Geodynamics & Tectonophysics (E-Journal) / Геодинамика и тектонофизика
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EARLY PRECAMBRIAN CRUSTAL EVOLUTION OF THE BELOMORIAN AND TRANS-NORTH CHINA OROGENS AND SUPERCONTINENTS RECONSTRUCTION
Get PDFComparative analysis of the crustal evolution of the Early Precambrian Belomorian and Trans-North China orogens (Fig. 1) has shown [Slabunov et al., 2015] that: Both belts were formed by the superposition of two Precambrian orogenies. The earth crust of the Belomorian belt was produced during the Mesoarchaean to Neoarchaean Belomorian collisional orogeny [Slabunov, 2008; Slabunov et al., 2006] and then was reworked during the Palaeoproterozoic Lapland-Kola collisional orogeny [Daly at al., 2006; Balagansky et al., 2014]. The earth crust of the Trans-North China orogen was formed during a Neoarchean accretionary orogeny and then was reworked during a Paleoproterozoic collisional orogeny [Zhao et al., 2012; Guo et al., 2012, 2005]. The Lapland granulite belt is the core of the Lapland-Kola Palaeoproterozoic collisional orogen in the Fennoscandian shield and the Khondolite belt occupies the same tectonic position in a Palaeoproterozoic collisional orogen in the North China craton.Comparative analysis of the crustal evolution of the Early Precambrian Belomorian and Trans-North China orogens (Fig. 1) has shown [Slabunov et al., 2015] that: Both belts were formed by the superposition of two Precambrian orogenies. The earth crust of the Belomorian belt was produced during the Mesoarchaean to Neoarchaean Belomorian collisional orogeny [Slabunov, 2008; Slabunov et al., 2006] and then was reworked during the Palaeoproterozoic Lapland-Kola collisional orogeny [Daly at al., 2006; Balagansky et al., 2014]. The earth crust of the Trans-North China orogen was formed during a Neoarchean accretionary orogeny and then was reworked during a Paleoproterozoic collisional orogeny [Zhao et al., 2012; Guo et al., 2012, 2005]. The Lapland granulite belt is the core of the Lapland-Kola Palaeoproterozoic collisional orogen in the Fennoscandian shield and the Khondolite belt occupies the same tectonic position in a Palaeoproterozoic collisional orogen in the North China craton
AN EARLY PERMIAN GARNET-BEATING PERALUMINOUS GRANITIC PLUTON IN THE SOUTH TIANSHAN OROGENIC BELT, NW CHINA: PETROLOGICAL, MINERALOGICAL AND GEOCHEMICAL CONSTRAINTS
Get PDFThe Ku’erchu granitic pluton (283±4 Ma) was exposed in the eastern part of the South Tianshan Orogenic Belt. The granites from the intrusion are mainly composed of orthoclase (~45 vol. %), plagioclase (~15 vol. %), quartz (~20 vol. %), muscovite (~10 vol. %) and biotite (~5 vol. %), with accessory minerals including garnet, zircon and Fe-Ti oxide.The Ku’erchu granitic pluton (283±4 Ma) was exposed in the eastern part of the South Tianshan Orogenic Belt. The granites from the intrusion are mainly composed of orthoclase (~45 vol. %), plagioclase (~15 vol. %), quartz (~20 vol. %), muscovite (~10 vol. %) and biotite (~5 vol. %), with accessory minerals including garnet, zircon and Fe-Ti oxide
EVOLUTION OF THE NORTHERN ALXA BLOCK IN THE PALEOZOIC: CONSTRAINTS FROM GEOCHRONOLOGY, GEOCHEMICAL CHARACTERISTICS AND ZIRCON HF ISOTOPES OF GRANITOIDS
Get PDFThe Alxa block is situated to the south of the CAOB, situated to the east of the Tarim block and west of the NCC. Voluminous intrusive and extrusive rocks outcrop in the northern Alxa block and adjacent southern CAOB. Most of them are thought to be related to the closure of the Paleo-Asia Ocean and subsequent collision [Wu, 1993; Wu et al., 1998; Zhang et al., 2013; Dan et al., 2016].The Alxa block is situated to the south of the CAOB, situated to the east of the Tarim block and west of the NCC. Voluminous intrusive and extrusive rocks outcrop in the northern Alxa block and adjacent southern CAOB. Most of them are thought to be related to the closure of the Paleo-Asia Ocean and subsequent collision [Wu, 1993; Wu et al., 1998; Zhang et al., 2013; Dan et al., 2016]
SHORT EPISODES OF CRUST GENERATION DURING PROTRACTED ACCRETIONARY PROCESSES: EVIDENCE FROM CENTRAL ASIAN OROGENIC BELT, NW CHINA
