scholarly journals A MODEL OF THE EVOLUTION OF THE LITHOSPHERE OF THE HIMALAYAN-TIBETAN OROGEN

2021 ◽  
pp. 89-107
Author(s):  
R.S. Alekseev, ◽  
◽  
Yu.L. Rebetsky ◽  
Keyword(s):  
Upper Mantle ◽  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
Indian Plate ◽  
Tibet Plateau ◽  
Small Scale ◽  
Continental Lithosphere ◽  
Principal Stresses ◽  
Vertical Movements ◽  
Reference Parameters

The Himalayan-Tibetan orogen is one of the active orogens on Earth. The processes caused by the collision of two continents have attracted attention of many researchers, and over the past decades, a large amount of geological and geophysical data has accumulated, on which models of the evolution of the region are based. The paper presents a model of the evolution of the Tibet plateau and the adjacent mountain chains, which complies with the modern concepts of the structure of the crust. The reference parameters of this model are the data on the values of stresses and on the patterns of the spatial distribution of principal stresses obtained in our own tectonophysical studies in region, as well as in other intracontinental orogens and in subduction zones between lithospheric plates. The basic assumptions of the model are the factors of the long stage of the Indian plate underthrusting beneath the Eurasian continent, metamorphic processes in the submerged slab (oceanic lithosphere) and in the continental lithosphere above it, combination of absolute horizontal movements of the Eurasian and Indian plates, small-scale convection in the upper mantle and vertical movements of matter, both in the continental lithosphere itself and in the upper mantle.

scholarly journals The role of Edge-Driven Convection in the generation of volcanism I: a 2D systematic study

2020 ◽  
Author(s):  
Antonio Manjón-Cabeza Córdoba ◽  
Maxim Ballmer
Keyword(s):  
Numerical Models ◽  
High Volume ◽  
Oceanic Lithosphere ◽  
Companion Paper ◽  
Small Scale ◽  
Continental Lithosphere ◽  
Transient Phenomenon ◽  
Mantle Viscosity ◽  
Wide Range

Abstract. The origin of intraplate volcanism is not explained by the plate tectonic theory, and several models have been put forward for explanation. One of these models involves Edge-Driven Convection (EDC), in which cold and thick continental lithosphere is juxtaposed to warm and thin oceanic lithosphere to trigger convective instability. To test whether EDC can produce long-lived high-volume magmatism, we run numerical models of EDC for a wide range of mantle properties and edge (i.e., the oceanic-continental transition) geometries. We find that the most important parameters that govern EDC are the rheological paramaters mantle viscosity η0 and activation energy Ea. However, even the maximum melting volumes found in our models are insufficient to account for island-building volcanism on old seafloor, such as at the Canary Islands and Cape Verde. Also, beneath old seafloor, localized EDC-related melting commonly transitions into widespread melting due to small-scale sublithospheric convection, inconsistent with the distribution of volcanism at these volcanic chains. In turn, EDC is a good candidate to sustain the formation of small seamounts on young seafloor, as it is a highly transient phenomenon that occurs in all our models soon after initiation. In a companion paper, we investigate the implications of interaction of EDC with mantle-plume activity.

scholarly journals Crustal and Upper Mantle Density Structure Beneath the Qinghai-Tibet Plateau and Its Surrounding Areas Derived from EGM2008 Geoid Anomalies

2016 ◽  
Author(s):  
Honglei Li ◽  
Jian Fang
Keyword(s):  
Upper Mantle ◽  
Initial Density ◽  
Density Model ◽  
Indian Plate ◽  
Tibet Plateau ◽  
Jinsha River ◽  
The Earth ◽  
Surrounding Areas ◽  
Geoid Anomalies ◽  
Qinghai Tibet Plateau

