Altanbold Enkhbold, U. Khukhuudei, Yeong Bae Seong, Yumchmaa Gonchigjav, Dingjun Li, B. Ganbold
The lake depressions in the Mongolian Altai Mountains, and the issues related to their formation have yet to be thoroughly examined in previous research. Previous studies primarily focused on the paleogeographical evolution and glaciation dynamics of the Altai Mountains. This study presents relationships between tectonic and glacial processes that have formed the lake depressions, such asKhoton, Khurgan, Dayan, Khar (western), and Khar (eastern) in the Mongolian Altai Mountains. The depressions of Khoton, Khurgan, and Dayan lakes are situated along regional fault zones, extending in an northwest-southeast direction, forming intermontane depressions directly connected to the Mongolian Altai Mountains. However, the depressions of Dayan, Khar (western), and Khar (eastern) lakes have been dammed by moraine deposits in the near portion of the depression. The compliance matrix of tectonic geomorphological criteria indicates that the Khoton, Khurgan, Dayan Lake, and Khar (western) Lake depressions are more than 50% compatible. Similarly, the compliance matrix for glacial eomorphological criteria indicates more than 60% compliance for all lake depressions. The Mongolian Altai intermontane depressions are thus of tectonic origin, whereas the lakes have a glacial origin, resulting from dammed moraine sediments. The significanceof this work lies in demonstrating how geomorphological research can be employed to provide a detailed understanding of the pattern of lake depressions.
{"title":"Geomorphological study of the origin of Mongolian Altai Mountains Lake depressions: implications for the relationships between tectonic and glacial processes","authors":"Altanbold Enkhbold, U. Khukhuudei, Yeong Bae Seong, Yumchmaa Gonchigjav, Dingjun Li, B. Ganbold","doi":"10.5564/mgs.v29i58.3237","DOIUrl":"https://doi.org/10.5564/mgs.v29i58.3237","url":null,"abstract":"The lake depressions in the Mongolian Altai Mountains, and the issues related to their formation have yet to be thoroughly examined in previous research. Previous studies primarily focused on the paleogeographical evolution and glaciation dynamics of the Altai Mountains. This study presents relationships between tectonic and glacial processes that have formed the lake depressions, such asKhoton, Khurgan, Dayan, Khar (western), and Khar (eastern) in the Mongolian Altai Mountains. The depressions of Khoton, Khurgan, and Dayan lakes are situated along regional fault zones, extending in an northwest-southeast direction, forming intermontane depressions directly connected to the Mongolian Altai Mountains. However, the depressions of Dayan, Khar (western), and Khar (eastern) lakes have been dammed by moraine deposits in the near portion of the depression. The compliance matrix of tectonic geomorphological criteria indicates that the Khoton, Khurgan, Dayan Lake, and Khar (western) Lake depressions are more than 50% compatible. Similarly, the compliance matrix for glacial eomorphological criteria indicates more than 60% compliance for all lake depressions. The Mongolian Altai intermontane depressions are thus of tectonic origin, whereas the lakes have a glacial origin, resulting from dammed moraine sediments. The significanceof this work lies in demonstrating how geomorphological research can be employed to provide a detailed understanding of the pattern of lake depressions.","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":"105 26","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140379626","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
During the late Permian in Mongolia, inertia-driven transtensive reactivation of primordial fracture zones gave rise to the development of a sequence of related, but isolated, fault-bounded sub-basins; some of these became the locus of substantial peat accumulation that evolved into economically important coal deposits. The present study focuses on late Permian coal measures in two widely separated areas: Area 1: located in central Mongolia, developed along the southern margin of the Mongol-Transbaikalian Seaway. The late Permian coal sequence forms a c. 420 m thick middle part of a Permo-Triassic succession which spans c. 2,600 m. The V-shaped, fault-bounded NE oriented sub-basin evolved under transtensive conditions. The thick infill records a transition from shallow marine and humid coal forming depositional environments during the late Permian to relatively arid desolate terrestrial conditions during early Triassic times, considered here to mark the dramatic drainage of the Mongol-Transbaikalian Seaway across the Permo-Triassic boundary. Area 2: situated in southern Mongolia, is a NE oriented elongate sub-basin, bounded by two wrench faults, which formed under transtensive conditions. Thickness of the late Permian coal-bearing strata is c. 650 m. The sedimentary strata record a transition from a humid coal-bearing environment to predominantly marine conditions. Both study areas are located proximal to two controversial suture zones. However, the zones do not show the presumed shortening, major thrusting, regional metamorphism and given the complete absence of tuffs within the studied Permo-Triassic successions it could be argued that the sutures are not only cryptic but non-existent.
