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1.
The Sanchahe quartz monzonite intrusion is situated in the middle segment of the North Qinling tectonic belt, Central China mainland, and consists chiefly of sanukitoid–like and granodioritic-monzogranitic rocks. The sanukitoid–like rocks are characterized by quartz monzonites, which display higher Mg#(55.0–59.0), and enrichments in Na2 O+K2 O(7.28–8.94 %), Ni(21-2312 ppm), Cr(56-4167 ppm), Sr(553-923 ppm), Ba(912-1355 ppm) and LREE((La/Yb)N =9.47–15.3), from negative to slightly positive Eu anomalies(δEu=+0.61 to +1.10), but also depletion in Nb, Ta and Ti. The granodioritic-monzogranitic rocks diaplay various Mg#of 6.00-53.0, high Na2 O+K2 O(7.20– 8.30%), Sr(455–1081 ppm) and(La/Yb)N(27.6–47.8), with positive Eu anomalies(δEu=1.03–1.57) and depleted Nb, Ta and Ti. Laser ablation inductively coupled plasma mass spectrometry(LA-ICPMS) zircon U-Pb isotopic dating reveals that the sanukitoid-like rocks were emplaced at two episodes of magmatism at 457±3 Ma and 431±2 Ma, respectively. The monzogranites were emplaced at 445±7Ma. Sanukitoid–like rocks have their εHf(t) values ranging from +0.3 to +15.1 with Hf–depleted mantle model ages of 445 to 1056 Ma, and the monzogranite shows its εHf(t) values ranging from 21.6 to +10.8 with Hf–depleted mantle model ages of 635 to 3183 Ma. Petrological, geochemical and zircon Lu –Hf isotopic features indicate that the magmatic precursor of sanukitoid–like rocks was derived from partial melting of the depleted mantle wedge materials that were metasomatized by fluids and melts related to subduction of oceanic slab, subsequently the sanukitoid magma ascended to crust level. This emplaced mantle magma caused partial melting of crustally metamorphosed sedimentary rocks, and mixing with the crustal magma, and suffered fractional crystallization, which lead to formations of quartz monzonites. However, the magmatic precursor of the granodioritic-monzogranitic rocks were derived from partial melting of subducted oceanic slab basalts. Integrated previous investigation for the adackitic rocks in the south of the intrusion, the Sanchahe intrusion signed that the North Qinling tectonic zone was developed in an early Paleozoic transitionally tectonic background from an island arc to back–arc.  相似文献   

2.
Tectonic Evolution of the Himalayan Collision Belt   总被引：5，自引：0，他引：5  
This paper discusses the tectonic divisions of the Himalayan collision belt anddeals with the tectonic evolution of the collision belt in the context of crustal accretion in thefront of the collision belt, deep diapirism and thermal-uplift extension and deep material flow-ing of the lithosphere-backflowing. Finally it proposes a model of the tectonic evolution-progressive intracontinental deformation model-of the Himalayan belt.  相似文献   

3.
The Taiwan Strait is a part of the continental-margin rift of eastern China, which can tectonically be divided into the Taiwan Strait basin, southwestern Taiwan basin and Penhu-Beigang uplift. The basins are structurally semi-graban down-faulted ones in character. The Cretaceous-Cenozoic sedimentary strata in the basins have a maximum thickness of over 10,000 m. The formation and development of the Taiwan Strait rift were not only affected by both the East China Sea basin and South China Sea basin but also closely related to the Central Range collision orogen of Taiwan. In the Cenozoic, the Taiwan Strait area experienced, under the influence of a multiple of tectonic mechanisms, three stages of evolution: poly-centre downfault-ing, down warping-faulting and foreland basin formation. The depositional centres of the basins migrated from west to east during the Tertiary, resulting in the thinning of the Palaeogene strata from west to east but that of the Neogene in the reverse direction. All this determine  相似文献   