As the most active plateau on the Earth, the Qinghai-Tibet Plateau has a complex crust-mantle structure. Knowledge of the distribution of such a structure provides information for understanding the underlying geodynamic processes. We obtains a three-dimensional density model of crustal and upper mantle beneath Qinghai-Tibet plateau and its surrounding areas from the residual geoid anomalies using the Earth Gravitational Model (EGM) 2008. We estimate a refined density model by iterations, using an initial density contrast model. We confirm that the EGM2008 mission products can be used to constrain the crust-mantle density structures. Our major findings are: (1). At 300-400 km depth, high-D anomalies terminate around Jinsha River Suture (JRS) in the central TP, suggesting that the Indian plate has been reached over the Bangong Nujiang Suture (BNS) and almost reach to the JRS. (2). On the eastern TP, low-D anomalies at the depth of 0-300 km together with high-D anomalies at 400-670 km further verified the current eastward subduction of Indian plate. The ongoing subduction provides forces to the occurrences of frequent earthquakes and volcano. (3). At 600 km depth, low-D anomalies inside the TP illustrate the existence of hot weak material beneath there, contributing to the external material inward-thrusting.

Origin of complex upper mantle structures in the southern Lewis Hills (Bay of Islands Ophiolite, Newfoundland)

1991 ◽  
Vol 28 (5) ◽  
pp. 774-787 ◽  
Author(s):  
Günter Suhr ◽  
Tom Calon ◽  
Sherry M. Dunsworth
Keyword(s):  
Fracture Zone ◽  
Upper Mantle ◽  
Oceanic Lithosphere ◽  
Strike Slip ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Small Scale ◽  
Spreading Ridge ◽  
Hill Area ◽  
Strike Slip Movement

The Springers Hill area (Lewis Hills, Bay of Islands Ophiolite) may represent oceanic lithosphere created in close proximity to the nontransform segment of an oceanic fracture zone. Upper mantle rocks exposed on Springers Hill were investigated to establish whether their development was affected by the thermal and rheological changes associated with oceanic fracture zones. Harzburgites of the Springers Hill area reveal complex structural patterns. On a small scale, foliations defined by orthopyroxene grains intersect foliations defined by spinel grains at various angles. Olivine petrofabric work demonstrates that only the spinel foliation is related to the preserved flow plane. The orthopyroxene foliation appears to be the result of pull-apart of formerly larger grains during high-temperature deformation. On the larger scale, orientation patterns of foliation, lineation, and dykes suggest that strike-slip movement occurred parallel and at high angle to the fracture- zone contact at various stages of a complex flow history. Given its location adjacent to a nontransform segment of oceanic lithosphere, the origin of the strike-slip movement parallel to the fracture zone must be clarified. It can be accounted for by movement of the older lithosphere past asthenosphere of the young spreading ridge during plate-driven flow.

Thermal processes in the formation of continental lithosphere

1978 ◽  
Vol 288 (1355) ◽  
pp. 415-429 ◽  
Keyword(s):  
Subduction Zones ◽  
Thermal Evolution ◽  
Oceanic Lithosphere ◽  
Thermal Processes ◽  
Low Density ◽  
Continental Lithosphere ◽  
Mantle Material ◽  
Near Surface ◽  
Depleted Mantle ◽  
Melting Fraction

The thermal evolution of continental lithosphere in atectonic regions has been interpreted in terms of (1) conductive cooling, in the same way as oceanic lithosphere, but over much longer periods; (2) conductive cooling accelerated by erosion; (3) erosional removal of near-surface concentrations of heat-producing elements; and (4) various special temperature conditions assumed for its base. Although all of these factors influence lithospheric temperatures, particularly early in the development of continents, for times greater than 10 9 a, the thickness of the lithosphere and the processes by which it forms are of overriding importance. Continental lithosphere may develop by cooling and the thermal accretion of mantle material which has not been depleted of a basaltic first melting fraction, or it may develop by diapiric accretion of low-density, depleted mantle bodies rising from the upper parts of lithospheric slabs heated during their descent in subduction zones. The former process alone could not generate continental lithosphere with the observed characteristics. The latter process is likely to be important, possibly in combination with the former.

Mantle heterogeneities and their significance: results from Lithoprobe seismic reflection and refraction – wide-angle reflection studiesThis article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent.Lithoprobe Contribution 1486.

