Geodynamics & Tectonophysics (E-Journal) / Геодинамика и тектонофизика
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ЧИСЛЕННАЯ МОДЕЛЬ МАГМАТИЧЕСКОГО МИНГЛИНГА (НА ПРИМЕРЕ БАЯНКОЛЬСКОЙ ГАББРО‐ГРАНИТНОЙ СЕРИИ, САНГИЛЕН, ТУВА)
Get PDFA new numerical model has been developed that makes it possible to describe the process of formation of a dyke of a combined composition on the basis of the dynamics of a viscous compressible fluid. The numerical thermo‐mechanical model shows the processes of magma mingling and taking into account multiphase interaction of melts which are different in composition and properties. The models suggest a mechanism for uplifting of high‐density mafic enclaves in a chamber/dyke filled with salic magma by gravitational floating in the enclosing gran‐ ite magma that has been cooled and lost volatile components. The performed simulation shows that the main parame‐ ter controlling the shape and size of the ascending bodies is the difference in densities. The viscosity contrast determines whether interpenetration and hybridization of magmas occur. The limiting ratio of felsic material in the mix‐ ture, which is capable of uplifting denser mafic enclaves, is estimated. The duration of melt uplifting in combined dykes is estimated with respect to the viscosity parameters. At a typical rate of 2–3 km per year, it amounts to almost 12 months.Впервые разработана численная модель, позволяющая описывать процесс формирования дайки комбинированного состава на основе динамики вязкой сжимаемой жидкости, а также численная термомеханическая модель процессов магматического минглинга, учитывающая многофазное взаимодействие разных по составу и свойствам расплавов. На основе моделирования предложен механизм подъема высокоплотных базитовых включений в камере или дайке, заполненной салической магмой, путем гравитационного всплывания во вмещающей гранитной магме, охлажденной и потерявшей летучие компоненты. Выполненное моделирование показывает, что основным параметром, контролирующим форму и размер поднимающихся тел, является разность плотностей. В свою очередь, контрастность вязкости определяет, происходит ли взаимопроникновение и гибридизация магм. Установлено предельное содержание доли кислого материала в смеси, способного транспортировать вверх более плотные базитовые включения. В зависимости от параметров вязкости оценена длительность подъема расплавов в комбинированных дайках, которая составляет около года при характерной скорости 2–3 км/год
ORE SYSTEMS: TYPES, AND GEODYNAMIC SETTINGS FOR THEIR OCCURRENCE (EASTERN SIBERIA)
Get PDFThe Mineralogy, Petrography and Minerals Department of the Irkutsk State Technical University (now the Irkutsk National Research Technical University) has been studying the structural, mineralogical and geochemical features of ore fields for over 30 years. We investigated more than 25 deposits of gold, uranium, rare, non-ferrous and ferrous metals, and published the prognostic metallogenic maps of the ore regions located in Eastern Siberia, Mongolia and Yakutia. Our experience shows that knowing only the genetic characteristics of ore objects is not sufficient for proper metallogenic studies. A complete set of deposit characteristics should include the data on structure, composition, localization conditions and other properties of ore objects and fields. We propose to introduce the “ore system” (OS) concept considering a combination of genetically (paragenetically) related and interrelated petrological, tectonic, metamorphic, mineralogical, geochemical and lithological elements formed during the pre-ore (preparatory) and ore-formation stages [Seminsky, 1990]. In contrast to the proposed OS concept, common terms, such as “ore-magmatic”, “oremetasomatic”, “ore-generating”, “ore-localizing” systems, usually consider only one aspect of the ore process or object [Russian Metallogenic Dictionary, 2003]. In our opinion, descriptions and typification of ore objects viewed as OS should refer to two groups of characteristics.The Mineralogy, Petrography and Minerals Department of the Irkutsk State Technical University (now the Irkutsk National Research Technical University) has been studying the structural, mineralogical and geochemical features of ore fields for over 30 years. We investigated more than 25 deposits of gold, uranium, rare, non-ferrous and ferrous metals, and published the prognostic metallogenic maps of the ore regions located in Eastern Siberia, Mongolia and Yakutia. Our experience shows that knowing only the genetic characteristics of ore objects is not sufficient for proper metallogenic studies. A complete set of deposit characteristics should include the data on structure, composition, localization conditions and other properties of ore objects and fields. We propose to introduce the “ore system” (OS) concept considering a combination of genetically (paragenetically) related and interrelated petrological, tectonic, metamorphic, mineralogical, geochemical and lithological elements formed during the pre-ore (preparatory) and ore-formation stages [Seminsky, 1990]. In contrast to the proposed OS concept, common terms, such as “ore-magmatic”, “oremetasomatic”, “ore-generating”, “ore-localizing” systems, usually consider only one aspect of the ore process or object [Russian Metallogenic Dictionary, 2003]. In our opinion, descriptions and typification of ore objects viewed as OS should refer to two groups of characteristics
