Processes of initial collision and suturing between India and Asia

The initial collision between Indian and Asian continents marked the starting point for transformation of land-sea thermal contrast, uplift of the Tibet-Himalaya orogen, and climate change in Asia. In this paper, we review the published literatures from the past 30 years in order to draw consensus on the processes of initial collision and suturing that took place between the Indian and Asian plates. Following a comparison of the different methods that have been used to constrain the initial timing of collision, we propose that the tectono-sedimentary response in the peripheral foreland basin provides the most sensitive index of this event, and that paleomagnetism presents independent evidence as an alternative, reliable, and quantitative research method. In contrast to previous studies that have suggested collision between India and Asia started in Pakistan between ca. 55 Ma and 50 Ma and progressively closed eastwards, more recent researches have indicated that this major event first occurred in the center of the Yarlung Tsangpo suture zone (YTSZ) between ca. 65 Ma and 63 Ma and then spreading both eastwards and westwards. While continental collision is a complicated process, including the processes of deformation, sedimentation, metamorphism, and magmatism, different researchers have tended to define the nature of this event based on their own understanding, an intuitive bias that has meant that its initial timing has remained controversial for decades. Here, we recommend the use of reconstructions of each geological event within the orogenic evolution sequence as this will allow interpretation of collision timing on the basis of multidisciplinary methods.     

Three-dimensional seismic velocity structure of the Tibetan Plateau and its eastern neighboring areas with implications to the model of collision between continents

Since the collision of Indian subcontinent to Eurasia, a huge quantity of crustal materials from India has been penetrated into the crust or mantle of Eurasia. Investigation of the place, on which those materials have been deposited is a key problem for constructing a model of collision between continents. The results of three-dimensional seismic velocity structure obtained from seismic tomography technique may provide an evidence of the deposit of anomalous materials in the crust and upper mantle of the Tibetan Plateau and its neighboring areas. A detailed analysis of the results from the seismic surface wave tomography has deduced a new model of the continental collision from India to Eurasia. It is compatible to the velocity data obtained from other geological and geophysical observations. The main points of the new model of the continental collision from Indian to Eurasia can be summarized as follows:

1. The Indian crust has been penetrating into the lower crust of Tibetan Plateau, instead of into the uppermost mantle beneath the crust or the asthenosphere of Tibetan Plateau;
2. The surplus materials from the Tibetan lower crust have been squeezed and thrusted into the asthenosphere of its eastern neighboring areas (Qinghai-Sichuan-Yunnan) through the broken Moho;
3. Some hot materials were intruded into the crust from the uppermost mantle in Tibetan Plateau and Sichuan-Yunnan provinces. The intruded hot materials may reach the ground surface (such as the Tibetan Plateau) or a depth about 25 km (such as Sichuan-Yunnan provinces) depending on the different local environmental conditions. The extensional geological structures in those regions are closely related to the intrusion of hot materials.

     

Stress field and seismicity in the Indian shield: Effects of the collision between India and Eurasia

Intraplate stresses and intraplate seismicity in the Indian subcontinent are strongly affected by the continued convergence between India and Eurasia. The mean orientation of the maximum horizontal compression in the Indian subcontinent is subparallel to the direction of the ridge push at the plate boundary as well as to the direction of compression expected to arise from the net resistive forces at the Himalayan collision zone, indicating that the intraplate stresses in the subcontinent, including the shield area, are caused by plate tectonic processes. Spatial distribution of historic and instrumentally recorded earthquakes indicate that the seismic activity is mostly confined to linear belts while the remaining large area of the shield is stable. The available conventional heat flow data and other indicators of heat flow suggest hotter geotherms in the linear belts, leading to amplification of stresses in the upper brittle crust. Many of the faults in these linear belts, which happen to be 200–80 m.y. old, are being reactivated either in a strike-slip or thrust-faulting mode. The reactivation mechanisms have been analyzed by taking into consideration the amplification of stresses, pore pressures, geological history of the faults and their orientation with respect to the contemporaneous stress field. The seismicity of the Indian shield is explained in terms of these reactivation mechanisms.     