4.
With increasing high-quality geological and geophysical data it becomes clear that seismicity of the continents is characterized by linear patterns which are closely associated with tectonic features. The aim of this paper is to give reasonable interpretation for the earthquake distribution in the contiguous continent of the United States. Seismic lines and earthquake concentrated zones are defined, which reflect the characteristics of the continental seismotectonics. Similarities and differences in seismotectonics between the continental part of China and the contiguous continent of US are analysed. It is demonstrated that the spatial distribution of earthquakes can provide the information of the active structures in the earth's crust. The authors consider that the patterns of continental seismotectonics are not only controlled by the pre—existing tectonic frameworks and the current boundary dynamic conditions, but also possibly affected by dynamic factors of global tectonics at a higher level.  相似文献   

5.
Nekrasov  G. E. 《Doklady Earth Sciences》2019,489(2):1391-1395
Doklady Earth Sciences - In this work we considered the origin of the Verkhoyansk–Kolyma, Chukotka, and Southern Anyui belts, which are part of the Verkhoyansk–Chukotka folded area. It...  相似文献   

6.
A comprehensive study has been carried out to subdivide and correlate the Upper Carboniferous and Permian sedimentary successions in the Junggar basin based on outcrops and drilling and geophysical data. The study results, combined with geological analyses of the basin's periphery and the basement, as well as studies of the sedimentary rocks within the basin, the unconformities, tectonic geometry, kinematics and geodynamics, lead to the conclusion that the Junggar basin was characterized by the development of foreland basin systems during the Late Carboniferous and Permian. During that period, three foreland basin systems were developed: (1) the northwest foreland basin system, which trended nearly north-south from Mahu to the Chepaizi Palaeo-mountain during its early stage of development and thus it was also referred to as the west foreland basin system; (2) the Karamaili foreland basin system in the east and (3) the Northern Tianshan foreland basin system in the south. These systems are different in s  相似文献   

7.
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8.
Based on the study of folds and related conjugate shear joints, the tectonic stress fields of the Urumqi-Usu region to the north of the North Tianshan Mountains have been reconstructed. Furthermore the author discussed the tectonic movements and their dynamic features. The early tectonic movement in the investigated region occurred from the end of the Late Jurassic to the initial stage of the Early Cretaceous, with the maximum (tensile) and minimum (compressional) principal stress trajectories in the tectonic stress field being in E-W and S-N directions respectively; the late tectogenesis took place from the end of the Early Pleistocene to the initial Middle Pleistocene, with the maximum and minimum principal stress trajectories in the late stress field striking in WNW and NE-NNE directions respectively. Through computer-aided simulated calculation by the finite element method and analysis of geological structure, it has been ascertained that the early tectogenesis is a nearly N-S compressive movement and the late one a NE to nearly N-S compressive movement with reverse shear. The dynamic force which caused the tectogeneses came from the movement of the southern major fault, i.e. the North Tianshan Mountains.  相似文献   

9.
The purpose of this study is to analyze and characterize recent landslide events in the Larji–Kullu Tectonic Window (LKTW), and to establish a relationship between the tectonic and lithologic characters of the terrain and the landslides activity. Using multispectral satellite image analysis with selected field investigation, a landslide occurrence database has been generated for the period between 1984 and 2015. To decipher the accelerated occurrences of landslides in the region, an integrated study is undertaken in the Kullu (also known as Kulu) valley of Beas River basin within the LKTW complex, to analyze the litho-structural and terrain slope interactions using morpho-tectonic parameters such as Topographic/Bedding Plane Interaction Angle (TOBIA) index, terrain surface roughness index and lithological competency analysis. A prominent clustering of landslides is observed in the north of Sainj River, contained within the tectonic window. Major sites of landslides are found to be located in the intensely fractured Manikaran Quartzite occurring within the core of the LKTW. The landslides are mostly associated with southern and southwestern-facing slopes and activations are pronounced in the ‘Orthoclinal’ slope class with gradient of 37°–48°. Thematic maps, e.g., geological, structural, geomorphological, slope and slope-aspect maps are generated and considered together to understand the morpho-tectonic scenario of the tectonic window. Observations from the above-stated thematic maps along with the occurrences of moderate magnitude earthquake epicenters helped to infer neotectonic movements along the Sainj River fault. Tectonic upliftment of the northern bank of the Sainj River along with increased precipitation through decades has resulted in recurrent landslides within the LKTW.  相似文献   