2010 ◽  
Vol 47 (4) ◽  
pp. 409-443 ◽  
Author(s):  
Ron M. Clowes ◽  
Don J. White ◽  
Zoltan Hajnal
Keyword(s):  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
P Wave ◽  
Wide Angle ◽  
Velocity Anisotropy ◽  
Tectonic Processes ◽  
Wide Range ◽  
Restricted Region

Within Lithoprobe’s 10 transects, data from more than 20 000 km of multichannel seismic (MCS) reflection profiling and 12 refraction – wide-angle reflection (R/WAR) surveys were acquired. While the main results related to crustal structure, the data also indicated substantial heterogeneity in the lithospheric mantle. Images of fossilized subduction zones from the Eocene to the Neoarchean demonstrate that current plate tectonic processes have been active for more than 2.6 Ga. The Canadian Cordillera has a thin (50–60 km) lithosphere that is likely receiving some dynamic support from the asthenosphere below. Vestiges of the last stage of accretionary tectonic processes that formed the Archean Superior craton are indicated by an unusual anisotropic high velocity layer that may represent relic oceanic lithosphere. Within the Paleoproterozoic Trans-Hudson Orogen, a restricted region of upper mantle P-wave velocity anisotropy is identified with the continental collision between the bounding Hearne and Superior cratons. In the Archean Hearne and Wyoming provinces, two dipping structures within the sub-crustal lithosphere are interpreted as subduction features related to the assembly of the two cratons. Finite-difference modeling of long-offset data (over 1300 km) reveals fine-scale heterogeneities within a layer between 90 and 150 km in the continental lithosphere, perhaps formed through lateral flow or deformation within the upper mantle. Based on Lithoprobe data, heterogeneities within the lithospheric mantle are reasonably common. They have a wide range of seismic signatures, include many different types and show differing scales. Nevertheless, their extent in the lithospheric mantle is considerably less than in the crust.

Continental collisions and the origin of subcrustal continental earthquakes

2019 ◽  
Vol 56 (11) ◽  
pp. 1101-1118 ◽  
Author(s):  
Dan McKenzie ◽  
James Jackson ◽  
Keith Priestley
Keyword(s):  
Subduction Zones ◽  
Depth Distribution ◽  
Oceanic Lithosphere ◽  
Simple Rule ◽  
Continental Lithosphere ◽  
Geological Evidence ◽  
Hindu Kush ◽  
Himalayan Belt ◽  
Almost All ◽  
Subcrustal Earthquakes

The existence of subcrustal continental earthquakes beneath the Alpine–Himalayan Belt was recognised more than 60 years ago. There is general agreement that most of those beneath the western part of the belt in the Mediterranean result from the subduction of oceanic lithosphere. There is less agreement about the origin of those beneath Vrancea in Romania, the Hindu Kush, and the Pamir. Because there is little evidence for the former existence of oceanic lithosphere beneath these regions, many authors have argued that these seismic zones result from the separation of the mantle part of the continental lithosphere from the crust before it sinks into the mantle. However, this model has become steadily less satisfactory. Detailed studies of the depth of earthquakes beneath all stable regions of continents have shown that substantial subcrustal earthquakes, with magnitudes greater than 5.5, are rare. We show that this distribution is controlled by temperature, with material hotter than ∼600 °C being aseismic. This simple rule accounts for the distribution of almost all earthquakes in oceanic and continental lithosphere, including those in subduction zones. We argue that the subcrustal continental earthquakes must also result from the subduction of oceanic lithosphere. This proposal is not new but has generally been dismissed because of the lack of surface geological evidence that suitable pieces of oceanic lithosphere existed. However, the depth distribution of continental earthquakes makes it steadily harder to avoid.

scholarly journals Depletion of the upper mantle by convergent tectonics in the Early Earth

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
A. L. Perchuk ◽  
T. V. Gerya ◽  
V. S. Zakharov ◽  
W. L. Griffin
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Upper Mantle ◽  
Subduction Zones ◽  
Convergence Rates ◽  
Oceanic Lithosphere ◽  
Early Earth ◽  
Plate Convergence ◽  
Depleted Mantle ◽  
Mantle Peridotites