{"title":"Tectonic evolution of a sequence of related late Permian transtensive coal-bearing sub-basins, Mongolia: A global wrench tectonics portrait","authors":"P. Michaelsen, Karsten M. Storetvedt","doi":"10.5564/mgs.v28i57.3200","DOIUrl":"https://doi.org/10.5564/mgs.v28i57.3200","url":null,"abstract":"During the late Permian in Mongolia, inertia-driven transtensive reactivation of primordial fracture zones gave rise to the development of a sequence of related, but isolated, fault-bounded sub-basins; some of these became the locus of substantial peat accumulation that evolved into economically important coal deposits. The present study focuses on late Permian coal measures in two widely separated areas: Area 1: located in central Mongolia, developed along the southern margin of the Mongol-Transbaikalian Seaway. The late Permian coal sequence forms a c. 420 m thick middle part of a Permo-Triassic succession which spans c. 2,600 m. The V-shaped, fault-bounded NE oriented sub-basin evolved under transtensive conditions. The thick infill records a transition from shallow marine and humid coal forming depositional environments during the late Permian to relatively arid desolate terrestrial conditions during early Triassic times, considered here to mark the dramatic drainage of the Mongol-Transbaikalian Seaway across the Permo-Triassic boundary. Area 2: situated in southern Mongolia, is a NE oriented elongate sub-basin, bounded by two wrench faults, which formed under transtensive conditions. Thickness of the late Permian coal-bearing strata is c. 650 m. The sedimentary strata record a transition from a humid coal-bearing environment to predominantly marine conditions. Both study areas are located proximal to two controversial suture zones. However, the zones do not show the presumed shortening, major thrusting, regional metamorphism and given the complete absence of tuffs within the studied Permo-Triassic successions it could be argued that the sutures are not only cryptic but non-existent.","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":"17 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139156971","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Batsaikhan Buyantegsh, M. Saneyoshi, Buuvei Mainbayar, Kentaro Chiba, Miho Takahashi, S. Ishigaki, Khishigjav Tsogtbaatar
The Upper Cretaceous successions are exposed at the Yagaan Khovil fossil locality in the central Gobi region, Mongolia. The successions comprise fluvial deposits that are divided into two units based on the lithological characteristics of the floodplain deposits. The lower unit (Unit 1) is characterized by eolian-influenced environments, whereas the upper unit (Unit 2) is composed predominantly of meandering river systems with lateral accretionary channel fill deposits that show concretion at the top of the bed. The shift in depositional processes from the lower to the upper unit can be hypothesized as the result of the change in the proximity of the eolian-affected area to the study area. The successions preserving the similar paleoenvironmental transition are also present in the Nemegt Basin, where the successions shift from reddish mud beds affected by eolian processes to meandering fluvial successions. Additionally, to the similar sedimentological features, similarities in vertebrate fossils between Yagaan Khovil and the formations in the Nemegt Basin imply the close relationship between the two areas in terms of environmental conditions, ages, and stratigraphic positions. To enhance the stratigraphic framework of the Upper Cretaceous strata in Mongolia, future work should integrate the findings of this study with new radiometric dating techniques.
