The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the ma...The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the magmatic rocks of Yanshanian stage in the south of Anhui Province are the typical crust source type and those in the northeast of Jiangxi Province have the characteristics of mantle source type. So the polymetal deposits having relation to the magmatic rocks of Yanshanian stage in the northeast of Jiangxi Province were developed better than those in the south of Anhui Province. The research results of the rare earth elements are confirmed by the studies of geophysics,tectonic setting and stable isotope at the same time. It also indicates that the rare earth elements are the effective approach to tracing the material sources of magmatic rocks.展开更多
REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and...REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and Ce anomalous values, and ∑REE, ∑LREE/∑HREE regular changes, which indicates that their magmas come from the same source and their digenetic mechanism is fractional crystallization. In three gold deposits, the mineral ores and related altered rocks have similar chondrite-normalized REE patterns and sharp Eu positive anomalous values. The REE contents reduced from the magmatic rocks to skamization or alteration magmatic rocks, skam type ores, sulphide type ores, wall-rocks limestone or marble. The REE geochemical characteristics of the ores and related rocks show that primary fluids originated from magmatic differentiation in lower pressure of shallow crust, ore-forming hydrothermal solutions gained REE and mineralization elements further from leaching the magmatic rocks, then superimposed and reformed the limestones or marbles and deposited ore-forming material.展开更多
The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagze and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an importan...The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagze and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4% and 64 % -69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66%-1.01%, much lower than those of continental tholeiite. The ∑REE contents of basalt and dacite are 60.3-135 μg/g and 126, 4--167.9μg/ g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb = 0.54--1.17 averaging 0. 84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb= 0. 74 -1. 06 averaging 0. 86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal Iherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.展开更多
Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon...Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon growth is characterized by colorlessness, high transparence and birefringence, low and dispersive Ipr and Ipy, weak and homogeneous BSE brightness, lower Hf content and depletion of U, Th and Y; the middle stage is characterized by abruptly increasing lpy, progressively strong and sectoral-zoning BSE brightness, higher Hf content and enrichment of U, Th and Y with Th/U 〉 1; the late stage of growth is characterized by brownish color, poor transparence, low birefringence, highest Ipr and Ipy, middle and oscillatorily-zoning BSE brightness, highest contents of Hf, U and Y with Th/U 〈 1. The stages are considered to be formed in a deep magma chamber, ascent passage and emplacement site, respectively. Due to the more or less long residual time of the magma chamber, the difference in age between the early and late stages of zircon might be great enough to be distinguished, which can be attributed to tectonic constraint for the magnlatism.展开更多
In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock(TMR),a three-dimensional numerical model of a panel of one sid...In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock(TMR),a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed.The simulation results were then compared with field monitoring data.The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects,i.e.,displacement field,stress field and energy field.The results show that in comparison to the full caving mining method,the bearing capacity of the goaf after backfilling was enhanced,the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body,and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture.Before TMR fracture,the subsidence displacement of TMR was reduced by 65.3%,the front abutment stress of panel decreased by 9.4%on average and the high energy concentration zone around panel was also significantly reduced.Overall,the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.展开更多
