulation of a range of unconfined turbidity currents overrunning the relay‐system topography. The flow, released from an upslope inlet gate 2000‐m wide and 50‐m to 100‐m high, rapidly expands and adjusts its thickness, velocity and sediment load to the substrate slope of 1.5°. A lower initial sediment concentration or smaller thickness renders the quasi‐steady flow slower and its sediment‐transport capacity lower. A 3D pattern of large interfering Kelvin‐Helmholtz waves causes fluctuations of the local flow velocity magnitude and sediment concentration. Four zones of preferential sediment deposition are recognized: a near‐gate zone of abrupt flow expansion and self‐regulation; a flow‐transverse zone on the counter‐slope of fault footwall edges; a flow‐transverse zone at the fault‐scarp toes and a similar transverse zone near the crest of the hanging wall counter‐slopes. The sand deposited on the counter‐slope tends to be re‐entrained and fed back to the current by a secondary reverse underflow. The spatial extent and sediment accumulation capacity of depozones depend upon the released current volume. The impact of relay system on an overrunning current depends upon the fault separation distance and stage of tectonic evolution. An early‐stage relay system, with small vertical displacement and little overlap of faults, is bypassed by the current with minimum flow disturbance and no pronounced deposition. An advanced‐stage system, with greater fault displacement and overlap, gives a similar hydraulic effect as a single fault segment if the fault separation is small. If the separation is relatively large, the flow tends to be internally redirected sideways from the ramp into the hanging wall synclinal depressions. Since normal‐fault relays are common features in extensional basins, the study bears important implications for turbiditic slope‐fan models and for the spatial sand prediction in subsurface exploration of faulted submarine slopes.

Differential extension and dynamic model of the deep-water area of the Pearl River Mouth Basin, northern South China Sea

Based on the flexural-cantilever model and flexural isostasy model, three independent quantitative methods have been used to calculate the stretching factors of the upper crust, whole crust, and whole lithosphere in the deep-water area of the Pearl River Mouth Basin, northern South China Sea. These results demonstrate that depth-dependent stretching has occurred within the lithosphere of the study area. The lithospheric extension shows lateral differences between the Baiyun Sag and the Kaiping–Shunde Sags. The broad forearc pre-rifting basement and hot thinned lithosphere tend to generate a structural style of wide half-graben in the Baiyun Sag, while the volcanic arc basement and normal or thickened lithosphere form a structural style of narrow half-graben in the Kaiping–Shunde Sags. In line with the lithospheric deformational features and tectonic evolution stages, we propose three various dynamic mechanisms at different tectonic stages, and they are probably uniform, composite, and depth-dependent extension models, respectively.

Neotectonic transformation of Cenozoic fold structures in the northwestern Caucasus

The performed morphotectonic regionalization of the northwestern Caucasus shows that the fold structures directly expressed in the topography of the territory and continuing to evolve under the settings of contemporary lateral shortening predominate in the northwestern Caucasus. A map of fold structures expressed in the topography of the northwestern Caucasus is presented. The districts distinguished therein correspond to the largest regional tectonic units, the fold topography of which occurs at various stages of tectonic evolution from primary brachyanticlinal ridges of the Taman and Sochi districts to the complex fold–thrust and inversion fold ridges of the axial zone. Data on active newly formed fold and inversion structures are given. These inherited structures develop under the combined action of selective denudation, beddingplane upthrow faulting, and thrusting.