Get PDFcontinental crust but the spatial and temporal distribution of crust generation within individual orogens remains poorly constrained. Paleozoic (~540–270 Ma) granitic rocks from the Alati, Junggar and Chinese Tianshan segments of the Central Asian Orogenic Belt (CAOB) have markedly bimodal age frequency distributions with peaks of ages at ~400 Ma and 280 Ma for the Altai segment, and ~430 Ma and 300 Ma for the Junggar and Chinese Tianshan segments. Most of the magma was generated in short time intervals (~20–40 Ma), and variations in magma volumes and in Nd–Hf isotope ratios are taken to reflect variable rates of new crust generation within a long-lived convergent plate setting.Accretionary orogens are major sites of generation of continental crust but the spatial and temporal distribution of crust generation within individual orogens remains poorly constrained. Paleozoic (~540–270 Ma) granitic rocks from the Alati, Junggar and Chinese Tianshan segments of the Central Asian Orogenic Belt (CAOB) have markedly bimodal age frequency distributions with peaks of ages at ~400 Ma and 280 Ma for the Altai segment, and ~430 Ma and 300 Ma for the Junggar and Chinese Tianshan segments. Most of the magma was generated in short time intervals (~20–40 Ma), and variations in magma volumes and in Nd–Hf isotope ratios are taken to reflect variable rates of new crust generation within a long-lived convergent plate setting
ДИНАМИКА МАНТИЙНО‐КОРОВОГО ВЗАИМОДЕЙСТВИЯ НА ГЛУБИННЫХ УРОВНЯХ КОЛЛИЗИОННЫХ ОРОГЕНОВ (НА ПРИМЕРЕ ОЛЬХОНСКОГО РЕГИОНА, ЗАПАДНОЕ ПРИБАЙКАЛЬЕ)
Get PDFIn the Chernorud granulite zone in the Olkhon region of West Pribaikalie, we studied gabbro‐pyroxenites composing tectonic plates (Chernorud, Tonta) and synmetamorphic intrusive bodies (Ulan‐Khargana), as well as nu‐ merous disintegrated boudins and inclusions embedded in the metamorphic matrix. Based on the results of compara‐ tive analysis of the chemical compositions, the gabbro‐pyroxenites are classified into a single island‐arc tholeiitic se‐ ries. The COMAGMAT software was used to simulate this series and to estimate the initial composition of the parent magma (magnesian basalt: SiO2=46.0 wt. %, TiO2=0.8 wt. %, Al2O3=15.3 wt. %, ΣFeO=9.0 wt. %, MnO=0.15 wt. %, MgO=10.5 wt. %, CaO=17.0 wt. %, Na2O=1.0 wt. %, K2O=0.2 wt. %, P2O5=0.05 wt. %, total = 100.0 %, Mg# = 67.5 %). It is concluded that the granulite metamorphism (P=7.7 to 8.6 kbar, T=770 to 820 °C) was due not only to dipping of the initial sedimentary‐volcanic series to a depth of 25–28 km, but also to the presence of a deep chamber of magnesian basalt magma. In our estimations, garnet‐pyroxenites (i.e. mafic rocks of the top facies in the above‐mentioned cham‐ ber) originated at P=8.0–8.3 kbar and T=900–930 °C. Considering petrology, the deep mafic chamber under the layer of granulite facies is evidenced by metamorphic magma mingling, as well as pipe‐shaped intrusions characterized by the specific morphology, internal structure and bulk rock compositions. Based on the data on the Ulan‐Khargana mas‐ sif and gabbro‐pyroxenite bodies involved in the structure of the marble melange, we propose a petrological model showing two stages of mafic injection – Stage 1: hydraulic fracturing of granulite series and the emergence of tubular structures and bodies, which are similar to kimberlite pipes or channels of different shapes; Stage 2: rising of the flu‐ idized residual alkaline melt through the emerging ‘pipes’ and fractures armored by hardened zones, which is fol‐ lowed by metamorphic magma mingling under viscous deformation conditions. The mafic magmas intruding to the level of the granulite facies facilitated the deep anatexis and formation of synmetamorphic hypersthene plagiogranites (U‐Pb isotope dating: 500–490 Ma) and high‐K stress granites. In the Chernorud granulite zone, intense ductile‐plastic and brittle‐plastic deformations accompanied the processes of metamorphism, intrusion and formation of gabbro‐ pyroxenites and the anatexis of the crustal substance. As a result, the intrusive bodies were fragmented, and specific tectonic structures termed ‘metamorphic magma‐mingling’ were formed. All the tectonic and magmatic structures were subsequently ‘sealed up’ by K‐Na synkinematic granites at the regressive stage under conditions of the amphibo‐ lite‐facies metamorphism (U‐Pb and Ar‐Ar isotope dating: 470–460 Ma).