AbstractPartial melting of mantle peridotites at spreading ridges is a continuous global process that forms the oceanic crust and refractory, positively buoyant residues (melt-depleted mantle peridotites). In the modern Earth, these rocks enter subduction zones as part of the oceanic lithosphere. However, in the early Earth, the melt-depleted peridotites were 2–3 times more voluminous and their role in controlling subduction regimes and the composition of the upper mantle remains poorly constrained. Here, we investigate styles of lithospheric tectonics, and related dynamics of the depleted mantle, using 2-D geodynamic models of converging oceanic plates over the range of mantle potential temperatures (Tp = 1300–1550 °C, ∆T = T − Tmodern = 0–250 °C) from the Archean to the present. Numerical modeling using prescribed plate convergence rates reveals that oceanic subduction can operate over this whole range of temperatures but changes from a two-sided regime at ∆T = 250 °C to one-sided at lower mantle temperatures. Two-sided subduction creates V-shaped accretionary terrains up to 180 km thick, composed mainly of highly hydrated metabasic rocks of the subducted oceanic crust, decoupled from the mantle. Partial melting of the metabasic rocks and related formation of sodic granitoids (Tonalite–Trondhjemite–Granodiorite suites, TTGs) does not occur until subduction ceases. In contrast, one sided-subduction leads to volcanic arcs with or without back-arc basins. Both subduction regimes produce over-thickened depleted upper mantle that cannot subduct and thus delaminates from the slab and accumulates under the oceanic lithosphere. The higher the mantle temperature, the larger the volume of depleted peridotites stored in the upper mantle. Extrapolation of the modeling results reveals that oceanic plate convergence at ∆T = 200–250 °C might create depleted peridotites (melt extraction of > 20%) constituting more than half of the upper mantle over relatively short geological times (~ 100–200 million years). This contrasts with the modeling results at modern mantle temperatures, where the amount of depleted peridotites in the upper mantle does not increase significantly with time. We therefore suggest that the bulk chemical composition of upper mantle in the Archean was much more depleted than the present mantle, which is consistent with the composition of the most ancient lithospheric mantle preserved in cratonic keels.

scholarly journals GEODYNAMICS

GEODYNAMICS ◽  
2020 ◽  
Vol 2(29)2020 (2(29)) ◽  
pp. 89-96
Author(s):  
M. I. Orlyuk ◽  
◽  
V. V. Drukarenko ◽  
O. Ye. Shestopalova ◽  
◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Curie Temperature ◽  
Transition Zone ◽  
Upper Mantle ◽  
Subduction Zones ◽  
Magnetic Anomalies ◽  
Oceanic Lithosphere ◽  
Magnetic Minerals ◽  
Native Iron ◽  
Lithospheric Plates

The purpose of the study. It needs to substantiate that sources of magnetic anomalies with wavelengths of the first thousand kilometers detected at the present time might have a magneto-mineralogical origin due to the existence of magnetic minerals at the mantle depths, in particular magnetite, hematite, native iron, as well as iron alloys. It should be also shown that present temporal changes of long-wave magnetic anomalies should be induced by changes of the magnetic properties of these minerals due to thermodynamic and fluid modes. According to numerous authors, the transformations of magnetic minerals occur in special tectonic zones of the upper mantle of the Earth, in particular at junction zones of lithospheric plates of different types, rifts, plumes, tectonic-thermal activation, etc. Areas of the upper mantle with temperatures below the Curie temperature of magnetite can be magnetic, such as subduction zones, cratons, and regions with the old oceanic lithosphere. Iron oxides might be a potential source of magnetic anomalies of the upper mantle besides magnetite and native iron, in particular hematite (α-Fe2O3), which is the dominant oxide in subduction zones at depths of 300 to 600 km. It was proved experimentally by foreign researchers that in cold subduction slabs, hematite remains its magnetic properties up to the mantle transition zone (approximately 410-600 km). Conclusions. A review of previous studies of native and foreign authors has made it possible to substantiate the possibility of the existence of magnetized rocks at the mantle depths, including native iron at the magneto-mineralogical level, and their possible changes due to thermodynamic factors and fluid regime. It has been experimentally proven by foreign researchers that in subduction zones of the lithospheric slabs their magnetization might be preserved for a long time at the mantle depths, as well as increase of magnetic susceptibility may observed due to the Hopkinson effect near the Curie temperature of magnetic minerals. Practical value. Information about the ability of the mantle to contain magnetic minerals and to have a residual magnetization up to the depths of the transition zone was obtained. It should be used in the interpretation of both modern magnetic anomalies and paleomagnetic data.