A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb ...A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb and Sm/Yb ratios found in mainly volcanic rocks in continental China. The ratios change with the depth of origin consistent with the correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios found in oceanic basalt. These ratios increase exponentially with the depth of origin, the lithospheric thickness, of a wide variety of Cenozoic volcanic basalt and Paleozoic kimberlite in the North China Craton, northeastern China continent and vicinity. This functional relationship with depth is shown in a plot of the ratios that forms a concordia curve, which is closely expressed by formulas using 8–degree polynomials. These provide a more accurate gage in measuring the lithospheric thickness than the traditional geophysical methods. When applied to volcanic rock of different ages it also reveals how the thickness has changed over time and thus, greatly aids the understanding of the tectonic history. Relations between the COcontent, mineral reactions and pressure in the upper asthenosphere beneath the base of the lithosphere appears to affect the proportions of REE in partial melts and brings about a close correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios in mantle–derived magmatic rock. This thickness gauge, for both continental and oceanic lithosphere, provides a new approach in analyzing the lithospheric thickness in different tectonic settings and geologic times.展开更多
Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton r...Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,展开更多
Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It be...Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It belongs to the West Kunlun orogenic belt on the northwest edge of the Qinghai-Tibet Plateau and is connected to the Sanjiang orogenic belt to the south （Spurlin et al., 2005）. In recent years, a series of Pb-Zn mineralized spots and deposits have been discovered in this area one after another, which is called the Huoshaoyun ore concentration area. Among them, the Sachakou Pb-Zn deposit has reserves up to140 Mt, which has reached a large scale. However, the study on the genesis of deposits in this area has only just begun. This work studied the genesis ofthis Pb-Zn deposit in order to provide new ideas for the genesis of regional deposits and regional prospecting.展开更多
The Mazhuangshan area lies in northeast to Aqikekuduke, where are distributed intermediate\|acid rocks, which were formed in the Middle\|Late Carboniferous epoch. The magmatic rocks are peraluminous and belong to calc...The Mazhuangshan area lies in northeast to Aqikekuduke, where are distributed intermediate\|acid rocks, which were formed in the Middle\|Late Carboniferous epoch. The magmatic rocks are peraluminous and belong to calcareous series. All values of ACNK(1.03-\{2.12\}), ANK(1.67-2.93), SI(4.1-33), δ(0.71-4.82), La/ΣREE(0.09-0.26) ΣLREE/ΣHREE(1.76-11.01), (La/Sm)\-N(1.60-6.35), (Sm/Nd)\-N(0.33-0.58), (La/Yb)\-N(4.7-12.1), La\-N/Lu\-X(5.9-11.8), (Ce/Yb)\-N(3.14-6.64), δEu(0.38-\{1.06\}), Rb\-N/Sr\-N(42-120) and Sr\+*(0.02-0.2) demonstrate they vary with DI(\{45-90\}). S\|B diagram also shows that the lithophile elements are abundant in acidic magmatic rocks. Moreover, it is concluded that the primitive magma originated from a subduction zone at the continental edge, and underwent fractional crystallization and contamination, then generated the magmatic rocks. The multi\|cation index (R1: 3055-3993, R2: 286-438) shows that the primitive magma originated from the mantle. All these conclusions are beneficial for exploring gold deposits in the area.展开更多
Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the la...Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the laser Raman spectroscopic investigation. There are significant differences in types of polymerized molecular network structure and degree of bond breakdown of the magmatic glass phases between the non-CO2 and CO2 gas pools: magmatic glass phases of fluid inclusions and matrix in volcanic rocks from the CO2 gas pool contain more sheet network molecules and have a greater degree of bond beakdown than those from the non-CO2 gas pool; and when gas bubbles occur in evolving magma, magma saturated with volatile components has more sheet network molecules. The results suggest the magmadegassing mechanism of the formation of CO2 gas pools in the Shengli oilfield.展开更多