{"title":"Lithofacies and paleoenvironmental analysis of the Upper Cretaceous successions: Yagaan Khovil fossil locality, central Gobi region, Mongolia","authors":"Batsaikhan Buyantegsh, M. Saneyoshi, Buuvei Mainbayar, Kentaro Chiba, Miho Takahashi, S. Ishigaki, Khishigjav Tsogtbaatar","doi":"10.5564/mgs.v28i56.3199","DOIUrl":"https://doi.org/10.5564/mgs.v28i56.3199","url":null,"abstract":"The Upper Cretaceous successions are exposed at the Yagaan Khovil fossil locality in the central Gobi region, Mongolia. The successions comprise fluvial deposits that are divided into two units based on the lithological characteristics of the floodplain deposits. The lower unit (Unit 1) is characterized by eolian-influenced environments, whereas the upper unit (Unit 2) is composed predominantly of meandering river systems with lateral accretionary channel fill deposits that show concretion at the top of the bed. The shift in depositional processes from the lower to the upper unit can be hypothesized as the result of the change in the proximity of the eolian-affected area to the study area. The successions preserving the similar paleoenvironmental transition are also present in the Nemegt Basin, where the successions shift from reddish mud beds affected by eolian processes to meandering fluvial successions. Additionally, to the similar sedimentological features, similarities in vertebrate fossils between Yagaan Khovil and the formations in the Nemegt Basin imply the close relationship between the two areas in terms of environmental conditions, ages, and stratigraphic positions. To enhance the stratigraphic framework of the Upper Cretaceous strata in Mongolia, future work should integrate the findings of this study with new radiometric dating techniques.","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":"37 4","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-12-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139167012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this paper, we extracted values of geomagnetic anomaly sourced in the lithosphere from the total intensity of geomagnetic that is measured on the 750 points on an area (100x100 km2) around the Khulj hot springs. The two-dimensional map of the distribution of the anomaly geomagnetic corresponding to this area was made via these extracted values of anomaly geomagnetic. The method of spectral analysis was used to estimate the Curie Point Depth, which is lost magnetic characteristics of the lithosphere with a temperature of 580o C and the depth of layer sourcing anomaly geomagnetic with high content of iron, nickel, and tungsten by these values of geomagnetic anomaly. On the Fig. 5, the isothermal Curie surface with the temperature of 580o C was visualized in three dimensions by these values of Curie Point Depth. The heat flows lost on Earth’s surface was also detected by the method of the gradient of temperature from the Curie Point Depth. And the two-dimensional map of heat flow around the Khulj hot spring was illustrated by the values of heat flows. Moreover, the average value of the heat flow for whole the area (100x100 km2) was about 60[mW/м2], and it was estimated at about 70[mW/м2], at the Khulj hot springs. When we carried out a same study near Ulaanbaatar in 2018, the average heat flows lost on Earth’s surface was determined about 40-50[mW/м2].
{"title":"heat flow losing via earth's surface around of Khulj hot spring","authors":"Shoovdor Tserendug, Bayanjargal Genden, Tumen Nasan-Ochir, Tsoodol Zolbadral","doi":"10.5564/mgs.v28i56.2671","DOIUrl":"https://doi.org/10.5564/mgs.v28i56.2671","url":null,"abstract":"In this paper, we extracted values of geomagnetic anomaly sourced in the lithosphere from the total intensity of geomagnetic that is measured on the 750 points on an area (100x100 km2) around the Khulj hot springs. The two-dimensional map of the distribution of the anomaly geomagnetic corresponding to this area was made via these extracted values of anomaly geomagnetic. The method of spectral analysis was used to estimate the Curie Point Depth, which is lost magnetic characteristics of the lithosphere with a temperature of 580o C and the depth of layer sourcing anomaly geomagnetic with high content of iron, nickel, and tungsten by these values of geomagnetic anomaly. On the Fig. 5, the isothermal Curie surface with the temperature of 580o C was visualized in three dimensions by these values of Curie Point Depth. The heat flows lost on Earth’s surface was also detected by the method of the gradient of temperature from the Curie Point Depth. And the two-dimensional map of heat flow around the Khulj hot spring was illustrated by the values of heat flows. Moreover, the average value of the heat flow for whole the area (100x100 km2) was about 60[mW/м2], and it was estimated at about 70[mW/м2], at the Khulj hot springs. When we carried out a same study near Ulaanbaatar in 2018, the average heat flows lost on Earth’s surface was determined about 40-50[mW/м2].","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":"151 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136263215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Altangerel Badmaarag, Deleg Sangaa, V. Sikolenko, L. Enkhtur
In this work, we studied the residual micro lattice strain of an onyx sample, which is a micro- to the cryptocrystalline variety of the mineral quartz SiO2. That the investigation has been carried out using in-situ stress experiments with the time-of-flight neutron diffraction method. The aim of the study is to investigate residual lattice strains and pressure directions in the sample using time-of-flight neutron diffraction, which is a powerful tool for the study of the residual strain behavior in bulk materials, like geological rock samples containing large grains. The residual strain was detected in different sample directions turning the sample in steps of 30° by 180° around the cylindrical z-axis. These experiments have been performed at the time-of-flight neutron strain diffractometer EPSILON, situated on the pulsed neutron source IBR-2M of the Joint Institute for Nuclear Research in Dubna, Russia. The results of this study will provide insights into the compressional and tensional residual strain of the crystallographic lattice planes, and will have implications for our understanding of the tectonic history of this region. These different strains are arranged in the sample by a sinusoidal distribution in radial directions.