The petrological and geochemical study of granitoid rocks from Mashhad area, Iran: Evidence for the Late Triassic Collisional Belt Northeast of Iran

2021 ◽  
Author(s):  
Banafsheh Vahdati ◽  
Seyed Ahmad Mazaheri
Keyword(s):  
Subduction Zones ◽  
Tectonic Setting ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Late Triassic ◽  
Common Belief ◽  
Thrust Tectonics ◽  
Wide Range ◽  
Lree Enrichment ◽  
Granitoid Rocks

<p>Mashhad granitoid complex is part of the northern slope of the Binalood Structural Zone (BSZ), Northeast of Iran, which is composed of granitoids and metamorphic rocks. This research presents new petrological and geochemical whole-rock major and trace elements analyses in order to determine the origin of granitoid rocks from Mashhad area. Field and petrographic observations indicate that these granitoid rocks have a wide range of lithological compositions and they are categorized into intermediate to felsic intrusive rocks (SiO<sub>2</sub>: 57.62-74.39 Wt.%). Qartzdiorite, tonalite, granodiorite and monzogranite are common granitoids with intrusive pegmatite and aplitic dikes and veins intruding them. Based on geochemical analyses, the granitoid rocks are calc-alkaline in nature and they are mostly peraluminous. On geochemical variation diagrams (major and minor oxides versus silica) Na<sub>2</sub>O and K<sub>2</sub>O show a positive correlation with silica while Al<sub>2</sub>O<sub>3</sub>, TiO<sub>2</sub>, CaO, Fe<sub>2</sub>O<sub>3</sub>, and MgO show a negative trend. Therefore fractional crystallization played a considerable role in the evolution of Mashhad granitoids. Based on the spider diagrams, there are enrichments in LILE and depletion in HFSE. Low degrees of melting or crustal contamination may be responsible for LILE enrichment. Elements such as Pb, Sm, Dy and Rb are enriched, while Ba, Sr, Nd, Zr, P, Ti and Yb (in monzogranites) are all depleted. LREE enrichment and HREE depletion are observed in all samples on the Chondrite-normalized REE diagram. Similar trends may be evidence for the granitoids to have the same origin. Besides, LREE enrichment relative to HREE in some samples can indicate the presence of garnet in their source rock. Negative anomalies of Eu and Yb are observed in monzogranites. Our results show that Mashhad granitoid rocks are orogenic related and tectonic discrimination diagrams mostly indicate its syn-to-post collisional tectonic setting. No negative Nb anomaly compared with MORB seems to be an indication of non-subduction zone related magma formation. According to the theory of thrust tectonics of the Binalood region, the oceanic lithosphere of the Palo-Tethys has subducted under the Turan microplate. Since the Mashhad granitoid outcrops are settled on the Iranian plate, this is far from common belief that these granitoid rocks are related to the subduction zones and the continental arcs. The western Mashhad granitoids show more mafic characteristics and are possibly crystallized from a magma with sedimentary and igneous origin. Thus, Western granitoid outcrops in Mashhad are probably hybrid type and other granitoid rocks, S and SE Mashhad are S-type. Evidences suggest that these continental collision granitoid rocks are associated with the late stages of the collision between the Iranian and the Turan microplates during the Paleo-Tethys Ocean closure which occurred in the Late Triassic.</p>

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