The Yarlung Zangbo suture zone extends more than2000 km along southern Tibet and marks the boundary between the Indian subcontinent and Eurasia.The Zedong terrane has been not suggested to represent the vestige of suc...The Yarlung Zangbo suture zone extends more than2000 km along southern Tibet and marks the boundary between the Indian subcontinent and Eurasia.The Zedong terrane has been not suggested to represent the vestige of such an intra-oceanic arc developed within the Neo-Tethys Ocean,as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic.In this study,we present detailed geochemical and geochronological data of various types of magmatic rocks widely exposed in the Zedong terrane to constrain the formation age and tectonic setting of the Zedong terrane.We found that the Zedong volcanic rocks belong to high K2O calc-alkaline series,whereas the diabase and gabbro plotted in the low-K calcalkline.The basalt rocks are highly enriched in LREE and LILE,but strongly depleted in HFSE,indicating they were derived from a metasomatized mantle.Both gabbros and diabase have similar N-MORB geochemistry indicates that the cumulates were produced from MOR setting.Zircons from four samples,including the basalt rocks(158-161Ma)are older than the gabbro(131 Ma),certificate the gabbro are as the vein intrude into the basalt rocks.This suggests that the volcanic eruption and plutonic emplacement were coevally developed in the Zedonghave similar positiveεHf(t)values(+2.0 to+15.6)and(+8.6 to+18.4),indicating they were stemmed from similarly depleted mantle sources,same with the gabbro and granitic rocks from the Gangdese arc.Therefore,we proposed that the basalt rocks in the Zedong terrane were formed through partial melting of the mantle wedge metasomatized by slab-released fluids/melts.A part of hydrous basalts were underplated in the thickened lower crust beneath the Zedong terrane,which gave rise to the cumulate and granitic rocks.This suggests that the Zedong terrane represents a slice of the active continental margin developed on the southern margin of the Lhasa terrane as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic,although a possible intra-oceanic arc setting cannot be excluded.展开更多
Within southern Mali, the Syama belt constitutes a linear major structure-oriented N-S, which host several gold deposits (e.g., Syama and Tabakoroni) and prospect areas (e.g. Tellem). The Syama Belt is formed by magma...Within southern Mali, the Syama belt constitutes a linear major structure-oriented N-S, which host several gold deposits (e.g., Syama and Tabakoroni) and prospect areas (e.g. Tellem). The Syama Belt is formed by magmatic rocks (basalts, lamprophyres, andesites, dacites and microgranites);sedimentary rocks (shales) and volcano-sedimentary rocks (pyroclastics). The magmatic rocks are divided into two main volcanic series: tholeiitic affinity rocks (basalts and lamprophyres) and calc-alkaline affinity (andesites) that are the most evolved. The field relationships between rocks of these two series suggest that the calc-alkaline series are younger the tholeiitic series. These tholeiitic series present the Mid-Ocean Ridge Basalt (MORB) affinity whereas the calc-alkaline series would be linked to an island arc-type. This coexistence is not an isolated case within the West African Craton (WAC). Otherwise, the Syama belt has all the characteristics of other belts, within which a number of gold deposits are developed, in the WAC.展开更多
Geochemical data and Sr-Nd isotopes of the host rocks and magmatic microgranular enclaves(MMEs)collected from the Oligocene Nodoushan Plutonic Complex(NPC) in the central part of the Urumieh-Dokhtar Magmatic Belt(UDMB...Geochemical data and Sr-Nd isotopes of the host rocks and magmatic microgranular enclaves(MMEs)collected from the Oligocene Nodoushan Plutonic Complex(NPC) in the central part of the Urumieh-Dokhtar Magmatic Belt(UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U-Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene(middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene(latest Chattian) for granodioritic and diorite porphyry units,respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite(SiO_2 = 47.73-57.36 wt.%; Mg# = 42.15-53.04); the host intrusions are mainly granite,granodiorite and diorite porphyry(SiO_2 = 56.51-72.35 wt.