Tectonic‒Thermal Coupling Metallogenic Models of Tethys Himalaya Pb‒Zn‒Sb‒Au Belt in Post-Collisional Stage

Geotectonics - Crustal-scale extensions occurred in the Tibetan Plateau during the post-collision stage, and leucogranites, N–S and E–W faults and other tectonic-thermal events were...     

珠江口盆地成盆‒成烃‒成藏:代序

珠江口盆地位于太平洋俯冲的东部动力系统、印度?澳大利亚板块与欧亚碰撞或新特提斯洋俯冲的西部动力系统相互作用的中间地带,因此其构造成因及南海海盆打开机制一直存在争论;且构造对南海北部陆缘盆地群的油气成藏有何作用也不甚清晰.本专辑以珠江口盆地为例,特别是以阳江东凹为精细解剖区,结合中国东部新生代盆地的研究成果,展开了以下问...     

Neoproterozoic Evolution and Najd‒Related Transpressive Shear Deformations Along Nugrus Shear Zone,South Eastern Desert,Egypt (Implications from Field‒Structural Data and AMS‒Technique)

The tectonometamorphic evolution of Nugrus Shear Zone (NSZ) in the south Eastern Desert of Egypt was reevaluated through an integrated study including field-structural work and magnetofabric analysis using Anisotropy of Magnetic Susceptibility (AMS) technique, complemented by detailed microstructural investigation. Several lines of evidence indicate that the Neoproterozoic juvenile crust within this high strain zone suffered an impressive tectonic event of left-lateral transpressional regime, transposed the majority of the earlier formed structures into a NNW to NW-directed wrench corridor depicts the northwestern extension of the Najd Shear System (NSS) along the Eastern Desert of Egypt. The core of the southern Hafafit dome underwent a high metamorphic event (M₁) developed during the end of the main collisional orogeny in the Arabian-Nubian Shield (ANS). The subsequent M₂ metamorphic event was retrogressive and depicts the tectonic evolution and exhumation of the Nugrus-Hafafit area including the Hafafit gneissic domes, during the origination of the left-lateral transpressive wrench corridor of the NSS. The early tectonic fabric within the NSZ and associated highly deformed rocks was successfully detected by the integration of AMS-technique and microstructural observations. Such fabric grain was checked through a field-structural work. The outcomes of the present contribution advocate a complex tectonic evolution with successive and overlapped deformation events for the NSZ.     

Ocean Redox State at 2500‒500 Ma: Modern Concepts

Modern concepts on variations of the redox conditions of Proterozoic ocean and atmosphere are reviewed. Generalized data indicate a non-linear evolution of the О₂ content in atmosphere and ocean for almost 2 Ga of the geological history. Contrasting distribution of minimum and maximum values of diverse proxies of the ocean redox state was found for the Great Oxygenation Event, Early–Late Proterozoic transition stage, and the Late Precambrian–beginning of Cambrian. The last interval is marked by a wide scatter of Mo, V, and U_sed concentrations and values of Мо/TOC, δ⁹⁸Mo, δ⁵³Cr, and δ⁸²Se in different geological objects. This time interval also coincided with one more large-scale oxygenation event, Neoproterozoic. Thus, according to the modern concepts, the О₂ contents near the Earth’s surface and in ocean significantly varied during the entire Proterozoic. These concepts are consistent with the assumption by Frolov and many other researchers concerning the heterogeneous distribution of рН and Eh in ancient hydrosphere and the existence of diverse, sufficiently contrasting “gas” facies. They also agree with conclusions by Sochava that the periodical variations of О₂ content in atmosphere and hydrosphere, especially at the Precambrian–Phanerozoic boundary, are related to the mass extinctions, emergence of adaptive response of animals (appearance of exoskeletons, food search strategy change, and others) and heavy taxonomic radiation of the latters.     

南海北部阳江‒一统暗沙断裂带与新近纪岩浆活动

阳江?一统暗沙断裂带是南海北部珠江口盆地极其重要的中?新生代构造带和转换带.基于钻井资料和大范围、高密度的二维、三维地震资料,本文初步揭示阳江?一统暗沙断裂带走向为NW-NWW向、宽约30 km,沿着断裂走向从陆架至洋陆边界断裂带可分为北?中?南三段,断裂在新生代选择性活化,具有多重走滑断裂叠合和基底岩浆底辟强烈等特点...     

Trend Analysis of Polynomial Surfaces and Surface Dynamics (TAPS‒SDs): A Paradigm from (MMT‒NPHMZ) in the Northwestern Himalayas,Pakistan

Geotectonics - Generation and interpretation of geomorphometric maps through remote sensing and GIS techniques are significant platforms for the investigations of neotectonics. This investigation...     