10.
The Wonaminta Block is bounded on its eastern and western margins by Lower Cambrian or upper Vendian intrusive and extrusive igneous rocks. The extrusive rocks include pillow lavas. Low‐grade metamorphism has not influenced the distribution of P2O3, Zr, Y, and Nb, but remobilization of Ti has occurred in rocks containing Ti within the oxide phases rather than in the silicate phases. Immobile trace‐element discrimination techniques indicate that the basalts on the western margin of the Wonaminta Block are alkaline whereas those on the eastern margin are tholeiitic. The possibility that these rocks represent petrological variants across an arc system is discussed.  相似文献   

11.
The Qinling Mountains separating the northern from the southern China plate is a key region for the study of structural evolution of eastern Asia. It is composed of the Palaeozoic fold belt in its northern part and the Variscan and Indosinian fold belts in its southern part. The evolution of the former is marked by the closure of a northward subducting oceanic basin in the early stage, followed by southward obduction of ophiolites and intracontinental thrusting during the Variscan; whereas that of the latter is represented by intracontinental, shallow crustal deformation on the basis of a large-scale detachment structure(with a horizontal slip of at least of 100 km). Since the late Palaeozoic, however, both of the belts have been cut by a series of east-west sinistral strike-slip faults.  相似文献   

12.
After the Variscan Cycle, the global tectonic framework underwent three major adjustments. The first occurred in the Late Triassic-initial Jurassic, the second in the Late Jurassic-early Early Cretaceous and the third in the Late Cretaceous-Eogene. On that basis, the post-Variscan tectonic history is divided into three tectonic cycles——the Indosinian, Yanshanian and Himalayan Cycles. The post-Neocom(k_1~1) andpre-Aptian(k_1~2) tectonic movement marks the end of the Yanshanian orogeny in eastern China and the initiation of the subduction of the Tethyan ocean in western China and represents the boundary between the Yanshanian and Himalayan Tectonic Cycles.  相似文献   

13.
This paper deals with deformation textures and fabrics of mantle-derived xenoliths and dislocation microstructures of olivine in the upper mantle in the Penghu Islands, Taiwan. According to the calculation of the chemical composition of xenolith minerals (pyroxene), the equilibrium temperatures and pressures were 986-1116@ and 1.50-2.60 GPa, respectively. Deformation events in the upper mantle may fall into three sequences' (1) uniform steady-state flow deformation with high temperatures and low stresses, (2) shear flow deformation with high temperatures and relatively high stresses on diapiric margins of the upper mantle, and (3) extraction deformation of {110} glide bands with low temperatures and high strain rates. Deformation events and thermal structure of the upper mantle in the study area show that eastern Fujian and the Penghu Islands are characterized by very similar rheological properties of the upper mantle. Volcanism of basalts in the Penghu Islands is related to hot spots of the upper mantl  相似文献   

14.
The spatial distribution of the epicenters and hypocenters is analyzed for earthquakes of 2 ≤ M < 6 that occurred in the northeastern segment of the Amur Plate in two phases of changes in the angular speed of the Earth’s rotation. Groups of seismic events in the magnitude interval of 5 ≤ M < 6 are distinguished in the form of NE-trending seismic clusters regularly alternating along the plane of latitude. The seismic clusters are up to 1500 km long and 180–240 km wide and cover the seismic zones with different geodynamic and seismotectonic conditions of seismicity origination. In terms of the epicentral distributions for earthquakes with 2 ≤ M < 4, seismic activity zones are distinguished; these zones are seen as seimolineaments coupling the Tan Lu seismic zones and the eastern flanks of the latitudinal seismic zones. A scheme of distinguishing the compression and extension zones from the spatial clusters of earthquakes with 5 ≤ M < 6 in two phases of changes in the angular speed of the Earth’s rotation is proposed. This scheme satisfactorily agrees with the model of seismotectonic reconstructions of the compression–extension fields and axes.  相似文献   