%; Mg# = 26.29-50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements(LILEs, e.g. Rb, Ba, Sr) and light rare earth elements(LREEs) relative to high field strength elements(HFSEs) and heavy rare earth elements(HREEs). These features, combined with a relative depletion in Nb,Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display ISr = 0.705045-0.707959, εNd(t) =-3.23 to +3.80, and the Nd model ages(TDM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition,with Isr ranging from 0.705513 to 0.707275 and εNd(t) from -1.46 to 4.62. The MMEs have TDM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust-and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle(SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr-Nd isotope data indicate that ～50% to 90% of the lower crust-derived melt and ～10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast,～45%-65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma(～35%-55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.展开更多
Carboniferous—Lower Permian volcanic rocks and small\|scale basic and ultrabasic intrusions occur in Chabu\|Chasang region of central Qiangtang plateau in northern Tibet Detailed studies of petrology and geochemistry...Carboniferous—Lower Permian volcanic rocks and small\|scale basic and ultrabasic intrusions occur in Chabu\|Chasang region of central Qiangtang plateau in northern Tibet Detailed studies of petrology and geochemistry of magmatic rocks further indicate that there were really a Late Paleozoic rift valley in Chabu\|Chasang area, and no so\|called Paleo\|Tethys suture zone existed there. The rift initially split in early Carboniferous, access the peak in Lower Permian, is closed and folded during Late Permian. The volcanic rocks composed of mainly basalts, a small amount of basaltic andesites and andesites, are zonally distributed, and occur alternately with flysch or flyschoid sandstones, slates, pebbled slates, radiolarian cherts and carbonate rocks. The sedimentary facies change rapidly toward both sides and show rapid deposits of proximal gravity flow.展开更多
21世纪是大数据的时代,数据、模型驱动下的科学研究新范式与知识发现成为当今科学领域的新态势。本文介绍了在“深时数字地球”(Deep-time Digital Earth,DDE)国际大科学计划框架下构建的DDE-岩浆岩数据库。该数据库以“数据+编图+研究...21世纪是大数据的时代,数据、模型驱动下的科学研究新范式与知识发现成为当今科学领域的新态势。本文介绍了在“深时数字地球”(Deep-time Digital Earth,DDE)国际大科学计划框架下构建的DDE-岩浆岩数据库。该数据库以“数据+编图+研究”三位一体的建库思路,基于岩浆岩知识体系,构建了岩浆岩数据库,包括后台服务(云端)、网站(Web端)和科研工作平台(桌面端)。数据主要来源于公开发表的文献、研究团队测试、实验室测试数据等,涉及全球重要造山带、克拉通及部分海洋(大洋钻探数据)等。此外,还设立了22个地域性、学科性专题数据库。数据类型为岩浆岩岩石类型、产状、空间位置等基本信息,以及年代学、地球化学、(Sr-Nd-Hf-Pb-O)同位素及非传统(或新兴)同位素数据。与国际最常用的有关数据库相比,本数据库具有以下优势:(1)“数-图-文”三位一体的设计思路,拥有编图和研究平台;(2)以研究为导向,组织构建了22个专题数据库,更多一线专家参与数据库建设,在某些地域和领域(如中亚、非传统同位素等)形成优势;(3)对数据都尽可能挖掘和补充了年龄、经纬度等时空信息;(4)创建了学科专家可以依据新的发展和需求及时调整数据库结构的技术与功能,而不需要重新编程;(5)有强大的DDE平台支持,为与国际有关数据库互联互通提供了有利条件。最后,利用DDE-岩浆岩数据库的核心数据(年代学、同位素等),对复杂大陆拼合过程、地壳生长、地球深部物质组成架构与演化等重大地球科学问题进行了探索并取得了一些进展,说明该数据库将对推动数据驱动的岩浆岩研究具有重要意义。展开更多
文摘The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the magmatic rocks of Yanshanian stage in the south of Anhui Province are the typical crust source type and those in the northeast of Jiangxi Province have the characteristics of mantle source type. So the polymetal deposits having relation to the magmatic rocks of Yanshanian stage in the northeast of Jiangxi Province were developed better than those in the south of Anhui Province. The research results of the rare earth elements are confirmed by the studies of geophysics,tectonic setting and stable isotope at the same time. It also indicates that the rare earth elements are the effective approach to tracing the material sources of magmatic rocks.
基金Project supported bythe National Natural Science Foundation of China (40472052)
文摘REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and Ce anomalous values, and ∑REE, ∑LREE/∑HREE regular changes, which indicates that their magmas come from the same source and their digenetic mechanism is fractional crystallization. In three gold deposits, the mineral ores and related altered rocks have similar chondrite-normalized REE patterns and sharp Eu positive anomalous values. The REE contents reduced from the magmatic rocks to skamization or alteration magmatic rocks, skam type ores, sulphide type ores, wall-rocks limestone or marble. The REE geochemical characteristics of the ores and related rocks show that primary fluids originated from magmatic differentiation in lower pressure of shallow crust, ore-forming hydrothermal solutions gained REE and mineralization elements further from leaching the magmatic rocks, then superimposed and reformed the limestones or marbles and deposited ore-forming material.