Numerical simulation of the collision between Indian and Eurasian Plates and the deformations of the present Chinese continent

In this paper the continental lithosphere of the East Asia is regarded as a continuum in a power law rheology. It lays on a relative soft upper mantle and limited in a trapezoid geological frame. The movement of the Indian Plate at the rate of 5 cm/a is assumed to be the main driving force for the Tibet Plateau(s uplift and the lithosphere deformation of the Chinese continent. The numerical simulation shows that the predicted horizontal deformation model of the Chinese continent is comparable with the results of the GPS observation. It implicates that the collision and compression between India and Eurasia Plates is the main driving force of the horizontal deformations of the Chinese continent. It is also shows that the patterns of the continental deformation are controlled by many factors such as the dynamical parameters of the lithosphere and the boundary conditions as well.     

Timing of collision of the Kohistan–Ladakh Arc with India and Asia: Debate

The Kohistan–Ladakh Arc in the Himalaya–Karakoram region represents a complete section of an oceanic arc where the rocks from mantle to upper crustal levels are exposed. Generally this arc was regarded as of Jurassic–Cretaceous age and was welded to Asia and India by Northern and Southern Sutures respectively. Formation of this arc, timings of its collisions with Asia and India, and position of collision boundaries have always been controversial. Most authors consider that the arc collided with Asia first during 102–75 Ma and then with India during 55–50 Ma, whereas others suggest that the arc collided with India first at or before 61 Ma, and then the India–arc block collided with Asia ca 50 Ma. Recently published models of the later group leave several geological difficulties such as an extremely rapid drifting rate of the Indian Plate (30 ± 5 cm/year) northwards between 61–50 Ma, absence of a large ophiolite sequence and accretionary wedge along the Northern Suture, obduction of ophiolites and blueschists along the Southern Suture, and the occurrence of a marine depositional environment older than 52 Ma in the Indian Plate rocks south of the Southern Suture. We present a review based on geochemical, stratigraphic, structural, and paleomagnetic data to show that collision of the arc with Asia happened first and with India later.     

Relation between the field of surface heat flow and the distribution ofP n -wave velocities for continents

Summary The dependence between P_n-wave velocities and the surface heat flow, temperature at the core-mantl boundary and thickness of the Earth's crust for continents (Europe, Asia, North America and Australia) was investigated statistically in connection with the problem of lateral inhomogeneities in the upper mantle. The relations obtained were compared with those determined under laboratory conditions. The conclusion is that temperature and pressure effects may provide additional explanations of the regional variations of P_n-wave velocities observed in most continents.

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Geothermic field and development of the structure of continents

Tectonic, magmatic and metamorphic processes combine into endogenous regimes. There is direct correlation between the degree of excitation of endogenous regimes and observed heat flow. There are grounds to suppose that all varieties of endogenous regimes, their distribution and their history depend on the heterogeneity in space and time of the Earth's thermal field.     

Vertical movements of the Earth's crust on the continents

Vertical oscillating movements of the Earth's crust on continents have occurred and are occurring everywhere on the Earth's surface, continuously throughout the entire geological history of the Earth. This provides grounds to consider them as the basic type of tectonic movements, which form the general background of the tectogenetic process, on which locally, and only at separate moments of time, other tectonic movements and deformations appear.According to the time of occurrence, the vertical movements are divided into recent, young, modern, and ancient. In compliance with this subdivision, different methods are applied to define and study the movements. The major characteristic of the vertical movements is their rhythm, or periodic change in sign of movement, which caused them to be calledoscillating. Rhythms of movements are of several orders. The largest rhythms, which comprise tectonic cycles, are manifested on a global scale; smaller rhythms have a local distribution. It is significant that, in the beginning and in the end of each tectonic cycle, an increase of intensity and contrast of movements is observed, no matter in which region or regime, whether stable or mobile, it occurs.     