LITHIUM ISOTOPIC CONSTRAINTS ON THE ORIGIN OF I- AND A-TYPE GRANITES FROM EAST JUNGGAR (NW CHINA) OF THE CENTRAL ASIAN OROGENIC BELT: IMPLICATIONS FOR LI ISOTOPIC FRACTIONATION DURING CRUSTAL ANATEXIS
Get PDFThough Li isotope fractionation during mantle melting and differentiation of basaltic melts have been proved insignificant, Li isotopic systems during crustal processes remain unclear. To study this, we report combined petrological, Nd-Sr and Li isotopic data for the late Paleozoic coexisting I- and A-type granites in the East Junggar orogen of the Central Asian Orogenic Belt. The granites were formed responding to underplating of mafic magmas in the lower crust in a postcollisional, extensional regime, and intruded into the Paleozoic foldbelts that formed due to extensive oceanic subduction-accretion processes.Though Li isotope fractionation during mantle melting and differentiation of basaltic melts have been proved insignificant, Li isotopic systems during crustal processes remain unclear. To study this, we report combined petrological, Nd-Sr and Li isotopic data for the late Paleozoic coexisting I- and A-type granites in the East Junggar orogen of the Central Asian Orogenic Belt. The granites were formed responding to underplating of mafic magmas in the lower crust in a postcollisional, extensional regime, and intruded into the Paleozoic foldbelts that formed due to extensive oceanic subduction-accretion processes
MELTING OF ACCRETIONARY WEDGE AND BUILDING MATURE CONTINENTAL CRUST: INSIGHTS FROM THE MAGMATIC EVOLUTION OF THE CHINESE ALTAI OROGEN, CENTRAL ASIA
Get PDFTectonic-magmatic reworking of accretionary wedges is a key process responsible for differentiation and stabilization of continental crustal in accretionary orogens. This generic problem can be exemplified by magmatic evolution of the Chinese Altai which represents a high-grade core of the world's largest accretionary system, namely the Central Asian Orogenic Belt (CAOB). In the Chinese Altai, voluminous SilurianDevonian granitoids intruding a greywacke-dominated Ordovician flysch sequence. These intrusions are classically interpreted to originate from predominant (70‒90 %) juvenile (depleted mantle-derived) magma. However, their close temporal and spatial relationship with the regional anatexis of flysch rocks, allows us to examine the possibility that they were mainly derived from flysch rocks.Tectonic-magmatic reworking of accretionary wedges is a key process responsible for differentiation and stabilization of continental crustal in accretionary orogens. This generic problem can be exemplified by magmatic evolution of the Chinese Altai which represents a high-grade core of the world's largest accretionary system, namely the Central Asian Orogenic Belt (CAOB). In the Chinese Altai, voluminous SilurianDevonian granitoids intruding a greywacke-dominated Ordovician flysch sequence. These intrusions are classically interpreted to originate from predominant (70‒90 %) juvenile (depleted mantle-derived) magma. However, their close temporal and spatial relationship with the regional anatexis of flysch rocks, allows us to examine the possibility that they were mainly derived from flysch rocks
ОПРЕДЕЛЕНИЕ ФОКАЛЬНЫХ МЕХАНИЗМОВ СЛАБЫХ ЗЕМЛЕТРЯСЕНИЙ И СОВРЕМЕННАЯ ГЕОДИНАМИКА ЮГА ИРАНА
Get PDFThe Southern Iran territory, including the Zagros region and the margins of the Arabian and Eurasian plates, is a seismically active area with large industrial facilities of Iran. In this respect, studying modern geodynamics of this area is a top research task. This article presents a part of the studies conducted by the IPE RAS Seismological Expedition led by the Doctor of Physics and Mathematics S.S. Arefiev in 1999–2001. The research team studied the seismic setting on the construction site of the Bushehr Nuclear Power Plant. The main results discussed in the present article are the focal mechanism solutions based on the data of the IPE RAS seismic network. The network was deployed in the junction area of the Fars and Dezful tectonic provinces (north of the Bushehr NPP) and covered an area of 100´100 km. A specific feature of the seismic network was that it comprised local networks, and each local station was focused, first of all, on determining the precise locations of earthquake epicenters in a particular section of the crust. However, the scarcity of stations in such local networks and the technologies available at that time did not allow us to determine the mechanisms of earthquake foci. This problem was solved by integrating the seismological and tectonophysical methods. In the analysis, we used the tectonophysical approach that is usually applied to reconstruct stresses from the