文摘The Early Jurassic bimodal volcanic rocks in the Yeba Formation, situated between Lhasa, Dagze and Maizhokunggar, composed of metabasalt, basaltic ignimbrite, dacite, silicic tuff and volcanic breccia, are an important volcanic suite for the study of the tectonic evolution of the Gangdise magmatic arc and the Mesozoic Tethys. Based on systematic field investigations, we carried out geochemical studies on representative rock samples. Major and trace element compositions were analyzed for these rock samples by XRF and ICP-MS respectively, and an isotope analysis of Rb-Sr and Sm-Nd was carried out by a MAT 262 mass spectrograph. The results show that the SiO2 contents in lava rocks are 41 %-50.4% and 64 % -69 %, belonging to calc-alkaline basalt and dacite. One notable feature of the basalt is its low TiO2 content, 0.66%-1.01%, much lower than those of continental tholeiite. The ∑REE contents of basalt and dacite are 60.3-135 μg/g and 126, 4--167.9μg/ g respectively. Both rocks have similar REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts have depleted Ti, Ta and Nb and slightly negative Nb and Ta anomalies, with Nb = 0.54--1.17 averaging 0. 84. The dacites have depleted P and Ti and also slightly negative Nb and Ta anomalies, with Nb= 0. 74 -1. 06 averaging 0. 86. Major and trace elemental and isotopic studies suggest that both basalt and dacite originated from the partial melting of the mantle wedge at different degrees above the subduction zone. The spinal Iherzolite in the upper mantle is likely to be their source rocks, which might have been affected by the selective metasomatism of fluids with crustal geochemistry. The LILE contents of both rocks were affected by metamorphism at later stages. The Yeba bimodal volcanic rocks formed in a temporal extensional situation in a mature island arc resulting from the Indosinian Gangdise magmatic arc.
基金This work is supported by the National Natural Science Foundation of China （No. 40572038）.
文摘Morphological and chemical studies on zircon grains from gabbro and granite of the Pingtan magmatic complex, Fujian Province, eastern China, show that there are three stages of zircon growth. The early stage of zircon growth is characterized by colorlessness, high transparence and birefringence, low and dispersive Ipr and Ipy, weak and homogeneous BSE brightness, lower Hf content and depletion of U, Th and Y; the middle stage is characterized by abruptly increasing lpy, progressively strong and sectoral-zoning BSE brightness, higher Hf content and enrichment of U, Th and Y with Th/U 〉 1; the late stage of growth is characterized by brownish color, poor transparence, low birefringence, highest Ipr and Ipy, middle and oscillatorily-zoning BSE brightness, highest contents of Hf, U and Y with Th/U 〈 1. The stages are considered to be formed in a deep magma chamber, ascent passage and emplacement site, respectively. Due to the more or less long residual time of the magma chamber, the difference in age between the early and late stages of zircon might be great enough to be distinguished, which can be attributed to tectonic constraint for the magnlatism.
基金Project(2017YFC1503100)supported by the National Key Research and Development Program of ChinaProjects(51974062,41672301,51811530312)supported by the National Natural Science Foundation of ChinaProject(N180101028)supported by the Fundamental Research Funds for the Central Universities,China。
文摘In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock(TMR),a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed.The simulation results were then compared with field monitoring data.The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects,i.e.,displacement field,stress field and energy field.The results show that in comparison to the full caving mining method,the bearing capacity of the goaf after backfilling was enhanced,the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body,and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture.Before TMR fracture,the subsidence displacement of TMR was reduced by 65.3%,the front abutment stress of panel decreased by 9.4%on average and the high energy concentration zone around panel was also significantly reduced.Overall,the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.
基金supported by the Ministry of Land and Resources of China under grant No.201211095
文摘A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb and Sm/Yb ratios found in mainly volcanic rocks in continental China. The ratios change with the depth of origin consistent with the correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios found in oceanic basalt. These ratios increase exponentially with the depth of origin, the lithospheric thickness, of a wide variety of Cenozoic volcanic basalt and Paleozoic kimberlite in the North China Craton, northeastern China continent and vicinity. This functional relationship with depth is shown in a plot of the ratios that forms a concordia curve, which is closely expressed by formulas using 8–degree polynomials. These provide a more accurate gage in measuring the lithospheric thickness than the traditional geophysical methods. When applied to volcanic rock of different ages it also reveals how the thickness has changed over time and thus, greatly aids the understanding of the tectonic history. Relations between the COcontent, mineral reactions and pressure in the upper asthenosphere beneath the base of the lithosphere appears to affect the proportions of REE in partial melts and brings about a close correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios in mantle–derived magmatic rock. This thickness gauge, for both continental and oceanic lithosphere, provides a new approach in analyzing the lithospheric thickness in different tectonic settings and geologic times.
