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1.
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2.
Stepanov et al. (Contrib Mineral Petrol, 2017) question our conclusion that the UPVs in southern Tibet were derived by partial melting of an old, metasomatized subcontinental lithospheric mantle (SCLM) of the subducted Indian plate. Instead, they propose that these ultrapotassic volcanic rocks (UPVs) are shoshonitic and were generated in two steps: direct melting of crustal rocks first, and then the melts interacted with mantle peridotite. However, the trace element, isotopic, thermal, structural, and seismic evidence is consistent with the xenolith evidence (Wang et al in Contrib Mineral Petrol 172:62, 2016) for hybridisation of ascending Indian subcontinental lithospheric mantle-derived UPV magmas with the deep, isotopically unevolved, Tibetan crust. This necessitates a model whereby partial melting of subducting Indian SCLM generates the UPV suite of southern Tibet.  相似文献   

3.
The results of synchronous measurements of temperature variations in a near-bottom thermocline, as well as microdeformations of the Earth’s crust and atmospheric pressure pulsing, recorded on-shore with the help of a laser strainmeter and laser nanobarograph, are presented. A string containing 20 thermosensors spaced at 0.5 m was used; it was placed by an anchored buoy in a place with 21-m depth and 500 m away from the shore. A good correlation between microdeformations and atmospheric pressure variations was observed for periods longer than 6 h. Quantitative estimates and spectral analysis via the Gilbert-Huang method for investigation of nonstationary and nonlinear processes lead to the conclusion that, on temporal scales from tidal to several minutes, the predominant way of formation of microdeformations in the Earth’s crust can be breaking of internal waves in a thermocline that leads to shallow water (i.e., in the zone of “internal breakers”).  相似文献   

4.
Dr. Li Li 《《幕》》2005,28(3):222-223
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5.
《Gondwana Research》2013,23(3-4):1060-1067
Convergence between the Indian plate and the Eurasian plate has resulted in the uplift of the Tibetan Plateau, and understanding the associated dynamical processes requires investigation of the structures of the crust and the lithosphere of the Tibetan Plateau. Yunnan is located in the southwest edge of the plateau and adjacent to Myanmar to the west. Previous observations have confirmed that there is a sharp transition in mantle anisotropy in this area, as well as clockwise rotations of the surface velocity, surface strain, and fault orientation. We use S receiver functions from 54 permanent broad-band stations to investigate the structures of the crust and the lithosphere beneath Yunnan. The depth of the Moho is found to range from 36 to 40 km beneath southern Yunnan and from 55 to 60 km beneath northwestern Yunnan, with a dramatic variation across latitude 25–26°N. The depth of the lithosphere–asthenosphere boundary (LAB) ranges from 180 km to less than 70 km, also varying abruptly across latitude 25–26°N, which is consistent with the sudden change of the fast S-wave direction (from NW–SE to E–W across 26–28°N). In the north of the transition belt, the lithosphere is driven by asthenospheric flow from Tibet, and the crust and the upper mantle are mechanically coupled and moving southward. Because the northeastward movement of the crust in the Burma micro-plate is absorbed by the right-lateral Sagaing Fault, the crust in Yunnan keeps the original southward movement. However, in the south of the transition belt, the northeastward mantle flow from Myanmar and the southward mantle flow from Tibet interact and evolve into an eastward flow (by momentum conservation) as shown by the structure of the LAB. This resulting mantle flow has a direction different from that of the crustal movement. It is concluded that the Sagaing Fault causes the west boundary condition of the crust to be different from that of the lithospheric mantle, thus leading to crust–mantle decoupling in Yunnan.  相似文献   

6.
We present the results of tectonophysical reconstruction of natural stresses of the Earth's crust in the Altai–Sayan mountain region using cataclastic analysis of fault slips and seismic data on the focal mechanisms of earthquakes. This method allows one to obtain the parameters of the total stress tensor by invoking additional data: generalized experimental data on the brittle fracture of rocks, seismic data on the released stress of strong earthquakes, and data on the topography and density of rocks. Results of the tectonophysical reconstruction of stresses showed significant inhomogeneity of the stress state, which is manifested not only in the variation of the strike and dip of the principal axes of the stress tensor, determining changes in the geodynamic regime of the Earth's crust, but also in the close location of the regions of high and low isotropic tectonic pressure in relation to the lithostatic pressure. The variance of the ratio of tectonic pressure to lithostatic pressure is in the range of 0.59–1.31, with an average value for the region close to unity. This paper discusses internal or external mechanisms capable of generating the stress field obtained by the tectonophysical reconstruction.  相似文献   