В пределах Чернорудской гранулитовой зоны (Ольхонский регион, Западное Прибайкалье) изучены габбро‐пироксениты, слагающие тектонические пластины (Черноруд, Тонта), синметаморфические интрузивные тела (Улан‐Харгана), а также многочисленные дезинтегрированные будины и включения, погруженные в метаморфический матрикс. Сравнительный анализ вещественного состава габбро‐пироксенитов позволяет объединить их в единую островодужно‐толеитовую серию, для которой проведены модельные оценки состава родоначальной магмы по программе КОМАГМАТ (магнезиальный базальт: SiO2=46.0 мас. %, TiO2=0.8 мас. %, Al2O3=15.3 мас. %, ΣFeO=9.0 мас. %, MnO=0.15 мас. %, MgO=10.5 мас. %, CaO=17.0 мас. %, Na2O=1.0 мас. %, K2O=0.2 мас. %, P2O5=0.05 мас. %, сумма 100.0 %, Mg#=67.5 %). Сделан вывод, что гранулитовый метаморфизм (Р=7.7–8.6 кбар, Т=770–820 °С) обусловлен не только погружением первичных осадочно‐ вулканогенных толщ на глубину 25–28 км, но и присутствием глубинного магматического очага магнезиальных базальтов. Оценки Р‐Т параметров условий образования гранатовых пироксенитов, представляющих собой базитовые породы прикровельной фации этого очага, составляют Р=8.0–8.3 кбар, Т=900–930 °С. Петрологическими индикаторами существования глубинного базитового очага под гранулитовым слоем являются также специфические по морфологии, внутреннему строению и вещественному составу трубообразные интрузии и метаморфический магма‐минглинг. На примере массива Улан‐Харгана и габбро‐пироксенитовых тел, участвующих в строении мраморного меланжа, предложена двухстадийная петрологическая модель базитовых инъекций. Первая стадия отвечает гидроразрыву гранулитовой толщи и возникновению трубообразных или иных тел, по аналогии с кимберлитовыми трубками или подводящими к траппам каналами различной формы. Вторая стадия отвечает подъему флюидизированного остаточного щелочного расплава сквозь возникающие трубы и разрывы, бронированные зонами закалки, и, как следствие, формированию метаморфического магма‐минглинга в условиях вязких деформаций. Внедрение базитовых магм на уровень гранулитовой фации способствовало глубинному анатексису, формированию синметаморфических гиперстенсодержащих плагиогранитов (500–490 млн лет, U/Pb изотопное датирование) и высококалиевых стресс-гранитов. Спецификой Чернорудской гранулитовой зоны являются интенсивные сдвиговые вязкопластичные и хрупкопластичные деформации, сопровождавшие процессы метаморфизма, внедрения и становления габбро‐пироксенитов и анатексиса корового субстрата, что привело к фрагментации интрузивных тел и формированию особого класса тектонических структур – метаморфического магма‐минглинга. Все тектонические и магматические структуры были впоследствии «запечатаны» K‐Na синкинематическими гранитами на регрессивной стадии в условиях амфиболитовой фации метаморфизма, 470–460 млн лет (U‐Pb/Ar‐Ar изотопное датирование)
EARLY CRETACEOUS EXTENSION IN UPPER-MIDDLE CRUST OF NE ASIA: EVIDENCES FROM WIDESPREAD SYN-THINNING GRANITIC DOMES
Get PDFNumerous Early Cretaceous syn-thinning granitic domes are widespread in Mongolia and China-Mongolia border area. We observed relationships between deformation and magmatic activity that occurred in Baoder, Naran, Hanwula, Erdene, Altanshiree, Nartyn dome[Daoudene et al., 2012; Cheng et al., 2014; Guo et al., 2015], which developed in eastern Mongolia and China-Mongolia border area during Early Cretaceous crust-scale NW–SE extension.Numerous Early Cretaceous syn-thinning granitic domes are widespread in Mongolia and China-Mongolia border area. We observed relationships between deformation and magmatic activity that occurred in Baoder, Naran, Hanwula, Erdene, Altanshiree, Nartyn dome[Daoudene et al., 2012; Cheng et al., 2014; Guo et al., 2015], which developed in eastern Mongolia and China-Mongolia border area during Early Cretaceous crust-scale NW–SE extension
DISCUSSION ON THE RELATIONSHIP BETWEEN DEEP SEISMIC REFLECTION PATTERNS AND TECTONIC UNITS OF THE EASTERN PART OF THE CENTRAL ASIAN OROGENIC BELT IN NORTHEASTERN CHINA
Get PDFDivision of tectonic units in the eastern part of the Central Asian Orogenic Belt in northeast China has been a major concern and resulted in much fieldwork, but the division of these tectonic units in NE China is still controversial. Although detection of tectonic units in seismic sections is not straightforward, for this meeting, we shall try to relate tectonic units with the crustal and upper mantle structure and deformation derived from a ~2500 km long reflection seismic profile (Figure, red lines) in this area, recently acquired or reprocessed with support of China Geological Survey and the Chinese SinoProbe Project.Division of tectonic units in the eastern part of the Central Asian Orogenic Belt in northeast China has been a major concern and resulted in much fieldwork, but the division of these tectonic units in NE China is still controversial. Although detection of tectonic units in seismic sections is not straightforward, for this meeting, we shall try to relate tectonic units with the crustal and upper mantle structure and deformation derived from a ~2500 km long reflection seismic profile (Figure, red lines) in this area, recently acquired or reprocessed with support of China Geological Survey and the Chinese SinoProbe Project