{"title":"Residual strain investigation of a polycrystalline quartzite rock sample using time-of-flight neutron diffraction","authors":"Altangerel Badmaarag, Deleg Sangaa, V. Sikolenko, L. Enkhtur","doi":"10.5564/mgs.v28i56.2451","DOIUrl":"https://doi.org/10.5564/mgs.v28i56.2451","url":null,"abstract":"In this work, we studied the residual micro lattice strain of an onyx sample, which is a micro- to the cryptocrystalline variety of the mineral quartz SiO2. That the investigation has been carried out using in-situ stress experiments with the time-of-flight neutron diffraction method. The aim of the study is to investigate residual lattice strains and pressure directions in the sample using time-of-flight neutron diffraction, which is a powerful tool for the study of the residual strain behavior in bulk materials, like geological rock samples containing large grains. The residual strain was detected in different sample directions turning the sample in steps of 30° by 180° around the cylindrical z-axis. These experiments have been performed at the time-of-flight neutron strain diffractometer EPSILON, situated on the pulsed neutron source IBR-2M of the Joint Institute for Nuclear Research in Dubna, Russia. The results of this study will provide insights into the compressional and tensional residual strain of the crystallographic lattice planes, and will have implications for our understanding of the tectonic history of this region. These different strains are arranged in the sample by a sinusoidal distribution in radial directions.","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41772884","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In practice, the reflected EM signal cannot be clearly observed in GPR data due to the high water content and other reasons. However, the antenna coupling signal through the ground interface is dominated in all the GPR measurements. This direct coupling signal that travels through the ground interface is called a lateral wave. The properties of the lateral wave directly depend on the subsurface properties, especially electrical parameters. We have numerically analyzed a lateral wave and its velocity. Subsequently, the relationship between lateral wave and dielectric permittivity was determined by polynomial regression. Analytically, it is challenging to analyze a lateral wave due to the parameters that can influence wave propagation. Antenna characteristics, surface roughness, etc need to be considered. Numerically, we designed a GPR system with a subsurface layer and observed a lateral wave. This numerical analysis can give a chance to use a lateral wave for near-surface soil water content. This analysis gives a more precise estimation of surface water content. Moreover, we analyze the antenna height effect that influences radar signals. We numerically observed that the GPR signal is highly affected by antenna height. The antenna height effect depended on the wavelength of the applied electromagnetic wave. By adjusting the antenna height, the unobservable GPR signal can be clearly detected.