7.
Doklady Earth Sciences -  相似文献   

8.
Geological, geochemical, and isotopic data (U-Pb for zircon and Sm-Nd for whole-rock samples) are summarized for Proterozoic and Early Paleozoic geological complexes known from various regions of East Antarctica. The main events of tectonothermal and magmatic activity are outlined and correlated in space and time. The Paleoproterozoic is characterized as a period of rifting in Archean blocks, their partial mobilization, and formation of a new crustal material over a vast area occupied by present-day East Antarctica. In most areas, this material was repeatedly reworked at the subsequent stages of evolution (1800–1700, 1100–1000, 550–500 Ma). Complexes of Mesoproterozoic juvenile rocks (1500, 1400–1200, 1150–1100 Ma) arising in convergent suprasubduction geodynamic settings are established in some areas (basalt-andesite and tonalite-granodiorite associations with characteristic geochemical signatures). The evolution of the Proterozoic regions in East Antarctica may be interpreted as a Wilson cycle with the destruction of the Archean megacontinent 2250 Ma ago and the ultimate closure of the secondary oceanic basins by 1000 Ma ago. The Mesoproterozoic regions make up a marginal volcanic-plutonic belt that combines three provinces of different ages corresponding to consecutive accretion of terranes 1500–1150, 1400–950, and 1150–1050 Ma ago. The Neoproterozoic and Early Paleozoic tectonomagmatic activity developed nonuniformly. In some regions, it is expressed in ductile deformation, granulite-facies metamorphism, and postcollision magmatism; in other regions, a weak thermal effect and anorogenic magmatism are noted. The evolution of metamorphic complexes in the regime of isothermal decompression and the intraplate character of granitoids testify to the collision nature of the Early Paleozoic tectonomagmatic activity.  相似文献   

9.
Paleoproterozoic Xuwujia gabbronorites in the northern margin of the North China craton occur as dykes, sills and small plutons intruded into khondalite (aluminous paragneisses, sedimentary protoliths deposited at ca. 2.0–1.95 Ga), and as numerous entrained bodies and fragments of variable scales in the Liangcheng granitoids (ca. 1.93–1.89 Ga). These gabbronoritic dykes are present at all locations where ca. 1.93–1.92 Ga ultra-high-temperature metamorphism is recorded in the khondalite. A gabbronorite sample from the Hongmiaozi dyke gives zircon 207Pb/206Pb mean ages of 1954 ± 6 Ma (core domains) and 1925 ± 8 Ma (rim domains). These ages, as well as previously reported ages, constrain the age of mafic magmatism to be at ca. 1.96–1.92 Ga (∼1.93 Ga). One sample from the Xigou gabbro intruded by the Liangcheng granitoids gives a zircon 207Pb/206Pb mean age of 1857 ± 4 Ma, which is interpreted as the age of a metamorphic overprint. The Xuwujia gabbronorites comprise mainly gabbronorite compositions, as well as some norite, olivine gabbronorite, monzonorite, quartz gabbronorite, and quartz monzonorite. Chemically, they are tholeiitic and can be divided into two groups: a high-Mg group (6.2–22.9 wt.% MgO) and a relatively low-Mg group (2.2–5.7 wt.% MgO). The high-Mg group shows negative Eu-anomalies (Eu/Eu* = 0.53–0.72), slight light rare earth element enrichment (La/YbN = 0.56–1.53), and small negative anomalies in high field-strength elements. The ?Nd (t = 1.93 Ga) values vary from +0.3 to +2.4. The low-Mg group shows varied Eu-anomalies (Eu/Eu* = 0.48–1.05), and is enriched in light rare earth elements (La/YbN = 1.51–11.98). The majority shows negative anomalies in high field-strength elements (e.g., Th, Nb, Zr, and Ti). Initial ?Nd (at 1.93 Ga) values for low-Mg gabbronorites vary from −5.0 to 0. The Xuwujia gabbronorites possibly experienced assimilation of crust, and fractional crystallization of initially olivine and hypersthene (the high-Mg group), and then olivine, clinopyroxene, and plagioclase (the low-Mg group). The slightly younger Liangcheng granitoids consist of garnet-bearing granite, granodiorite and quartz-rich granitic compositions. They are intermediate to felsic calc-alkaline rocks, thought to be derived from surrounding metasedimentary crust. Xigou gabbro could represent early cumulates. The granitoids have relatively high-Mg numbers (up to 54), and show some chemical affinities with the gabbronorites, which could have resulted from incorporation of gabbronoritic melts. The occurrence and chemical variations of the Xuwujia gabbronorites and Liangcheng granitoids can be interpreted to have resulted from crust–mantle interaction, with mingling and partial mixing of mantle (gabbronoritic) and crustal (granitic) melts. The Xuwujia gabbronorites originated from a mantle region with high potential temperatures (∼1550 °C), possibly associated with a plume or more likely a ridge-subduction-related mantle upwelling event. They could have had extremely high primary intrusion temperatures (up to 1400 °C). Emplacement of these magmas was likely responsible for the extensive crustal anatexis (Liangcheng granitoids) and the local ultra-high-temperature metamorphism. These sequences may have followed ca. 1.95 Ga continent–continent (arc?) juxtaposition and were themselves followed by significant regional uplift and exhumation in the northern margin of the North China craton.  相似文献   