Fragmentation and assembly of the continents,Mid-carboniferous to present

Eighteen maps showing the motions of the major continents following the break-up of Wegener's Pangaea in the Early to Mid-Jurassic are presented. Palaeolatitudes are determined palaeomagnetically, palaeolongitudes mainly from sea-floor spreading evidence. The break-up commences with the opening of the southern North Atlantic in the mid-Jurassic and its extension north and south in the Cretaceous and Cenozoic. Concurrently the northern continents move northwards away from the southern continents (Gondwana) and a continuous east-west seaway is formed between them in the Cretaceous. Successive fragmentation of continents then created the Arctic, Indian and Antarctic Oceans. Five maps showing the disposition of land in the Permian are also given. These are based on the palaeomagnetic evidence and the idea of minimizing the motions required to bring the continents into their known Early Jurassic configuration. The Permian maps show Gondwana situated further east than in the Pangaea configuration of Wegener. There are severe problems in constructing palaeogeographical maps for the Triassic and none are presented. Palaeomagnetic results from smaller crustal fragments are also reviewed and the evidence for the former dismemberment of Eurasia and the western part of the North American cordillera are set out. The results indicate that most orogenies are to some degree collisional in nature.     

The relationship between significant wave height and Indian Ocean Dipole in the equatorial North Indian Ocean

Based on reanalysis data, we find that the Indian Ocean Dipole (IOD) plays an important role in the variability of wave climate in the equatorial Northern Indian Ocean (NIO). Significant wave height (SWH) in the equatorial NIO, especially over the waters southeast to Sri Lanka, exhibits strong interannual variations. SWH anomalies in the waters southeast to Sri Lanka correlate well with dipole mode index (DMI) during both summer and autumn. Negative SWH anomalies occur over the oceanic area southeast to Sri Lanka during positive IOD events and vary with different types of IOD. During positive prolonged (unseasonable) IOD, the SWH anomalies are the strongest in autumn (summer); while during positive normal IOD, the SWH anomalies are weak in both summer and autumn. Strong easterly wind anomalies over the southeast oceanic area of Sri Lanka during positive IOD events weaken the original equatorial westerly wind stress, which leads to the decrease in wind-sea waves. The longer wave period during positive IOD events further confirms less wind-sea waves. The SWH anomaly pattern during negative IOD events is nearly opposite to that during positive IOD events.     

Spherical harmonic expansion of the continents and oceans distribution function

Summary An algorithm is derived to compute the coefficients of a spherical harmonic series for the functionE(, ) representing the distribution of continents and oceans with the least-squares method. Some properties of the system of normal equations, when measuring points are distributed in a regular grid, are discussed. The fully normalized complex coefficients to the ninth degree are given in the table.

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Early spreading history of the Indian Ocean between India and Australia

A revised model of seafloor spreading between India and Australia from the inception of spreading 125 m.y. to the change to a new system at 90 m.y. stems from the wider recognition of the M-series of magnetic anomalies off the southwestern margin of Australia, from a revised pole of opening between Australia and Antarctica, and by the extension in the central Wharton Basin of the Late Cretaceous set of magnetic anomalies back to 34. The phase of spreading represented by the later anomalies has been extended back to 90 m.y. in order to give a resolved pole that describes the rotation of India from Australia consistent with the M-series anomalies, DSDP site ages, and fracture zone trends. An abandoned spreading ridge in the Cuvier Abyssal Plain indicates a ridge jump within the first ten million years of spreading. Elsewhere, two kinds of ridge jump (one to the continental margin of Australia or India, the other by propagation of the spreading ridge into adjacent compartments thereby causing them to fuse), are postulated to account for other observations.     