{"title":"Velocity analysis of a lateral wave","authors":"Tsogtbaatar Amarsaikhan, Motoyuki Sato","doi":"10.5564/mgs.v28i56.2794","DOIUrl":"https://doi.org/10.5564/mgs.v28i56.2794","url":null,"abstract":"In practice, the reflected EM signal cannot be clearly observed in GPR data due to the high water content and other reasons. However, the antenna coupling signal through the ground interface is dominated in all the GPR measurements. This direct coupling signal that travels through the ground interface is called a lateral wave. The properties of the lateral wave directly depend on the subsurface properties, especially electrical parameters. We have numerically analyzed a lateral wave and its velocity. Subsequently, the relationship between lateral wave and dielectric permittivity was determined by polynomial regression. Analytically, it is challenging to analyze a lateral wave due to the parameters that can influence wave propagation. Antenna characteristics, surface roughness, etc need to be considered. Numerically, we designed a GPR system with a subsurface layer and observed a lateral wave. This numerical analysis can give a chance to use a lateral wave for near-surface soil water content. This analysis gives a more precise estimation of surface water content. Moreover, we analyze the antenna height effect that influences radar signals. We numerically observed that the GPR signal is highly affected by antenna height. The antenna height effect depended on the wavelength of the applied electromagnetic wave. By adjusting the antenna height, the unobservable GPR signal can be clearly detected.","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45970597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Tarvagatai Block is located in the northern part of Central Mongolia, which is a widespread occurrence and occupies roughly 60% of the whole exposure along the Khangai fault and the Tarvagatai uplift. Granitic magmatism was emplacement during the Middle Paleozoic, which is predominantly composed of granite-granodiorite and gabbro-diorite and rarely gabbro. This article represents petrographical, geochemical, and U-Pb zircon age data from the Telmen Complex of the Tarvagatai Block, Central Mongolia. The U-Pb dating of zircon yields a Late Silurian emplacement age (419±3 Ma) for the Telmen Complex. Geochemically, the Telmen Complex is an I-type intrusion of metaluminous nature with a SiO2 content ranging from 53.06 to 72.25 wt.% and mainly of medium to high K calc-alkaline series. Telmen Complex granites show enrichments in light rare earth elements, depletion in heavy rare earth elements, with a ratio of 4.053, (La/Yb)N =9.15, and weak positive or normal Eu anomalies. A spider diagram indicates that these rocks are enriched in Ba, K, Pb, and Sr and depleted in Nb, Ta, and Ti. The Early Paleozoic Telmen Complex granitics have trace element features, for example, Nb-Ta depletions, which indicate that these rock units were emplaced in a convergent-margin setting and typical of the lower continental crust. In addition, the geochemical data show that the volcanic arc tectonic setting and, moreover, the continental arc array setting display on the Nb/Yb versus TiO2/Yb diagrams. Therefore, we suggest that they were probably positioned in an active continental setting and in a Silurian ~419 Ma.
{"title":"Paleozoic Granitic Rocks from the Telmen Complex in the Tarvagatai Block, Central Mongolia: Petrogenesis, U-Pb geochronology, and its tectonic implications","authors":"Naidansuren Tungalag, B. Ganbat, Sukhbat Baasansuren, Gansukh Orgil, Davaadorj Enkhhtsatsral, Myamarsuren Batmunkh","doi":"10.5564/mgs.v28i56.2427","DOIUrl":"https://doi.org/10.5564/mgs.v28i56.2427","url":null,"abstract":"The Tarvagatai Block is located in the northern part of Central Mongolia, which is a widespread occurrence and occupies roughly 60% of the whole exposure along the Khangai fault and the Tarvagatai uplift. Granitic magmatism was emplacement during the Middle Paleozoic, which is predominantly composed of granite-granodiorite and gabbro-diorite and rarely gabbro. This article represents petrographical, geochemical, and U-Pb zircon age data from the Telmen Complex of the Tarvagatai Block, Central Mongolia. The U-Pb dating of zircon yields a Late Silurian emplacement age (419±3 Ma) for the Telmen Complex. Geochemically, the Telmen Complex is an I-type intrusion of metaluminous nature with a SiO2 content ranging from 53.06 to 72.25 wt.