10.
The paper is focused on recent displacement rates in the Altai-Sayan region, obtained by hydroleveling, leveling, and satellite geodesy. Effective elastic moduli and viscosity parameters of the crust are used in the modeling of coseismic and tectonic processes. The elastic moduli are determined from measurements of periodic vertical displacements during seasonal loadings of the Sayano-Shushenskaya hydropower plant. We present the results of the modeling of coseismic displacements during the earthquakes of 10 February 2011 (M = 6.1) and 27 December 2011 (M = 6.7) in Tuva and West Sayan. The results of GPS determinations for postseismic displacements in the Chuya earthquake zone (Gorny Altai, 27 September 2003, M = 7.5) are analyzed; models for the geologic medium are selected; and its effective viscosity is estimated. The tectonic component of the recent crustal displacements in the Altai-Sayan region is defined.  相似文献   

11.
An integrated geological and geophysical study was performed to investigate the region of junction of the eastern part of the Central Asian Fold Belt and the Siberian Platform in the Skovorodino–Tommot 3-DV reference profile line (52°–60° N, 122°–129° E), where the belt is separated from the Aldan–Stanovoi Shield of the Platform by a series of deep faults. The main results are as follows: Seismic, density, and geoelectric characteristics of rocks were obtained and used to determine (refine) the intracrustal boundaries of tectonic structures; large-block structure of the Earth’s crust, caused by mantle faults, and the difference between the layered structure of the crust for the shield and fold regions were established; and available paleomagnetic data were used to perform palinspastic reconstructions for 180 and 140 million years, the most productive metallogenic epoch in the region, coeval with collision processes at the closure of the Mongol-Okhotsk paleobasin.  相似文献   

12.
The analysis of 3D relief models of the lower Amur region and several adjacent areas suggested that the structure of the region is related to the horizontal tectonic layering of the upper part of the Amur plate. When it was dislocated to the northwest at the terminal Cretaceous, some fragments of the upper layers were displaced not strictly synchronously but with some lag relative to the whole plate. This scenario was responsible for the formation of the main morphostructural elements of the region: river valleys, mountain ranges, and graben series. These inferences are supported by field observations and some geological data. The proposed hypothesis can also be applied for several other regions.  相似文献   

13.
The results of electromagnetic sounding of the Earth??s crust in the vicinities of the SG-6 and SG-7 superdeep boreholes (Yamal-Nenets Autonomous Okrug) are presented. The studies were conducted in the fields of natural sources (AMT-MTS) and in the field of the Zevs ULF antenna located at a distance of more than 2000 km from the receiver points. In the vicinity of the SG-7 superdeep borehole, where the small industrial noise was observed, the results of inverse problem solution are completely consistent with the electric logging data. The conducting layers have been identified at the depths of 150 m and 1.1 km. The roof of rocks having small electrical conductivity and belonging to the Permian-Triassic trappean complex has been found at the depth of about 7 km. The response of the Zevs signal (the frequency range of 44?C182 Hz) has indicated the properties of the upper part of the geoelectrical section better than audiomagnetotelluric sounding for both boreholes. Based on the sounding in the vicinity of the SG-6 superdeep borehole, with the data of the Novosobirsk observatory taken into account, the distribution of resistivity down to about 800 km depth has been obtained. This distribution can serve as additional information in calculation of the temperature and rheological regime of the lithosphere and the upper mantle in the region of Western Siberia.  相似文献   