data on slickensides. This approach is based on a specific algorithm of the kinematic method developed by O.I. Gushchenko, which is used in the absence of sliding direction signs. It became possible, in addition to a few signs from the first P-wave arrivals (1–2 confident signs), to use the data on the S-wave polarization direction. By applying the Gushchenko algorithm to such data, the areas of P and T axes were quite reliably localized on a single hemisphere for determining the focal mechanisms. The focal mechanisms computed for 72 earthquakes correspond to the Kazerooni-Borazdzhan shearing zone and, at the same time, are indicative of the presence of crust incision mechanisms in the Bushehr Peninsula. The focal mechanisms computed in our study, as well as the mechanisms reported in the Global CMT Project Catalogue, show that the Bushehr Peninsula is located near the western boundary of the zone of strike-slip faults, which extends from the north (Zagros) to the south (the Persian Gulf) and widens as a horsetail-shape structure. In the crust of the Persian Gulf coast, the intensity of the strike-slip component in the earthquake focal mechanism is minimal. The earthquake mechanisms in this region are mainly related to thrusting, reverse faulting and even the crust incision.Южный Иран в районе Загроса и границ Аравийской и Евразийской плит является сейсмически активной территорией, на которой находятся крупные промышленные объекты. В этой связи понятна актуальность изучения современной геодинамики региона. В работе представлена небольшая часть исследований, выполненных в процессе проведения изысканий сейсмологической экспедиции ИФЗ РАН под руководством д.ф.-м.н. С.С. Арефьева в 1999–2001 гг. Работы были связаны с изучением сейсмической обстановки в районе строительства АЭС Бушер. Главным результатом, обсуждаемым в статье, являются решения фокальных механизмов, полученных по данным сейсмической сети ИФЗ РАН. Сеть была развернута в области сопряжения тектонических провинций Фарс и Дезфул (к северу от АЭС Бушер) и охватывала область 100´100 км. Особенностью сейсмических сетей локальных станций является ее нацеленность, прежде всего, на точность локации эпицентров землетрясений определенного участка коры. При этом немногочисленность станций таких локальных сетей и существовавшие в то время методы не позволяли определять механизмы очагов землетрясений. Эта задача была решена на основе комплексирования сейсмологических и тектонофизических методов. В ходе анализа был использован тектонофизический подход, который обычно применялся при реконструкции напряжений по данным о зеркалах скольжения. Он основан на специфическом алгоритме кинематического метода О.И. Гущенко, используемом в случае отсутствия знаков в направлении скольжения. Это дало возможность в дополнение к небольшому числу знаков по первым вступлениям P-волны (1–2 уверенных знака) использовать данные о направлении поляризации S-волны. Применение алгоритма метода О.И. Гущенко к таким данным позволило на единичной полусфере достаточно достоверно локализовать области выходов осей P и T при определении механизмов очагов. Полученные фокальные решения для 72 землетрясений соответствуют Казерун-Боразджанской зоне сдвигов и в то же время показывают наличие взрезовых механизмов для коры полуострова Бушер. Обобщение этих данных, а также данных о фокальных механизмах из базы «Global CMT Project» свидетельствует о том, что п-ов Бушер расположен вблизи западной границы зоны сдвигов, простирающейся с севера (Загрос) на юг (Персидский залив) и расширяющейся в виде конского хвоста. В коре побережья Персидского залива интенсивность компоненты сдвига в механизмах очагов землетрясений минимальна, здесь преимущественно возникают землетрясения с механизмами надвигового, взбросового и даже взрезового типа
NO EXCESSIVE CRUSTAL GROWTH IN THE CENTRAL ASIAN OROGENIC BELT: FURTHER EVIDENCE FROM FIELD RELATIONSHIPS AND ISOTOPIC DATA
Get PDFWe provide new field observations and isotopic data for key areas of the Central Asian Orogenic Belt (CAOB), reiterating that no excessive crustal growth occurred during its ca. 800 Ma long orogenic evolution. Many Precambrian blocks (microcontinents) identified in the belt are exotic and are most likely derived from the northern margin of Gondwana, including the Tarim craton.We provide new field observations and isotopic data for key areas of the Central Asian Orogenic Belt (CAOB), reiterating that no excessive crustal growth occurred during its ca. 800 Ma long orogenic evolution. Many Precambrian blocks (microcontinents) identified in the belt are exotic and are most likely derived from the northern margin of Gondwana, including the Tarim craton
GEODYNAMICS OF THE KAZAKHSTAN OROCLINE, CENTRAL ASIA