Permian-Triassic magmatic evolution of granitoids from the southeastern Central Asian Orogenic Belt: Implications for accretion leading to collision

Many orogenic belts in the world exhibit accretionary and collisional orogenic phases to varying extents. How accretion evolves into collision of the Central Asian Orogenic Belt(CAOB), the largest Phanerozoic accretionary orogenic belt,is an intriguing question. In this paper, we present new U-Pb age, geochemical and isotopic data for Permian-Triassic granitoids from middle Inner Mongolia, Northern China in the southeastern CAOB, and delineate the magmatic transition from subduction to(soft) collision. The magmatic record of soft collision is identified and characterized by thickened lower crust-derived high Sr/Y granitoids with a sub-linear distribution along the Solonker suture zone. Granitoids from Early Permian to Late Permian became more enriched in whole-rock Nd and zircon Hf isotopic compositions(ε_(Nd)(t) values from 2.4 to-19.5, ε_(Hf)(t) values from 11.6 to-33.7), indicating increasing incorporation of old crust. The change in peak timing of magmatism from west(ca. 264 Ma)to east(ca. 251 Ma) along the Solonker suture zone implies "scissor-like" closure of the Paleo-Asian Ocean. Integrated with previous studies, a three-stage tectonic model from the Permian to Triassic by accretion leading to collision on the south-eastern margin of CAOB is proposed.(1) Early Permian( ca. 285 Ma): Juvenile magmatism on an active continental margin with double-sided subduction of the Paleo-Asian Ocean;(2) Middle Permian to Middle Triassic(ca. 285–235 Ma): Magma source transition from juvenile to old crust induced by a tectonic switch from arc to "scissor-like" closure and subsequent intracontinental orogenic contraction;(3) Late Triassic( ca. 235 Ma): A-type and alkaline magmatism in response to post-collisional extension.     

Oceanic subcrustal flow toward the continents and constancy of global sea-level

Summary From the conservation of the mass of the earth including the hydrosphere it can be concluded that continental growth has been connected with subcrustal flow from the ocean toward the continents. Calculations show that the volume of ocean bottom subsidence nearly equals to the volume of the uplifted continental masses above the level of the primeval ocean bottom. The sea level has not changed appreciably since Precambrian. Change of ocean bottom topography and emergence of continents do not effect global sea level. Transgression and regression are figurative terms and really indicate subsidence resp. uplift of the continental crust blocks around the shoreline.     

黄海的地壳速度结构与中朝-扬子块体拼合边界

利用中国、韩国和ISC台站的地震走时数据反演了黄海地区的地壳P波速度结构,对比重力异常和断裂体系、Pn波速度及其各向异性,分析了不同地球物理异常的相互关系以及黄海东部和西部的结构差异,为厘定黄海东部断裂暨中朝—扬子块体的拼合边界提供了新的信息.反演结果表明,北黄海和南黄海西部具有沉积盆地的地壳结构特征,P波速度明显偏低且深度较大,说明盆地内部沉积层较厚、沉降幅度较大,以北黄海、南黄海海州湾和苏北—南黄盆地最为突出.南黄海中部、胶东半岛、辽东半岛和朝鲜半岛显示出构造隆起区的地壳速度特征,其中南黄海中部的高速异常具有北东方向的伸展痕迹,与胶东地区的区域构造走向趋于一致,但是与朝鲜半岛的高速异常并不相连,其间存在明显的分界.据此推测南黄海与朝鲜半岛之间可能存在一个近南北方向的深断裂——黄海东部断裂,至于该断裂是否可以作为中朝—扬子块体在海区的拼合边界,尚需获取黄海东部及朝鲜半岛更详细的相关资料提供依据.     