Deformation Mechanisms of Darreh Sary Metapelites,Sanandaj‒Sirjan Zone,Iran

The Darreh Sary metapelitic rocks are located in the northeast of Zagros orogenic belt and Sanandaj-Sirjan structural zone. The lithological composition of these rocks includes slate, phyllite, muscovitebiotite schist, garnet schist, staurolite-garnet schist and staurolite schist. The shale is the protolith of these metamorphic rocks, which was originated from the continental island arc tectonic setting and has been subjected to processes of Zagros orogeny. The deformation mechanisms in these rocks include bulging recrystallization (BLG), subgrain rotation recrystallization (SGR) and grain boundary migration recrystallization (GBM), which are considered as the key to estimate the deformation temperature of the rocks. The estimated ranges of deformation temperature and depth in these rocks show the temperatures of 275–375, 375–500, and >500°C and the depths of 10 to 17 km. The observed structures in these rocks such as faults, fractures and folds, often with the NW-SE direction coordinate with the structural trends of Zagros orogenic belt structures. The S-C mylonite fabrics is observed in these rocks with other microstructures such as mica fish, σ fabric and garnet deformation indicate the dextral shear deformation movements of study area. Based on the obtained results of this research, the stages of tectonic evolution of Darreh Sary area were developed.     

Structural Evolution and Halokinesis of Khaje Salt Diapir,North‒West of Iran

Geotectonics - The northeastern part of the Tabriz, Khaje area has been studied to determine the relationship between the orientation of local structures and regional tectonics, and the influence...     

Lithostratigraphy and geochemistry of Upper Vendian‒Lower Cambrian deposits in the northeastern Baltic monocline

The results of investigations of Upper Vendian?Lower Cambrian deposits in the northeastern part of the Baltic monocline specify views on the evolution of depositional environments of sedimentary successions constituting the basal part of the sedimentary cover in inner areas of the northwestern East European Platform. It is shown that the Late Vendian and initial Cambrian were characterized by the consecutive influx of relatively mature terrigenous detrital material that originated from both the weathering crust of the Baltic Shield and new sources. Its deposition was interrupted by notable, although likely asynchronous, hiatuses, which are registered at the base of the Upper Vendian Vasileostrovskaya and Voronkovo formations and Lower Cambrian Lomonosov Formation. In the Late Vendian, sedimentary material was transported from the Baltic Shield, while beginning from the initial Early Cambrian the additional contribution to the formation of the sedimentary cover of the Baltic monocline was provided by coarse-grained sedimentary material from the Timan margin of the Baltica as follows from U?Pb isotopic ages obtained for detrital zircons. At the same time, lithogeochemical parameters of fine-grained rocks experienced no substantial changes.     

珠江口盆地渐‒中新世古气候及物源特征:以阳江东凹为例

珠江口盆地阳江东凹处于太平洋构造域与新特提斯构造域交汇处,地球动力学背景、构造演化历史复杂,对于盆地物源特征和物源区古气候演化方面研究比较薄弱。选取珠江口盆地阳江东凹A钻井岩心中的珠海组-韩江组砂泥岩样品,对其进行地球化学分析,结果显示,样品呈轻稀土元素富集、重稀土元素平坦的配分模式,有明显的负Eu异常特征,与花岗岩相似;Al_2O_3/TiO_2、F1-F2、La/Th-Hf和Co/Th-La/Sc判别图解表明源岩以长英质为主,并有镁铁质岩石的混入;Al_2O_3/TiO_2、Cr/Zr和Th/Sc值也体现出长英质成分为主的物源特征;(Fe_2O_3+MgO)-TiO_2、Th-Co-Zr/10和Th-Sc-Zr/10构造环境判别图解显示,大部分样品落在大陆岛弧和主动大陆边缘区域,综合研究表明源区岩石特征与中国东南沿海大面积发育的岩浆岩极为相似。化学蚀变指数(CIA)、化学风化指数(CIW)、斜长石蚀变指数(PIA)等指标以及Mg/Ca值,指示珠江口盆地阳江东凹晚渐新世至中中新世物源区经历了中等程度的化学风化,对应温暖湿润的古气候环境,且从早到晚气温降低、降水量减少。     

In-bearing potential of tin‒sulfide mineralization in ore deposits of the Russian Far East

The increased demand for indium has made it necessary to revise prospects of In-bearing tin ore deposits in the Russian Far East on the basis of geological data and results of recent analytical methods (X-ray fluorescence with synchrotron radiation, atomic absorption, and ICP-MS). The average In contents in ores of the Tigrinoe and Pravourmiiskoe deposits vary from 55 to 70 ppm, which allows tin ore deposits with Sn?sulfide mineralization to be considered as quite promising with respect to In production from ores of Russian deposits. By their estimated In reserves, the Tigrinoe and Pravourmiiskoe deposits may be attributed to large ore objects.     