ОЦЕНКА ЛОКАЛИЗАЦИИ ГИПОЦЕНТРОВ КОРОВЫХ ЗЕМЛЕТРЯСЕНИЙ ОТНОСИТЕЛЬНО ГЛУБИНЫ И РЕЛЬЕФА ПЛОТНОСТНОЙ ГРАНИЦЫ РАССЛОЕНИЯ В ЗЕМНОЙ КОРЕ СЕВЕРО-ВОСТОЧНОГО УЧАСТКА ОПОРНОГО ГЕОЛОГО-ГЕОФИЗИЧЕСКОГО ПРОФИЛЯ 3-ДВ
Get PDFThe total length of the seismic profiles in the northeastern regions ofRussiaand, accordingly, the area of the territories covered by the seismic data interpretations, remains insignificant in comparison with the total area of these regions. At the same time, the geological objects in the northeastern regions attract much attention in view of their prospects, including potential mineral resources. The challenge is to construct the regional models of the crust structure without deep seismic survey data, and to analyze the regional seismicity that depends on the features of the deep crust structure. We develop a density model of the crust structure using the new interpretational gravimetry method. The density modeling results show that the density changes in the crust can be used to estimate the position of a surface separating the lower (quasi-homogeneous) and upper (heterogeneous) parts of the crust, i.e. to assess the density boundary of stratification. This boundary is formed due to a complex of physical and chemical processes that facilitate the transition of the material in the lower part of the crust into the quasi-uniform (homogeneous) state. The study area is the junction zone of the Ayan-Yuryakh anticlinorium and Inyali-Debin synclinorium (62‒63°N, 148‒152° E). The initial interpretation of the deep seismic survey data on the reference geological-geophysical profile 3-DV was available, so the ambiguity of the density modeling was reduced. In turn, the density modeling results can provide additional information for geological-geophysical interpretation of the DSS results on the sites wherein the seismic profiles go along the fault zones. The relationship between seismic events and the relief of the density boundary of stratification in the crust was studied quantitatively on the basis of the data from the regional catalog of seismic events and the results of the earlier analysis of seismicity in the study area. The analysis shows that 74 % hypocenters are located above the density boundary of stratification. The earthquake hypocenters located at depths ranging from 20 to35 kmare usually confined to the systems of long-living regional crustal faults and occur below the density boundary of stratification. The energy class of such earthquakes does not exceed9. Inthe study area, the seismically active zones are mainly confined to the areas of subduction of the density boundary of stratification. Most of the earthquake epicenters (80 %) occur in the zones where the gradient of the relief change of the density boundary does not exceed 1. The number of recorded seismic events practically reduces to zero in the regions where the dip angle of the density boundary exceeds 65°.Протяженность сейсмических профилей, пройденных по территории северо-востока России, а соответственно площадь территорий, для которых имеются результаты интерпретации сейсмических наблюдений, остаются незначительными в сравнении с ее общей площадью. В то же время геологические объекты северо-востока вызывают большой интерес в связи с их перспективами, в том числе и на полезные ископаемые. Построение региональных моделей структуры земной коры без использования данных глубинных сейсмических исследований и анализ сейсмичности территории, определяемой особенностями глубинного строения, являются актуальной задачей. Для построения плотностной модели структуры земной коры в работе использованы методы новой интерпретационной гравиметрии. Результаты плотностного моделирования показывают, что по характеру изменения плотности в земной коре можно выделить поверхность, разделяющую ее нижнюю (квазиоднородную) часть и верхнюю (гетерогенную) область, – плотностную границу расслоения. Причиной образования данной границы следует считать комплекс физико-химических процессов, способствовавших переводу вещества нижней части земной коры в квазиоднородное (гомогенное) состояние. Объектом исследования выступила земная кора зоны сочленения Аян-Юряхского антиклинория и Иньяли-Дебинского синклинория в пределах координат 62‒63° с.