基金financially supported by National Science Foundation of China(grant No.41303026)the funded project of the China Geological Survey(grants No.DD20160030,DD20160351 and DD20160029)
文摘Objective Petrogenesis of the Paleoproterozoic mafic dikes and their tectonic implications are of great significance to the tectonic evolution of the Yangtze craton as well as the paleoposition of the Yangtze craton relative to the Columbia supercontinent.Till now,
基金the 8th Geological Brigade of Aksu,Xinjiang, the Institute of Geology of the Chinese Academy of Geological Sciencesthe Beijing Research Institute of Uranium Geology,CNNC
文摘Objective The Sachakou Pb-Zn polymetallic deposit is located in Hetian County, Xinjiang （geographical coordinates of E78° 57＇ 54.30＂-78°59＇ 53.63＂, N34° 39＇ 27.50＂-34° 40＇ 57.21＂）. It belongs to the West Kunlun orogenic belt on the northwest edge of the Qinghai-Tibet Plateau and is connected to the Sanjiang orogenic belt to the south （Spurlin et al., 2005）. In recent years, a series of Pb-Zn mineralized spots and deposits have been discovered in this area one after another, which is called the Huoshaoyun ore concentration area. Among them, the Sachakou Pb-Zn deposit has reserves up to140 Mt, which has reached a large scale. However, the study on the genesis of deposits in this area has only just begun. This work studied the genesis ofthis Pb-Zn deposit in order to provide new ideas for the genesis of regional deposits and regional prospecting.
文摘The Mazhuangshan area lies in northeast to Aqikekuduke, where are distributed intermediate\|acid rocks, which were formed in the Middle\|Late Carboniferous epoch. The magmatic rocks are peraluminous and belong to calcareous series. All values of ACNK(1.03-\{2.12\}), ANK(1.67-2.93), SI(4.1-33), δ(0.71-4.82), La/ΣREE(0.09-0.26) ΣLREE/ΣHREE(1.76-11.01), (La/Sm)\-N(1.60-6.35), (Sm/Nd)\-N(0.33-0.58), (La/Yb)\-N(4.7-12.1), La\-N/Lu\-X(5.9-11.8), (Ce/Yb)\-N(3.14-6.64), δEu(0.38-\{1.06\}), Rb\-N/Sr\-N(42-120) and Sr\+*(0.02-0.2) demonstrate they vary with DI(\{45-90\}). S\|B diagram also shows that the lithophile elements are abundant in acidic magmatic rocks. Moreover, it is concluded that the primitive magma originated from a subduction zone at the continental edge, and underwent fractional crystallization and contamination, then generated the magmatic rocks. The multi\|cation index (R1: 3055-3993, R2: 286-438) shows that the primitive magma originated from the mantle. All these conclusions are beneficial for exploring gold deposits in the area.
基金This research was supported by the National Natural Science Foundation of China grant 49573186.
文摘Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the laser Raman spectroscopic investigation. There are significant differences in types of polymerized molecular network structure and degree of bond breakdown of the magmatic glass phases between the non-CO2 and CO2 gas pools: magmatic glass phases of fluid inclusions and matrix in volcanic rocks from the CO2 gas pool contain more sheet network molecules and have a greater degree of bond beakdown than those from the non-CO2 gas pool; and when gas bubbles occur in evolving magma, magma saturated with volatile components has more sheet network molecules. The results suggest the magmadegassing mechanism of the formation of CO2 gas pools in the Shengli oilfield.
