Changes in the manner of tectonic movements under the Earth’s evolution

Variations in the O, Sr, Nd, and Hf isotopic compositions in rocks of various ages, minerals, and mantle temperature in the geological history are considered. Two periods in the Earth’s history are studied: the beginning of the formation of the planet until the turn of (3.4) 2.7–2.5 Ga and the tectonic movement period in the last 2 Ga, and also the transitional period within 2.7–2.0 Ga.     

Barrier effect of degassing and destruction of the Earth’s crust

Doklady Earth Sciences -     

Siderite formation and evolution of sedimentary iron ore deposition in the Earth’s history

The role of siderite in Phanerozoic and Precambrian iron formations is discussed. Various types of iron formations are characterized, and their place in the evolution of sedimentary iron ore deposition is outlined. In Precambrian iron ore deposition, siderite is a primary mineral, whereas in Phanerozoic iron formations it becomes a secondary mineral and is commonly related to diagenetic and catagenetic processes.     

Estimation of the stress state of the Earth’s crust and the upper mantle in the area of the Southern Kuril Islands

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.     

Main stages and geodynamic regimes of the Earth’s crust formation in East Antarctica in the Proterozoic and Early Paleozoic

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.     

Structure and evolution of the Earth’s crust in the region of junction of the Central Asian Fold Belt and the Siberian Platform: Skovorodino–Tommot profile

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.     

Extraterrestrial factors and their role in the Earth’s tectonic evolution in the Early Precambrian

The paper is focused on the fundamental problem of influence of extraterrestrial factors on the Earth’s geologic and tectonic evolution. Extraterrestrial factors played a decisive role in the Earth’s genesis, the formation of the first Hadean continental crust, and the beginning of the Archean era. Their significant influence persisted in the later epochs: Even in the Phanerozoic, extraterrestrial factors might have had a considerable influence on the environment. The sialic cores of protocontinental crust (4.4-3.9 Ga) with first-generation greenstone zones (3.8-3.2 Ga) and the global system of granite-greenstone belts (3.1-2.7 Ga) formed in the rotation-plume regime, mainly in the subequatorial hot belt. The formation of these global structures was, to a large extent, influenced by asteroid impacts, which caused the impact-triggered genesis of mantle plumes. Dramatic changes in the subsequent geologic history began at 2.7-2.0 Ga; at 2.0 Ga they terminated with the Moon’s transition to an orbit similar to the present-day one (50 ± 3 Earth’s radii), accompanied by the abrupt slowdown of the Earth’s axial rotation, the termination of formation of the layer D", and the start of recent plate tectonics, which is accompanied by the plume tectonics.     

Precessional motions of structural blocks of the Earth’s crust

Instrumental observations revealed a new type of motion previously not described in the literature, the precessional motions in the structural blocks of the Earth’s crust. The precession-nutation motions are caused largely by a complex response of a structural block and the adjacent tectonic structure, acting as a discontinuous zone between blocks, to tidal deformation. Irregular precession with a period of about one day complicated by the half a day period nutation defines a complex loading pattern characteristic of the internal structure of faults adjacent to the block.

     

Connection between variations of the stress-strain state of the Earth’s crust and seismic activity: The example of Southern California

A three-dimensional geomechanical model of Southern California, including mountain relief, fault tectonics, and characteristic internal borders, such as the roof of the consolidated crust and Moho surface, was created. The initial stress state of the model is determined by the gravitational force and horizontal tectonic movement, established on basis of GPS observations. Monitoring of variations in the stress state of the Earth’s crust and lithosphere, which are generated by seismic processes, has shown that the model enables us to predict an increase of seismic activity in a region and to mark the places in which average earthquakes can occur in the following two weeks.     