The effective elastic thickness of the lithosphere in the collision zone between Arabia and Eurasia in Iran

The effective elastic thickness, T_e, has been calculated in the collision zone between Arabia and Eurasia in Iran from the wavelet coherence. The wavelet coherence is calculated from Bouguer anomalies and topography data using the isotropic fan wavelet method, and gives T_e values between 14.2 and 62.2 km. The lower value is found in the Central Iranian Blocks and the East Iranian Belt which are bounded by several large strike-slip faults with lithospheric origin. The higher value occurs in the east of the South Caspian Sea Basin. The resulting T_e map shows positive and negative correlation with shear wave velocity and surface heat flow, respectively. A comparison between the seismogenic thickness (T_s) and T_e in Iran suggests that T_e > T_s. Results of the load ratio in Iran indicate that in most of the study area surface loads are much more prevalent than subsurface loads, except in the Central Iranian Blocks and NW of Iran. Intermediate to low T_e values in Iran were inherited from multiple rifting and orogenic activities from Late Precambrian (∼650 Ma) to present day which are not only reflected in thin and warm lithosphere but also an increasing seismicity rate.     

具有不同表面特性的物体碰撞全过程分析

本文首先建立了颗粒碰撞的数学模型,利用改进的Hertz接触理论推导运动方程和耗能因子,然后通过有限元分析验证了理论的合理性.运用该数学模型分析了颗粒各项表面特性对碰撞耗能的影响,进而得到产生较大阻尼的条件.本文随后提出耗能系数的概念,通过对比该系数可以得知材料耗能能力的优劣,方便工程中选材.最后通过试验,在一个单自由度结构上附加颗粒阻尼器并采用不同的颗粒材料,测试其振动特性,得出与理论分析一致的结论.     

Excitation ofT waves in the Indian Ocean between Srilanka and southern India

T phases of three earthquakes from the Indian Ocean region, recorded by a short-period vertical-component seismic station network located in the vicinity of Kanyakumari on the southernmost tip of India, are studied. Two of these earthquakes are located west of 90°E ridge and one in the Nicobar Island region. However, seven other earthquakes which occurred 150–200 km south of Kanyakumari in the ocean did not produceT phases. An analysis ofT-waves (tertiary waves) travel time reveals the zone ofP-wave toT-wave conversion (i.e.,PT phase) region to coincide with the western continental slope of Srilanka. Further, it is observed that the disposition of the bathymetry between Srilanka and southern India strongly favours the downslope propagation mechanism ofT-wave travel to the southern coast of India through SOFAR channel. These observations are reported for the first time from India.     

The role of initial signals in the tropical Pacific Ocean in predictions of negative Indian Ocean Dipole events

Using reanalysis data, the role of initial signals in the tropical Pacific Ocean in predictions of negative Indian Ocean Dipole (IOD) events were analyzed. It was found that the summer predictability barrier (SPB) phenomenon exists in predictions, which is closely related to initial sea temperature errors in the tropical Pacific Ocean, with type-1 initial errors presenting a significant west-east dipole pattern in the tropical Pacific Ocean, and type-2 initial errors showing the opposite spatial pattern. In contrast, SPB-related initial sea temperature errors in the tropical Indian Ocean are relatively small. The initial errors in the tropical Pacific Ocean induce anomalous winds in the tropical Indian Ocean by modulating the Walker circulation in the tropical oceans. In the first half of the prediction year, the anomalous winds, combined with the climatological winds in the tropical Indian Ocean, induce a basin-wide mode of sea surface temperature (SST) errors in the tropical Indian Ocean. With the reversal of the climatological wind in the second half of the prediction year, a west-east dipole pattern of SST errors appears in the tropical Indian Ocean, which is further strengthened under the Bjerknes feedback, yielding a significant SPB. Moreover, two types of precursors were also identified: a significant west-east dipole pattern in the tropical Pacific Ocean and relatively small temperature anomalies in the tropical Indian Ocean. Under the combined effects of temperature anomalies in the tropical Indian and Pacific oceans, northwest wind anomalies appear in the tropical Indian Ocean, which induce a significant west-east dipole pattern of SST anomalies, and yield a negative IOD event.