14.
A new general model describing the extended evolution of fore‐arc terrains is used to analyse the evolution of the southern Tasman Geosyncline and the concomitant growth and kratonisation of the continental crust of southeast Australia during the Palaeozoic. The southern Tasman Geosyncline comprises ten arc terrains (here defined), most of which are east‐facing, and several features formed by crustal extension. Each arc terrain consists of several strato‐tectonic units: a volcanic arc, subduction complex and fore‐arc sequence formed during subduction; and an overlying post‐arc sequence which post‐dates subduction and is composed of flysch, neritic sediments or subaerial volcanics.

When these materials attained a thickness of c. 20 km their internal heat‐balance caused partial melting of the subduction complex and the hydrated oceanic lithosphere trapped beneath it, to yield S‐ and I‐type granitic magma. The magma rose, inducing pervasive deformation of each arc terrain and emplacement of granitoid plutons at high levels in the evolving crust. Transitional basins then developed in many terrains on top of their volcanic arcs or the thinner parts of the buried accretionary prisms. After deformation of the transitional sequences, platform cover accumulated, marking the completion of kratonisation.

Analysis of each arc terrain in terms of the above units leads to a predicted ‘stratigraphy’ for the continental crust of southeast Australia. The crust is complexly layered, with lateral discontinuities reflecting the boundaries of arc terrains which were successively accreted, principally back‐arc to fore‐arc, during crustal development.  相似文献   

15.
The catastrophic Shikotan earthquake of October 4 (5), 1994, occurred in the Pacific Ocean. Its focus was located 80 km eastward of Shikotan Island. The stress state of the Earth’s crust in this area was estimated by the method of the cataclastic analysis of the whole range of the earthquake mechanisms. The performed reconstruction of the parameters of the current stress state of the Earth’s crust and the upper mantle in the area of the Southern Kuril Islands made it possible to establish that this area is characterized, on the one hand, by the presence of extensive areas of steady behavior of the stress tensor parameters and, on the other hand, by the presence of local sections of anomalously fast changes in these parameters.  相似文献   

16.
The geological structure and tectonophysics of the Gusinoozersky Basin—a tectonotype of Mesozoic depressions in the western Transbaikal region—is discussed. New maps of the fault-block structure and state of stress in the Earth’s crust of the studied territory are presented. It is established that the Gusinoozersky Basin was formed in a transtensional regime with the leading role of extension oriented in the NW-SE direction. The transtensional conditions were caused by paths of regional tension stresses oriented obliquely to the axial line of the basin, which created a relatively small right-lateral strike-slip component of separation (in comparison with normal faulting) along the NE-trending master tectonic lines. The widespread shear stress tensors of the second order with respect to extension are related to inhomogeneities in the Earth’s crust, including those that are arising during displacement of blocks along normal faults. Folding at the basin-range boundary was brought about by gravity effects of normal faulting. The faults and blocks in the Gusinoozersky Basin remained active in the Neogene and Quaternary; however, it is suggested that their reactivation was a response to tectonic processes that occurred in the adjacent Baikal Rift Zone rather than to the effect of a local mantle source.  相似文献   

17.
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18.
A study based on computation of D-function anomalies (method of joint gravity and magnetic data analysis) along profiles in the Bering Sea has been performed in both the Aleutian Basin with oceanic crust and the Bering continental shelf. This study revealed extended faults that affect not only the Earth’s crust but also the upper mantle. This is supported by seismic profiling. The calculated palinspastic reconstructions of the position of North America relative to “immobile” Eurasia 80, 52–50, 50–47, and 15–20 Ma ago allowed us to show that the revealed strike-slip faults are probable relics of an echeloned transform boundary between the Eurasian and North American lithospheric plates. The formation of this boundary beginning from the Late Cretaceous was apparently related to opening of the North Atalantic, which determined the large rate of displacement of North America relative to Eurasia.  相似文献   