Metallogeny of deep structures of the Earth’s crust in Southern Sikhote-Alin: Evidence from gravity data

The spatial relations between ore deposits in Sikhote-Alin and deep density inhomogeneities of the Earth??s crust down to a depth of 30 km have been examined. The ore areas and regions show a discrete correlation with the anomalies of the normalized density of the equivalent spherical sources of gravity anomalies at depths of 1 to 2, 4 to 5, 10?C12, and 24 km presumably provoked by magmatic bodies of different compositions. The depth of the magmatic bodies with the intermediate-to-basic composition of the initial magmas and the southeastward-decreasing vertical range of their correlation with the ore regions depend on their structural position. In the case of magmatic bodies of felsic and mixed compositions, the metallogenic specialization of the corresponding ore-magmatic systems is correlated with their inferred vertical range. Tin ore systems are characterized by a smaller vertical range (5?C10 km) of the correlation with density inhomogeneities, whereas tin-tungsten-gold ore systems are marked by a wider range (20?C25 km). Tin-lead-zinc systems occupy an intermediate position (12?C20 km). The ore-controlling role of the boundaries between the lithostructural complexes of the Earth??s crust and the central-type structures in the distribution of deep sources of ore mineralization is shown.     

The influence of tropical cyclones upon the Earth’s crust

Doklady Earth Sciences - This paper discusses the influence of tropical cyclones (TCs) upon the Earth’s crust beneath the ocean bottom, which is associated with rapid variations of pressure...     

Recent structures and tectonic regimes of the stress–strain state of the Earth’s crust in the northeastern sector of the Russian Arctic region

A comprehensive investigation aimed at determining seismotectonic types of destruction and the stress–strain state of the Earth’s crust in the main seismogenerating structures of the Arctic–Asian seismic belt is conducted for the territory of the northeastern sector of the Russian Arctic region. Based on the degree of activity of geodynamical processes, the regional principles for ranking neotectonic structures are elaborated, and neotectonic zoning is carried out based on the substantiated differentiation of the corresponding classes. Within the limits of the Laptev Sea, Kharaulakh, and Lena-Anabar segments, we analyzed I the structural–tectonic position of the most recent structures, II the deep structure parameters, III the parameters of the active fault system, and IV the parameters of the tectonic stress field, as revealed from tectonophysical analysis of Late Cenozoic fault and fold deformations. Based on the seismological data, the mean seismotectonic deformation tensors are calculated to determine, in combination with geological and geophysical data, the orientations of the principal stress axes and to reveal the structural–tectonic regularity for tectonic regimes of the stress–strain state of the Earth’s crust in the Arctic sector of the boundary between the Eurasian and North American lithospheric plates.     

Proportions of massive-sulfide and strata-bound lead-zinc mineralization during the Earth’s evolution

Massive-sulfide base-metal deposits of the volcanic rock association and strata-bound Pb-Zn deposits in terrigenous and carbonate-terrigenous formations contain over 70% of the total world reserves of Pb and Zn. It has been found, based on an analysis of original databases on the corresponding mineral deposits found all over the world, that correlation in time and distribution in the Earth’s geological evolution of massive-sulfide deposits of the volcanic-rock association and lead-zinc deposits of the SEDEX type, as well as their reserves, was determined by changes in tectonic settings, by the evolution of the composition of the continental lithosphere, and by irreversible changes in the atmosphere, hydrosphere, and biosphere of the Earth.     

Stress state of the Earth’s crust of the Kuril Islands and Kamchatka before the Simushir earthquake

The field of modern tectonic stresses was reconstructed for the Earth’s crust of the northwestern segment of the Pacific subduction zones. For this purpose, we used the method of cataclastic analysis and data on the magnitude of the stresses released at the source of the Simushir earthquake of 2006, which allowed us to determine both the orientation of the principal stress axes and the magnitude of the stresses and to estimate the effective strength of rock masses. The effective cohesion was estimated for this region of the Earth’s crust as 12 bar, and the maximum shear stresses are no higher than 300 bar. The analysis of the reconstructed stress field in the zone of the preparation of the Simushir earthquake showed that this region was almost free of domains with high stresses where brittle failure requires considerable energy inputs. The medium level of effective pressure indicates that this region is most favorable for the development of a large-scale brittle failure.     