基金funded by grants from the Ministry of Science and Technology of China (Sinoprobe-05-02)the NSF China (Nos. 41502062, 41672046, 41202036)+2 种基金the China Geological Survey (Nos. DD20160023)grants from the Institute of Geology, Chinese Academy of Geological Sciences (J1526)IGCP-649
文摘The Yarlung Zangbo suture zone extends more than2000 km along southern Tibet and marks the boundary between the Indian subcontinent and Eurasia.The Zedong terrane has been not suggested to represent the vestige of such an intra-oceanic arc developed within the Neo-Tethys Ocean,as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic.In this study,we present detailed geochemical and geochronological data of various types of magmatic rocks widely exposed in the Zedong terrane to constrain the formation age and tectonic setting of the Zedong terrane.We found that the Zedong volcanic rocks belong to high K2O calc-alkaline series,whereas the diabase and gabbro plotted in the low-K calcalkline.The basalt rocks are highly enriched in LREE and LILE,but strongly depleted in HFSE,indicating they were derived from a metasomatized mantle.Both gabbros and diabase have similar N-MORB geochemistry indicates that the cumulates were produced from MOR setting.Zircons from four samples,including the basalt rocks(158-161Ma)are older than the gabbro(131 Ma),certificate the gabbro are as the vein intrude into the basalt rocks.This suggests that the volcanic eruption and plutonic emplacement were coevally developed in the Zedonghave similar positiveεHf(t)values(+2.0 to+15.6)and(+8.6 to+18.4),indicating they were stemmed from similarly depleted mantle sources,same with the gabbro and granitic rocks from the Gangdese arc.Therefore,we proposed that the basalt rocks in the Zedong terrane were formed through partial melting of the mantle wedge metasomatized by slab-released fluids/melts.A part of hydrous basalts were underplated in the thickened lower crust beneath the Zedong terrane,which gave rise to the cumulate and granitic rocks.This suggests that the Zedong terrane represents a slice of the active continental margin developed on the southern margin of the Lhasa terrane as a result of the northward subduction of the Neo-Tethys Ocean during the Late Jurassic,although a possible intra-oceanic arc setting cannot be excluded.
文摘Within southern Mali, the Syama belt constitutes a linear major structure-oriented N-S, which host several gold deposits (e.g., Syama and Tabakoroni) and prospect areas (e.g. Tellem). The Syama Belt is formed by magmatic rocks (basalts, lamprophyres, andesites, dacites and microgranites);sedimentary rocks (shales) and volcano-sedimentary rocks (pyroclastics). The magmatic rocks are divided into two main volcanic series: tholeiitic affinity rocks (basalts and lamprophyres) and calc-alkaline affinity (andesites) that are the most evolved. The field relationships between rocks of these two series suggest that the calc-alkaline series are younger the tholeiitic series. These tholeiitic series present the Mid-Ocean Ridge Basalt (MORB) affinity whereas the calc-alkaline series would be linked to an island arc-type. This coexistence is not an isolated case within the West African Craton (WAC). Otherwise, the Syama belt has all the characteristics of other belts, within which a number of gold deposits are developed, in the WAC.
文摘Geochemical data and Sr-Nd isotopes of the host rocks and magmatic microgranular enclaves(MMEs)collected from the Oligocene Nodoushan Plutonic Complex(NPC) in the central part of the Urumieh-Dokhtar Magmatic Belt(UDMB) were studied in order to better understand the magmatic and geodynamic evolution of the UDMB. New U-Pb zircon ages reveal that the NPC was assembled incrementally over ca. 5 m.y., during two main episodes at 30.52 ± 0.11 Ma and 30.06 ± 0.10 Ma in the early Oligocene(middle Rupelian) for dioritic and granite intrusives, and at 24.994 ± 0.037 Ma and 24.13 ± 0.19 Ma in the late Oligocene(latest Chattian) for granodioritic and diorite porphyry units,respectively. The spherical to ellipsoidal enclaves are composed of diorite to monzodiorite and minor gabbroic diorite(SiO_2 = 47.73-57.36 wt.