% and mainly of medium to high K calc-alkaline series. Telmen Complex granites show enrichments in light rare earth elements, depletion in heavy rare earth elements, with a ratio of 4.053, (La/Yb)N =9.15, and weak positive or normal Eu anomalies. A spider diagram indicates that these rocks are enriched in Ba, K, Pb, and Sr and depleted in Nb, Ta, and Ti. The Early Paleozoic Telmen Complex granitics have trace element features, for example, Nb-Ta depletions, which indicate that these rock units were emplaced in a convergent-margin setting and typical of the lower continental crust. In addition, the geochemical data show that the volcanic arc tectonic setting and, moreover, the continental arc array setting display on the Nb/Yb versus TiO2/Yb diagrams. Therefore, we suggest that they were probably positioned in an active continental setting and in a Silurian ~419 Ma. ","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2023-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46055733","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
O. Javkhlan, A. Chimedtseren, O. Gerel, Batkhishig Bayaraa, B. Munkhtsengel
The Edren range of the Trans-Altai zone is situated in the central south part of the Central Asian Orogenic Belt. The Edren range is composed primarily of volcano-sedimentary rocks that were weakly metamorphosed during the Devonian to Carboniferous periods. These rocks were then intruded by granite plutons during the Carboniferous to Permian periods. The area is further divided into two units, the Edrengiin Nuruu and Davkhar Khar, which are separated by the Khyariingun thrust fault. Three episodes of magmatism have been recognized in the Edren range. The earliest episode of magmatism at c. 360 Ma is present in the Edrengiin Nuruu unit. A younger episode of magmatism at c. 330 Ma is present in the Davkhar Khar unit. The youngest episode of magmatism, dated at c. 300 Ma is represented by rhyolite porphyry dykes in the Edrengiin Nuruu unit. The first episode of c. 360 Ma volcanism, developed in a continental arc setting, produced relatively contaminated basalt-andesite magma (SiO2=49.39-57.65 wt%; Mg#=27-47; (La/Yb)N=3.24-15.39) with relatively low initial ɛNd-values (from ca. +1.9 to +4.3) by subduction of the oceanic crust, developed on Devonian continental juvenile crust. Following subduction, steady northward transition of volcanic arc occurred. At c. 330 Ma continuous subduction of oceanic crust produced basalt-andesite-rhyolite magma (SiO2=47.16-72.76 wt%; Mg#=4-48; (La/Yb)N=1.34-10.91) with higher initial ɛNd-values (from ca. +1.6 to +5.8). At c. 300 Ma, rhyolite porphyry dykes (SiO2=75.70-75.86 wt%; Mg#=5-6; ɛNd=+2.6) developed in the Edrengiin Nuruu unit by subduction or collision-related magmatism.
{"title":"Geochemistry and geochronology of Carboniferous volcanic rocks from the Edren range, Trans-Altai Zone, SW Mongolia","authors":"O. Javkhlan, A. Chimedtseren, O. Gerel, Batkhishig Bayaraa, B. Munkhtsengel","doi":"10.5564/mgs.v27i55.2688","DOIUrl":"https://doi.org/10.5564/mgs.v27i55.2688","url":null,"abstract":"The Edren range of the Trans-Altai zone is situated in the central south part of the Central Asian Orogenic Belt. The Edren range is composed primarily of volcano-sedimentary rocks that were weakly metamorphosed during the Devonian to Carboniferous periods. These rocks were then intruded by granite plutons during the Carboniferous to Permian periods. The area is further divided into two units, the Edrengiin Nuruu and Davkhar Khar, which are separated by the Khyariingun thrust fault. Three episodes of magmatism have been recognized in the Edren range. The earliest episode of magmatism at c. 360 Ma is present in the Edrengiin Nuruu unit. A younger episode of magmatism at c. 330 Ma is present in the Davkhar Khar unit. The youngest episode of magmatism, dated at c. 300 Ma is represented by rhyolite porphyry dykes in the Edrengiin Nuruu unit. The first episode of c. 360 Ma volcanism, developed in a continental arc setting, produced relatively contaminated basalt-andesite magma (SiO2=49.39-57.65 wt%; Mg#=27-47; (La/Yb)N=3.24-15.39) with relatively low initial ɛNd-values (from ca. +1.9 to +4.3) by subduction of the oceanic crust, developed on Devonian continental juvenile crust. Following subduction, steady northward transition of volcanic arc occurred. At c. 330 Ma continuous subduction of oceanic crust produced basalt-andesite-rhyolite magma (SiO2=47.16-72.76 wt%; Mg#=4-48; (La/Yb)N=1.34-10.91) with higher initial ɛNd-values (from ca. +1.6 to +5.8). At c. 300 Ma, rhyolite porphyry dykes (SiO2=75.70-75.86 wt%; Mg#=5-6; ɛNd=+2.6) developed in the Edrengiin Nuruu unit by subduction or collision-related magmatism.","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-12-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43228995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Odgerel, B. Ganbat, V. Antipin, Dorjgochoo Sanchir, Choinbol Tumurchudur