Polymer Particles in Solid Atmospheric Precipitation in the Northwestern Kola Peninsula in 2020‒2021

Doklady Earth Sciences - From December 2020 to April 2021, in the northwestern part of the Kola Peninsula, including the infrastructure of the city of Murmansk, the quantity of polymer particles in...     

Paleostress Analysis from Fractures in Kalosh Anticline,Kurdistan Region,North‒East of Iraq

Geotectonics - Fractures analysis carried out throughout traverses across Kalosh anticline. The anticline is located ~30 km south of Sulaimaniyah city, Kurdistan region, NE Iraq. It extends...     

Isotopic age and heterogeneous sources of gabbro‒anorthosites from the Patchemvarek massif,Kola Peninsula

New U?Pb (SHRIMP II) data on the age (2661.8 ± 7.1 Ma) and isotopic (Sm?Nd) composition of the Patchemvarek gabbro?anorthosite massif located in the junction zone between the Neoarchean Kolmozero-Voron’ya greenstone belt and Keivy paragneiss structure are discussed. The established age and geological?tectonic position of gabbro?anorthosites allow the prognostic metallogenic estimate of Ti?V?Fe mineralization to be extended to the entire Kolmozero-Voron’ya?Keivy infrastructural zone of the Kola?Norwegian province of the Fennoscandian shield.     

元谋‒昔格达断裂及其附近上新世以来的构造应力场特征及地貌响应

基于传统的古构造应力场重建方法,依据元谋?昔格达断裂及其附近的构造形迹,恢复了区域构造应力场.结果表明,研究区自上新世以来,主要受早期(中更新世之前)的NNE-SSW向和晚期(中更新世以来)的NNW-NWW向水平主压应力作用;而江边?下雷弄、化同?秧田井、一平浪?罗川一带的元谋?昔格达断裂晚第四纪倾滑特征与相应段落处的...     

Structure and stages in development of the cataplatform cover in the Central Russian‒Belomorian province

The results of correlation between seismic sequences (based on the CMP data) and lithostratigraphic units (based on drilling data) of the preplate sedimentary section are discussed. By the structure and interrelations of seismic sequences, as well composition and facies features of lithological varieties, three successive stages in the formation of the cataplatform cover of the province are recognizable: (1) main stage of the graben formation in the Central Russian and White Sea?Pinega regions; (2) terminal stage of the graben formation?initial stage of postrift subsidence in all regions; (3) the formation of a ‘protosyneclise” (non-riftogenic depression) in the Orsha region. The model for explaining the formation of the Orsha depression is proposed.     

Subsurface Modeling of Digboi‒Dilli Ghat Oil Bearing Structures (India) Using 2D Move

Geotectonics - The first discovery of commercial hydrocarbon in India was in 1889 in a structural trap at Digboi in Assam. Ever since the discovery, geologists have mapped and modeled the...     

Details of Interaction between CaCO3 and Fe at 4 GPa and 1400‒1500°C

Doklady Earth Sciences - The issue of the stability of carbonate matter (CaCO3) in subduction zones under reduced conditions remains topical. In addition, carbonates may be one of the key sources...     

The Durulgui rare-metal granite‒pegmatite system in the eastern Transbaikal region: Petrological and geochronological aspects

The Durulgui granite?pegmatite system unites the Dedova Gora granite massif and pegmatite field with the Chalotskoe beryl deposit. New geochronological data on micas from porphyric biotite granites, fine-grained biotite granites, two-mica granites, and Be-bearing pegmatites are discussed. The plateau age of 128.5(±1.5)–131.2(±1.5) should be considered as indicating the formation time of the granite?pegmatite system as a whole. The age of the system implies the possibility of its formation owing to several magmatic pulses. This assumption concerns porphyric and fine-grained biotite granites and two-mica and muscovite granites, the contact between which is locally sharp. At the same time, the succession “two-mica granites → muscovite granites → granite?pegmatites → microcline pegmatites → microcline?albite pegmatites → albite pegmatites” demonstrates gradual facies transitions between rocks, which indicates their emplacement during a single magmatic pulse.