Supercontinental cyclicity in the Earth’s evolution

The Earth’s evolution is determined by supercontinental cyclicity with a period of 400 Ma. A supercycle consists of a supercontinental proper and an inter-supercontinental stage, each of which includes two phases, respectively: integration-destruction and fragmentation-convergence. The worldwide analysis of geologic-historic and isotope-geochronologic data supports the existence of such cyclicity. In all, ten supercontinental cycles of supercontinents have been identified; in this case, the most ancient proto-supercontinent was recognized tentatively, Supercontinents identified previously by other researchers fit into this cyclicity. An association between magmatism from mantle plumes and certain phases of supercontinental cyclicity was revealed. Amalgamation and breakup of supercontinents occurred against the background of disymmetry of the Northern and Southern hemispheres of the Earth, which changed its polarity between the cycles.     

Electric and magnetic signals due to constrained movement of blocks of the Earth’s crust

Doklady Earth Sciences -     

Computer modeling of granite magma diapirism in the Earth’s crust

A new point of view describing processes of partial melting and development of gravitational instability in a thickening crust with increased thickness of the granite layer is suggested. Numeral experiments support the following main conclusions. The critical volume of partially melted material should be formed for the beginning of flotation in a gravitational field. Due to model estimations, the height of the melting area in the granite crust should be not less than 6–7 km. A mushroom-shaped form of the floating body was observed in all models regardless of the thermal source size (fixed or variable width): the high temperature channel (magma leader) and head body of the diapir are formed. The height of diapir floating depends on rheological features of the surrounding crust: 10 times increase in the yield strength (from 1 to 10 MPa) while temperature decrease confines the possible level of rising to a depth of 15–16 km. An elevation of about 750 m is formed in the day surface relief above the axis part of the diapir.     

The tectonic history of Adelaide’s scarp-forming faults

A series of linear to arcuate fault scarps separate the Mount Lofty Ranges from the Cenozoic St Vincent and Murray basins of South Australia. Their tectonic, sedimentary and geomorphic evolution is traced from the oldest rock record through to present-day seismicity. The scarps are the latest manifestation of repeated compressive reactivation of ancient, deep-seated crustal faults and fractures whenever the stress field was of appropriate orientation. Formation of the basins and uplift of the ranges resulted from the same processes of repeated compressive reactivation. Continental crust was intensely fractured during three episodes of Neoproterozoic–Cambrian rifting that led to the formation of the Adelaide Geosyncline and break-up of Rodinia. Neoproterozoic eastward-dipping, listric extensional faults provided accommodation space for deposition of the Burra Group. Sediments of the Umberatana and Wilpena groups were deposited under mainly sag-phase conditions. In the early Cambrian, new extensional faults formed the deeply subsident Kanmantoo Trough. Cambrian rift faults swung from east–west on Kangaroo Island through northeasterly on Fleurieu Peninsula to north–south in the easten Mount Lofty Ranges, cutting across the older meridional rifts. These two sets of extensional faults were reactivated as basement-rooted thrusts in the ensuing Delamerian Orogeny. The Willunga Fault originated as a Cambrian rift fault and was reactivated in the Delamerian Orogeny as a thrust dipping southeast under a regional basement-cored antiform on southern Fleurieu Peninsula. Much of southern Australia, including the eroded remnants of the Delamerian highlands, was covered by a continental ice sheet in the Carboniferous–Permian. The preferential preservation of glacial sediments on Fleurieu Peninsula may have resulted from extensional reactivation of the Willunga Fault, possibly in the early Mesozoic. Fleurieu Peninsula was then warped into an open, southwest-plunging antiform, spatially coincident with the much higher amplitude Delamerian antiform. Glacial sediments were eroded from uplifted (up-plunge) areas before formation of a ‘summit surface’ across deeply weathered bedrock and preserved glacial sediments in the later Mesozoic. This surface was covered with fluvial to lacustrine sediments in the middle Eocene. Neotectonic movements under a renewed compressive regime commenced with reactivation of the Willunga Fault, restricting subsequent Eocene to Miocene sedimentation to the St Vincent Basin. The Willunga scarp was onlapped in the Oligocene–Miocene concomitant with continuing uplift and formation of a hanging-wall antiform. In the late Cenozoic, repeated faulting and mild folding, angular unconformities, ferruginisation and proximal coarse sedimentation took place on various faults at different times until the late Pleistocene.