Get PDFCurved mountain belts, commonly referred as to oroclines that result from bending of quasi-linear orogenic belts, have fascinated generations of geologists. Such structures are widely recognized in modern and ancient orogens, and are fundamentally important for understanding geodynamics of convergent plate boundaries. However, how and why orogenic belts become bent has been in debate. Here we investigate the Kazakhstan Orocline in the Central Asian Orogenic Belt with an aim at understanding the geodynamics of oroclinal bending in accretionary orogens.Curved mountain belts, commonly referred as to oroclines that result from bending of quasi-linear orogenic belts, have fascinated generations of geologists. Such structures are widely recognized in modern and ancient orogens, and are fundamentally important for understanding geodynamics of convergent plate boundaries. However, how and why orogenic belts become bent has been in debate. Here we investigate the Kazakhstan Orocline in the Central Asian Orogenic Belt with an aim at understanding the geodynamics of oroclinal bending in accretionary orogens
МИНГЛИНГ-ПРОЦЕССЫ В ЗЕМНОЙ КОРЕ: ГЕОЛОГИЧЕСКИЕ НАБЛЮДЕНИЯ И МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ
Get PDFThis issue of Geodynamics & Tectonophysics presents the state-of-the-art studies of mingling processes and investigations of the interactions between the mafic and acidic melts of contrasting compositions at various depths of the Earth's crust. The diagnostic features and the genesis of magmatic and synmetamorphic mingling are discussed with respect to the reference objects of Altaides and Uralides. Several papers report on the results of mathematical simulation used to discover the mechanism for lifting the high-density basite inclusions in a chamber or a dyke filled with salic magma. This special issue is intended for researchers and specialists in geology, petrology and geodynamics of magmatic processes in the crust, as well as for lecturers, post-graduate students and university students.Специальный выпуск журнала Geodynamics & Tectonophysics отражает современный уровень исследований минглинг-процессов, свидетельствующий о взаимодействии контрастных по составу базитовых и кислых расплавов на разноглубинных уровнях земной коры. На примере эталонных объектов алтаид и уралид рассмотрены диагностические признаки и генезис магматического и синметаморфического минглинга. На основе математического моделирования предложен механизм подъема высокоплотных базитовых включений в камере или дайке, заполненной салической магмой. Спецвыпуск предназначен для специалистов в области геологии, петрологии и геодинамики магматических процессов в земной коре, а также для преподавателей, аспирантов и студентов вузов
FIRST DATA ON THE CONCENTRATIONS AND DISTRIBUTION OF NOBLE METALS IN NI-CU SULFIDE ORES OF THE SOUTH MAKSUT DEPOSIT (EAST KAZAKHSTAN)
Get PDFThe magmatic sulfide deposits in the Central Asian orogenic belt are hosted in a series of mafic–ultramafic intrusions in the Maksut zone (E Kazakhstan), the Kalatongke and the Huangshan zones in Xinjiang (NW China) and the Hongqiling zone in NE China. In the Maksut zone there are several intrusions, the best studied from which is the South Maksut intrusion with Cu–Ni–PGE mineralization.The magmatic sulfide deposits in the Central Asian orogenic belt are hosted in a series of mafic–ultramafic intrusions in the Maksut zone (E Kazakhstan), the Kalatongke and the Huangshan zones in Xinjiang (NW China) and the Hongqiling zone in NE China. In the Maksut zone there are several intrusions, the best studied from which is the South Maksut intrusion with Cu–Ni–PGE mineralization
ВОЗРАСТ ГРЯЗЕВОЙ БРЕКЧИИ ГРЯЗЕВЫХ ВУЛКАНОВ АКАДЕМИЧЕСКОГО ХРЕБТА ОЗЕРА БАЙКАЛ
Get PDFLakeBaikalis the only freshwater reservoir on Earth with gas-hydrate accumulations in its bottom sediments, partly due to the activity of mud volcanoes. This paper describes a group of mud volcanoes recently discovered on the slope of the Academician Ridge between the northern and central LakeBaikalbasins. Our analysis of diatom skeletons in the mud breccia sampled from the study area shows a high abundance of Cyclotella iris et var. These extinct species were also discovered in a core sample from BDP-98 borehole. Based on the biostratigraphic and seismostratigraphic correlations, the age of the mud breccia in the studied mud volcanoes ranges from the Late Miocene to the Early Pliocene (4.6 to 5.6 Ma). The correlations suggest that the material originated from a depth of less than310 m below the lake bottom.Озеро Байкал является единственным пресноводным водоемом, в донных отложениях которого обнаружены скопления газовых гидратов, часть из них связана с деятельностью грязевых вулканов. В настоящей работе представлена группа грязевых вулканов, обнаруженных с помощью съемки многолучевым эхолотом на склоне подводной возвышенности Академический хребет между средней и северной котловинами озера Байкал. Анализ скелетов диатомей в грязевой брекчии выявил в массе вымерший вид Cyclotella iris et var., который ранее был обнаружен в керне скважины BDP-98. При помощи биостратиграфической и сейсмостратиграфической корреляции было установлено, что материал, входящий в грязевую брекчию исследуемых грязевых вулканов, имеет возрастной интервал от позднего миоцена до раннего плиоцена (от 5.6 до 4.6 млн лет) и мог быть поднят с глубины не более310 м ниже дна.