15.
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16.
This study focuses on the zircon U–Pb geochronology and geochemistry of the Bairiqiete granodiorite intrusion(rock mass) from the Buqingshan tectonic mélange belt in the southern margin of East Kunlun. The results show that the zircons are characterized by internal oscillatory zoning and high Th/U(0.14–0.80), indicative of an igneous origin. LA–ICP–MS U–Pb dating of zircons from the Bairiqiete granodiorite yielded an age of 439.0 ± 1.9 Ma(MSWD = 0.34), implying that the Bairiqiete granodiorite formed in the early Silurian. Geochemical analyses show that the rocks are medium-K calc-alkaline, relatively high in Al2O3(14.57–18.34 wt%) and metaluminous to weakly peraluminous. Rare-earth elements have low concentrations(45.49–168.31 ppm) and incline rightward with weak negative to weak positive Eu anomalies(δEu = 0.64–1.34). Trace-element geochemistry is characterized by negative anomalies of Nb, Ta, Zr, Hf and Ti and positive anomalies of Rb, Th and Ba. Moreover, the rocks have similar geochemical features with adakites. The Bairiqiete granodiorite appears to have a continental crust source and formed in a subduction-related island-arc setting. The Bairiqiete granodiorite was formed due to partial melting of the lower crust and suggests subduction in the Buqingshan area of the Proto-Tethys Ocean.  相似文献   

17.
Extensive volcanism is one of the important features of Cenozoic geology in China.Based on temporal-spatial distribution,the volcanism was associated with three major different geological settings:1)the continental rift basalts in Northeast and North China;2)the tension-fault basalts on the continental margins of Southeast China; and 3) the collision-zone high-K volcanics in the Qinghai-Xizang Plateau and its vicinities.The characteristics of “depletion in the south and enrichment in the north“of the China continental mantle are strongly supported by isotopic evidence.The Cenozoic continental cal characters,into the following geochemical provinces:1)the depleted mantle in South China;2)the primary mantle in Northeast and NorthChina; 3)the hybrid and transi-tional mantle in the region of Shandong ,Anhui,Jiangsu and northern Zhejiang;4)the depleted mantle around the Bohai Bay and the Lower Liaohe River;5)the K-metasomatic enriched mantle in the northern part of Northeast China;and 6)the re-cycled enriched mantle in the ancient subduction zone in the Qinghai-Xizang Plateau and its surround-ings.These geochemical characteristics on a regional scale must be a reflection of the nature of lithosphere evolution.  相似文献   

18.
Please refer to the attachment(s) for more details.  相似文献   

19.
The northern margin of the Alxa block is the junction of a tectonic units. Four first-order tectonic units are distinguished: 1. the Yagan structural zone characteristic of an immature island arc; 2. the Zhusileng-Hangwula structural zone, which was a passive continental margin in the Early Palaeozoic and was transformed into an active continental margin in the Late Palaeozoic;3. the Shalazha structural zone characteristic of a mature island arc; 4. the Nuru-Langshan structural zone, which was a Proterozoic orogenic belt and later evolved into an extensional transtional crust in the Palaeozoic. The above-mentioned tectonic units differ remarkably in sedimentary formations, magmatic rock associations, metamorphism and geochemistry and are bounded by faults between one another.  相似文献   

20.
Doklady Earth Sciences - The large massifs of ancient granitoids of the South Yenisei Ridge are divided into three complexes that differ in the geological, geochemical, and geochronological...  相似文献   

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