The Orkhon-Selenge Belt is a Late Permian to Early Triassic volcanic plutonic belt located in northern Mongolia and is part of the Central Asian Orogenic Belt. The Selenge Complex, which is a part of the Orkhon-Selenge Belt, is a key area for studying the tectonic and magmatic evolution of the Central Asian Orogenic Belt. This study aims to contribute to understanding of the geodynamic evolution of the Orkhon-Selenge Belt by investigating the petrology, geochemistry and geochronology of the rocks in the region. Our results indicate that intrusive rocks were characterized as high-K, Calc-alkaline series and metaluminous to weakly peraluminous I-type granite affinities and their geochemical characteristics are indicating as arc-like geochemical signatures with depleted in elements such as Nb, Ta, Ti and Y and enriched in elements such as Rb, Cs, Th, K and light rare earth elements. Using zircon U-Pb dating, we determined an age of 257.3±0.73 Ma for the alkali granite, suggesting that south-western part of the Orkhon-Selenge Belt formed during the Late Permian time. The Selenge pluton, which is closely related to Erdenet-Ovoo porphyry type mineralization, is a composite intrusion. However, the zircon grains display magmatic and low oxygen fugacity conditions, which characteristics are likely the effect of weak mineralization of magma ascent with Late Permian tectonothermal event in the south-west part of the Orkhon-Selenge Belt. The results of this study will provide insights into the formation and evolution of the north-western segment of the Mongol-Okhotsk Belt, and will have implications for our understanding of the tectonic history of this region.
{"title":"Geochronology and Petrogenesis of the Gol Mod Massif: Implications for the Geodynamic Evolution of the Orkhon-Selenge Belt, Northwestern Mongolia","authors":"D. Odgerel, B. Ganbat, V. Antipin, Dorjgochoo Sanchir, Choinbol Tumurchudur","doi":"10.5564/mgs.v27i55.2310","DOIUrl":"https://doi.org/10.5564/mgs.v27i55.2310","url":null,"abstract":"The Orkhon-Selenge Belt is a Late Permian to Early Triassic volcanic plutonic belt located in northern Mongolia and is part of the Central Asian Orogenic Belt. The Selenge Complex, which is a part of the Orkhon-Selenge Belt, is a key area for studying the tectonic and magmatic evolution of the Central Asian Orogenic Belt. This study aims to contribute to understanding of the geodynamic evolution of the Orkhon-Selenge Belt by investigating the petrology, geochemistry and geochronology of the rocks in the region. Our results indicate that intrusive rocks were characterized as high-K, Calc-alkaline series and metaluminous to weakly peraluminous I-type granite affinities and their geochemical characteristics are indicating as arc-like geochemical signatures with depleted in elements such as Nb, Ta, Ti and Y and enriched in elements such as Rb, Cs, Th, K and light rare earth elements. Using zircon U-Pb dating, we determined an age of 257.3±0.73 Ma for the alkali granite, suggesting that south-western part of the Orkhon-Selenge Belt formed during the Late Permian time. The Selenge pluton, which is closely related to Erdenet-Ovoo porphyry type mineralization, is a composite intrusion. However, the zircon grains display magmatic and low oxygen fugacity conditions, which characteristics are likely the effect of weak mineralization of magma ascent with Late Permian tectonothermal event in the south-west part of the Orkhon-Selenge Belt. The results of this study will provide insights into the formation and evolution of the north-western segment of the Mongol-Okhotsk Belt, and will have implications for our understanding of the tectonic history of this region.","PeriodicalId":52647,"journal":{"name":"Mongolian Geoscientist","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45852934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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