19.
 Mafic and ultramafic rocks sampled in the Garrett transform fault at 13°28′S on the East Pacific Rise (EPR) provide insight on magmatic processes occurring under a fast-spreading ridge system. Serpentinized harzburgite from Garrett have modal, mineral and bulk chemical compositions consistent with being mantle residue of a high degree of partial melting. Along with other EPR localities (Terevaka transform fault and Hess Deep), these harzburgites are among the most residual and depleted in magmatophile elements of the entire mid-ocean ridge system. Geothermometric calculations using olivine-spinel pairs indicate a mean temperature of 759 ± 25 °C for Garrett residual harzburgite similar to the average of 755 °C for tectonite peridotites from slow-spreading ridges. Results of this study show that mid-ocean ridge peridotites are subject to both fractional melting and metasomatic processes. Evidence for mantle metasomatism is ubiquitous in harzburgite and is likely widespread in the entire Garrett peridotite massif. Magma-harzburgite interactions are very well preserved as pyroxenite lenses, plagioclase dunite pockets or dunitic wall rock to intrusive gabbros. Abundant gabbroic rocks are found as intrusive pockets and dikes in harzburgite and have been injected in the following sequence: olivine-gabbro, gabbro, gabbronorite, and ferrogabbro. The wide variety of magmas that crystallized into gabbros contrast sharply with present-day intratransform basalts, which have a highly primitive composition. Ferrogabbro dikes have been intruded at the ridge-transform intersection and as they represent the last event of a succession of gabbros intrusive into the peridotite, they likely constrain the origin of the entire peridotite massif to the same location. In peridotite massifs from Pacific transform faults (Garrett and Terevaka), primitive to fractionated basaltic magmas have flowed and crystallized variable amounts of dunite (±plagioclase) and minor pyroxenite, followed by a succession of cumulate gabbroic dikes which have extensively intruded and modified the host harzburgitic rocks. The lithosphere and style of magmatic activity within a fast-slipping transform fault (outcrops of ultramafic massif, discontinuous gabbro pockets intrusive in peridotite, magnesian and phyric basalts) are more analogous to slow-spreading Mid-Atlantic Ridge type than the East Pacific Rise. Received: 13 October 1997 / Accepted: 5 February 1999  相似文献   

20.
We have conducted a paleomagnetic investigation on the Middle–Upper Jurassic marine strata exposed in the hanging wall of the Tanggula Thrust system near the Yanshiping area, northern Tibet. Progressive demagnetization experiments successfully isolated stable magnetization over a broad spectrum of demagnetization temperatures. The mean direction of the characteristic remanent magnetizations for the Middle–Late Jurassic Yanshiping Group in stratigraphic coordinates (D/I (Declination/Inclination) = 5.6°/60.3°, k = 22.9, α95 = 12.9°, N = 7 s) is much more clustered than the mean direction in geographic coordinates (D/I = 345.5°/37.2°, k = 2.5, α95 = 48.4°), indicating magnetization was not acquired after folding. Although the conventional fold test is positive, incremental untilting test on the characteristic remanent magnetization reveals that a maximum value of precision parameter k occurs at 82.1 ± 4.6% untilting (D/I = 3.3°/57.8°, k = 43.9, α95 = 9.2°), which indicates the ChRMs are probably acquired during Late Cretaceous folding. This synfolding magnetization component is therefore secondary. The corresponding pole position (84.4°N, 119.4°E with dp/dm = 13.5/9.9°) is inconsistent with Jurassic–Early Cretaceous paleopoles of the region, but the paleolatitude is consistent with the Late Cretaceous paleolatitude observed in the Qiangtang terrane and its periphery. The synfolding component is carried by both magnetite and hematite, which were identified by isothermal remnant magnetization acquisition experiments, unblocking temperatures of stable magnetic components, and Curie temperature determination and correlated with observed hydrothermal veins. Available geological evidences indicate that the synfolding magnetization is probably the result of chemical remagnetization caused by orogenic fluids or hydrothermal sources during the early uplift of the Tibetan Plateau.  相似文献   

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