%; Mg# = 42.15-53.04); the host intrusions are mainly granite,granodiorite and diorite porphyry(SiO_2 = 56.51-72.35 wt.%; Mg# = 26.29-50.86). All the samples used in this study have similar geochemical features, including enrichment in large ion lithophile elements(LILEs, e.g. Rb, Ba, Sr) and light rare earth elements(LREEs) relative to high field strength elements(HFSEs) and heavy rare earth elements(HREEs). These features, combined with a relative depletion in Nb,Ta, Ti and P, are characteristic of subduction-related magmas. Isotopic data for the host rocks display ISr = 0.705045-0.707959, εNd(t) =-3.23 to +3.80, and the Nd model ages(TDM) vary from 0.58 Ga to 1.37 Ga. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition,with Isr ranging from 0.705513 to 0.707275 and εNd(t) from -1.46 to 4.62. The MMEs have TDM ranging from 0.49 Ga to 1.39 Ga. Geochemical and isotopic similarities between the MMEs and their host rocks demonstrate that the enclaves have mixed origins and were most probably formed by interactions between the lower crust-and mantle-derived magmas. Geochemical data, in combination with geodynamic evidence, suggest that a basic magma was derived from an enriched subcontinental lithospheric mantle(SCLM), presumably triggered by the influx of the hot asthenosphere. This magma then interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on Sr-Nd isotope data indicate that ～50% to 90% of the lower crust-derived melt and ～10% to 50% of the mantle-derived mafic magma were involved in the genesis of the early Oligocene magmas. In contrast,～45%-65% of the mantle-derived mafic magma were incorporated into the lower crust-derived magma(～35%-55%) that generated the late Oligocene hybrid granitoid rocks. Early Oligocene granitoid rocks contain a higher proportion of crustal material compared to those that formed in the late Oligocene. It is reasonable to assume that lower crust and mantle interaction processes played a significant role in the genesis of these hybridgranitoid bodies, where melts undergoing fractional crystallization along with minor amounts of crustal assimilation could ascend to shallower crustal levels and generate a variety of rock types ranging from diorite to granite.
文摘Carboniferous—Lower Permian volcanic rocks and small\|scale basic and ultrabasic intrusions occur in Chabu\|Chasang region of central Qiangtang plateau in northern Tibet Detailed studies of petrology and geochemistry of magmatic rocks further indicate that there were really a Late Paleozoic rift valley in Chabu\|Chasang area, and no so\|called Paleo\|Tethys suture zone existed there. The rift initially split in early Carboniferous, access the peak in Lower Permian, is closed and folded during Late Permian. The volcanic rocks composed of mainly basalts, a small amount of basaltic andesites and andesites, are zonally distributed, and occur alternately with flysch or flyschoid sandstones, slates, pebbled slates, radiolarian cherts and carbonate rocks. The sedimentary facies change rapidly toward both sides and show rapid deposits of proximal gravity flow.
文摘21世纪是大数据的时代,数据、模型驱动下的科学研究新范式与知识发现成为当今科学领域的新态势。本文介绍了在“深时数字地球”(Deep-time Digital Earth,DDE)国际大科学计划框架下构建的DDE-岩浆岩数据库。该数据库以“数据+编图+研究”三位一体的建库思路,基于岩浆岩知识体系,构建了岩浆岩数据库,包括后台服务(云端)、网站(Web端)和科研工作平台(桌面端)。数据主要来源于公开发表的文献、研究团队测试、实验室测试数据等,涉及全球重要造山带、克拉通及部分海洋(大洋钻探数据)等。此外,还设立了22个地域性、学科性专题数据库。数据类型为岩浆岩岩石类型、产状、空间位置等基本信息,以及年代学、地球化学、(Sr-Nd-Hf-Pb-O)同位素及非传统(或新兴)同位素数据。与国际最常用的有关数据库相比,本数据库具有以下优势:(1)“数-图-文”三位一体的设计思路,拥有编图和研究平台;(2)以研究为导向,组织构建了22个专题数据库,更多一线专家参与数据库建设,在某些地域和领域(如中亚、非传统同位素等)形成优势;(3)对数据都尽可能挖掘和补充了年龄、经纬度等时空信息;(4)创建了学科专家可以依据新的发展和需求及时调整数据库结构的技术与功能,而不需要重新编程;(5)有强大的DDE平台支持,为与国际有关数据库互联互通提供了有利条件。最后,利用DDE-岩浆岩数据库的核心数据(年代学、同位素等),对复杂大陆拼合过程、地壳生长、地球深部物质组成架构与演化等重大地球科学问题进行了探索并取得了一些进展,说明该数据库将对推动数据驱动的岩浆岩研究具有重要意义。