ш. и 148‒152° в.д. Наличие первичных данных по интерпретации результатов глубинных сейсмических исследований опорного геолого-геофизического профиля 3-ДВ позволило минимизировать неоднозначность плотностного моделирования. В свою очередь, результаты плотностного моделирования могут быть использованы как дополнительный материал для геолого-геофизической интерпретации результатов ГСЗ на участках, где сейсмический профиль проходит вдоль зон разломов. Содержание регионального каталога сейсмических событий и результаты проведенного ранее анализа сейсмичности территории позволили провести анализ их связи с рельефом плотностной границы расслоения в земной коре на количественной основе. Установлено, что 74 % гипоцентров располагаются выше плотностной границы расслоения. Гипоцентры землетрясений, расположенные в интервале глубин от 20 до35 км, как правило, приурочены к системам долгоживущих сквозькоровых региональных разломов, при этом они локализованы в области, расположенной ниже плотностной границы расслоения. Их энергетический класс не превышает 9. Для данной территории зоны повышенной сейсмической активности в основном приурочены к областям погружения плотностной границы расслоения в земной коре. Эпицентры землетрясений преимущественно локализованы в зонах, где градиент изменения рельефа плотностной границы расслоения не превышает значения 1 (80 % гипоцентров землетрясений). В областях, где угол падения плотностной границы расслоения превышает 65°, количество зарегистрированных сейсмических событий практически сводится к нулю
GEOCHEMICAL AND CLAY-MINERAL STUDY OF HEALING MUD FROM WUDALIANCHI, NE CHINA
Get PDFOver the centuries, people have used healing mud (peloids) to draw toxins out of the body, boost the immune system, cure psoriasis, acne, depression, and hair loss. The beauty industry has used mud-clay masks, body wraps, soaps, and baths. The useful properties of mud were established empirically. The most popular healing-mud spars are known in the Dead Sea in Israel, Baden-Baden in Germany, Calistoga in California, Budapest in Hungary, Akhtala and Kumisi in Georgia, Paratunka in Kamchatka, Wudalianchi in China.Over the centuries, people have used healing mud (peloids) to draw toxins out of the body, boost the immune system, cure psoriasis, acne, depression, and hair loss. The beauty industry has used mud-clay masks, body wraps, soaps, and baths. The useful properties of mud were established empirically. The most popular healing-mud spars are known in the Dead Sea in Israel, Baden-Baden in Germany, Calistoga in California, Budapest in Hungary, Akhtala and Kumisi in Georgia, Paratunka in Kamchatka, Wudalianchi in China
FORMATION AND EVOLUTION OF THE DUNHUANG BLOCK
Get PDFDunhang Block is located between the North China and the Tarim Cratons (Figure). It is bounded by the Beishan Orogenic Belt to the north and Altyn Tagh Orogenic Belt to the south, respectively; in the west the Qiemo-Xingxingxia fault separates the block from Tarim Craton, and in the east the Altyn Tagh Fault separates it from the Alxa block of western part of the North China Craton. Although Archean-Paleoproterozoic basement rocks, which are referred to as Milan Complex, exposed along the Northern Altyn Tagh Orogenic Belt, some researchers suggested that their rock associations, metamorphisms and evolutionary history present obviously different with those of the Dunhuang Complex in Dunhuang region, Gansu Provence, thus the Milan Complex should be excluded from the Dunhuang Block, and is considered as basement rocks of the southwestern Tarim Craton.Dunhang Block is located between the North China and the Tarim Cratons (Figure). It is bounded by the Beishan Orogenic Belt to the north and Altyn Tagh Orogenic Belt to the south, respectively; in the west the Qiemo-Xingxingxia fault separates the block from Tarim Craton, and in the east the Altyn Tagh Fault separates it from the Alxa block of western part of the North China Craton. Although Archean-Paleoproterozoic basement rocks, which are referred to as Milan Complex, exposed along the Northern Altyn Tagh Orogenic Belt, some researchers suggested that their rock associations, metamorphisms and evolutionary history present obviously different with those of the Dunhuang Complex in Dunhuang region, Gansu Provence, thus the Milan Complex should be excluded from the Dunhuang Block, and is considered as basement rocks of the southwestern Tarim Craton